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Old 11th December 2003, 10:07 PM   #1
nar is offline nar
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Default An Aleph X pre

This is for you pass fans and audio gurus : So to consider the succes of the Aleph X as a power amp here in this forum , I was wondering if possible to use the same topology but for a preamp now .

The only difference with Grey's design would be

Use regular current sources instead of active Aleph CCS ( remove resistor and series capa to the base of bipolar )

Use higher voltages . As a pre , we always !!! work in the high impedances values for inputs of the amp ( around 10 k or 20 k balanced )

The CCS for differential could be made with bipolar + led for lowest noise here . If you want to use regular zener , go ahead

A 9610 differential at 20 mA global , and 610 for the 2 CCS and output stages , round 40 mA each half of the circuit

PSU with +/- 60 V , as the ZLS by the way .

Gain set wherever you want . SuSy applied . Adjust C on the 2 X feedback resistors to get proper working of the circuit ( see with gain setting )

In the layout engeneering , make traces as symetrical as possible . To control offset drift , Grey's method should be fine , and put all mosfets in line on the same heatsink ( huge ) should allow direct coupling to the power amp ( yes , use input caps at the inputs of your Aleph X !! )

Has anybody tried that ? I thought coherent to use same pattern for the pre ans the amp .... and use SuSy of course !

Any feedback ?
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Old 11th December 2003, 10:10 PM   #2
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Nelson ? Any hints ? Are you there ?
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Old 5th January 2004, 01:11 AM   #3
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If you remove the feedback connections that make the Aleph current source an Aleph, you're left with a Zen. Nothing wrong with that, but you'll have to watch what you call the circuit, so as to avoid confusion.
That said, X preamps are certainly possible. I've put together eight or ten variations on the theme and have ideas I haven't even had time to try yet.

Grey
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Old 5th January 2004, 06:47 AM   #4
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Hi Grey ,

Basically you are right - we are left with some kind of Zen X circuit , regardless the CCS on both sides ( the original Zen pre does not have them ) -

The difference is 2 gain stages series each half instead of 1 -
possibility to make a better use of SuSy I think than with the previous X Zen - and more advantages

1) Open loop higher
2) Larger bandwidth
3) Independance of input impedance vs output impedance
4) Lower output impedance
5) Thus the diff pair is matched , and current sourced and output mos matched we can get better behaviour with unbal in / bal out ( amplitudes same value , better differential rejection of noise )
6) The gain can be set different values , and higher values than X ZLS without compromise on bandwith/value of input impedance , this one can be higher than the previous X ZLS too

Definitely , CCS give a more elegant way to get good performances than resistors to bias devices

The DC drift can be an issue . Sure . But DIYers are known to get rid of that kind of problems

The question I have : can the attenuator found in the Aleph P work well with that kind of output stage ?

Humm.I would try leaving in place the Aleph CCS resistor + capacitor not to worry Nelson

Who knows ? Perhaps with SuSy + Aleph OS we get here a goood combination to get a wonderful sound ...???

Regards

Anael
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Old 6th January 2004, 01:07 AM   #5
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Preamps don't need much in the way of output current, so desiging an amplifier-style output stage is overkill. On the other hand, it might sound great, so feel free to try it.
A low-Z output, however, is a good idea.
Volume controls? Knock yourself out. Just keep in mind that you'll need to adjust both phases of the output simultaneously. If you're not using both phases, you'd be just as well off going with a single-ended preamp.

Grey
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