The Nemesis 813 PP Amplifier

[izzy wizzy]

Sorry chaps. This might have been less confusing if I'd posted a circuit. This is what I'm on about.

And combined this idea from MJ with this thread on Diyaudio https://www.diyaudio.com/forums/tubes-v ... -amps.html due to my history of oscilation with this amp. Just trying to get some ideas together in the pursuit of problems to come and maybe some that have arrived already.

Cheers,
Stephen

[pre65]

I seem to remember our Nick had details of how to stop the mains transformer ringing. Might that help as well ?

[Mike H]

Not sure its the type of snubber thats being discussed here Mike (or it wasn't). MJ started talking about a RC network across the choke as you describe, though with a C value that would put the resonance much higher than 100Hz. But he pointed out that the RC provides a path to HF past the choke so suggested a different network, a cap from the input of the choke to 0v and from the output of the choke to 0v, thus not providing a path for HF to bipass the choke.

Oh right, OK.

[Nick]

I seem to remember our Nick had details of how to stop the mains transformer ringing. Might that help as well ?

That was this

https://www.diyaudio.com/forums/power-s ... t-jig.html

[izzy wizzy]

I now have two channels going ... sort of. Two output stages going with a minor bit of buzz/hum. Can't make too much noise coz young people in bed.

Now to decide how to pursue this hum/buzz.

What would the panel suggest be a first step?

Here's what's built so far. Power supply as previous.

Cheers,
Stephen

[Nick]

I assume the hum/buzz wasn't there for one channel?

Again, what does it look like?

It could be grounding, or it could be that the double current has caused more B+ ripple which is what you are hearing. Is it a choke or cap input supply?

[izzy wizzy]

I assume the hum/buzz wasn't there for one channel?

Again, what does it look like?

It could be grounding, or it could be that the double current has caused more B+ ripple which is what you are hearing. Is it a choke or cap input supply?

Both channels are the same-ish for buzz/hum

See page 1 of this thread for psu, pcb it's made on and rough idea of chassis stack. I can take more photos if needed.

Double current?? Choke input - see page 1

Thanks.

Cheers,
Stephen

[Ant]

I think he means double the current will be pulled from the psu as it is now running 2 output stages instead of one and the higher current being pulled is causing a higher amount of ripple in the psu

[izzy wizzy]

I think he means double the current will be pulled from the psu as it is now running 2 output stages instead of one and the higher current being pulled is causing a higher amount of ripple in the psu

They're monoblocks.

I once built it as a stereo amp, the first one. It was about 1m square and so heavy, it was built in situ. It was monoblocks after that.





Cheers,
Stephen

[Nick]

Must use 866's again some time, still got a heater transformer for four of them.

So if they are monoblock, the obvious thing to try is does the hum/buzz only happen when you turn the second on. If so, how far apart can they be and cause that to happen.

[Mike H]

I once built it as a stereo amp, the first one. It was about 1m square and so heavy, it was built in situ.

Flippin' 'eck

[izzy wizzy]

Must use 866's again some time, still got a heater transformer for four of them.

So if they are monoblock, the obvious thing to try is does the hum/buzz only happen when you turn the second on. If so, how far apart can they be and cause that to happen.

Those MVs above are GU20. Way bigger than 866 but because of that, the glow isn't as big. Don't know what I was thinking. 866s look nicer IMO but their heater transformers will be powering the 46s to begin with here. If it's successful, then I'll get dedicated transformers for the 46s and try and get the 866s fired up.

For one of the first times ever that I remember building these things, having two go at the same time results in the same amount of buzz/hum. In other words, no more than when one on. They are about 6ft apart. Previously it didn't matter how far apart they were for them to turn into a Theremin. Hopefully I'm on to something this time.

Keep the suggestions coming please.

Cheers,
Stephen

[izzy wizzy]

I once built it as a stereo amp, the first one. It was about 1m square and so heavy, it was built in situ.

Flippin' 'eck

Well exactly. They were made for the Acoustats and it made me think, if I need an amp like that to make them sing, then I got the wrong speakers so the amp was pulled apart, the speakers stored and I went on to Tannoys and haven't looked back. But if you've got the parts lying around ..... kinda like an itch that won't go away.

Cheers,
Stephen

[Mike H]

Yep.

[Nick]

Other buzzes seem to have pretty much gone. The hum now is very low 4.2mV true RMS so the scope says.

I now have two channels going ... sort of. Two output stages going with a minor bit of buzz/hum. Can't make too much noise coz young people in bed.

Now to decide how to pursue this hum/buzz.

having two go at the same time results in the same amount of buzz/hum. In other words, no more than when one on.

Hopefully you can see our confusion.