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Old 1st February 2010, 02:29 PM   #1
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Default Threshold amps DC Protected

Hi,

Does anybody know if the Threshold S/1000 Series II or SA/1 provide DC protection or any other amp for that matter from this second generation Stasis designs?

Thanks
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Old 1st February 2010, 02:41 PM   #2
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The short answer is no.

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Old 1st February 2010, 03:59 PM   #3
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Thank you for your swift and clear answer.
The long version would probably lead to the same answer
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Old 1st February 2010, 04:25 PM   #4
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Quote:
Originally Posted by BrianEno View Post
Hi,

Does anybody know if the Threshold S/1000 Series II or SA/1 provide DC protection or any other amp for that matter from this second generation Stasis designs? Thanks NP: The short answer is no
In general - there are different possibilities to add a DC protection like fuses and relais controller like TA7317.
But I prefer only an ultimate solution without relais contacts and fuses between the power amp output and the speaker terminal.
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Old 2nd February 2010, 09:29 AM   #5
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Quote:
Originally Posted by tiefbassuebertr View Post
In general - there are different possibilities to add a DC protection like fuses and relais controller like TA7317.
But I prefer only an ultimate solution without relais contacts and fuses between the power amp output and the speaker terminal.
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.
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Old 2nd February 2010, 09:34 AM   #6
AndrewT is offline AndrewT  Scotland
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I think fuse in the power supply line works reasonably well.
I size it at ~ 50% of Ipk for maximum power into nominal load resistance.
Some size it smaller at 50% of Irms for maximum power into nominal load resistance.

This fuse must be F type and must not be over-rated or a substantial current could flow through the speaker if the amp goes faulty.

eg.
F2A or F2.5A in each supply rail of a push pull solid state amplifier delivering ~100W into 8r0.
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Last edited by AndrewT; 2nd February 2010 at 09:36 AM.
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Old 2nd February 2010, 09:52 AM   #7
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Originally Posted by AndrewT View Post
I think fuse in the power supply line works reasonably well.
I size it at ~ 50% of Ipk for maximum power into nominal load resistance.
Some size it smaller at 50% of Irms for maximum power into nominal load resistance.

This fuse must be F type and must not be over-rated or a substantial current could flow through the speaker if the amp goes faulty.

eg.
F2A or F2.5A in each supply rail of a push pull solid state amplifier delivering ~100W into 8r0.
My Thresholds SA/1 have the standard 20 Amps Fastacting (Bussmann GBB ceramic series) railfuses reflecting it's continiously amp-rating according to the manufacturer. They drive Acoustat electrostatics that are 4 Ohms nominal but in reality taper of in the hights to under 1 Ohm. Especially when a female voice starts to sing hard the powermeters on the amp move significantly to the right.
I can of course lower them to 8 Ohms F.
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Old 2nd February 2010, 10:31 AM   #8
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by BrianEno View Post
Thresholds SA/1 have the standard 20 Amps Fastacting
F20A is what I would put in for a 1200W into 2r0 amplifier.

Keep in mind that an F20A fuse will pass a continuous 20A of DC current for quite a long time before finally blowing. The speaker will probably be dead by then.
F20A can pass 40A of DC current for a few to many seconds, depending on tolerances.
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Old 2nd February 2010, 11:23 AM   #9
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Quote:
Originally Posted by AndrewT View Post
F20A is what I would put in for a 1200W into 2r0 amplifier.

Keep in mind that an F20A fuse will pass a continuous 20A of DC current for quite a long time before finally blowing. The speaker will probably be dead by then.
F20A can pass 40A of DC current for a few to many seconds, depending on tolerances.
Okay, I'll just ordered 7A Very Fast Acting ceramic fuses to replace the 20 amp versions that are in place now.
That's a lot saver I think. The SA/1 delivers 600 Watts at 2 Ohms according to the graphs that Nelson Pass supplied for the review of the Audio Januari, 1987 issue. Strange thing is though that the reviewer (Leonard Feldman)stated: "Although I did perform some measurements of power output at 2 Ohms, it soon became clear that if I tried to push the amplifier to its limits with that type of load, I would blow its fuses." So that's why Nelson supplied those 2 Ohms graphs for this review.
So even with the standard railfuses the amp could not be pushed to its limits. I have several German reviews of Threshold poweramps that confirm this finding and do not give a specification for 2 Ohm other then a dash (-) at that rating. Railvoltage is approx. 63 Volts for these amps.
But it's a bit peculiar when you have an amp that can deliver lots of current to low loads but is curtailed by its fuses.
I'll try them out anyway...
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Old 2nd February 2010, 11:51 AM   #10
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by BrianEno View Post
do not give a specification for 2 Ohm other then a dash (-) at that rating. Railvoltage is approx. 63 Volts for these amps.
But it's a bit peculiar when you have an amp that can deliver lots of current to low loads but is curtailed by its fuses.
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.

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.
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