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Old 12th September 2011, 10:06 PM   #1131
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After building several of these fine amps I have decided that 33-34 volts D.C. is a little on the high side for continuous 4 ohm loads. My amps always ran very hot. I finely connected up the BPA 150 units by themselves and ran with less output. This is a very accurate sound. Extremely detailed.

Your build looks very neat and professional. You should get several years of enjoyment out of this construction. DIY is the ONLY way to have quality stereo in your home.

Tad
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Old 13th September 2011, 05:47 PM   #1132
toufu is offline toufu  United States
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Has anybody compared the sound between PA150 and BPA300? I have built PA150 and was wondering if anything can be gained by building the BPA300 other than the power? But then again, I already have very efficient speakers (Zu Druids).
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Old 13th September 2011, 11:10 PM   #1133
bcmbob is offline bcmbob  United States
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Hi Tad, A couple questions if you don't mind. I'm not sure what you mean by "connected up the BPA 150 units by themselves". Are you saying you went from 300 to 150 by separating two PCBs? Also, were you able to get the DC offset all the way to zero and what size transformer did you settle on?

I am very impressed with the sound I'm getting.

Thanks
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Last edited by bcmbob; 13th September 2011 at 11:29 PM.
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Old 14th September 2011, 09:26 AM   #1134
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I am assembling my BPA-300 to support out-of-the-box using it as an stereo BPA-300 (2x BPA-300) or as 4x PA150 amplifiers (for bi-amping purposes, or running 4 different speakers when needed for party )

I am using a 3 position switch for the inputs (explained for one channel, so half of the amplifier). It switchs input ground too:

-RCA (unbalanced input)-> input balance transformer-> 2x PA150 boards-> speaker between the two output binding posts (BPA-300)
-XLR (balanced input)-> 2x PA150 boards-> speaker between the two output binding posts (BPA-300)
-2x RCA (unbalanced)-> one input for each PA150 board-> one speaker between out and ground, another speaker between the other out and ground. For this purpose, I added a third binding post hooked-up to ground.

I am using a 4-pole switch, the 4th position hooked to a LED to show the position selected (hot, cold, ground, led).

Will upload some pictures of the progress as soon as I can, you'd love 'it. MASSIVE in all aspects.
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Last edited by regiregi22; 14th September 2011 at 09:31 AM.
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Old 14th September 2011, 11:05 AM   #1135
bcmbob is offline bcmbob  United States
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regiregi22,

I have the same question for you. How close to zero Vdc were you able to get after the pot adjustments with all three chips active? Did you build the SMD or the thru-hole version?
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Old 14th September 2011, 03:50 PM   #1136
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Quote:
Originally Posted by bcmbob View Post
regiregi22,

I have the same question for you. How close to zero Vdc were you able to get after the pot adjustments with all three chips active? Did you build the SMD or the thru-hole version?
Have built smd version. I have managed to get an offset as low as 1mvDC and as high as 5 or 6 mvDC, depending of the temperature, it varies. They were calibrated when the IC were warmed up at idle operation. But with an smallish heatsink (those ones from Pentium II, without the attached fan), temperature was 50-60, what I expect to get playing music with a bigger heatsink.

What I did was to solder everything EXCEPT the three 0.2ohm output resistors. Then I trimmed each LM3886 with its own trimmer. After playing with offset and readjusting after some minutes, when I was happy with the readings stability, I soldered the output resistors. Final offset won't be 0mvDC, but will be a small value. Then, in the final assembly, I will test them and maybe readjust the pots a little, but the thought work has already been done.

Anyway, when doing the final wiring between the boards, lets say I get those readings from the 4 boards:
-9mvDC
-17mvDC
20mvDC
8mvDC
What I have to do then is bridge board 1st with 4th, and board 2nd with 3rd. This way I will end up with -1mvDC and 3mvDC respectively seen at the speaker terminals. By having 4 boards with 3 trimmers each own, you are able to play quite a little to achieve 0mvDC, don't you think so?

Will tell ya when finally closing it
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Old 14th September 2011, 04:30 PM   #1137
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bcmbob,
The original Jeff Rowland designed BPA300 which Alexw so kindly layout out and supplied the gerber files for us was a bridge parallel amp. Alex first used an opamp to separate and drive the the two signals. He has since incorporated a transformer to split the incoming signal.
Anyway, the bpa300 is two to the bpa150 boards together, one driving the plus input signal the other the minus. You should get close to 300 watts into 4 ohms with the two boards and 150 watts with the single board. The single board will not have the input signal split it will just be plus and ground. I could not tell any audible change in sound quality either way.

I do know that the 150 was much simpler and easier to layout. I am driving a rather unconventional load and have since gone to a discrete Leach type layout. It handles down to 2 ohms with know overheat issues.

The current job on the workbench is my 160 Gu-50 tube amp courtesy of a nice gentlemen on the German web -- Christl Ludwig. He has done all of the hard brain work, including transfromer winding data and such.

Accuracy wise the Jeff Rowland clone BPA300 is right on.

Tad
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Old 14th September 2011, 09:02 PM   #1138
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Quote:
Originally Posted by tryonziess View Post
I am driving a rather unconventional load and have since gone to a discrete Leach type layout. It handles down to 2 ohms with know overheat issues.
The LM3886 handles loads down to 4ohms, this question go for the experts: May we assume then that 3 of them in parallel will handle 1.33ohms as a minimum? If so, for how long can you scale it? what load will suppor a 6 or even 12 IC in parallel?

Regards,
Regi
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Old 14th September 2011, 10:15 PM   #1139
bcmbob is offline bcmbob  United States
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regiregi22 and ted - thanks for your responses. It sounds like the techniques are all very similar. I didn't try adjusting the pots with no resistor - I did each leg with its associated 0,2R in place. I'll give that method a try.

Are you guys using attenuator or preamp/buffer for volume control?
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Old 14th September 2011, 10:36 PM   #1140
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I use that DAC direct to the F5, DC coupled. That DAC outputs no DC current. It has its own volume control:

EMU 0404 USB - really the best?
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