Bertje:
The difference in the input capacitance of the FETs is generally what causes the problem. The originals have a Ciss of ~1500pf. The replacements have a Ciss of ~2000pf. The transistors (MTP50n05E) in the amp I have here have a Ciss of 3000pf. I paralleled a 1000pf cap across the gate and source and the current draw at idle was still very low (0.863A).
This was a surprise... I changed the value of the timing resistor to increase the power supply frequency. At 68kHz, the current flow is actually less than at 56kHz. It's only 0.806A at 68kHz.
I no longer believe it's the operating frequency that's causing the high current draw.
While it's entirely possible that the replacement FETs are causing the problem, I'd suspect something else.
razirafi:
Have you tried measuring the voltage across the emitter resistors to determine if the problem is excessive current flow through the audio output transistors?
The difference in the input capacitance of the FETs is generally what causes the problem. The originals have a Ciss of ~1500pf. The replacements have a Ciss of ~2000pf. The transistors (MTP50n05E) in the amp I have here have a Ciss of 3000pf. I paralleled a 1000pf cap across the gate and source and the current draw at idle was still very low (0.863A).
This was a surprise... I changed the value of the timing resistor to increase the power supply frequency. At 68kHz, the current flow is actually less than at 56kHz. It's only 0.806A at 68kHz.
I no longer believe it's the operating frequency that's causing the high current draw.
While it's entirely possible that the replacement FETs are causing the problem, I'd suspect something else.
razirafi:
Have you tried measuring the voltage across the emitter resistors to determine if the problem is excessive current flow through the audio output transistors?
This one shows the Gate waveform on top and the toroid center-tap (+12V supply) on the bottom.
Is this ripple the cause of the overheating filter caps? By the way, is it safe to cut-off the supply rails from the rest of the circuit to check for idle current without any load whatsoever?
Is this ripple the cause of the overheating filter caps? By the way, is it safe to cut-off the supply rails from the rest of the circuit to check for idle current without any load whatsoever?
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Did you check the voltage across the emitter resistors to see if one channel was passing too much current?
The ripple is excessive (assuming that the vertical amplifier is set the same as the top waveform). It looks like both banks of FETs are on at the same time causing the ringing.
You can pull the rectifiers to break the connection to the rest of the amp. I've never had a problem doing this but you need to be careful and extra observant in case there is a problem.
The ripple is excessive (assuming that the vertical amplifier is set the same as the top waveform). It looks like both banks of FETs are on at the same time causing the ringing.
You can pull the rectifiers to break the connection to the rest of the amp. I've never had a problem doing this but you need to be careful and extra observant in case there is a problem.
Hello again guys. I set this thing aside to work on a ZAPCO Z300C2 which would intermittently go into protection mode.
Anyway, I ordered a new 3524 and when I installed it into the Soundstream's circuit, the meltdown scenario was gone
As for the original 3524 that came with the amp, it promptly found its way into the garbage bin..hehe
Thanks for the interaction guys!
Anyway, I ordered a new 3524 and when I installed it into the Soundstream's circuit, the meltdown scenario was gone
As for the original 3524 that came with the amp, it promptly found its way into the garbage bin..hehe
Thanks for the interaction guys!
I see that you have a schematic for this Soundstream amp, can you email it to me? My email is junglejuice72@hotmail.com
Cheers, Junglejuice,,,,
Cheers, Junglejuice,,,,
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