Aleph J illustrated build guide

[Zen Mod]

1A7

 

[2 picoDumbs]

Stock Aleph J is biased to 2A per channel (4A total)

Are you saying you have biased each output mosfet to 0.85A?

 

[mhgawel]

I just quoted what 6L6 wrote in post #3:

"400mV bias = .85A = 18W/device"

 

[2 picoDumbs]

I was certain the stock Aleph J was biased at 2A.
6L6 may have suggested reducing the bias because of heatsink limitations.
I haven't read this thread so I can't say for sure why he suggested that bias point.
I could be mistaken though, my memory is from when I first built it back when Peter Daniel did PCBs many years ago.

 

[mhgawel]

He also wrote:

"As this amp is built in a 5U chassis, I will crank the bias to the hottest I want to take it (where the Mosfets are just under 160F / 70C) This is slightly above the 65C recommended for good longevity. The heatsinks are about 130F/55C. I suspect that if I were to use the Keratherm red silpads or thin mica&grease I would have slightly cooler devices and warmer sinks. 500mV bias = 1.06A = 22.55W/device. This is hot. You could not do this if you build your amp in the 4U chassis without a fan somewhere. "

So it's the matter of temperature and heatsinks size.

I think that I can put 2A to simulations and I'll be on the safe side

Regards,
Maciek

 

[Zen Mod]

in that case , having 2 x 0A75 per channel , means you're having 4 x 0A75 for 2 channels

CCS for sim needs to be 3A


regarding Iq ...... it's pretty arbitrary , depends of heatsink capacity mostly

you can count on figures 6L6 gave in his thread as pretty good ones

and , I really never read that Pa said that Aleph J is biased to 2A per channel

I'm pretty sure that value of 2A goes from our estimation, taken from claimed dissipation (juice from wall) numbers .......... and Pa is sometimes slightly misleading with those

 

[2 picoDumbs]

Or possibly 4A depending on his bias point and assuming regular stereo powersupply.

 

[Zen Mod]

so , take CCS with value of 4A , then count that everything will be as simmed , or even better

 

[mhgawel]

Thanks Zen Mod and 2 picoDumbs

 

[platon.rado]

hello guys
I am also the owner of this super amplifier,I have the problem, because of when I switch off amplifier, I hear bangs from the speakers. I measured 2V in the part of output

Dc offset I have 4mV and BIAS 400mV.Thank you for your answer.

 

[Zen Mod]

point to exact schematic you are using and describe if you changed any value

for power on and off behavior , few RC constants at pcb are important , especially one in LTP CCS

 

[platon.rado]

R8-1k
R27-5k trimer

 

[Zen Mod]

decrease c4 to 1u

situation will also improve somewhat later , when you shorten all those wires between PSU And channels

 

[platon.rado]

thanks.. zen mod

 

[WalterW]

decrease c4 to 1u

situation will also improve somewhat later , when you shorten all those wires between PSU And channels

Oh, didn't know that. I will try to lower C4 also. Got a big turnoff bang....

 

[platon.rado]

Which pre-amplifier could be to Aleph J..by Nelson Pass

 

[Zen Mod]

B1 or B1T

 

[platon.rado]

And PASS LABS CLONE - XCCS-BOSOZ premplifier PCB ????

 

[xrk971]

Just starting...

 

[cumbb]

Less solder;-!
Solder, plumbum, sounds horrible. Stannic too.
Undefinied signal paths sound horrible.
...-)