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Old 25th October 2012, 04:29 AM   #11
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yes i would...
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Old 25th October 2012, 04:39 AM   #12
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Will do... Thanks Let you know the results
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Old 26th October 2012, 03:51 PM   #13
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OK, Installing two more Z44 MOSFETs worked no problem.
Now for the DC off-set problem...
Was at 60 mV on the Rt speaker output.
After checking the res readings on the darlington pairs (finals) one was way high compared to the rest. Replaced them and now I'm down to about 30mV on the Rt channel. Next I looked at the MPSA06/A56 trans used and started checking the Hfe value on all my new spares and there is quite a spread in values. I picked out the closely matched ones and installed them and that balanced the differential amp much better. I'm next going to check the MPSU07/57 (next stage) and see if I can get it down further.
Question though....
I noticed that the +/- 15 coming out of the power supply is reading +15.5 and -16.02. There are zener diodes along with TIP31C/32C for that section of the power supply. On the differential amp section, I noticed that the MPSA06 pare use -16.02 fed through a 3.9k resistor and then to the emitters of that pair and the MPSA56 pair use the +15.5 through the 3.9k to emitters. SEE Part of schematic here.... diyAudio

Could this be an issue?
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Old 27th October 2012, 06:32 PM   #14
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Default Closed issue

The amp works fine
Special thanks to Perry and 1moreamp for skoolin me on dc off-sets and determining that the engineering on this amp was poor. I learned allot about audio amps on stuff I thought I knew. I felt like I was in first grade.
Its all buttoned up so know its off to re-cap the few Soundstreams I have.
Thanks all.
Oh, When I heat up Q20 (MPSA06) or Q17 (MPSA56), the offset starts going towards 0v from +40mV.
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Last edited by 90scaraudio; 27th October 2012 at 06:37 PM.
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Old 12th September 2013, 02:16 AM   #15
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Default Quick up-date

So I also checked and had some ripple issues on the rails so I replaced the filter caps with some Panasonic's and put all the semi's back to stock (the originals that were in it when I got it). The ripple is gone and the dc offset is now 30mv on each channel. Sounds great.
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Last edited by 90scaraudio; 12th September 2013 at 02:34 AM. Reason: PICS
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