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Does anyone know of a good DIY MC phono section?

Hello Neil,

I would try to build an earth-star (on your picture the LP-ground looks like a good guy for it ...) and connect all earths to it but especially the phono-board stars ! (and not going back to the TRs !).
Let us know :)
Olivier
 
I have a feeling Neils Phono stage is a bit tired and emotional at the moment.

Olivier, its on its way to you!
 
Do you get the hum with nothing at all connected to the inputs?

I've been wanting to have a play with this circuit since the original post on DIYAudio... Did you make more than one board?

Paul
 
Neil, I'm no expert, but I think I'm agreeing with Binnie. Connect all your grounds to the star point in the lower left only:
  1. Power ground from connector
  2. TR grounds
  3. Board stars
  4. ALL signal in and signal out grounds
 
flashgo said:
Neil, I'm no expert, but I think I'm agreeing with Binnie. Connect all your grounds to the star point in the lower left only:
  1. Power ground from connector
  2. TR grounds
  3. Board stars
  4. ALL signal in and signal out grounds
Click to expand...

It's about the only permutation I haven't tried ...so here goes...
 
Dang! I expect other phono pre's are working just fine, and hum implies 60Hz pick up, so it's not some circuit oscillation.

It's sounding like a bad solder joint, probably at a ground connection. Both channels, IIRC, so it's unlikely to be on the cards, unless you've got 2 bad joints.

Have you checked all the grounds connecting to the outside? Power ground, signal grounds L and R / in and out? Any one of those could be an antenna, contaminating you good star ground.

Just thinking out loud. Wish I could help more. :(
 
Just for purposes of diagnostics, can you run it off batteries for a bit? This will entirely eliminate PSU related ground loops as an explanation; I would have though +/- 9V for the input stage and +/- 18V for EQ stage would work well enough to hear if the hum is still there. Nasty little PP9, tranny radio batteries would do for the test.

If the hum is still there, it isn't related to PSUs or PSU earthing, and must be getting in somewhere else.

If the hum goes away, it is either coming in via PSU, or is related to PSU earthing.
 
Hello Neil,

it seems (difficult to see it in this picture http://i26.photobucket.com/albums/c114/neiljadman/Phono%20Stage/BaseLayout-fullwiring-StarGrnd.jpg) that the earth coming from both "signal In" BNC-earth is also going directly to the main earth-star.
In fact, the signal-in earth should be directly connected to the phono-cards (as you called it: the star earth from the phono card).
Then another wire should connect the star earth from the phono cards to the main star-earth.
The signal-in earth goes from the BNC directly to the cards and then from the cards to the main earth-star.
I dont think that this is the raison for the hum but since you are here ...
Keep on, you will get it :)
Olivier

Olivier, its on its way to you!
Click to expand...
thank You Andrew :)
 
Johhny, I've split the power rail so that the cards are effectively split into RIAA section and a gain stage, each powered separately. That's the reason for the black cap you can see tucked away on the back of the cards.

Flashgo, I alwasy intended running it with four, though it did briefly exist with just the two as I was getting my head round the rail split and additional decoupling cap insertion.

(I haven't actually listened to it yet as I'm without deck for a while yet, i'll pop over to Ynwans later on0.
 
sq225917 said:
Neil you could try one of these...

http://media.bestkiteboarding.com/mm/323_quadded.jpg
Click to expand...

Hmm I would still say that the earthing on the signal side is not optimal though.

Read about it here http://www.pinkfishmedia.net/forum/showthread.php?t=45649

I found that if I attached the input's earth to a star earth where all the PSU earths meet then the sound quality was compromised. If I attached the input's earth to the 323 card and then another wire from the 323 to the star earth the whole thing sounded far better.

This image illustrates how NOT to do it. The input signal's earth runs directly to the star earth, the chock block. Input's on top.

2008_03150319.jpg


This image is the right way. Notice the grey wires, signal in earths run to the base of the 323 card on the vero board.

00406.jpg


If you don't believe me, have a look at the tracks on the inside of a 32.5/42/42.5/62/72/etc. The signal earth always goes to the base of the 323 and nevr directly to the star earth point.

dsc00346.jpg


Try it
 
chiily said:
I found that if I attached the input's earth to a star earth where all the PSU earths meet then the sound quality was compromised. If I attached the input's earth to the 323 card and then another wire from the 323 to the star earth the whole thing sounded far better.
Click to expand...

I'm not doubting you but why do you think this happens Chilly? Also, is the earthing arrangement you suggest only needed for the signal input and not the output?
 
Chilly

What's the sound electrical reasoning behind doing it that way, other than because we think Naim 'might' have explored the options. 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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