Output power (voltage/current) meter with Paramounts

[Anton]

Hello,
Has anyone tried putting a meter on their amp to show output power? I think it would look pretty cool. Something like this
http://www.starmarinedepot.com/Blue+Sea+9353+AC+Analog+Voltmeter+0-150+Volts+AC.html
http://www.partsconnexion.com/CONNEX-75111.html

I couldn't find power meter, only voltmeter, but since voltage should be proportionate to the instantaneous power (as far as I remember) - this should work, right?
I just was wandering if anybody in the community tried it? And two subsequent questions:
1. Which meter did you use (I prefer analog one)?
2. How to connect it to the Paramount circuit?

Thank you
Anton

 

[Paul Joppa]

Power is voltage squared divided by resistance (the load); Paramount wired for 8 ohms would produce 8 volts RMS at full power with a sine wave. A true power meter would have to measure both voltage and current and compute the product - pretty difficult!

I would recommend a VU meter (look up the wikipedia article). They are not cheap, but they are an audio standard. They reflect the perceived loudness pretty well, and the averaging time makes them about as fast as the human eye can follow. (There are of course many other meters that measure different things - peak voltage, RMS voltage, average voltage, etc, and with different averaging times.)

A standard VU meter would read zero VU at 1.21 volts, which is 183mW at 8 ohms. The full 8 watts is 16dB greater. But on well recorded material with good dynamic range, the peaks will be around 14dB greater than the VU indication, so with a VU meter on such material, the amp will be close to clipping on peaks when the indication is above +2VU. On compressed material, or when overdriving the amp (most of us do that more than we think!) a standard VU meter will be pegged, so an attenuator ahead of the meter would be a useful modification in many systems. Note that for standardized ballistics the meter should be fed from a constant 3900 ohm resistance, so constant-resistance pad would be preferable to just a variable resistor - if you want to keep the ballistics.

There are many cheap meters called "VU" meters that don't meet the spec but can still be useful and fun.

 

[Anton]

Hi Paul,
Thanks for clarifying this for me.
I looked it up on eBay - the prices for VU meters vary and can go up to several hundred dollars.

http://www.ebay.com/itm/40pc-Panel-VU-Meter-TN-73-0dB-1-288V-76x59mm-LED-NISSEI-/140686799132?pt=LH_DefaultDomain_0&hash=item20c196311c

http://www.ebay.com/itm/Ampex-Burlington-Vintage-VU-Meter-Good-Condition-Works-Properly-/320921640012?pt=US_Vintage_Pro_Audio_Equipment&hash=item4ab86b9c4c

http://www.ebay.com/itm/TEAC-TASCAM-VU-METER-2-PIECES-/150909658254?pt=Vintage_Electronics_R2&hash=item2322eaa48e

Would you recommend any particular manufacturer or model? I am looking for something more or less compact (and not very expensive), I want to integrate it somehow into the Paramount (e.g. drilling a big hole in the side of the base and insert it in there). Any recommendation or advice would be appreciated

Anton

 

[Paul Joppa]

The last time I looked into this, we were thinking of making a dual-VU meter panel to match the high end Tape Preamp, for studio use. So we were looking at the $200 and up meters.

An ordinary level meter, such as the kinds used in tape or cassette machines, is probably good enough if you do not need a calibration to studio standards - i.e. you can trim its sensitivity to where you see useful things, and learn where it starts to overload in your system. These things are available from the usual electronics sources. I don't know if the cool-looking ones are still made by the classic meter manufacturers, but as said, they are not inexpensive. Used and caveat emptor are your best bets for those. Personally, I love the look of the small round ones!

 

[Paul Birkeland]

http://www.ebay.com/itm/40pc-Panel-VU-Meter-TN-73-0dB-1-288V-76x59mm-LED-NISSEI-/140686799132?pt=LH_DefaultDomain_0&hash=item20c196311c

Hmm, 40 pieces for $800 is a nice price, might be worth considering a group buy.  FWIW, you could use an inexpensive diode bridge to make power for the light on these from the filament winding on the Paramount (I'd get one in the KBL package and solder it right to the tabs on the meter to keep it secure).  Sadly though, these will be tough to mount into wood with how they are constructed; better to go with some round meters.

-PB