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Old 14th December 2011, 08:45 PM   #541
Botte is offline Botte  United States
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With my BA-3, the P3 null of the second harmonic is very touchy. As you move ether way you increase the second harmonic smoothly not linearly more logarithmic. I found that having the harmonics out of phase (P3 turned toward Q2) give an unflattering sound, space but no body. Keeping it in phase (P3 turned toward Q1) adds air and space and warms it up a bit.
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Old 14th December 2011, 08:54 PM   #542
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Quote:
Originally Posted by Botte View Post
With my BA-3, the P3 null of the second harmonic is very touchy. As you move ether way you increase the second harmonic smoothly not linearly more logarithmic. I found that having the harmonics out of phase (P3 turned toward Q2) give an unflattering sound, space but no body. Keeping it in phase (P3 turned toward Q1) adds air and space and warms it up a bit.
Very interesting. Thanks!
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Old 14th December 2011, 09:28 PM   #543
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Botte and BAckbones,
Has it been difficult to get food offset when tuning P3?. I have found that moving towards Q1, offset close to zero is more difficult. It could be because i am running with only 4.7uF caps instead of 10, but wanted to try the Obbligato FIlm in Oil.
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Old 14th December 2011, 10:18 PM   #544
Botte is offline Botte  United States
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Quote:
Originally Posted by buzzforb View Post
Botte and BAckbones,
Has it been difficult to get food offset when tuning P3?. I have found that moving towards Q1, offset close to zero is more difficult. It could be because i am running with only 4.7uF caps instead of 10, but wanted to try the Obbligato FIlm in Oil.
Assuming you are talking about the junction of Q3 and Q4, did you use 1k for P1 and P2 or 500 ohm? With the 1K you have more range.

If you are talking about the follower stage then it should not change with P3 as the capacitor is isolating it from DC from the front end and the size of the cap wont matter except for the cutoff on the low-end.
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Old 14th December 2011, 10:26 PM   #545
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I was talking about FE. I used 500 ohm, but needed changes are too extreme it seems. I think the Cap does play into the ease of offset adjustment.
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Old 15th December 2011, 05:47 PM   #546
jprco is offline jprco  Canada
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Hello gang, new to this thread. I have been following it for some time and decided to purchase the kits from DIY Audio. Had no problem with the BA2 pcb's - nice amplifier.
However, I did have problems with the BA3 pcb's. Once the smoke cleared, I noticed an error in the "P-BAGSN-1v20" BMO. I haven't scanned this thread completely to see if this has been reported before and there has been no revision to the BOM that I can see. My apologies if it has but I will repeat it here for the late comers...to save them from blowing expensive MOSFET's!
Q3 and Q4 are reversed on the BOM and the 2SJ313 is described as a N-channel MOSFET. Hence the smoke if you assemble the pcb using the directions on the BOM.
Took some time to figure it out but now, the boards are ok and the amp does sound very nice too. But boy these are hot babies.
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Old 15th December 2011, 06:20 PM   #547
generg is offline generg  Germany
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the BOM in the european store seems o.k. to my eyes.....


but you are correct it was wrong some time ago...
Attached Images
File Type: jpg BA-3 BOM.jpg (82.2 KB, 516 views)
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Last edited by generg; 15th December 2011 at 06:24 PM.
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Old 15th December 2011, 06:41 PM   #548
jprco is offline jprco  Canada
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Thanks, generg.
The version of the BOM I got from the USA store back in September was V1.0 08/18/2011.
I just checked the site again and it has been corrected to the same version (V1.0a 10/11/2011) that you showed.
All is well in the world once again.
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Old 15th December 2011, 07:03 PM   #549
generg is offline generg  Germany
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look here

Burning Amp BA-3b (Balanced)

post 49 JoJoD818

the post was unfortunately put in the balanced BBA-3 thread....

and I mixed the Q3 Q4 up myself.....
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Old 15th December 2011, 08:33 PM   #550
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Quote:
Originally Posted by buzzforb View Post
Botte and BAckbones,
Has it been difficult to get food offset when tuning P3?. I have found that moving towards Q1, offset close to zero is more difficult. It could be because i am running with only 4.7uF caps instead of 10, but wanted to try the Obbligato FIlm in Oil.
With regard to the offset, no, I have not had any problems after adjusting P3. I am moving P3 about 20 degrees or more either side of the midpoint position and I can zero (roughly) the DC offset using p1 and p2. Even after a substantial P3 move it doesn't take much P1 and P2 movement to get the DC offset sorted. However, if the Idss of the jfets is low (which mine were originally) you will not be able to achieve 1V across R10 and R11 with only 500R for P1 and P2. I needed 1K in the end before I swapped the fets for Idss of about 8-9mA.
Also if the fets are poorly matched (which mine were) you will have to alter P1 or P2 more than the other. If you then alter P3 it may take one of the pots beyond what it can cope with. I had two very poorly matched fets to begin with and I coud get almost 1V on p1 but couldn't get p2 to bring up the voltage to anything near what was required.
I think you might miss out on some lower end weight with only 4.7uF.

Last edited by Backbones; 15th December 2011 at 08:38 PM.
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