Voltage measurement at output stage

[Grey Owl]

Hi there all out in BFm land,
Some help for a poor pilgrim please?
How can I easily measure the actual true voltage output from my Carvin PA800 amp please?
Thing is, I can find no relative relationship between the amp voltage output and the number on the volume knob, if you know what I mean.
Some websites on the unit attached.
http://www.carvin.com/images/product/PA800C1.jpg
http://www.carvinguitars.com/manuals/PA1200.pdf
BFm topics frequently talk about output and transducer realationships so I would like some way of doing that.
My electronic skills are not great but I'm interested to find out in the interests of better sound.
I do have a multimeter if that helps.
Look forward to hearing from you.
Cheers
David
Ps: hot and humid here in New Zealand today. No rain for a month but I suppose at least it's not SNOWING

[Gregory East]

UR kidding! No rain for a month? We have had so much rain in Qtn the grass is GREEN. And a week back we got SNOW on the tops too ! Some summer, all good now though.

Back to voltmetering, this is something I've yet to get a complete handle on. So if I sum up what I know in a nutshell someone else can tell us if I got it all wrong, the beauty of the internet:

There's a standard reference output voltage for mixing desks and I forget what it is exactly. It rhymes with 1.83...2.83??? With the "normal" signal input your mixer, reading unity gain, 0dB,, spits out that reference voltage. A similarly rated amplifier is expecting that input voltage to achieve its rated RMS power output.

Some mixers put out more or less than the "standard" voltage with 0dB registering on their meter so be careful.

Crank the amp and see what voltage is being put to the speaker output with the cranked mixer being fed from a computer signwave at 40/50/60 Hz. Maybe not a good idea to crank the mixer too hard but if it's not peaking off the scale then you're probably safe.

WARNING, don't do that with a valve amp. They need the speaker load present or they make with the magic smoke.

[Gregory East]

Haha, I just looked at the jpg. Mixer amp allin1! So just crank it to before it shows the clip on the main out level.

[Bill Fitzmaurice]

Thing is, I can find no relative relationship between the amp voltage output and the number on the volume knob

There is none, the volume knob adjusts gain but not output, which is why a limiter is a necessity to control output.

[Gregory East]

Methinks Bill didn't look at the jpg either. I dunno how you'd even rig a limiter in that thing.

[Bill Fitzmaurice]

Methinks Bill didn't look at the jpg either. I dunno how you'd even rig a limiter in that thing.

With the limiter running on the pre-amp to power amp inserts. If you don't have that capability you can't limit.

[David Carter]

Methinks Bill didn't look at the jpg either. I dunno how you'd even rig a limiter in that thing.

Someone correct me if I'm wrong, but I think that's one of the down sides to powered mixers. You don't have any way of connecting all the external signal processing gear without bypassing the built-in power amps.

As for the original question of how to measure the output voltage, The easiest thing would be use your multimeter, a speaker cable, and some test leads with alligator clips on them. Plug the speaker cable into the 1/4" speaker out jacks on the back of the mixer (without connecting the other end to a speaker), use the alligator clips to connect the 1/4" on the end of the speaker cable to you multimeter probes (one probe connected to the tip of the 1/4" jack and the other to the ring of the 1/4" jack). You should then be able to see the voltage rise and fall as you raise and lower the volume on the mixer while playing a test tone.

If you've got someone to help you, you don't need the alligator clips. You could just hold the meter probes against the tip and ring of the 1/4" jack while the other person raises and lowers the volume.

[Bill Fitzmaurice]

Methinks Bill didn't look at the jpg either. I dunno how you'd even rig a limiter in that thing.

Someone correct me if I'm wrong, but I think that's one of the down sides to powered mixers. You don't have any way of connecting all the external signal processing gear without bypassing the built-in power amps..

If they don't have inserts you can use subs either. Self-powered is OK for small setups with no subs, but not for a major PA.

[Landl.livesound]

Methinks Bill didn't look at the jpg either. I dunno how you'd even rig a limiter in that thing.

Someone correct me if I'm wrong, but I think that's one of the down sides to powered mixers. You don't have any way of connecting all the external signal processing gear without bypassing the built-in power amps.

As for the original question of how to measure the output voltage, The easiest thing would be use your multimeter, a speaker cable, and some test leads with alligator clips on them. Plug the speaker cable into the 1/4" speaker out jacks on the back of the mixer (without connecting the other end to a speaker), use the alligator clips to connect the 1/4" on the end of the speaker cable to you multimeter probes (one probe connected to the tip of the 1/4" jack and the other to the ring of the 1/4" jack). You should then be able to see the voltage rise and fall as you raise and lower the volume on the mixer while playing a test tone.

If you've got someone to help you, you don't need the alligator clips. You could just hold the meter probes against the tip and ring of the 1/4" jack while the other person raises and lowers the volume.

If I am seeing the picture correctly, it appears to have line level inserts right before the main outputs. So theoretically you could put insert whatever you want there and get the signal back in before the power amp stage. So I guess you could build/use an insert cable to insert a limiter/EQ/DSP or whatever and then the signal could go back in right before the power amp stage. I guess you could always take the signal out of that insert and never let it go back to the power amp. It won't be balanced so you will lose 6dB that would be at a regular output of a console, but it seems like it could be done and you wouldn't have to ever return the signal back to the internal power amp.

Practice safe sound and there is no reason for limiters as long as you know and understand your system, so I wouldn't beat your head to a wall trying to set limiters, because you will most likely not be able to set them that well at all. (I don't personally have what I would consider the *right* limiters to truly "protect" my system. And if you size you amps appropriately there is especially no need for a peak limiter, which is what most limiters we see would be.)



Here is a good paperhat helps explain the basics and why I've found "basic" limiters in really world practice to be little to no use since they either act as a warning sign for you to not push any more level to the amps. So they start squashing the signal, therefore raising the average level and getting closer to where VC will burn out anyway. While making it sound like "poo" cause it is squashing all the dynamics out of the music as well.

http://campuspa.com/downloads/Loudspeak ... entals.pdf


Anyway, just some musings,

Take Care!