Tube Buffer for gain clone.

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H

huangyong

Member
Joined 2003
200412114113926.jpg


Can i use this buffer for my gainclone?
my plan is to remove all the power supply section, and feed in +/-24V or +/-30V. any amendment that i should make?

Thanks.
 
Franz G

Franz G

Member
Joined 2004
Not very suitable for a gainclone:

this is an preamp, not a buffer!

This amp is working with some gain eg. voltage amplifier.

The input and output impedances are too high, for todays use.

And: there is a frequency dependent feedback in this circuit (including an electrolytic :-( notabene in the signal path). Maybe it is a phono preamp?

Franz
 
J

joensd

Member
Joined 2002
Simple understanding, the buffer is unity gain or small gain.
Click to expand...
A buffer has unity gain or slightly less.

+0dB max. or +4dB max(such as mixer console).
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I´m not sure what you mean but a preamp with 0dB gain is a buffer
and 4dB a rather low gain that is quite uncommon in preamps.
Maybe you are thinking about vu-meters and reference input line level signals?
 
Franz G

Franz G

Member
Joined 2004
The purpose of a buffer is impedance matching, not amplification.

Gain of a buffer is normally = 1, so no amplification, the input signal is not smaller than the output signal.

A preamp does some amplification (gain >1), the output signal is stronger than the input.

Franz
 
S

Sheldon

Member
Joined 2003
huangyong said:
many Thanks folks, i still dont understand whether it's a pre or buffer? pls just tell me suitable or not, i am newbie in tube.
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It's not suitable, as is. As others have said, it will have some voltage gain, so its technically an amplifier with the present feedback resistor values, not a buffer. But that's not the main problem. As Franz said, you have frequency dependent feedback (or gain, if you will). If I read the circuit correctly, the 10uf in parallel with 470k would give you increasing gain at very low frequencies (anyone care to speculate on the function of this part?), and the 100p in parallel with 15k would give decreasing gain above about 10k hz. It might work if you eliminate the two caps and the 470k resistor. The overall gain with the present feedback resistor might work ok, or you could play with the feedback resistor to get whatever gain you want.

I'm new to this stuff too, so I'd make sure someone can confirm this. Also, I'm not sure if you would have an imput impedence problem, as Franz suggested. Franz, care to elaborate a bit?

You could try to get this one to work, or you could try one that's already being used in this application, as Franz has suggested. Depends on how adventurous you want to be.

Sheldon
 
Joe Rasmussen

Joe Rasmussen

Member
Joined 2003
customanalogue.com
Franz G said:
When you are looking for a tube buffer for a gainclone:

Did you miss this site up to now?

http://members.ozemail.com.au/~lisaras/index.htm

Regards
Franz
Click to expand...

Hi Franz

Back in Oz again. Yep, http://members.ozemail.com.au/~lisaras/index.htm, that is still the original (but not best?) tube buffer for gainclone. ;)

Regards

Joe R.

PS: The jet lag was a killer, then I got the flu and when getting over that, got bronchitis. Seems I paid for the sudden change in weather/temparature.
 
S

Sheldon

Member
Joined 2003
Sheldon said:



It's not suitable, as is. As others have said, it will have some voltage gain, so its technically an amplifier with the present feedback resistor values, not a buffer. But that's not the main problem. As Franz said, you have frequency dependent feedback (or gain, if you will). If I read the circuit correctly, the 10uf in parallel with 470k would give you increasing gain at very low frequencies (anyone care to speculate on the function of this part?), and the 100p in parallel with 15k would give decreasing gain above about 10k hz. It might work if you eliminate the two caps and the 470k resistor. The overall gain with the present feedback resistor might work ok, or you could play with the feedback resistor to get whatever gain you want.

I'm new to this stuff too, so I'd make sure someone can confirm this. Also, I'm not sure if you would have an imput impedence problem, as Franz suggested. Franz, care to elaborate a bit?

You could try to get this one to work, or you could try one that's already being used in this application, as Franz has suggested. Depends on how adventurous you want to be.

Sheldon
Click to expand...


Oops, I goofed there. The second lp filter is actually around 30khz, so it's outside the audio band. Still don't know what the cap and 470k resistor is for, and and with the feedback resistor set for low gain, most of distortion produced by that bigger cap will show up in the output. So, as Franz said, you'd probably want to eliminate that. As far as input impedence being too high, I don't see why you couldn't use a lower value than the 1meg shown. Actually, other than that, the basic topology looks pretty interesting. People have reported good results with anode followers in pre-amp circuits. I'd like to find out more about it. With some changes, it might be pretty good, but I don't have enough experience to make specific recommendations.

Sheldon
 
H

huangyong

Member
Joined 2003
Thanks jaudio,
I have built that buffer and it sounds good to me. but my concern is i am going to build monoblocks ;and utilizing only one channel of the tube in one block is not good. so i m looking for any buffer taht use 2 channel of the tube to maximize it's usage.

Thanks.
 
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