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.
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!
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.
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.
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.
look here
http://www.diyaudio.com/forums/pass-labs/201281-burning-amp-ba-3b-balanced-5.html#post2742161
post 49 JoJoD818
the post was unfortunately put in the balanced BBA-3 thread....
and I mixed the Q3 Q4 up myself.....
http://www.diyaudio.com/forums/pass-labs/201281-burning-amp-ba-3b-balanced-5.html#post2742161
post 49 JoJoD818
the post was unfortunately put in the balanced BBA-3 thread....
and I mixed the Q3 Q4 up myself.....
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.
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Hi!
I'm sorry to hear you got the V1.0 of the BOM. The error was corrected as soon it was discovered.
Making tens of BOMs at the same time is really bound to have errors I guess, but it's not an excuse so I checked everything again and again.
Please, if you guys discover anything suspicious in the BOMs, please do send me a PM and I'll gladly see to it.
J
Every time you change this you need to adjust the bias on Q3 and Q4. So it's not quite as easy as a switch.
Seemed too good to be true..Thanks.
So it has to be a MULTI GANG switch that can adjust 3 different settings per channel- once they are figured out.. That's a lot of work!
In theory, could i set the Ba3 to the lowest distortion setting and then reintroduce the second harmonics into the scheme on the output using the Leaving Class A setup. THis way you retain the no feedback topology throughout the stages, with uber low distortion, but still have some second harmonic at low power as a result of the SE current source on the output.