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Old 24th May 2014, 04:25 AM   #3291
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Quote:
Originally Posted by hose4 View Post
Comparison was done with 2 Hypex SMPS1200 vs 1 Hypex SMPS1200.
...
Single power supply is powerful enough for 2 channels, maybe even more. there are sound tradeoffs in this config. I would say that single power supply is like having pink glasses in front of your eyes. It can be little more romantic. Some people like that. I could live with single PS if I had not heard dual PS.
Hi hose4

Thanks for the input taking your time to explain our findings regarding single vs. dual SMPS and grounding solutions, appreciate it alot.

Single power supply offers cheaper, easier to realize solution, recommended for less demanding applications, like smaller low frequency reduced speakers drive, PA or similar. Dual SMPS offers better channel's separation, independent full power reserved for each channel only, better grounding solution, at the end all resulting in better overall sound quality.

The fact is, however one may turn, dual SMPS is an ultimate way to go powering a stereo power amplifier. Of course that takes some effort to lay-out proper in chassis grounding wiring avoiding interference currents. Bottom line is that an ultimate solution is just that, no compromise design that can be reproduced at any given time.

Hearing is believing.

Regards L.C.
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Old 2nd June 2014, 09:58 AM   #3292
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Quote:
Originally Posted by Lazy Cat View Post
Single power supply offers cheaper, easier to realize solution, recommended for less demanding applications, like smaller low frequency reduced speakers drive, PA or similar. Dual SMPS offers better channel's separation, independent full power reserved for each channel only, better grounding solution, at the end all resulting in better overall sound quality.
I'm not fully convinced, while i trust fully your listening impressions.
Because it contradict a lot of experiments done in the past on my side.

This is an interesting point, on my point of view, and need to be clarified by more experiments in order to reach to some kind of 'LAW' for the future.
(You know, the things you know they work and save time and money)

First, the comparison has to be fear: 1X2000 W. SMPS vs 2X1000 W. same CAPS, double value.
Second, great care about ground wiring, preferably in a symmetrical configuration (trafos ?) or bridged amps to minimize leakage evils for this experimentation.

My argue is better stereo image stabilty to be expected from a single configuration, a lot more important than crosstalk issues we don't care of.

The second point is regulated VS unregulated.
I am not satisfied by the results i read near everywhere: "Non regulated sound better".
Let's make the things clear. I reached the same conclusions long time ago and still stay on this position.
But it goes against logic and theory.
So what are the evils at work with regulated PS ? Regulation not fast enough ? Did some of you tried some active cap multiplier between a regulated SMPS and amplifier (it always gave me better results than simple unregulated ones, in fact the best of all the combinations i tried with linear PSUS, never had time to try-it with SMPS) ?

At the level of quality both VSSA and FO (and some other CFA amps) can reach, i believe all the efforts has to be addressed power supply side, now.
Each time i tried experimental batteries PS, the improvement was so amazing, even with midfi amps !!!!
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Last edited by Esperado; 2nd June 2014 at 10:06 AM.
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Old 2nd June 2014, 01:27 PM   #3293
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Quote:
Originally Posted by Esperado View Post
Each time i tried experimental batteries PS, the improvement was so amazing, even with midfi amps !!!!
Hi Christophe

Yes, but batteries are unregulated low Z power source.

Dual mono unregulated SMPS sounds better of them all, excluding batteries.

I would not be convinced to say it so firmly if there would not be an extra pairs of ears to confirm the obvious.

That's the case, anyone can check it anytime.

It is not system setup related because it was consistent in all cases.

Regards, L.C.
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Old 2nd June 2014, 02:26 PM   #3294
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Originally Posted by Lazy Cat View Post
Yes, but batteries are unregulated low Z power source.
I believe the improvement is due to:
- Perfect isolation between ground of preamp, and ground of amp, because you can have good result, powering your amp with AC, and your sources with batteries,
- No RMI RFI because, it is yet better when both are powered with separated batteries.
Quote:
Originally Posted by Lazy Cat View Post
Dual mono unregulated SMPS sounds better of them all, excluding batteries.
WHat i said is your experiments with FO Power supplies were too short to can reach such a definitive and general conclusion.
Your dual VS mono was unfair (half of the power when mono). And what about isolated ground during those tests, as well as various AC sens ?
For the moment, i just believe "Dual mono unregulated SMPS sounds better of all the combinations we tried". See what i mean ?
And, anyway, we need to fully understand why.
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Old 3rd June 2014, 09:19 AM   #3295
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While I had a hard time finding a good combination of grounding in the dual supply, Single ended VSSA, and even had to suppress the ground-lift 10OHM resistors on board to make it hum-free and good sounding, it was a total relief to work with X-VSSA's and a big surprise to get them work perfectly the same with and without the connection to the GND. No matter how many stupid mistakes I intentionally have done in creating ground loops inside the case of XVSSA, I had absolutely no issues. of course, I left XLR pin1 tied to the case and only two wires connected to the inputs of the modified VSSAs. It seems very important to get the speaker out of the ground and you're a big step forward.

My XVSSA's are playing happily since their first day, powered from single (not dual + and - vs gnd, just plus and minus) supply for each channel and resistor divider for virtual GND. Not any issue with this setup.

I will be doing the First one's still single ended, to keep the price and the power down to what I am allowed. But I guess i will do a First one balanced in the future (hoping the offer from LC will still be there).

Not sure if Andrej will have an out-of-the-box balanced solution in the future. (wondering)

Cheers!
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Old 4th June 2014, 03:28 PM   #3296
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Hi.Can not we use 2sa1380 and 2sc3502 ? It seems they have lower Cre 1,2pF npn and 1,7pf pnp. Or can we use 2sc3503 and 2sa1380 together.They will have almost same Cre then.
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Old 4th July 2014, 10:07 AM   #3297
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After one year or so, I finally managed to built two VSSA channels.Calibration was a demanding procedure , but at the end I got 120mV between TP1 and TP2 and <2mV DC offset at the output.Next time I switched the amplifier on, DC offset was around 50-60 mV,both channels.I trimmed it with much difficulty down to 2-3 mV.After that,when the amp was turned on again ,the DCoffset climbed to 160 mV in one channel and to 330 mV in the other.Rotating TR1 and TR2 had no effect.I have to say that, by mistake,I tried to measure voltage during the initial calibrating procedure with the DMM set on diode check mode!Could this have made some damage to the transistors?Or have I destroyed the trimmers?Anyway,apart of DCoffset,the amp shows no sign of audible distortion and is completely silent with no input signal.Right now I am listening to it through a pair of Q 1010i speakers, source is a PAL Tivoli radio and the sound is really pleasant.
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Old 6th July 2014, 07:54 AM   #3298
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yep its demanding, smt is not diy friendly IMO.
LC, I now have 4 channels of this amp that don't work, any chance you can send me a real schematic with some test points and voltages?
From what I can tell, I read some instructions to modify the board, I cant find it now, but what I did was short both bases with a jumper to ground. Now all I get from the second pair of modules is heavily distorted sound.
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Old 6th July 2014, 12:04 PM   #3299
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Quote:
Originally Posted by umut1001 View Post
Hi.Can not we use 2sa1380 and 2sc3502 ? It seems they have lower Cre 1,2pF npn and 1,7pf pnp. Or can we use 2sc3503 and 2sa1380 together.They will have almost same Cre then.
Hi, of course you can use 2SA1380/2SC3502
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Old 6th July 2014, 12:09 PM   #3300
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Quote:
Originally Posted by kimon View Post
After one year or so, I finally managed to built two VSSA channels.Calibration was a demanding procedure , but at the end I got 120mV between TP1 and TP2 and <2mV DC offset at the output.Next time I switched the amplifier on, DC offset was around 50-60 mV,both channels.I trimmed it with much difficulty down to 2-3 mV.After that,when the amp was turned on again ,the DCoffset climbed to 160 mV in one channel and to 330 mV in the other.Rotating TR1 and TR2 had no effect.I have to say that, by mistake,I tried to measure voltage during the initial calibrating procedure with the DMM set on diode check mode!Could this have made some damage to the transistors?Or have I destroyed the trimmers?Anyway,apart of DCoffset,the amp shows no sign of audible distortion and is completely silent with no input signal.Right now I am listening to it through a pair of Q 1010i speakers, source is a PAL Tivoli radio and the sound is really pleasant.
It looks the trimmers has gone, meaning slider lost connection to resistance material.

TR1, TR2 serves to set VAS bias current and output DC offset at the same time. Easiest way is to observe both values and see how rotating changes values. Once recognized it is trivial.

TR3 serves to set output bias current after TR1, TR2 has been properly set.
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