Thanks Fab, hope I'll have time to do that tomorrow.
Cheers
So, after having checked the Diodes, checked for shorts, resoldered a few joints, everything worked as it should. So both channels functionable now. [emoji4]
Cheers
So, after having checked the Diodes, checked for shorts, resoldered a few joints, everything worked as it should. So both channels functionable now. [emoji4]
I always really take care of building the right way without failure, because searching bugs is not my cup of tea. I really dislike it. So I am happy, that it worked out so quick!
Thanks a lot.
Now my Italian rear chassis plate is waiting for mechanical treatment and I am keen to hear the amp!
A nice Sunday to all of you.
Cheers
Thanks a lot.
Now my Italian rear chassis plate is waiting for mechanical treatment and I am keen to hear the amp!
A nice Sunday to all of you.
Cheers
I think nobody really likes to troubleshoot a defective board.....That is the reason the USSA manuals are divided in multiple testing stages so the partial builds are validated until the next stage. At the end of assembly you know that it is only the preceding stage assembly that needs to be looked at.
Please report once you have finished and then some comments after breakin period.
Fab
Please report once you have finished and then some comments after breakin period.
Fab
I have finished the boards everything was ok until the 8.17.1 adjust output mosfet current close to intended final bias. I was reaching the 50mVdc with P1 and P2 then checking the output offset I turned P1 e P2 but after a while both TP2 and TP4 went to 0mV on both boards. Turning P1 and P2 they don't make any change.
I have done again all the biasing from the start .
I did the Current sources adjustment and I have the stated 28mV in TP9-TP10 and TP11-TP12.
I did the Adjust current in input stage but TP8-V- and TP7-V+ are firmly at 0V regardless of P1 and P2 position.
Any help would be appreciated.
Thank you
I have done again all the biasing from the start .
I did the Current sources adjustment and I have the stated 28mV in TP9-TP10 and TP11-TP12.
I did the Adjust current in input stage but TP8-V- and TP7-V+ are firmly at 0V regardless of P1 and P2 position.
Any help would be appreciated.
Thank you
Hello Patriz
Be careful because the BIAS settings and output offset are interactive by P1 and P2 and so by wanting to set the lowest possible offset you can significantly increase the BIAS on an output mosfet and destroy it if the heat dissipation is not not enough.
Be careful because the BIAS settings and output offset are interactive by P1 and P2 and so by wanting to set the lowest possible offset you can significantly increase the BIAS on an output mosfet and destroy it if the heat dissipation is not not enough.
actually the output mosfet weren't hot at all, C3 was really hot on some settings. Already checked for short or cold welding on the boards.
Hi Patriz
If it was working fine until step 8.17.1 then I would check for shorted parts due to possible excessive current. Can you check diodes d1 to d4 and M1/M2 or M3/M4 D-S shorts to start.
Also, voltage across R3 and R4.
If C3 was hot it is very abnormal. Check for proper cap polarity installation.
A picture of your assembled pcb can sometimes show things that one cannot see..
Fab
If it was working fine until step 8.17.1 then I would check for shorted parts due to possible excessive current. Can you check diodes d1 to d4 and M1/M2 or M3/M4 D-S shorts to start.
Also, voltage across R3 and R4.
If C3 was hot it is very abnormal. Check for proper cap polarity installation.
A picture of your assembled pcb can sometimes show things that one cannot see..
Fab
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Hi Fab,
do you use an active or passive preamp with this design or just a pot with a buffer? What would you recommend?
Cheers Ernst
do you use an active or passive preamp with this design or just a pot with a buffer? What would you recommend?
Cheers Ernst
Hi Ernst
Passive preamp using only a pot needs short interconnect cables and low pot value to prevent high frequency attenuation. Also pot value must be much lower than amplifier input impedance to prevent changing volume log effect. Not my recommendation. Pot and buffer works well.
Active preamp is my preferred choice and most of the time it increases perceived dynamic compared to passive.
Of course I recommend my USSPA preamplifier...😉😛
Fab
Passive preamp using only a pot needs short interconnect cables and low pot value to prevent high frequency attenuation. Also pot value must be much lower than amplifier input impedance to prevent changing volume log effect. Not my recommendation. Pot and buffer works well.
Active preamp is my preferred choice and most of the time it increases perceived dynamic compared to passive.
Of course I recommend my USSPA preamplifier...😉😛
Fab
Fab, I asked because I read, that for full power USSA-5 needed just about 1.8V rms. So an active pre would give some more, even if it were a low gain type, which means amplifaction for attenuation.
I'll check what fits better, SALAS DCB1 oder SALAS DCG3, or Whammy or tube, or low resistance lightspeed attenuator.
Your USSPA preamp does look good to me. Are there still some pcbs available? The canadian GB seems to have come to an end as far I could find out with my very limited French.
I would be very interested in building another very nice preamp. And I have the toshibas available 🙂
Cheers
Ernst
Ernst
I will receive shortly a small batch of USSPA pcbs since I had a few inquiries already. This will not be a group buy but only for very motivated builders. An USSA5 or 3 builder is motivated in my book....
There will be 2 possible versions of USSPA:
1) using Toshiba as output
2) using Sanken bjt as output
Both works with same pcb but some resistors changes needed.
I will reserve you a stereo pcb.
In the mean time I will prepare a preliminary build manual.
Fab
I will receive shortly a small batch of USSPA pcbs since I had a few inquiries already. This will not be a group buy but only for very motivated builders. An USSA5 or 3 builder is motivated in my book....
There will be 2 possible versions of USSPA:
1) using Toshiba as output
2) using Sanken bjt as output
Both works with same pcb but some resistors changes needed.
I will reserve you a stereo pcb.
In the mean time I will prepare a preliminary build manual.
Fab
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Mervellieux, merci! I am very happy to hear that. Have most parts available for this build.
Cheers, Ernst
Cheers, Ernst
Ernst,
In my book, I'm very positive you will love this preamplifier. I've assembled two of them and love them!!
Do
In my book, I'm very positive you will love this preamplifier. I've assembled two of them and love them!!
Do
Fab, i would be interested in the USSAPA pcb also, still enjoying my USSA5 currently with Nelson’s Korg Nutube Xmas gift pcb as a preamp; it exceeds my expectations! Together great musical enjoyment.
Hi Asanden
I am glad you like your setup.
I just read about this very special Korg Nutube device. Although the USSPA can be adjusted for increased H2 it may not be as drastic as the Korg device....
In any case I can reserve you a stereo pcb too.
Fab
I am glad you like your setup.
I just read about this very special Korg Nutube device. Although the USSPA can be adjusted for increased H2 it may not be as drastic as the Korg device....
In any case I can reserve you a stereo pcb too.
Fab
Hallo Ernst,
I am in a similar boat: I already have too much gain (CD, considering reducing it as listening at 3 O' Clock) or say the rightish gain (Phono), so using a passive pre and not looking to any further gain.
It will be indeed very intersting to read your comparo of the USSA-5 with SALAS DCB1 or SALAS DCG3, or Whammy or tube, or low resistance lightspeed attenuator - and see how they do vs Fab's probably fabulous and well suited USSPA... but then with probably a very strong attenuation (depnding on its gain?)
MFG
Claude
Hi Asanden,
Nice to read this... and also looking to your comparo of USSPA vs Korg... The Korg is attracting me, but it has sadly 16dB gain, so clearly not just a buffer - that's putting me off (more than the 3 caps in the signal path, but then Nelson knows his stuff).
At what position is your volume potentiometer?
Claude
I am in a similar boat: I already have too much gain (CD, considering reducing it as listening at 3 O' Clock) or say the rightish gain (Phono), so using a passive pre and not looking to any further gain.
It will be indeed very intersting to read your comparo of the USSA-5 with SALAS DCB1 or SALAS DCG3, or Whammy or tube, or low resistance lightspeed attenuator - and see how they do vs Fab's probably fabulous and well suited USSPA... but then with probably a very strong attenuation (depnding on its gain?)
MFG
Claude
Hi Asanden,
Nice to read this... and also looking to your comparo of USSPA vs Korg... The Korg is attracting me, but it has sadly 16dB gain, so clearly not just a buffer - that's putting me off (more than the 3 caps in the signal path, but then Nelson knows his stuff).
At what position is your volume potentiometer?
Claude