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M2Clone boards with 120mm UMS spacing

Posted 17th February 2010 at 12:26 AM by Tea-Bag
Updated 19th February 2016 at 01:06 PM by Tea-Bag

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M2C clone boards
Special thanks to Gerd, CRT and RusselC for assisting with this board concept and implementation.

The board is ~215mm x 50mm each channel
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Click the image to open in full size.
The board thickness is 2mm, the copper is 2oz copper double sided.

For C2, There are a number of options.
1. standard is to use a 10uf Elna Silimic 2 35v cap.
2. Use a cap to fit over the outlined block. This will require some headroom over the power resistor, but allow for a film cap.
3. As I display in one channel, use an ecap, and then use a 15mm film cap as a bypass for it.

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Click the image to open in full size.

Here I make special note of my mistake in construction. Somewhere between looking at the datasheet, remembering the symbology as presented for DIP-6 devices and soldering it in, I put mine in backwards. The amp mostly worked, but it did not settle down it's bias to the .650v that is expected once it gets going. So, since the 4N35 was square and the dot on one side, the dot goes towards the curved back end of the optocoupler. The large C3 cap (18mm spacing, no snap in) charges up and then slowly ramps up the bias. There is an optional bypass cap (15mm lead spacing) for C3 as well, as Zen Mod recommended, so there it is if you choose. He is swell guy.

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Click the image to open in full size.
Click the image to open in full size.

Why does R7 look all ghetto and with antennas? Well this allowed me to try a few different resistors to trim my negative offset I had started with.With IRF240,IRFP9240 transistors, I got negative offset so increased R7 to 52.3k, and then using the pot I was able to get a settable offset range. Conversely, if you get too much positive offset as measured on the out + and out ground, then raise R8 higher.

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The orientation for the Edcor transformers is hopefully self-explanatory. Pins 1 and 2 are 'close together' so they fit into the board well. Since these boards are mirror images (to keep the transformer to the back of the chassis), their orientation is opposite from left to right side.

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Here we see a couple shots of the printout in a diyaudioStore chassis, verifying that it will fit all right. Thanks to Russellc for helping out here. So far I have not managed to pick one up.
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Close up
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The boards I used for the power supply is my standard Dual Rail Power Supply option
Power supply used pass of other board.
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More about this linked to PS blog.

Here is a schematic swiped from Zen-Mod for further use here. I like it. Its got the tranny pinouts and other goodies listed. I added a few notes of my own.

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Implementation of FETs

In my setup I swapped out the IRFP9240's by Vishay for NOS Harris units, that I am also putting up for sale with the boards.

A previous note from Pass describing differences.
"The sound of the IRFP9240 has an artifact. If you place
emphasis on measurements, then you would not use the
IRFP9240. I personally don't care for it when the device
is used in common-source mode.

Comparisons between it and the Harris and Fairchild
equivalents in common-drain mode, particularly in
balanced circuits reveal a subtle warmth that is preferred
by a percentage of listeners"

I am not one of those listeners. I got a certain glare on the top end, or shrill upper end if you will with the standard Vishay IRFP9240. I dont want people blaming me for this outcome, so I am offering Harris IRFP9240 with the Vishay IRF240 combo. This is more relaxed and balanced to my ears. The price of the non-ROHS complaint NOS devices is not too bad, and they are researched by the company I bought them from to trace Serial Numbers to legitimate sources. They are a local business and their business is to have NOS parts to 'extend the service life of products'. This makes a whole lot of sense in my other line of work where things are made obsolete a lot, and repairs for products become difficult.

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Click the image to open in full size.


Here is what I recommend for boards, 16ga wiring is easy fit into boards. If you look closely I am agianst the grain here and use solid core.

For signal wiring, I originally used a pccc solid core japanese copper.
I noted that my mu-metal shields did not make a difference with noise (which was not noticable listening, but was with ear 6" from speaker. I noticed that moving the signal wiring around, I would get more or less noise. So out that went, and in went Mogami Low Noise No. W2330. Real cheap stuff, but it really gets the job done in this place, and also works great in RIAA setups to for me.

Youtube link to running amplifier

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