BOSOZ L/R imbalance problem

[hifimaker]

I'm looking for suggestions of where to start looking to identify the problem.

The right channel is slightly louder than the left channel.

I've switched cables, sources, Amp channels, attenuators, etc. and the imbalance remains consistent with the same channel on my BOSOZ.

When connecting the BOSOZ to my Aleph30 in unbalanced mode, the left and right channels are even, and when connected in balanced mode the right channel is slightly louder.

Another interesting symptom... I started to play a CD with the BOSOZ errantly turned off, and the right channel was playing music albeit very very distorted and nothing from the left channel.

It seems like the left -(neg) phase side might be suspect.

Any ideas what I should check for?

BTW, I'm using KK's BOSOZ boards.

Thank you,

-David

 

[Zen Mod]

BTW, I'm using KK's BOSOZ boards.



-David

and schematic is...........?

are you sure that you have right values of resistors in all positions?

I know for at least one case with KK's boards (kits) with that issue.......

 

[jleaman]

I'm looking for suggestions of where to start looking to identify the problem.

The right channel is slightly louder than the left channel.

I've switched cables, sources, Amp channels, attenuators, etc. and the imbalance remains consistent with the same channel on my BOSOZ.

When connecting the BOSOZ to my Aleph30 in unbalanced mode, the left and right channels are even, and when connected in balanced mode the right channel is slightly louder.

Another interesting symptom... I started to play a CD with the BOSOZ errantly turned off, and the right channel was playing music albeit very very distorted and nothing from the left channel.

It seems like the left -(neg) phase side might be suspect.

Any ideas what I should check for?

BTW, I'm using KK's BOSOZ boards.

Thank you,

-David

I had this same problem when powering up my Bos Pre. It sounds like a voltage problem.. Maybe more power on the rails on the other channel ?

 

[hifimaker]

Re: Re: BOSOZ L/R imbalance problem

I had this same problem when powering up my Bos Pre. It sounds like a voltage problem.. Maybe more power on the rails on the other channel ?

Thanks Jason for the tip.

I removed one of the two PSU,'s so only one PSU is driving the BOSOZ. The negative rail is -59.67 and the positive rail is 59.77

Here's a link to the schematic: http://www.kk-pcb.com/bls.html

-David

 

[jleaman]

Re: Re: Re: BOSOZ L/R imbalance problem

Thanks Jason for the tip.

I removed one of the two PSU,'s so only one PSU is driving the BOSOZ. The negative rail is -59.67 and the positive rail is 59.77

Here's a link to the schematic: http://www.kk-pcb.com/bls.html

-David

Do both Psu's show same rail voltage ?

 

[hifimaker]

I would think the PSU's are not the problem, since I'm only using one PSU now and the rail voltages are the same for both right and left sides.

-David

 

[Zen Mod]

I would think the PSU's are not the problem, since I'm only using one PSU now and the rail voltages are the same for both right and left sides.

-David

do you have same voltages at 10UF-750 ohms junctions on both sides (unequal currents through halves) ?

did you matched IRFs ?
at least in channels?

 

[hifimaker]

do you have same voltages at 10UF-750 ohms junctions on both sides (unequal currents through halves) ?

did you matched IRFs ?
at least in channels?

The IRF's are not matched.

Thanks Choky, you might be onto to something.

Voltages at each 10uf-750 ohms junctions:
Left side (neg): 31.165vdc
Left side (pos): 31.127vdc
Right side (neg):31.110
Right side (pos):30.789

-David

 

[poobah]

The Fet with the low voltage has short between drain and gate... replace it.

Edit:

or there is some junk on the circuit board...

 

[hifimaker]

The Fet with the low voltage has short between drain and gate... replace it.

Edit:

or there is some junk on the circuit board...

Thanks Poobah, I'll replace the FET. The board is clean, I'm a very good at soldiering and I cleaned the board with a flux cleaner.

I'll change the Fet and reply back.

-David

 

[poobah]

Don't destroy the FET if you can manage it... just off the cuff guess.

The giveaway is that it works (well sorta) with power off...

 

[jleaman]

Don't destroy the FET if you can manage it... just off the cuff guess.

The giveaway is that it works (well sorta) with power off...

Really ? You don't think it could be because there is still power left in the psu ?

 

[jh6you]

Any ideas what I should check for?

Another suspect could be the 100K resistors connected from the input and output points to the ground. I would check whether all four (per chanhhel) are of the same value.

Regards

 

[CheffDeGaar]

Hi,

- Try to make the 124R resistance variable. So you can adjust the gain and match both channels (Min R value=max gain)
- Check the transconductance of your mosfets : Measure the Vgs of each mosfet @ two different currents using current sources (10 & 20 mA for example) Transconductance is given by Delta(I)/Delta(Vgs).The gain of the BLS depends on the 124R, the Drain resistors and the transconductance...

HTH

 

[hifimaker]

The values of all the resisters were checked and they are correct. I also changed the Fets, and the imbalance still remains.

I just got a topend B&K DMM that has a capacitance function. All the 10uf caps measure to about 10.5uf.... except one on the left channel -(neg) phase, I get no reading at all.

I'm going to order a new 10uf cap, and I bet I'll be in good shape.

-David

 

[Alessandro]

Select the 750 Ohm resistors (they estabilish the point of work).
Another way is to control the cap on the output, are you sure that they work well ?