No ZM. It is the protective zeners that are the problem, just like Nelson warned about in the Bosoz paper. You need a small resistor in line with the input, as Nelson suggested.
then just remove them
to be safe (again) , include one per mosfet , ditto G-S , with cathode on G
to be safe (again) , include one per mosfet , ditto G-S , with cathode on G
This was the most elaborated and well published search for the possible Aleph p 1.7 oscillation i saw.
Impressive Albert and thanks for sharing!
Impressive Albert and thanks for sharing!
I`ve got oscillations distortion or what else too.
Solved with 221 before the protection zener
Had no possibility to look with a scope at this problem.
But the audible distortion was gone.
Aleph P 1.7 distortion/clipping?
much fun with your Aleph P
Solved with 221 before the protection zener
Had no possibility to look with a scope at this problem.
But the audible distortion was gone.
Aleph P 1.7 distortion/clipping?
much fun with your Aleph P
If only I had found your post earlier haha. Glad to see it confirmed. It was interesting to hunt down the problem. I have learnt a lot the last few weeks!
Last edited:
I have a set of AP1.7 boards from Veteran that I built over 10 years ago and thought I had made a mistake somewhere or had ground loops or burned/bad mosfets ... could never get rid of the hum/hiss and then gave up. I should also add that I've never tried it with any attenuator on the input, only on the output.
Thank you AlbertNL for the work you did and for sharing this because I never found DangerMouse's post in all these years and I never would have been able to investigate as you did. I will try adding 221R to the input of my boards and let you know if it cures the noise for me as it did for you! Thank you Danger Mouse and Generg as well!
And of course, thank you Nelson Pass!
Thank you AlbertNL for the work you did and for sharing this because I never found DangerMouse's post in all these years and I never would have been able to investigate as you did. I will try adding 221R to the input of my boards and let you know if it cures the noise for me as it did for you! Thank you Danger Mouse and Generg as well!
And of course, thank you Nelson Pass!
I used REW to have a look at the output of the amp (with the 221R resistors in series with the input). I think I have tamed the oscillation.
Interesting to note that I measure dominant in-phase 3rd harmonic. I am new to REW and similar software, so not sure if my measurement setup was correct. More testing in the coming days I think.
Interesting to note that I measure dominant in-phase 3rd harmonic. I am new to REW and similar software, so not sure if my measurement setup was correct. More testing in the coming days I think.
Attachments
nulling of 2nd is normal thing with balanced stages
you need to deliberately spoil symmetry , to invoke 2nd
you need to deliberately spoil symmetry , to invoke 2nd
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.
😀
Hearing it you could suppose that it is k2 dominant.
😀
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:
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!).
- 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 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!).
Attachments
Congratulations Albert!
Bah, a wheel chair is really a powerful device!
Maybe you find some XA25 pucks in it!
😀😀
Bah, a wheel chair is really a powerful device!
Maybe you find some XA25 pucks in it!
😀😀
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
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
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
Mark
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.
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.
If the 1.7 gets SE in will it be balanced out like the Bosoz? I will feed it from the B I with the Korg Nutube.