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]

Low power

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]

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.

 

[Nelson Pass]

It may be that the bump isn't all that huge. Try it.

 

[dieringe]

Wow. I will...
m.

 

[uniper]

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

I used a long wire and a switch at the back of the amp. But I don´t change the resistor, the standard R19 is still on the pcb, I just switch in a smaller value in parallell with R19.

 

[dieringe]

Wow. I will...
m.

Well now I tried - I put 47k resistors in parallel to the existing 47k+100k pot. It works great - BUT: absolute DC offset goes to -14.5V and I can't adjust this. This is about maximum negative voltage, I run it on a 2x12V transformer and 3.2 A normally. After a few seconds it begins to emit white noise.
I have absolute offset problems anyway. When cold, I have to readjust because the current regulation doesn't make it (gives 2.5A instead of 3.2 and the amp begins to hum after a few seconds). Anybody knows what's wrong and can help?

martin

 

[Adrie]

low power standby mode for Alpeh 5

I tried the simulated low power mode by changing R19 (221k) down to even 10 k but no decrease in bias current

Simulations show that under 20k a significant lowe bias current

Anyone with the same experience ?

Another option I consider is to use a 2R resistor (R40-42) for the current source and a switch for a high power mode

Just one the current source resistor with the feedback to Q5

Anyone tried this ?


So far I like Aleph 5 a lot but sound is not any better than the 2 FET model (of Aleph 5) I built with my own PCB design

Thanks

Adrie

 

[Nelson Pass]

I have lowered the bias current in standby by increasing the
positive current flow into the NPN base junction on Alephs
and have not experienced anywhere near this much offset,
so I suspect you have other issues. If the (-) input is
capacitively coupled as with the stock unit, this offset will
be minimized, but only by about 6 dB.

 

[Adrie]

Low power mode for Aleph 5 works great - "green Aleph ???" or "Aleph Kyoto proof ???&

I've reduced R19 (221k) in the Alpeh 5 design to get the bias current down for low power operation.

The idea is to use this for normal usage like radio
So in this mode the heatsink will stay cool and no unnecessary power consumption.

I changed R19 down even to 20k without any DC offeset problems
The bias current per FET is then about 160 mA

Power consumption is now about 70 watt in low power mode with dual 30V power supply

The difference in quality seems to be fairly small, based upon about 6 CD tracks of listening

I will use a switch to swicth between the 2 modes of operation

Haven't made a decision yet which value I use for low power operation. I will probably go for 250 mA per FET.