low power standby current mode for Aleph 5

[Nelson Pass]

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

[dieringe]

Wow. I will...
m.

[uniper]

Originally posted by dieringe

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]

Originally posted by 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]

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]

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.