Why Single-Ended?

+1 Charles.

Regarding this comment in Kijanki’s post:

In order to provide good common mode rejection two halves of FULLY balanced amp cannot be independent. Negative cross-feedback has to be used to equalize gains of each half and that might be far from perfect.

With some fully balanced architectures the need for negative cross-feedback, or even any feedback, can be minimized or avoided. For example, Ralph’s designs employ an architecture based on differential stages, and are typically spec’d as using just 1 or 2 db of feedback. And in the solid state domain many fully balanced Ayre amps employ zero feedback, and I believe most or all fully balanced Pass amps use very minimal amounts of feedback.

Also, as stated in one of the papers at Ralph's site, "for a given number of stages of gain, differential amplifiers have about 50% more parts," rather than being closer to the equivalent of two single-ended amps that are otherwise comparable. Although with some other balanced architectures the parts count may indeed be close to double.

Best regards,
-- Al

almarg, thanks for the advice.

I have a pair of ISO-MAX PI-2xR converters I have used in the past, but it's a bit a kluge.  I hadn't thought to try converting just one side of the KUBE link to balanced -- a half kluge.

An alternative in the manual for the KEF 107/2s is to insert the KUBE in the tape loop of the preamp, but it's not obvious to me how that works.  The JC 2 BP does have a fixed output for recording but no monitoring capability.  I suppose that output could go to KUBE, but where would the output of the KUBE go?  If to one of the JC 2 BP inputs it would become the source.  

The manual for the Ayre phono stage (I use a JC 3) includes diagrams that seem to suggest converting an RCA plug from a turntable to a balanced input, but I may be misreading that.

Finally, the noise level of the system is low enough to be inaudible even with an ear pressed to the mid/HF driver.  My concern is maximizing sound quality of an excellent sounding setup, so maybe it's wild goose chase.

db  

Al, since I don’t see removal of even harmonics (while leaving odd harmonics intact) as an advantage, then the only thing that speaks for Fully balanced amp is better noise rejection in comparison to amp with True balanced input. Balanced input of my amp goes to instrumentation amp (THAT1200) that has CMRR of 90dB@60Hz and 85dB@20kHz. I don’t believe that it can be achieved without cross-feedback in Fully balanced amp. 90dB would be equivalent to overall gain setting (all stages) resistors matching to 0.003%. This cannot be done (be stable) even with multiturn trimpots, etc. Perhaps Fully balanced design offers better rejection at higher frequencies, but I doubt it - frequency response of both halves would have to be identical. 

Perhaps it is achievable using differential stages, but unless gain setting resistors are not on the same substrate stable 90dB does not seem possible.  Perhaps he is using very expensive matched resistors, but price of his amps justifies the cost of components.

I can hear the difference between different XLR ICs - perhaps Ralph was talking about matched 600ohm input/output designs that I’m not familiar with. In any case, it is valid for both True balanced and Fully balanced.
Again, I would buy an amp if it sounds good and not because it is Fully balanced. If anything, I would avoid fully balanced amps as too complex (too many parts to fail).

bdp2The Tim Paravicini-designed EAR-Yoshino tube circuits are all single ended, the pre-amps and power amps having transformers on the XLR/balanced inputs and outputs.

This brings up an interesting concept that I have been thinking about. In the case of a SE designed preamp, what would be the preferred way to send the signal to the amp; use unbalanced RCA cables, or go thru transformers with XLR’s which will be converting the signal back to single-ended? And depending on the type of transformer, the gain may be increased on the output, or it may be a 1:1 conversion. Seems like an unnecessary step.

But if the preamp was fully differential, then it would be advantagous to output a balanced signal to the amp’s XLR/balanced inputs.
Am I correct?

Converting single ended - balanced - single ended using transformers, makes sense if you have a lot of electrical noise and connection is long. Otherwise transformers won’t add anything positive to sound. They will introduce some low frequency distortions. If your preamp and amp are both differential you still might like single ended connection more. (my power amp has only balanced input - I had no choice).  XLR cable's shield is grounded on both ends shorting that way chassis and possibly creating ground loops.