Aleph-X builder's thread.

[nevera]

Hi I'm making me a alepx, but the surprise has been that we have tried entering the RCA and only gives 30 watts of power,
We know you have to go balanced but may provide 100 watts to Balak (is a stage should go qeu balanced)
I would appreciate please indicate if it is normal
thanks

[Zen Mod]

did you ground neg. input , while giving unbalanced input ?

if everything is OK , that's just matter of needed greater input swing

[vmcfer]

Originally Posted by Zen Mod

did you ground neg. input , while giving unbalanced input ?

if everything is OK , that's just matter of needed greater input swing

Hi members,
I am looking for PCB's for the Aleph-X amplifier.
I need 3 amplifiers so I would like to buy the PCB necessary.
Thanks ,Victor

[Eric]

After living with my Aleph-X amps for some time now, I've become interested in upgrading my input caps.

Currently, I'm using Dayton Metalized Polypropylene 4.7uF caps (from PartsExpress) and R18/R19 are each 10kohms. If I measure across the XLR- and XLR+ input pins with my meter, I get an input impedance of about 38.7kohms.

Using the formula f=1/2*Pi*R*C, it looks like a 0.47uF cap will give me an 8Hz high pass filter, which should be fine.

So, after hours of reading, I've narrowed things down to 3 possibilities for the type of cap I should use: Intertechnik Audyn Cap True Copper MKP for about $25 each, Mundorf Silver/Gold/Oil for about $60 each, and Clarity Cap MR MKP for about $38 each.

Am I unncessarily splitting hairs here, or will these three caps largely be indistinguishable from one another as compared to the Daytons that I am currently using?

Also, the Mundorf caps seem to have an upper temperature of 55c. This seems to be a bit too close for comfort to use inside my Aleph-X chassis.

Should I just go for the Audyn Cap as a lower cost option?

[Zen Mod]

8Hz isn't good enough

think about phase twist

twist 'n' shout ...

2Hz ......

btw. - 10nF ( and upwards ) of polycarbonat cap - as bypass - is making wonders

[Eric]

I'm sorry, you've lost me here... What is 'phase twist' and why is 2Hz necessarily better than 8Hz for HP?

[Eric]

OK, ignore my previous post. It looks like if I use a 1.8uF cap, this will provide me with a 2.2Hz high pass filter (I was trying to save some money). I've read through Tony's capacitor test and found the same reference to using a 0.01uF Vishay MKP1837 polypropylene as a bypass. These are cheap enough - I'll grab a dozen or so...

[Eric]

While poking around trying to learn more about input caps for amp, I found this interesting link that provides some background on corner frequencies and phase shifts associated with input caps.

[Garbz]

Hi All, I'm finally at the end of the line. I built some Aleph-X amps a while ago and have been battling getting them going for months. The main problem was stability and for a while an inability to bias the amp. Finally put bias problems down to a dead C5 cap. Anyway I'm now 90% there and I'm out of ideas battling my instability issues.

Basically my amp most closely resembles Eric's running about 8A a side with +/-20V rails. The basics of the amp work, as in nothing is bursting into flame and a small input signal is amplified, power supplies are stable, it's drawing the correct current, and I have 11mA going down the input pair.

The problem I am having is oscillations and absolute DC offset, and the two are related. Here's what I've seen so far:

- I power up my amp with V2 set to zero and the amp oscillates at a messy 180kHz + 230kHz. Changing V2 does nothing to the stability. Absolute DC Offset starts at around -2VDC and heads south to around -11VDC.

- I added a 1n C9 and C10 and now when I turn on I get reasonably clean looking oscillation at 150kHz at each channel. However after the amp heats up and the Absolute DC Offset gets below -7.5VDC the oscillations appear again.

- I upped C9 / C10 to 3n3 and now I can get the offset down to -3VDC with lots of tweaking of V2 before the oscillations appear again. Of note is that the amp seems to start up with a higher Absolute Offset now, so from cold start it still seems to take 1+ minute to stabilise.


And now I'm here with the perplexing question. Am I destined to just battle the oscillation by upping C9/10 until the amp has an unhealthily anorexic bandwidth? Or can someone hint at what I'm doing wrong? Schematic and scope capture of bandwidth attached.

[Zen Mod]

pictures ?

11mA through each input mosfet , I suppose ?