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Pass Aleph P 1.7 preamp builders thread
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Old 31st January 2019, 09:12 AM   #591
Zen Mod is offline Zen Mod  Serbia
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Pass Aleph P 1.7 preamp builders thread
nulling of 2nd is normal thing with balanced stages

you need to deliberately spoil symmetry , to invoke 2nd
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Old 31st January 2019, 09:42 AM   #592
generg is offline generg  Germany
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My experience is that the Aleph P 1.7 sounds despite its k3 dominance with a good body.

Hearing it you could suppose that it is k2 dominant.

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Old 2nd February 2019, 08:30 AM   #593
albertNL is offline albertNL  Australia
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It looks like the distortion/oscillation issue is finally fixed. Just to reiterate, I run the amp with the 10k input resistors bypassed and made 3 modifications:
  • gate stopper resistors (gain irf610's only; 4x) changed from 221R to 620R. Did not fix the problem but I left them in as I could not be bothered to remove the board from the case again. I may suffer some high frequency roll off as a result, but at my age I will probably not hear it.
  • added 221R in series with the input (IN+ and IN-, L + R; 4x). Fixed the problem.
  • 10uF film cap across psu zener stack (dual mono; 2x).
If anyone runs into oscillation problems, try the following:

If you have the input protection zeners installed, try switching the 10k input resistors in series with the input. If this cures the oscillation try 221R input resistors like I did. If it does not help or you did not have input protection zeners, you have a completely different problem than I had.

My amp is playing beautiful music in my workshop where it will stay for a while to make sure it keeps working normally before it moves to my study.

I have added 2 ARTA screenshots. They show some mains noise but with unpotted transformers in the amp case that is to be expected.

Overall, I am happy with my new AP1.7!

Thanks to everyone for your help!

Albert

PS If you are doing precision measurements, switch off your power wheelchair. I was surprised how much noise my wheelchair electronics generate until I realised that it is unshielded, close to the bench (duh!) and the motors require huge amperage to move from standstill (the controller outputs 120A per motor!).
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File Type: png Arta Right channel Vol 41.png (49.0 KB, 122 views)
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Old 2nd February 2019, 08:57 AM   #594
generg is offline generg  Germany
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Congratulations Albert!

Bah, a wheel chair is really a powerful device!

Maybe you find some XA25 pucks in it!

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Old 2nd February 2019, 12:35 PM   #595
Bfpca is offline Bfpca  Canada
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Quote:
Originally Posted by albertNL View Post
It looks like the distortion/oscillation issue is finally fixed. Just to reiterate, I run the amp with the 10k input resistors bypassed and made 3 modifications:
  • gate stopper resistors (gain irf610's only; 4x) changed from 221R to 620R. Did not fix the problem but I left them in as I could not be bothered to remove the board from the case again. I may suffer some high frequency roll off as a result, but at my age I will probably not hear it.
  • added 221R in series with the input (IN+ and IN-, L + R; 4x). Fixed the problem.
  • 10uF film cap across psu zener stack (dual mono; 2x).
If anyone runs into oscillation problems, try the following:

If you have the input protection zeners installed, try switching the 10k input resistors in series with the input. If this cures the oscillation try 221R input resistors like I did. If it does not help or you did not have input protection zeners, you have a completely different problem than I had.

My amp is playing beautiful music in my workshop where it will stay for a while to make sure it keeps working normally before it moves to my study.

I have added 2 ARTA screenshots. They show some mains noise but with unpotted transformers in the amp case that is to be expected.

Overall, I am happy with my new AP1.7!

Thanks to everyone for your help!

Albert

PS If you are doing precision measurements, switch off your power wheelchair. I was surprised how much noise my wheelchair electronics generate until I realised that it is unshielded, close to the bench (duh!) and the motors require huge amperage to move from standstill (the controller outputs 120A per motor!).
Thank You Albert for doing such a great job of documenting and explaining this problem. You have shown great patience and determination throughout the process. I wish you happy listening with your 1.7. I may have to revisit my Aleph J now, as I desperately need a balanced preamp.

P.S.- Power transformer potting will likely reduce mechanical noise from the transformer but I don’t believe it will reduce electrical noise being transformed from the primary to the secondary side. A good line filter is something I like to include in my preamp designs.

Regards
Brian
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Old 4th February 2019, 07:40 AM   #596
albertNL is offline albertNL  Australia
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Quote:
Originally Posted by Bfpca View Post
P.S.- Power transformer potting will likely reduce mechanical noise from the transformer but I donít believe it will reduce electrical noise being transformed from the primary to the secondary side. A good line filter is something I like to include in my preamp designs.
Thanks Brian. With regard to the transformers I think I did not explain myself correctly. I meant to say that I have 2 "naked" 30VA R-Cores plus a 30VA toroid in the same case as the amp board. The transformers could be the reason I am picking up mains noise. The transformers have no shielding, so not the fancy ones like Toroidal transformers SUPREME AUDIO GRADE V2 - Shop Toroidy.pl
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Old 4th February 2019, 11:55 AM   #597
Mark Allen is offline Mark Allen  United States
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My transformer is unshielded yet I have no noise. I believe the original Pass transformers were also unshielded. My SN measured out at over 90 db.

Mark
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Old 4th February 2019, 12:12 PM   #598
albertNL is offline albertNL  Australia
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Hi Mark,

I don't hear any noise but the Arta FFT graphs above show there is some measurable mains noise. About 110dB below the primary signal, so it is fine. :-)
I assume it can be lowered by moving the transformers and rectifier diodes to a separate box, but at this level I will not bother.
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