low power standby current mode for Aleph 5

[Adrie]

If you decrease R19 (221k) to a lower value the biascurrent will drop.
I want to use this to create a low(er) power standby mode for Alpeh 5.

I have simulated that for R19 at 7k it still works with 8 ohm load and the bias current per FET will drop to 110mA.
With 10k the idle current per FET is 250mA

Has anyone used this principle ?
My plan is to use a pot meter and a minimum value resistor for standby and low volume background music. For "quality" listening just increase the bias current again.

Any recommendation for a minimum value to guarantee a stable output signal. From simulations I can see that if you choose a value too low the output will become discontinuous and there will be a DC problem

Thanks

Adrie

[Nelson Pass]

It works fine. Just watch out for DC offset at the output.

[uniper]

I used this on my Aleph 5. I use a switch to select full or low power. I can´t remember what resistor value I put in there, but the current is about 300mA per mosfet.
I use the low power mode a lot. The amp sounds best in full power, but the difference is smaller than I would have guessed.

Switching current-mode is quite silent, no big bumps or such. The DC offset increases a little in low power mode, but is still well under 20mV.

[Jarno]

Hello Adrie,

Keep us posted on your "non-critical listening/ environmentally friendly/ negative electricity bill coefficient" mode switch!
Just added this to my requirement specification of my aleph 5 in the works (will post pictures later).

Shouldn't this switch between two sets of resistors to cope with the problem of DC offset ( R14 for DC adjust, R19 bias adjust (aleph2 schematic))? And then of course one switch per channel.


Thanks,

Jarno.

[wuffwaff]

you could make it a bit more complicated and change together with the bias also the ac-current-gain. Say from 2.5A 50% to 1A 65%. This won´t reduce power too much and will cut consumption and heat by a factor 6.25.

You just switch between alternative R19 and R21 values.

William

[Jarno]

And this won't have an influence on the amount of DC on the output?

[wuffwaff]

Jarno,

I´ve changed bias and ac-current-gain in wide ranges without having any problem with dc-offset (stays around 20-30mV).

William

[dieringe]

Originally posted by uniper
I used this on my Aleph 5. I use a switch to select full or low power. I can´t remember what resistor value I put in there, but the current is about 300mA per mosfet.

can it be done with a long wire to the case front or do I have do use a relay?
it should also be possible on an aleph-x or is that too dangerous w.r.t.
offset or switching both halves at the same time?

martin

[wuffwaff]

Hi,

I would use a relay.
I would be more carefull in an Aleph X with all the problems with DC-Ofset. Theoretically it should also be possible her although you´ll need to change at least two resistors per channel.

William

P.S. in my previous mail I made a mistake concerning the reduction in power consumption. This should be 2.5 instead of 6.25

[dieringe]

yes, I guess I would get serious bumps when switching in operation
even with a 2-contact-relay
m.