I'm REALLY hearing the transformer!! Literally...

[Ian MacGregor]

Ok, so I've got this Neve mic pre clone that I'm working on. The board is my own design, but is pretty much a BA283. The transformers are the Sowter versions of the input and output.

Anyway, when I'm on a reasonably high gain, I can hear the test tone coming from the preamp! It seems that I am hearing the output transformer. Is this normal??? The preamp is not connected to anything else that would produce sound. Just a sig gen and a scope. Any ideas??


Ian

[PRR]

> I am hearing the output transformer. Is this normal???

Yes. Transformers and capacitors are terrible loudspeakers, but they do speak.

[owel]

You're not alone. At loud gain settings, I can hear music/test signal coming from my Neve transformers.  It's sort of "disconcerting" . It's like listening to a faint AM radio.

[Svart]

sure those aren't your teeth fillings?   :green:

[owel]

No, I'm sure. I'm a toothless grandpa  :shock:

[mcs]

I can "hear" my old HP signal generator at certain frequencies also...

Best regards,

Mikkel C. Simonsen

[zebra50]

And my Altec compressor clone sings at certain frequencies - I always figured it was the tubes.

[CJ]

The windings are probably not impregnated, which is good.
Or it might be the lams, but I doubt it.

[owel]

The windings are probably not impregnated, which is good.
Or it might be the lams, but I doubt it.

>The windings are probably not impregnated, which is good.

Can you explain why it's a sign of a good transformer?  

Mine are Carnhills, BTW.

[CJ]

There seems to be a desriable effect, possibly a mechanical derived feedback, from leaving the windings partially free to move. At least in most of the vintage iron, this seems to be the case.  If a conductor moves thru a magnetic field, there will be a voltage induced. So if a transformer winding moves slightly at an upper frequency, there might be enough displacement to cause a slight voltage shift in the reverse polarity of the main voltage induced in the winding. I am no expert on this, but am researching it as time permits.
cj

[Ian MacGregor]

On a side note:

When I first had the preamp setup on my test bench, I had the input and output transformers relatively close to each other and I was getting a TON of oscillation. Now that I've moved them apart, it gets better. Is this normal? Aren't the transformers really close in a Neve Module??

Ian

[MikoKensington]

I can hear my HP 200AB when it's turned on.  Such a frisky thing, it is.  I was weirded out when I could hear a sweep without it plugged into aything.

[tommypiper]

...I can hear the test tone coming from the preamp! It seems that I am hearing the output transformer. Is this normal???
...Ian

Yes it's normal.  I've heard it with a 1272, and a V76.  At the time I asked two friends with more experience and was assured it's normal.  The sound is "output transformer magnetostriction and capacitor vibration at high signal levels."  

One of them laughed, and said that's why the V76 has its transformers mounted on pads, to reduce microphonic effects, IIRC.

[tony dB]

this explains why i hear gtramps making noise when connected to a dummyload instead of a speaker.
I thought it were the tubes but could be them trannies too  :shock:

[clintrubber]

I recall to have heard somewhere someday that even transistors can make sound by themselves  - like an old TO-3 power device in an output stage. There will be relatively long bonding wires, but I can't really come to an explanation for this right now.

   Peter

[CJ]

everybody has heard 15,750 coming out of a flyback tranny, rite?
use to hear it at least...