SVTs and 8-ohm loads

[LiquidMidnight]

The recent thread about 2x10s and impedance got me thinking about this. I didn't reply to the thread, but I'm pretty squarely in the camp of 8-ohm 2x10s making the most sense. Then I thought, "...with the exception of if you're playing an SVT through a single one." Now, ignoring the whole idea that it's pretty sacrilegious to be playing an SVT through a single 2x10 to begin with (), I think it does raise the question: How come Ampeg has never made tube SVTs that can handle 8-ohm loads?

Historically, my guess is that since the SVT was made to be paired with the 8x10 (or if you want to get technical, two 8x10s), it made sense for the amp to be able to handle both 4 and 2 ohm loads. However, there are a lot of 4x10, 2x12, and 1x15 boxes out there that are 8-ohms and are probably more than sufficient to cover the gig for most working musicians...which then leads me to wonder why Ampeg never made an 8-ohm all-tube SVT.

While I'm sure there are a couple other amps that we could think of, for the most part, the SVT is the only mainstream bass amp by a major manufacturer that I can think of that will not do an 8-ohm load. Does it have something to do with the output transformers used in SVTs? Is it just remaining true to the SVT heritage (no pun intended)? Is Ampeg marketing still branding the idea that the SVT will always be paired with a big, 4-ohm cabinet? Maybe Jerrod will stop by and give us the low-down (that pun intended).

Inquiring minds want to know.

[Downunderwonder]

Maybe they needed 8 in a box to make a decent noise and they were 8 ohm, so the cab had to be 4 ohm....

Or the transformer windings needed to be less for 4 ohm but thicker wire...

[B-string]

Most multi speaker cabs of that day were 4 ohm. Magnavox/Ampeg contracted for 32 ohm 10s to make the 810. It was not reasonable to expect any single speaker to survive that much power and as speaker's nominal impedance in those days were 8 ohms, it was not useful to provide a 8 ohm tap. That was the past anyway.

Why MTI then SLM and now LOUD Tech carries this on may be related?

[LiquidMidnight]

Like I said, I figured the reason they were originally a 2 or 4 ohm amp was because of the 8x10's impedance. What I'm asking is that now with a lot of loud, 8-ohm 4x10 options and such, how come Ampeg hasn't updated the SVT to handle 8-ohm loads.

Sorry if I wasn't clear about that. *lol*

[B-string]

It would require a new output transformer to be designed. No one wanted to fool that much with a proven, stable, iconic design?

[JimmyM]

Originally Posted by B-string

It would require a new output transformer to be designed. No one wanted to fool that much with a proven, stable, iconic design?

That's my guess. I don't know what it would take to do it, but if it screws with the tone even a little, I'm not interested.

[beans-on-toast]

Mercury Magnetics sells a repro vintage SVT output transformer with 4, 8, and 16 Ω taps for $400. It would be interesting to hear how it sounds.

[B-string]

Any MM I have installed did sound different than stock. Mostly guitar amps though which can be lacking in OT design.

[beans-on-toast]

I guess the question is different good or different bad? I expect a new transformer to sound like they did when they were new.

The SVT transformer is supposed to be an exact duplicate for the original. Or so they claim. I haven't used their products in a bass amp but I have in guitar amps. I like their output transformers.

[B-string]

Originally Posted by beans-on-toast

I guess the question is different good or different bad? I expect a new transformer to sound like they did when they were new.

The SVT transformer is supposed to be an exact duplicate for the original. Or so they claim. I haven't used their products in a bass amp but I have in guitar amps. I like their output transformers.

I don't know it would be interesting. I've also had great results with Magnetic Components transformers, but again guitar amps.

[LiquidMidnight]

This discussion of after-market OTs reminds me of a thread from a year or so ago where some guy was on here talking about completely rebuilding his practically brand-new SVT because his friend who builds guitar amps or something said that the stock components were junk. He was pissed off because the caps were from China or something like that. LMAO

Do you remember that thread, Jimmy?

[Downunderwonder]

I remember smart arses giving him a hard time over it but when he was done he inspired a well respected SVT restoration dude to have at it as well.

[JimmyM]

Originally Posted by Downunderwonder

I remember smart arses giving him a hard time over it but when he was done he inspired a well respected SVT restoration dude to have at it as well.

The resto dude was bassoballs, who works at Metro Amps, and had done a lot of SVT modding already. And the dude with the thread was totally judging it on looks rather than sound. While it's true that they use Chinese parts now, they still sound like SVT's to me. And quite honestly, the best mod they could have done with that SVT was practice but you can't tell them that. I did, however, talk myself into the Heyboer OT mod in my upcoming Heritage rig, but I practice enough already

[Downunderwonder]

Originally Posted by JimmyM

The resto dude was bassoballs, who works at Metro Amps, and had done a lot of SVT modding already. And the dude with the thread was totally judging it on looks rather than sound. While it's true that they use Chinese parts now, they still sound like SVT's to me. And quite honestly, the best mod they could have done with that SVT was practice but you can't tell them that. I did, however, talk myself into the Heyboer OT mod in my upcoming Heritage rig, but I practice enough already

Thanks, but my memory isn't so bad:

Originally Posted by Bassoballs

I ended up swapping out the caps in both the VR and 2-pro. I believe it was definitely worth the time involved. The big difference (post mod) was the increased low end response at higher volumes. When the amps would reach break-up, the low end was still very pronounced. I was quite curious as to how the new caps would react considering both of these amps had already been modded with a Metro/Heyboer OT, preamp mods, NOS pre tubes, and Winged=c= power tubes. The final result is two of the best sounding bass tube amps that I've personally ever heard. If anyone is in the Mid Michigan area, either of these amps are available for demo.

[JimmyM]

I think he could have turned up the bass knob and gotten the same result

Just kidding, Bassoballs! Sort of...

[Boot Soul]

I don't know why Ampeg doesn't offer an 8 Ohm tap on the SVT, like on the V4B. But there is a, sort-of, workaround. Many, if not most 8 Ohm multi-driver cabs (410, or 212) can be rewired to 2 Ohms. I rewired a Bag End Q10BX-D to be switchable from 8 Ohms to 2 Ohms, so I can use it with an SVT-II non-pro. A 2-pole, dual gang 15 Amp (or better) switch can be used - many options to choose from. The impedance of the tweeter is negligible and the tweeter sounds the same with the cab switched to 2 Ohms, as it does at the specified 8 Ohm load.

The Bag End is a completely different cab design from an Ampeg fridge, but it works very well with the SVT-II. The Bag End is an efficient cab, and this rig can get very loud. I never need to turn up to more than "3" on the volume.

[craig.p]

My guess regarding this no new transformer question is there'd be no return on investment when you figure in all the underlying costs of making the change.

[Downunderwonder]

Sometimes tone is worth chasing though.

[craig.p]

Absolutely, but I was referring to a decision by the Ampeg design team whether or not to change the transformer. Sorry, I should've been clearer.

[oboylebass]

Originally Posted by LiquidMidnight

The recent thread about 2x10s and impedance got me thinking about this. I didn't reply to the thread, but I'm pretty squarely in the camp of 8-ohm 2x10s making the most sense. Then I thought, "...with the exception of if you're playing an SVT through a single one." Now, ignoring the whole idea that it's pretty sacrilegious to be playing an SVT through a single 2x10 to begin with (), I think it does raise the question: How come Ampeg has never made tube SVTs that can handle 8-ohm loads?

Historically, my guess is that since the SVT was made to be paired with the 8x10 (or if you want to get technical, two 8x10s), it made sense for the amp to be able to handle both 4 and 2 ohm loads. However, there are a lot of 4x10, 2x12, and 1x15 boxes out there that are 8-ohms and are probably more than sufficient to cover the gig for most working musicians...which then leads me to wonder why Ampeg never made an 8-ohm all-tube SVT.

While I'm sure there are a couple other amps that we could think of, for the most part, the SVT is the only mainstream bass amp by a major manufacturer that I can think of that will not do an 8-ohm load. Does it have something to do with the output transformers used in SVTs? Is it just remaining true to the SVT heritage (no pun intended)? Is Ampeg marketing still branding the idea that the SVT will always be paired with a big, 4-ohm cabinet? Maybe Jerrod will stop by and give us the low-down (that pun intended).

Inquiring minds want to know.

OK, here's my take on it:

The Ampeg SVT is rated at 300 watts@4 ohms, although some heads have an impedance switch in the back allowing the user to run the head at 300 watts@2 ohms (switch between 2 & 4 ohms).

If you run an SVT at 8 ohms (an 8 ohm speaker cabinet) the amp will only put out approx. 175 watts (don't hold me to this). Thus, it is absolutely fine to use ANY 8 ohm speaker cabinet with an SVT.

My main gigging rig is an all-tube SVT2-PRO that I use with an older Ampeg 210 PRO cabinet (two ten inch speakers, 8 ohms). I have been doing this for years without any issues, and it's PLENTY loud enough.

Hope this helps.