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Wasin 20th January 2004 12:58 PM

Diy Xa-op Amp
2 Attachment(s)
First of all I'm sorry for my poor English.

At first I've got Idia from Passdiy for my diy op amp
So I apply Aleph X circuit For my own diy op amp
but I remove the constant current source
and I use resistor instead.

My purpose is a cheap price that anyone can build it.

Result is a miracle sound for my cheap VCD in a cheap budget.
It was more than I expected

Have any comment.

Wasin 20th January 2004 01:22 PM

2 Attachment(s)
This is the XA-op amp that I build

GRollins 20th January 2004 01:51 PM

I'll try to get back and look at the circuit in detail later, but I did see one thing. It looks as though you're using a single-ended input. Assuming that you intend to use a balanced output, I think you'll find that the opposite phase is very weak--almost non-existant. To get a good balanced out, you'll need to use a current source under the input differential.


Wasin 20th January 2004 02:34 PM

thank for your comment.

I intend to use Single end input because My cheap VCD
player does not Balance DAC out put.

I notice that XA op amp better than normal Aleph op amp that I build before. I don't know why but I satisfied with this result so much. May be I want to add Current source later.

But my purpose need it simple and cheap as could as possible.

and one thing I need to use the component that I had already.

Nelson Pass 20th January 2004 05:57 PM

Maybe it would be better to call it an X type gain stage, as
the X topology doesn't lend itself well to the definition of an
op amp, and isn't that good at doing some of the tricks an op
amp can.

GRollins 21st January 2004 01:00 AM

Use an oscilloscope and look at the positive and negative phases of your outputs and you'll see why I'm recommending a current source. A differential doesn't make a good phase splitter unless it has a lot of resistance under the Sources/emitters/cathodes. If you're using resistors, you need to think in terms of 10k or more. Run through the math on that vs. your rails, and you'll quickly find that you'll need really, really high rail voltages. A current source provides theoretically infinite resistance--and will do it with the same rail voltages that you're using now.
A current source need not be elaborate or expensive. I often use a somewhat more intricate design, but another IRF9610 with a Zener and three resistors would do the trick--look at the front end of an Aleph amplifier for the layout. If your rails are quiet and regulated, you could even dispense with the Zener and use a voltage divider at the Gate.
You would not have to give up your current circuit board, either. I have been known to make a small circuit board with inputs and outputs the same width apart as a resistor. That board then stands off of the main circuit board. Presto! Instant daughter board. The smallest board I've made yet was about the size of a postage stamp...and yes it was a current source.
I'm assuming that you're running 15V rails because that's the transformer you had on hand, but if you can increase the rails, you'll get somewhat better performance.


Wasin 21st January 2004 03:52 AM

Thank alot for your daughter board idia.

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