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Mordor 8th December 2010 06:29 PM

help for a tube distortor
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Hi, today i played with ecc83: i want a distorsion !!!

ive make this circuit, but sound terrible distorted and dirty, drammaticali compressed ( like a fart, or dc component ).

I think the problem is impedance.... i want insert this circuit in line in / out in my rack equipments. Line out from preamp -> circuit -> line in compressor.
Please help me!

p.s. op amp is a burrbrown opa2277p, -v is connected to ground, +v to 12 vdc. there is a 7812.

Minion 8th December 2010 11:36 PM

Well , Running at 12ax7 at 12v isn"t going to give you a Very nice distortion , Ive tried several 12v Tube curcuits and couldn"t get anything nice sounding , the lowest voltage I was able to run the plates and still get a nice clean distortion was 45v .....

You are right about the impedance though and putting a high impedance buffer at the output is a good idea so you get the best signal transfer but instead of building the buffer and maybe finding out that is doesn"t help , just plug the output of the tube cuircuit into a effects Pedal and use that as a buffer .....

Also you should put a 500k or 1m pot between the 2 tube stages so can controll the overdrive/distortion effect .......


Mordor 9th December 2010 06:18 AM

ive try to connect only tube, without buffers, in a high z in of premplifier. Sound better, gain is low, and level distortion is low ( old rock style ). If i use a low volume in guitar sound is very warm. I dont understand why with buffer sound low and dirty: seem not a distortion of a tube. Ok tube at 12 v is not good, but this circuit dont work. This evening i record the distortion...

Nigel Goodwin 9th December 2010 12:58 PM

No bias on the valves, far too low an HT rail, and a completely spurious opamp in front of it, ruining the input impedance.

Stick 200-300V HT feeding the valve, bias them correctly, and dump the first opamp.

Mordor 9th December 2010 03:41 PM

I put only the valve at 100 200 300 vcc. Output opamp can be explode:)?

Nigel Goodwin 9th December 2010 06:43 PM


Originally Posted by Mordor (
I put only the valve at 100 200 300 vcc. Output opamp can be explode:)?

Best if you keep the opamp fed from a suitable low voltage (assuming you still want to use it? - as it's presumably going to be feeding a guitar amp input, the valve could feed it directly) :D

Mordor 9th December 2010 08:25 PM

im doing a particolar fx for me. I want do build a vocal distort. There is an ic that do 2 channell mixing with eq and volume via i2c, a digital i2c pot for change gain and a i2c filter. An atmel change presets via midi and drive an lcd. For distortion i want use an ecc83, whit catodic digital potentiomer for gain setting ( i must measure voltage at k, high voltage may melt digipot, or i will use a photoresistor with led & pwm lol )

Minion 9th December 2010 10:14 PM

Run the Plates at a High Voltage , put a voltage divider on the output of the tube stage to knock down the output voltage to 1/10 , then put the Buffer at the ouput .... Marshal does this in some of their ValveState amps .....

Printer2 9th December 2010 10:29 PM

12AX7 is not suppose to work well at low voltages, too much gain and no headroom. 12AU7 is suppose to work better at low voltages. I am sure if you do a quick search you will come up with a suitable circuit.

Peckerwood 10th December 2010 08:55 PM

Minion, are you saying that he won't get nice distortion because he is using a 12AX7? Or because he is running it at 12 volts?

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