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ADS A/D/S P640
ADS A/D/S P640
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Old 9th May 2012, 08:24 PM   #1
Dr Zeus is offline Dr Zeus  United States
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Default ADS A/D/S P640

Repairing this amp for a friend because it was poping 30A fuses. I found one of the two rectifiers shorted internally so I replaced both of them.

Amp now powers and plays on all channels, but the rail voltage is just a meer +-22vDC. Is that too low for this amp? Regulated voltage is ok (about +-15V)
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Last edited by Dr Zeus; 9th May 2012 at 08:26 PM.
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Old 9th May 2012, 11:13 PM   #2
1moreamp is offline 1moreamp  United States
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ADS wasn't known for high voltage power amps, so unless the replacement diodes have some unusual Voltage drop issues its likely a acceptable rail supply for a 6 times 40 watt amp.

If in doubt you could always setup a simple resistive test loads and scope the output of the amps channels into those loads driven by a clean sine wave just below clipping on the scope and measure the RMS AC voltage across the loads and use ohms law to calculate its power level.

Here is a link to a online ohms law math calculator:
Ohm's Law Calculators

P = E 2 / R
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Old 12th May 2012, 05:43 AM   #3
JLH is offline JLH  United States
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That's about right for a 40Wrms per channel amp. Since it is a class A/B amp you can only get within about 4 volts of each rail before clipping sets in.

So this is what I come up with for +/-22V rails: (44V - 8V) = 36Vpp
36Vpp = 12.7278Vrms
12.7278Vrms/4 ohms = 3.18195Arms
12.7278Vrms*3.18195Arms = 40.499Wrms
Looks about right to me.
Ah, how beautifully the orchestra sounds before a rain! In a dry sunny day there is no way for the instruments to sound this way!
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