New DSM project...XTC preamp..PCB!!

[GonzoFonts]

1st Post

No, that is the schematic for the Bogner XTC preamp with tubes.

I am looking for the schematic for the pedal after the conversion of tube to fet.

Thanks.

[dschwartz]

there´s no schem.. just replace the triodes with fets and B+ for 9 volts

[GonzoFonts]

there´s no schem.. just replace the triodes with fets and B+ for 9 volts

Thanks... but I thought when you did the tube to fet conversion, there were some additional modifications (i.e. added caps?) that had to be done.

Is that not the case?

Thanks.

[dschwartz]

oh, indeed..i added 220pf caps from gate to source of each fet for miller capacitance.

[nico21]

the schem i use is the one from xtc 100B
So it's the same as the schem in the first post, but little differences:

1n cap across R6
R12 after R15, not before
no C8

I did the red and blue channel (2 x 1M pots, in the schem it's 2 x 500k pots) and did not install the Pre eq switch (470p, 4,7n or no cap across gain pots)
I use the pcb and power supply of the Dr boogey, the scaled tone stack, miller caps, no structure switch
2nd cathode resistor is 2.7k, going to try around 2.2k
3rd cathode resistor is 10k, going to try around 3.3k (as in the dr boogey, it's 3.9k for 39k in real one)
For the moment, sounds very good to me  (good tone, versatility, no oscillations, no squeals, .....)
Will report asap, with sound clip too
In the same time i'm doing the FET version of the Fish Brown channel...(think i will report in another thread...)

Nicolas

[pravudh]

Hi all.
dschwartz .after read this topic i try something with your idea about tube-fet
so i just finish my SLO today and sound good maybe better than dr.boogie
anyway next time i will start with your layout
thank you 

[dschwartz]

HAHA.. I WAS STARTING TO WONDER WHATWAS WRONG WITH MY LAYOUT THAT NO ONE USED IT..
IT´S NICE!

[deaconque]

i was hoping someone would tackle the xtc.  i've been wanting to try that one for a while but it's a little over my head right now.  so can someone tell me exactly what the structure switch does?

[GonzoFonts]

For the XTC build... what FETs would you recommend? Have you tried different FETs? If you have, can you comment on the change in tone?

Thanks.

GF

[dschwartz]

i was hoping someone would tackle the xtc.  i've been wanting to try that one for a while but it's a little over my head right now.  so can someone tell me exactly what the structure switch does?

the structure switch boosts the hell out of second gain stage, and cuts a bit of low end..at the same time, clipping is different with or w/out source cap..

fisically the switch connects the bypass cap to ground and adds a 4.7k resistor in parallel with the 4.7k source resistor, reducind source resistance= increasing gain.

is like a boost switch, but since is not exactly a boost (it changes the freq response and behavior of the fet) it´s called "structure".

my guess is that it gives a nice vintage med gain distortion versus high lead tone..


and gonzo.. i haven´t build this yet..
but it is designed to be used with j201´s (and probably better to put a mpf102 at the first stage..)

[deaconque]

i can't wait to build this one.  this "need to build" list just gets longer and longer.

[nico21]

Hi guys!

Could anyone explain me the aim of the 3rd stage (with the 10k resistor), how it behaves? (in a real tube amp) , is it just to had some gain, assymetrical clipping.....

This question in order to re- create it as close as possible in a fet stage

Thx !
Nicolas

[aziltz]

Does anyone have a schematic of the pedal?

Thanks.

GF

a FET schematic of the pedal, the OP has a TUBE Schematic of the amp.

[sm3000]

has anyone done a proto of this?

[Maik]

what is the size of the pcb?

[therecordingart]

I missed this one david....
The layout looks pretty good. I need to look at it closer though to be sure.
Just make sure to put the Level pot on the other side of the tone pots and not next to the gain pot as this may cause oscillation.

The input stages should stay away from the output stages, left to right. If you could mount the board so the gain pot is routed as far away from the tone and level pots that would be best. Like the DB layout.

John

John,

Can you elaborate on this? I'd like to understand with it would oscillate. That may be too loaded of a question so if there are any resources you can point to I'd be in debt to you, sir.