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Old 10th May 2013, 03:52 AM   #351
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They came from an HH V800 I scrapped out that had multiple issues with the outputs not being one of them. So, I ended up with eight of each polarity guaranteed to be genuine and matched.
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Old 10th May 2013, 04:14 AM   #352
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Quote:
Originally Posted by jkuetemann View Post
They came from an HH V800 I scrapped out that had multiple issues with the outputs not being one of them. So, I ended up with eight of each polarity guaranteed to be genuine and matched.
I wondered that!
Thanks!
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Old 10th May 2013, 08:31 AM   #353
PMI is offline PMI  United States
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Offset is set via an additional resistor in parallel with the 15k current injectors, as per Shaan's schematic. I just used a pot to zero it out and put in the closest standard value. Offset comes in under 10mV with one standard value in place.
Thanks. I decided to leave both trimmers in place on the first two boards, just in case there was a change over time and temperature, but so far I have not seen it change more than a few mV.

Next set of boards, I will try to make do with a single resistor and see how that goes, but I would like to get maybe 50-60 hours of normal volume play on the first set b/f I build another one, or change this one.
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Old 10th May 2013, 09:59 AM   #354
shaan is offline shaan  India
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Closely matched input pair and VAS pair will in most cases need no manual trimming and give offset of less than 20mV. Currently one of my boards has 3mV and the other has 8mV, untouched.
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Old 10th May 2013, 11:51 AM   #355
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Pretty nice ! ... and well done too.
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Old 10th May 2013, 06:48 PM   #356
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Quote:
Originally Posted by shaan View Post
Closely matched input pair and VAS pair will in most cases need no manual trimming and give offset of less than 20mV. Currently one of my boards has 3mV and the other has 8mV, untouched.
Both of my boards started w. about 15mV DC offset, but untrimmed, the measured offset changes a bit as voltage from bench supply is gradually raised. I did not really investigate that further. Trimmed to zero after warmup, seems to drift +/-5 mV. On the first board, I reset it to zero again when I switched from a regulated bench supply, to an unregulated rectifier/filter.

How do you match your resistors, by hand or using a meter/transistor tester?
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Old 10th May 2013, 07:16 PM   #357
shaan is offline shaan  India
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How do you match your resistors, by hand or using a meter/transistor tester?
By hand with a meter.

Only the feedback network is matched.

Last edited by shaan; 10th May 2013 at 07:30 PM. Reason: blame my cellfone
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Old 10th May 2013, 07:39 PM   #358
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Ooops, meant to say TRANSISTORS. I spent too much time listening to the amp last night, too little time sleeping...
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Old 10th May 2013, 08:40 PM   #359
shaan is offline shaan  India
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Don't worry. It's a common obsession among SSA owners. Me included. The amp may even make you forget where you are...
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Old 10th May 2013, 09:03 PM   #360
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Ooops, meant to say TRANSISTORS. I spent too much time listening to the amp last night, too little time sleeping...
Still mono?
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