Suggestions for really good attenuating input transformers

[etheory]

Hi there!

I am looking for opinions based on experience for a good input transformer that can attenuate 8.2:1 at least, more preferably something like 10:1 / -20dB or even better, close to -30dB as cleanly as possible, with a 10K input impedance, or there abouts, and a wide-full frequency range, when loaded on the secondary by either 10K, 1K, or 100R, or something around that value, possibly as high as directly to the input of an opamp too (i.e. effectively infinite input impedance, or "freaking high").

Any suggestions?

The best I can find, and will probably buy for testing seem to be:

Edcor: 8.2:1 - http://www.edcorusa.com/p/146/wsm10k-150
Edcor: 8.2:1 - http://www.edcorusa.com/p/159/xsm10k-150
Carnhill 12:1 - CA-18-VTB9072
Carnhill  - VTB 9072 - which can go to -21dB or -27dB but doesn't have the right impedance characteristic IMO for what I want to do, i.e. the input impedance seems too high for a line input.

The use case is the input of a new JFET compressor I am designing.
The prototype I have on my breadboard seems to want about 30dB input attenuation max for lowest distortion.
So I am thinking of knocking down a portion using an input transformer (with the benefit that it also balances the input), and then knocking down even further with resistive attenuation before the rest of the circuit.
Currently I have 10K/100R voltage divider at the input to get 100:1 and that seems to work OK. The less I can do there, the better the SNR I can achieve.

Anyone else have experience knocking an input signal down really far with an input transformer but retaining as much frequency response as possible?
If so any preferences?

cheers,

Luke

 

[CJ]

Jensen JT-10K61 use backwards with parallel sec winds,

8:1  20-20K  +/-  0.01 db

signal would have a nice 10K load, do not know if your fets would like the 150 ohm side,

 

[gyraf]

What is your application? Knowing that would help a lot...

Jakob E.

 

[etheory]

What is your application? Knowing that would help a lot...

Jakob E.

I know I'm rather verbose, but it's contained in the brain dump at the start of the thread.
Basically the input transformer for a jfet compressor design I've been working on. Most of the design is done, but I want to try switching from a front-end resistive attenuator to one done partly by a transformer.

Jensen JT-10K61 use backwards with parallel sec winds,

8:1  20-20K  +/-  0.01 db

signal would have a nice 10K load, do not know if your fets would like the 150 ohm side,

Luckily the 150R on the other side feeds the + input of a DOA.
The fet sits comfortably hidden under the - input.

So I think that should be fine actually.

Thanks for the suggestion, sounds great! I'll source one of those for comparison also.

 

[gyraf]

You would only really benefit from using a transformer IF you could use the increased current for lowering circuit input noise, which you can't in this case, as the fet needs a significant series resistor for attenuating anyway. I think you're best off with resistors - or trafo+resistor to go balanced.

Jakob E.