MPP

[Joachim Gerhard]

Input resistance can be 450 x 3,5 = 1.575 Ohm.

 

[Joachim Gerhard]

Then we go Rbb parallel to 100 Ohm is 3,38 Ohm.
100 / 3,38 = 29,59

 

[Joachim Gerhard]

Ok, and then is the divider 1.575 but that is not much

 

[Joachim Gerhard]

Ooooh , the cartridge!

 

[as_audio]

Can't follow

 

[Joachim Gerhard]

And then the 470 Ohm.... and so it goes...

 

[Joachim Gerhard]

Speculation right now.

 

[Joachim Gerhard]

I think this circuit changes gain with cartridge impedance.

 

[Joachim Gerhard]

Gain can be reduces by lowering the upper 100 Ohm resistor I think.

 

[Joachim Gerhard]

What I really do not 100% understand is the 100 Ohm base resistor. For one it is a stopper for parasitics so it can stop Oszillation tendencies.

 

[as_audio]

This is the -main- feedback resistor

 

[Joachim Gerhard]

Another approach. Current combined in the 2 input transistors is 12mA. Ube is around 0,6V.
So dynamic impedance from base to emitter is 50 Ohm. But there is the cartridge in parallel.
In my case a Lyra Atlas with 5 Ohm winding impedance.

 

[as_audio]

Not sure what is going on here.
Check your calculations ..

 

[Joachim Gerhard]

One Glas wine too much .......

 

[Joachim Gerhard]

Gain

......

 

[as_audio]

.

 

[Joachim Gerhard]

I am in a process to make a single ended pre-pre with no cap at the input and compare the sound to the circuit I showed here recently.

 

[Joachim Gerhard]

Next comes a circuit with no cap at the input AND the output. That is parallel symmetric though.

 

[Joachim Gerhard]

AS Audio asked in another thread if there is a phono amp available with adjustable input offset. For one there is the Paradise with a trimmer at the input.
Marvel has shown designs with input servo.
I am working on a single ended circuit that needs no input cap. Here we have PNP transistors at the input with an NPN Rush Cascode. It can be level shifted to bias the input transistors to Ube positive ( ca. 0,67V ). Than can be made adjustable. Do not take the circuit too serious. I am still working on the values. It should work though.

 

[as_audio]

Somebody wrote : "some phone amps have the possibility to adjust the DC offset" so I
asked for examples. He did not show up again. I assumed he meant commercial amps.