Tiny Neutrik NTE10/3 transformer for microphone output 10:1 for tube and FET
- Thread starter ln76d
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Matador
Well-known member
ln76d said:There were for some time, over the web, some bulls**t stories about ccda circuits as it have really low impedances before the transformer, since it look like cathode follower etc. If someone will calculate impedance with online tube circuits calculators - yes it's really low but in fact it isn't. There is somewhere here my topic where PRR (if i remember corectly) made calculation for the output impedance. Impedance in the most of these circuits is rather high.
I tried in stock circuits low ratio transformers and the lowest which works well was 6.3:1.
I was hoping to mod some ccda to use 12at7 and 3:1 transformer but i couldn't go lower than 6.3:1.
Always sucks
Yes, the stock setup isn't biased very well, and these designs (stock) don't pull much idle current to keep the filtering simple. The output impedance is roughly 1/gm, but gm drops as a function of current. And the 270k resistor is probably much too high at these design points. So the actual output impedance is probably a few k (and I'm just spitballing here). It pretty easy to re-bias the tube up to around the 1 mA mark and then the output impedance would drop down below 1k.
However not so many people are running into real 600 ohm inputs either. Into a preamp of at least a few k, even the stock values aren't too bad.
RuudNL
Well-known member
It is not screened, so it will pick up a lot of hum in case there is a transformer in the neighbourhood...
orange4boy
New member
Would these work as mc cartridge step up transformers or are they too small?
Marik
Well-known member
It should "somehow work", but won't be an optimal choice, unless you have a high impedance cartridge (some 30 Ohm and up). The low impedance ones would need quite a bit higher ratio of some 1:30. From memory the NTE10/3 Pri inductance is somewhere 80--90H. This makes it more like a 20KOhm:200 Ohm transformer, which will need to be connected backwards. The 200 Ohm side is way overkill with high copper resistance and as a result added high noise level and not enough step up.
Best, M
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