MPP

[jcarr]

Or you could use something like Syn08's HPS 5.1 as a starting point.

Given that the high transconductance JFETs are in your possession, it would be a shame to throw away the noise advantage with a differential topology.

Hps 5.1

 

[Joachim Gerhard]

Sorry, I forgot the resistor that sets the idle.

 

[Joachim Gerhard]

AS, yes, please redraw it.

 

[Joachim Gerhard]

I build circuits like Hps 5.1. I used 4 x 2Sk369 and I got a dead quiet result. The sound of that circuit is Good but soundwise I can do better.

 

[Joachim Gerhard]

That stage we called Daniela because Daniela Manger used it on a HighEnd show in Munich.

 

[Joachim Gerhard]

This one...

 

[Joachim Gerhard]

Cascode

A way to lower the input capacitance is cascoding. Here are some examples.

 

[Joachim Gerhard]

Daniela

I found the Daniela Circuit. The advantages over the Hps 5.1 are:
I need only a single stage of amplification and it is completely DC coupled.

 

[Joachim Gerhard]

I am just installing a two pole compensation and an optional rumble filter.

 

[Joachim Gerhard]

I am just installing a two pole compensation and an optional rumble filter.

 

[RCruz]

optical rumble filter ????

Would you care to explain ?

 

[as_audio]

optional, isn't it ?

 

[as_audio]

Given that the high transconductance JFETs are in your possession, it would be a shame to throw away the noise advantage with a differential topology.

I see no noise penalty because he is using both outputs of the diff pair

 

[Joachim Gerhard]

Optional, sorry. Yes, the circuit is low noise. I run 12mA in each Fet. Maybe some more gives even less noise but I am already quite happy.

 

[Joachim Gerhard]

Cascode

Here are some pictures of the test circuit.
I tried to cascode with BJT transistors but I got a strange offset problem.
However I trim ( in the drains, in the sources, I Abe an initial offset of 10V at the output that jumps straight to -10V when I trim and there is nothing inbetween. Latchup ?

 

[keantoken]

Check that the LTP negative input is getting a signal from the first opamp output. If it is latching then that means one stage has the wrong polarity IE swapped drains on the Jfets or something like that. Latching would show hysteresis which means you would have to trim the potentiometer all the way the other direction before it would flip the other way.

 

[Joachim Gerhard]

That is exactly what happens.

 

[Joachim Gerhard]

I think I swapped the drains. Tomorrow more.

 

[hifidaddy]

cascode inputs like to oscillate, remedy is some 1k in the base junctions of the BJTs used in the cascode, and/or some 100R in the collectors.

BTW, when I had 2SK369 more than 20yrs ago, and did some subjective evaluation(*) in my circuits, I sorted them out and gave them to Allen Wright, who lived in the 'hood at that time ...

(*) the basic question is always: what is this doing to the favourite music of mine

best regards, Hartmut

 

[Joachim Gerhard]

Mama, i swopped the drains. Now I can adjust for Offset.