Setting Gain Structure with a Pre & Power Amp Setup

[rjc309]

I'm running a BMAX into a DCM1000 into a 610HLF.

If I understand correctly, my power should be fine as the cab is rated at 600 RMS @ 4 ohms and the amp is 1000 RMS @ 4 ohms. That should put me right in the 1.5x - 2x zone I've heard around here.

But in this set up how should I go about setting the gain structure?

I don't have the luxury of a clip LED on the BMAX and the Carvin only has channel clip LEDs that "flash when each channel has reached its maximum output".

Any advice is welcome!

[B-string]

Originally Posted by rjc309

I'm running a BMAX into a DCM1000 into a 610HLF.

If I understand correctly, my power should be fine as the cab is rated at 600 RMS @ 4 ohms and the amp is 1000 RMS @ 4 ohms. That should put me right in the 1.5x - 2x zone I've heard around here.

But in this set up how should I go about setting the gain structure?

I don't have the luxury of a clip LED on the BMAX and the Carvin only has channel clip LEDs that "flash when each channel has reached its maximum output".

Any advice is welcome!

You have heard this CORRECTED around here! It is not "safe".

[i_got_a_mohawk]

It shouldn't matter as long as you are sensible (and pay attention to the cab complaining if it does), but, a cab that can handle 600 watts RMS and an amp that can output 1000 watts RMS?

If you have a glass that can hold 600 ml of water would you try and fill it with 1000ml?



Anyway. You could just set the gain on the power amp near-max and control the volume entirely using the output from the BMAX.

[Mykk]

Well, I know my approach is far less scientific.

I would set the poweramp to max. Or perhaps 3/4 volume for protection (assuming you don't get any audible noise or hiss from the power amp this way) and the BMAX Master will act as the rigs master volume. If you get distortion at low volume, turn the BMAX gain down.

I ran an Ampeg SVT-IIP and a Crest VS1500 for years this way, worked great for rehearsals and shows. The Preamp would almost never get turned up past 1/4 master for ample volume.

[Bob Lee (QSC)]

A cab rated at 600W continuous, driven by an amp rated at 1000W continuous power, should be fine if you generally avoid clipping and don't use a lot of bass boost.

Regarding gain structure, set your pre to produce a decently strong signal with the input gain, and deliver a strong signal with the output or master gain. Use as much gain in the power amp as you need.

[audioglenn]

I'm with Bob on this one. Most of the time people blow speakers from not having enough power and the amp starts clipping. I don't know of any speakers that like square waves produced from clipping.

[Bob Lee (QSC)]

Uh, no. Loudspeakers don't care about square waves or other shapes.

Having not enough power is less dangerous than having too much.

[B-string]

Originally Posted by Bob Lee (QSC)

Uh, no. Loudspeakers don't care about square waves or other shapes.

Having not enough power is less dangerous than having too much.

Exactly.

[Bass_Pounder]

Originally Posted by audioglenn

I'm with Bob on this one. Most of the time people blow speakers from not having enough power and the amp starts clipping. I don't know of any speakers that like square waves produced from clipping.

Swing and a miss..............

[B-string]

I wonder if we are going there AGAIN??
We are in inning 1500 with this one?

[rjc309]

Originally Posted by i_got_a_mohawk

It shouldn't matter as long as you are sensible (and pay attention to the cab complaining if it does), but, a cab that can handle 600 watts RMS and an amp that can output 1000 watts RMS?

If you have a glass that can hold 600 ml of water would you try and fill it with 1000ml?



Anyway. You could just set the gain on the power amp near-max and control the volume entirely using the output from the BMAX.

That's a really good analogy, but where I get tripped up is the people who make the "glass" say it can fit up to 1200 "ml". How does this change things?

[Bass_Pounder]

Originally Posted by rjc309

That's a really good analogy, but where I get tripped up is the people who make the "glass" say it can fit up to 1200 "ml". How does this change things?

Easy...............

Disregard any spec that says "peak power" - They are BS

Want to get even more confused ?

The RMS ratings are thermal (point where the voice coil melts). It has nothing to do with mechanical abilities of the speaker. In many cases (depending on how heavy you EQ the low end) speakers hit their low end mechanical limit at around 1/2 the thermal rating.

[B-string]

If the 1200 ml is just given by the marketing department than it means nothing. Cabs are for the most part, but not by everyone, power rated at 1Khz. This has no bearing on the much lower power handling of any cab used for bass where the information we play is much more power demanding.

[rjc309]

Having spent time in both communities, it seems there's a lot of similarities between audio and fitness. Everyone has an opinion of what you should do, but there's rarely a steadfast consensus.

I mean that lovingly. I appreciate everybody's input.



So essentially there isn't an optimal signal level that should reach the power amp?

I think where I get tripped up is having three different variables that affect the overall volume.
It seems at least one or two should or could be fixed. Math was really never my strong suit though.

So my approach should be to:
- set the input gain as high as I can without distorting the signal
- fiddle with the master on the preamp until good things happen
- adjust the power amp output to a suitable level for the environment


Am I close?

[Downunderwonder]

That's the ticket. Essentially you're using your ears. The harder you can push each subsequent stage without overdriving it, the greater is your clean headroom aka dynamic range. Your cab is going to run out of puff.

[odineye]

Originally Posted by Downunderwonder

That's the ticket. Essentially you're using your ears. The harder you can push each subsequent stage without overdriving it, the greater is your clean headroom aka dynamic range. Your cab is going to run out of puff.

I always understood this scenario a little bit different. Not that I haven't been wrong before. But I always run my power amp wide open, the idea being that was leaving the most headroom, and working the master volume on the pre-amp to set whatever room volume was needed.

Though in the OP's case, I would run the power amp about 3/4, just to save over powering the cabinet.

[audioglenn]

I stand corrected. Sorry for the misinformation. Thanks, Bob!

[derrico1]

Originally Posted by rjc309

But in this set up how should I go about setting the gain structure?

A DCM 1000 into that Ampeg cab is a good pairing. (The 610HLF isn't the most sensitive cab but it will get loud, while the DCM is neither expensive nor terribly heavy, so carting a bit more power than you need in your rack isn't unreasonable.) You'll just need to listen for signs of speaker stress when you're pushing the cab hard. (It's rated at 125 dB max SPL, but I'd expect you'd be driving under the caution flag well sort of that level.)

With that much juice on tap, you just want to make sure the pre is hitting the DCM with a decent level of signal; you won't need to absolutely optimize the gain structure for volume.

Set the tone and processing in the ballpark. (I wouldn't have the comp or sonic maximizer acting on the signal, but YMMV). Set the BBE's gain for tone, but at least a couple notches below audible clipping. Bring the BBE's master up so that the Carvin's green "signal present" light is lit, but not so high that the amp's clipping LED lights. Bring the DCM's attenuator up to gig volume. (I'd do this slowly, just on principle. Unless your idea of gig volume is an outlier, you should find the DCM/610HLF rig gets you there safely.) Note that you might need to tweak your eq once you're at gig volume.

There's a school of thought that calls for running any power amp full-tilt, and adjusting the gain at the pre. However, I wouldn't recommend that approach when running a rig with considerably more juice than your stage volume calls for, and I suspect that you might find this rig in that category.

[odineye]

Originally Posted by Bob Lee (QSC)

A cab rated at 600W continuous, driven by an amp rated at 1000W continuous power, should be fine if you generally avoid clipping and don't use a lot of bass boost.

Regarding gain structure, set your pre to produce a decently strong signal with the input gain, and deliver a strong signal with the output or master gain. Use as much gain in the power amp as you need.

Like I said. "Not that I haven't been wrong before."

[audioglenn]

Odineye, I always thought the same thing as well. You are not alone.