My new trannies try to be loudspeakers...?

[volki]

i jost got some 1:1 line o/p trannies out of a tab/telefunken distribution amp. they measure like +15dbu max - but in the area of +10db and up, they resonate acoustically. driving from a 40 ohms balanced load. should i be worried? :green: not that i'm completely worried, iimean, they do pass program material fine, even above +15db, but maybe, if they keep resonating, in the long run something could be damaged...

or is it that my scope presents too high a secondary resistance, meaning the secondary isn't loaded properly? hence i get power loss, resulting in physical movement of the trannie...?

 

[mcs]

Try to test again with a load. The 1M or 10M impedance of a scope isn't really a load.

Best regards,

Mikkel C. Simonsen

 

[PRR]

> in the long run something could be damaged...

No. Power distribution transformers sometimes "sing" 50/60Hz very loudly at high power for several decades.

Your other concern: does it affect the "sound"? I suspect it must. 100 Watt transformers with a small "sing", I don't worry. It is difficult/impossible to make the iron sheets and copper windings so rigid that they won't move a little under high electromagnetic forces. But I don't remember many transformers singing audibly at the 0.010 Watt level you are testing at. See if anything is loose and tighten bolts, shims, etc to stiffen it.

Loading should not matter except at the top resonance, typically 15KHz-50KHz. I would not worry much about a little 15KHz singing.

 

[Ian MacGregor]

I have had a similar problem with Sowter Neve clone output transformers. I never really got to into it, because the preamps sound great as they are. I did need to make sure the input and output xformers were physically placed far away from each other tho, or else I got some gnarly oscillation.

This brings up a question: Since most new gear that a mic pre will drive these days will have fairly high input impedence, should a dummy load resistor be placed across the secondary of the output transformer to make the output "see" 600 ohms or whatever? Of course this is would only be applicable for gear designed to drive 600 ohm loads. Any ideas?

Ian

 

[tk@halmi]

It must have something to do the way the transformer is driven as well. I was trying different discrete circuits on the output and got very different results. Some outputs made the transformer "sing" like a bird. Others would make it chirp only when changing gain very fast.

 

[Guest]

[quote author="Ian MacGregor"]
This brings up a question: Since most new gear that a mic pre will drive these days will have fairly high input impedence, should a dummy load resistor be placed across the secondary of the output transformer to make the output "see" 600 ohms or whatever? Of course this is would only be applicable for gear designed to drive 600 ohm loads. Any ideas?
Ian[/quote]
I remember this problem at MW transmitter, if they want use
OPTIMOD.
All transmitter gear was designed to 600 Ohm.
Optimod input was 47 kOhm symmetric.
Then someone put 600 Ohm resistor paralel to optimod input
and every was O.K.
xvlk