Balanced vs Single Ended

[TheDecameron]

I'm no engineer, but I believe plenty of designers produce balanced, zero-feedback circuits, like Charles Hansen of Ayre:
http://www.ayre.com/technology.htm

I have an Ayre P-5xe phono preamp that I run balanced in and out and it sounds noticeably cleaner, clearer and more dynamic in balanced mode than single-ended.

That is a formidable phono stage.

 

[sq225917]

Graham the first circuit isn't just a balanced circuit, it's balanced to single ended, not at all what we were talking about, but never the less. You could split that straight down the middle up until the output of the first op-amp and run either side as a +or- single ended circuit- ergo it's two circuits- with half the signal only going through each half, either above or below gnd. That actually confirms what i was saying.

The point you continue to miss remains the same as stated earlier.

 

[Arkless Electronics]

It depends on what knowledge of electronics you are referring too, and seeing that you have mentioned the soft smelly stuff on here a few times, plus farting in a lift I'm assuming you are from the Peter Sellers School of Electronics...

You know I'd expected better of you....

Your first example of course has lousy CMRR unless driven from a zero impedance source... and even then has virtually no CMRR as frequency approaches zero... I'll leave you to work out why G.T.

More interesting is that your second example uses exactly the same signal path as the first and with the same amount of active components..the first obviously has a variable gain stage after the input stage but that is irreverent as it could just of easily been applied to the second one.

Both use ONE op-amp in this configuration! it's basically (as an op amp is!) a long tailed pair being used with either one input grounded or as a true diff. amp... Absolutely no difference in the signal path as regards components!

Bit more CM distortion in the non inverting single ended layout of course.... but that's another story!

 

[GT]

Graham the first circuit isn't just a balanced circuit, it's balanced to single ended, not at all what we were talking about, but never the less. You could split that straight down the middle up until the output of the first op-amp and run either side as a +or- single ended circuit- ergo it's two circuits- with half the signal only going through each half, either above or below gnd. That actually confirms what i was saying.

Forget the SE output in the first circuit - I was using this to show twice the number of parts in the first stage so ignore the stage after the first op-amp.

Yes, you can spilt it down the middle as two circuits (both for + & -) as that is what true balance is: two independent circuits, one for the + part of the signal and one for the - negative part. Each part going through different active devices (for each part of the + & - wave forms) plus associated components with each active device. Regarding the number of active devices required (for both + & - signals): this depends on the design and the amount of gain required.

 

[GT]

You've not really chosen good examples. For example the first circuit implements phantom power, which mandates a balanced input.

Paul

I had assumed the phantom power would have been ignored seeing as it was just sitting across the input.

 

[Paul R]

I had assumed the phantom power would have been ignored seeing as it was just sitting across the input.

But the phantom power mandates the use of at least that trivially simple balanced input which is adding an extra passive component or two. I thought you might offer something like,

http://www.vacuumstate.com/images_upload/gross/rtp3c_s.gif

Paul

 

[GT]

But the phantom power mandates the use of at least that trivially simple balanced input which is adding an extra passive component or two. I thought you might offer something like,

http://www.vacuumstate.com/images_upload/gross/rtp3c_s.gif

Paul

Thanks Paul. I didn't have a lot of time last night to search for circuit examples. I was also trying to keep valves out of the discussion (FET input accepted on the Allen Wright design) but the circuit you have shown highlights the additional complexity involved.

Regarding the extra passive components on the first circuit: the coupling caps (C2 & C3) are normally included by most manufacturers in an attempt to protect the cartridge coils from any DC voltages (accepting phantom power was present on my example). One could remove these but at the risk of damaging the cartridge. Some MC cartridges like the Allaerts are extremely sensitive to DC voltages.