balanced preamp

Thank You all for your helpfull replies.. I have tried my P.S.Audio PW DAC 11 via the Balanced out directly to the M.L.336 and was impressed with the results, I do not want to take a step back the First Sound pre does a lot of things right.. I have aways enjoyed a tube pre but find more solid state balanced pre in the market.
Atmosphere I am not sure if there is a dealer near me nor have I had a chance to hear one of your pre's

Kijanki, you are correct about the distortion product. However the less distortion is made the better. If you do the design right, the primary harmonic to show up will be the 3rd. If you don't, you'll have a mess on your hands :)

I don't find in practice that cost is much of an issue. If you are to build a world-class preamp, it will have to have good power supplies whether it is balanced or single-ended. All the things you have to do to make a single-ended preamp really work right cost about the same.

In practice I've not found your comment about gains being perfectly matched to be correct. I've seen minor differences that show up if you have unmatched tubes and the like, yet the CMRR is still quite good (there is a lot to be said for a good CCS design!). If the preamp were balanced but not differential then you might have a point.

Atmasphere, If preamps are balanced and differential then at the spot where summing takes place (input of power amp or speakers) common mode interference will appear as signal. For instance, if one leg has gain of 30 and the other gain of 30.3 than your gains are mismatched 1% meaning your CMRR is limited to poor 40dB and 1% of junk goes thru. We can take for comparison input module in my Rowland 102 with THAT1200 instrumentation amp (instead of transformer) with CMRR=85dB (DC-20kHz).

Many people like warm sound. Removing even harmonics might not to be to their liking. Main beef is with odd harmonics that are left intact (perhaps not big problem in tube amp).

In case of your amplifiers - power supply has to be way heavier while number of tubes and output transformers and expensive capacitors doubles, chassis gets much bigger etc. It should cost a lot more. Your amps are state of the art and might not meet objectives of typical person (most bang for limited bucks).

Kijanki, we don't have any output transformers so we don't have that expense anyway...

Is it me or is 85 db a poor CMRR figure?

Like I said a lot depends on an effective CCS circuit. I have to say I am quite surprised to see how poor they are in most differential circuits I see. Poor CCS leads to poor CMRR response! You can't do it with a single-stage CCS...

Atmasphere, 85dB is decent especially when you take into account effect of twisted pair rejection, in addition to shielding, in XLR cable. In order to match 85dB rejection in fully balanced amplifier gains would have to be matched to 0.005% - not possible IMHO.

I forgot, you have no transformers but you have a lot of tubes. Not only cost of tubes but they also require more power.