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Post by 4real on Dec 8, 2011 17:37:29 GMT -5
Hmmm...well perhaps will try an few more things today including the blend things...perhaps some of the construction work that will mount these things into the guitar as that might make things a bit more 'organised'...
....
Drops to fast. seems to be 0 volume at 8, so more like a switch in effect, even with a passive HB
The problem is that you just cant get higher than 100K dual gang pots...any number of decent conventional pots of various types.
I've heard of such resistors being used to modify pot taper and such, so perhaps need some more cohesive plan other than to just add on resistors in the 'hope' for the required result.
...
I had envisaged this system like three volume controls. The blender a pair turning up the piezo in one direction, mag in the other, a bit of both in the middle...then a master volume control...single gang for a blended master or dual gang for separate outs...
Is this the way to conceptualize things?
Getting parts, the cost and time and that they are not operating as expected and the usual frustrations such as the weird connection in the piezo power and the inevitable 'mistakes' and over reaching my abilities is a little...well, it puts one off endless experimenting and with a few days now actually working this thing, I would have liked better progress or even finished this part of a far bigger project.
On the up side, there is promise in the results in a way. But it seems to be excessively hard for some reason and for all the internet ordering and such, parts a lot harder than they were a little while back where you could go to any local shop and get a dual gang pot of 0.2mm enamelled wire and such...it's become\ing far less a DIY world I fear and many parts seem to be simply unobtainable...these 500k pots for instance, far harder than anticipated, looked at all teh usual suppliers and even a huge conglomerate like element14 (farnells, et al) dont have access to them. Mouser, more likely, but then $40 postage and not replying to an email enquiry is not at all encouraging. I've already spent far too much on the wiring side of this and going to have way to many excess parts through minimum order and multiple order minimums than I am happy with...grrr...
No to worry, part of the season too, will be away for a few days and perhaps next week I can get something viable and get on with other aspect of the project and life in general...lol
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Post by reTrEaD on Dec 9, 2011 14:07:01 GMT -5
I had envisaged this system like three volume controls. The blender a pair turning up the piezo in one direction, mag in the other, a bit of both in the middle...then a master volume control...single gang for a blended master or dual gang for separate outs... Is this the way to conceptualize things? any way you do this will have advantages and disadvantages. having a master does give you the advantage of being able to quickly adjust the overall volume without changing the "blend". Drops to fast. seems to be 0 volume at 8, so more like a switch in effect, even with a passive HB This seems to be relevant: Static resistors can be subbed for a blend pot if you want. One in series with each buffer out and then their junction to the output. Basically you need some resistance between the two buffers, so they have more load than just each other. By adding resistance in series with each of the low impedance outputs, you can greatly reduce the loading that causes the "switch-like" drop in output. This comes at a price. You slightly reduce the voltage at the summing point. And greatly increase the output impedance after the summing point. But if you have a buffer stage after the summing point, you get back to having a low impedance output. |
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Post by 4real on Dec 9, 2011 16:55:45 GMT -5
Thanks reT
Yes...what are the disadvantages of a master volume control? With the solo guitar thing, I have enough to worry about without multiple controls but I do need to be able to control the dynamics and turn the guitar off easily.
It is definitely worth a try and another buffer, well there are going to be a few already, so what is one more? As long as I don't add excessive hiss and such it should be ok...but for an 'acoustic instrument' there certainly is a lot of 'electronics' in this guitar.
Arranging things so switches and things are completely hidden is something I need to get on to as well. I'm loath to drill anything in the guitar till things work plus there is no way to work on the installed electronics in this instrument so it needs to be kind of modular and fit in the back end output jack hatch.
I'm off the island for a couple of days and will attempt things afresh in the next week and see how things go...thanks to all for the interest, suggestions and encouragement...
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Post by JohnH on Dec 10, 2011 19:59:11 GMT -5
Pete - here is another candidate, which I think may tick the current boxes. It will give one or two outputs, master volume, blend and uses a 100k log dual gang for the master and a 500k lin single for blend. All outputs are buffered so therefore versatile as to what they go into. There’s never more than two buffers in the signal chain, so noise should be OK. Volume level should be consistent as you pan the blender (and thats a problem for some other types of blending that we might discuss, such as a dual gang blender).  If you just want a mono out, use Out1, or to get both pickups separated, use both and blend Out1 all the way to mag, with Out2 being all piezo. The one thing to be checked is the blending ability, to fade from one signal to the other. At full volume it will be fine, but at half volume on the master volume, there is a small amount of one signal present when blended fully the other way. The reason is that the 100k volume pot, when set at 50% increases the output resistance of each signal from about 2k up to a maximum of 25k. The result is that the max blend ratio, with volume pot set half way is 25/525 (21 to 1), which is 26.4db difference between the two signals. Is this a problem? If this was a pan between two different signals, it would be too much cross talk. But when it is a mix between two very similar signals (both guitar sounds, and in phase) I think it is OK, ie, if you have one signal -26db below the other, I don’t think you can hear it. But if this arrangement seems like it has legs, you’d have to test with your discerning ears. But I did a simple preliminary test here, using my Piezo/mag system: The question is, if Piezo and mag are mixed, with Piezo being reduced by 26db, can you hear the Piezo or does it sound like all mag? www.soundclick.com/bands/page_songInfo.cfm?bandID=674084&songID=11280880There are four strums. The first is a quiet strum of Piezo only, mag turned off. The second strum has that same amount of Piezo in it, plus a mag signal (neck single coil) which I estimate is 24db louder. It sounds all mag to me. Then, 100%mag and no Piezo. Finally. The full Piezo signal for reference. The question is, can you hear a noticeable and undesirable difference between the second and third strums? If not, then 24db difference is enough to sufficiently diminish one pickup, (ie 26db per the proposal is even better). And note that this would be at half volume, at full volume the max separation is much better, more like 250 to 1. Also, below 50% volume setting, maximum separation improves again. Worth a try? Could also drop the volume pots down to a 50k dual gang, which will give another 6db of maximum seperation, without changing the buffer designs. Cheers John |
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Post by 4real on Dec 13, 2011 23:04:50 GMT -5
Hi there...
ok, well having another go today. So far, got a 500K dual gang master volume...a buffer on the mag...into the 500K vol, then a 100K dual for the blend (no buffers) and the piezo back to the other gang of the volume.
So, all the signals to the output are separated and seems to work ok.
Now, see if I can work out a 'switch' with these sockets so that when the piezo out is connected, it will disconnect from the mag/blend...the blend control now being a 'pan' between the two outputs...
So..am I missing something in this scheme, it only uses one buffer circuit and the piezo's preamp? Would they help to say put a buffer for each signal on the blend/pan control?
Unusually effects, there is a slight boost at either end of the blend/pan (or a diminishing in the middle I guess) not huge though and there does not seem to be that bad an effect.
About to go to work on a bracket to hold the S/P and 'dark' switch just inside the f-holes...
Any thought would be appreciated, I have two more buffers built of course and at least something is working enough to install something and start to move things on a little more (and get my dining table back)!
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Post by 4real on Dec 14, 2011 2:36:45 GMT -5
Hmmm Another frustrating day on this, but some progress... I made this for instance...  Made of brass it is held in by the volume pot and holds the switches just out of site, the small one is the 'passive' switch and the mag buffer fits as well. Some of the things were encouraging but not there yet. I think I do need a 500K linear dual gang and found that stew mac is selling them for blending. It was blending with the 100K as a dual volume control kind of thing. The 500K dual log is behaving a bit better for the volume so that should be ok I imagine I have been frustrated with the output jacks. These have two spst switches that are OPEN when a plug is connected. I tried using one on the piezo jack socket so that when that is inserted the piezo signal to the 'blend' out is cut...however it still puts mag back into the piezo socket...any thoughts how one might use this kind of thing, I have two such switches on each socket to play with 'open' when a lead is connected. They are also 'stereo' if that helps at all in that department. I did not try the buffers on the end of everything yet, thinking though of adding two as volume controls for each gang and system on the blend to keep things separate but I must confess this is confusing me. The sounds out of it are decent though and little noise and it is coming along...just not there yet. Having the stereo switch when the second socket is used would be ideal |
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Post by JohnH on Dec 14, 2011 5:45:16 GMT -5
Hi there... ok, well having another go today. So far, got a 500K dual gang master volume...a buffer on the mag...into the 500K vol, then a 100K dual for the blend (no buffers) and the piezo back to the other gang of the volume. So, all the signals to the output are separated and seems to work ok. Sorry but I'm not quite following exactly how that is wired. can you sketch a diagram? |
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Post by 4real on Dec 14, 2011 6:02:29 GMT -5
LOL...I'm not sure I get it, I think there are superfluous wiring...it does blend but I think it must need the buffers as things sound a little as if there is a blanket on things compared to un-blended... I found a 500K dual linear blend pot from stew mac, so have to wait a little for that...something like this perhaps?  Does that seem to be something that fulfils the 'brief'...not saying it worked out that way and the 100K blend without buffers seems to be a bit of a 'concern'...the master seems to work ok though. Not sure if I am on the right track there though, basically a master volume and chained volumes on each. When a lead in the piezo jack, the piezo disconnects to the mag and therefore should 'pan', if no jack, it is connected to the mag and so blends...yes? I'll give it another go tomorrow, but I did something like this but without the last buffers...not sure why things are a bit 'muffled' or how to address it, probably the resistance there...more buffers fix it LOL? |
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Post by newey on Dec 14, 2011 6:37:36 GMT -5
I'm not sure I'm following exactly what you've got there, but it seems to me that, with a 100K pot for the blend, that should be after the buffers on each circuit, not before. Likewise with the jack connection between the two sides.
As far as the output jack, again, I'm not clear on how you have it at present. On my stereo Tele project, I have it set up with one switched jack and one TRS jack such that inserting a plug into the switched jack disconnects that side from the other, giving a separate output from the switched side and isolating the other jack.
So, the jack without the switch is the default jack, both channels A + B go to that jack when no plug is inserted into the switched jack. Insert the second plug. and the jack without the switch is channel A, the switched jack becomes a separate output for channel B.
The two switches on the switched jack are used to switch both the pos and neg so that the ground is not shared between the two stereo channels.
Is that how you're doing this between the piezo and mag sides?
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Post by JohnH on Dec 14, 2011 7:09:56 GMT -5
still not clear on what it is that you have built today! what did you think of the circuit I posted above? you have all the parts to try it
If im understanding your diagram correctly, it may suffer from loss of volume and issues of connecting teh two output buffers together when in mono mode
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Post by 4real on Dec 14, 2011 13:48:22 GMT -5
Thanks John and Newey This would be an ideal solution to the switching...I didn't switch the ground...can you give me a link to this diagram? I've ordered a stew mack 'blend pot' 500K www.stewmac.com/shop/Electronics,_pickups/Potentiometers/Blend_Pots.html as it seems to be the appropriate part for the job of blend/pan and could not find it elsewhere. I had wondered where the buffers should be...perhaps I need an explanation of how these fit together, why the ground needs lifting in the above, why there are issues connecting the two together and such... Basically my thoughts were that what is needed is two separate outs that could be 'blended/paned' and so was wired pretty much as two volume controls in the above, a master and separate controls. What I tried was a basic version of this kind of thing, just a mag buffer after the 470 log volume on the mag. Then connected both signals to the 100K lin blend. I wired this with signal in middle leg, signal out outer leg, ground to the other side. As I was working in stages and this was having something like the required effect, I wired the piezo to the other gang of the volume pot and to an output jack. I then tried wiring two jacks...so was trying things a bit piecemeal there for lack of a precise plan and parts I could not do the last one and most for lack of a 500K dual gang linear, the stewmac seemed to be the only one I could locate (the price is cheap, but 2x work out as $20+) so this might at least allow for something to work as devices. I only have dual gang linear 100Ks on hand and 470K logs. The brass plate thing worked out ok, basically a way to hold the switches on for the HB with the master volume control and these work ok. I left the power/passive switch on there, though I doubt I will use it and a little hard to reach (at least I wont hit it by accident) and serves really just to route around the HB buffer after the volume control and turn off the power to it. Sorry I cant easily draw a diagram of the thing as it is a bit piecemeal and hanging out of the guitar and all in shielded wire but the pots are 'loading' things I suspect in the middle of the blend travel and taking away some tone, but there is a mix of things of sorts. Disconnecting things can reveal a better sound it seems, but I only used the one buffer on the mag and the piezo preamp so did not expect miracles. Might take a little bit to get these pots in but they are built for this kind of thing with a centre detent it seems www.stewmac.com/shop/Electronics,_pickups/Potentiometers/Blend_Pots.html?tab=Instructions#details The last diagram showed the buffers after the blend, so that would have been the next step, as per the above basic plan I imagined. Not sure why the pot values keep changing there and I wanted to see if I could get more of a pan effect as well and explore the possibility of these switch pots since I am using them anyway. |
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Post by 4real on Dec 14, 2011 17:55:33 GMT -5
WOULD YOU BELIEVE
the battery had been going flat and this morning some kind of mystery fault. Replaced the battery and everything came alive as wired yesterday (albeit with a little hiss from the piezo side).
So, a single cable in one socket and the 100K pot works as a blender, insert two cables and the thing works as a pan in stereo from too amps...
Perhaps a 500K blend pot might work a little better, I'm not sure...since I ordered two doh!
So...with this scheme I am only using one buffer on the Mag...what are the advantages of more buffers, impedance?
I will also have to organise a better power switch I guess, the power switching jack of the piezo was wired around, so perhaps I will have to rewire that to be switching to ground some how with the stereo jack on the main output...I found all that a bit confusing when I was looking at it so took the power for the buffers direct from the battery itself...
So, some progress after all
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Post by newey on Dec 14, 2011 19:53:20 GMT -5
Here's the schematic for the Stereo Tele- on which slow progress is being made, believe it or not. . .  Now, this has a rotary switch interposed between the two jacks, so you'd need to sort-of interpolate a bit. And sumgai pointed out after I posted this that I had inverted the tip and ring connections, putting the two stereo outputs OOP (aurally). I don't think I actually ever corrected that, it was obvious what went where once I actually wired it up. |
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Post by 4real on Dec 14, 2011 20:24:09 GMT -5
Ah...i have not seen that one...thought it was the 'stealth' piezo kind of thing...
As above, once I changed the battery for new, the guitar came back to life as I had wired it. Might wait to get the new pot and add buffers after it but it sounds pretty good and seems to function well with both blend or pan.
Everything on my guitar is pretty much grounded including the strings together so separating things could be difficult...will have to do something about the power though and and always have a spare battery about...don't know how old that was but when it failed, it failed quick!
I can say that the 'stereo' sound is pretty amazing when it works, no ground loop present with the amps as they sit around the house...a fender HR deluxe and roland GA60 about 10' apart was tried. A giant sound and over a hundred watts LOL! It is interesting to be able to pan from one side to another and combine different amp characteristics.
I'm not fully convinced that this scheme is 'the one' but it is close. the bigger blend pots and a couple of buffers after to change the impedance might be in order...and got to work out how the piezo power switching operates and add that into the main stereo jack.
I like the idea of a pair of leads rather than a priority 'stereo cable' as it is quite likely you will want to go to separate amps anyway and things go wrong with cables so a special stereo one is perhaps asking for it. I am thinking eventually of having a lead with 4 signals with the hex but breaking out to three 1/4 phones on either end, perhaps into some kind of pedal board or something myself.
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Post by ashcatlt on Dec 14, 2011 21:52:23 GMT -5
The dual 100K pot is a Pan (not Blend) pot, no? That is, at center, both wipers are at half resistance? It remains to be seen, I suppose, whether the 500Ks you've ordered work that way or as actual blend pots, where there is no resistance on half of the travel of each wiper. This makes a couple differences.
First thing that comes to mind:
If it's a true blend then at center there will be no resistance between the piezoelectric and mag sides when using the blended output. Now you're back to that thing with the active outs "fighting" one another. So you'll have to add series resistance to each side.
OTOH - If it's a pan pot, the buffers will always have the full value of thepot's R between them. That's good in terms of the above concern, but I think you lose the benefit of the bigger pot here.
The bigger pot will help to keel the load Z seen by your buffers up, which would help to retain treble on the way to the amp if you chose to go without those final buffers. I envision you using this thing with that pot closer to center more often than not. Kind of the point, right? This means that there will be significant series resistance on each side - raising the source Z seen by the amp. I think this might then rob you of the treble you thought to preserve with the bigger pot.
Kind of looks like you'd want to buffer after your pan/blend thing either way, in which case the bigger pot only helps if you feel there's too much crosstalk. I didn't listen to John's thing yet, but I'm thinking 26db is plenty for this.
So, is 500K better?
I've got another concern here. The only way to wire this is as you've described - wiper to "input" from buffer or piezo, output to one outside lug and ground to the other. Do it the other way and you get silence at either end of the pot travel.
But this is the Wrong Way to wire a volume control. Firstly, in "pan" mode, when you've got two cables inserted, you pan all the way to one side and leave the other cable pretty much wide open. It just hangs there acting like an antenna, feeding all the noise it can catch straight into the amp. It may not be noticeable at your house, but get it into a cafe or bar with the neon and the coolers and the florescents ...
Second, and possibly worse, no matter how many cables are plugged in this shorts the output of the unused active stage directly to ground. If these are "bare" amp stages, the load (current demand) approaches infinity. Not good for batteries, transistors, or much of anything else. The cure for this part of the problem is (again) series resistance for current limiting. The piezo preamp probably already has this. I honestly just haven't looked to see if JohnH's modules include such a thing.
I'm afraid I don't have a solution for that noise thing, though. Wireless maybe?
As for the power switching. The stereo jack should be wired such that the circuit's power ground is on either the ring or sleeve and the battery's negative wire goes to the other. I'd probably prefer to have circuit ground with the "guitar ground" on the sleeve, but I don't think it much matters. When you plug in a mono cable the plug sleeve acts to jumper jack sleeve to ring and the DC power circuit is completed. Unplug and it's open, no power. Plug in a stereo cable and it's also open.
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Post by newey on Dec 14, 2011 21:54:29 GMT -5
Well, I'm still building this guitar, so this idea is not yet implemented. But my thought was to have the separate jacks, but then just wire up a "Y" adapter to take it down to a single stereo cable.
Throw the Y adapter in the guitar case, so I've got it with the guitar at all times. If I need a single stereo cable out, I've got it, or two separate cables can still be used.
The stereo cable can then be run for a distance to a stompbox A-B splitter so that only one cord need be run for the long reach.
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Post by ashcatlt on Dec 14, 2011 22:09:03 GMT -5
I recommend XLR for an application like that. A dual 1/4" > XLR cable long enough to reach the floor when plugged in, and an XLR input at the splitter, or a second XLR > dual phone cable orL whatever. Then you can use any mic cable in between. XLRs generally lock together more positively than phone plug/jacks. Since they've got male plugs at one end and female at the other they can be chained for miles. Maybe not a great selling point with passive pickups, but with low-Z active outs like 4real is gonna have...
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Post by 4real on Dec 15, 2011 1:07:51 GMT -5
It is getting complex, but I am not sure it needs be...there may be ways to build on this... Power, well after a lot of 'a-do' I finally worked out how this piezo was powering and hacked into it to do the socket/ground switch thing...it appears to working now, as long as I remember to plug it in... Stew mac blend pots.... in the link shown for their use... www.stewmac.com/shop/Electronics,_pickups/Potentiometers/Blend_Pots.html?tab=Instructions#details  They appear to be wired this way...not sure I am following the potential problem. As in what I proposed, possibly influenced by this, as the pot turns it progressively shorts to ground and the reverse for the other gang. I don't see the input 'hanging' there...but I could be missing the point. I do have a spare switch in the piezo socket btw. As I see it, it is in blend mode with one cable, with two the connection of the piezo to the removed in favour of it's own socket and so connected to another amp. Turn the blend/pan and the signal progressively shorts to ground and the input sees the resistor between signal and output. Is this not how volume controls are normally wired? (see neweys vols above for instance...three legs, one to ground, signal in and signal out?!)...might need a second opinion or more laypersons explanation there. Perhaps it is better that it does not have after blender buffer stages if shorting them to ground is going to hurt them...although there is no getting around the situation with the mag buffer I don't think as this comes before the blend. I was under the impression that perhaps a lower impedance out might be advantageous is all. The 500K pot might be advantageous with a de-tent and the bigger value give better 'travel' between sounds...don't know. It does sound a little dire there ash...but I am not seeing anything too different from what has already been proposed and is normal practice (though I am not too familiar with active systems). On the Noise thing, the mag side is pretty much silent even with the buffer stage, so it is just the usual background hiss of the piezo and can be tamed with the EQ on it which is has a lot of range. Given the amount of volume this guitar it is not bad really and typical of piezo systems I imagine. Yurning the gain on the preamp down helps balance things out a bit. ... Anyway, obviously I am working in the dark a bit so opinions and advice as always appreciated...it seems to be ok as is, just rewired and put it back together again with the power off switch and tidied things up a bit but it seems to be ok so second third or more opinions needed perhaps... |
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Post by newey on Dec 15, 2011 7:11:13 GMT -5
The diagram presuppose that you are using a stereo output jack. With the switch "up" (per the diagram), and using a mono cable, you get both sources blended to the output. Flip the switch "down" and you get stereo output with the use of a stereo cable. (The problem with this arrangement is, if you're in stereo mode with a stereo cable, flipping the switch to mono mode cuts out source B. You don't have this issue with your separate jacks and two mono cords) But the potential issue ashcatlt mentions arises either way. I say "potential" because a "hanging from hot" doesn't guarantee noise problems, it just raises the potential for them. As ash mentions, changing environments, fluorescent light ballasts in circuit, etc., may prove noisy. Or not. The issue only arises when: - You have two cables plugged in for stereo use.
- You have the pan pot turned all the way to one side or the other.
Because the pan pot is wired opposite of the way most volume controls are wired, you never get completely "off" with the pot turned all the way to the opposite side. While most of the one signal is going to ground, not all of it is- and the portion that is not is indeed "hanging from the hot" side of its separate output jack. As ash notes, with the pan pot you are forced to wire it "backwards" from a standard volume pot. In a "standard" volume pot, the center wiper is wired to the output; the input goes to the CW lug (for right-handed operation). Your wiring, with the input to the center, is the way many Les Pauls, etc. are wired. It works fine except that you have to use the switch to turn one pickup all the way off- rotating the volume won't do it. But that wiring in an LP doesn't have the "hanging" issue because both outputs are ultimately going to the same place- a single mono output jack. As always, however, the proof is in operating it, and theory be damned. If it works OK and isn't unduly noisy, the don't worry about it. If you do get in the "noisy cafe" ("noisy" from an electrical perspective, that is), then the problem is easily solved by either using the mono mode or by not rotating the blend control all the way to one side or the other while in stereo mode. Having a low Z output is useful for the same reasons it's useful in any guitar- the ability to plug into a low Z input like a mixer as well as the ability to run a long cable without treble losses. If neither of those things matter, and if it's blending fine as is between mag and piezo, I'd say don't sweat the extra buffer. My experience with the purchase of "blend" pots tells me that what you'll get is indeed a "pan" pot. The only "true blend" pots I found anywhere were the Fender OEM part no. ones. So the "active inputs fighting each other" in the center detent shouldn't arise. Of course, testing for resistance in the center position when you get the pot will tell the tale. But, I'll lay you odds you'll see resistance there . . . |
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Post by ashcatlt on Dec 15, 2011 9:21:22 GMT -5
I raised two issues re: the blend/pan pot.
The noise issue has nothing to do with the inputs to that module. It's the output that worries me. In a "normal" volume control the output is shorter, so that the cable can't generate any noise. This won't hurt an active input connected downstream because that's an input - not bein asked to supply any current. Wired "backward" like this, the output has the full value of the pot across it. It's almost the same thing as unplugging the cable at the guitar end. Try plugging a cable into your amp without anything on the other end and then turn it up to stage volume and I think you'll see what I'm getting at here.
The other problem is with the inputs to the pot. These are coming from active outputs, which are being asked to supply current across the load of the pot in parallel with whatever comes after. I=V/R. If V stays "constant", and R heads toward zero, then the current demand I gets really big. I'm almost wondering if this isn't the reason your battery seemed to have such a short lifespan.
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Post by reTrEaD on Dec 15, 2011 13:12:25 GMT -5
Wired "backward" like this, the output has the full value of the pot across it. It's almost the same thing as unplugging the cable at the guitar end. Try plugging a cable into your amp without anything on the other end and then turn it up to stage volume and I think you'll see what I'm getting at here. I haven't been following this closely, but I think there is a buffer after the blend pot. So the buffer should provide a fairly low impedance at the cable. The other problem is with the inputs to the pot. These are coming from active outputs, which are being asked to supply current across the load of the pot in parallel with whatever comes after. I=V/R. If V stays "constant", and R heads toward zero, then the current demand I gets really big. I'm almost wondering if this isn't the reason your battery seemed to have such a short lifespan. I think there is a capacitor on the output of the buffer. Without a signal, there shouldn't be an increased current demand. However if the backwired pot is at zero, the capacitor would be shunting the output. So your concerns about current drain would be quite valid when a signal is present. If a buffer is used after the blend pot, I think it can be wired "normally". That is, with the input to the resistive element and the output from the wiper. The two wipers can't be connected directly together. But if we put a resistor that is similar in value to the resistance of the pot, in series with each wiper, the summing point between those two resistors will behave rather well. |
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Post by JohnH on Dec 15, 2011 14:36:08 GMT -5
I’m glad the blending is starting to work better.
I’m not a supporter of those dual gang blend pots for active systems however, for all the reasons stated above. All of the work-arounds that I can think of that fix the problems create other issues, such as loss of signal strength. There’s also a tendency for uneven on/off blending, where as you move away from the centre, one signal falls off very quickly. Series resistors can smooth that out to some extent, but signal is lost. Hence some gain in the preamp may be needed – not a big problem but another small complication.
The simple one- gang linear pots used for blending between two low impedance signals (ie as I have been sketching) works so well that I cant see any advantage in a more complicated system. For these blenders between pickups, I like to consider how they will work if both signals were exactly the same. The single gang blender will give the same output level at every position, and the proportion from each source will change smoothly across the whole range.
Pete if you have one of these working at 100k between Piezo and mag buffer, output from the wiper, then if you are happy that it gives a full range from mag to Piezo, then there’s no advantage in a 500k version in that case.
A few principles, that Ive been using here:
If you have a pot followed by another pot (eg a volume pot before or after a blend pot and no buffer between), then the second one should be higher value than the first to avoid excess signal loss, eg a 500k follows a 100k. Any pot directly to a mag pickup needs to be 500k or 250k, which means after that, you should preferably have a buffer before any more blend pots etc. Having output from pots direct to the output jack is fine for your guitar amps, but buffers right at the output will help keep output even and full strength if you plug into a mixer line-in.
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Post by ashcatlt on Dec 15, 2011 14:50:34 GMT -5
He wants to use the dual gang thing in order to get the "panning" thing happening with the separate outs to two amps.
asmith - I think you're saying that a low-Z active output would be less like a wide open cable. I think that I agree with this. It will need series resistance after each of these "final" buffers in order so that the mix signal will work. That then, I think, starts to cause the noise issues again, but IDK.
I also see where a buffer on each side after the blend/pan pot allows us to wire the pot as normal volume type thing, and just might solve most of the issues I've raised.
BTW - I finally followed the link to the pot. It says something about having both sources at full in the center. These seems to imply that it fits ChrisK's definition of a True Blend pot. This will have it louder in the center than at either end. Might be cool for the two amp thing, but maybe not what you want in a blender.
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Post by reTrEaD on Dec 15, 2011 16:01:24 GMT -5
The simple one- gang linear pots used for blending between two low impedance signals (ie as I have been sketching) works so well that I cant see any advantage in a more complicated system. This one, right? The reason is that the 100k volume pot, when set at 50% increases the output resistance of each signal from about 2k up to a maximum of 25k. The result is that the max blend ratio, with volume pot set half way is 25/525 (21 to 1), which is 26.4db difference between the two signals. While not perfect, I'd guess that -26dB would be more than adequate. But that's based on the supposition that the signals from the mag and piezo are starting at the same level. As long as they're similar, life is good. But if there is a large disparity, whichever source is inherently stronger won't make it to -26dB as the blend is turned in the other direction. Then again, we're still looking at the worst-case example, where the dual-gang pot is at the midpoint of its resistance. |
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Post by 4real on Dec 16, 2011 0:27:31 GMT -5
Thanks for all these contributions... It does work as is though a little quirky and could do 'better' after all, when the blend/pan is in the middle both are turned down so has the effect of diminished volume if not tone. I cant get 500K log and everything is costing too much and things keep changing and to things that are not available. Dual gang pots I have two 500k log and 2x 100K linear...and these two blend pots coming. I can make any number of buffers now. In the diagram I happened to put up there, they use a switch to go from mono to stereo... I don't quite see how what I have done is really that different except for using the switch in the jack to go to stereo with an extra jack inserted. I'd like to make it work as best as I can and fulfill it's potential sonically, anticipated that it might be tricky...but not quite the diffiuclty that seems to have emerged or my failure to quite 'get' what is going on in these designs....and now apparently risks and noise...hmmm A big part of these things is to try and be as noise free as possible after all and it is true, I can't know what situations this guitar might end up in. It is not working to the volume quite of a 'normal guitar' I don't think and it does kind of get a 'boost' at either end of the vlend/pan thing. On the other hand, this scheme does in fact both blend and pan and is one would think the more 'obvious' approach to get to the functionality required to run in stereo while still having 'control' as well as minimizing eliminating switching and further complications in a wiring that is not easy to do all hanging out of the guitar like this. Hmmm...it is frustrating, at least no one has suggested that I am at risk of electrocution...yet. Weekend is here and everything needs to be packed away again and will leave the guitar in it's present state and see if you guys can think of a way in which to improve things somewhat...I'm not even sure the concerns or where I should go from here. I could add buffers if that might help, the last scheme and most of them do not provide for a controllable stereo effect (the piezo goes directly to the second amp output). Anything that has a pan pot at half volume...there are conflicting reports here www.stewmac.com/shop/Electronics,_pickups/Potentiometers/Blend_Pots.html?&offset=10&tab=Details&read=reviews#reviews and no real details of the specs... Does it need more 'gain' to make up for losses, hard to say. I am kind of surprised at how difficult this seems to be to get the result required of blend or stereo with an on-board control to operate it. You can imagine that one might want to change the sound on the fly on a chorus or verse perhaps and I am thinking of the control as a kind of 'tone' control for the guitar. Anyway, weekend is almost upon us and the weather has picked up (though I don't seem to be today) so keep you thinking hats on for a bit and all of the contributions are greatly appreciated...  watch out for the rays...and stay cool and watch for teh salt in your eyes...unless you are 'over there', then stay warm and keep out of the water...  |
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Post by JohnH on Dec 16, 2011 0:53:34 GMT -5
Pete - if you have time before you go, could you have one more go at describing or preferably sketching how you are wired up. Im not sure right now exactly what you have, and i reckon if you could do that then we can figure out why you are getting the unwanted volume drop and lower levels generally.
have a great weekend!
cheers
John
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Post by 4real on Dec 16, 2011 1:29:41 GMT -5
Sure John, little tricky in paint and all, perhaps I can try and draw and scan it a little later...got to head out for a bit and a heap of laundry and housework to do as well LOL...thanks...
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Post by 4real on Dec 16, 2011 4:38:17 GMT -5
 Not sure if this makes sense enough. There is a passive switch around the buffer and S/P and tone switch before the volume control...on the blend, "2" is the middle off the pot on the annotation and reversed for each gang. It is simple born of adding a piece at a time, the control plate just holds the switches and volume pot and mag buffer. The intention was to look at each system as a separate channel with dual volume pots I suppose, trying them on one output, then two, adding in the blend pot as volume controls, wiring the piezo blend back to the master volume control (hence that might look a bit odd or fiddly but the effect is I assume the same). Everything is wired with shielded cable. I have redone the power from teh piezo which was a little confusing, it also has some kind of 'power switch' that allows a short duration of power it seems to use the tuner even if not plugged in. The battery may well have been going flat anyway but there was no indication from the low batt light. Performance dropped off as it was going flat and the scheme worked reasonably well once that was replaced. The only significant noise is 'hiss' from the piezo and only if the treble and presence is cranked and the volume on max. I suspect is would be better if this system was not driven so hard though it does not sound 'bad' at all...it could be that having the blend pot attenuationg things does not help or something. The hiss was more noticable through the valve amp than the GA60 transistor amp which is more transparent. I just noticed that I am having to turn the amps up a fair bit compared to other guitars for a similar volume, or so it seems. ok...hope that helps a little...cheers... |
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Post by JohnH on Dec 16, 2011 19:27:28 GMT -5
Thanks for doing the diagram. I’m assuming the input to the blend pots from the pickups is to the centre lugs? In that case I am a bit worried that the buffers get shorted to ground when blended off. Thats fine with passive pickups but not most active circuits, including the buffer modules. Chance of damage is small but not zero If on the other hand the centre blend pot lugs were towards the output, then I think in mono mode, you would be getting no sound when blended fully to one pup, and so I assume thats not the case Some questions on this volume drop you get: 1. When blended to full Piezo or full mag, do you think you have the full output available at max volume or is it being reduced by the pot circuitry? 2. At mid blend, you would get half of each signal, and that may sound quieter than all of one signal since they are different signals. If both were the same, Id expect more consistent volume with your arrangement. So it may be just a case of thats how it is. 3. Do you feel the need to boost the volume generally? – I have a simple gain/buffer design I could post 4. Are you happy that the ‘max mag volume and Piezo volume are similar enough to each other? But I had some more thoughts about the circuit, and i think there may be a very nice way to use the Stewmac pots that you ordered, if they turn out to be the type that provide full output at the mid detent. I promise you will like this one.....!  So, mag pup goes to buffer. Then dual-gang master volume, 100k log. (its 100k so it can be followed with a 500k blend pot). Then to the Stewmac blender. On the diagram, I’ve put a heavy line on the half of each half pot that has low/zero resistance. So the signals after the blend pot, with volume at max and blend half way, are each the full pickup signals. Then there are resistors, I’m suggesting 47k or 100k but that could be reviewed, then buffers to two outputs. So you have your two stereo outputs, each under master volume and blend-pot control. Actually in stereo mode, I would call the action of the ‘blend’ pot a ‘balance’ pot ie, it is adjusting the levels of two signals but not mixing them. Then, the final feature, the mono stereo switch – which joins the two channels to combine them. It happens after the resistors, so no distortion due to shorting active circuits together. In mono mode, you have two outputs of the blended mix. The gradualness of the blending depends on the resistor value – actually 100k instead of 47k will give a more gradual blend. The mono/stereo switch could be part of one of the output jacks (needs an isolated switch as shown, but it could be adapted to use a simple switched jack). But, I think it would be much fun to have a separate mono/stereo switch. You could use it at a poignant moment to make a leap from a centrally placed mono blend to the two channel stereo image. Cool? ReTread, Ash, newey and others – what do you guys think? John |
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Post by 4real on Dec 16, 2011 20:19:17 GMT -5
Thanks john, only got a sec and no time to test the guitar further now.
I only have 100k linear dual gangs...so...well...
the 500K 'blends' are an unknown till the arrive I guess.
This is more along the lines I was thinking of, but a little in the dark about the concerns that have been raised re active circuits, surely the same thing happens with any guitar with a volume control and an active buffer as is often suggested?
blend is such that there is signal in to the centre lug, signal out one side, ground at the other...in the current scheme.
The piezo preamp has it's own volume control so balance can be adjusted with the mag with that...maxing it out is probably a little much. I expected the guitar to be louder and was in testing with signals alone, so there is some diminishing of volume compared to a normal guitar I suspect...
ok, GF here, got to run...
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