Aleph-x bias adjustment

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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
 
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bach2800 said:
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
 
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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............
 
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bach2800 said:
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
 
Hi,

setting bias on an X isn´t 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 don´t know how many fets you´ve used but you´ll 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 that´s normal.

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

William

P.S. read the WIKI for more information
 
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
 
Ok, did some change to the board, I put in bc550c, I was using bc550b.
Now I did my setup like this: No load, and both inputs short to gnd.

For the left side I'm getting .47V at minimum. And for the right side .31V at maximum. potentiometer only give me about .04V of variation.I haven't check the DC offset so far.

I've checked again all the values of the resistors and everything is fine. Could it be something that is not match close enough?

There is definitely something wrong with this board.
 
I finally found my problem, I had a bad connection between my mainboard and my driver board on the right side:smash: .That was the last time I'm using crappy connectors from local surplus.

But now I have both side that are having stable .5V across source resistor, tomorrow I'll adjust everything.

Thank you all for your help
Thierry
 
Hi, I have another quick question.

When I'm trying to adjust the amplifier if I set the bias to get .5V at the source resistor I'm getting 40mV of relative DC offset. If I'm working to get it down to 0V the reading I get on the source resistor is .512V on one side and .476V on the onther side.

My question is: Sould I aim for 0V of relative DC offset and live with the bias difference or the other way around? Or something in the middle?

Thank you
Thierry
 
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bach2800 said:
Hi, I have another quick question.

When I'm trying to adjust the amplifier if I set the bias to get .5V at the source resistor I'm getting 40mV of relative DC offset. If I'm working to get it down to 0V the reading I get on the source resistor is .512V on one side and .476V on the onther side.

My question is: Sould I aim for 0V of relative DC offset and live with the bias difference or the other way around? Or something in the middle?

Thank you
Thierry


40mV is practically nothing
 
bach2800 said:
Hi, I have another quick question.

When I'm trying to adjust the amplifier if I set the bias to get .5V at the source resistor I'm getting 40mV of relative DC offset. If I'm working to get it down to 0V the reading I get on the source resistor is .512V on one side and .476V on the onther side.

My question is: Sould I aim for 0V of relative DC offset and live with the bias difference or the other way around? Or something in the middle?

Thank you
Thierry


Hi,

you should set the bias the same for both sides (now you´ve got 10% difference) and then see what relative offset you get. If it´s under 100mV that´s allright. If not change the input diff pair for a better matched set.

Allways check the absolute dc and keep it around 0V for a warmed up amp (it will start between 5 and 10V from cold)

William
 
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