[sdiy] Flanger???

John L Marshall john.l.marshall at gte.net
Sat Jun 29 06:36:54 CEST 2002


Gene,

33 Volts RMS will be around 47 Volts peak and over 93 Volts peak to peak.
Your amplifier was clipping.

Triangle is an odd only series with the amplitude dropping by the square.
The phase of each harmonic also alternates. Something like f - 3f/9 +
5f/25 - 7f/49 ....

Many common power transformers are suitable from 50 Hz to 400 Hz and beyond.
The impedance seen in the primary is load dependent, square of the turns
ratio. Normal transformers are completely reciprocal. Turns ratio equals
voltage ratio. Turns ratio equals inverse current ratio. Power out equal
power in minus a small donation to copper resistance loss, eddy currents in
the core, and core hysteresis. At 60 Hz transformers typically have about 4
turns per volt. The low frequency limit depends on how much iron the
transformer is packing. As the frequency goes up eddy and hystersis  losses
increase.

Could the sound have come from the lamp filament?

You are on the right track. I did exactly you are doing many years ago and
it worked well. If I remember right, the amplifier was a kit from SouthWest
Technical Products. Walter (Wendy) Carlos did an article in Electronic Music
Review about a VCO that he built to control his large Ampex tape recorder.

Take care,
John
---------------------------------------------------------------------------
Pacific Northwest DIY Synthesizer meeting, July 20, 2002
See: www.sound-photo.com
---------------------------------------------------------------------------

----- Original Message -----
From: "Gene Stopp" <gene at ixiacom.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Friday, June 28, 2002 6:03 PM
Subject: RE: [sdiy] Flanger???


> Hi John,
>
> I suspect you're right - I suspect what I'm dealing with is amp clipping
> rather than triangle wave direction reversal stressing the amp output
> structure. I do remember that 120 VAC is something like 170V P-P on a
scope
> (is that right?). Therefore my 33 VAC needs 46V P-P on the scope, right?
> Should be well within the power rails of the amp running complimentary
> outputs (assume +/-40VDC). However there will be drops, as the output
> push-pull transistor junction goes thru a power resistor to the output
> terminal. Maybe I am hitting the rails more than I think.
>
> The harmonic series for a triangle is harmonic amplitude = 1 over the
> harmonic number squared, odd only, right?
>
> I think I forgot to mention that I "heard" the failure when it happened.
It
> was kind of a little buzzy zappy sound coming from the transformer when I
> turned up the frequency, at least I think it was the transformer - I
dunno,
> I'm used to sound coming from speakers.... Perhaps the transformer changed
> impedance when I deviated from 50-60 hertz, and this caused excessive
> clipping. I didn't watch the scope at the time frankly, I was watching the
> incandescent bulb to see how it liked the higher frequency. When it went
> out, I reactively pulled the plug.
>
> How close is a power transformer "tuned" to the intended mains frequency?
> I've never played with aircraft parts. Would the impedance go up, or down
> with frequency? I would think that it starts out very low (almost dead
short
> at zero hertz) and goes up from there, but does it go back down again?
>
> Best Regards,
>
> - Gene
>
> -----Original Message-----
> From: John L Marshall [mailto:john.l.marshall at gte.net]
> Sent: Friday, June 28, 2002 4:48 PM
> To: Gene Stopp; synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Flanger???
>
>
> Gene,
>
> The harmonic distortion from a triangle wave should not be a concern. The
> third harmonic is 1/9 amplitude of the fundamental.
>
> But, the amplifier must be capable supplying peak voltage which will be
some
> factor above the RMS voltage, for sine waves that will be square root of
> two.
>
> Have you ever looked the waveform of those cheapie voltage inverters that
> plug into the cigar lighter? Rectangular waves with dead zone. No
similarity
> to a sine wave, yet most electronics, including transformers and motors
work
> without complaining.
>
> Take care,
> John
>




More information about the Synth-diy mailing list