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Old 1st January 2009, 02:52 PM   #1
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Unhappy threshold s/500 power amplifier

Can someone please tell me how to fix the power supply on a Threshold S/500 STASIS Power Amplifier? I have some schematics, but they're general overviews for several later designs. I need the specific technical information on this particular model. Hopefully, someone can tell me the voltage, tolerance, and bias.
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Old 1st January 2009, 06:41 PM   #2
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Can you be a little more specific as to what's wrong? Honestly, it's unlikely that the power supply itself has died, unless you've got an old cap that's given up the ghost. There's not much else to screw up. There's a power transformer, bridge diode, and caps for each channel. Nothing fancy.
I've got two S-500s and have done a little of this and that over time. It's been a while, but I seem to recall that the S-500 rails are around +70 or 75V. The bias is set, not so much by voltage, as by the temperature of the heat sinks.
You'll need to specify what it is you're seeking the tolerance of.

Grey
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Old 1st January 2009, 08:06 PM   #3
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Default Threshold S/500

I've got to get it back out to look. Another person looked at it and told me that was the problem. If you still have yours are able to take a picture of the inside for me . The area where the AC line comes in has had some serious physical damage. A small PCB (approx. 40mm x 80mm) has places where wires were and some missing components. I'll try to get to it ASAP. Thanks a lot for your help. It was sooner than expected.
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Old 1st January 2009, 09:34 PM   #4
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Cheers George
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Old 1st January 2009, 09:52 PM   #5
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Ditto
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Old 1st January 2009, 09:55 PM   #6
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And Ditto

This however is the S300 mono supply, the S500 is dual and similar in design.

Cheers George
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Old 22nd December 2009, 06:45 PM   #7
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hello,
good evening to all of you,
I am newbie of this forum and would like to ask something about my amp (threshold S500 II )bought used a few months ago. I bought it to drive my Apos Centaur. But result was a little disappointing: very good bass and dynamics, large front soundstage but reduced trasparence and little definition and airiness. So, I would like to replace the old capacitors in main power supply with fresh ones ( bypassed with Jantzen HighEnd Z-Superior Cap 0,47 uF - 800V).
I wanted to know if instead of the originals from 29000uF could I put 4 from 47000uF or if this could cause problems with the bridge for the increasing current, and therefore it is better to stop with only 33000uF.
I have also inspected the 5 fuses (to renew them with the magic liquid of Van der Hul) and I discovered that the previous owner had them all replaced with SLOW fuses instead of fast. I changed them with those of the original type ... but the sound is much worse: low lighter and confused, small dynamic, aggressive medium-high. The amplifier has more than 20 years (though it seems, even within, upon leaving the factory) and who knows how long have those kind of fuse. None of you has done the same change on your Threshold? Which are the really risks ?
Many thanks
Alessandro
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Old 22nd December 2009, 08:30 PM   #8
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Quote:
Originally Posted by abettibecucci View Post
But result was a little disappointing: very good bass and dynamics, large front soundstage but reduced trasparence and little definition and airiness.


I concur with your conclusions. Have one of the smaller brothers in a cupboard somewhere. Seriously doubt that power supply improvements will help the transparency enough. Maybe from a wet blanket to an almost dry blanket But on the bright side so many other designs will fit the case and the heatsinks.

If you are increasing the capacitance a new discrete rectifier may help the sound a little bit more, especially using nice Schottky diodes.

Fuses generally suck soundwise but if you really must have them why not give the new ones a chance to break in? And maybe try a few different makes.
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Old 9th April 2010, 10:48 PM   #9
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@ georgehifi:

hmm,

What do you think is the correct S500 bias:
the chart (#4) says 100/75 mV for S500,
the schematic (#5) says 20 - 30mV for all.
Think it's a pretty big difference.

Assuming the voltage across the 1R emitter resistors is meant...

Cheers,
Gerhard
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Old 9th April 2010, 11:04 PM   #10
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I would use the one that allows you to keep hands on the heatsinks for 5-10 sec comfortably before having to remove them on a ambient hot day of 30c.
I think Nelson suggests similar hands on test if metering is not used.
Cheers George
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