Unusual amp from 1987

[alexcp]

A protection diode in series with the base or in anti-parallel with the emitter junction is a customary solution to that problem. A better protection is found in the Bolshevik amp @ RCL-electro.ru (the linked forum is Russian-speaking):

 

[minek123]

A better protection is found in the Bolshevik amp @ RCL-electro.ru (the linked forum is Russian-speaking):

You mean T3 added?

 

[alexcp]

Yes, T3.

 

[minek123]

Continuation of the amp presented in post #1737:
https://www.diyaudio.com/community/threads/unusual-amp-from-1987.357369/post-7515758
with logic level NMOS output devices.
The amp/chassis is finished and playing music.
Great sound, no problems with the build, no surprises. Little (TO-220) HUF75842 transistors (2 pairs per channel) seem to be
perfect choice for a small (25W) amp. This is also 1st time for me to use 1inch black nylon slab for a chassis, with thinner Alu
top. Easier and faster to machine than metal.

 

[minek123]

Continuation of the Hafler P7000 inspired amp from post 1709
https://www.diyaudio.com/community/threads/unusual-amp-from-1987.357369/post-7492293

I had an idea to 'improve' it slightly - see attached schematic, by using Hawksford cascode for VAS.
I gave it a try, and while in the sim it was showing faster rise times, but the reality didn't follow the sim.
From the initial tests, it behaves exactly the same a first amp; the only possible improvement I see is its stability.
I experimented with different transistors, feedback RC values, and this amp shows rock solid stability in all conditions.

 

[minek123]

Both channels ready, and playing music. Sounds excellent 🙂
DC output offset 0.1mV
Idle current 50mA per output pair (3 pairs per channel).
Rails 50V.

 

[von Ah]

Really enjoy reading about and seeing pictures of your designs, Minek. I would like to build one of these ‘unusual’ amps this year.

 

[inyashd]

Please share details for build one.
As show above designs, 👍minek.

 

[minek123]

I'm not planning to design a PCB dedicated to this amp. I only have small daughter board for the input/Vas circuitry, that is plugged into my
'amp platform' with Output Stage. This whole concept doesn't really make sense to someone who wants to build just 1 amp.
If you want to build it as a standalone amp, you will need to design a PCB by yourself, perhaps using examples of similar boards built
for previous amps in this thread.

Daughter board of the 1st Hafler amp:

Of course I can share PCB design for it.

 

[stanislav1957]

Hello colleagues. Good luck, health and happiness to all.I haven't been here for a long time. There are so many new things.

 

[minek123]

Hi Maxim! Good to hear from you. Where have you been?

 

[stanislav1957]

Yes, at first my wife was ill, then I was not up to the forums.

 

[minek123]

Hope you are both fine, and you'll continue to participate in this thread.
Many good amps were built since you were gone 😀

 

[stanislav1957]

I'll take a look at this topic. Maybe I'll show my own, if there are branches in the topic.
Now I am restoring the soviet amplifier "Corvette100-068cm" . A good device

 

[stanislav1957]

Congratulations. The progress is impressive. It's a pity there are few followers, only readers. Well, it's like everywhere else. The usual story.

 

[minek123]

Here is the newest amp I'm simulating. Perhaps a next build candidate.
Check it out.
Perhaps someone can propose improvements..

 

[stanislav1957]

I can't order printed circuit boards. Not up to them yet. Other concerns. By the way, while I was recovering here, I took up roses and clips. one of them.The roses are mine

 

[minek123]

I see - no LTP, so servo was needed?
The final amp looks great.

 

[stanislav1957]

Many people need simpler amplifiers. That's why I removed the ou.The parameters are very decent. Is YouTube off-topic here, for example?

 

[minek123]

Youtube links are fine, many people links to youtube..