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Old 21st January 2003, 12:43 PM   #1
Mark25 is offline Mark25  United Kingdom
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Default problems using 2 bridges for p3a

Hi All,
I have a problem with my dual mono p3as. They were working fine, but I have just changed them to the tnt, one bridge per supply rail system, as in fig 4 of this link below, instead of one bridge for + and rails.

http://www.tnt-audio.com/clinica/ssps2_e.html

Now they intermittently have 2A bias current. The supply drops from 43v to 37v and the o/p trs (mje15003/4) get hot quickly. Does anybody have any ideas why this might be? When its working, the sound seems to be better with this mod!

Thanks in advance
Mark
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Old 21st January 2003, 01:21 PM   #2
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Default Re: problems using 2 bridges for p3a

Quote:
Originally posted by Mark25
Hi All,
I have a problem with my dual mono p3as. They were working fine, but I have just changed them to the tnt, one bridge per supply rail system, as in fig 4 of this link below, instead of one bridge for + and rails.

http://www.tnt-audio.com/clinica/ssps2_e.html

Now they intermittently have 2A bias current. The supply drops from 43v to 37v and the o/p trs (mje15003/4) get hot quickly. Does anybody have any ideas why this might be? When its working, the sound seems to be better with this mod!

It sounds as if the bias transistor, which probably is in contact with the output heatsink/transistor, is working intermittentingly or not tracking the heat increase as it should.

If the new supply is wired correctly and the voltages are the same that were before (and they should), the problem seems to be elsewhere.

My first suspect would be the bias transistor. Have you tested it? How is it secured to track temperature?


Carlos
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Old 21st January 2003, 01:22 PM   #3
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Default 2 bridges

Mark,

Is there a chance that the two secondaries are not fully separated?

Jan Didden
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Old 23rd January 2003, 06:09 AM   #4
Mark25 is offline Mark25  United Kingdom
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Hi Carlos and Jan
Thanks for your replies.

Carlos; the bias transistors are mounted on vero board away from the main transistors, this has not caused any problems in the last couple of months of prolonged hard use. The bias current does not seem to drift much at all really. I have tried freezer spray on all the active devices including the bias transistors, but it does not have the effect I am looking for, just small changes in bias current as expected. The fault I have is an instant increase from 100mA to 2A.

Jan; the two secondaries are not mixed in any way, they go straight to their respective bridges. I am now running the two amps from one supply to check interaction here is not the problem. The fault is still there.

After some further testing it seems you are correct Carlos, I have developed a problem during the mod to two bridges somehow. These p3as have worked fine for months now, but since this mod they will not even work as they were before, with only one bridge per mono amp. As soon as each of the mono amp is connected to another piece of equipment (cd or pre) the bias goes from 100 mA to 2A. Even if the equipment is not plugged in! I think I have an earth or oscillation type fault. Thanks again for your help.

Mark
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