Soul-O-Tube preamp

[GibsonGM]

I would attenuate the output of this using a voltage divider, down to something approaching the expected level for the VCF....but yeah, you'll certainly gain more headroom with higher V, all things being held equal.  That's why tube amps run on high voltage, in the first place.  More swing available.     Lowering the plate resistor value might help, too.

[Isak]

Thank you.
Just to make sure that I'll do the voltage divider as it should..
I'll be using 100k trimmer( or greater?), the right outer pin will be input, the middle pin will be output, the left outer pin will be going to ground.
This is a voltage divider, right  

[Isak]

Hi guys.

I really need help here.
I built the charge pump but only till 45V, using 7660S.
It works alright.
But...(there is always a but ) after connecting the 45V to power the "soul o tube" it doesn't work and the 7660S becomes very hot, when measuring the charge pump output while connected to the soul o tube I get only 9V, when disconnecting I get 45V.
It works well with 12V and 15V, above that V what I describe happens.
I checked for shorts and don't know what to check or do next.

Just to make sure I'm connecting the 45V to right place, To pin 1 and pin 6 before R3 and R4.

I'll be greatful if someone will help out here.
Cheers,
Isak E.

[tubegeek]

Try connecting a resistor to the power supply instead of the preamp to see if the charge pump behaves with some moderate load on it.

[Isak]

Thank you for replying.
You mean from the output of the charge pump, resistor to ground?
If yes, what would be an appropriate value?

[Isak]

ok, ive been reading and i found that i dont suppose to give the heaters more then 12V?
if i'm not mistaken pin5 and 4 are the heaters, right?
as i see in the scheme, pin 4 is going to ground and pin 5 is going directly to the plates!
now, correct mt if i'm wrong, heaters (pin5) need to get 12V and plates can have what ever i give them, say 45V, right?

[duck_arse]

you are entirely correct, and have found the reason your charge-pump didn't put the good volts. seperate the pin 5 heater connection from the R3//R4 point, and take the heater to your 12V supply. the two resistors may need a value change (an expert needed here), but they connect to your "HT" from the charge pump.

as it was connected, the IC was trying to supply current to the filament, much more than its rated for.

[Isak]

Thank you, so happy I found the problem
Now it works as It should (I gusse).
I need to adapt it to synths and do mods to have overdrive.
Surprisingly the output of preamp is very low compering to the synth sound source Vpp.
I was wandering if I can have more output volume? I thought that if I'll give the plates more then 12V I will have high level output, I was wrong.
I tried to reduce R3 and R4 to 10k instead 100k, even with 45V the results was the same.
To make it overdrive I bypass C2, that didn't helped.
I also tried to put a pot instead R2, that didn't helped.

Well, if someone here can please say...
1 - how to have more output volume.
2 - how to make it smooth overdrive, like it's giving it a small amount of overdrive boost.

Thanks in advance

[tubegeek]

It's a little hard to know what you'll get from this circuit using a low power supply voltage like 45V (assuming that's what you did end up with.) That voltage is still somewhat lower than what is typical for a tube circuit. Some general info though: C2 is there to increase the gain, also C4. Bypassing either one with a short circuit will upset the bias of the tube (you will have 0 Vbias and that will give you no headroom and other things you don't want). Removing either C2 or C4 from the circuit will lower the gain.

[Isak]

Ok,

It seems I missed a jumper to ground C2, now everything works and sound amazing!
Such a high level, this is exactly what I wanted
To tell you the truth...it is hell clean, I need some drive here man
This is the last thing I need from this circuit, only overdrive with overdrive gain/amount.

Cheers

[Isak]

Hi

I found how to make overdrive but very gentle I need more gain.
What I did is take out 1 leg of R5, the leg that goes to pin 8 of the tube and connect it to outer side of a10k pot, the other outer side of the pot is connected between pin 8 of the tube and ground.
What happanes is when I turn the pot CCW I have clean preamp, when turning the pot CW I get a nice overdrive, I will want more overdrive gain if possible, is it possible?

Cheers.

[duck_arse]

how did you connect C4 with the 10k pot? if you hang C4 from 10k pot wiper to ground, what happens to your boost/clean/tone?

[Isak]

i did it like the next pic...



as said, when turn pot CCW i have clean preamp, when turn pot CW i have drive, exactly as i want it to be, but i need more gain.
BTW...i have something strange with the drive pot i have the same thing with the VALVECASTER..
when i turn the drive pot CW to about 3 o'clock the gain till this point is as it should be.
from 3 o'clock and above (going to max) the general vol is going down and i have this strange noise from this point to max.
i didnt saw anyone experience this issue in the valvecaster thread.
isn't it strange that i have it in both? i mean the same exact thing.
i did a pic that will show you exactly the change points..