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-   -   Aleph-x bias adjustment (http://www.diyaudio.com/forums/pass-labs/83085-aleph-x-bias-adjustment.html)

bach2800 12th July 2006 10:09 PM

Aleph-x bias adjustment
 
Hi all, after a laborious seach in thread about aleph-x I haven't been able to locate a clear procesure on how to adjust the Bias for aleph-x amp.

Currently I have one channel making music.
I'm using Kari's board using kk's schematics. If anyone can point me to a post regarding bias adjustment it would be really nice.

Thank you
Thierry

Zen Mod 12th July 2006 10:13 PM

Re: Aleph-x bias adjustment
 
Quote:

Originally posted by bach2800
Hi all, after a laborious seach in thread about aleph-x I haven't been able to locate a clear procesure on how to adjust the Bias for aleph-x amp.

Currently I have one channel making music.
I'm using Kari's board using kk's schematics. If anyone can point me to a post regarding bias adjustment it would be really nice.

Thank you
Thierry


post here KK's schematic
you can't often expect that others must do physical part of work to help you

bach2800 12th July 2006 10:19 PM

Sorry about that

http://www.kk-pcb.com/alephx.html

Zen Mod 12th July 2006 10:31 PM

with 200E trimer you can adjust offset between outs and ground,and in smaller degree -bias ;as I recall ,that's called-relative offset (but who knows-I maybe just mixed relative and absolute ;) )

with left and right 50K trimmers you can set left and right biases,and-in same time ,absolute offset (offset between outputs)

procedure is iterative-every twitch on every pot have influence in same time on offsets and Iq
just be patient and you'll be rewarded.


advice- do triple check and compare all values with proved schematics in X thread............

bach2800 12th July 2006 10:40 PM

And where do I take my measurement from?And what should it be?
Do I need to apply a signal? and load at the output?

Thierry

Zen Mod 12th July 2006 10:57 PM

Quote:

Originally posted by bach2800
And where do I take my measurement from?And what should it be?
Do I need to apply a signal? and load at the output?

Thierry


for relative offset-you need two VOM -from each output to ground (black to gnd,red to output hehe)

for absolute offset-you need just one VOM- connected between two outputs.

you don't need signal for that ,in fact -it's best to ground inputs during that settings.also-you don't need load for that

Iq -you can measure Iq with two VOMs -put probes of first VOM across one left 0E39 resistor,and probes of second VOM across one right 0E39 resistor.....

according voltage difference across mentioned resistors will tell ya how much of current you have in each half of amp


whoa-for complete picture ,you need at least 5 VOMs,or fast hands and eyes ;)


don't hurry-read more through forum ,and let things settle in head,before actuall work

wuffwaff 13th July 2006 09:55 AM

Hi,

setting bias on an X isnŽt that difficult.

Start on one half and set the desired bias with the trimpot connected to the active current source. You can measure the bias by measuring the voltage over the source resistors and calculating the current with I = V / R

I donŽt know how many fets youŽve used but youŽll have to measure each source resistor and ad the values (Note: only measure the current source fets)

So first you set one side than the other the same way. Now you can set the absolute dc with the centre pot (connected to the diff pair current source) for 0V (outputs to ground) after an hour of warmup. It will vary a bit (plusminus one volt or so) but thatŽs normal.

Now you can recheck both halves if the bias is still OK and adjust if neccessary, after that youŽll have to adjust the absolute offset again.

William

P.S. read the WIKI for more information

jh6you 13th July 2006 12:28 PM

Quote:

Originally posted by Zen Mod

(but who knows-I maybe just mixed relative and absolute ;) )


You are right soon after removing "maybe" and changing ;) to :).

Absolute offset between the output node and the ground.
Relative offset between the two output nodes.

Otherwise, I will return the "mebe" back to you.

bach2800 14th July 2006 01:54 AM

Hi again, I have took some measurment on my board. I'm getting confuse, doesn't seem to be good at all.
I'm using 12 irfp044 per channel.
I have 0.520V across source resistors on both side for the CCS mosfets and 0.490V for the gain mosfets.The thing is the gain mosfets are getting really hot compare to the ccs mosfets.
Is that normal?

Thierry

wuffwaff 14th July 2006 05:35 AM

Hi,

what is your absolute offset (output to ground)?

If this is positive (wich I think it is) the gain fets will dissipate a lot more power and get hotter.

YouŽll have to set the central pot for minimum absolute offset.

William


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