The Nemesis 813 PP Amplifier

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Mike H
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#166 Re: The Nemesis 813 PP Amplifier

Post by Mike H »

Excellent. :D
 
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izzy wizzy
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#167 Re: The Nemesis 813 PP Amplifier

Post by izzy wizzy »

It's about time to tear myself away from listening and do something responsible like try and troubleshoot the 813 filament noise. Overall, it isn't intrusive while music is playing that I notice at the moment but in between I can hear it. The amp is very addictive to listen to so would be nice if it was technically better in the noise department.

These are 3 traces at the output of the SMPS which is 10V supplying 10A.

This one looks like roughly 33kHz with some much higher harmonics riding on top
smpa10u.jpg

This one looks like about 550Hz riding on something much lower
smps1ms.jpg

This I think shows the hum possibly half wave at 50Hz that the 550Hz is riding on
smps10ms.jpg

I'm not quite sure what to do to get rid of this stuff. Pointers would be appreciated please.

Cheers,
Stephen
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izzy wizzy
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#168 Re: The Nemesis 813 PP Amplifier

Post by izzy wizzy »

This is what appears on the output terminals with no input connected. Looks to be directly related to the SMPS noise I think.
smpshumbuzzop.jpg

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Stephen
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Nick
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#169 Re: The Nemesis 813 PP Amplifier

Post by Nick »

Have you tried treating it like normal hum and tried to remove it with the hum pots?
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#170 Re: The Nemesis 813 PP Amplifier

Post by izzy wizzy »

Nick wrote: Sun Dec 09, 2018 1:12 pm Have you tried treating it like normal hum and tried to remove it with the hum pots?
No I haven't tried a thing yet other than starting to look at stuff on the web for inspiration. Not too hard to try I think. Thanks.

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Stephen
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#171 Re: The Nemesis 813 PP Amplifier

Post by izzy wizzy »

Hum pot had no effect whatsoever. I guess it's a matter of filtering the output. Mike suggested the CM chokes. I would have thought some differential filtering would have helped too but not sure what to use.

I'm guessing you just can't strap on some big ol caps to an SMPS without causing issues. Are smaller caps OK? Or is this very SMPS specific?

Any ideas appreciated.

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Stephen
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Mike H
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#172 Re: The Nemesis 813 PP Amplifier

Post by Mike H »

common-mode2.jpg
common-mode2.jpg (1.84 KiB) Viewed 3977 times
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Get on Internet and search for CM chokes for 10 Amps, should look like largeish ferrite ring with thick wire wound around it.

You will also need a suppressor / filter type capacitor (polyproplyene) to go across the output pins of each one, I would guess 0.1 - 1.0 uF
 
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#173 Re: The Nemesis 813 PP Amplifier

Post by IslandPink »

Try a small cap first then the CMC as Mike suggests. I did find in the work we did on Andrew's fil supplies that adding CMC's to either low-Zout or high -Zout supplies didn't work that well, though it might depend on the value. Basically anything that makes the Zout change too much as a function of frequency, somewhere in the audio band, can spoil that area of the frequency range.
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Mike H
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#174 Re: The Nemesis 813 PP Amplifier

Post by Mike H »

CMC will only take out the ultrasonic, but means the amp is not having to do something with it. :D
 
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#175 Re: The Nemesis 813 PP Amplifier

Post by Nick »

I never had much luck getting noise out of SMPS's
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#176 Re: The Nemesis 813 PP Amplifier

Post by izzy wizzy »

Mike H wrote: Sun Dec 09, 2018 5:04 pm CMC will only take out the ultrasonic, but means the amp is not having to do something with it. :D
And I guess it's that aspect that changes the sound so that will be interesting to try. I've yet to do a proper comparison between channels to see the sound difference.
Nick wrote: Sun Dec 09, 2018 5:06 pm I never had much luck getting noise out of SMPS's
Well that doesn't bode well. What did you do after that didn't work?

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#177 Re: The Nemesis 813 PP Amplifier

Post by Mike H »

I did, at least according to my 100 MHz bandwidth 'scope. Altho I guess it helps to keep wiring out of the way of sensitive areas. See my PCL86 amp topic, I have separate SMPS units (1 heater, 1 HT), the filters are in the back of the amplifier case so it's filtered as soon as it comes into the box.
 
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#178 Re: The Nemesis 813 PP Amplifier

Post by izzy wizzy »

Mike H wrote: Sun Dec 09, 2018 5:23 pm I did, at least according to my 100 MHz bandwidth 'scope. Altho I guess it helps to keep wiring out of the way of sensitive areas. See my PCL86 amp topic, I have separate SMPS units (1 heater, 1 HT), the filters are in the back of the amplifier case so it's filtered as soon as it comes into the box.
I think that's a good idea to keep it away from the signal stuff. It might be better to site the SMPS in the power supply section as I can't get it far away from the signal section otherwise. I'll check your thread out, thanks.

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Stephen
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#179 Re: The Nemesis 813 PP Amplifier

Post by Nick »

Well that doesn't bode well. What did you do after that didn't work?
I started using Andrews heater supply.
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#180 Re: The Nemesis 813 PP Amplifier

Post by izzy wizzy »

Nick wrote: Sun Dec 09, 2018 6:26 pm
Well that doesn't bode well. What did you do after that didn't work?
I started using Andrews heater supply.
I'm guessing that is probably the best solution. A proper DC supply be it Andrew's or Rob Coleman's. I should go and look at Andrew's thread again.

The thing I'd really like to do is just use a LCL supply but my goodness, that would be super expensive and very heavy at 10A. Maybe long term that could be the answer while the SMPS be the short term solution.

Or for now, spend even more time trying to get the AC to work but not sure how or what to do to improve things in that area.

None of this is getting me down or is discouraging coz it sounds really good to my ears. I'm tempted to get proper transformers for the 46s which will liberate the current ones for the 866s. I also will see what transformers I have for a seperate supply for the 46s.

Cheers,
Stephen
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