XXL stompbox mod help please

[sonofspy]

Hi,

I have a Tech 21 XXL stompbox (1st version w/the chrome swirl top)
The distortion is just way over the top for my needs, so I thought I could
just increase the resistance on the gain circuit and make it more of a clean boost/overdrive.

The drive pot is a 100K Linear taper, Being poor and living in the stix like I do I added a SPDT
switch which allows me to add 130K resistor to the circuit (for a max of 230K).
This does decrease the volume a little (the box has tons of volume so that's not a problem)
and it cleans up the signal a bit, but not as much as I hoped (or expected)
So I think I am going about this in the wrong way to achieve my desired effect (no pun intended).

Here's the schematic.


Suggestions?

sonofspy

[Belt]

Have you tried any other resistance values other than 130K?

[anchovie]

The signal has already been amplified once before it gets to the stage with the Drive control. Try a lower value for R9 - maybe a trimpot so you can experiment more easily.

[b_rogers]

Mine cuts bass so badly I haven't plugged it in a while..good grit, but no bass..need to open er up. I think mine is newer in the black box..

[sonofspy]

Firstly thanks all for replying,

Belt:

I previously tried 47K but the difference although you could hear it ... was minimal.

anchovie:

Will try a trimpot jumpered over R9...The reason I started externally to the board is they have
made it a real PIA to remove the circuit board, you have to desolder the input or output jack
to get access.

b rogers:

You are familiar with the <<Strange>> active tone control on these things?

"At Max, frequency response if flat, however as you go towards the mid-point
it boosts the low end and adds body giving you the warmest sound. Then as you decrease
from the mid-point it cuts highs--without changing the level.."

Will post after experimentation...

Best Regards,

Sonofspy

[b_rogers]

i think mine may be defective because i get NO BASS no matter what i do with the tone control. every amp i tried it thru hated it so far. mines goin on the bay

[grolschie]

Sonofspy, what about breaking the circuit and inserting a 100k pot between C10 and VB - just like the drive pot config on the next stage?

[darron]

pun?

[sonofspy]

pun?

Sure..."my desired effect" has 2 meanings in this context

1) effect as the result of a change in the circuit.....I desired much less distortion in the sound

2) effect as the effects box itself I want an overdrive/clean(er) boost pedal

Cheers!

sonofspy

[darron]

i thought that's what you meant.... i consider them both the same meaning i suppose... sorry, must have been in a very specific mood yesterday... disregard! haha

[sonofspy]

Well having opened 'er up. There's a problem.


How do I get inside THIS:




grrr.

[edvard]

HA!
I was waiting for that... 

I had the unfortunate task of repairing a stomped-on volume pot on one of these things and the guy from the music shop said (very quietly) something that sounded like "copy this one - it sounds awesome".
Imagine my surprise... 

I'm also surprised to see a circuit for it. Did the old ones not have the potted rectangle?
It might be worth it to build one, check that it actually works and sounds the same and use that in the old enclosure instead.
I always wondered what the 'Warp' control did. Looks like it tweaks the bias to the first op-amp.
Tried that once in a design of my own. Nice effect, but not as usable as I thought it would be.