Burning Amp BA-3b (Balanced)

[2 picoDumbs]

I calculated based on a conservative 4V loss on each half of the circuit ie 16V for 20V rails (or 32Vpk for the balanced circuit) but it can probably swing a little higher than that, as pointed out by 6L6

P= 32*32/8 = 128Wpk
= 64W avg

Difference between a 32Vpk signal and a 36Vpk signal is very small on the audibility scale

 

[6L6]

Difference between 32Vpk signal an 36Vpk signal is very small on the audibility scale

Precisely.

 

[poseidonsvoice]

Power is VRMS squared divided by load in ohms.

The balanced BA-3 can swing voltage to roughly 10% of the rails, where the source resistors start to steal a bit of output.

20V rails, on a balanced amp is 80V pk-pk, -10%, so it can swing ~72V

72V pk-pk is equal to 25.4V RMS (72 x .3535)

25.4^2 = 647.8 / 8(ohms) = 80W (which is actually close enough to 60W as to make little meaningful difference...)

And there are enough output devices on this amp to be able to give full output current into 8 and 4 ohms as well.

That said, if you have the transformer on hand, by all means use it and don't think twice, but if you are buying one, buy a 18+18v or 20+20v

Thanks. I worked out the math myself, and that's pretty much what I got as well.

Given that we are talking about a balanced mono block version of the BA3, which in total would need (4) 10 uf film capacitors [on the two BA-3 boards, at position C3], I was curious to know what the corner frequency was that Mr. Pass was aiming for. I vaguely recall it being 0.3Hz, but I wonder if that requirement could be relaxed a bit in this design. In other words, would 4.7uf be a bad choice here instead? If 0.3Hz is true, then, 4.7uf should be about 1.5Hz, for the -3dB point.

Best,
Anand.

 

[2 picoDumbs]

I'd be happy with anything under 5Hz

 

[wengtech]

hello,
since i can not found more info about BBA3 driving single-ended output followers, (so please see attachment) my questions are:

1. Is this how the BBA3 FE will be wired to the BA SE output stages?
2. so each output (+) and (-) has its own bias circuit,
3. the speakers will be connected to the (+) and (-) output, without the ground
4. what is the voltage rails and current needed for one channel (i plan to use 12 mosfet per channel, 6x(+) and 6x(-) as balanced)

hope found the best answer here.

thanks.

 

[6L6]

Well...

That looks logically correct, but I will be the first to admit that I honestly don't know. Hopefully somebody who has real knowledge can answer...

Paging Mr. Pass, Mr. Pass,
Mr. Nelson Pass,
Please pick up the White courtesy phone,
Mr. Pass.
Thank you.

 

[Zen Mod]

hello,
since i can not found more info about BBA3 driving single-ended output followers, (so please see attachment) my questions are:

1. Is this how the BBA3 FE will be wired to the BA SE output stages?
2. so each output (+) and (-) has its own bias circuit,
3. the speakers will be connected to the (+) and (-) output, without the ground
4. what is the voltage rails and current needed for one channel (i plan to use 12 mosfet per channel, 6x(+) and 6x(-) as balanced)

hope found the best answer here.

thanks.

1. off course it is
2.off course
3. yup
4.due to mosfets internal capacitances nature , I wouldn't go bellow 18V rail and 130-150mA per mosfet pair , pair taken vertically

 

[Nelson Pass]

Paging Mr. Pass, Mr. Pass,
Mr. Nelson Pass,
Please pick up the White courtesy phone,
Mr. Pass.
Thank you.

This conversation has been simultaneously going on in email.

 

[Zen Mod]

why aren't we all included ......

 

[Nelson Pass]

1. Is this how the BBA3 FE will be wired to the BA SE output stages?
2. so each output (+) and (-) has its own bias circuit,
3. the speakers will be connected to the (+) and (-) output, without the ground
4. what is the voltage rails and current needed for one channel (i plan to use 12 mosfet per channel, 6x(+) and 6x(-) as balanced)

1. Yes
2. Yes
3. Yes
4. How much power did you want?

 

[wengtech]

Well...

That looks logically correct, but I will be the first to admit that I honestly don't know. Hopefully somebody who has real knowledge can answer...

Paging Mr. Pass, Mr. Pass,
Mr. Nelson Pass,
Please pick up the White courtesy phone,
Mr. Pass.
Thank you.

1. off course it is
2.off course
3. yup
4.due to mosfets internal capacitances nature , I wouldn't go bellow 18V rail and 130-150mA per mosfet pair , pair taken vertically

1. Yes
2. Yes
3. Yes
4. How much power did you want?

thanks all for the bold and to the point explanations...
and since mr.pass also confirmed, so i think i am good to go with this balanced setting now.

How much power did you want?
well, since this is a burning amp, i will definitely expecting high watts in class A with single ended outputs, let say 100W RMS if it is not superfluity.
i have 24Vac transformers, 35Vdc caps banks, and 0.47ohm source resistors, in hand.
how much bias i must set, to achieves 100watts into 8ohm speakers.

thanks.

 

[2 picoDumbs]

If Single ended it surely will be a burning amp

You will need 5A bias on each half of the balanced output stage. (That will be 10A drawn from the power supply for each channel (20A for stereo)).

You will need very large transformers. What VA rating are your current transformers?

 

[6L6]

There is no klunk...

 

[2 picoDumbs]

That's a nice benefit.

 

[2 picoDumbs]

well, since this is a burning amp, i will definitely expecting high watts in class A with single ended outputs, let say 100W RMS if it is not superfluity.

EDIT: I had a look at your post #505. Everything is clear.

Just to be absolutely clear.
Are you saying Balanced Single Ended output?
Or are you saying Non-Balanced Output?

 

[wengtech]

If Single ended it surely will be a burning amp

You will need 5A bias on each half of the balanced output stage. (That will be 10A drawn from the power supply for each channel (20A for stereo)).

You will need very large transformers. What VA rating are your current transformers?

5A bias on each half...
so if i use 6 devices on each half, that's mean about 0.8A per device.
with 0.47R it must be about 0.4V through this source resistors, is it correct?

transformers are 600VA.

EDIT: I had a look at your post #505. Everything is clear.

Just to be absolutely clear.
Are you saying Balanced Single Ended output?
Or are you saying Non-Balanced Output?

i mean balanced output stages / follower.
(instead of connectors)

 

[2 picoDumbs]

5A bias on each half...
so if i use 6 devices on each half, that's mean about 0.8A per device.
with 0.47R it must be about 0.4V through this source resistors, is it correct?

Assuming you mean 6 pairs, like in schematic in post #505.

Yeah that is close enough if we are talking approximations.

 

[2 picoDumbs]

2 x 600VA Transformers with 24VAC secondaries is borderline acceptable.

800VA would be better.
But if you already have them you may as well give it a try. You may or may not get some mechanical transformer buzzing. If the transformers are noisy then you may need to reduce the bias or buy bigger transformers.

If you do decide buying new transformers is necessary, then 18V to 20V AC secondaries is more than adequate to give you 100W in a balanced circuit.

 

[2 picoDumbs]

We will need to modify the biasing circuit for the negative rail or consider using different source resistor for CCS (around 0.75Ohms)

Or leave biasing circuit unmodified and run 8 or 9 pairs instead of 6 pairs

 

[2 picoDumbs]

We might be good to go with addition of R131 in your schematic