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Does anyone know of a good DIY MC phono section?

Yes, this morning :)
And it looks very, very good :cool:
I will open it (very carefully ... I swear) this evening to have a look of the internal.
Thank you again Andrew !
Olivier
 
So then boys, next mod topic, has anyone fiddled with the cartridge loadings on their NAim cards? has anyone come up with a novel flexible adjustable solution, browndog legs in pcb holes or similar?
 
Thanks flashgo for the link (I changed it) !

In my 322s I have two Muse NZ as feedback.
I may continue the experimentation by by passing them with the MMKs as I did with the 321s (2 x 47µF as feedback :rolleyes:).
Olivier

PS: pictures ... I will try ...
 
So a second power supply - this time just a trafo into a bog standard bridge rectifier and 2 4700uF/40v caps giving +/- 35v out...same result...


...I think the next thing to try is the connection to ground inside the PS...
 
You know what you want to do Neil? You should record the output noise digitally and put it on the web so all us 'golden ears' can listen to it and proffer suggestions as to what the cause might be. ;-)

Do you have a layout for the circuit board we could look at?
 
Neil,

Try my battery suggestion - if the noise is there when running off batteries, it is nothing to do with the PSU or earth loops involving the PSU. If it goes away, we know it is not inherent in the circuit, or coming in via the source.

Should be quick enough to try.
 
If you like, I'll put my 323 K boards in the box with the other stuff. One needs repairing, but I bought another set already, so i don't need them.

Can be barter towards all the teddy regs and fleas you can put into my cd3(?).

Colin
 
Given my dearth of technical knowledge, I really shouldn't even be participating in this discussion. But, hey, it's the www so what the heck. At this point, I would make sure the ground loop isn't related to the source (in this case the Technics TT) or source(s)--if there is a CD player in the system. Can you substitute the Linn and see if the hum is still there?

And as long as I'm at it, have you tried a Dynavector phonostage? I know that would take the DIY fun out of it but I think it is a really killer phonostage (waaay better than a stageline, imho--not sure about prefix). And pretty cheap on the used market (or even new).
 
PigletsDad said:
Neil,

Try my battery suggestion - if the noise is there when running off batteries, it is nothing to do with the PSU or earth loops involving the PSU. If it goes away, we know it is not inherent in the circuit, or coming in via the source.

Should be quick enough to try.
Click to expand...

Well I finally hooked one channel up to 6 PP9s - and the hum goes away...so I guess that makes it something to do with the power supply/grounding...is this progress?
 
Have you looked at your power supply on a scope? Maybe a bad filter cap just after the rectifier?
 
neiljadman said:
Well I finally hooked one channel up to 6 PP9s - and the hum goes away...so I guess that makes it something to do with the power supply/grounding...is this progress?
Click to expand...

Sigh, helps slightly.

If it hadn't gone away, we would have known it was something to do with the TT, or direct pickup. As it does go away, I think we can split the problem into two parts:

Either, the hum is coming in on the power rails,

Or, it is an earth loop.

If you have the batteries still to hand, try powering one channel with the batteries, while using the mains supply on the other channel, and the normal interconnection between the channel earths. I would expect the usual hum in the mains channel; the battery channel has the same earth connection, so will hum if it is an earth loop, but be quiet if it is coming in through the power supply path.

Does this make sense?
 
PigletsDad said:
If you have the batteries still to hand, try powering one channel with the batteries, while using the mains supply on the other channel, and the normal interconnection between the channel earths. I would expect the usual hum in the mains channel; the battery channel has the same earth connection, so will hum if it is an earth loop, but be quiet if it is coming in through the power supply path.

Does this make sense?
Click to expand...

It does make sense - only I have already tried two different power supplies and Paul has used his own - all with the hum - so I had mentally ruled out the PS since I thought it unlikely that all 3 were noisy.

  • Paul's supply was his regulated bench supply.
  • My supply #1 - a toroid, one of Hackers original boards with 6 x 2200uF/63v Nichicons
  • My supply #2, an old E-core with standard full bridge rectifier and 2 4700uF Nichicons

What are the chances that all 3 are noisy?

This was also reinforced by Paul's initial report:

I've got this powered up, and you might be entertained to know that there's significant 50Hz on the output. This is running from a regulated bench supply. I'm sure this is not a ground loop, and in similar circumstances a Naim 323 doesn't hum.​
 
My StarFish build was humming on one channel. Jim suggested a hum sniffer – a probe hooked up to a powered speaker. Once you find hum in your circuit, you desolder a connection in the middle and probe either side. Keep at it until you've whittled it down to something you just can't believe, and that's it. To make a very long story short, I finally tracked the hum down to a spurious connection between an interconnect socket and the case. I don't know what all that mains hum is doing on the case, but heaven help you if it gets into your circuit.

I can highly recommend the hum sniffer and doing a systematic dissection.
 
I'm baffled too; both the original build of this on 4 tiny boards, and the production version have very low hum levels in use. In fact the production version has the toroid for the pre-amp power supply mounted on the far end of the main PCB, only about 12 inches away from low level circuits.

How much 50Hz is there at the output; can you (or Paul) try tracking it back through the circuit?
 
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