Burning Amp BA-3b (Balanced)

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#382
permaneder said:
Sorry, I misunderstood your comment. But SE in and balanced out is not an issue, too. Connect the right channel RCA in to your source and stick a shortcut U-plug into the XLR in (from – in to ground). That’s all.
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sorry Im slow 😀

but allow me to 'rewrite' your post this way

for SE to balanced drive connect shorted RCA connector into 'negative side' RCA input plug

to make it into normal 2 channel SE simply pull the shorting RCA on negative side

along with the swithing of output like you have shown it, ofcourse
but if replacing the mini switch with a multipole switch it ought to be possible to wire it to do it all
 
#388
Store case question

Sorry if this is off topic, please ignore if it is.

I'm planning on building a balanced BA output stage, full 6 pairs per channel, using the store's boards. I was considering getting the store's 5U "deluxe" chassis.

It seems that it will not be possible to fit, depth-wise, the two boards onto the two heatsinks that make up the side of the store's 5U case? Also, if it somehow possible, do the machined holes in the "deluxe" case allow efficient placement of two boards per side onto the heatsinks?

The case is not a trivial expenditure, just want to verify before I buy.

Thanks.
 
#389
-So for 2 channels you'd want 8 output boards total?

-Nelson Pass has stated in the past that his chassis' he gave away happened to have 6 MOSFET pairs per side not that that it was optimal to have that many. I believe the best specs are down around 2 or 3 pairs per side. OTOH, if it's balanced I guess more are a good idea for low impedance loads?

I don't think more than one board will fit per side using the drilled hole (UMS) One solution is to put one above the other, but that would require custom holes so you would need the standard chassis and custom drill and tap it. That's also a lot of cooling required for even the 5U chassis. Or get 2 4U chassis' and use one per channel as mono-blocks with 3 pairs per side.
 
#391
Variac said:
if it's balanced I guess more are a good idea for low impedance loads?

get 2 4U chassis' and use one per channel as mono-blocks with 3 pairs per side.
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It's for driving Acoustat 2+2's, 4 ohm nominal, down to 2 ohms in certain places. Plus it needs power, so I think it's better to do the six pairs/channel. And I do want balanced if feasable on a 5U case as monoblocks.

I'll have to do start saving money to get two standard 5U's.

Thanks a lot for the advice.
 
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#392
Mr. dB said:
The heatsinks for the big case are pre-drilled for 12 output devices per side.
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But not for 2 boards. I guess the way to go might be to use pretty tall standoffs for mounting the board, then bend the MOSFET legs for one row so they barely go through the board, and on the other side of the board have short wires to the MOSFETS. It could look fine I think. Where do the wires come from? well some of the traces are quite wide so they'd be easy to drill, or the devices could be wired in parallel with the ones that go into the board holes? Possibly by wrapping the wire around the board installed MOSFETs legs..
 
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#394
use can use two stereo pots
2x stereo conversion would also be simple

much depends on whether, and, or where you have SE or balanced
but the BA-3 frontend might do high-Z input, thus just connect the att pot(and avoid a buffer)
maybe the present 47K is enough to do passive, I dont know
but if you have low impedance source .....
 
#399
I did not test this, remind that in the UGS from Cheff there are two pots to set the absolute and differential offset to zero. We do not have these pots in the circuit, and nobody has heard this combination against the NonFB version,so for a try I would stay with the original circuit....


🙂
 
#400
I considered the possiblity that the bias pots could trim this out, but did not consider the differential offset. I am also unsure if the level shifter is as stable a bias setting point as the drain based bias section found in the F5. Thank you. Gives me something to think on.
 
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