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Old 11th March 2013, 06:22 PM   #1
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Default Bipolar Transistor Matcher

Hat tip to Peter Demchenko for his article in EDN -- I simmed it with 2 different BF devices.

Click the image to open in full size.

Click the image to open in full size.

Vs should be (approximately) = 2 * (Vbe1 + Vd + Vbe2 ). R1 and R2 should be sourced appropriate for the current. Diode is a blue LED
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Old 11th March 2013, 09:40 PM   #2
RNMarsh is offline RNMarsh  United States
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Default same, same -

And, the same idea was published in TAA 1982 -->
or go to DIY "Marsh headphone amp" -- line #566.
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Old 12th March 2013, 01:39 AM   #3
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A la:

Click the image to open in full size.

When that article was written I still had no gray hairs and only 2 kids! I couldn't have afforded a MC cartridge at the time. The beauty of the article was, however, was in the delightful MC pre-pre design using low cost components. I am wondering if you've given thought to updating it.

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Old 12th March 2013, 02:12 AM   #4
RNMarsh is offline RNMarsh  United States
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No, as I dont have a MC to try it with any more. How does it SIM out? It was quiet -in that I heard no hiss/noise. Couldnt measure it at the time. I can now. Try it.
I cooked that circuit up in my own little brain on my own while working at LLNL. I recall that John Curl saw it and called me to talk about it. Geeeze, you guys have great memories about these things. :-)

Thx-Richard

Last edited by RNMarsh; 12th March 2013 at 02:21 AM. Reason: MC Pre-pre original design -
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Old 12th March 2013, 06:35 AM   #5
RNMarsh is offline RNMarsh  United States
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And, all along I thought no one was paying attention so I stopped writting until recently when I am near retirement.

Thx-RNMarsh
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Old 12th March 2013, 07:14 AM   #6
Johno is offline Johno  Australia
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Prof Marshall W Leach published the same circuit sans emitter resistors and current mirror in 1978 in the Audio Magazine and called it the Common Base Head Amp or some such. The then editor advised him to call it a pre amp and suggested the 2N4401/4403 transistors which have very much lower noise than the 2N5210/5087.

I have built the circuit with the low noise transistors and its in my pre amp now - but like RNMarsh I do not have a MC. Bummer!

Last edited by Johno; 12th March 2013 at 07:16 AM. Reason: correction
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Old 12th March 2013, 10:41 AM   #7
RNMarsh is offline RNMarsh  United States
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It is not the same circuit at all.... only thing in common is the common-base input. There is no overall nfb to lower distortion and to lower the input Z further. The input Z is very low and damps the cartridge was the main point to my design. M.Leaches circuit doesnt have these features.

Thx-RNMarsh

Last edited by RNMarsh; 12th March 2013 at 10:46 AM.
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Old 12th March 2013, 11:16 AM   #8
Johno is offline Johno  Australia
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Perhaps I should have said 'similar'. My focus is on the push-pull common base input which I think has a rare beauty and elegance so credit to you both for recognising this. However I suspect we are hijacking this thread, apologies.
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Old 12th March 2013, 09:15 PM   #9
RNMarsh is offline RNMarsh  United States
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M.Leach MC designs of which there were at least 3 all required cap coupling, also.
I got the input idea from a tube designer (David Manley) who showed me his design he was working on for my comment/input.... input was to the cathode in his MC circuit. I also wanted to lower thd with neg feb and to lower the input Z. Plus be all direct coupled. I think the design you are referring to is below:

C-coupled MC pre.jpg

This seems to be the one you made? But the other one M.Leach published was a common base input. But again at that time/era everyone still required cap coupled circuits. I put a compl push-pull on the output and feed the fb signal back to the input.... later a line level variation of mine was published which pre-dated the current-mode fb IC. Mine has in principle zero dc volts on output. Later, i invented the idea of dc servo for drift/offset.

C-coupled Mleach MC pre.jpg

In any case matching compliments is always a good idea.

Thx-RNMarsh

Last edited by RNMarsh; 12th March 2013 at 09:44 PM.
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Old 19th July 2013, 10:35 PM   #10
nnx is offline nnx
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Default My transistor matcher....

Hi all,

Here is my take on Demchenko's transistor matcher. I needed something "quick & dirty" to match the outputs for my amplifier build: Trust, the most delicious Dx Amplifier

The circuit is turned upside down so that gnd becomes reference for current measurements across the 100ohm resistors. A switch is added across R5 for base current selection. And diodes are installed in the main current paths so that the sensitivity for the red and green led's is increased. Please note that D1 and D3 are not installed but replaced by a short. Tho whole thing is fed by a lab supply, I used 15v when matching output transistors and drivers, and 8-10v for small signal transistors.

This matcher works rather well, the red and green led's indicate which side is "stronger" and a voltmeter across M+ and M- tell the difference between the two. A measurement between GND and M+ or M- will indicate the actual current through the transistors.

I may build a better one that displays hfe and vbe directly in the future, but this will do for now.....
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File Type: jpg Transistor Matcher.jpg (440.3 KB, 77 views)
File Type: png Transistor Matcher1a.png (9.7 KB, 123 views)
File Type: png Transistor Matcher2.png (14.9 KB, 115 views)
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