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Does anyone know of a good DIY MC phono section?

But what about my earthing question? I genuinely want to know your thoughts please.

Oh, hang on - is your answer above to the earthing question and you've accidentally linked to the wrong quote?

Edit: Now that I've actually read some of the thread you kindly linked to (other than just looking at the pics) I understand - will give it a try tomorrow on my phonostage.
 
sq225917 said:
Chilly

What's the sound electrical reasoning behind doing it that way,
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Because it mixes any raw supply noise directly into the input signal. (Hacking your words there Jiim!) http://www.pinkfishmedia.net/forum/showpost.php?p=567421&postcount=2

sq225917 said:
...other than because we think Naim 'might' have explored the options. .
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I wasn't holding Naim up in any glory here. I believe it is just good practice implimented in a fair number of audio designs. My ref to a NAC was only that was the pre-amp I had owned previously, I had refered to in my original thread and the only pre-amp I'd looked inside.

sq225917 said:
If it's the done thing for the signal ground to follow the signal path as closely as possible then I can see this making sense.

But because Naim do it that way isn't enough to get me snipping.
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I'm just speaking from experience really. I did it one way and thought, 'That sounds like a backward step', I asked a couple of people who know more than me about these things, followed their suggestions and the sound came back. But your mileage may vary though.

In fact I was having a look at Les's NCC200 and it has the same arrangement there the signal earth goes to the board rather then to the caps. Checking the Starfish it implements the same configuration.

Anyhow, feel free to try it. I do remember someone on this forum changing the earthing scheme of a MC card set up and agreed that the positioning of the earths did make a difference.

Apologies to Neil for pointing his thread in the wrong direction.
 
Right I see jims quote, but how does running a wire from the input to the card earth and then to the star make any difference to running straight to the star from the input? Other than the fact that the return off the card carries all the signal earth in one wire when does as proposed.

I can see why keeping the power grounds and the signal grounds separate for as long as possible 'might' make a difference, but in the case proposed, as long as possible is just 5cm of wire more.

Anyone got a earthing for dummies guide i can read?


Don't bother I found it, 'Potential' and referencing.....
 
OK, so last revision to the grounding made...see: latest redux - still the same.

I'm going to revisit the power supply, though not sure why it would be a problem - it's a simple Antek toroid and one of Hackers boards with MUR820 Diodes and it's CRCRC - with IIRC 0.47 wire wound resistors and 2200uF caps in line...nevertheless I might lash up an alternative power supply - possibly two HP bricks in parallel
 
What's the sound electrical reasoning behind doing it that way, other than because we think Naim 'might' have explored the options.
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Given a single ended power supply the 0v wires are carrying return current from the power supply. This current is signal related. So the 0v at the phono card rises above the 0v at the PSU according to how much current the phono card uses, the wire between the two having a finite resistance.

A phono cartridge floats, and generates very little current in real terms. If you connect it's common to the star then the 0v at the phono stage and the 0v at the cart will differ (by an amount related to the power consumption of the phono stage).

The phono stage amplifies the difference between its 0v and the cartridge's signal. The signal is then generated relative to the star 0v. Which differs from the phono stage 0v. So we have a small error into a stage with lots of gain.

It makes sense to me anyway. Connect the cart 0v to the 0v at the phono card.

Better to use + and - supplies and keep currents out of the 0v path.

Paul
 
should I perhaps have a connection from 0v to chassis ground?
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My external phono-stage is in a plastic box and is positioned on top of the CDI and I have no hum ... but OK they are MM (322s) so may be not so critical.
But in fact I had some strong hum problems. It happened as I switched the DIN cable from the CDi back to the phono stage (I still have only one cable).
But the problem always disappeared by "playing" a little bit with the DIN plug at the rear of the phono-stage. I have no ideas what the problem was, but maybe you can check the solders/connections ?

What's about the LP-ground, did you check it against another phono-stage or used another LP ?
Olivier
 
statman308 said:
Neil,

If the chassis is bonded to mains earth, as I would expect, then conecting 0v as well introduces the risk of a ground loop.

Paul
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That's the logic I normally follow (ie. cases are connected to mains earth via a wire between the ground lug on the IEC socket and a chassis bolt).

However, strangely enough, the only way I could get rid of the last vestige of hum from my (non-Naim) phono stage when I gave it a new PS, was by tying PCB ground to the case via a 10ohm res. :confused:

So that's what I have! :eek: Throughout the rest of the system, PCB ground does not touch case earth/mains earth. Maybe phono stages are strange beasts, in this regard? :D

Regards,

Andy
 
chiily said:
I'd be very interested to see if there is any improvemnt.
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Well, I've done it and the short answer is that it does make a difference and it is better. Many thanks for drawing this issue to my attention.

Before I changed the earth there was always a bit of residual noise from the phonostage (other than hiss) - with no signal and the volume at max a small amount of high frequency vibration existed on the speaker cones. After rerouting the input earths as described this noise has completely vanished. As to the sound, well background noise does seem a bit lower which makes dynamic contrast appear a little greater. In addition, images seem slightly more tightly defined (though it was pretty good in this regard before).

However, I've just listened to sq225917's phonostage which he's just succeeded in getting to work. This consists of rebuilt Naim 323 cards (not unlike my own) and powered by four Super Teddyregs fed from a power supply consisting of a Hacker board and twin transformers. Although perhaps not quite as 'airy' as mine (some more 323 mods are planned) it does have quite remarkable bass punch, extension and definition. As a result, I intend to modify my phonostage in a similar manner (not so hard to do).
 
'twin traffos and twin hacker boards'.... Still needs load matching to your Troika, they aren't K cards. And i haven't wielded the bypass capacitor anywhere inside it yet, so feedback caps and decoupling caps are still ripe for bodging.

I'm happy with for now.

Yours sounded good, more crystalline on that synth stuff.
 
Well, I've just succeeded in scoring most of the required parts (many, many thanks to Mr Flat P :)). I'm only intending to use one transformer and one Hacker board though - I hope the results will be as good (or very nearly as good). I can fit the mods into my existing cases so actual construction should be pretty easy.
 
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