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Old 6th July 2011, 07:57 PM   #1
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Default How much overhead is required

I was playing the Verdi Requiem -- the "Dies Irae" is one of the loudest choral passages in memory -- decided to put it on the scope -- the result is about the same whether I use my cheappo Samsung player, or the high end Sony SACD player. The first 4 peaks are the tympani:
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Old 7th July 2011, 12:59 AM   #2
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Cool. My St70 manual indicates 1.3v rms in for 35 W out. 1.3X1.4=1.9v peak each way around zero. You're showing about 0.8 V peak, one way. This signal will need a little boost in the preamp to max out the ST70. My Pas2 has 340 V headroom on the low gain 12AX7 stage, my RA88a disco mixer has +-7.5V supplies on the op amp low gain stage. NO PROBLEM.
The signal I have to L-pad down is the reverb output of the H182 organ, it is about 8v PP.
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Old 7th July 2011, 01:14 AM   #3
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by jackinnj View Post
I was playing the Verdi Requiem -- the "Dies Irae" is one of the loudest choral passages in memory -- decided to put it on the scope -- the result is about the same whether I use my cheappo Samsung player, or the high end Sony SACD player. The first 4 peaks are the tympani:
I'm not suprised, why would you think it would be different ...?
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Old 7th July 2011, 01:29 AM   #4
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Music is incredibly dynamic.
I found my first amp designs didnt work very well as they clipped very quickly.
I learned to use higher voltage power rails to cope with the transients.
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Old 7th July 2011, 11:13 AM   #5
AndrewT is offline AndrewT  Scotland
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CD and other digital sources have a built in limiter. The output can never be greater than the analogue equivalent of 0dBfs.
Most CDP have an analogue output for 0dBfs of between 2Vac and 2.2Vac (~6Vpp, ~3Vpk). A test disc and a DVM will confirm the maximum outputs from your digital sources.

The only way to get higher than this is from interference being added to the audio signal. Just take action to ensure the interference is kept at a low and acceptable level.

The average level from CDP and digital can be set at any level below that 0dBfs.
Again, a DVM can measure typical music levels off any disc and allow one to compare them to 0dBfs. Some of the extracting software does this for you. Some software allows one to reset the average level so that all recordings can playback at similar levels. I have that facility in iTunes, but don't use it.
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Old 7th July 2011, 06:20 PM   #6
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. A test disc and a DVM will confirm the maximum outputs from your digital sources.
I'm glad you bought a serious DVM. My Sears 82195 is totally insensitive to music from the organ except at 50 and 60 Hz. 8 VAC signals out are totally invisible to the DVM. Most of the hobby repair people on organforum also find that inexpensive dual slope integrating DVM's are not suitable for testing their organ output or even worse, intermediate signals. I found a used 20 mhz scope much cheaper than one of the prestige brands of DVM's. The Fluke sales brochures linked to on WWGrainger Consolidated Electric Supply etc do not specify what frequencies their AC scale is sensitive to.
The fluke meter designed for the factory floor I had from work was incapable of seeing music frequencies.
By contrast, the Simpson analog 100kohm/volt meter with the 2 VAC scale, was quite useful for testing out the ST70 in 1976-84 before I dropped it.
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Old 10th July 2011, 01:16 AM   #7
jwb is offline jwb  United States
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What performance/recording?
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Old 10th July 2011, 02:17 AM   #8
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What performance/recording?
"You talkin' to me?"

It's track 3 of the Verdi Requiem "Dies Irae", on an EMI CD with Giulini in the drivers seat.

Another test using my test CD and the scope, @ -20dB FS is 254mV.
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Old 10th July 2011, 10:06 AM   #9
AndrewT is offline AndrewT  Scotland
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.....CD and the scope, @ -20dB FS is 254mV.
is that mVpk or mVac?
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Old 10th July 2011, 10:13 AM   #10
Bonsai is offline Bonsai  Taiwan
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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.
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