carnhill vtb2291 wiring

I am using this as the output transformer for a tube mic pre.

What have I done wrong here?  I can scope a signal to the input of the transformer, but don't see it on the output.



Signal appears at pin 1 from the circuit output.  (this is a tube mic preamp)

This is the data sheet.  I am clearly not grasping something here

Hve you measured the resistance of the windings? Maybe a faulty transformer?

Is the output totally floating (ie. neither end connected to ground)?  If so, you'd need to connect the scope probe ground clip to one of the ends of the secondary, and the tip to the other end.

Transformers measure ok.

Pin 3 is connected to ground on the primary side.  I checked the output through a line input/interface so it’s not a scope issue.

The secondary isn’t grounded, is this my issue?

For it to work properly, you will need to load it with 600 ohms. So you could put a 600 ohm resistor across the secondary and then measure across that. But if you're just plugging it into a line input, you need to adjust the load to account for it being in parallel with the load of the line input. For example, if the line input is 10K, then you need a 638 ohm load. Although you could go a little higher like 680 or even 1K.

I’m not sure I follow.  I plugged a microphone into the input and the output into my interface.  I got nothing.  I got my scope out and I see amplified signal going into the transformer, but not coming out.

I am not sure I wired the secondary of the transformer correctly

> I am not sure I wired the secondary of the transformer correctly

Shrink the photo so we can see it. Flip/rotate to match the factory drawing. Crayon-on the wiring you have done.

You don't need a 600r load to "work", only to get the specs you were sold.

All four windings should work individually. Put some signal in 1-2, check what comes out 3-4, 5-6, 7-8. Some will be bigger than others, but they should all have signal.

Check the jack wiring? Are they XLRs? Is the line input balanced?

The signal will be attenuated by 12dB so maybe you just need more signal?

well, thanks for the help.  It turns out I should be nominated for "moron of the week" as I have a higher chance than usual of winning.

Turns out the XLR combo jack only handles TRS for "Line" signals on my UAD apollo interface.  I have this wired with XLR into my patch bay.

It works and sounds great!

I guess the only question is if I have wired it as intended (10K to 600 ohms) but I believe I did.  If so, for those of you in the future, here ya go!

rockinrob86 said:

I guess the only question is if I have wired it as intended (10K to 600 ohms) but I believe I did.  If so, for those of you in the future, here ya go!

Click to expand...

I think you did because both primary and secondary are wired in series and the datasheet says that is 9800:600. I use this same transform with the primaries in parallel for 2400:600 working.

Cheers

Ian