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Old 2nd February 2010, 02:03 PM   #11
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Quote:
Originally Posted by AndrewT View Post
It's not peculiar.
Very high output currents tend to be very fast transients, not sustained sinewaves.
An amp that can deliver very high transient currents does not need to also deliver that same current output into a test load on a long term test.
I know that the dynamic nature of music produces fast transients that would in turn require sudden bursts of current. But why do the American audio highend companies that manufacture amplifiers like Krell, Levinson, Rowland and Pass all produce amps with very stiff powersupplies with almost no dynamic headroom? Isn't that then a waist of resources. I believe Carver and Harman Kardon produced cheap amps that could boast enormous loads of instaneous power when needed.
The rating for this amp is 40 amps continuously and 150 amps peak. So I suppose the hardware can sustain such a output otherwise this rating is useless. That's probably why Threshold decided to incorporate 20 amp railfuses each for the positve and negative portion to underline the potential of this amp although I think your reasoning is valid also.
Quote:
It sounds like the amp is rated @ ~350 to 400W into 4ohm speakers.
The peak current into a 4r0 load will be ~14Apk = ~10Arms.
If you use 4ohm speaker then an F7A or F5A fuse is suitable.
This fuse will allow sustained high power bass currents to pass and similarly will allow fast transient currents to pass without blowing.
I don't know if you can buy F7A you may have to go to either F5A or F6.1A or F8A.
I just ordered ten FF7A (FF = very fast acting devices) to try out.

I was just wondering how the reviewer of Audio could claim that he was about to blow the FF20 amp fuses, when he tried to measure the 2 Ohm output.
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Old 2nd February 2010, 02:20 PM   #12
AndrewT is offline AndrewT  Scotland
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I believe that "stiff" supplies sound better than limp supplies that sag under load.

I also believe that "dynamic headroom" is a measure of the badness of a power amplifier, rather than what the advertising would have us believe.

I note the ratio of almost 4:1 of transient peak to continuous current. That makes a lot of sense in the context of what you said about big US made amplifiers.
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Last edited by AndrewT; 2nd February 2010 at 02:23 PM.
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Old 2nd February 2010, 05:25 PM   #13
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Quote:
Originally Posted by BrianEno View Post
What would be such a solution?
Is there a simple solution that would give DC protection but won't impede on the musicsignal? Probably not otherwise my amps would have such a scheme.
Maybe I should browse for such a solution in this forum first.
My solution is to snip (cut) the secondary GND terminal of the power transformer after make all necessary modifications
(see attachement, third schematic).
Please note - necessary modify not work for beginners and no using of "low cost" capacitors (no use of high CV product) !!!
And one (only by full range mode clearly) disadvantage there is present by too low internal spaces for the new caps: to high -3db cutoff frequency through the 6 db high pass function.
If your Acoustat electrostatics currently works as full range loudspeakers, you must add and adjust an appropriate subwoofer

Please note additional, above solution is only for existing amps useful. The royal way for new amplifier projects is the use of non symmetrical voltage supply (one supply range = GND at the same time) and a high quality electrolytic capacitor between output and speaker terminal (always better than relais contacts and fuses). Any few manufacturers uses even a transformer, but this solution is much more expensive than a very high quality computer grade cap.
Attached Files
File Type: pdf DC protect without relais.ckt.pdf (43.8 KB, 156 views)

Last edited by tiefbassuebertr; 2nd February 2010 at 05:35 PM.
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Old 2nd February 2010, 10:07 PM   #14
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Quote:
Originally Posted by AndrewT View Post
I believe that "stiff" supplies sound better than limp supplies that sag under load.

I also believe that "dynamic headroom" is a measure of the badness of a power amplifier, rather than what the advertising would have us believe.
I know what you mean, the perfect voltage source is an amp that doubles it's current with every halving of the load it has to drive. I has no Dynamic headroom at all.
Saying that, do we need this kind of behaviour when amplifying music?
Heavily biased Class A designs of course need a lot of hardware to sustain the quiescent current drain on their powersupply and the generated heat needs to be deflected by massive coolingfins.
A moderate AB design could perhaps need a lot less hardware to deliver the musical transients you speak about.
Quote:
I note the ratio of almost 4:1 of transient peak to continuous current. That makes a lot of sense in the context of what you said about big US made amplifiers.
A story about the ability to handle short bursts of power to handle musical peaks:
At the januari 1984 CES in Las Vegas, Phase Linear demonstrated that their DRS-900 power amplifier with the same 150 Watts continuous rating as a Threshold S/300, did not clip when high transients of current where asked to be delivered. The Threshold S/300 showed visible clipping on the oscilloscope when it had to deliver the same high transients of current as the DRS-900.
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Old 2nd February 2010, 10:10 PM   #15
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Quote:
Originally Posted by tiefbassuebertr View Post
If your Acoustat electrostatics currently works as full range loudspeakers, you must add and adjust an appropriate subwoofer.
Thanks for your solution.
My Acoustats are Fullrange ones and adding a subwoofer would probably introduce other problems to deal with.
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Old 2nd February 2010, 11:21 PM   #16
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Quote:
Originally Posted by BrianEno View Post
Thanks for your solution.
My Acoustats are Fullrange ones and adding a subwoofer would probably introduce other problems to deal with.
Yes, but if create solutions for all problems the sonic transmission is much more better in all respects than presently. To do this is my main work.
Unfortunately this isn't to realize with "Plug and Play"
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Old 12th July 2012, 04:30 PM   #17
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In the meantime I have prepared several smaller amps (mostly integrated amps) in the kind as described in post #13 without any trouble, despite the fact, that I must halved the values ​​of capacity - cause twice of the voltage strength is necessary).
For big amps like this
Threshold S/1000 Series II
there are good caps available in the meantime from Munforf, made by FTcap:
http://www.mundorf.com/english%201.1/kondensatoren2.htm
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Old 13th July 2012, 04:37 AM   #18
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Your playing with fire lowering the fuse value - easier to blow with a low impedance load and when they do the output goes to the remaining DC rail voltage - not nice. A 2 pole breaker works better, both poles open at the same time.- John Curl likes that approach too. You'll have to experiment to see which value doesn't trip with your load.
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