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Old 5th October 2013, 08:28 AM   #1111
mikelm is offline mikelm  England
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Further fodder for our consumption:

http://www.audiophonics.fr/images2/6189/SMPS300R.pdf

I don't know that much about switch mode design so I'll get some expert advice on this but I don't like the look of the 100nF cap across 10R connecting system ground to mains ground. In my conventional supplies I just have 100R in this position . . . . ahh further down the datasheet it says that there is a link the bottom of the board that makes this optional - this is encouraging

Thx for your comments meanman but I should say that I now regard some of my input in the original thread as uninformed hogwash !

In particular, having now tried O/P chokes I find that they play a very valuabe role with this design by increasing stability in the feedback loop and thereby improving the subjective sound - Thx Hugh

But about very low noise PSUs my views remain unchanged

cheers

mike

Last edited by mikelm; 5th October 2013 at 08:32 AM.
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Old 5th October 2013, 10:33 AM   #1112
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Most important thing is the FetZilla is sounding suber in my ears.
Mike notice that the 300RE is slight different than the 300RS
The new RE version doesn't have the 10R/100n combo(C33/R33)

Last edited by meanman1964; 5th October 2013 at 10:47 AM.
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Old 5th October 2013, 11:12 AM   #1113
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Just to mention...not all SMPS are regulated. If we have unregulated SMPS this is simple DC-DC converter, without feedback. So it is similar than classical PSU. For audio, I would rather recommend non regulated one. Also it should be made exactly for audio, that means that filtering is much more improved, also against noise injected back into mains. Actually a good audio grade SMPS should not look much different on osciloscope than classic PSU, but the advantage of using first one is huge. Dynamic, headroom, bass definition are simply superb to classic PSU.

But it is important, not to use any aditional capacitors between amplifier boards and SMPS!
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Old 5th October 2013, 11:48 AM   #1114
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The SMPS I bought is an unregulated one and made for audio
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Old 5th October 2013, 12:23 PM   #1115
mikelm is offline mikelm  England
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Every PSU has some degree of regulation and this one seems to have quite a high degree of regulation.

The issue often discussed is wether there is regulation involving loop feedback but this issue has different parameters and significance in a SMPS.

If less regulation is desired some series resistance can be added.

I think I'm gonna buy a couple of these units to see how they perform.
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Old 5th October 2013, 12:53 PM   #1116
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Yes Mike you're right I miss readed it
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Old 8th November 2013, 04:33 AM   #1117
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Default Case < SMPS and heatsinks < quiescent currents and rails

Hi

Until I can reclaim some ongoing workbench space and get soldering, Iím making my way through the threads, looking into *all the parts etc - including the case

SMPS: assuming further reports & tests are encouraging, I want to get a case big enough to fit the SMPS. The SMPS300RE is a PS for *both channels, right?

Iím working back: case < heatsinking < quiescent current - and rails.

I want to be able to run higher quiescent currents, inc what Greg found it sounded best at: 1 A.
Forgive me if this has already been discussed:
A heatsink rated 0.42 C/W is right for 500 mA with 36 V rails, or 1 A with 24 V rails.

With 1 A, what would be the output and ability to drive lower impedance loads with rails of either 24 or 36 V?

While the Fetzilla boards were (I believe) sized to run on a 0.42 C/W heatsink, if running 1 A with 36 V rails, what rating heatsink would be sensible?

Thanks
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Old 8th November 2013, 04:43 AM   #1118
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Otto,

If you run 1A through the output stage, you will be dissipating 2 x 36 = 72W from each channel if your rail voltage holds up.

This is a lot of heat. If we assumed a max ambient temp of 35C, and a max heatsink temp at 65C (just on the limit of holding your fingers on it), then you are warming it 30C above ambient.

For a heatsink rising from 35C to 65C for 72W, and note that TWO heatsink, well apart, are required for a stereo amp, you need a 30/72 = 0.42 C/Watt, which will be at least 300m long (12 inches) and 75mm tall (3"). This is a minimum requirement. If the thermal capacity is better than 0.42C/watt, say 0.35C/watt, this would be better.

Cheers,

Hugh
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Old 8th November 2013, 06:01 AM   #1119
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Hi Hugh

Thank you for your prompt response!

And at 1 A, would there be a difference in output and/ or ability to drive lower impedance loads with rails of either 24 or 36 Volts?

At 1 A, do you know what the class A watts would rise to?

Did Greg post his specific thoughts on the aspects he preferred in sound at the higher current?

Cheers
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Old 8th November 2013, 08:09 PM   #1120
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Hi Otto,

At 1A quiescent the Class A mode would be much more. Using LTSpice, it reveals that output rises to 22.6Vp for inactive side to turn off, which represents to 45.2Vpp into 8R.

Corresponding, this is 31.9W Class A - a very impressive figure.

At 24V rails the output devices would each be dissipation 24W rather than 36W. This is a far better loading. This change would mean that essentially the output would drop to 17.4Vp max, but with quiescent adjusted to 1A again this too would be in Class A, which is 18.9W.

To change to 1A quiescent current, you might be to greatly increase the value of the resistor in the diode string on the bias generator. For 36V rails it would increase to 295R, and with 24V rail it rises to 520R. A 500R trimmer and 47R resistor would be a good change to accommodate this.

Yes, the sound will change, since the distortion profile would skewed to lower order harmonics, H2+H3+H4. It would sound very tubey....... of course, no guarantee that everyone would like this.

Cheers,

Hugh
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