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[Mark Wilkinson]

In trying to learn a little more about speaker building and system design, I've been making some sensitivity measurements.

Been using smaart generated pink, and dialing in an amp output voltage as close as I can get to a 2.83v average reading made with a good fluke.
All works well, and measurements with a calibrated mic are all making sense.

Making sense except for.....on the PLD at idle, I get a constant 0.39v output from PLD channels,.......both with a muted signal to the amp, and even with input cables unplugged.
Meter says the freq is 396 khz.

PL amps in contrast, show 0 volts at idle as expected, with all conditions the same.

Any ideas why?  Thx,  mark

edit: probably should have added there is of course no audible output from PLD at idle....

[Ivan Beaver]

Making sense except for.....on the PLD at idle, I get a constant 0.39v output from PLD channels,.......both with a muted signal to the amp, and even with input cables unplugged.
Meter says the freq is 396 khz.

I think you might want to look at the freq again.

Is it a single freq?  Or Multiple freq?  Of course at that freq you can't hear it anyway and no loudspeaker can reproduce it.

I would not consider it a problem-if indeed that is the correct freq.

[Mark Wilkinson]

Thank you Ivan,

396 khz confirmed, single freq shown on scope
Checked two different amps.... same for any of the output channels whether run singly or parallel in combo...
One other maybe related puzzle ?...rms voltage reads 0.4 on voltmeter(189) and 1.3 on scope(fluke 123)

Like you say...can't hear it....no problem really..
Curious more than anything....

[Ivan Beaver]

Thank you Ivan,

396 khz confirmed, single freq shown on scope

Personally, I would not worry about 396Khz.

You can't hear it, the speakers impedance will be extremely high there so it won't be an issue.

[Josh Millward]

In trying to learn a little more about speaker building and system design, I've been making some sensitivity measurements.

Been using smaart generated pink, and dialing in an amp output voltage as close as I can get to a 2.83v average reading made with a good fluke.
All works well, and measurements with a calibrated mic are all making sense.

Making sense except for.....on the PLD at idle, I get a constant 0.39v output from PLD channels,.......both with a muted signal to the amp, and even with input cables unplugged.
Meter says the freq is 396 khz.

PL amps in contrast, show 0 volts at idle as expected, with all conditions the same.

Any ideas why?  Thx,  mark

edit: probably should have added there is of course no audible output from PLD at idle....

Considering the extremely low level and the very high frequency, I would expect that to be the switching frequency for the power supply in that amplifier.

I would expect it to be nothing to worry about.

[Steve Anderson]

I stumbled on this myself with another amplifier (believe it was a Powersoft M50)…

[Correction: it was a Powersoft X8]

There's a constant ripple 2Vp-p on the output at 192kHz. Here are two pics. First showing the actual ripple on it's own, the second showing the ripple superimposed on an audible signal

Interestingly, it's 4 x 48kHz. I wonder if the PLD is actually at 384kHz?

And wondering what the reasoning behind the power supply switching freq being a multiple of "the usual suspects" in audio freqs?

[Mark Wilkinson]

Interestingly, it's 4 x 48kHz. I wonder if the PLD is actually at 384kHz?

And wondering what the reasoning behind the power supply switching freq being a multiple of "the usual suspects" in audio freqs?

Yeah, Josh's switching supply explanation makes sense.

I was wondering along the same lines re "the usual suspects", but I keep getting 396kHz with different test instruments........?
Maybe switching freq in the powersoft is a  coincidental multiple?

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