X Aleph Project Down Under

[macka]

I always thought the silence of the lambs comes before the roast.

Ian

[macka]

Following the contruction of the Aleph J project and trialing those amp for a bit I revisited the Jfet input stage.

To cut a long story had a good listen to the amps tonight and I think subject to some minor adjustments they are at perfection.

To give to an example and I have this Blue Note Jazz Cd I have been using that I bought at the Blue Note Jazz Club in N.Y by Francisco Mela Melao.

Never before heard such high frequency resolution ever from a loudspeaker. Sounds like a grand statement I know but well I am comparing to every other Pass amp in the house.

The vocals have an un canny clarity and the bass rocks. The transient peformance from loud to deep silence is quite amazing even on relatively small loudspeakers like my JBL 4208 time aligned near field monitors.

This for me is a real break though using the Jfets. I can hear subtle but quite audible differences between all my digital sources.

I can only wonder what a hi end digital source would do.

An analogy is like going from 16 bit 44.1 to 24 bit 192 recordings.

So at this stage I will let it burn in a bit more for a few days and take some key measurement and hard wire the driver board wiring.

So what were the mods.

Teflon microphone OFC wiring in key areas so that the gates of the followers are wired in groups of two (not diasy chained from the driver board.)

I feed the Jfets on the daughter boards direct from the balanced input cable direct to the gates of the Jfets via a sole 10K Dale resister.

The new Silmic 11 capacitors in the current source bypassed with Panasonic PP film foil 0.022 capacitors.

Bypass the negative supply rail on the Jfet daughter board with a Panasonic 0.33 PP film foil capacitor.

Reducing the source resisters down by 30% in the output stage to 0.5R and as yet some fine adjustment to the current source current gain.

All these mods meant collectively rebuilding the amps.

I am thrilled with the outcome though and I think those that tackle this project will be quite pleased.

The feedback resisters are 220K and 22 K to ground.

I guess the key point here is careful implementation in terms of contruction and layout. Use very high quality signal wiring to minimise stray capacitance and keep all signal paths as short as possible.

If you are wondering how. Just drop Erno Borbley a line and he will kindly match some Jfets for you.

cheers

Ian