UTM 2572 vs OEP A187A15C in the Twin Line Amp

[Holger]

A quick, not very scientific comparison.

I finished a second dual channel tube mic pre based in Ian Thompson-Bell's Twin Line Amp.
I usually use the OEP A187A15C but had the idea to try something different, in this case the UTM 2572. Both are in the
same price range but the UTM is much bigger and not PCB mountable, at least not in a 1 RU case.

Both TX are similar regarding THD+N as well as Noise floor, slight advantage for the UTM maybe. We are talking about decimal points here.

Frequency response. First measured at mic level:

Both are fine.

Next line level:

Two things: in the TLA topology the OEP has a HF roll off that starts a bit too early for my taste. The UTM has a clear
ringing. This can be tamed with a 560pF strapped across the secondaries.

Conclusion: since the device is intended as a mic pre there is no reason to change the horse.

 

[ruffrecords]

Interesting results. I have noticed with the OEP that on mic input there can be a peak at 25Khz, a bit like the UML on line input but not as pronounced. I usually get a flat response with the OEP on line input but I will check to make sure. Both transformers are clearly sensitive to source impedance but in different ways but then most transformers are.

Cheers

Ian

 

[C12VR]

Is the UTM wired for 1:20 or 1:10? I assume by "mic" and "line" you mean 150 and 600 ohm, 1:20 and 1:10 respectively?

 

[Holger]

Sorry for any ambiguity. The UTM was wired 1:10. The part before the transformer is attached. When I refer to Mic the signal goes through the lower part of the schematic, Line goes through the other I/P. I used 4k3 instead of 3k3 there.

 

[C12VR]

Ah. If it's not too much bother it would be interesting to see if the response is fine 150ohm source into 1;20. thanks for your work so far! Very cool.

 

[Holger]

I'll probably see the device again next week.

 

[Clakejr]

Question do you know if you can use Telefunken type of tunes for this build?