AMZ Mosfet Boost DC(?) Noise

[vanhansen]

Hey all.  I hope somebody has an answer on this.  I did search and found one thread that might have pertained to the issue I'm having but it's not clear whether it's the same issue or not.  So, let me explain what's going on.

My simplest signal path where this happens is guitar, AMZ Mosfet Boost, amp.  Now, with the pedal disengaged all is fine, no issues.  With it engaged and the guitar volume rolled all the way off, I hear what sounds like runaway DC noise.  As I roll up the guitar volume, the noise goes away until the volume is all the way open and then it comes back.  This happens with ALL of my guitars no matter whether the pickups are humbuckers or single-coils.

I cannot hear this happening with a buffered pedal before or after it but I can hear it if there's a true bypass pedal before or after it and the TB pedal is bypassed.  As soon as the TB pedal is engaged, the noise goes away.

Bizarre?  You bet.  I double-checked everything I could think of and still the noise is there.  I even tried the pedal using a battery and it's still there. 

The pedal works great otherwise and it's one of my favs, but with this noise there, I cannot use it.  It's the only pedal that I've made where this happens when it's engaged.

Any ideas as to what could be going on?

Do I need some incoming DC filtering? 

[Cliff Schecht]

Filtering might help. Try that first. But also, how is your grounding scheme on the build? Weak/thin grounds can act resistive and cause all sorts of problems (i.e. voltage developing across your ground). An oscilloscope is a useful tool for looking at how noisy your grounds are. Or maybe the effect is noisy until you touch a piece of metal on the guitar (i.e. the volume knob)? Even getting your fingers close to some metal can add some capacitance to ground which will kill noise that is otherwise heard at the output.

What fet are you using?

[vanhansen]

I'll throw some filtering across the incoming voltage then and see what it does.  This build is on perfboard with a layout like Torchy's stripboard layout (at least I think it was Torchy's - been a few years).  The Mosfet is a BS170.  The volume knob it self on my guitars is plastic so touching that won't do anything.  Touching the strings will and even then, the noise is still there.  I can even unplug the guitar and still hear the noise.  I don't own an O-Scope so I'll have to use my meter to check for stray voltage though last time I checked it, everything was good.

Will post back with updates.

[solderman]

Hi
I had a sort of the same kind of problem whist a project built on the AMZ JFET booster. It started like yours but ended with that the signal path was blocked and the effect muted it self. The problem was that the IN cap was not attached in bot ends all the time and the IN cap couldn't bleed out its charge. The solution was to add a bleed resistor so that the Cap always could bleed to GND (R5 in the schematics) also assure that the IN is grounded when the true bypass is switched off.

Here's The schematics of the Mini Man
http://solderman.fatabur.se/Mini_man/Shcematics_MiniMan.jpg

And how it looks


//Solderman   

[vanhansen]

Thanks for the replies.  I think I just found the issue.  This morning I decided to start from the beginning and go guitar, Mosfet Boost, amp and then slowly add stuff in from my pedalboard.  At first I had thought my Phase 90 was causing it in bypass mode since I had done some surgery work on it this week but it's OK. 

Then I went to this A/B switch I had built that goes between my acoustic preamp and my electric guitar pedals (2 inputs, 1 output).  Guess what, that's the problem.  I don't know why there is this noise there but the AMZ Mosfet Boost is just making it noticeable.  It's just 3 jacks and a DPDT toggle.  I guess I need to look at it's wiring.

Thanks for the tips shared.

[vanhansen]

Oh GREAT!  Now my tuner too?  This is ticking me off. 

Guitar - Mosfet Boost - Amp = no noise
Guitar - Mosfet Boost - Phase 90 - Amp = no noise
Guitar - Mosfet Boost - Phase 90 - switch box - Amp = noise
Guitar - Mosfet Boost - Phase 90 - tuner - Amp = noise

The thing is, with the tuner, I hear the noise in the middle travel of the volume pot and with the switch box it's at either end like in the original post.  It's like a ground noise or a DC leakage noise.

And no, it's not the guitar(s), I'm positive of that.

The tuner is a Planet Waves pedal tuner, BTW.  Power supply is a Visual Sound OneSpot and the OneSpot daisy chain.

[solderman]

Hi

OK, what i think you have to do is to start with disassemble everything and start from scratch

1. Guitar -- Cable-- Amp.

2. Take one effect/function at the time in between and see if the problem reuccure. if it does you have fin the faulty link. Test and crosstest every possibility or case and do not change more than one thing at the time.

Check the A/B switch. If you let a hot wire from an amp be unconnected and un grounded or connected and un grounded (like if you put a cable in your amp and only touch the hot part of the jack) you will definitely get a hum, the same goes for all kind of circuts, Eg. if you go not ground the unused guitar (if you use the switch for that) and it collects hum).


Guitarr cables can be a reason so do not forget to test different cables.

//Solderman

[vanhansen]

I already narrowed it down to being the tuner as the culprit.  But thanks.