Autoformer and buffer combo for a line stage
Posted: Wed Nov 23, 2016 6:58 pm
The inimitable ZEN MOD at DIYaudio has come up with an elegant approach to a simple line stage.
He has been working on this for a few months.
Simplicity itself - his recommendation is to wire a 1:1 transformer as a 1:2 autoformer (+6 dB) and drive this with a simple complementary buffer using the 2SK170/2SJ74 FETs. He is working on a diamond buffer, also.
I am using the FET one driving a 1:5 Slagle autoformer to balance levels between the above and below 500 hz amplifiers. The gain is used on the amp driving the 100 to 500 hz speaker. I refuse to use resistors to pad down the above 500 hz drivers. Before I was using the feedback resistor to raise the gain of the 100 to 500 hz amplifier. This worked OK but the buffer/autoformer works/sounds much better.
There is something good about iron in audio circuits.
When ZM gets the diamond buffer circuit PCBs ready I am looking forward to using this as a line stage after the SOEKRIS and my phono stage. Both could use a little extra gain but I am not aware of a line stage I can afford that sounds as good as I want it to. Would rather live with a little less gain.
Who knows if this will work as well as I WANT it to? But I think the chances are good. I like the idea of separating the voltage and current gain duties, especially when the voltage gain is achieved without electricity!
I guess one could use batteries but I will be using ZMs latest shunt reg for the DB - one wonders if batteries would even make a difference with the CMRR of the diamond buffer? I bet I know of ONE person ...
Seems like something that would interest the TIR NA folk.
He has been working on this for a few months.
Simplicity itself - his recommendation is to wire a 1:1 transformer as a 1:2 autoformer (+6 dB) and drive this with a simple complementary buffer using the 2SK170/2SJ74 FETs. He is working on a diamond buffer, also.
I am using the FET one driving a 1:5 Slagle autoformer to balance levels between the above and below 500 hz amplifiers. The gain is used on the amp driving the 100 to 500 hz speaker. I refuse to use resistors to pad down the above 500 hz drivers. Before I was using the feedback resistor to raise the gain of the 100 to 500 hz amplifier. This worked OK but the buffer/autoformer works/sounds much better.
There is something good about iron in audio circuits.
When ZM gets the diamond buffer circuit PCBs ready I am looking forward to using this as a line stage after the SOEKRIS and my phono stage. Both could use a little extra gain but I am not aware of a line stage I can afford that sounds as good as I want it to. Would rather live with a little less gain.
Who knows if this will work as well as I WANT it to? But I think the chances are good. I like the idea of separating the voltage and current gain duties, especially when the voltage gain is achieved without electricity!
I guess one could use batteries but I will be using ZMs latest shunt reg for the DB - one wonders if batteries would even make a difference with the CMRR of the diamond buffer? I bet I know of ONE person ...
Seems like something that would interest the TIR NA folk.