I've got a Soundstream DA-1 that arrived quite literally as a basket case. Everything seems to be here, including two sets of amplifier boards. One Rev A, the other Rev B.
The Rev B boards are heavily damaged and have a lot of component substitutions and additions. Components are different between the two boards. Since I have no schematic to determine what should be there, I've set them aside for now.
The Rev A boards are in good shape and look to have mostly original components. I replaced the failed components on one board and brought it up on a lab power supply. It seemed to work fine. Bias and DC offset were adjustable but high. Bias (as measured across one of the emitter resistors) couldn't be adjusted below about 20mv. DC offset would vary all over the map as I twisted the POT (a new one by the way). It won't adjust below about 40 mv. Feeling pretty good about things, I put it back in the chassis and powered it up. Things seemed OK. I did a load test and suddenly smoke began rising from one of the emitter resistors and a fuse blew. Two output transistors had shorted under load.
Questions:
1. I've looked high and low for a schematic and failed. Anybody got one?
2. Any idea what the bias and DC offset should be and how it should be measured?
3. Any theories as to why it died under load? I have two guesses - counterfeit transistors or perhaps bias was too high.
And an interesting note. This amp board seemed to be very prone to go into oscillation. When running it outside the chassis on the lab supply, it would easily oscillate until I added the Zobel filter at the output. The filter is on the binding posts in the chassis, so when running the board out of the chassis I had to add it to prevent problems.
Thanks.
The Rev B boards are heavily damaged and have a lot of component substitutions and additions. Components are different between the two boards. Since I have no schematic to determine what should be there, I've set them aside for now.
The Rev A boards are in good shape and look to have mostly original components. I replaced the failed components on one board and brought it up on a lab power supply. It seemed to work fine. Bias and DC offset were adjustable but high. Bias (as measured across one of the emitter resistors) couldn't be adjusted below about 20mv. DC offset would vary all over the map as I twisted the POT (a new one by the way). It won't adjust below about 40 mv. Feeling pretty good about things, I put it back in the chassis and powered it up. Things seemed OK. I did a load test and suddenly smoke began rising from one of the emitter resistors and a fuse blew. Two output transistors had shorted under load.
Questions:
1. I've looked high and low for a schematic and failed. Anybody got one?
2. Any idea what the bias and DC offset should be and how it should be measured?
3. Any theories as to why it died under load? I have two guesses - counterfeit transistors or perhaps bias was too high.
And an interesting note. This amp board seemed to be very prone to go into oscillation. When running it outside the chassis on the lab supply, it would easily oscillate until I added the Zobel filter at the output. The filter is on the binding posts in the chassis, so when running the board out of the chassis I had to add it to prevent problems.
Thanks.
Hi Wayne,
Not sure if you are still active on this board, but I read your post on the SoundStream DA-1 on the Carver Stereo Forum today - I just picked up a blown DA-1 that I'd like to bring back to life. I tried to register on that forum so I could PM you for a copy of the schematic you created, but I can't seem to get the system to send me a confirmation email so I can log it. Thought I'd try you here.
Rich
Not sure if you are still active on this board, but I read your post on the SoundStream DA-1 on the Carver Stereo Forum today - I just picked up a blown DA-1 that I'd like to bring back to life. I tried to register on that forum so I could PM you for a copy of the schematic you created, but I can't seem to get the system to send me a confirmation email so I can log it. Thought I'd try you here.
Rich