Another Aleph X up and running

[wuffwaff]

Hi,

I did some tests too and posted them in my original thread:

http://www.diyaudio.com/forums/showt...47#post1190647

William

[sinuko]

Dear William,
in my tests I obtain the best results witn 3.3nf between B-C of q3 and q8.

Now I can see a residual of "the strange distortion" just before the clipping.

Paolo

[wuffwaff]

Hi,

with 3n3 it´s gone but then the other problem is present (heavy distortion into lower impedances at high frequencies).

William

[sinuko]

Hi,
Which is a "lower impedances" for you? 6R 4R or lower?

in any case I'll try next week.
Thanks Paolo

[wuffwaff]

Hi,

4R and lower. I only test at 8, 4, 2,8 and 2R because that´s the way my power resitor bank is build.

William

[RoboMan]

It seems there is no discussion on the situation in posting 39. I think this is a parasitic oscillation (not ringing).

I saw this in my Aleph5 and this can be cured by adding a 1000pF (1nF) cap across the gate resistors of the gain MOSFET and the output, i.e. -out and C of Q4 ; +out and C of Q9 (Grey's version dated 5/24/02).

The waveform is reproduced here:

[CheffDeGaar]

Hi Xavier

Just curious about your generator...
Do you use a CD player with a recorded square wave on a CD ? Your waveform looks like truncated Fourier series attempting to reproduce a square signal, or if you prefer, the Gibbs phenomenon.
If its ringing, it is damped as it begans to decrease until half the high or low levels of your squre wave. But then, why does it begin to re-rise agian after ? The ringing must follow a level change, not precede it Or get a patent on time reversal
If it's oscillations, why are they damped in the middle of the high and low levels ? And why is it so symmetrical ? The duration of a level is an exact multiple of the oscillation frequency. Seem to be too much luck...

Just have a look at the pictures here : http://en.wikipedia.org/wiki/Gibbs_phenomenon
Pretty the same, hu ?

May be I'm completely mistaken, but it strongly reminds me a digital problem... Just tell us where your square signal comes from

Cheers

[RoboMan]

Cheff, you may be right. It was labelled as 1KHz and made me thought it was oscillation. I think it is actually a 10KHz signal (5 X 2 uS per cycle).

[xavier1000]

Originally posted by CheffDeGaar
Just tell us where your square signal comes from

You are right, Cheff. The signal is generated by a PC from a wav file and then feeds the preamp. It already has this shape at the input of the AX.

Xavier

[macka]

Hi guys,

This link may help with understanding what is a happening.

http://stereophile.com/solidpoweramp...ss/index4.html

As I recall the review samples were not biased correctly but the clues are perhaps there. In that respect take the absolutes with a grain of salt but there is a trend with lower load impediances. In any case amp reviewed impressively compared to the Halcro on a subjective basis as one would expect.

Note the tests were done at 2 watts.

At 20 kherz the output impediance is relatively higher and given a 4 ohms load this has an effect on the FR response tests particularly at high power levels when doing such test.

With that increase in output impediance I suspect the voltage drop is converted to heat and you get the effect you have been discussing. I doubt if this is an issue in normal operation.

This is only my educated theory and I hope it facilitates some productive discussions.

best

Ian