Burning Amp BA-3

.............And anyway, with 2 transformers it would be very difficult to lift...

....... I would rather build monoblocks than a fully dual PSU - if you are that far you might as well go all the way.

:D I know - with two toroids mine comes in at 48 pounds.

If monoblocks - can the PS be split, or would a second full cap board be best? This will be my first build with the diyAudio store board. I fabricated my own for the SE build.
 
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Official Court Jester
Joined 2003
Paid Member
48 pounds ?

that's medium sissy amp

:devily:

not so sissy ones are around 58.5 pounds

:rofl:

ntg4ceg
 
"If monoblock you need 2 PSU as you will have 2 chassis."

Understand that - just not familiar with the amount of flexibility of the new (to me) blue board and didn't see any info in the PS build guide. I have this on each side. Are you suggesting I would get better performance with the full eight cap set if used in the SE?

@ZM - See there, that's why you need to switch to water cooled.:p
 

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Ok, so I'm about to start the BA-3 build for my MG2.7QR:

- monoblocks, each with 2x24V 800VA toroid, CLC filter (~2mV ripple under load)
- 6 deep per channel, biased at 3A total
- heatsink for one channel should withstand ~200W with natural convection, up to 370W with forced convection (Noctua fans) with 35°C above ambient temperature

Given this configuration, I planned to do the following:
- to cut the FE board and place it inside each monoblock
- to use the same PSU for FE and output section
- to connect the output section boards with fastons, so I'm able to listen the difference between 6-deep@3A and 3-deep@6A (dissipation will be within ~30W per device)

In this configuration I should have into 4 Ohm:

- dissipation: ~32*3*2=192W
- peak power: ~(28*28)/4=196W or 98W RMS
- class A power: 4*3^2=36W RMS or 72W peak
- with C-filter derating factor of 0.7, transformer will work full time at 36% of its capability.



Then I started to wonder about the BA-3B.
I'm able to get matched transistor, so no problem with this aspect. I also have 2 bias boards per channel, and the faston connection method would provide some flexibility in rearranging the configuration, which will be 3-deep balanced.

In this case, keeping the same bias, I should have into 4 Ohm:

- dissipation: ~32*3*2=192W? Or will it double (64*3*2=384W)?
- peak power: ~(56*56)/4=784W or 392W RMS
- class A power: 4*3^2=36W? Or will it change?
- I suppose the transformer will be inadequate. It will work at 72% of its capability full time, but it won't be able to deliver the potential peak power.


I think that the passage from SE to balanced can be done without too much harm, and it can be done in the future (if I ever will have a bigger listening room :D):
- if necessary, I can pile up another transformer
- I will assemble and select the FE board with components in a way that matching will always be granted
- I can take care of the the additional dissipation with fans

My concern in this case will be the performance of a 3-deep balanced output section with MG.


Any comments or advice? Any calculation is wrong (especially for balanced version)?
Thank you,
Giulio
 
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6L6

Moderator
Joined 2010
Paid Member
Idle power dissipation doesn't change with a balanced amp, although you room will be hotter because you need two amplifiers...

Also, transformer size will not really effect peak power, that's handled by the cap and choke filter.

With making an amp of that size (and desired power) I would suggest using smaller Mosfet source resistors, perhaps 0.68R or 0.47R. This will help get the large voltage swings at maximum output.

Also, remember to make your capacitor bank voltage rating higher than normal, a CLC filter has a voltage spike upon start-up.
 
Idle power dissipation doesn't change with a balanced amp, although you room will be hotter because you need two amplifiers...

Also, transformer size will not really effect peak power, that's handled by the cap and choke filter.

With making an amp of that size (and desired power) I would suggest using smaller Mosfet source resistors, perhaps 0.68R or 0.47R. This will help get the large voltage swings at maximum output.

Also, remember to make your capacitor bank voltage rating higher than normal, a CLC filter has a voltage spike upon start-up.

I will have in any case two amplifier: if I plan to do it, I will switch from two monoblocks SE 6-deep to two monoblocks balanced 3-deep (because I will use the same output boards within each chassis).

OK for source resistors, and thanks also for the suggestion on voltage rating of filter caps (I already have them @50V)
 
Giulio, I did what you are thinking about..almost. I started with two ba3 mono blocks, 4 pairs of outputs per amp. Listened for a while and then converted to balanced. Just as you are thinking I all ready had the matching ba3 front ends set up so the switch was easy.
I also use a clc filter and 800va transformers. A difference is my output devices are laterals biased at 1 amp each. 8 amps total per monoblock.
I like the sound of the balanced set up. I built up a volume control/input selector that has a pair of jensen transformers http://www.jensen-transformers.com/datashts/11p1.pdf so I can plug in balanced and single ended sources.
Enjoy...Evan