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-   -   Aleph/Aleph-X/super symmetry (http://www.diyaudio.com/forums/pass-labs/11878-aleph-aleph-x-super-symmetry.html)

Bernhard 2nd March 2003 10:54 PM

Aleph/Aleph-X/super symmetry
 
Hi,

the Aleph and Aleph-X have a few of these 220myF or so Caps in the signal path usually to the current sources.

There is no other choice left over than electrolytics, is the sound getting better from that ?

I like to built a no compromise amp, is it better to wait for the super symmetry with OP amps ? As far as is seems - no caps at all :devily:


What about switching power supplys ? If the rails were 12V or 24V - no problem.


Greetings, Bernhard


P.S. NOT "the" Bernhard, but "the" Bernhard with "the" plasma tweeters...

Nelson Pass 3rd March 2003 12:33 AM

X amplifiers do not require any capacitors as such. You presumably are referring to the capacitors in the Aleph current source. One of these is a supply bootstrap, and the other conveys information to the current source about output current. I don't particularly consider them "in the signal path" any more than power supply capacitors.

If you are clever and wish to spend more money, (as in lots more) you can easily remove these capacitors, but the performance of the amplifier isn't going to get much better for your trouble.

:wiz:

Bricolo 3rd March 2003 07:11 AM

Bootstraps!
 
Quote:

Originally posted by Nelson Pass
X amplifiers do not require any capacitors as such. You presumably are referring to the capacitors in the Aleph current source. One of these is a supply bootstrap, and the other conveys information to the current source about output current. I don't particularly consider them "in the signal path" any more than power supply capacitors.

If you are clever and wish to spend more money, (as in lots more) you can easily remove these capacitors, but the performance of the amplifier isn't going to get much better for your trouble.

:wiz:

Can you explain what a bootstras is?
The gainclone I'm building is based on a TDA7294, and has a bootstras pin that must be connected to the output via a 22F cap, but I haven't understood what it's for

Bernhard 3rd March 2003 07:47 AM

Quote:

...and the other conveys information to the current source about output current.
Thanks, this was my error, I may understand now, just the output stage orders more current from the current source if the signal gets larger.

Nelson Pass 3rd March 2003 05:38 PM

Re: Bootstraps!
 
Quote:

Originally posted by Bricolo
Can you explain what a bootstraps is?
A bootstrap is where you use the output of the amplifier to get more swing or impedance out of an earlier stage. A fine example is on the Aleph current source where the npn transistor which drives the top bank of Mosfets is itself biased by a resistor attached to the + supply. Ideally, we want that resistor to feed constant current into the npn transistor so that the parameters for it remain constant, but of course the resistor's current will vary a lot with the output voltage swing of the amp. So we put a cap from the output of the amplifier, which has lots of current to spare, to the point between two resistors, one going to the + supply and the other going to the Collector of the NPN transistor, so that on an AC basis, the current fed to the npn transistor is constant.

On a monolithic amp chip, usually this technique is used for a different purpose; to give supply voltage well above the rail to an earlier part of the gain stage so that it will drive the output stage right up to the supply limits.

:wiz:

Bernhard 3rd March 2003 07:09 PM

Little bit off topic:

In Nelsons DIY OP amp in figure 10, how does the output of the Op amp know it has to be 0 volts ?:bawling:

Thanks...

Nelson Pass 3rd March 2003 09:25 PM

Quote:

Originally posted by Bernhard
In Nelsons DIY OP amp in figure 10, how does the output of the Op amp know it has to be 0 volts ?
In figure 10 you see the input resistor to ground, Rc. This gives a reference, absent anything else.

Bricolo 3rd March 2003 09:53 PM

Re: Re: Bootstraps!
 
Quote:

Originally posted by Nelson Pass

A bootstrap is where you use the output of the amplifier to get more swing or impedance out of an earlier stage. A fine example is on the Aleph current source where the npn transistor which drives the top bank of Mosfets is itself biased by a resistor attached to the + supply. Ideally, we want that resistor to feed constant current into the npn transistor so that the parameters for it remain constant, but of course the resistor's current will vary a lot with the output voltage swing of the amp. So we put a cap from the output of the amplifier, which has lots of current to spare, to the point between two resistors, one going to the + supply and the other going to the Collector of the NPN transistor, so that on an AC basis, the current fed to the npn transistor is constant.

On a monolithic amp chip, usually this technique is used for a different purpose; to give supply voltage well above the rail to an earlier part of the gain stage so that it will drive the output stage right up to the supply limits.

:wiz:

have they stolen your patent # 5,710,522? :D

Bernhard 3rd March 2003 09:55 PM

Quote:

In figure 10 you see the input resistor to ground, Rc. This gives a reference, absent anything else.
But how does kollektor of Q3 know, it has to be on 0 volt ?

Nelson Pass 3rd March 2003 10:11 PM

Feedback.

:bigeyes:


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