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Power Amp Question

Lazarus.Bird

Lazarus.Bird

Mr. Personality
Aug 16, 2010
10,577
1,367
Pittsburgh
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#1
So I've been digging and searching, trying to sell and swap gear to go from my SVT-3 to a similar amp that can run 2 ohms. I don't know why this never occurred to me before, and I don't have much power/pre amp experience so pardon my question, but couldn't I just use the Pre Amp Out on the SVT-3 into a power amp that supports a 2 ohm load and connect my cabs to the Power Amp, essentially getting the same sound but with more power options?

If this is true, can someone recommend me some power amps to look at? I've heard Crown is good but that's really the extent of what I know. I want something that can run two ohms and possibly send at least 500W+ to each 4 ohm cab, so I guess I'm looking for something that can do over 1000W at 2 ohms, correct?
 
#3
Yes, you can go out the " pre amp out " to a power amp and have more power. Some good power amps to look at are Crown and QSC. I've never run a power amp at 2 ohms, but some of them can go down that low. I actually use my MarkBass F1 as a preamp sometimes into my Crown XLS 1000.
 
#5
tearalong said:
You could do it that way, but it seems a way to carry around a lot more weight than you need to. The SVT-3 would weight a lot more than a preamp alone.
If you really look like your avatar, then that's probably not a problem.
Click to expand...

Haha. I'm not that big but close enough!

My two main reasons for doing this would be:

1. I absolutely love my SVT-3 tone and the only reason I'm trying to sell it is I want to run 2 4 ohm cabs.
2. I'm having a hell of a time trying to even sell my SVT-3 and need the money from it to fund a replacement.

Is the SVP essentially the identical preamp from the SVT-3, or will I get a different sound? I suppose I could try to hunt one down and pair it with a power amp.
 
#7
silvertones said:
Why don't you just rewire the cabs.
For instance if each cab has a pair of 8ohm 15 then wire each box in series. That'll make them 16 ohms and when you hook both up it'll be 8 ohms.
Don't need to buy anything
Click to expand...

While I have no doubt I could figure out how to do this, I don't have much knowledge in terms of actual cabinet tuning, construction, etc. I am using EarCandy BassBombs and Tim from EarCandy (who've I've had great support from) told me the speakers are installed using the spinning method and he highly recommends against opening the cabs up if they are working properly.

Plus I'd like to have the diversity to swap different cabs in and out without worrying about impedance. It seems it's a growing trend that lots of amps are now being created in such fashion that they can go down to 2 ohms.
 
#8
many stereo and mono power amps can run at 2 ohms (although the stereo ones cannot run at 2 ohms bridged) and yes you could use your current head as a preamp to drive it...

It won't give you exactly the same sound but it'll be relatively close. As I understand it, part of what makes the SVT3 sound so good is the use of driver tubes between the pre and poweramp which you will not be getting the benefit of if you use the pre out but like I said, it shouldn't be that big a difference...
 
#10
Why not buy a small PA amp and keep using the Ampeg to power one box? The external amp will be slaved from the Ampeg and one of it's channels can power the second box. At least one box will then benefit from the extra tube in the Ampeg drive stage...
Almost any smallish, no-name PA amp can get the work done. And it will not be more expensive than buying an Ampeg pre, I guess.

Additional benefit; the unused channel in your PA amp is a good backup for your band, or to power monitors or drumfill.

/Alexander
 
#13
Lazarus.Bird said:
Hmm. Interesting idea. I appreciate the suggestion.

When did they discontinue the Ampeg preamps? That's annoying.

Also, I'm assuming a power amp is a power amp is a power amp, but do I need to looking for anything "bass" specific when looking at power amps?
Click to expand...

Basically all power amps are the same, you just need "enough" power ... people will argue brands, but in essence you are correct.

The benefit of keeping your current amp is you always have a backup onsite! Yes its more weight .. if you want to go dedicated pre-amp, I vote Sansamp.

I thought the tube section of the Ampegs WAS in the pre-amp section, not the power section ... isn't that all solid state?
 
#14
The SVT-3 Pro has an entirely SS power amp section, yes. What makes the SVT-3 different is aside from its 3 12AX7 preamp tubes, it also has a 12AX7 and a 12AU7 as driver tubes. Son of Bovril stated he believed these driver tubes came into play between the pre and the power, which would make sense. As far as if they are actually used when the pre-amp out is used, I have no idea!
 
#17
Lazarus.Bird said:
The SVT-3 Pro has an entirely SS power amp section, yes. What makes the SVT-3 different is aside from its 3 12AX7 preamp tubes, it also has a 12AX7 and a 12AU7 as driver tubes. Son of Bovril stated he believed these driver tubes came into play between the pre and the power, which would make sense. As far as if they are actually used when the pre-amp out is used, I have no idea!
Click to expand...

Really, the final 12AX7 and 12AU7 drivers are part of the power amp in the most practical sense: if you plug a signal into the "Power Amp In" jack, it bypasses the preamp, but still goes through these last two tubes. The "Preamp Out" jack is the signal before it hits these drivers.

The solid state part of the power amp is a big bank of power MOSFETs that are nothing but current drivers - no voltage amplification of their own. The voltage gain is all in those last two tubes, and if you drive the power amp hard, they will saturate. The "Tube Gain" (or Plate Voltage, depending on the vintage) knob controls the way they saturate.

With all that said - based on experience with my SVT-3PRO, I think a lot of the good tone comes from the preamp. I've gotten some sounds very like an SVT (the classic all-tube one) cranked to stadium volume - straight out of the DI and into the recording deck.

So if I were in your happy situation with a nice sounding spare cab, I'd buy a nice powerful SS power amp for it, and run it off the Preamp Out of the 3PRO. Double the total power, double the speaker area, minimal expense, keep the SVT3 tone you love, what's not to like about that?
 
#18
I owned an Ampeg B5R and loved the tone, not tubes but i still liked it. I was 500 watts @2 ohms. I also own 2 4 ohm cabs, an Avatar B210 Neo and an Ampeg BXT115, so in order to get full 500 from the amp i always had to go full stack. I bought a QSC GX-7 power amp, 650 per side @4 ohms, so i ran the preamp out from the head to the amp and the each cab got 650 watts. So i had a choice of 1 or 2 cabs.
 

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