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Does anyone know of a good DIY MC phono section?

neiljadman said:
Looking for another project and I need a new MC phono preamp, so...
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Hi Neil,

If by "MC phono preamp" you mean a phono stage suitable for a LOMC then this typically needs a MM RIAA stage, preceeded by a "head amp" to boost the 0.2-0.5mV output of a LOMC by, say, 20. Right? :)

If you get in touch with Hugh Dean, the designer of the AKSA amps ([email protected]), he should be able to help you.

I say "should" because he certainly has the components you need, it's just that he hasn't packaged them together as a "phono stage". Tell him you want the phono stage section of a GK-1M board - plus suitable PS - coupled with the "Paris" headamp board (which is battery powered). He may supply the PCBs already "stuffed" ... or he may not! :)

However, if what you really mean is a line-stage preamp which also includes a phono stage ... then you need the full GK-1M preamp kit (with MM phono option) plus a "Paris" headamp.

I have a GK-1 ... IMO it's a very fine preamp. However, its phono stage is not as good as my "Phantom Audio" phono stage - so I use that. The "Paris head amp is sensational, IMO - dead quiet and lightning fast! :)

Regards,

Andy
 
Hi Geordie
I have built a pair of Avondale NCC200's, Les at Avondale is a great helpful guy and the build cost is very reasonable if you buy the PCB's and source the components yourself, these are basically Naim power amps, and you could run them easliy as monobloks, Les sells all the power supply parts too.
For the pre-amp, may I suggest the AD815 that Hacker is currently sourcing PCB's for, this would represent a great pre-amp and I hope there will be a group guy on this soon!!! Carl ????
Paul
 
Hi Neil,

If you're handy with Google, you could take a look at building a Pass Labs Aleph Ono or Xono clone. This will be one my projects for this year. The design has MC + MM input and an RIAA stage. If it's anything to go by, the commercial versions have won various awards in the last few years.

There are a few different implementations in the DIY world, Here are some links:

http://www.r-stens.de/diy/AlephOno/diy_aleph_ono_en.php (old link)
http://www.rstaudio.de/AlephOno/ono_en.html (new version)
http://netti.nic.fi/~tfrisk/riaa.html
http://www.diyaudio.com/forums/showthread.php?s=&threadid=19585

Cheers,

Ron
 
I've also recently published a phono stage, with MC option, based on the same ideas as went into the Maclaren 402/602. The circuit is deliberately different in a number of ways, as I signed an undertaking not to disclose the original to competitors when I worked for Maclaren. The differences are things that I view, with the benefit of hindsight, as improvements.

See the later pages of this thread for circuits and descriptions: http://www.diyaudio.com/forums/showthread.php?s=&threadid=114339
 
andyr said:
...If by "MC phono preamp" you mean a...
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To clarify, it's going to get sandwiched between my Linn LP12 (Dynavactor Te Kaitora Rua at the business end) and my Starfish.

Thanks all, good reading here so far - keep 'em coming.

Neil
 
What output and impedance does the Dynavector have? I can suggest optimal values for the front-end settings to suit it.
 
Thanks PD, I'm trying to figure this one out.

So here's my initial thoughts - are they reasonable?

Build the two pairs of two stages together on one board. Use local regulators (TeddyRegs or is a simple LM317/337 setup good enough?) to supply the appropriate voltage to each stage - possibly even build them on to the board.

Power it with a single unregulated linear 30v supply rail from a SNAPS or a printer power supply.


Neil
 
The circuit is deliberately different in a number of ways, as I signed an undertaking not to disclose the original to competitors when I worked for Maclaren.

As a matter of interest PD, what products did you design for Zetka?
 
PD - are there alternatives for the 2SA1084 and 2SC2546? Can't find these anywhere this side of the pond.

Of course if someone has some spare...

Neil
 
2SA1085 and 2SC2547 should be available, and are basically the same - they have a higher voltage rating, which is irrelevant. Dalbani and RS both have them.

In principle 2SA1083 and 2SC2545 would do (lower voltage, 60V, but still OK), but I have never seen them for sale.

If you get really stuck, I can probably find you a set out of my own stock, but I don't have that many spares and am loathe to do that.

For PSU, you need dual rail, plus and minus, at the two voltages. I suggest you use 317/337 for the +/-24V, and then derive the +/- 12V from the 24 with a VBE or similar - that should be quiet enough.

RustyB, my circuits were the basis of the 402 and 602 preamps, and some of my ideas went into the matching 702 and 902 power amps. The rest of the design work on these was done by the in-house engineer.
 
neiljadman said:
Thanks PD, I'm trying to figure this one out.

So here's my initial thoughts - are they reasonable?

Build the two pairs of two stages together on one board. Use local regulators (TeddyRegs or is a simple LM317/337 setup good enough?) to supply the appropriate voltage to each stage - possibly even build them on to the board.

Power it with a single unregulated linear 30v supply rail from a SNAPS or a printer power supply.


Neil
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I can't see why you shouldn't put it all on one board. The original prototype had several tiny boards, one per gain block. Integrating the regulation onto the boards is a great idea.

For your Dynavector, I think you probably want a bit more gain. I would leave R5 at 5.6 Ohm, and put R4 up to 1K - this will give you a first stage gain of 180. The second stage has a gain at 1kHz of about 9, so you will get 400mV out for nominal levels. As records have big peaks above the reference level (unlike CD, where the quoted level is the maximum), this should be a useful level match, while still having masses of headroom.

Because it is dual rail, a SNAPS or printer supply won't cut it - you need two rails! I would get a small toroid (say 30VA, 20-0-20 secondary), a diode bridge, and two electrolytic caps - 2200uF, 50V is fine. This will give you about +/- 29V raw to play with (probably a bit more because of the transformer regulation, as the voltage is quoted at full load, and we will draw hardly anything). Do you need more details for this?
 
Thanks PD, I finally got around to laying out the board. One per channel with the gain and RIAA sections together along with local regulation. Initially I tried 4 full TeddyRegs per card, boy was that a crowded board, so I ended up splitting the TR and using the LM317/337 sections to power the RIAA stage at 24v and then feeding the supply to the VBE section to step it down to 12v for the gain stage.

I may have missed some opportunities, but I could not get it to fit a straight one sided board - so had to add a couple of links to carry power or ground across a few signal tracks, since I don't fancy trying to make 2 layer boards by hand!

I'll probably try etching a test board this week.
 
PigletsDad said:
I signed an undertaking not to disclose the original to competitors when I worked for Maclaren. [/url]
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PD,
The lawyers say it's ok, you can disclose to us.
We are hardly competing with MacLaren...

Neil,
I wouldn't dare plug something like the Kiri Te Kanawa into a homebrew diy stage.
 
Hi PD

Could you please link your phono schematics to this site? The reason I ask is that I am not a member of the other site, so I cannot download from there.

Thanks, Andy
 
neiljadman said:
I may have missed some opportunities, but I could not get it to fit a straight one sided board - so had to add a couple of links to carry power or ground across a few signal tracks, since I don't fancy trying to make 2 layer boards by hand!

I'll probably try etching a test board this week.
Click to expand...

I'm not surprised! The prototype had hand drawn double side boards, and the production circuit was also double sided. Actually hand drawn double sided is very easy using a PCB resist pen. The trick is to drill the holes first. You then ink the tricks in by "joining the dots", and then let the resist dry for minute, then etch.

Single sided with a few jumpers sounds fine.
 
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