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Apt Holman plug-in MC expansion board
Apt Holman plug-in MC expansion board
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Old 13th February 2020, 05:01 PM   #11
seanc is offline seanc  United States
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Quote:
Originally Posted by jaddie View Post
It was one board, no cart-specifics. If I ask the right guy real nice, I might come up with a schematic, though I'm sure yours will be just fine. Remember, the parts available in 1978 were not like what we have now.
Yah, the AD797s work fine, so I wouldn't try to replicate the original, but it would be very interesting to see, just for curiosity sake. It's surprising that with all the Apts still in the wild, nobody has found one with an MC option installed.

Quote:
I'll just toss this in because it came up...there was evidently a change in manufacturing of the TLO72 some time when TI moved the factory some time late 1980s, early 1990s, and the later ones "weren't as good", I think in the noise spec. But useful to note that if you have to change a original dead TLO72 it might be work considering something else....
Appreciate the heads up, but all the TL072s were upgraded with newer parts during the rebuild.

This is what I have in mind for the 2nd. version:

Apt-MC-ex1.jpg
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Old 13th February 2020, 05:07 PM   #12
seanc is offline seanc  United States
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Originally Posted by GKTAUDIO View Post
I can vouch for the design concept and execution by HalfApt! He was kind enough to provide a board for me to build, which I did using the same high-quality, close-tolerance parts, adjusting only for R and C loading of my cartridge. Because this was essentially a beta version, there were a couple of parts tacked into position, but the new board design will conserve on space and provide some additional flexibility for loading.
Thanks for being a willing beta-tester/guinea-pig!
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Old 13th February 2020, 06:12 PM   #13
GKTAUDIO is offline GKTAUDIO  United States
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Thank you for asking for my input, Sean!
As you know, I've got 3 Apt Holman preamps, so I'm in for 2 more MC cards!
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Old 18th March 2020, 12:56 AM   #14
seanc is offline seanc  United States
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Version-2 is built, tested, installed and working great!

This one has on-board low-noise split-supply adapter, so 100% plug-n-play. No more tapping into -18v from main board.

Load resistance jumper selectable. Gain resistors & load capacitor socketed, so easy to change at will (w/out de-soldering re-soldering) to accommodate any cartridge.

Sounds fantastic, slightly lower noise than first version.

It's a tiny thing, the SMT parts were challenging:

completed-board.jpg

installed-close.jpg

in-hand.jpg
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Old 18th March 2020, 02:24 AM   #15
elwood625 is offline elwood625  United States
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Beautiful work! Work of art with the SMD parts, very impressive.
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Old 19th March 2020, 01:52 AM   #16
seanc is offline seanc  United States
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Originally Posted by elwood625 View Post
Beautiful work! Work of art with the SMD parts, very impressive.
Thank you! It did turn out better than I expected.

I had done very little SMD hand-soldering before, but I knew going in, with the complexity and close spacing on this board, that I couldn't do it by hand, so went to a more "pro" approach (that I wanted to learn anyway).

Used a stencil & solder paste, did the actual soldering via the "hot-plate" method on the kitchen cook stove! Was able to match the solder thermal profile to w/in 5%.

Most important, it works great, every bit as good as the first version, perhaps better, with less noise!

It's a keeper!
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Old 22nd May 2020, 03:27 PM   #17
georgesgiralt is offline georgesgiralt  France
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Hello,
I'm late on the subject, but do you plan to sell some ?
And if yes, at what price ?
I own an Apt Holman preamplifier and would like to own one.
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Old 22nd May 2020, 07:35 PM   #18
seanc is offline seanc  United States
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Originally Posted by georgesgiralt View Post
Hello,
I'm late on the subject, but do you plan to sell some ?
And if yes, at what price ?
I own an Apt Holman preamplifier and would like to own one.
Not selling, sorry. Only 3 boards were made and they are all spoken for.

I'd be happy to provide board files if you want to have some made, and a parts BOM, but you'd have to build it yourself.

The surface mount parts are very challenging, I would not recommended if you're not comfortable soldering tiny parts (0.5mm pin-spacing).
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Old 23rd May 2020, 01:52 PM   #19
georgesgiralt is offline georgesgiralt  France
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Thank you for your answer.
Oh yes, I would like to get the files ! and a shop or a list of shop having the connector (my search did not get much, but I live in France) !

I thank you again in advance !
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Old 23rd May 2020, 02:47 PM   #20
GKTAUDIO is offline GKTAUDIO  United States
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I'm the builder of the other 2 cards that Sean has created (one built, the other waiting for me to build up my confidence to do the next round of SMD placement and soldering), and I built one of his Version 1 boards. Version 2 is much more self-contained, very versatile, and excellent-sounding. However, the SMD construction does require careful planning and execution. I messed up my first attempt when I installed a resistor in the wrong location, and in testing fried a couple of $10 components. However, that experience has helped me develop a slightly different process that I'll use on my second board.

Sean's Version 1 was excellent, but his Version 2 design is really impressive. I have never owned the original Apt MC board, but I really prefer the advantage of more state of the art components and design and DIY nature of Sean's board. Here are a couple photos of my build.
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File Type: jpg SeanMC.jpg (944.1 KB, 35 views)
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