Re: Punch cards

On Tuesday 08 April 2008, Tim wrote:
[...]
The lastest thing to expend my time on has been restoring a 1960s or
1970s audio mixer (haven't quited figured it out), with all discrete
components (you could keep it going until it mechanially falls apart),
multi-tapped coil passive equalisation, P&G faders, and transformer
coupling everywhere. While playing, I discovered something I really
didn't expect - if you ground one side or the other of a floating
transformer output, the voltage across the output terminals changes.

Crude ASCII-art transformer cct:

signal source ----- || ------|
3 || E |
3 || E VU meter on output
3 || E |
3 || E |
ground ----------- || ------|

You get three different meter readings depending on whether you don't
ground either output terminal, or which side of the meter you do ground.
There's about a 2dB change. No, it's not grounded anywhere else, nor is
anything other than a passive VU meter connected to the transformer, and
I can't find any primary/secondary leakage. The sound source is a
symmetrical sine wave.

There's always something out there to surprise you.

In this case, I believe I would insert a transformer between the signal source
and your input transformer. I'd suspect something in the generator was
responding to the grounding of its output, particularly if the generators
output is an electronically balanced output without a transformer to isolate
it. Grounding one side will often cause a rise in the opposite sides output
because of the extreme levels of feedback in such circuitry.

If you still see that effect then, there is something bogus about that input
tranny. And since they are often wound with 40+ gauge wire, I would not be
willing to bet they are really good as little as 5 years later, due as much
to the solders amalgamation with the copper of so fine a wire, the failure
rate under those conditions is legendary.

--
Cheers, Gene
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If this is a service economy, why is the service so bad?

--
fedora-list mailing list
fedora-list@xxxxxxxxxx
To unsubscribe: https://www.redhat.com/mailman/listinfo/fedora-list

Relevant Pages

  • Microhm Bridge (Avtron T207)
    ... I have one of these that I picked up at a Hamfest probably ten years ago, and now that I am thinking of designing a DLRO I thought I would learn how this unit works. ... The panel consists of a transformer with three high current windings, one of which also passes through a smaller transformer. ... There is a metal shielded box behind the meter which contains two PC boards, having four 2N525 transistors and assorted resistors, capacitors, and diodes. ... I connected a DC power supply to the battery leads and when the voltage reached about 15VDC a lamp inside the plastic indicator for the dial started to flicker, and the current stabilized at about 100 mA. ...
    (sci.electronics.design)
  • Re: 3 phase - the ultimate irony!
    ... supply to my workshop and come back on Thursday to fit the meter. ... transformer on poles and had to dig a joint pit to make a join. ... lending them my 3/4 ton excavator. ... Well they were cheerful Irish contractors so it had to be Jameson! ...
    (uk.rec.models.engineering)
  • Re: Electrical Code question
    ... transformer to the inside panel main breaker. ... not even a meter to pull since my usage is ... needed a disconnect and he asked where the panel will be. ...
    (alt.home.repair)
  • Re: Design for my garage shop
    ... Here's a link to some pics of the "Two Meter Problem". ... you can indeed feed a transformer on the pole both ways ... ... it can be fed 120v and put 12,000 volt back in the transmission line. ... This is the major reason why, when feeding a house panel from a backup generator during a power outage, that a cut off is required. ...
    (rec.woodworking)
  • Re: Coupling coefficient of industrial transformers
    ... inductance meter, but are deriving the inductance of a winding from the ratio of ... Make sure that your meter doesn't measure true RMS AC+DC; ... If I put the appropriate air gap in the core of the transformer, ...
    (sci.electronics.design)