How to get a buffer with overdrive from a 12AX7 ?

-_nando-_ · 24th July 2006, 02:21 AM

Hello !

I need a buffer, and the only easily avaliable tube here is the 12AX7. The imput impedance of the amplifier is 100K I believe. The amp is a BPA200 already buffered with a OPA2134 opamp, that have a 100K resistor to the ground (to avoid oscilation and noise) in it's imput.

The buffer must be capable to deliver clean and distorced signal, with a potentiometer to choose "how dirty" the sound will be.

Isn't a hard task right? But I never did anything with tubes before !

Thanks !!!

-_nando-_ · 24th July 2006, 03:01 AM

It must have a frequency range of 20 ~ 20.000hz, very plain if possible. Yes, it will be used in a Hi-Fi system, consisting in Beyma Studio Speakers, etc.

Gain of 3db is enough.

Thanks !

-_nando-_ · 26th July 2006, 04:22 PM

hello ?

leadbelly · 26th July 2006, 05:33 PM

Quote:

Originally posted by -_nando-_
hello ?

You are probably not getting help because this has been discussed many times. Also the way you phrased the question is a bit silly, since a buffer stage, unity gain, cannot drive a 12AX7 into clipping. You would need extra stuff to do what you want.

May I suggest you just build one of the various 12AX7 overdrive stomp box schematics on the 'net as a front end for your GC?

-_nando-_ · 26th July 2006, 08:55 PM

Hi, I didn't know that was not possible to get overdrive from a simple buffer.

What I really need is the distortion from the tube, can I drive the 12AX7 into clipping with an buffer IC ?

I know that valve buffers were discussed many times, but I did search and I found myself a little lost, because there was nothing simple the way that I want.

What do I need to drive the tube into clipping? Can I work with low voltages like 15+15V with the 12AX7 ?

The big problem is, I must use only ONE tube

Thanks for the answer !

leadbelly · 26th July 2006, 11:16 PM

Maybe you should back up and explain what you are trying to accomplish. You want a tube distortion front end on a GC, for a hi-fi application, not a guitar amp? Why? And why go to all the trouble of adding a tube stage but putting such heavy restrictions on it like +/- 15V rails and only one tube? You are bound to be disappointed if you put up such guidelines instead of just asking "what will it take to get to this point?"

DoctorJ · 27th July 2006, 01:39 AM

You could do it with one tube and you will need a voltage quadrupler to get the voltage up high enough for the tube. You can get a tube to distort very easily by putting an opamp in front of it which drives the tube into distortion.

-_nando-_ · 27th July 2006, 02:00 AM

Sorry, you're completely right. I just didn't know how to ask for it in a good way.

I need tube distortion for a guitar amp, what do I need?

Can I use only one tube?

Thank you leadbelly.

DoctorJ, I loved your post, can you draw how this should be? How many volts ?

I'm planning to use an SMPS Step Up low current converter to increase the voltage.

Thank you all again !

24th July 2006, 02:21 AM	#1
-_nando-_ diyAudio Member Join Date: Dec 2005 Location: São Paulo	How to get a buffer with overdrive from a 12AX7 ? Hello ! I need a buffer, and the only easily avaliable tube here is the 12AX7. The imput impedance of the amplifier is 100K I believe. The amp is a BPA200 already buffered with a OPA2134 opamp, that have a 100K resistor to the ground (to avoid oscilation and noise) in it's imput. The buffer must be capable to deliver clean and distorced signal, with a potentiometer to choose "how dirty" the sound will be. Isn't a hard task right? But I never did anything with tubes before ! Thanks !!!

26th July 2006, 11:16 PM	#6
leadbelly diyAudio Member Join Date: Dec 2002 Location: Calgary, Alberta	Maybe you should back up and explain what you are trying to accomplish. You want a tube distortion front end on a GC, for a hi-fi application, not a guitar amp? Why? And why go to all the trouble of adding a tube stage but putting such heavy restrictions on it like +/- 15V rails and only one tube? You are bound to be disappointed if you put up such guidelines instead of just asking "what will it take to get to this point?" __________________ Aerodynamics are for people who can't build engines. Enzo Ferrari

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24th July 2006, 03:01 AM	#2
-_nando-_ diyAudio Member Join Date: Dec 2005 Location: São Paulo	It must have a frequency range of 20 ~ 20.000hz, very plain if possible. Yes, it will be used in a Hi-Fi system, consisting in Beyma Studio Speakers, etc. Gain of 3db is enough. Thanks !

26th July 2006, 04:22 PM	#3
-_nando-_ diyAudio Member Join Date: Dec 2005 Location: São Paulo	hello ?

26th July 2006, 08:55 PM	#5
-_nando-_ diyAudio Member Join Date: Dec 2005 Location: São Paulo	Hi, I didn't know that was not possible to get overdrive from a simple buffer. What I really need is the distortion from the tube, can I drive the 12AX7 into clipping with an buffer IC ? I know that valve buffers were discussed many times, but I did search and I found myself a little lost, because there was nothing simple the way that I want. What do I need to drive the tube into clipping? Can I work with low voltages like 15+15V with the 12AX7 ? The big problem is, I must use only ONE tube Thanks for the answer !

27th July 2006, 01:39 AM	#7
DoctorJ diyAudio Member Join Date: Mar 2006 Location: Georgia	You could do it with one tube and you will need a voltage quadrupler to get the voltage up high enough for the tube. You can get a tube to distort very easily by putting an opamp in front of it which drives the tube into distortion.

27th July 2006, 02:00 AM	#8
-_nando-_ diyAudio Member Join Date: Dec 2005 Location: São Paulo	Sorry, you're completely right. I just didn't know how to ask for it in a good way. I need tube distortion for a guitar amp, what do I need? Can I use only one tube? Thank you leadbelly. DoctorJ, I loved your post, can you draw how this should be? How many volts ? I'm planning to use an SMPS Step Up low current converter to increase the voltage. Thank you all again !

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