Burning Amp BA-3b (Balanced)

Build the first one, exactly the way Nelson Pass designed it, using the parts Nelson Pass suggested.

Then if you feel the need to attempt an upgrade, build the second one according to your own inner voice. As they said at Burger King, Do It Your Way. Maybe you'll like it even more. Beware of "Proud Parent" bias, it's been recognized for 60+ years.

Beranek's Law:
It has been remarked that if one selects his own components, builds his own enclosure, and is convinced he has made a wise choice of design, then his own loudspeaker sounds better to him than does anyone else's loudspeaker.
 
I think the comment is more along the lines that you have the PCB and therefore the ability to observe and measure the size of parts intended for the PCB, and yet bought enormous (although properly specced otherwise) capacitors that don't even remotely fit the board. Voltage rating and capacitance are not the only parameters you need to look at when ordering.
 
I think I used the same 1000uF 35V Slimic IIs in mine. I just leaned them over so they are mounted at a 20-30 degree angle (can't remember if that was inwards or outwards). I might look a bit weird, but with the box closed nobody will see it. And you'll know you have nice Silmic IIs in there 😎
 
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I'm sure many of us have ordered parts that don't quite fit the PCBs on hand. (For example, I have a lot of trimmers with foot prints/adjustment knob locations that make their inappropariate) So just be mineful of dimensions/footprints and using the filtering tools (and reference datasheets as needed) will help avoid this in the future.

Slightly off topic: I'm trying to understand what's the expected voltages across C1 and C2 (at least under 'reasonable' operating condition (not grossly clipping) ). The BA3 article mentioned "The bias current here is about 50 mA, and it will deliver peaks of approximately 100 mA." Let's say Q3 gives 200mA, then the voltage acrosss R10 is 4.4V and the Vgs of Q3 (depending on what part you use) might be in the 3V (Toshiba) or 5-ish (Fairchild) range. Let's say 6V. So the voltage from the R6/R8 junction to V+ is should be less than say 12V.

Is this argument correct?
 
This sounds right to me - it is definitely much less than the supply voltage and lower voltage rated caps could be used, which is why my previous statement was nonsense.
Just measured my old boards with Fairchild Mosfets at 50 mA bias and the voltage drop across the caps is around 5V. In this case the 1V drop from R10 and 0.8V drop from R6 equalize so that the voltage is around the bias voltage of the mosfet. For AC signals the cap is more or less a short so that the voltage across the cap should really only depend on the biasing regardless of supply voltage even.
 

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Thanks for the explanation. I had wondered about the actual voltage across the caps, but I'm not smart enough to figure it out on my own.
BTW, I was able to get the big caps to fit by bending a couple of 90s in the leads and mounting them about 1/4 inch above the PCB. I also glued them together for additional stability. They seem pretty solid. Hopefully, using the big caps won't adversely affect the sound quality.
 

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Hi, this has been talked about but am still somewhat confused.
I am planning on building a ba-3b with complementary ba2 push/pull output. They will be monoblocks.

On the back panel i wish to have both XLR and RCA inputs. I wish to have a switch on back panel to enable selection of XLR/RCA input but am unsure of wiring and switch type. Can anyone point me to how this is done?

Regards

David
 
A double pole double throw switch will suffice. You would connect ground from XLR (pin1) and ground from the RCA port to signal ground on the front end without a switch and the signal like this:
DPDT.png

This makes sense, if there are different sources connected at the same time and one output might short the other. If that is not the case just wire the RCA parallel to XLR Pin 2 and optionally short Pin3 to Gnd (Pin1), if RCA is used like Papa does:
images (1).jpeg


If you want to also switch the ground for gnd-loop reasons or so make it a triple pole double throw switch, where the 3rd pole has all the gnds connected to it. Edit: If gnd is also switched, no live switching! The equipment has to be turned off prior to switching.
 
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Hello, I need help please.
I have a problem with my ba-3b. Up to a certain point the system is quiet without hissing, but when I turn it up I get a hissing sound at 7250Hz that keeps getting louder, even without any sources connected.
I have already tried a different volume control and the same problem.
CD player connected to amplifier via adjustable output, no hissing.
BA-3 B with Muses controller on Aleph JX.
 
Do you have a scope so you can look at the noise/signal at different stages? I'd start by trying to isolate where it comes from: separating channels (both L/R and +/- all affected same?), volume control, relays, shielding, power supply, is the noise also there at low volume, just not audible? questions like that
 
Thank you,
I'll have a look at all the L/R +/- channels with and without volume control on the scope.
White or pink noise for testing should be ok.
When I have found something I will get back to you.
 
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