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SRPP with different brand of tubes ?

AC439

Member
2007-06-14 1:50 pm
Hi all,

I have recently built a 12AU7 standard SRPP preamp due to the simplicity of the schematic with an output capacitor of 2.2 uF and Rk of 680 ohms. I have read here the general consensus appears to prefer a difference topology than SRPP but I gave it a try anyway since I have parts on hand. I read about the driving impedance issue etc.

Anyway, I have two 12au7 tubes (old stock, not new) of different brand. I think it is better if both tubes are of the same brand because there are some variance due to different manufacturers. All these mean I don't have a matched pair. But I rather have the same sound characteristic on both L and R channel so I decided to use one tube for top triode and another tube for bottom triode, i.e. the top and bottom triodes are from different tube (different manufacturers).

I know this is not ideal. I do have a reasonable sound quality from this amp but I also notice I like my other 12au7 preamp better (a two stage direct coupling cathode follower output topology). When I compare them, they are close though. But I kind of feel that the SRPP amp has a higher distortion just listen by ears.

680 ohms of Rk gives current of about 5ma. The bass is not weak and the amp is dead quiet (I elevated the heater voltage), no hiss or hums.

Before I convert it to another topology, any suggestions that I can do to improve it so that I would keep it SRPP ? (I know try better tubes and same manufacturer but any thing I missed ?).

I'm still learning all this and I appreciate any input.

- AC
 
Hi all,

I have recently built a 12AU7 standard SRPP preamp due to the simplicity of the schematic with an output capacitor of 2.2 uF and Rk of 680 ohms. I have read here the general consensus appears to prefer a difference topology than SRPP but I gave it a try anyway since I have parts on hand. I read about the driving impedance issue etc.

Anyway, I have two 12au7 tubes (old stock, not new) of different brand. I think it is better if both tubes are of the same brand because there are some variance due to different manufacturers. All these mean I don't have a matched pair. But I rather have the same sound characteristic on both L and R channel so I decided to use one tube for top triode and another tube for bottom triode, i.e. the top and bottom triodes are from different tube (different manufacturers).

I know this is not ideal. I do have a reasonable sound quality from this amp but I also notice I like my other 12au7 preamp better (a two stage direct coupling cathode follower output topology). When I compare them, they are close though. But I kind of feel that the SRPP amp has a higher distortion just listen by ears.

680 ohms of Rk gives current of about 5ma. The bass is not weak and the amp is dead quiet (I elevated the heater voltage), no hiss or hums.

Before I convert it to another topology, any suggestions that I can do to improve it so that I would keep it SRPP ? (I know try better tubes and same manufacturer but any thing I missed ?).

I'm still learning all this and I appreciate any input.

- AC
srpp is easy and simple .if have oscilloscope can see sin an square wave .no need to Chang 12au7 .input gain of your amp ?
 
SRPP is a good circuit where it is appropriate. An audio line stage is not the right place for SRPP, neither is the voltage amplifier in a simple power amp. Mu follower is better if you want low distortion, but then you get more gain - a 12AU7 SRPP already has too much gain for a line stage.

Start from your requirements, then design a circuit which meets them.
 

AC439

Member
2007-06-14 1:50 pm
SRPP is a good circuit where it is appropriate. An audio line stage is not the right place for SRPP, neither is the voltage amplifier in a simple power amp. Mu follower is better if you want low distortion, but then you get more gain - a 12AU7 SRPP already has too much gain for a line stage.

Start from your requirements, then design a circuit which meets them.

Thanks for reply. I am reading about Mu follower at the moment and would give it a try !