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Old 25th April 2012, 02:46 PM   #11
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Richard is akso the designer of of the
Multicap and Marsh electronics.
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Old 2nd May 2012, 06:28 PM   #12
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The boards cost just under $3.00 then with bubble mailer, PayPal fees, postage etc. let's make it $6.50 for non US and $5.00 US and I should be about break even. I'm not going to set anything up until the boards get back and I can test them out.
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Old 2nd May 2012, 07:02 PM   #13
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The article and schematics are in linear audio vol3?
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Old 13th May 2012, 07:54 PM   #14
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Quote:
Originally Posted by johnferrier View Post
from the Linear Audio site . . .
Click the image to open in full size.
"If you are looking for that ultimate headphone replay amplifier, you couldn’t do any better than with this discrete circuit. Richard Marsh develops his circuits from the well-known diamond topology but with a twist. His headphone amp is a very clean and linear discrete design that’s equally at home driving low-impedance or high impedance ‘phones. But Richard doesn’t stop there; he realizes that many headphones do not produce flat frequency response at your ears. Therefore, he borrows from ‘room equalization’ technology and develops a simple way to use that to equalize the headphone response at your ears.'


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Can someone help me understand this circuit? I'm looking to learn something here. It looks like unity gain buffer to me, but can't be sure. I'm confused about the input jfet's function, for example. I can see that Q1 and Q3 are emitter followers, and that Q7 appears to be a constant current arrangement. Thanks.
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Old 14th May 2012, 02:57 PM   #15
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The full development of the circuit, description and determination of component values etc are in Linear Audio Vol 3.

jan didden
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Old 14th May 2012, 03:01 PM   #16
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Quote:
Originally Posted by janneman View Post
The full development of the circuit, description and determination of component values etc are in Linear Audio Vol 3.

jan didden
OK. I guess that means I have to buy the magazine (or article?) in order to understand this circuit. Thanks.
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Old 14th May 2012, 03:34 PM   #17
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Quote:
Originally Posted by homemodder View Post
Hmmm, this is just a combination of two well known circuits, both of which I have showed here on this forum. The input is the buffer as shown by JLH, the second part is as I described in Mpp thread to tweak JLHs headphone amp. Does this designer frequent DIY audio ??

Anyway it will sound and measure very well indeed.
Both stages are both so close to Sziklai connected devices (1956) that I don't see much of a point to press.
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Old 16th May 2012, 07:25 PM   #18
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Boards arrived this morning. I could probably tweak this up a bit by matching the input JFETs. The values of R3 and R4 aren't specified in the article, so I used some machined female pins and inserted values of 47R5 and 150R to see what an FFT would look like:
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File Type: jpg PrintedCktBoard.jpg (70.2 KB, 1361 views)
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Old 17th May 2012, 12:50 AM   #19
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The above was into a 250 ohm load -- similar to my Sennheiser HD-650's -- tomorrow i will run the amp into the "worst case" 30 ohm load.

The DC offset changed by only a milliVolt after a few hours which is very good indeed. The output transistors should be happy bolted to the chassis with the appropriate insulators.

I don't know if I'm going to run it off a wall wart and a couple of DC-DC converters, or make up a quiet push-pull switcher.

This would probably be a tremendous line amp if A=10.

...edit...and the bandwidth is much greater than suggested in the article.

Last edited by jackinnj; 17th May 2012 at 12:58 AM.
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Old 17th May 2012, 07:14 AM   #20
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Quote:
Originally Posted by janneman View Post
The full development of the circuit, description and determination of component values etc are in Linear Audio Vol 3.

jan didden
Who sells the pcb, Jan?
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