2. amps-preamps
  3. 152666-1458

Transformer coupled vs Capacitor coupled?

Guys,

I’m sure their are different schools of thoughts on these typologies but are transformer coupled better in terms of sound quality in regard to pre-amps.

Thanks,
Wig
128x128wig
atmasphere's avatar
atmasphere
11,851 posts
 
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.

wig's avatar
wig OP
1,274 posts
 
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 👍


bdp24's avatar
bdp24
9,861 posts
 
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.
georgehifi's avatar
georgehifi
10,312 posts
 
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.
I’m not 100% sure (please correct me) but I was told once, that was just to get xlr input and an output connections, but everything inside in the active tube circuit is SE (single ended) in between those input and output transformers.

Cheers George
bdp24's avatar
bdp24
9,861 posts
 

That is correct George. The EAR-Yoshino circuits themselves are single-ended, the transformers are just to provide balanced connections, as is standard in recording studios, where Tim does a lot of work (Roger Waters’/Pink Floyd’s studio in England being one such).

Roger Modjeski provides a balanced input (only) on his Music Reference RM-200 amplifier, but he told me he did that with discrete components, not transformers. The RM-200 is also a single-ended circuit.

Ralph Karsten’s Atma-Sphere designs are true dual-differential balanced circuits, as far as I know unique amongst currently-available tube amps and pre-amps.

I believe it is Ralph’s contention that balanced circuits themselves provide benefits over single-ended, Tim and Roger that balanced transmission is what they find of significant value, not the circuit itself. About that I may be mistaken ;-) --- Eric.

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