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Author Topic: Where to find Sony C37 Output Transformer?  (Read 1588 times)

argibbo

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Where to find Sony C37 Output Transformer?
« on: May 31, 2014, 06:27:59 am »

Hi
Can anyone recommend a transformer to suit the Sony C37a cathode follower circuit please? I have built a mic based on the Sony circuit and used a transformer I had lying around. I now want to replace the unknown transformer with one optimised for this circuit.
Thanks
Andy
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klaus

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Re: Sony C37a transformer
« Reply #1 on: May 31, 2014, 10:36:59 am »

I'd contact Oliver Archut to see whether he has one in his assortment of retro transformers he offers (oliver@Tab-Funkenwerk.com), because to my knowledge no one currently makes a tube mic with cathode follower circuit.
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Jim Williams

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Re: Sony C37a transformer
« Reply #2 on: May 31, 2014, 12:02:16 pm »

The very popular Apex 460 tube mic does use the second tube stage as a cathode follower. The output transformer is a 4/1 ratio, not the 12/1 as used in C-12 designs.

With some circuit changes and a decent capsule, it's a rather nice sounding mic. Not too bad for the initial cost of $189.
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klaus

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Re: Sony C37a transformer
« Reply #3 on: May 31, 2014, 02:49:28 pm »

I have limited experience with cathode follower mics and transformers. Historically, aside of AKG's late-period tube mics, and a Sony here and there, these were the exception to the rule of at least 6:1, often higher ratios in plate pick-up circuits. 
And I could never tell much of a difference in sound when I experimented with different transformers in mics with cathode-follower circuits.

My question: do 4:1 or similar low-ratio mic level transformers show less of a sonic difference than the higher ratio ones typically used in classic mics? And is that because of the lower ratio between primary and secondary windings, and the relatively uncomplicated processing of such transformers?
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Jim Williams

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Re: Sony C37a transformer
« Reply #4 on: June 01, 2014, 01:16:00 pm »

In my experience, thd is lower with a cathode follower output and a lower ratio output transformer. A 6072 tube has a tough time with a 100 k output impedance driving the primary coils of the transformer, this is why a higher primary turns ratio transformer is used so loading is reduced. It's still a rather low DC resistance the tube is driving.
The Jensen DB transformer has been a favorite for decades in home-brew C-12 clones as it has the 12/1 ratio and a 140k ohm input impedance.

The cathode follower design is a much lower output impedance, it has the ability to drive a much lower transformer primary impedance without distortion. I hear that thd the low end, less 'fizz' and the top end is quite a bit clearer as well. Some may not like that change as the 'aural excitment' factor famous in C-12 designs is tamed.
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klaus

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Re: Sony C37a transformer
« Reply #5 on: June 01, 2014, 01:31:04 pm »

Thank you.
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Klaus Heyne
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