Trouble with matsumin ts-808 srv special

[zhx]

Hi

I'm building the srv special using Ulysses' layout and Matsumin schematic
http://www.aronnelson.com/gallery/main.php/v/ulysses/ulysses_layouts/ulysses_ts_srv_special/ulysses_ts_srv_special_vero_1_01.gif.html
http://www.aronnelson.com/gallery/main.php/v/ulysses/ulysses_layouts/ulysses_ts_srv_special/matsumin_ts_srv_special_schem.gif.html

I'm having trouble both with the output buffer section and the tone control.

First of all, the tone knob seems to be doing nothing, and the whole tone circuit used here keeps me puzzled. I really dont get it. A resistor + cap to ground would make sense, but this... I have checked and doublechecked, but it won't work. I have tried several IC:s with no result. Would a simple cap to ground work here?

Secondly the output buffer/volume -section isn't working (and is also a bit confusing to me, I don't understand this bias thing...). The pot doesn't do anything. I tried replacing it with another pot, but no effect. It's on full volume the whole time. I tried bypassing the buffer, by getting the signal straight out from the pot mid lug wwith audio probe, and I seem to get a signal out just fine that way. I could always just wire a standard volume control there, right? (one lug to circuit, one lug to ground, one lug to output?) What use is there for an output buffer in a true bypass circuit anyway?

The first gain stage (or whatever the gain pot -section is) works fine. I get loads of overdrive.

For comparison, I was looking at MarkM's layout of the same circuit, and there is an extra 1 uf cap between the IC:s pin 3 and input buffer tranny emitter. What is the purpose of this?
There is also a 10 ohm resistor between the output buffer and the output cap, what's that?
The output buffer of the vero/ doesn't seem to have that 510 K resistor to bias either. Should there be one?
The gain section cap goes to ground in MarkM's layout, but into bias in the vero...what...!?
(And of course there's that 1N4001 for reverse polarity protection, but that shouldn't matter.)

It seems people have had successful builds with this vero layout, why are there differences then? Shouldn't this be the same circuit?

Sorry for the long post, but I hope someone could take the time to help a bit.

[Eb7+9]

What use is there for an output buffer in a true bypass circuit anyway?

that's a good question, though it has nothing to do with the true-bypass aspect ... if you compare the sound of the circuit with the buffers omitted the response is harsher and fizzier ... the output buffer has much less drive than an op-amp output and therefor carves a waveform will less sharp corners ... the combination of poor ground on the first op-amp clipper stage and the output buffer together work to provide some semblance of tube OD by producing somewhat softer clipping (edges) than just using an op-amp with good grounding ... there's another aspect going on to that has never really been explained properly either ...

sorry, I can't say what's going on in your build ...

~jc

[zhx]

Thanks for the reply. Makes sense, I guess.

I found the problem. I had mixed up the leads to the tone pot and the voulume pot. A really stupid mistake.
A good reminder to doublecheck the wiring too, and not just the circuit board.