using a transformer for balanced to unbalanced conversion
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 3rd January 2007, 11:28 AM #1 h_a   diyAudio Member     Join Date: Sep 2006 Location: Graz, Austria using a transformer for balanced to unbalanced conversion Hi all! I'm thinking of using balanced connections from my cartridge (a MM) to the phonostage and converting the signal there to unbalanced (since that is what is used internally). Is it correct that I gain with balanced wiring +6dB voltage from the cartridge? That would mean double voltage?! But how's that possible? That would mean that the - signal is also used (instead of being connected to ground), ok then I should have +6dB. On the other hand the secondary of the transformer is again grounded and I do get the full voltage - so this should be true also for the cartridge which would mean that there is no double voltage then. Please help me out of this! Thanks a lot!! With kind regards, Hannes
 3rd January 2007, 06:55 PM #2 Steve Eddy   diyAudio Member     Join Date: Sep 2002 Location: Sacramento, CA There would be no voltage gain, assuming you're using a 1:1 transformer. The reason people have this notion of balanced somehow inherently meaning a 6dB voltage gain is because often what's done to create a balanced output is to send a single-ended signal to two amplifiers, one non-inverting and one inverting. That will give you 6dB of voltage gain over the single-ended output. When using a 1:1 transformer to do balanced to unbalanced or unbalanced to balanced conversion, the voltage out is equal to the voltage in. Ideally anyway. There will be some amount of insertion loss with any realworld 1:1 transformer, but that's beside the point. se
 3rd January 2007, 07:42 PM #3 phn   diyAudio Member     Join Date: Oct 2004 I'm as big a transformer fan as they get. But I would never use transformers is this case. Whatever pros there may be, I can't see them outweight the cons.
Steve Eddy
diyAudio Member

Join Date: Sep 2002
Location: Sacramento, CA
Quote:
 Originally posted by phn I'm as big a transformer fan as they get.
Oh yeah? I bet I'm a bigger transformer fan than you are! So there!

Quote:
 But I would never use transformers is this case. Whatever pros there may be, I can't see them outweight the cons.
Yeah. The cartridge's output is already balanced so there's no need to use a transformer to balance it, especially if it's just going to feed an unbalanced input at the phono stage.

An input transformer at the phono stage would be helpful for providing a good deal of common-mode noise rejection, but it would make cartridge loading a bit problematic.

se

 4th January 2007, 08:33 AM #5 h_a   diyAudio Member     Join Date: Sep 2006 Location: Graz, Austria Guys you got me wrong. I want to use the balanced output from the cartridge to the phonoamp and convert it then to unbalanced! That's the point the trafo comes in. However I do understand now that there's no voltage gain, in contrast to what I was repeatedly told by some manufacturer. Indeed Steve Eddy - thanks!! - explained what the manufacturer seems not to be able to!! What about cartridge loading? I just need to add the capacitors (MM needs them) on the primary side, from + to ground and also from - to ground, right? Since this would be a 1:1 trafo, the 47k on the secondary side will also appear on the primary - right? Thanks for all your help!! With kind regards, Hannes
 4th January 2007, 12:07 PM #6 pooge   diyAudio Member   Join Date: May 2003 Location: Northern Va. The phono cartridge is not necessarily balanced. While it may start off that way, one side of the coil may be connected to ground in the headshell.
 4th January 2007, 12:24 PM #7 phn   diyAudio Member     Join Date: Oct 2004 Lets say you add 50k:50k input transformers on the phono stage and add XLRs. Still there would be little to gain. And if you go this distance you can just as well get a step-up transformer insted of the 50k:50k one and a MC cart.
 4th January 2007, 01:13 PM #8 h_a   diyAudio Member     Join Date: Sep 2006 Location: Graz, Austria @phn: MC is not generally better, although highend-people believe so. What do you mean with 50k:50k? Trafo-impedance? I usually see values like 600Ohm for MCs or mics and 10k for line input? @pooge: yes you're perfectly right! In most cartridges at least 1 channel is balanced, the other - regardless wether it's MM, MC or something else - is usually connected to the cartridge's case. However even then the balanced solution should work, since the trafo sees double height + & GND instead of + & -?? Or I can isolate the cartridge from the tonearm, so there would be no connection to ground then. Of course the case is then electrically active and no longer grounded...do you think this would cause problems? Thanks for your replies!! With kind regards, Hannes
 4th January 2007, 01:49 PM #9 AndrewT   diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders Hi, some cartridges have a removable shorting link from one pin to the case/arm. __________________ regards Andrew T.
 4th January 2007, 02:19 PM #10 h_a   diyAudio Member     Join Date: Sep 2006 Location: Graz, Austria Which ones? Could you name some brands? I want to use a Shure and a Nagaoka cartridge. At least the Shure has a visible link from one pin to its case but it doesn't look removable. The Nagaoka hints about internal grounding in its operating manual. Do you think I would run into problems isolating the cartridge from the arm? It would become electronically active and would be no longer grounded. What do you think? Cheers, Hannes

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