Revisiting some "old" ideas from 1970's - IPS, OPS

Update!

I have slightly updated the schematic and Jeff has designed a great layout for the beast. There is a trimmer for DC offset adjustment now.

R23 = 130R, VAS current = 5.5 mA, good for Slewmasters.
R23 = 47R, VAS current = 15mA, good for driving the MOSFETs directly (e.g. Tubsumo).
 

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You have 5 comp. caps ? Lead /lag , miller , and a shunt ! How did you arrive at these ?

BTW , a very interesting "blameless" -mutant. I like the decoupled low voltage input and overload clamp.

OS

Each comp cap is responsible for particular part of the curve :) At the same time - most of them are rather small.

Key topology specialty - a "vertical" differential cascade, doing a lot of good things at once. The whole thing is going to be pretty fast for VFA ;)
 
Funny that we have to look back to the 70's to find really good amps. I'd say that is because stereos "mattered" back then. Having a great stereo was a status symbol and folks were willing to pay good money to impress their friends. Today they need to stuff 6 channels into a small box that will fit on a shelf under their flat screen.

How I remember going to the audio store and listening to Emerson, Lake and Palmer through a huge set of speakers and monster amps. Bass you could feel and mids and highs that seemed to come from every corner of the room. The store was filled with young men dreaming of owning that perfect "system". Those were the days! Great memories.

Yeah - those were the days ))
Well, in the end of the century there were some sort of "no compromise" designs as well. Just came across Sony TA-NR1 the other day. Imagine two Slewmaster power sections with 5 pairs of MT200 Sankens each, connected in parallel (PD+ to PD+, ND- to ND-, output to output), and biased to class A. This is just one channel :eek: Huge power supply. 47.5kg of metal. Monumental engineering ;)
 
Yeah - those were the days ))
Well, in the end of the century there were some sort of "no compromise" designs as well. Just came across Sony TA-NR1 the other day. Imagine two Slewmaster power sections with 5 pairs of MT200 Sankens each, connected in parallel (PD+ to PD+, ND- to ND-, output to output), and biased to class A. This is just one channel :eek: Huge power supply. 47.5kg of metal. Monumental engineering ;)

Those were the days when Sony's car audio was excellent as well. The old C90 was an incredible cd player. The tuners weren't very good though. 4 years later their flagship was worth $400 and sold in big box stores. That's a huge shift in engineering in a short time.
 
I have slightly updated the schematic and Jeff has designed a great layout for the beast. There is a trimmer for DC offset adjustment now.

R23 = 130R, VAS current = 5.5 mA, good for Slewmasters.
R23 = 47R, VAS current = 15mA, good for driving the MOSFETs directly (e.g. Tubsumo).

Can you double check the orientation of the VAS transistors? I think the 3D model is backwards in Diptrace. I think I have them installed correctly(ECB) but Diptrace is showing the metal side out.
 
Symmetric design - the last one in this series (I believe ;))

One more implementation - for those, who likes symmetry ;)
Symmetric slew and clipping by design, rather high speed, very low distortion.
I made it DC-coupled. If someone wants to add a cap at the input - a good way to do it is to have 2 pairs of input RCA's (DC and AC coupled) and solder the cap right on their pins.

Worth testing.

Jeff, are you up to one more layout? ;)
I'm sure it can be kept within 3"x3" as well :)

Cheers,
Valery

P.S. Sorry. JPG schematic if difficult to read - PDF looks much better.
 

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One more implementation - for those, who likes symmetry ;)
Symmetric slew and clipping by design, rather high speed, very low distortion.
I made it DC-coupled. If someone wants to add a cap at the input - a good way to do it is to have 2 pairs of input RCA's (DC and AC coupled) and solder the cap right on their pins.

Worth testing.

Jeff, are you up to one more layout? ;)
I'm sure it can be kept within 3"x3" as well :)

Cheers,
Valery

P.S. Sorry. JPG schematic if difficult to read - PDF looks much better.

Hi Valery,

I have often wondered about DC coupling. I know a couple of your earlier designs provided for both. Can you please explain to me the advantage/disadvantage to DC vs AC coupling?

Thanks, Terry
 
Hi Valery,

I have often wondered about DC coupling. I know a couple of your earlier designs provided for both. Can you please explain to me the advantage/disadvantage to DC vs AC coupling?

Thanks, Terry

Hi Terry,

The key advantages of having the power amp DC coupled:
- there is virtually no bandwidth limitation at the low end - the amp works starting from DC. The only limitation is DC servo, but its time constant is more than 2 seconds, so it does not really influence the audio bandwidth at its low end;
- there are no large capacitors anywhere throughout the signal path - more long-lasting amp characteristics. All the small compensation ceramics work far above the audio bandwidth and they are rather stable in a long run.

Disadvantage - you need to make sure there is no offset at the output of the preamp or other source, connected to your power amp, or the offset is low enough to be handled by the servo (couple of hundred mV is ok).

In many cases, there is a decoupling cap at the preamp output already, or it is also servo-ed, or just well-balanced, so the whole thing will work fine. Preamp, having an offset at the output is not a good design preamp.

Cheers,
Valery