Timmy vs Zendrive

frankus

So everyone knows they're alike,

So I investigated that seeing if I could mod a poodle pedal parts fat Buddha PCB to do the job...

Of course the Timmy PCB is a couple of quid cheaper

Majorscale

I have both on my board and really don't think they are similar at all!

ThePrettyDamned

Majorscale said:

I have both on my board and really don't think they are similar at all!

I think he means circuit wise - the big question is which came first, as they were both released pretty nearly the same time. 

So one is a sort of clone of the other. Maybe.  

ICBM

They appear to be nearly identical circuits, but there are quite a lot of small differences in component values, and one critical difference in component type (the clipping diodes), both of which can make a big difference to the sound.

GuyBoden

ICBM said:

They appear to be nearly identical circuits, but there are quite a lot of small differences in component values, and one critical difference in component type (the clipping diodes), both of which can make a big difference to the sound.

Yes I agree, small differences in component values can change the tone dramatically.

I'm looking at the schematics, I think the treble control between the two opamps was an original Timmy idea by Paul Cochrane.

Zendrive

Timmy

frankus

For the record I've a Timmy and I've had a Zendrive (currently got a Zenkudo) ... I love both sounds and I think they work seperately and together...

This was merely an exercise in electronics and fitting a Timmy into a 1590a ( the fuzzdog Zendrive PCB fits in one ... and so will the Timmy PCB it appears.)

Now I've just got to figure out how Mr C gets that amazing finish on Timmys

oh and are the transistors being used as transistors in the Zendrive?

GuyBoden

frankus said:

oh and are the transistors being used as transistors in the Zendrive?

The Mosfets 2N7000 in the Zendrive are used for soft clipping in the feedback loop with Bat41 diodes. I like using piggy back Mosfets for an even softer clipping sound.

ICBM

GuyBoden said:

I'm looking at the schematics, I think the treble control between the two opamps was an original Timmy idea by Paul Cochrane.

No, it's like the Rat.

Essentially both of them are Tube Screamer overdrive with Rat filtering and variable bass control (fixed on the Rat).

GuyBoden

ICBM said:

GuyBoden said:

I'm looking at the schematics, I think the treble control between the two opamps was an original Timmy idea by Paul Cochrane.

No, it's like the Rat.

Essentially both of them are Tube Screamer overdrive with Rat filtering and variable bass control (fixed on the Rat).

I'm confused, the Rat only has one opamp, so how can the Rat have as I stated "a treble control between the two opamps" like a Zendrive, I've experimented and built both circuits a few times. The Rat is single Opamp the Zendrive is a dual Opamp.

ICBM

The Rat uses a discrete transistor instead of the second op-amp, but the filtering arrangement - both for the treble, which is a variable series resistor feeding a shunt cap to ground in the signal path after the clipping amplifier, and the bass which is a HF pass to ground in the NFB loop of the clipping amp (fixed in the Rat, variable in the Timmy and Zendrive) are identical in concept. The Rat and the Timmy both use a dual cap arrangement for the bass, the Zendrive only one, but otherwise are the same.

The bigger difference is that the Rat uses clipping diodes to ground after the first gain stage, whereas the Timmy and Zendrive have them in the NFB loop like a Tube Screamer. So in concept (if not detail) they are both a "Tube Screamer with Rat filtering". The TS uses the second op-amp stage as a tone control instead.

monquixote

Why is it that reducing the bass on the Zendrive increases the amount of distortion?

ICBM

Because it operates in the negative feedback loop of the clipping amplifier, so it actually works by boosting everything except the bass, rather than by cutting the bass. So you get more gain in the mids and highs.

monquixote

Ahh that makes sense. 

Cheers!