[sdiy] Flanger???

harry harrybissell at prodigy.net
Thu Jun 27 05:27:20 CEST 2002


Hi Gene...

Gene Stopp wrote:

> Powered down again. Checked everything. Powered up again. My scope was
> monitoring amp output on channels 1 and 2 (to show complimentary triangles
> plus any potential amp clipping), and things looked OK there. Still no AC on
> the lamp side, and of course no light.
>
> Took out the transformer and measured DC ohms on primary and secondary -
> about 0.9 ohms on secondary, and about 1 ohm on primary. I know I hosed up
> the transformer, but not sure why yet.
>
> Anyway, that was my excitement for the weekend... anybody have comments on:
>
> a) Are power transformers *that* sensitive to frequency when running at
> load?

Power transformers are prone to saturation... which could be from asymmetrical
drive... or from DC in the windings.  Usually 50Hz is not 'too' low... but
DC will kill them dead.  I'd be suspicious  of your 'quasi-bridge' mode on the
amp.
Try a resistive load on the bridge and look for DC... with the really low DC
resistance even a small offset will cause amps of current.

If the amp outputs are AC coupled this might not be a problem.  I would use a
resistor across the transformer primary (33V side you are driving)  The resistor
will
give some load for the amp at the frequency where the load is pure reactive...
and
also give a path for flux decay if necessary.

>
> b) Or did I just pick a crummy transformer?

Maybe ???

>
> c) It was about 4" cubic, so I would estimate in the 5-10 amp range. Is that
> too small for inverter purposes?

You are stepping up... so the 33V transformer is about 1:4 ... that is a 4 amp
load at the power amp side.   If you were in bridge mode... how much voltage
were you really putting into the transformer ?

> d) Any experience out there with driving power transformers backwards like
> this?

I've done this often. We step up 120VAC from an inverter (a bastardized sine
wave UPS) to 480VAC using a control transformer.  Using the 120V line as
a source we step up to any voltage using this technique... but always with the
right amount of primary voltage.

I don't think the triangle wave would hurt you much BTW...

H^) harry

PS... why not press a thumb on the reel flange for that "authentic" sound...
:^P

>
>
> Best Regards,
>
> - Gene

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