Phono MC/MM who is running balanced?

rjm

Member
Paid Member
2004-05-02 2:41 pm
Kyoto
phonoclone.com
The wiring is the same whether to balanced or unbalanced, it's just the connectors that change.

A balanced phono stage has, all things being equal, a 3 dB higher noise floor.. for the simple reason that the input signal seen by the + and - inputs with respect to ground is only half the the full voltage, while an unbalanced input sees the full voltage. (each input has 6dB more noise (or 6dB less signal for the same gain, if you prefer), but some of that noise cancels at the output together with the common mode noise, end result +3 dB)

Where low input noise is the primary concern (and for a phono stage, it should be) unbalanced is the preferred circuit topology.
 
It's not even important to use different connectors, the standard RCA plug & socket works just fine as long as it's not earthed anywhere - if the electronics are fully balanced.

Our fully balanced RTP3D preamp has three phono inputs:

1. balanced XLR

2. balanced REDEL/Lemo, our house preference - simply the best sounding audio connector we have found

3/ a floating RCA socket which makes a perfect interface with 99% of good MC cart RCA equipped tone arms And even if the cable is a shielded unbalanced cable, as long as it's not grounded, I've never had any hum or other problems.

Regards, Allen
 

Bksabath

Banned
2007-12-01 11:21 pm
WoW started this tread couple of weeks ago and now loads of imput.
I have been running myne balanced for a while (LAC suply and passive RIA no caps on signal pat job whit silver revired arm)
Sound beter than what I had before but is one of those multy leghed critters job
so I was asking why not a balanced Pearl (may see Papa reply).

main advantages to me no noise from the input cables and just one resistor to adjust the gain

At present I am vorking on a balanced F5 but once done I was loking for a fully balanced set up.

Joachim Gerhard I am sorry I missed the Article can you drop me a link to it please?

Al
 
Bksabath, here is my original schematic. The version shown was for a very demanding customer so it has some very expensive parts in it.
What is not shown is the servo. For more details i sugest you do youself a favour and get you a Linear Audio Vol.0. That bookzine has a lot of other interesting articles.
The servo shown there works only when you transfer balanced into unbalanced at the output. I designed a new servo that holds the DC offset to less then 1mV, single ended and differentially and it will be published in a follow up in Vol.1 i hope.
As soon as we have stuffed the new PCBs and tested them, i will also publish the changes on my MPP thread. Jacco, thanks for the enthusiatic words. From my point of view it´s a classic.
P.S. concerning the noise, when i compare balanced to unbalanced, balanced has a 3dB noise disadvantage provided we use the same amount of input devices, BUT it is much more robust in terms of hum pickup, so in a realistic setup it may be less noisy overall.
 

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Bksabath

Banned
2007-12-01 11:21 pm
Joachim


Tank you for the schematics.

I regard to Linear Audio I can’t think of a better present for myself for Christmas just ordered and now I have to sit by the door.

Not that it will do any good as our Postman waits for everyone to go out before making a delivery

Tank you

I just had a quick look at the schematics have you tried THAT 1646 as balanced line driver

I will start to use them in the next couple of weeks but from specs look like the OPA1632 may be a better choice

So tanks for that pointer as well

Irakli

Tanks for the schematics

Jacco tanks for the link worked mighty well

AL