prof. tweed build and doing some strange things

[dschwartz]

HI all there!!!
I finally build a prof tweed...i let it with an 0.01uf negative feedback cap. Used a j201 for the first stage as recommended and MPF´s for the rest...AND i added a 39nF bypass cap at the first stage....WHY??

Cause at the front of my amp (peavey triumph PAG120) it sounded as a totally farty, muddy and blatty..ugly overdrive, specially on the low notes, so i thought that cutting the bass ant the first stage will clean it up...

The thing is that i tried it with a Marshall jcm800 clone at a friend´s home (w/the BP cap) and it sounded freakin´good!!!!! nice breakup, totally fender-type sound, all i expected from this pedal, even more..great!!...

so i brought it back home with high hopes, plugged it to my amp, and still sounded like crap , even with the bypass cap mentioned...

what´s going on folks??? please help!!!
ps: sorry i reloaded and posted twice...didt find how to delete it

[psyche]

maybe it is overloading your amp's input.Did you try lowering the volume of the tweed??Try playing with the tweed through different amps.If it plays well, like on jcm 8oo, then have a look at your amp's input stage.Maybe there is something wrong.

[jakenold]

The tweed is surely a strange pedal! Mine caught fire in my first build 

[markm]

The tweed is surely a strange pedal! Mine caught fire in my first build 

I had trouble with mine firing up when first built but, then it was fine......didn't catch on fire though, I would've remembered that!

[psyche]

Hehe!!Caught fire???Did you checked the trimpots before you place the fets???Where all the electrolytic caps in correct order????Things you should check before you power on any electronic unit you built!!!!Also check for the correct oreder of the fet "legs".Today i perfboarded a blackface preamp using 2n5458 fets and i put the fets reversed!!Hehe, to my luck i reversed them and everything is ok.By the way it sounds great.A few tweaks to be done and i will post the schematic, the layout and a soundfile.

[spudulike]

To get back to the OP's issue it sounds like an odd impedance problem. I dont know your amp, but try running the Prof into a buffer before the amp (even just a Boss pedal in bypass). If that clears the problem then tack on an LPB and try it ...

[oldrocker]

Never had a problem with my PT but when I tried the J201 in the first position I couldn't get it to bias right for some reason.  But using all MPF102's mine sounds fairly decent.  Put it in front of your TS808 and it rocks.

[jakenold]

I'll try to build another one when I get home tomorrow.

It was the trimmer connected to the Q1 that started to burn. Very, very odd. All the other components are fine, as I dismantled the setup and checked them. So now I'll try my luck with a fresh PCB.

Sorry for going a little off course you guys...

[oldrocker]

Was that a Radio Shack trim pot?  On some circuits you should use a plastic tip screw driver when adjusting RS trim pots or they may smoke.  It happened to me a couple of times.

[jakenold]

Was that a Radio Shack trim pot?  On some circuits you should use a plastic tip screw driver when adjusting RS trim pots or they may smoke.  It happened to me a couple of times.

No, it was an Alpha I think. Good quality, never failed me. It must be me who messed up somewhere, even though I spent a lot of time looking through it all (I perfed it).

[psyche]

Sometimes when you solder the trimpots or other plastic components watch out not to keep the soldering iron too much time on the component, it melts and then it is useless.Happened to me sometimes when i was a beginner years ago!

[jakenold]

Sometimes when you solder the trimpots or other plastic components watch out not to keep the soldering iron too much time on the component, it melts and then it is useless.Happened to me sometimes when i was a beginner years ago!

Yeah, that could have been why it happened. Strange, as I've soldered in probably a thousand trimmers in the last years...

[dschwartz]

well i put an output fet buffer, and the farting was still there, so is not my amp input impedance..

i´m pretty sure its the 2nd fet that´s farting, i changed it and didnt work, so soon i´ll reduce the input fet´s source cap...

[psyche]

well i put an output fet buffer, and the farting was still there, so is not my amp input impedance..

i´m pretty sure its the 2nd fet that´s farting, i changed it and didnt work, so soon i´ll reduce the input fet´s source cap...

Are you sure?You said that when you plugged it in the jcm it was ok.Check each fet's pinout and install new ones.Also check for the correct voltages on the fets.Try to adjust the bias to VCC/2 and then do "micro" adjustment with your ear to where it sounds more clean.Check it with your amp and if possible plug it into your soundcard you will get a point of what's happening!You need to be a little more carefull with fets.Waiting for your progress!

[dschwartz]

ehmm.. im confused or very happy....

i played a line 6 flextone the other day, and at the bssman mode..it had the same farty distortion!!!!!!!!!!

i couldnt believe it!!!

[stm]

Well, this is because the Professor Tweed has become so acurate that now reproduce the "undesired" aspects of the amp as well.    Well, maybe not!

Seriously, the farting you describe is to be expected since there is no bass cut in the first and second stages.  Based on your initial description I thought it was due to some problem in the build, FETs or whatever, and didn't think about an intrinsic aspect of the circuit.

If you want to change the bass response I'd suggest you try the following changes in order, and testing between each one:

1) Reduce the 22uF cap at the source of Q1 to 1uF

2) Reduce the 22n coupling cap at Q1-drain to 1nF, 680pF or even 470p (see what you like best in terms of Bass)

3) If more gain is desired (to evercome bass gain loss by the previous changes), then place a 22uF cap between Q2-source and ground. You can try smaller caps if you prefer.

4) Check if removing the 22k+1uF feedback network improves the sound.  At least gain and output level should raise a bit.

Cheers.