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Old 5th March 2014, 07:14 PM   #1571
Ryssen is offline Ryssen  Sweden
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Anyone compared the sound of BA-3 t an F5?
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Old 8th March 2014, 11:23 PM   #1572
bcmbob is offline bcmbob  United States
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All's well in the kingdom again !. The culprit was a bad Q204 on the bias board. As reported, no mosfet to sink continuity showed up till that last wire (V-) was attached between the bias and output boards. The pic shows the link.

Also, after a loonngg phone conversation with Mr. 6 (who graciously schooled me by walking through all three schematics) the higher reading (.58 V) on the alternating mosfets is due to the output/CCS layout on the board. Had to go way back to the BA-1 article to see the SE schematic.

Both channels now respond properly (0.00 - 3+mV) to trimmer adjustments on the output mosfets. The second pair of output boards will be put back in this evening, and hopefully there will be more good news in the morning.

Great learning experience - thanks all.

Jim, you're a champ !
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Old 8th March 2014, 11:25 PM   #1573
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Old 8th March 2014, 11:32 PM   #1574
6L6 is online now 6L6  United States
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Bob -- Fantastic news! I'm glad you could determine what was the bad component.

Quote:
Originally Posted by Ryssen View Post
Anyone compared the sound of BA-3 t an F5?
I've driven an F4 with a BA-3 front-end as a preamp, which is 99% a BA-3 complimentary. It's a very similar sound, as the follower output stage is almost completely invisible, and the BA-3 FE is strongly related to the F5... But the BA-3 is smoother and prettier without any loss of detail, and can run a lower-impedance load with ease. The F5 is a great amp, I've built no less than 3, and think it's a fantastic project that anybody interested should do, as you will love it.

If you are willing to take on the (not insignificant) extra complication of the BA-3, I think it's worth it.

Last edited by 6L6; 8th March 2014 at 11:38 PM.
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Old 8th March 2014, 11:42 PM   #1575
bcmbob is offline bcmbob  United States
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@ 6L6 - Couldn't have done it without you telling me what all those squiggly little lines were all about. :
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Old 9th March 2014, 12:29 PM   #1576
bcmbob is offline bcmbob  United States
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Everything is back together and sounding fine. Hitting on all 24 cylinders. Chassis and cooler work can now continue.
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Last edited by bcmbob; 9th March 2014 at 12:36 PM.
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Old 19th March 2014, 01:53 AM   #1577
bcmbob is offline bcmbob  United States
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Still Tuning !!

I've been able to adjust to 0.000 VDC across R13 on the front end - and 0.000 VDC offset on the output boards. Those appear stable after about 15 minutes. The only discrepancy is source resistors at 0.6 - 0.61 mV instead of 0.58 (nothing below .58 so far) as called out on the SE schematic. Is that close enough or should I try further adjustments?

Readings across R10 & R11 on the front end range between 0.9 - 1.1 volts.
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Old 19th March 2014, 01:58 AM   #1578
Zen Mod is offline Zen Mod  Serbia
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close enough

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Old 19th March 2014, 02:11 AM   #1579
6L6 is online now 6L6  United States
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Yes. Probably in the range of tolerance of the resistors.

With your offset zero it seems logical to relax and listen to it for awhile.
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Old 19th March 2014, 02:18 AM   #1580
bcmbob is offline bcmbob  United States
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Great - Have to give you your props as your advice to ignore the many suggestions and just shoot for the zeros brought it home.

Another point of confusion were the multiple tips to find 0.2 mv somewhere on the output boards. A closer look at the schematic (BA-1 article) shows ALL the mosfets have a tie to a 0.58 bus on the SE board.

Point of humor - The first sound test produce a horrible hum. Was just a loose plug on the Walkman I use for bench tests.

@6L6 - I'll try but this is the closest I've come to generating an worry ulcer. The output levels are much better with proper voltages - funny how that works
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