Transformer coupled vs Capacitor coupled?

Transformer-based volume control in a pre-amp is probably the best sounding kind. Implementation is king though. Transformers on inputs/outputs bring system-wide benefits in terms of isolation from common-mode noise that capacitors cannot give.

wig
Transformer coupled vs Capacitor coupled?

So long as the stage before is good in design low output impedance and has more than enough current and all your doing is stopping any dc offset, then a good cap is far better than a good transformer that will always have coloration’s.

But then doing a dc servo instead and having it all dc coupled, is then better than both.

Cheers George

The problem with transformers is bandwidth. Usually in a preamp level situation their bandwidth can be fairly wide, but to prevent phase shift in the audio band the bandwidth of the preamplifier circuit has to be from 2Hz to 200KHz and even in smaller sizes this is tricky for a transformer to do. But its not tricky at all for a coupling capacitor as long as the timing constants have been taken care of around the capacitor.

As George has pointed out, it is also possible to direct-couple. The trick with direct-coupling is the servo circuit has to have good stability.  Many don't and so 'hunting' (oscillating around the correct value) can be a problem. Servo theory is a field of considerable girth bit if a servo is done properly there's no going back to coupling caps or transformers.

Thank you all for your informative posts, I now have a better understanding of those designs and their limiting factors utilized for cost saving measures.

Wig 👍

Tim de Paravicini uses transformers on the balanced/XLR inputs and outputs of his EAR-Yoshino 868 and 912 pre-amps, but of course not on the RCA's.