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MA6600 bias setting?

tutor_turtle

tutor_turtle

AK Subscriber
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I have a MA6600 on my bench for a (right channel) Power Guard issue.
This same unit was in seven years ago for the same issue (left channel)
Then, as now, I purchased the output board as a whole to simplify the repair as it is a direct coupled design, the pre-drivers were likely damaged as well.
I must have set the bias back then, but I have since moved and lost my notes on this information.
Does anyone know what the bias setting should be?

Best,
Steven M.
 
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Not sure about the 6600 or how much it differs from the 6500, but here's the procedure for the 6500. Might compare what the bias reading is on the other channel. Or you could use a distortion analyzer, ensuring in the process you don't set the bias too high.

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w3jn said:
Not sure about the 6600 or how much it differs from the 6500, but here's the procedure for the 6500. Might compare what the bias reading is on the other channel. Or you could use a distortion analyzer, ensuring in the process you don't set the bias too high.

View attachment 3039335
Click to expand...
Thank you.
I found my notes: 25mv cold, no signal, no load, after a 10 minute warm up.
Good thing too, the unit was set at 50mv and running a little hot.
 
Last edited:
tutor_turtle said:
Thank you.
I found my notes: 25mv cold, no signal, no load, after a 10 minute warm up.
Good thing too, the unit was set at 50mv and running a little hot.
Click to expand...
Hi tutor, my ma6600 got the exactly same problem as yours, sadly. Would you please describe how you fix it with more detail？Especially how do you message the 25mv voltage. Thank you.
 
The unit was in power guard, the fix was to replace the driver/output board.
This thread was about setting the bias in that new board.
The good news is McIntosh still has the board, the bad news it was about $350 for the kit.
And I had to solder on the output transistors (provided)
I was told I got one of the last (partly) assembled boards.
However, I was told they have lots of blank cards and all the parts to populate it.
The service and parts department was very helpful.
 
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