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Old 3rd December 2013, 11:22 PM   #21
zog666 is offline zog666  Australia
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Thanks for the feedback, looks like (on the odds) it's worth a try, but I'll get a dedicated 24-27Vdc SMPS as that seems to have given good results.

As I have quite sensitive HF speakers I'm after ones that run quiet.
I'm getting the "Zoe Tsang" ebay JLH 1969 amp kit.
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Old 4th December 2013, 12:55 AM   #22
zog666 is offline zog666  Australia
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Originally Posted by Bigun View Post
I haven't bought from them myself but these guys could be a good alternative for an SMPS: Connexelectronic
Yes, I have a connex PSU on one of my other amps (and several Connex amp modules) and it is going well.
I'm looking at locally sourced ones I can get quickly at the moment though.
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Old 30th December 2013, 04:48 PM   #23
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I'm thinking of using this SMPS with my JLH 1969. I got a chance to mount it on some proper heatsinks and it sounds really good using the Server supplies I showed in post #16. The server supplies are over-kill and have fans which add a little noise so I would prefer the SMPS if it will work. Is 300W enough for the 69?

Thanks, Terry
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Old 30th December 2013, 04:59 PM   #24
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Originally Posted by hiktaka View Post
I'm always fascinated about SMPS usage for pure class A amps, assuming it is done right (not for skimping purpose, as most SMPS are).
One important note is that SMPS shouldn't run between loaded/unloaded state. On average, it wants a rather constant load. For class A, this isn't much of a problem. For class A/B or Gainclones, tho, it means no good.
For class A/B and Gainclones, you can bleed SMPS output for about twice or three times the bias current, so that SMPS won't go unloaded.
You're correct, but...

You can find the equations for the output inductors, or transformer magnetizing inductance needed for different SMPS modes from vendors like TI, ST or Linear. Linear will walk you through it in their datasheets for their low noise switchers and gate drivers.

If you are going to run an amp in AB with a switcher, you'll just need to design a bigger inductor/transformer.

Don't just slap any old inductor on the output of a switcher -- often the problem is switching noise radiated backwards from the SMPS into the line cord which just acts as a big antenna/radiator (a PEM or "power entry module" is helpful here and there are tons for sale surplus). Wrong size inductor on the output rail of the switcher just raises the impedance with frequency.

Last edited by jackinnj; 30th December 2013 at 05:02 PM.
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Old 30th December 2013, 05:04 PM   #25
john65b is offline john65b  United States
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I built a Bobo Zen (basically an F5 with no protection circuitry) powered by a pair of Laptop Power Supplies (19v 3.4A each - direct, no power supply caps, each output device at just over 1 amp bias) and sounded great. Traded it for some woodwork, but planning on building another - this time same supplies, but a full blown F5 PCB from DIYAudio. This was my simplest and cheapest amp so far - the four laptop power supplies were $40 shipped from China, and sinks were what I had laying around...

I give all my amps / preamps to a friend for a "review" and he said it was the best amp he heard so far (he hasn't tested my KSA-50 Clone, as it weighs a ton), and he has heard quite a few of my experimental amps (including my Aleph 5, JLH, Elliot Sound P101, and a couple tube amps)....

I will have to try the High Power JLH again with a SMPS...
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Old 30th December 2013, 06:07 PM   #26
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Wink My 2 cents

Well... I don't fully understand the hum and noise issue with traditional linear transformer-based PSU.

I give you an example. Simple experinent. Audiolab 8000x7 power amp, in front of it there is a subsonic filter that I have recently mentioned at the other thread. In front of it there is a digital audio processor. All of them are connected with RCA analog cables. No analog volume control - from the processor to the power amp output - full throttle, maximum gain.

Now, you can put your ear against the speaker, even touch the grill with your ear. Nothing. Not even "silence" . Literally nothing. I can't say if the whole system is on or off unless I see it or feed the input signal.

What I want to say - if you hear hum, noise or other artefacts, it means either bad design or a bad build. In most cases - second option.

I'm not against SMPS - they are effective, low-pulse, stable (in most cases), though when it comes to critical load - may go off and on (by design), somebody already mentioned this.

The other drawback of SMPS - most of them have got a fan, getting on at higher loads. Well - ok for the stage-type-of equipment, but may be not so good for a living room.

I would use SMPS, "surviving" 8-10 A of peak current, for a 50W amp or so. Maybe a bit more. But for a 150-200W per channel amp I would use a linear one, with appropriate filter (capacitors). Heavy, but holding 15-20 A at the peaks with no hustle, having no option of going off - you can control the rest with the right protection algorythm.

Cheers,
Valery
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Old 30th December 2013, 07:01 PM   #27
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Originally Posted by vzaichenko View Post
Well... I don't fully understand the hum and noise issue with traditional linear transformer-based PSU.
Simple.

1. Power supply rejection in the JLH is decent but by no means astronomical. Going by the headphone version, we are talking about a bit over 70 dB input-referred in the relevant frequency ranges. More advanced concepts may reach over 100 dB here.
2. We are talking about a class A amplifier with an idle current of about 1 amp. Substantially higher levels of supply ripple are expected to be encountered compared to an AB amp. JLH himself suggested a supply with active ripple filtering, otherwise the reservoir capacitance would have gotten fairly huge.

A good conventional regulated power supply should work just as well as a SMPS. It obviously is a lot heavier and less efficient though. The downside of SMPS' is that often you don't know what you're getting in terms of construction quality, RFI suppression etc.. When going split supply with 'em, you don't want a model whose ground is tied hard to safety earth either.
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Old 30th December 2013, 08:50 PM   #28
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OK, class A assumes relatively constant power consumption, so in this case SMPS is an option, especially bearing in mind its high energy performance. Just need to have enough power reserve.. so that the fan does not go on in normal operation...
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Old 30th December 2013, 11:33 PM   #29
zog666 is offline zog666  Australia
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Originally Posted by vzaichenko View Post
Now, you can put your ear against the speaker, even touch the grill with your ear. Nothing. Not even "silence" . Literally nothing. I can't say if the whole system is on or off unless I see it or feed the input signal.

What I want to say - if you hear hum, noise or other artefacts, it means either bad design or a bad build. In most cases - second option.
With what sensitivity speakers?
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Old 31st December 2013, 12:31 AM   #30
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Originally Posted by zog666 View Post
With what sensitivity speakers?
Not really sensitive - Monitor Audio RS series, particularly RS-8 at the front channels. Anyway, power amplifier has got roughly 30db gain, but nothing is audible at the output without signal...
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