Aleph 3 needs HELP!

[Jesse]

Hello,

I just finished my Aleph 3 project (not quite actually). But the voltage check shows strange results.

R120 - 0,38V ?
R121 - 0,33V ?
R122 - 0,41V ?
R123 - 0,29V ?

R106 - 4,7V
R108 - 4,2V
Q105 - 4,2V


The supply rails are 26VDC.

The strange thing is :.the values are nearly the same for both channels (within +- 0,01V)!!!

I tried to increase the R111 & R113 to 4,75K & 200K, as described in previous threads. The values are raised by +0,15V. However, the differences are still remain the same.

Where should I check? or should I re-group these FETs according to the voltage reading across the source resistor?

Please help! Thanks!

[wuffwaff]

Jesse,

what you could try is leave the two upper fets in place (0,38 and 0,33 isn´t that bad) and change on of the other two with the other channel.
For example: 0,41 right channel with 0,29 left channel. This could make them more equal.

What kind of resistors are you using (tollerance)?

Does the amp work (like sound coming out of the speakers)?

william

[Jesse]

Hi William,

Thanks for reply!

The resistors I am using are Holco 0,5%tol, while the sourse resistors are from FUKUSHIMA 5%tol wirewound.

This amp is working good (I am building the chasis for this little monster). But I read a post from Mr. Pass that the matching of the FETs is very important, and certainly influnce the sound quality.

What I don't understand is that I DID match the FETs before I soldered them. And the strange thing is: IF I did wrong with the matching, how come these voltage readings are the same for both channels? Did I do something wrong with other components?

Second, if I would re-group those FETs, like:

0,38V x 2 go with the 0,41V x 2 for one channel
0,33V x 2 go with the 0,29V x 2 for another channel

Does it make sense?

Thanks!

Jesse

[wuffwaff]

Hello Jesse,

that would also be a possibility.

Are you shure you´ve matched them with the right current?

If not I would do it again (you only need 4 pairs)

As for sound quality, I don´t think it´s that important that they are perfectly matched. This is only important for current (and power) sharing. So if there´s 10-15% difference in current from one to another it doesn´t really matter.

william

[Jesse]

Hi William,

Thanks!

I will re-group the FETs and report what happens.

See you later!

Jesse

[Jesse]

The resulte comes:

old voltage reading:

R 120 121 122 123
---------------------------------------------------------
L-channel
V 0,365 0,32 0,395 0,29
---------------------------------------------------------
R-channel
V 0,375 0,33 0,41 0,29
---------------------------------------------------------

I switched L-channel R122 (0,395V) with R-channel R123 (0,29V).
Then the voltage reading becomes:

R 120 121 122 123
---------------------------------------------------------
L-channel
V 0,365 0,32 0,41 0,28
---------------------------------------------------------
R-channel
V 0,375 0,33 0,31 0,40
---------------------------------------------------------

It seems not from the FET matching. Maybe I should match the source resistor??

Any suggestion?