Unusual amp from 1987

[egra]

First image 10kHz square wave on 6Ohm, the second one is same, but with 1u capacitor parallel with load.

 

[minek123]

22 ohms in supply rails caused the clipping problem. So I left them, now everything seems right. I think it will be good already, I'm going to design the PCB. Minek, did you simulate Gain and Phase margin?

this open loop gain sim

 

[stanislav1957]

@Maxim. Since the missing parts are already on way from mouser, I would like to finalize the circuit of qhex version and I'm going to design the PCB. The amplifier shows ugly clipping characteristics when R1 = 33 Ohms are used. It looks much better with 100 Ohms (In original Wiederhold it is 1k). What do you think? Also, since I don’t have enough knowledge in LTSpice, could anyone simulate the Phase and Gain margin of the circuit? Currently I only have +/-33V Power Supply. This is why I set the simulation to 33V. Thank you for the help.

1u extreme!!!

 

[minek123]

First image 10kHz square wave on 6Ohm, the second one is same, but with 1u capacitor parallel with load.

1uF is way too much...

 

[minek123]

Egra, check out this post:

Determining Phase and Gain Margins in LTSpice

 

[egra]

6 Ohm+100nF

 

[egra]

Egra, check out this post:

Determining Phase and Gain Margins in LTSpice

Thank you!

 

[minek123]

6 Ohm+100nF

Stability of an amplifier under capacitive loading

Try with 10n to 20n, that's way more reasonable...

 

[stanislav1957]

cheat sheet

 

[minek123]

This is Sukhov's amp from 1989 (Radio #6)...

 

[egra]

Stability of an amplifier under capacitive loading

Try with 10n to 20n, that's way more reasonable...

Decent. Just a slight difference compared to resistive load.

 

[egra]

10 kHz pure resistive load.

 

[minek123]

can you attach your asc file with square AC source?

 

[egra]

can you attach your asc file with square AC source?

 

[egra]

Something is wrong with cascaded driver. Using single transistor to drive VAS everything seems to be OK (original version). Even on 2 Ohms.

 

[minek123]

This is Lomakin/Parshin amp.
Different than Wiederhold (compensation), and this is not quasi...
Can't really be compared

 

[minek123]

>can you attach your asc file with square AC source?

Change R5 to 1k2 in your wiederhold1977_qhex-3_egra_sqw.asc
and retry 4 ohm

I mentioned this R5 change in one the previous posts...

 

[egra]

>can you attach your asc file with square AC source?

Change R5 to 1k2 in your wiederhold1977_qhex-3_egra_sqw.asc
and retry 4 ohm

I mentioned this R5 change in one the previous posts...

Thank you. Perfect now.

 

[minek123]

I removed some stuff added, and restored original values, at 45V rails, with R5=910, and square at 4 Ohm look ok to me, even at 1.2V AC input (instead of 0.7)

Either C9/C12 should stay at 120pF (this value depends on output fets, for IRFPs might be different), or removal of diodes in the rails helped...

 

[egra]

OK. Thank you. Now its time of Sprint Layout.