Subharmonics in Ampeg SVT?

[Steve Conner]

Hi all

The other day I was playing through an Ampeg SVT2 (the rack mount one with tubes and the graphic EQ) and I was wondering what gives the thing its nice growling sound when you crank it up. Not that my band ever let me crank it above 3 :(

Anyway, the sound reminds me of some experiments a friend was doing, with an analog synth filter that generated a subharmonic at half the frequency when it was overdriven. So I'm wondering if there's something about the SVT circuit that makes it do that too? Does anyone know anything about this?

Thanks

Steve

[David Schwab]

Anyway, the sound reminds me of some experiments a friend was doing, with an analog synth filter that generated a subharmonic at half the frequency when it was overdriven. So I'm wondering if there's something about the SVT circuit that makes it do that too? Does anyone know anything about this?

Yes it has an octave divider built in. It's the same as the the SCP-OCT Bass Octave Pedal:

http://www.ampeg.com/products/ampeg_pedals/scp-oct.html

[Steve Conner]

Surely there isn't an octave divider in the SVT2. I thought it was just the guts of the original SVT squeezed into a rack case with a graphic EQ bolted on. I looked round the back and there was a nice row of Sovtek 6550s, so I'm sure it wasn't one of the solid-state SVT Pro's (the SVT-5PRO does have the octave divider)

What I'm wondering is whether there's any quirk of the tube SVT circuit (like a too small output transformer with NFB round it driven too hard, or the iron cored midrange inductor maybe?) that makes it generate a bit of sub-octave at high volume, and whether the octave dividers in solid-state amps are designed to emulate that.

[David Schwab]

OK.. my bad!

Admittedly I'm not very familiar with Ampeg's current lineup... I'm just not a fan of their amps. I had remembered reading they had an octave divider in one of their heads, but I see it's in the SVT-5PRO.

Is it the SVT-2PRO? The one that looks like a Mesa 400+?

It's probably just some kind of harmonic distortion causing that effect. I know my Mesa get's that type of tone when you crank it up.

[Steve Conner]

The one I was playing was the old version of what's now sold as the SVT2 Pro.

http://www.lucan.nl/gitaar/gitaarplaatjes/ampeg-svt2-mesa-diesel-1516.jpg

It does look pretty similar to the Mesa Bass 400+. I wonder who copied who :confused:

I'm looking for ideas for a bass amp design of my own, and it was interesting to see the parametric EQs on Mesa's newer bass amps. I could never decide whether parametric or graphic is better.

[David Schwab]

I think the 400+ was out first. Mesa says they've been making it "for over two decades."

I think Ampeg was just making the regular SVT back then.. they came out with all the newer models more recently.

[Enzo]

I don't think putting a tube bass amp in a rack chassis constitutes copying. Ampeg SVTs in various forms have been around a lot longer than MEsa anythings. But really, a handfull of power tubes in a rack chassis, and controls/features suited to bass. How much different would they look?

[David Schwab]

I don't think putting a tube bass amp in a rack chassis constitutes copying. Ampeg SVTs in various forms have been around a lot longer than MEsa anythings. But really, a handfull of power tubes in a rack chassis, and controls/features suited to bass. How much different would they look?

Well that's true as far as rack mounting, but look at the two of them, and the control layout, where the EQ is and stuff. Personally they look the same to me. Then look at some of the other rack mount tube amps like the Sadowsky and Aguilar, and even the newer Mesa stuff ... they look totally different.