transformer buzz

[George R. Gonzalez]

This is a super-neat idea! I've tried tuning a piano with an
audio-generator and it was really hard!
Like I had to call in a REAL piano-tuner to clean up my mess!

But some questions come to mind:

#1: Why 200+ secondaries? You'd think you could get by with far fewer,
especially since one side of the strings are common.

#2: Why not a (well-shielded) switching power-supply? I guess weight is
not a major
issue if you already have a BIG piano.

Regards,

George

 

[eromlignod]

#1: Why 200+ secondaries? You'd think you could get by with far fewer,
especially since one side of the strings are common.

Well, possibly. The problem is the current involved. If I drive each
string at one volt and 2 watts, that takes 2 amps of current. No big
deal, right? But when I start grouping strings, the supply current
adds up to big-time juice in a hurry. I was hoping to keep currents
low by using a separate circuit for each string (or maybe for each
note...notes have three strings tuned in unison; that would only be 6
amps).

Of course, the ground line still has big current, but it is all one
line and doesn't have to be PWM controlled. So I can attach all the
secondary grounds to a copper bus bar and then connect it to the harp
with a heavy cable, or maybe just mount it directly to the underside
of the harp itself.

I am also hoping that since I don't have all that rectification
circuitry and big capacitors it might save some money. Custom-wound
transformers are getting more and more common.

Thanks to everyone for all this help. I'm an ME, so I get in over my
head sometimes.

Don

 

[Paul Hovnanian P.E.]

Guys:

I am designing a device that will be used in a musical recording
studio environment. It involves a transformer (1 kVA) that buzzes.
The primary is 120 Vac and there are several low-voltage/high-current
secondaries--about 2V @ 2A ea.

Is there a standard, reliable, simple way to eliminate this buzz?

Don

Use a switched mode power supply with an operating frequency well above
the audible range.