Volume on rack power amp?

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Gordo

Gordo

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I recently aquired a Marshall JMP 1 and 9100 monobloc amp. I was running the gain all the way up on the monobloc and using the jmp 1 output as a master volume. Is this ok or should I back the amp down. Another guitarist told me he does not recommend running the gain all the way up. Need some more professional opinions. Thanks
 
It seems like you'd be increasing your signal to noise ratio that way, I really don't know though...
 
I am just wondering where you guys run your power amp gain in you rack system. I guess i was kinda treating it like a pa power amp where you run all your power amps full up and use the board as your master.
 
Do whatever sounds best and/or has the least noise.

If you break it down into simple components, you're effectively comparing this:
Preamp -> Volume (cranked) -> Volume (low) -> Power amp

to this:
Preamp -> Volume (low) -> Volume (cranked) -> Power amp.

It looks pretty similar, doesn't it?
 
I run the master on my preamp and volumes on my power amp, both about half way. That's just what sounds good to me. Of course, I can never leave well enough alone. Ask me again in a month...
 
I didn't know if running the gain all the way up would be hard on the tube life. Just trying to get different opinions. Thanks
 
The only thing that really affects your tube life is the actual volume coming out of the amp.
It doesn't matter where the knobs are set.
 
whether its my Bogner Fish, soldano x-88r,or customshop Badcat preamp, they all go into my vht classic and 2150 w/ both power amps usually on at least 1-2 o"clock.....when you get those power sections cooking,its tone,tone, tone!
 
Sixtonoize":2crjcqrp said:
The only thing that really affects your tube life is the actual volume coming out of the amp.
It doesn't matter where the knobs are set.
Click to expand...

I wouldn't think so. I would think that if you crank your power amp you're working the tubes much harder, even if you then curb the output volume with another device or attenuator, whatever. Pushing the tubes harder is what makes the sound different than having your power amp on a low volume.

If that's incorrect, I'd love to know because I'm always hesitant to leave my power amp set at 10, and control volume elsewhere, just thinking of tube life and wear on the unit itself.
 
But if you're turning down the volume before it gets to the cranked master on the power amp, you're not really pushing the tubes harder at all.

If you turn down the volume on your preamp, you're still sending the power amp a very small signal, which gets amplified.
The fact that the Master on the power amp is cranked is meaningless unless the Master on the preamp is ALSO cranked. Unless you're using a device that comes after the tubes to control your volume (i.e. an attenuator), you're not driving you tubes any harder by cranking the Master on your preamp and controlling the volume in the preamp.

Now, using an attenuator is different than what the OP is asking, and that will definitely affect tube life.
In the OP, he's asking about the difference between using the Preamp's master vs. the Power Amp's master to control the volume...and in either case, the power tubes receive the same voltage which will drive them equally hard at a given volume.
 
Sixtonoize":1m6cs5pu said:
But if you're turning down the volume before it gets to the cranked master on the power amp, you're not really pushing the tubes harder at all.

If you turn down the volume on your preamp, you're still sending the power amp a very small signal, which gets amplified.
The fact that the Master on the power amp is cranked is meaningless unless the Master on the preamp is ALSO cranked. Unless you're using a device that comes after the tubes to control your volume (i.e. an attenuator), you're not driving you tubes any harder by cranking the Master on your preamp and controlling the volume in the preamp.
Click to expand...

But letting the poweramp Master volume at full throttle, regardless of how much signal is coming into it, would still affect the tone of the resultant signal, wouldn't it. Well at least it does sound a little different.
 
It's entirely possible that you'll get a different tone when you crank the Master on the power amp - after all, you're changing the input impedance of the following gain stage and are taking any bright caps (if they exist) out of the circuit.

However, this is not the same as "driving the tubes harder," like some people tend to think.
The only real way to "drive the tubes harder" is to make a LOT of volume (then, possibly, reduce it with an attenuator).

In the end, the only right answer is to do whatever sounds best.
 
Thanks for all the info. I backed the gain down a tad. Can't hurt to split the difference in opinion!
 
petejt":2eo2zolm said:
But letting the poweramp Master volume at full throttle, regardless of how much signal is coming into it, would still affect the tone of the resultant signal, wouldn't it. Well at least it does sound a little different.
Click to expand...

The master volume knob is usually just a pot positioned before the power valves.

Say you've got the output of your preamp putting out a signal of 16 volts peak to peak into the power amp, but the master volume is turned down so it's reduced to 2 volts. That means a signal of 2 volts is getting amplified by the power valves.

Or, you could turn down the output of the preamp so it's 2 volts peak to peak, and have the master volume turned all the way up so it doesn't reduce the signal at all. again, the signal getting to the power valves is 2 volts.

Either way, the power valves are getting a signal of two volts and amplifying it. They're not being worked harder one way or the other. But those two ways might sound different because the pot will impart its own tone on the signal, just like the volume and tone pots in a guitar.

That's my understanding of it, anyway. disclaimer: i don't know what the actual voltages are likely to be, I just made up those numbers
 
Your description is totally correct - the only things that are off are the voltages.
Most power amps are rated with 1v (line level) at the input, so it's more like you'd be sending .1v and .01v

But your description of how the system operates is 100%.
 
Sixtonoize":31321qo2 said:
Your description is totally correct - the only things that are off are the voltages.
Most power amps are rated with 1v (line level) at the input, so it's more like you'd be sending .1v and .01v

But your description of how the system operates is 100%.
Click to expand...

Cool cheers :thumbsup:
 
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