balanced to unbalanced conversion for musical instrumentamplification?

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Hello!
I use a transducer and preamp (from Schertler Corp.) for my double
bass. When I upgraded, the new preamp had only balanced out, but my
amp has only unbalanced in. A Radio Shack adapter works, but I don't
like the way it sticks out of the amp. I tried a cable connecting pin
2 of the XLR to the tip of the 1/4" jack. It sort of worked, but there
was huge attenuation which made S/N an issue . What I'd like to do is
mount a matching transformer inside the amp (Hartke) itself with a TRS
jack. Can anyone recommend a simple circuit using a transformer
commonly available from Mouser or the like? FR should be at least 30
to 10k Hz, and I'm hoping not to spend a princess's dowry.
Thanks,
Rob

[Eeyore]

wrote:

> Hello!
> I use a transducer and preamp (from Schertler Corp.) for my double
> bass. When I upgraded, the new preamp had only balanced out, but my
> amp has only unbalanced in. A Radio Shack adapter works, but I don't
> like the way it sticks out of the amp. I tried a cable connecting pin
> 2 of the XLR to the tip of the 1/4" jack. It sort of worked, but there
> was huge attenuation which made S/N an issue .

You mean you left pin 3 open ? That's why.


> What I'd like to do is
> mount a matching transformer inside the amp (Hartke) itself with a TRS
> jack. Can anyone recommend a simple circuit using a transformer
> commonly available from Mouser or the like? FR should be at least 30
> to 10k Hz, and I'm hoping not to spend a princess's dowry.

Provided they aren't centre tapped transformer outputs (and almost none
are any more - I last came across one several decades ago) or 'unservoed
types' you can wire a balanced connection straight to an unbalanced input.

Join the screen to the 'cold' / black / outphase / pin 3 signal and wire
to the screen on your input. Wire the 'hot' / red / inphase / pin 2
signal to the tip of your 1/4" jack.

Best to consult the manufacturer to make sure but decent gear works fine
like this. Do you have a model number ?

Graham

[bg]

wrote in message
>...
>Hello!
>I use a transducer and preamp (from Schertler Corp.) for my double
>bass. When I upgraded, the new preamp had only balanced out, but my
>amp has only unbalanced in. A Radio Shack adapter works, but I don't
>like the way it sticks out of the amp. I tried a cable connecting pin
>2 of the XLR to the tip of the 1/4" jack. It sort of worked, but there
>was huge attenuation which made S/N an issue . What I'd like to do is
>mount a matching transformer inside the amp (Hartke) itself with a TRS
>jack. Can anyone recommend a simple circuit using a transformer
>commonly available from Mouser or the like? FR should be at least 30
>to 10k Hz, and I'm hoping not to spend a princess's dowry.
>Thanks,
>Rob


If your output uses a transformer -
XLR pin 2 to the tip
XLR pin 3 and pin 1 to the sleeve
If your output is an active (ie opamps) or Z balanced (resistor in the low
side) -
XLR pin 2 to the tip
XLR pin 1 to the sleeve
Leave XLR pin 3 disconnected

The second option will put out half of the output voltage(6db down).
Good transformers are not cheap, so a 6db drop is nothing to be concerned
with if you can make it up with whatever you are driving.
I'd assume the radio shack transformer is an in line trans? You can always
get an extension cord so the trans doesn't stick out.

[Eeyore]

bg wrote:

> wrote in message
> >...
> >Hello!
> >I use a transducer and preamp (from Schertler Corp.) for my double
> >bass. When I upgraded, the new preamp had only balanced out, but my
> >amp has only unbalanced in. A Radio Shack adapter works, but I don't
> >like the way it sticks out of the amp. I tried a cable connecting pin
> >2 of the XLR to the tip of the 1/4" jack. It sort of worked, but there
> >was huge attenuation which made S/N an issue . What I'd like to do is
> >mount a matching transformer inside the amp (Hartke) itself with a TRS
> >jack. Can anyone recommend a simple circuit using a transformer
> >commonly available from Mouser or the like? FR should be at least 30
> >to 10k Hz, and I'm hoping not to spend a princess's dowry.
> >Thanks,
> >Rob
>
> If your output uses a transformer -
> XLR pin 2 to the tip
> XLR pin 3 and pin 1 to the sleeve

Fine.


> If your output is an active (ie opamps) or Z balanced (resistor in the low
> side) -
> XLR pin 2 to the tip
> XLR pin 1 to the sleeve
> Leave XLR pin 3 disconnected

Not always completely true in the case of a (servoed) op-amp balanced stage.
May work acceptably but with minor defects like non-flat frequency response.

Those manufacturers who simply use an inverting op-amp driving pin 3 deserve
to be taken out and shot.

Graham