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Post by JohnH on Dec 8, 2009 14:45:34 GMT -5
Its a puzzle, particularly how it seems to be dependent on the amp set up, with no problem being evident on your aer.
Some random ideas:
Was there a whistle on the pre-mod clips?
If there is an electrical intereference to pick up, a mag pup might catch it but a piezo probably wont. A whistle like that could be generated externally by some equipment, such as your PA and then picked up. Or it could be a sort of feedback where a strong signal in an output wire induces a signal in an input or pickup, which then is amplified and results in a feedback occuring - like acoustic feedback due to too loud an amp, but electrically based.
With the whistle occuring, does moving around the room make any difference?
If you move the internal wires inside the guitar, does it change? - particularly the wires to the mag pup and to the output jack
Im wondering if shielding of the mixer is needed. All the other signal carrying wires are already shielded. Sometimes Ive experimented with that by putting a circuit inside a small plastic bag then wrapping it in kitchen foil clipped to ground.
Does grounding the strings make a difference? (easy to test by clipping wires to the tuners , but harder to do permanently on an acoustic)
John
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Post by D2o on Dec 8, 2009 16:56:09 GMT -5
Interesting ... I had another listen, and the piezo is silent Pre AND Post.
It seems to be the magnetic pickup that causes the squeal, Pre AND Post ... shrieking with both pups blended, and noisy but not as bad with just the magnetic pup selected (but, again, silent when only the piezo is selected).
D2o
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Post by ashcatlt on Dec 8, 2009 17:46:20 GMT -5
Unfortunately, I don't have any good ideas where this might be coming from. Seems like it's got to be something unique to the mag pickup side of the equation. I couldn't download this to measure it, but it's an extremely high frequency. I wouldn't be surprised if even a PA speaker would fail to reproduce it to some extent.
The first thing I would suspect would be power supply, but since it's a battery, that should be mostly silent. You might try adjusting the supply voltage either downward or upward and see if that changes things.
I like JohnH's idea of shielding everything that's not nailed down, and you should make sure that the strings are grounded.
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Post by treguiers on Dec 8, 2009 21:22:45 GMT -5
soundclick.com/share?songid=8430001Just reposted the offending article. I will try all that was suggested. As I need to go "into" the guitar again, any further thoughts on a master volume? There seemed to be impedance issues. I did a couple of gigs with it where there were long silent pauses between songs, and it's an uneasy feeling knowing its live. It makes turning pages or amp adjustments a bit more tentative. I also like a difference between rhythm and lead vols. will keep you all posted, but it's getting into the silly season for me. lots of playing to very drunk people at Christmas parties, so it may be a bit before I tend to the above suggestions. But I will keep an eye here so that when I can go at it, i'll be armed with good info. Take care........
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Post by sumgai on Dec 9, 2009 3:14:15 GMT -5
tre, Unique to the mag pickup? I'd want to swap in another one, just to see what happens...... Sounds like this might a case of microphonics. Barely audible, and only at the very high end of the frequency spectrum, but certainly not unheard of. BTW, I can't get your posted clip, soundclick is high on my list of untrustworthy websites.....  sumgai |
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Post by JohnH on Dec 9, 2009 4:49:57 GMT -5
Well I snuck into soundclick and downloaded the two mag notes files, before and after mod, plonked them into Audacity which revealed this: i731.photobucket.com/albums/ww316/JohnDHewitt/GN2/treguiresmagpup091209.gifThe upper trace is pre-mod and the lower is post-mod, on the mag pickup. The 'tone is there in both - you can hear it and also see it as a spike at the right of both spectrum graphs, and it is always 12.8kHz. Interesting, yes, do I know what it means, no! discuss.... cheers John |
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Post by D2o on Dec 9, 2009 10:01:35 GMT -5
John,
I don't know what it means either, but I had an idea to do somewhat the same thing, recording the actual squeal with Wavepad (made by an Aussie software firm, by the way), but I don't believe that it has frequency analysis ... that's pretty neat!
I was going to post the actual "squeal" part of the audio from each of the scenarios and amplify it for easier "listening" but decided that it really didn't reveal anything other than the mag pup squeals ... which we are already aware of.
Ash, my seat of the pants / hair in the ears feeling is that the squeal's frequency is not very high - it was easily audible on earphones, speakers or anything else and I would imagine it would be intrusive if it ends up in the signal. Whether it ends up in th signal during "normal" operation, as opposed to the specific layout/location treguiers used for recording the clips ... who knows?
John, if any part of that frequency analysis includes the squeal, it is more useful than I first realized! It actually confirms, scientific-like, rather than relying on my ears, that the squeal is well within the freqency range heard by normal humans.
As for me, well ... I hear ringing all the time ... and I see dead people.
D2o
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Post by JohnH on Dec 9, 2009 14:39:40 GMT -5
D20 - the squeal is definitely there in both traces, the last spike near the right in both, above 11kHz and measurable as 12.8kHz using audacity. Also, I tried making a tone at that frequency and it confirms that its that.
I'm quite pleased to find out that I can still hear tones so high!
It seems the mixer mod is not he root of the issue, since it was there before. I'm suspecting the PA/recording setup, somehow sending out a spurious signal that the mag pu picks up, since the aer amp does not have this issue. Also, both pickups are top-drawer Fishman (ie, not some dodgy circuits downloaded off the Internet from some unknown dude down under!).
tg, you don't want to risk your gigging axe at this time of year, but easy tests include the one where you move around the room to see if it changes, trying a different length of cord (see if the frequency of squeal changes), trying a different PA setup if you have access to one, and try grounding the strings.
On the desire for master volume, is that mainly to allow you to mute the guitar? - a kill switch is very easy to add, that disconnects the output and grounds it. For a lead volume boost, I prefer a stomp-box, it keeps my hands free to play. It would be an easy project if you wanted to build one, not harder than what you have already done.
John
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Post by treguiers on Dec 9, 2009 20:52:09 GMT -5
Well guys, discovered the problem with the freq. I moved around the room like you said, and when I moved the guitar near the computer screen the thing howled. Luckily I wasn't wearing cans at the time, but problem solved. I'll just have to record the soundclips onto an external device and post them. You might also get away with just a single pot of 100k or 50k after the whole output. Theres a risk to the tone with that last one, Which value would be best impedance wise, and which would be less risky tone wise. I want to stress that this is a minor thing, I am delighted with the guitar cheers lads |
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Post by treguiers on Dec 9, 2009 21:41:26 GMT -5
one way involves another identical mixer circuit, this time with one input grounded and the other coming from the current mixer output. On second thoughts i may try this option. Will this invert the signal and is that a problem. Would a 500k pot be a runner? Audio or linear? Does anyone know why width of these threads has increased dramatically, or is it just me. Have i inadvertently hit some "very wide thread" button |
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Post by ashcatlt on Dec 9, 2009 22:47:49 GMT -5
JohnH's big old screenshot is hanging off the edge. I don't recall having noticed earlier, but...
I think for simplicity sake the simple voltage divider volume pot is best. After all the active stages already in there, the pot isn't likely to make much noticeable difference tone-wise.
I'm glad you found the source of this particular noise. Can you record with the screen off? Well, that doesn't solve the problem anyway. The fact that it affects the signal the way it does points to poor shielding at some point in the circuit, and apparently that point is somewhere unique to the mag pickup. Somewhere down the road you'll find yourself in a situation where there's noise coming through which is not so easily dealt with.
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Post by JohnH on Dec 10, 2009 7:39:27 GMT -5
sorry about the picture - Ive reduced it to just a link so it doesnt blow the screen size out.
On those 100k or 50k pots, I have the same out put stage in my piezo/mag Strat design, so Ill run a test to see how that works - finding out if there is any significant volume or tone loss, there may be but Im not sure
john
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Post by treguiers on Dec 10, 2009 20:28:55 GMT -5
Other possibilities are a dual gang pot of about 50k per section with each half between a pickup and the mixer input. The only reason I'm opting for another mixer circuit is that i don't know what a dual gang pot is. What are they? Are they like a stereo blender pot with a notch in the middle for panning left and right. If one pup is one side and the other pup the other side, is it another blender switch? I'd go out and get one tomorrow if i knew what they did. In the meantime I'll search the net and get the skinny on them |
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Post by newey on Dec 10, 2009 21:21:48 GMT -5
Look here: www.mouser.com/catalog/specsheets/TW-700160.pdfA dual-gang pot is just 2 pots on a single shaft. They can be wired independently, but are controlled via a common knob/shaft. These are not to be confused with concentric pots, which have control of each pot individually. |
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Post by JohnH on Dec 11, 2009 7:04:26 GMT -5
I tried putting a 100k pot after the whole circuit on my guitar. It was fine at full volume but as the volume reduced some extra noise got into the signal, particularly going into a guitar amp. Also, at lower volume it was not driving my mixer line input so well as at full volume. I don't think a 50k would make it right, so I'm withdrawing recommendation for this.
I think the best master volume option is probably a second active mixer board. It would be built the same as the first, but could use a 100k pot instead of 500k. The input to this new board from the first mixer board would be In2, and In1 would not be used, in fact, the green blob representing the track cut behind In1 would be omitted, thus grounding that lug and turning the circuit into an active volume control.
Or, if you want to try the dual gang pot (as newey explained it) a 50k one should work - with each half, one outer lug grounded, other outer lug to one of the pups output, the inner lug connected to In1 or In2. i think this should work OK, but not tested.
For any of these options, whether you use a log or a linear pot for a volume control is up to you. I would prefer a linear pot to give better control near max volume. But if you want a big reduction with a small amount of turn, you could use a log lot.
John
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Post by treguiers on Dec 11, 2009 8:05:41 GMT -5
So would the i/p to this new board be the o/p of the existing mixer? ie would I insert the new board between the mixer and the o/p jack?
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Post by JohnH on Dec 11, 2009 13:50:21 GMT -5
Yes thats right - simple enough once you have the new board built and tested. So you would disconnect the current output wire at the jack, and use that to connect to the In2 connection of the new volume board. You can also use the outer screen of that cord to connect the ground. Then a new screened output wire goes from the volume board to the jack (similar to the old one). The last thing is a wire to connect the + battery power to the new board, from the old board.
As noted before, omit the track cut behind In1 so it gets grounded.
Is that clear enough? if not I can do another doagram - its just cut and paste from the old one so its not much work.
john
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Post by treguiers on Dec 12, 2009 9:04:23 GMT -5
Hi John,
No a diagram won't be necessary. I'm gonna start building after the w'end, I'll keep you posted on developments.
Thanks man.
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Post by treguiers on Dec 14, 2009 19:25:25 GMT -5
OK, Did the master vol and looks like it works a charm Thanks john and +1 man(I'd give you +10 if I knew how). I have recorded some soundclips: soundclick.com/share?songid=8480236If you can imagine the blend pot as being from 8o'clock(all mag) to 4 o'clock(all piezo). The above soundclip sweeps from 8 o'clock round to 4 o'clock and back to 8'oclock again soundclick.com/share?songid=8480235As stated previously the piezo is quite hotter than the mag. This particular soundclip above,has the blend pot fixed at 9o'clock as the volume of the piezo sweeps from zero to full and back to zero. I find this particular approach interesting. I would add that the EQ on the original piezo pre-amp has a profound effect on the overall sound. What can I say guys Thanks. and a +1 to Ash sumgai, newey and of course john, and hey because I'm over the moon about the guitar D20 gets one too. Thanks guys |
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Post by JohnH on Dec 15, 2009 6:41:02 GMT -5
good stuff - well done!. the tones sound good.
John
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Post by newey on Dec 15, 2009 9:12:27 GMT -5
What started as a question about modifying an onboard preamp has become one of our longest threads!
Good work, treguiers, JohnH and all who helped.
Tre, please repost the final version of this that you built to the schematics section for future reference- it's a bit tough to go through 8 pages to get the nuts and bolts of this project.
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Post by D2o on Dec 15, 2009 9:35:00 GMT -5
Between the knowledge (JohnH, sumgai, ashcatlt, etc) and the zeal (tre ... and, I suspect, just a little bit of knowledge in his own right, no?) ... well, this is fantastic!
Great stuff!
D2o
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Post by sumgai on Dec 15, 2009 14:17:17 GMT -5
I can see the Press Release now.....
NEW! Exciting news from Canada!
Introducing the revolutionary new On-board Pre-amp for Acoustic Beer Can Holders!!
;D ;D ;D ;D ;D
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Post by treguiers on Dec 16, 2009 12:31:23 GMT -5
Hi Newey,
My particular set-up required a master volume. JohnH recommended that I build basically the same circuit as the blend circuit, using a 100k pot. This would be placed in series between the blend circuit and the o/p jack. The only difference between the master vol circuit and the blend circuit, besides the 100k pot, is that one side of the 100k pot goes to ground and the other is the o/p of the blend circuit.
But really I only followed JohnH's instructions. He would be a much better person to finalize the project.
I'm afraid the next thing on my "to do" list is to learn how to post and manipulate schematics on this site. So sorry Newey but for the minute I can't help you on the Schematic front.
But I have since gigged this guitar, and I'm happy to report that it's a fantastic success. Master vol is a huge addition for me and the icing on the cake that is my "new" axe.
Thanks guys
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Post by sumgai on Dec 16, 2009 14:14:33 GMT -5
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Post by JohnH on Dec 16, 2009 14:48:37 GMT -5
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Post by antoinesoul on Aug 1, 2023 4:41:41 GMT -5
Hi John -and others-
I am actually trying to get the best solution to blend to sources in my good all massive classical guitar.
After 30 years of playing (pro) and tried many systems pickups for folk and electric, didn’t find yet the good way for electrified a classical guitar.
Can’t afford the super expensive system they K&k, LR, and Fishman purpose.
I would like to blend a JJB multi piezo with either a goose neck or an Ust B-band (still have one- a little better than typical quacks piezzos)
I just read the thread on the Dyi Activ blender and I am very interesting.
Can you tell me more ?
Diagram? Picture of “real life” build of the unit ?
Many thanks
Antoine
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Post by newey on Aug 1, 2023 4:56:04 GMT -5
antoinesoul-
Hello and Welcome to G-Nutz2!You are resurrecting a very old thread here- nothing wrong in doing so, but you would likely garner more responses by posting this as a new question in a separate thread. While your questions are certainly related to the topic, this thread sort of got off topic, and the title of this thread doesn't really reflect what you're asking about. As for diagrams, the thread is 14 years old, I'm not sure if the diagrams referenced are still available. JohnH would be the one to ask. To make certain another member sees your question, it is best to "tag" that member by using the "@" symbol in front of the username. So I'm tagging JohnH so he sees this post.
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Post by JohnH on Aug 1, 2023 16:24:46 GMT -5
hi antoinesoulWelcome to GN2. I haven't got anything much new in this area since the old threads that you've seen, but I'm happy to help think about it. The key issues are what type of transducers are being used, what output do they have and what sort of preamp they need. The module described before in this thread was set up for mixing a signal that already had a preamp, with either another one, or a magnetic pickup. Looks like the jbb systems are an array of 2, 3 or 4 piezos that go straight to a jack. They also seem to have a preamp that they made as a seperate box, though listed as not available. Gooseneck systems would be a small mic, and maybe a built-in preamp or maybe not? The under saddle systems are piezo, maybe with a preamp? So, could you describe some more about what you have and what you've tried. What kinds of pickups and what preamp and settings? Or have you been using external mics? The best recorded acoustic tones I've found have been from a pair of small diaphragm condensers (Rode M5), into a mixer. But you have to stay in position and room or bleed from other things need to be considered. |
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