Question on P1.7 measurements

[JC Fardo]

Hi all

I finished aleph p1.7 and first measurements indicate some discrepancy, IMHO.

Components designation are as per Veteran´s schematic and PCB

Vsource = 61.0 Vdc, both channels

On both L/R channels:

Vdc at T2 -T3 drain pins = 2.6V (28.9V)
Vdc at T9-T10 drain pins = 10.0V (28.9V)

Vdc across resistors

R channel:

R17 = 0.185V (0.65V)
R18 = 0.825V (0.65V)
R35 = 0.60V (0.65V)
R36 = 0.60v (0.65V)

L channel

R17 = 0.34V (0.65V)
R18 = 0.83V (0.65V)
R35 = 0.59V (0.65V)
R36 = 0.60v (0.65V)

I´m using unbalanced input, so -In is grounded and -out is open. Volume control is 10K alps at output. Values between ( ) are default ones from a chinese article from Diyzone.

Major discrepancy is on R17s that ground T1 and T8. I´m not sure if this is result of unbalanced input connection or other problem. I just like to clear this out before play the preamp with my monoblocs.

Thanks to all

 

[noelectrix]

hi jose,
i wanted to do the check-measuements but i remembered that there was a difference in the pcb-render picture and the original (just one ore two resistors). can you make a picture what resisors you mean?
but on the other hand, don´t you think it is enough just do AC/DC-check at the output?
any pics of your aleph (just for interest)

nice day
stefan

 

[analog_sa]

I´m not sure if this is result of unbalanced input connection or other problem. I just like to clear this out before play the preamp with my monoblocs.

Thanks to all

The unbalanced connection cannot affect dc operating points. You have either miswiring or defective components. When asking for help it's much better to use the component designators from the Pass manual rather than some random numbering. It appears your dc level at output is completely wrong.

Btw using a 10k pot at output makes this behave like a passive pre with a buffer in front: quite pointless.

 

[JC Fardo]

Hi

Thanks for replies.
Due to short time I went slow these weeks troubleshooting my P1.7

I replaced all fets and bipolars and results were promissing, in one channel at least

Vsource = 61.5 and 61.9 Vdc, L/R channels with 5R for R77 measured across 15K resistor.

R channel:

Vdc at Q15-Q16 (T2 -T3) D pins = 32.4V (28.9V)
Vdc at Q18-Q19 (T9-T10) D pins = 32.3V (28.9V)

Vdc across resistors

R70 (R17) = 0.645V (0.65V)
R55 (R18) = 0.635V (0.65V)
R44 (R35) = 0.653V (0.65V)
R59 (R36) = 0.659V (0.65V)

L channel:

Vdc at Q15-Q16 (T2 -T3) D pins = 12.8V (28.9V) ?
Vdc at Q18-Q19 (T9-T10) D pins = 1.0V (28.9V) ????

Vdc across resistors

R70 (R17) = 0.218V (0.65V)??
R55 (R18) = 0.636V (0.65V)
R44 (R35) = 0.241V (0.65V)??
R59 (R36) = 0.645V (0.65V)

Components numbers are as original Pass Manual and between ( ) as Veteran schematics.

Surely "L channel" is out but I don´t know what components to check others than those listed. R55 and R59 seem right but R70 and R44 don´t. That´s really confusing me a lot

Replace everything again OK but insane

BTW both channels sinks got IMHO scary hot

ANY help is ultimately appreciated.

 

[analog_sa]

R70 (R17) = 0.218V (0.65V)??
R55 (R18) = 0.636V (0.65V)
R44 (R35) = 0.241V (0.65V)??
R59 (R36) = 0.645V (0.65V)

These voltage drops are merely the forward biased BE drops on the bipolar transistors. Check the transistors with abnormal drops.
Your results are very strange. Are you using new/tested components?

 

[peterpan188]

Did you connect the jumper right under one of the 2 big caps? Just a easy point to miss.

Peter

 

[JC Fardo]

These voltage drops are merely the forward biased BE drops on the bipolar transistors. Check the transistors with abnormal drops.
Your results are very strange. Are you using new/tested components?

Hi Analog

I´using new and HFE tested BC550C/560C. Pin out is oposite to ZTX but this was double checked. They are thight located and soldering overheat must have happened.

Could this abnormals bipolares affect the associated FETS?.

Did you connect the jumper right under one of the 2 big caps? Just a easy point to miss.

Peter

Hi Peter. How is yours? Didn´t miss the jump. I took D pin measurements to input GND, then it´s fine.

Thank you both a lot.

 

[analog_sa]

The BC550/560 are of course fine to use. The good thing is you have a working channel you can always use to swap parts.

Sorry, i have no further suggestions. It's either faulty components or miswiring.