The Aleph-X

[BrianGT]

Originally posted by jh6you
Thanks for the ohm's law.

I am a very simple minded engineer, and therefore, P = VI is not ohm's law...?!?!
The designer put the 0.22R to get the maximum DC current of 3A (bias current). No? How do you explain then? For what MPSA18 working???

Probably, there must be something I do not know.

JH

You are quite right... V^2/R is a combination of P=I*V (power law) and V=I*R (ohm's law). I meant to write ohm's law in there. I made a mistake in the calculation. It should be v/r=i, which gives 2.27*2 = ~4.55A, with the current being the same on both sides. Sorry for the confusion.

Where are you getting this figure of 3A of current? Look at the first page of the thread:

Grey wrote:
The circuit, as drawn, will pull a bit over 4.5 amps

--
Brian

[eLarson]

If the "v^2" is intended to mean "v-squared", then
v^2/R would be the power dissipated by "R" when there are "v" volts across it.

<Gettin' all pedantic... now>
Ohms law is V=I*R.
Power equals Voltage (V) * current (I).

Restating in terms of current, Ohm's Law is
I = V/R

Therefore P = V * V/R (or V^2/R as was written above.)
</pedantic>

Erik
(Is this my first post to the Aleph-X thread? I can't really remember anymore...)

Edit (Of course I was a hair slow typing it all in. )

[jh6you]

Brian

We need to understand for what MPSA18 is playing.
MPSA18 is playing to maintain about 0.66V across the 0.22R.
That gives us about 3A (I = V/R) bias.

JH

[mrfeedback]

I am keen now to build a low power version for my nearfield monitors at my workstation.
I figure modern pc power supplies will supply 5v at 20 and more ameres, are self contained, regulated and cheap, real cheap.
Also that lower power devices are cheaper, and smaller, and less heatsinking required.
So can the ouput stage be powered from 5v and the ccs from 12v, or can the whole stage be powered from 5v successfully,
and what sort of output powercan be expected into 4 or 8 ohm ?.

Eric.

[jh6you]

The circuit, as drawn, will pull a bit over 4.5 amps.

Brian

Yes, I see it on the first page.

You know? 4.5A = 3A + 1.5A.
The 3A is DC bias current and 1.5A (50% of 3A) is maximum peak AC current gained by the active current source. He meant the 4.5A of the static+dynamic current. Unless Fred Dieckmann comes in and gives me a hammer punch with his “NO! NO! NO! a-shole…”, I am right.

JH

[Fred Dieckmann]

There are two halves the balanced circuit so each half is pulling about 2,25 amps or about 0.56volts across the 0.25 ohm source resistor. Some addtional base current to transistor is supplied by a 100K pot and 47k resitor to the transistor's base from the postive supply to allow adjustment of the bias current through the output mosfets. Check the Zen variations articles out for better description of the circuit function.

http://www.passdiy.com/pdf/zen-v4.pdf
http://www.passdiy.com/pdf/zen-ver2.pdf

No name calling required,
Fred

[jh6you]

No name calling required,

Sorry for my overaction.

JH

[AudioFreak]

JH,

It's been said before, the Aleph current source produces double the bias current on peaks when set to 50%.

2.25amps idle current per side.

[jh6you]

I agree on 2.25amps idle current only if the 0.56volts are across the 0.25R.

I said 3amps, considering the 0.66volts and the 0.22R. Then, I made two mistakes: (1) with the 0.66volts as in Zen and (2) with the 0.22R as shown on the original circuit.

Thanks.

JH

[jh6you]

By the way,

Fairchild data sheet says that MPSA18 has Vbe(on) of 0.7V. How could we get the 0.56V across the source resistor? Due to +/- 20% tolerance? I am really confused. Your explanation would much appreciate.

JH