Burning Amp BA-3b (Balanced)

The one and only
Joined 2001
Paid Member
It's straightforward. The input stage cares mostly about the difference
between the two input voltages - in other words it is floating. So if you
ground one input and drive the other, it just treats ground as if it were an
input signal, and amplifies the difference between ground and the input
that you are driving.

:cool:
 
Thanks Mighty Zen. Will a 1:1 transformer do the trick? The sound from the mixer is precise but a bit bright and metalic. Adding some 2HD would help to make the sound a little warmer and less metalic.

The input pair has unity gain. Whether reducing this will obviate the action of the THD pot, is something I am not sure of.

What I need is a unity gain buffer which adds its desired signature. I realise that if the 1st and 2nd stage of BA-3 were to be designed for unity gain (the first stage already is unity gain, as per manual), P3 may not have much effect.

The other requirement is to be able to handle 14Vrms input signal.

Hence, my question whether to attenuate signal by increasing input resistor or to throw away gain of the 2nd stage with increased local feedback.

Thanks.
 
Official Court Jester
Joined 2003
Paid Member
regarding xformers - you must to try this and decide ;

regarding other things - with input resistors increasing you'll not gain anything ( wrong approach - there is no attenuation with that , or at least - there you can gain wrong type of attenuation) , but you need to decrease already mentioned 200 ohms resistor ( but not much - maybe 20%) ......... and also ( which I forgot to wrote , before first morning coffee ) - increase R10 and R11 to 27R , and decrease R13 to same value ;
same on both sides

dunno - that's heavy bleeding of things , I didn't tried it ;
so - you need to test it
 
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Isn't it all against the second merit of BA-3 front end i.e.:
"Potentiometer P3 is provided for those of you who have distortion analyzers or want to play with the mix of second vs third harmonic. As with the F5 amplifier, you will find that you can iteratively trim P1 through P3 for minimum distortion. I do so at approximately the 1 watt output level (2.8 V). You should start out with the setting at the mid-point. The minimum distortion point will generally be where the plus and minus halves of the amplifier balance to such a degree as to null out the second harmonic. By introducing an imbalance you can variably re-introduce the second harmonic, and depending on which way you turn the pot, you can choose the absolute phase of the second harmonic."
I mean with balance version get rid of second harmonic. (the first merit of BA-3 is lack of negative feedback of course).
 
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Official Court Jester
Joined 2003
Paid Member
Isn't it all against the second merit of BA-3 front end i.e.:
"Potentiometer P3 is provided for those of you who have distortion analyzers or want to play with the mix of second vs third harmonic. As with the F5 amplifier, you will find that you can iteratively trim P1 through P3 for minimum distortion. I do so at approximately the 1 watt output level (2.8 V). You should start out with the setting at the mid-point. The minimum distortion point will generally be where the plus and minus halves of the amplifier balance to such a degree as to null out the second harmonic. By introducing an imbalance you can variably re-introduce the second harmonic, and depending on which way you turn the pot, you can choose the absolute phase of the second harmonic."
I mean with balance version get rid of second harmonic. (the first merit of BA-3 is lack of negative feedback of course).

you have symmetry effect between halves due to common 200 ohms resistor and overall effect of bridging .
if Papa sez that invoking 2nd harmonic can still be higher than symmetry effects , I'm not doubting that ....
 
Member
Joined 2009
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O.k. BBA-3 sounds pretty darned good.

I have now too much gain........for Lowthers, F4 with 1:5 xformer ( must stay in! For my golden ears!)

I looked at Zen Mods recommendations and

lowered R13 and brothers to 116 Ohm and increased R10/11 to 44Ohm, now I am in a region I can use my pots in the lower positions.

Does anybody see a problem in doing this? Of course I increased the voltage over R10/11 to 2V. :)