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Vintage Marantz SR4000

O

oldradioman

New Member
Hi, I am new to the Fourm. I have a Marantz SR4000, the vintage receiver, not the newer AV unit. The STK 0050 output packs have offsets of -5 volts on one channel and +8 volts on the other channel. They both have audio out and the power meters work, with lots of distortion on one channel. I have only connected a speaker through a cap to test because of the high offset voltages. With no load, the output packs do not get warm. Also, there is a STK 3062 voltage amplifier that does get very hot. Anyone had this problem before? Also, does anyone have a schematic for this receiver? I haven't had any luck searching on the web. The SR4000 AV keeps showing up. Any help is really appreciated.
 
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Welcome to AK!

The STK 0050 in itself can't be the cause of this offset. The offset comes from the STK 3062. This voltage amp must be heat sinked, or it will fail.

If you look at datasheetarchive, you will find many data sheets for the STKs and some data sheets provide application notes. The actual circuit in your amplifier stage may be very close to the circuits shown on those application notes.
 
ecluser said:
Welcome to AK!

The STK 0050 in itself can't be the cause of this offset. The offset comes from the STK 3062. This voltage amp must be heat sinked, or it will fail.

If you look at datasheetarchive, you will find many data sheets for the STKs and some data sheets provide application notes. The actual circuit in your amplifier stage may be very close to the circuits shown on those application notes.
Click to expand...

Thanks, I looked at the data sheets and checked all the associated outboard parts, caps, resistors, etc. and they all look OK. I then unhooked the outputs from the STK 3062 to see what happens. Now the STK 0050's stay cold and the offset voltage is around .0032 volt, which is probably normal for them. Also, the STK 3062 still gets pretty hot. Thinking about ordering a new STK 3062 and try that. You mentioned that the voltage amp must be heat sinked, it isn't. It only has a wire hold-down clip on it.
 
ecluser said:
Can you post a picture of this?

Clipped to the pc board? See this thread:

http://www.audiokarma.org/forums/showthread.php?t=118395

The 3042 was fixed on the board with "scotch tape" before I fixed it to a heat sink on that Akai amplifier.

If you can find a 3082 for the same price than a 3062, go for the 3082.
Click to expand...


I ordered a new STK3062 and will let you know if that is the fix. I will try to make a heatsink in the meantime. Thanks!
 

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Update, I received and installed the new STK-3062 today, and that fixed it! Offsets are in the millivolts. Sounds great with my Monitor 10's. I also made a heatsink out of copper sheet and attached it. Runs much cooler now. Thanks for all of your help! Great forum!!
 
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