Tekko dreams up another poweramp

[Tekko]

I just dreamt up this amplifier, based on the Sony/Apex topology with the fully symmetrical IPS, but with a triple deep darlington output stage similar to that of the Leach Low TIM amp.

It simulates 0.00381% THD at 20kHz at a RMS power of 200+ watts into 4 ohms, with a phase shift of only 0.64 degrees.

The DC offset with the values shown is about 32mV which is acceptable, bias is about 60-70mA per output pair.

The first draft schematic:

[vedmitraa]

Hello Mr. Tekko,
Can you please send spice file or multisim file of this amp.
regards.
Vedmitra Sharma

[AndrewT]

I do not see Leach Lo Tim in there.

Why only 200W+ into 4r0 from 4pr output stage on +-60Vdc supply rails?

Did you mean to type 300W+?

[Tekko]

The 200W was based on the only transformer i have that gives me 60V rails.

However i realized minutes after posting this that VAS was dissipating almost 5 watts and the IPS around half a watt.

After correcting this and getting the offset back down to 30mV or less, THD had risen to 0.4%
so it needs some extreme work.

[AndrewT]

200W into 4r0 requires an output of 40Vpk and 10Apk.
Into a 4ohms speaker expect transient currents to approach 30Apk.

You shouldn't need +-60Vdc supply rails to get to those targets.

[Nico Ras]

Along the lines of an old KRELL KSA50 but with CCS in the input. Once optimised it should sound good. Complimentary symmetrical amps sound somewhat clinical but I like that kind of cold characterless sound.

Just on brief inspection, I would increase R9, R11. Reduce the input pair's current somewhat and increase R10, R12. Decrease values of C1, C2 and maybe add a cap across R18 to extend phase margin.

[Nico Ras]

Maybe cold and characterless was the wrong choice of words, but I think you know what I mean. It is opposite to warm lazy SE class A kind of sound. This amp sounds particularly nice when over biased a bit - say 2 to 4 watt or so.