Audio samples - Crimson vs Cinemag input transformers

[justinheronmusic]

The Crimson is the clear winner in this circuit IMO. It sounds as close as I could expect to any A-10 I've ever heard. I'll save the laundry list of subjective descriptors and just say it sounds fantastic.

I concur with you, Dan, that there is something slightly metallic in the mids of the Cinemag. I'm a Cinemag fan, but in this scenario it's not as nice as I'd expect.

And Justin Heron, I realized I never directly answered the implied question in your comment above: "The turns ratio of the Crimson and the Sowter I have are totally different, yet they still both work."

So while "any old transformer" won't work (or work well) as you can see from the simplified description of selection factors above, many will work acceptably well, even if not ideal for the front end.

Just realized that I never followed up. I wanted to say thanks for getting back to me. The transformer knowledge you and the others shared really set me on a path to learn even more about transformers. While I am still not sure how all the technical details would translate into fel and sound, it was a fun rabbit hole looking into the papers on Sowter's website.

Still debating on whether or not to swap out the Sowter for the Crimson input transformer. I have my (D)LA2A open here, trying to solve a meter problem - I can't get the meter to zero anymore.

When I swapped out the stock MIC transformer in my Chameleon Labs 581 for the Carnhill, it was a pretty clear and obvious difference, but that was going from a very inexpensive transformer to a really really nice transformer. The sound was much more free flowing and impactful after the swap.

To be honest I have never swapped a good transformer out with another good transformer, so I don't know that I would feel the same way - but the turns ratio alone would impact the tone, as would the make/model.

One this is for sure, my LA2A does not sound as rich, weighty, and syrupy as the first vintage LA2A I had heard, but it DOES sound very nice. Kenetek T4B, NOS RCA 12BH7, and Amperex Bugleboy 12AX7, Carnhill output transformer. I am debating if the Crimson is the last ingredient in the secret sauce, or if I can live without it.

 

[abbey road d enfer]

It was common in the 60s and 70s for manufacturers to use 1:10 mic input transformers with discrete opamp and BJT input stage preamps, despite the fact that in many cases a lower turns ration would yield lower noise. The "free" gain from the 1:10 step up was desirable, so that's what they went with. And noise performance was still acceptable.

The finest designers of the day knew how to tune their circuits to match the impedance of these transformers. Some ran their input device at about 20uA. The main reason for using the 1:10 xfmrs is that it was what allowed minimizing the input transistors Rbb', not so much the free gain.
Modern transistors have much lower Rbb', which allows using higher collector current, resulting in a much lower OSI, which in turn results in lower ratio xfmrs, that resonate (and roll-off) at a much higher frequency.