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Post by JohnH on Dec 28, 2011 15:12:46 GMT -5
On the battery running down, the three buffer boards will be taking about 0.5mA total. (ie small - JH preamps are not guilty!).
I suspect we dont know the current draw of the piezo system, but I'm guessing 1 to 2mA. Ive seen some that use less, but yours has a tuner. Are there any LEDs that are permanently lit? - if so, current draw is higher than if not.
Even if we reckon 2.5mA all together, and base an estimate on a pp3 battery holding 600 mA.hours, and reckon to use say 2/3 of that before its too flat, you should have about (600 x 2/3)/2.5 = 160 hours per battery. Hard to see how all that has been used since last Friday?
Unless the power is not getting switched off when you pull the jack. Is that possible? Its hard to imagine any other kind of fault that would also allow the system to work generally.
On the 220k resistors - yep, chop-em out! They were a compromise design that should not have been needed if the pot taper was better. I actually dont mind linear volume controls, I find them better for taking a few db off when needed, which is all I need when playing clean. But here's an offer: I found a dual gang 500k log pot in my spares box. Its 16mm diameter and has about a 6mm or 1/4" shaft (ie, needs about a 6.5mm hole). At mid turn, the resistance is about 20%, which is not too harsh a taper. Yours in an envelope to you if it would help.
For the power thumps, reT may be right, but I dont have a big issue with my active guitars with similar output stages, not much different to plugging in a passive guitar. A full solution to silient switch-on is to use a switched jack, where the switch is fully isolated from the socket. Have the battery connected through a small resistor, then put a cap across the circuit + to -. Then the battery is connected without touching the jack, and the circuit sees a slow ramp up as the capacitor charges. Details and values can be provided if wanted, but likely its about 100 Ohms and about 220uF - not critical values but depends on current draw.
A power switch is not a bad idea too, but may also need de-thumping
John
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Post by 4real on Dec 28, 2011 15:20:49 GMT -5
Ohhh...I just remembered...Adrian Legg I saw in his old customizing book, used to put a mercury switch in his guitar that turned the battery off when the guitar was upright on it's stand...hmmm...thinking...now I know why...not a bad idea at all
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Post by 4real on Dec 28, 2011 16:17:53 GMT -5
Thanks John... I'll take out the resistors and see how that goes, linear seemed even harder to impossible to get easily but could well have been better...the size of the pot in it meant an over large hole and it is a little tricky to take things in and out of the guitar so I'll have a tinker in due course and take you up on it if it still bothers me. All the jacks are switch jacks and have two normally closed switches, if that's what you mean. So yes, a de-thump would be a good thing...I didn't quite expect that. It is a disincentive to unplugging the guitar. The Mercury switch is an interesting idea...you definitely don't want a thump in performance...so yes, how to wire this up would be good, it is easy enough to get to the jacks...might as well and likely have such parts. And yes, I was very surprised to find that the battery went flat so fast...I had replaced it with a new one when the last went flat suddenly so wondered if something had gone wrong there as there was talk about massive current flow when buffers are shorted, etc. The guitars tuner goes off, it has LED's only when the tuner is in operation (so the tuner can be used 'acoustically' without having to plug in the guitar), but it goes to sleep or can be turned off with a 'power' button on it's console. There is a 'low batt' warning LED, but I've only seen this flash on when the lead is connected...hmm... It's unplugged now, so will be more attentive and see if it goes flat again....could well be something is not turning it off, but it seemed to be ok...it's just connecting the ground through any of the plugs. I admit I do have a tendency to have whatever guitar I am favouring to be handy and plugged in ready to play at all times...I'm structuring practice a little more, but one can log up a lot of time, a little at a time that way. I'd gone through a phase of neglecting the playing side, so started to address that. However, it is not a bad thing to do and guitar can be like a bit of a 'meditation' for me, you know, getting lost in the 'zone' and a little bit here and there with lots of breaks to 'consolidate' things and give the hands a rest. ... String tree, well, another reason one might need them...my strat has two. The nut slot is deep enough and I didn't need to alter it for the light top strings...I don't need it to add pressure to the strings, just to stop them 'popping out'...and it is only the high E. Playing with fingers over a pick seems to attach the string in different ways of course and open strings are used more than usual, so likely a good idea for 'insurance' anyway. I might get some time to shim the neck a little today...but I doubt that will 'fix it'. ... I expected that playing it would bring out a lot of little niggles and tweaks that still need to be done. Lifting the top and supporting it significantly helped with the intonation (It's pretty darn good) but I am sure this too will need some little adjustment...not the easiest thing to do on a pretty much fixed saddle and not to be done lightly. Correcting the action though is an important step in that process and may well bring it back to 'perfect' again...'it's so close' anyway. Thanks again and will let you know on the volume pot john, very kind offer... A pic then...  How I used to keep my guitars handy...frames made of cheap pine with fabric stretched over and a screw hook from the hardware store and hung from the 'picture rail' in the last house I had in town...a significant improvement on the manky walls of that house. The fabric made a nice cushion to protect the guitars, looked good both with and without the guitars on it, cheap and effective, and the guitars were always hanging over my head behind the couch below...so no excuse not to play them yet off the floor so I don't trip over them or it take over over the furniture as they tend to do. I notice that the strat still has wires hanging out the back of it there, it took a while to get around to that one. The fretless bass, well I love the sound, but really don't put the time in to play it and the acoustic...well, I might be selling that one now (never quite took a shine to it but hoped it might satisfy my thoughts on an electro acoustic). |
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Post by JohnH on Dec 30, 2011 17:57:46 GMT -5
Any further on the power issues? Im assuming you are using a stereo socket for the output jacks, and connecting the battery negative to the ring terminal, so it gets shorted to ground when a mono plug is inserted.
If you add a toggle switch to the battery negative line, then you can have the option of leaving the guitar plugged in, and also, make sure the switch is off when you insert a plug, if the amp is also on, so there is no temporary connection from tip of jack to battery as it is pushed past.
If, with that switch, you get a thump when switching the power with it, then a resistor on the battery (can be to + or - wire), and a cap across the power rails on any circuit board. Likley values as above, but it would be really good if you can measure the current draw with a multimeter - ie, insert meter between battery and battery clip and set to a curent range, then these values can be properly worked out.
cheers
john.
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Post by 4real on Dec 30, 2011 18:27:40 GMT -5
Sorry John, not had time yet
I can report that the battery is still ok with a little playing and unplugged for a bit so far...going away for a few days, so that should perhaps see if anything has been drawing on it for a while perhaps.
I will attempt some of those tests next week perhaps...
the plug-in 'squark' is not something you want to subject an audience to and if needing constant 'unplugging' is going to wear thin.
What do you think of a 'mercury switch'...using such a switch to turn off the power when the guitar is 'upright' on a stand a'la adrian legg's suggestion? Would that likely to 'thump' do you think?
I ordered a couple of string trees off of ebay and strap-locks cheap, might take a while, but a roller tree wont have an adverse effect and will ensure no strings 'fly off' once installed.
...
I'm off to the 'big smoke' for NYE apparently and off island for a few days...all the very best and stay safe...personally, I'd prefer a quiet night under the stars and the sensational crescent moon we have had lately.
Northern hemisphere types will be glad to know that summer has finally got going and 28C yesterday, 33C today and up to 38C (100+F) on Monday. Pyramid Rock festival here for a few days so the island is a little 'invaded' by the young and beautiful but I am sure they will have three days of fun in the sun out there on the cliff tops in a 'woodstock-esque' tradition...
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Post by JohnH on Dec 30, 2011 18:52:33 GMT -5
What do you think of a 'mercury switch'...using such a switch to turn off the power when the guitar is 'upright' on a stand a'la adrian legg's suggestion?  ....Jimmy couldn't understand why he seemed to lose 'Tone' when striking his best axe-hero poses..... |
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Post by reTrEaD on Dec 30, 2011 20:24:50 GMT -5
That's funny, John.
Mercury switches are sensitive to movement as well as position. I'd be a bit concerned about problems just from swaying side to side.
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Post by thetragichero on Dec 30, 2011 23:40:39 GMT -5
maybe it's just me, but i plug everything in before i even turn on the amp
should fix your problem
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Post by 4real on Jan 3, 2012 22:32:09 GMT -5
Ok...got a bit of work done on this today.
Shimming the neck...in deference to C1's wood preference I shaped a thin shim into a wedge etc...but unfortunately this ended up a little bit too thick...again reinforcing that you don't need much to have a big effect. I noticed that the upper end of the fretboard also seemed to have a
slight 'lounge rise' of sorts when this far shimmed anyway so that was not going to 'work'...
In the end and after three shims and the GFS breaking yet another string...hmmm...I used a small piece of celluloid stuff...at first at teh back of the neck pocket but after stringing, not quite enough...so taking the neck off again...I moved this forward, to about the centre of the neck pocket. Screwing it down tight I got the correct shim and it even seemed to pull that high fret 'lift' a little more evenly.
So, that all helped once right, a little better in the intonation and nicer to play for sure. It is not a super low action because I want it a little higher than perhaps most might like anyway (I like the guitar to fight back a little) and to allow the strings to vibrate freely, especially on this guitar all strings can be dropped as much as a tone or perhaps lower...so it needs the space anyway to avoid rattling. I am attempting other techniques too that work better with a bit of height in the action (thumb bass slaps, etc) that this aids...swings and round abouts as always.
Still, seems to be good now. With the neck off I could add in the strap button under the neck pocket as well, so now I can use a strap.
I have ordered a string tree and strap-locks...so that will be fixed when they arrive.
...
I also took the electronics out a bit...took the resistors of the volume control which I think is better. I checked that there was no drain on the battery when the guitar was unplugged and this seems to be the case though I did not do the drain test.
Problems...
I have been getting a few problems/niggles though that should be addressed.
One is that the dark switch, basically putting a tone cap to ground, sounds great..but...the blend then makes a 'thump' when turned to full Mag.
The volume control too seems to have developed some 'crackling' of sorts. This pot is sealed and new so a bit of a mystery there and I think related to the above.
There is still a 'dip' in volume in the mid 'blend' where the 'magic' happens and likely area for when used in stereo. Not bad or unusable but there.
...
The sound is generally great though and coming improving with each little 'tinker' I guess. Generally I am using it through my old Roland SS amp with a 15 inch extension box to handle the bass and it is a great solid sound able to handle the clean for the piezo and does a nice job clean on the mag as well. I hope to try a few mild effects on the guitar and may try a few experiments with a few things with a view perhaps of making a pedal broad for it in the future.
...
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Post by reTrEaD on Jan 3, 2012 23:25:36 GMT -5
Problems... I have been getting a few problems/niggles though that should be addressed. One is that the dark switch, basically putting a tone cap to ground, sounds great..but...the blend then makes a 'thump' when turned to full Mag. The volume control too seems to have developed some 'crackling' of sorts. This pot is sealed and new so a bit of a mystery there and I think related to the above. The first thing I'd check for is DC on the pots. Maybe a failed coupling capacitor on one of the buffers? |
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Post by 4real on Jan 3, 2012 23:49:18 GMT -5
errrgg...
well, that's a little difficult to get into...it is not like unscrewing the cover after all...hmmm.
The thump is only on teh mag side of the blend in complete turn on the last 'click' and when the tone switch is activated.
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Post by reTrEaD on Jan 4, 2012 2:07:55 GMT -5
well, that's a little difficult to get into...it is not like unscrewing the cover after all...hmmm. The thump is only on teh mag side of the blend in complete turn on the last 'click' and when the tone switch is activated. I was almost gonna say you could check at the output jack for DC, but iirc you have a buffer after the the volume and blend controls. |
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Post by JohnH on Jan 4, 2012 2:35:01 GMT -5
The thump is only on teh mag side of the blend in complete turn on the last 'click' and when the tone switch is activated. Could you say a bit more please?. Does it thump as you turn the blend pot to mag, or when you insert the jack (or is that a different thump?) Also, on th volume drop at mid blend, is that just in mono blend mode or is it also in stereo mode? cheers john |
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Post by 4real on Jan 4, 2012 3:21:27 GMT -5
The thump is only on teh mag side of the blend in complete turn on the last 'click' and when the tone switch is activated. Could you say a bit more please?. Does it thump as you turn the blend pot to mag, or when you insert the jack (or is that a different thump?) Also, on th volume drop at mid blend, is that just in mono blend mode or is it also in stereo mode? cheers john Will try, but now it seems to be doing something else...hmmm moving the volume control when the tone switch is engaged (cap to ground) creates a very loud crackly pot...Very LOUD! The similar sound at the full extent of mag blend, just as going into full mag was creating a similar kind of sound but now appears to ahve stopped for the volume control noise which is worse. The noise is only when the controls are turned, not an ambient sound in the signal. The volume pot is making a quieter 'crackling' scratchy pot sound when moved. I don't recall this being there before and the only mod was to remove the resistors on the volume pot. I don't think anything was damaged in removal although it is not easy to do...all teh wires were triple checked soldered and secured with tape before it went in so I can imagine that this would be the problem. The volume pot could potentially ahve gotten damaged on removal but the plastic pot is well sealed and that seems not to explain a light 'scratchy pot' all, the time and extreme version when 'dark' switch is engaged. Or that the blend has stopped doing a similar thing now though the dark switch is engaged. ... I was mistaken on the blend...the mag in series is now quite powerful and louder than the piezo even on full (although this is with a flat EQ) so the dip is more of a reduction of volume from full mag into blend then even...this could actually be a useful 'feature' or could be corrected by lowering the Mag further and of course running tow amps the volume can be balanced there...so, no problem now the 'noise' has been shifted to the volume control...but that noise is unexceptable really, and with the dark switch engaged, speaker and ear destroying at volume! ... Does that give any clues? |
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Post by JohnH on Jan 4, 2012 3:48:34 GMT -5
reTreAd also hinted at it, but 'scratchy pot' , when there is no sound sigtnal, is often caused by dc running through them.
When you are not playing, all the pots should have all lugs at zero volts because they are seperated from everywhere except ground by caps, which should block dc. So the inevitable connections and disconnections as a pot wiper slides over the track should make very little noise, because all points are at zero. It is kind of suggesting something wrong with the output cap on the mag buffer (thats the 2.2uF). If you can get in there with a meter, measure dc volts from ground to mag buffer output, where it connects to the blender. It should be a very small voltage or zero, but if it is highre than say 1/4V, it will explain the noise and we'll move on from there
The effect of this tone switch is a puzzle - is it a cap directly across the pup (as I thought), or after the buffer?
John.
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Post by 4real on Jan 4, 2012 4:17:48 GMT -5
scheme goes S/P switch, phase switch then 'dark' cap connected to ground switch => then mag buffer => then blend => then volume => then buffer => then out.
so cap before all buffers. Definitely only happens when this is engaged other than a light crackling on the volume pot. The blend has stopeed doing it now, so I am not sure what that is about.
...
It is tricky to get into it and I don't think that any damage could have happened to the buffers from today but obviously something is not quite right. Short of taking teh buffers apart, can another cap be added some where to correct this if that is the problem?
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Post by 4real on Jan 4, 2012 5:50:57 GMT -5
Ok...taken it apart again...
moved the buffers across just in case something is shorting but it seems ok.
I do seem to be getting some voltage in the pot between ground...it's hard to tell...reading between ground and the volume pot lugs might be reading something...slightly. Putting into the millivolt range, teh meter seems to cycle through tiny numbers on it's own (disconnected for some reason) so any reading seems consistent with such background 'noise' there.
Getting to any of the output caps would be difficult...is there another place one could add one to repair it (add a cap before the power or something?...are we sure that is the problem. The cap to ground when connected is definitely a part of it and needs to be fixed...can't think what is going on there.
Would the power conditioner like thing to stop the plug in 'squark' help at all? How exactly should this be wired in?
In fact, the extreme pot noise is very much like that plugging in 'squark and is at the extreme max volume.
It is definitely related to the dark switch. I got the same symptom from the extreme mag end of the blend earlier though that has mysteriously stopped.
I would think that this must surely be a clue...keeping it 'open' for over night while the fault is considered. checking things have not come adrift seems to has yielded nothing.
Could it be a faulty pot that has got damaged. I have another if necessary.
As an alternative, I ahve another 100K linear...I didn't quite understand why you need to ahve a larger pot after the blend...what is the effect of the same pot value do you think? Would such a pot perhaps give a better response or something?
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Post by JohnH on Jan 4, 2012 5:52:38 GMT -5
No chance of measuring voltage on the blend pot, from ground to each lug?. Its all a bit strange and need to have more data.
Does it settle down after being on for a while? thinking caps might be slowly charging.
EDIT - just seen your post above, will review
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Post by 4real on Jan 4, 2012 6:26:55 GMT -5
Now you gone make me take the blend module out too...no voltage reading between ground and blend pot lugs either...that I can detect...
same symptoms still.
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Post by JohnH on Jan 4, 2012 15:21:41 GMT -5
Puzzling - but can you consider the question above: Does it settle down after being on for a while? thinking caps might be slowly charging.
What Im thinking is: having been off for say 10minutes or more, plug in and twiddle the knobs, and identify the noises. Then leave it plugged in for 10minutes and try again. What Im thinking of here is that the output caps on each buffer are fairly large, designed to drive low impedance inputs. they may be taking too long to settle down into a steady state when not loaded.
maybe do that first
Power conditioner - prefereably wanted to know the current draw from the whole circuit to work this out, but If measuring that is not possible, put a resistor in line with the battery from battery -ve to ground and a large cap after the resistor, from +ve to -ve on one of the buffer boards. Resistor is 100 to 390Ohms best guess, maybe around 220 Ohms. cap to be 100uF to 490uF, see what you have lying around . If you try this, please just do as simple a test wire up of it first, before building it in, its not a definate answer.
On the use of two 100k pots, the risk will be a further dip in volume at mid blend. The blender module has an output resistance that changes from about 2k at one end to 25k in the middle. In blend mode, it is loaded by the two halves of the volume pot in parallel, which would be a 50k load. Therefore, the signal wil be reduced at mid-blend by a factor of 50/(25+50) = 2/3.
John
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Post by 4real on Jan 4, 2012 16:51:14 GMT -5
Puzzling - but can you consider the question above: Does it settle down after being on for a while? thinking caps might be slowly charging. What Im thinking is: having been off for say 10minutes or more, plug in and twiddle the knobs, and identify the noises. Then leave it plugged in for 10minutes and try again. What Im thinking of here is that the output caps on each buffer are fairly large, designed to drive low impedance inputs. they may be taking too long to settle down into a steady state when not loaded. maybe do that first Power conditioner - prefereably wanted to know the current draw from the whole circuit to work this out, but If measuring that is not possible, put a resistor in line with the battery from battery -ve to ground and a large cap after the resistor, from +ve to -ve on one of the buffer boards. Resistor is 100 to 390Ohms best guess, maybe around 220 Ohms. cap to be 100uF to 490uF, see what you have lying around . If you try this, please just do as simple a test wire up of it first, before building it in, its not a definate answer. On the use of two 100k pots, the risk will be a further dip in volume at mid blend. The blender module has an output resistance that changes from about 2k at one end to 25k in the middle. In blend mode, it is loaded by the two halves of the volume pot in parallel, which would be a 50k load. Therefore, the signal wil be reduced at mid-blend by a factor of 50/(25+50) = 2/3. John It is a bit of a mystery I must say...hmmm...it was not always doing this obviously... The power is drawn from the piezo circuit, so kind of would have thought that the pre-amp there would have had a 'power conditioning circuitry and such though perhaps the buffers are taken direct...it's not a big thing...just never plug it into a live amp as suggested. I'm so used to having a guitar on a stand plugged in and always at hand and with multi-amps or effects the rig is not something that you want to take down all the time. (I accidentally left the guitar plugged in last night for instance, the battery survived). It is a mystery, the dark switch thing is a great sound...effectively the tone rolled right off...I assume this is fine with active circuits, but definitely where the most disastrous "bang" comes in. There appears to be no 'build up' in the caps or change in teh condition...I will try it now... Nope...does not seem to be the case. Does not settle down nor better for rested...consistent. The guitar was played for at least 4 hours yesterday...it is getting a lot of use so I think I'd notice. As I say, seems to be a particular problem with the dark switch though it is obviously no good having crackles in the volume pot...I will replace it to see if there is any change from that today...it might potentially have been damaged though would seem odd...I don't hold much store in these 'plastic pots with plastic shafts and all...but have not experienced excessive heat or anything. I've tested it with different amps and different leads...(my old SS amp has a temperamental scratchy pot)...but that makes no difference to these noises. There is no 'aberrant' noises from the guitar until the volume control is turned and while 'scratchy' the 'thump' occurs when turned to full volume. Not turning the knob and all is fine and guitar works as expected, dark switch mode and all... All else I can think of doing is taking off a few switches and seeing if anything could have been shorted or compromised...but I doubt it, anything that I thought might come adrift or short out was insulated against...so at a loss my end. Sorry about the measuring seemingly a bit vague. I have an old 'meter' analogue multimeter and used that to check of DC voltage in the pots and it seems to indicate nothing at all while reading the battery voltage fine...so I can not detect a DC voltage in the pot. It's not encouraging for my first truely 'active' guitar but the sound is worth it I am sure...the HB sound is certainly improved and I am still tempted to 'active' at least one of my other guitars with HB's to get that level of clarity. Unfortunately with my 'triple burger' stacking of the circuits, it would be easier to rebuild all three buffers than to take them apart...so to be avoided unless the cause and solution 'identified'...hmmm ... On more positive news. The Trilogy is proving it's worth and am learning a few tunes and techniques in altered tunings. DADGAD is particularly nice and learning some of Lawerence Juber's arrangements in this tuning... as is dropped D and open G...hard to get used to leading the bass notes with the little finger so often, but a lot of fun to explore and can certainly get sounds impossible without it. Bracing the top really helped matters...the strings need to have settled in a bit and it requires a bit of tinkering to get it right, but once it is set, as long as the guitar is in tune, it would appear to very reliably instantly alter tunings reliably. The guitar has a nice 'woody' sound to it even in full magnetic mode and can produce a lot of 'bass' in it, (might be the heavier strings contributing to it) while being well balanced. The piezo system helps to bring out some highs and complexity and the two together work well to tame any 'quack'... I seem to prefer an 80-20 mix of mostly magnetic pickup and sounds better to my ears, at least in this style, with a clean SS amp with a lot of range to it. It does sound great with a more conventional amp, very warm sound and would be a great blues or classic rock guitar too I'm sure. I've been playing it a lot louder lately and did a bit of a 'feedback test' and it seems to be fine there...you can get a controlled feedback effect if you stand with it in front of the speaker but no uncontrolled squeal or the like from it which I had concerns about. If we get this electronics side of things sorted, I will do some kind of recordings of course...   The Melbourne 'spire' on the concert hall on fire post NYE fireworks...LOL...my woes with this may well turn out to be no more mysterious I guess... |
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Post by reTrEaD on Jan 4, 2012 17:00:47 GMT -5
Puzzling - but can you consider the question above: Does it settle down after being on for a while? thinking caps might be slowly charging. I've been trying to imaginate what might be the cause of this. But it's extremely difficult without seeing the entire circuitry. Worth noting is that the "dark switch" exacerbates the problem. I usually avoid 'hot melt glue' from a gun but it is ideal for this allowing the buffer 'cube' to be securely glued to the brass plate. This makes me wonder if the hot glue is providing a resistive path in parallel with a coupling capacitor. Or from B+ to output after the coupling cap. scheme goes S/P switch, phase switch then 'dark' cap connected to ground switch => then mag buffer => then blend => then volume => then buffer => then out. so cap before all buffers. Definitely only happens when this is engaged other than a light crackling on the volume pot. The blend has stopeed doing it now, so I am not sure what that is about. But the dark switch is before the buffers. I can't quite wrap my head around a failure that would fit all the symptoms. |
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Post by JohnH on Jan 4, 2012 17:21:52 GMT -5
RetreAd - Im very glad you are looking at this - and I have the same issue! I cant figure out a scenario where the pre-buffer dark switch affects the post buffer pots and output. Just to summarise the circuit, without showing the mag pup S/P and dark switch, which are all passive before the buffer, the overall block diagram is this:  and each of the three buffers is this:  Shown there, the blend pot is built in, but 4real is just using the buffer x3 and has blend and volume pots per the sketch above. cheers John |
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Post by 4real on Jan 4, 2012 17:31:45 GMT -5
I checked the glue just now with the sensitive analogue meter and there is absolutely no reading in it. It is only on the edge to hold it on, not 'encapsulated' or anything LOL...I would ahve expected it to be quite a good insulating material...not something I'd use often though, but seemed ideal for this application. I covered the tracks of the circuit with PVC tape too as well as the near by brass plate around anything like this...just in case... The circuit is as per john's last scheme...the only additions are a S?P, tone and phase switch on the HB before everything else. A buffer on the mag before the blend control, volume, then two buffers and out. The layout is three 'modules'. The piezo preamp (power goes from here to the switch jacks then back to the buffers), the 'volume control' plate which includes the three HB switches and all buffers, and the 'blend' plate which has only the blend pot and 4pdt stereo switch on it. The two plates are connected by a multicore shielded cable for send and return of signals from the vol plate where it leaves the buffers to go to the outputs also via shielded cable.     Absolutely, the 'dark' switch is something to do with it, but definitely before the buffers as are the other HB switches. The 'dark' switch is the one to the right of the buffer sandwich with the cap on it... There is little that can 'move' in this to create faults...there are a lot of wires and potentially delicate though...hence the amount of black tape used to try and stop shorts or leads being 'pulled' and the like. yes...mysterious...any suggestions appreciated. As the 'dark switch seems to be involved, I'll extract it to see if there is any obvious problem today...I've already moved the buffers a little to the left but that had no effect either so not hopeful of there being a reason there. It is close to the buffers and from where the mag signal emerges into the buffer next to it which is the first 'mag' buffer I believe. |
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Post by reTrEaD on Jan 4, 2012 18:15:04 GMT -5
RetreAd - Im very glad you are looking at this - and I have the same issue! I cant figure out a scenario where the pre-buffer dark switch affects the post buffer pots and output. When a symptom stops making sense, regarding the circuit on paper, it's time to stop taking some basic things for granted. Things like power supply distribution and grounds. In this case, I'd be more suspicious of grounds. Just because some ground connections are located next to each other on paper, doesn't mean the actual wiring goes that way. Sometimes grounds from different parts of the circuit are connected directly together but have some resistance to "true" ground. Perhaps a cold solder joint. Since these buffers have a very low idle current, it's probably going to require a fairly large resistance in a ground path to cause problems. But experience leads me to suspect something like this as the root cause. If I have time, and the right frame of mind, I'll attempt to reason out a place where shared grounds with some resistance to true ground could cause a thump when the volume pot is rotated. |
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Post by 4real on Jan 4, 2012 18:24:20 GMT -5
Thanks...in the mean time, with this in mind, I will have a look at the wiring, take it apart a little and clean things up further. Originally I had grounds to all required points from a central location on teh dark switch as it happens. Much of this was removed...for instance, the 'sandwich' of buffers connects via two ground and one power wire to all three, so that removed several ground wires and power connections. You can see where red (power) and green (grounds) have been clipped on the circuits. Similarly, ground wires were removed where there was a shielded connection that made them obsolete. It is tricky to work with these 'loose' things and it is a concern that having things out and 'hanging' can cause damage and so potential multiple faults...
As I say, a mystery of sorts there, gald for teh help...frustrating I can not offer more than pics and descriptions and relies on me doign the work...LOL
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Post by 4real on Jan 4, 2012 19:38:28 GMT -5
OK...took things apart...definitely power in the ground, seems like half voltage perhaps...hmmm. The 'dark' switch is the last in the chain of switches and also the 'star ground' for all grounds....
Pull the switch out and if it touches the 'brass plate, lots of crackling noise there...
ok...so perhaps something to do with the 'power supply' system?
a bit under water still though...will see if I can clean up the wiring perhaps, reduce grounds but still...all grounds are connected so if there is power in it...hmmm...
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Post by 4real on Jan 4, 2012 20:26:34 GMT -5
Ok...took most of the vol/buffer module apart. un-taped and tidied up any obvious wiring though all looked well. Thought I'd take the spacer nuts out from the switches so they are a little easier to reach while I am at it.
So...some 'progressd' of sorts...even though now I don't know why...hmmm...
The 'scratchy pot' symptom seems to have completely gone now. Well, that's nice...But...
Still, switching to the 'dark' mode you still get the effect of 'thump' etc...
The voltage seems to be fine, about 8.5 now +v to ground and only when plugged in...that to me indicates that all is as it should be...and it works now in the normal mode.
I did recheck the buffers and seemed to be fine but to be sure, took out and re-insulated the plate under and reglued. As it works other than the 'dark switch' I think we can assume it 'works' there. No indication that any noise has switched back to the 'blend control' and recall this seems to only involve the HB Mag side of things of which the 'dark' is effecting.
Tricky, would a resistor between the cap and ground help? Seems to me it is just a tone on full, so can't think why.
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Post by JohnH on Jan 4, 2012 21:03:53 GMT -5
I reckon there was some unwanted connection that you have now cleared. Still the dark control is a puzzle, as you say it is just a tone control at full cut. I could understand a pop or thump just when switching it on, but after that, it should not affect anything else.
Maybe check all the symptoms again, now that you have cleared some problem? If it is just a pop when you engage dark, a high value resistor from cap to ground (say 1, 2 or 3M), which gets bypassed by the switch when you go ' dark', should keep it from building up any pop-causing static charges.
John
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Post by reTrEaD on Jan 4, 2012 22:13:43 GMT -5
Maybe check all the symptoms again, now that you have cleared some problem? If it is just a pop when you engage dark, a high value resistor from cap to ground (say 1, 2 or 3M), which gets bypassed by the switch when you go ' dark', should keep it from building up any pop-causing static charges. John Let's hope. I would have expected the scratchy pot and blend pot causing a thump were related. If those are both okay now, the thump caused by engaging the dark switch is likely a different cause. Not certain it's just static charges being built up on the cap, though. Whatever the voltage on the cap when the switch is opened, should in theory be the voltage on the cap when the switch is closed. Chances of the waveform being in the right part of the cycle to have a similar voltage when closing the switch are not good at all. Bleeding the cap to ground does help with the worst case scenario: If the cap was disconnected on the negative part of the cycle then reconnected on the positive part of the cycle. (or vice versa) But I think a little better might be to use the resistor to tie the cap to the signal. It won't follow directly, it will lag somewhat behind and be at a lower amplitude. But that's likely to be a bit closer match during the switching, on average. And if using a value similar to a tone pot, say 470k ~ 1Meg, it won't dull the signal much. |
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