Paul Marossy

I would think that any electronics based curriculum these days would center around computers and "consumer electronics". Audio engineering is kind of a sideshow to that stuff as computers and games need audio. These days it seems like the software engineering is just as much as the electronics portion is.

That's the way I see it anyway.

EDIT: There are some other areas where you could make money. Like in controls for example. Also the automotive industry (which is doing poorly right now), manufacturing, and security systems.

I read once somewhere that you also want the pot bodies and switch bodies grounded, so they don't act like antennas for EMI/RFI. But I guess that is a moot point if you don't use the back of the pot(s) as a place to solder wires to ground...

One thing I don't fully understand about the guitarnuts article: one makes a Faraday cage of the cavity and grounds the cage to the bridge/trem. The audio circuit inside stays isolated from this, if I interpret the article corrrectly. Wouldn't that leave the audio circuit floating?

If you are having a problem with hum and/or buzzing, then you must have something wrong with your grounding. Are you sure that all of your shielding has continuity between itself and ground? Or, another common mistake people often make is reversing the hot & ground wires on the output jack, which has the same symptoms.

The idea behind star grounding is to ground your circuit in only one place, and not have redundant paths to ground, which some people believe causes ground loops. The Farady Cage is what shields the circuit from EMI & RFI, is connected to ground and is effectively part of the ground system. However, it does little or nothing for noisy pickups that like to pick up every interference that comes their way. That is a function of the pickups themselves. That is why I have some Fender noiseless pickups in my Strat, because I have never been able to really truly ever eliminate hum from any single coil pickups.

It could be any number of things causing that. Check out this page here: http://www.geofex.com/ampdbug/smoke.htm

Basically any burning smells and/or smoking coupled with a reduction in power in a tube amp means that something got really overheated and possibly damaged.

You really should take it to someone competent that knows how to work on tube amps and have them check it out.

Whoever did that could have been a little more conscientous about the wiring. There's way too much extra wire in there from what I can see...

I would venture to suggest making sure you're not playing near electrical sockets or your computer monitor, or any other source of electrical interference; obviously the high gain setting only makes it all the more noticable.

DJ

I agree. Flourescent lighting can also cause a buzz in the system, as well as wall warts, fans, motors, etc.

His grounding is fine if touching the strings makes it go away.

Uh, no... That IS what happens when There is a ground missing, or something ground related usually.

That is what I thought, too. When you touch the strings, and they are not grounded, YOU become the ground...

I'm not positive. I de-soldered everything, then started from scratch. I first did the pup to jack - fine. Then added the pot - fine. No issues after I re-did the whole thing. The most likely explanation is that I had something reversed, but I honestly don't know.

Maybe... that or maybe you had a cold solder joint (one that wasn't making a good connection). Anyhow, glad you got it fixed!

Thanks! So to do as suggested above, I would buy a push to make momentary switch, then simply add one new wire going from the jack plug ground terminal to one side of the new switch, and add a second new wire going from the live terminal of the jack plug to the other side of the new switch, yes?

Yes, that's one way that it could be done.

I am, in effect, shorting out the signal - as opposed to interrupting it?

Yes, that is correct.

And if I chose to do it the other way (ie. push to break switch on the live wire) it would kill the sound, but could leave the humming sound? Would that be similar to the sound you get in the background when everything's not earthed properly I suppose?

I'm not sure if there would be a hum or not. I would think not since you would be interupting the signal, and all that there is left is ground. Apparently, you might have some problems with noise, though - I suppose kind of like how a scratchy pickup selector switch sounds.

What did it turn out to be?

Are you certain that you didn't reverse the hot & ground connections on the jack?

Also, what make & model of pickup do you have? Maybe it's not wired correctly. I know on DiMarzio pickups with 4-wires plus a ground wire, it's not that hard to miswire one (been there done that). In addition, usually the pick up baseplate is grounded. Maybe a wire came loose or there is a cold solder joint on the baseplate?

Just throwing out ideas...

Good luck with that...

Nope the rev. E was the first to put the jacks on the board. I believe rev F is the first with the buffer.

Huh, I didn't know that. I will file that for future reference.

No... you want a normally open(push-to-make) switch. You press it to ground the signal.

With the normally closed switch, you'll get noise when you press the switch, even though it can also be wired to kill the signal.

Oh, I get the idea. I wan't thinking about it just grounding the signal, I was thinking of breaking the signal path. Sorry about that, not enough sleep last night...

His grounding is fine if touching the strings makes it go away.

This is just what passive pickups do, especially single coils.

The fact that your body shields it when you touch the strings suggests that you might benefit from some shielding inside the guitar.

I was thinking that perhaps one or more of the pot bodies and/or the pickup selector switch body are not grounded. If that is the case, grounding those and adding shielding might help with that "slight buzz".

Well i just wanted to ask you electronically smart fellas a quick question. Just finished my semi hollow and whilst i was playing the guitar with a fair bit of gain today i noticed the guitar buzzing just slightly when not being played, but if you touch the strings it stops. Now before you all go "you need to ground the bridge D**khead" I did! I did pull a wire out of the TOM bushing hole and pressed it in with the bushing so it rests between the timber and bridge bushing, Then the post obviously screws into this.

Now im thinking that maybe this is not getting a really good ground and thats why there's a slight buzz, but i thought there could be something else going on that you electronic experts may be able to point me towards!

Your help on this matter would be greatly appreciated.

Cheers Chad.

P.S If theres no solution thats cool. Its not really a big deal, it is like i said "real slight" but being the person i am i would like it silent and to just be able to hear the gentle hum of my fender tube amp!

Without knowing exactly how you wired it, all I can suggest is to double check your grounding.

Thanks Paul. I'm learning about amps and circuits and such, and figured the electrolytics were for filtering after looking at the schematic. My Rev. E board doesn't have the buffering circuit, so I'm gonna do the true bypass mod on it, if I can get it up and running. Just wasn't sure what the cap values were, so thanks for the help.

It doesn't have a buffer circuit on it?

i did some reading a while back on killswitches and form what i under stand the best one to use is a normaly open switch and have it ground the signal (just like a volume nob) it is suposed to give a little less pop and also silences your signal instead of having that unplugged humm you get with just breaking the signal.

But i haven't tryied it either way so what do i know

It would have to be a normally closed switch or else you would have to be pushing the button continuously when you're playing a tune. With a normally closed switch, it's making contact all the time until you break the signal path by pushing the button. Also, I would think that you want the type of switch that immediately springs back to a closed position vs. one that stays open/closed after it clicks - they do make both types.

Yeah, there are (2) 0.22uF caps and (2) 0.01uF caps in the signal path, one of which is the "sweep cap". The 0.1uF cap and the 100uF caps are for power filtering when being operated on a DC wall wart power supply.

I wouldn't worry about the small differences in the power filter cap on your circuitboard vs. the schematics - they seem to always be making minor changes to some of the components. The basic wah circuit essentially remains unchanged from the original for the most part, though. They only changed what they had to in order to use more modern transistors and they added the input buffer to avoid "tone sucking" when in bypass mode.

Take a look at this IC chip and see if it will do what you want to do:

http://www.analog.com/static/imported-file...heets/AD633.pdf

i havent read the whole document yet, but by the looks of it, i can make this work!

how did you find this chip? if you dont mind me asking

is there some sort of chip database that you went to?

and it's analog! awesome!

Cool, glad I could help. I asked your [re-phrased] question at another forum I am part of to get that answer. I didn't know that sort of IC chip existed, so this one is going in the mental rolodex!

I have the basic GCB-95 schematic shown here: http://www.diyguitarist.com/DIYStompboxes/WahMod1.htm

The only thing on that schematic might differ from yours is the resistor value on the emitter of second transistor.

To figure this one out, I would send it a continuous tone from an audio oscillator or similar device and then use an audio probe to follow the signal path to see where the signal is dying. Where it dies is going to be where your problem area is. It's very easy to build one, you can see how to do that here: http://www.diyguitarist.com/PDF_Files/DIY-AudioTester.pdf

I suggest the audio probe because it could be any number of reasons why it is behaving like that - it could be an input/output jack, the bypass switch, a bad cap, a bad transistor, a crack in the PCB somewhere (like at the input/output jacks, seen that before), something shorting to ground somehow, the wiring harness, etc., etc.

Take a look at this IC chip and see if it will do what you want to do:

http://www.analog.com/static/imported-file...heets/AD633.pdf

It almost sounds like you are designing a differential amplifier circuit or something like that.

A differential pair amplifies the difference between two input signals/voltages, and has an inverted and a non-inverted output. The DC offset bias on each input signal affects how the output waveforms look. That seems to be basically the same thing you are trying to accomplish...

seems like youre describing an opamp. but no, an opamp can only add/subtract signals together, then multiply them by a constant. that is different from multiplying the two together.

Yeah, I guess that would be a dual opamp, wouldn't it?! Doh!

Hmm... not sure on that one. I'm intrigued by this concept. I'll do some asking around.

It almost sounds like you are designing a differential amplifier circuit or something like that.

A differential pair amplifies the difference between two input signals/voltages, and has an inverted and a non-inverted output. The DC offset bias on each input signal affects how the output waveforms look. That seems to be basically the same thing you are trying to accomplish...

Yes I know about the different wire gauges..... However im surprised to hear that they told the resonant peak.

This info has been quite helpful....

Just noticed the breed dont use the dual-resonce coil patent....

They sent me back an email trying to blow me off, but I was persistent and wrote a second email to which they responded with the information I wanted. Yeah!

I can tell you that the DiMarzio FRED has a DC resistance of 10.07K and a resonant peak around 5.34kHz - I got the resonant peak info straight from the engineering dept at DiMarzio via email. Maybe you can work the numbers backwards to figure out what gage of wire to use?

They should have the DC resistances for all of their pickups listed at their website. They don't include the resonant peak info on their website because they say there is no standard for measuring that, so they don't publish it.

I can also tell you from looking at DiMarzios patent documents, that on their humbuckers, they use a different gage wire for each coil. DiMarzio claims that by using two different wire gages with the same amount of turns on each bobbin improves the 60 cycle humbucking while improving frequency response.

I hope that helps...