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Old 10th July 2011, 09:16 AM   #11
AndrewT is offline AndrewT  Scotland
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I have a range of DMM with AC & DC ranges.
I can confirm that none of them are any good at reading transients. They make a half decent attempt at averaging the signal.
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Old 10th July 2011, 09:18 AM   #12
Bonsai is offline Bonsai  Taiwan
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Yes, that is my experience as well.
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Old 10th July 2011, 12:39 PM   #13
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Quote:
Originally Posted by AndrewT View Post
is that mVpk or mVac?
pk-pk

this was the "warbled 1kHz -20dBFS" test tone on the stereophile test CD.
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Old 10th July 2011, 12:52 PM   #14
Pano is offline Pano  United States
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Sorry Jack - not sure what you're trying to say here. Nor why you posted it in Analog source.
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Old 10th July 2011, 02:24 PM   #15
AndrewT is offline AndrewT  Scotland
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As I mentioned earlier 0dBfs is ~6Vpp.
-20dBfs should therefore be ~600mVpp.
It seems the DVM is seriously under-reading the peak voltages of that warbled signal.
Try a simple 500Hz sinewave at -20dBfs.
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Old 10th July 2011, 04:15 PM   #16
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Quote:
Originally Posted by Pano View Post
Sorry Jack - not sure what you're trying to say here. Nor why you posted it in Analog source.
It's a just a preamp question -- how much input voltage should the preamp front end be designed for -- my FM tuner is way down from the output of the CD player, so the CD sets the extreme.
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Old 10th July 2011, 04:16 PM   #17
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Quote:
Originally Posted by AndrewT View Post
As I mentioned earlier 0dBfs is ~6Vpp.
-20dBfs should therefore be ~600mVpp.
It seems the DVM is seriously under-reading the peak voltages of that warbled signal.
Try a simple 500Hz sinewave at -20dBfs.
I observed it on a TDS3014B.
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Old 10th July 2011, 04:22 PM   #18
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by jackinnj View Post
It's a just a preamp question -- how much input voltage should the preamp front end be designed for -- my FM tuner is way down from the output of the CD player, so the CD sets the extreme.
if the input to the pre-amp is the track of the volume attenuator then the power dissipation of the track determines the maximum input that the pre-amp can accept. I would expect a domestic listening pre-amp to accept at least 10Vpp (~3Vac) but I would aim much higher, capable of accepting 10Vac.

10Vac into a 10k pot results in a maximum dissipation of 10mW (10^2/10000=0.01W). Any half watt pot can easily accept 10Vac or even 20Vac.
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Last edited by AndrewT; 10th July 2011 at 04:25 PM.
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Old 10th July 2011, 06:17 PM   #19
Blues is offline Blues  United States
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Quote:
Originally Posted by Bonsai View Post
I would question the use of a DVM to measure AC music signals. I would suggest you use a scope and then take a look at the peak and calculate back from this.
The specs needed for a DVM to measure transient signals is for it to have "True RMS" AC voltage capability. The 2nd function needed is for it to have "Record Min/Max"...this capability registers the maximum transient signal at a preset time interval, otherwise you will be looking at an ever changing value or in other DVMs average value. Then Vpk=Vrms*1.414

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Old 10th July 2011, 06:42 PM   #20
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by jackinnj View Post
It's a just a preamp question -- how much input voltage should the preamp front end be designed for -- my FM tuner is way down from the output of the CD player, so the CD sets the extreme.
For a "digital" source such as CD the "overhead" needs be only what the CD can output when the disc is recorded at 0db. In simple terms, if the max level is 2 volt RMS from a particular player then the preamp will never ever be asked to handle more than that. It's cast in stone. 2 volt RMS is a typical level although some players do have more output.

All you need is a test CD recorded at 0db and measure the output from the player. If the frequency is low, say <400hz then any DVM will measure it.

As an aside to this, and many of you will have seen it,
So how much power do you really need for domestic listening ?
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