AX100 100W Aleph-X Monoblocks

[macka]

Hi Graeme,

I am still tweaking but with more subtle gain changes.

I expect this could take some time to fully evaluate

Ian

[gl]

Hi Ian,

I agree with your aural impressions completely. It takes time for the amps to burn in and open up. I believe that the JFETs make the difference. Like you, I am continuing to hear and learn new things about these amps.

Graeme

[macka]

I did some variations over a closed loop gain range last night.

I am incliend to think in the end its to degree system dependant and taste.

What I found is low feeback sounded open, light and relaxed with some what less clarity. This favoured simple musical passages like acoustic / vocals.

Increasing feedback increase apparent bandwidth. However the extension in bandwidth without sufficient damping may not suit all loudspeakers.

Therfore a bit more feedback (but not too much) can be batter in some instances

Imac

[macka]

Sorry I lost my interent connection earlier.

Too much feeback and the sound clamps up and become dry, sterile and lifeless.

So of my earlier X Aleph incarnations no doubt share similar behaviours but I never bothered to adjust them.

So I am carefully trying different closed loop gain settings because settings in such simple low open loop gain circuits I think there is a sweet spot that suits the individual.

I have done this on the basis of Nelson's earlier post. But at this stage have only adjusted the feedback and not the open loop gain wth source degeneration or adjusted the current source.

Graeme's JFT no douby hav different ids to mine, he uses a number of output device and source resisters, higher supply rails so I have not doubt I not getting an identical out come.

Bit this is what diy is all about

[china zhao]

ding

[macka]

Hi Graeme,

To simplify assembly I moved the feedback network and drain resisters back on to the main pcb.

I also tried a different variety of capacitor in the current share loop and got quite different results. This has kind of blown away my previous impressions and have gone back to 26 db of gain for now.

My plan is to also try some small Zetex mosfet for the differential pair like those used on the Pass diy opamp article. Perhaps this will be best done in a new thread.

[macka]

After re organising the amps I think Graeme has hit on a nice set up with the Jfets in this configuration. I tried lower gain settings and nop it just did not happen for me.

With 26 db gain it just sounds just right imho

iMac

[michaelbehrendt]

Here a scematic idea, i don´t know this will work, have to changed the Fet´s to FQP3P20 and FQP4N20 and the bt to 2SC4793 and 2SA1837, who can answer.

Michael

[gl]

Hi Michael,

I'm not sure if this thread is the right place to post your new design. Perhaps starting a new thread would be a better idea or maybe the Aleph-X builders thread.

Graeme

[macka]

Hi Graeme,

I will look at using the 3 parrellel Jfets this week and increase in bias current to 36 ma.

At this point I am quite pleased with the Jfet option and my small fet option is coming along.

From the adjustments I have done so far it would seem that any of the X Aleph diy incarnations my be working circuits but may be far from optimised to the get the best out of the Aleph cu/susy.

I would therefore encourage those who have built them and put them to one side to pull them out and have a look at the gain and feedback. Small adjustments can bring surprising results and I am certain susy works best with less rather than more feeback.

For those interested the Jfets can be purchased matched from Erno Borbely.

I plan to have a version of the ZVP2210 input stage working soon. This appears a much better option than the old 9610 part in lower voltage versions of the circuit.