question about power amps

[bobodechimp]

on power amps, you know pa types like a crown or what not, they have a gain knob. this gain knob, is that like the gain knob on a bass amp or is it more like the master knob on a bass amp. ie. does it limit the watts traveling to the speakers. thank you



knob

[bassbrad]

It is an input sensitivity or input gain control, those types of power amps are always running on full power. Some amps have limiters to prevent overload others do not.

[T-Bird]

Hi.

Originally Posted by bassbrad

It is an input sensitivity or input gain control

No, it's not. Not on any "pro" rack-amp anyway.

There are amps that can have their input sensitivity changed for different applications, but not many.

It's an input attenuator, that's why the numbers are usually "backwards", ie. from infinity to 0, not from 0 to 10.

Regards
Sam

[B-string]

Originally Posted by bassbrad

It is an input sensitivity or input gain control, those types of power amps are always running on full power. Some amps have limiters to prevent overload others do not.

Woa! PA amps do not run at full power all the time!!
Input control is just like a old MI amp without a master volume, your home stereo or car stereo. The more signal (turn the control clockwise) the more signal gets to the output stage. The louder the output, or more power is output from the amp.

[bongomania]

It absolutely does not limit the watts. I have to emphasize this because a lot of people have that misunderstanding.

What it does is control how much your input signal is multiplied. This control is located after the input buffer stage on the amp, so it also does not prevent the input from clipping.

[B-string]

Originally Posted by T-Bird

Hi.



No, it's not. Not on any "pro" rack-amp anyway.

There are amps that can have their input sensitivity changed for different applications, but not many.

It's an input attenuator, that's why the numbers are usually "backwards", ie. from infinity to 0, not from 0 to 10.

Regards
Sam

The graduations are calibrated in a db reference instead of 1 to 10. It serves the same function but is more useful to pro audio being referenced to a useful scale.

[bobodechimp]

so if beheriger is to be believed there i nuke1000 will put out 1000watts at 4 ohms into my 800 watt rms 1600 peak 4 ohm cab not pefect but safe and i would use my preamp then to limit the over all volume? making it 1000 quieter watts, well sort off

[B-string]

Originally Posted by bongomania

It absolutely does not limit the watts. I have to emphasize this because a lot of people have that misunderstanding.

What it does is control how much your input signal is multiplied. This control is located after the input buffer stage on the amp, so it also does not prevent the input from clipping.

I agree with this but with the control fully counter-clockwise no signal should get past the buffer, the output (wattage output) will be very close to zero.

[bobodechimp]

woh i just don't want to blow stuff up thats all

[bongomania]

Originally Posted by bobodechimp

so if beheriger is to be believed there i nuke1000 will put out 1000watts at 4 ohms into my 800 watt rms 1600 peak 4 ohm cab not pefect but safe and i would use my preamp then to limit the over all volume? making it 1000 quieter watts, well sort off

Check it: the amount of wattage your amp puts out is directly dependant on the level of signal you feed it. If you crank up every single knob on your rig, but don't play a note, zero watts come out of the amp. ...at least until it starts howling with feedback.

[Passinwind]

Originally Posted by bobodechimp

woh i just don't want to blow stuff up thats all

Just use your ears, not your eyes.

[B-string]

Your preamp should have input gain and an output control. The specs for the output voltage should be available in db (ie. 0.775v= 0db). Set the input on the PA amp switch to 0db (not +10 or +20) and the input control on the amp to 0 or slightly less. The output control on your preamp should then control the signal to the PA amp without risk of UNWANTED clipping.

[bobodechimp]

ok i was just afraid that i would not be able to limit the watts cause if it's 1000 watts full time it doesn't matter if my ear is saying hay that sounds bad if i can't do any thing about it. so what you are saying is to use the master on the pre to limit the total out put and i'll be fine

passinwind love your avatar

[B-string]

Originally Posted by bobodechimp

ok i was just afraid that i would not be able to limit the watts cause if it's 1000 watts full time it doesn't matter if my ear is saying hay that sounds bad if i can't do any thing about it. so what you are saying is to use the master on the pre to limit the total out put and i'll be fine

passinwind love your avatar

Yes the master on the preamp is the master to the PA amp. Just set the gain control on the PA amp to match your preamp's full output voltage and clipping at the power amp will not be any worry. Watts are only output if there is a signal getting through to amplify, Controls at full off (counter-clockwise) no power is output to the speakers.

[T-Bird]

Hi.

Originally Posted by B-string

The graduations are calibrated in a db reference instead of 1 to 10. It serves the same function but is more useful to pro audio being referenced to a useful scale.

Yes, obviously, but my point was that since the dial graduations shows a decrease clockwise, it's suposed to give people an idea that it's attenuation of the signal they're performing when turning the knob CCW, not decreasing gain, and the dial shows the level of attenuation, not the level of gain, not the master volume.

So in a sense (and in reality) power amps always run at full blast by design, it's the level of attenuation that determines the level of amplification to the signal.

Originally Posted by bobodechimp

woh i just don't want to blow stuff up thats all

Then just listen when the speakers start to complain and back down a bit.

In theory it's possible to damage a power amp with too hot a signal, but that would require quite a bit more juice than any functioning pre can give.

A power amp is nothing more than a highly regulated power supply, and can -and often is- obviously used as such. Power amps are not as fragile as people think, it takes a lot of abuse to eff one up.

Regards
Sam

[bobodechimp]

ya monster rig here i come now does any buddy know where i can get some free money?

[B-string]

Originally Posted by T-Bird

Hi.



Yes, obviously, but my point was that since the dial graduations shows a decrease clockwise, it's suposed to give people an idea that it's attenuation of the signal they're performing when turning the knob CCW, not decreasing gain, and the dial shows the level of attenuation, not the level of gain, not the master volume.

So in a sense (and in reality) power amps always run at full blast by design, it's the level of attenuation that determines the level of amplification to the signal.


Then just listen when the speakers start to complain and back down a bit.

In theory it's possible to damage a power amp with too hot a signal, but that would require quite a bit more juice than any functioning pre can give.

A power amp is nothing more than a highly regulated power supply, and can -and often is- obviously used as such. Power amps are not as fragile as people think, it takes a lot of abuse to eff one up.

Regards
Sam

I still disagree in bold unless it is a class A design. All others draw very little from the mains with zero signal to amplify. IF they ran all the time at full power your power draw from the mains would be VERY high with no signal (this in reality would be DC smoking speakers). Full power output with no AC signal = DC voltage and many unhappy owners. Class A operates differently yes but the net output is the same.

[bongomania]

Where you guys are missing each other is the fact that power amps can run at full potential all the time, not full power. That is, with the knobs all the way open, they have the potential to put out their maximum wattage. The gain knobs adjust the range of that potential.

[T-Bird]

Hi.

Originally Posted by bongomania

Where you guys are missing each other is the fact that power amps can run at full potential all the time, not full power. That is, with the knobs all the way open, they have the potential to put out their maximum wattage. The gain knobs adjust the range of that potential.

I blame my inability to express myself clearly with a foreign language, but then again that's always a handy excuse if one's not getting their message through on an international forum .

The way I see it, we're agreeing, just not seeing it due the aforementioned inability of mine.

There is however a distinctive difference between attenuation and gain in an amplifier circuit, to me anyway, and when people tend to get 'em mixed up, it always gets my attention.
I'm flawed that way .

Regards
Sam

[billfitzmaurice]

Originally Posted by B-string

Woa! PA amps do not run at full power all the time!!

Yes, they do. Even with the attenuator turned almost completely off it's still possible for the amp to be driven to full power if the output voltage of the mixer or pre-amp driving it is high enough. And that's why the position of the attenuator bears no relationship with how loud the amp can go and/or how much power it can produce.
The actual function of the attenuator is to allow matching the power amp input sensitivity to the output level of the mixer/pre-amp for maximum signal to noise ratio and headroom.