Why arent all amps 2 ohm stable?

[johnk_10]

there are many amps today that have the same distortion specs at 4 and 2 ohms, so on those amps it doesn't matter. even on the ones that don't, their distortion specs comes into play when running them at full rated power, and since the power often doubles when switching from 4 to 2 ohms, having more power makes it less likely that you'll drive the amp to its limit. so in that the case, it's possible that you'd have less distortion running it at 2 ohms.

 

[Bob Lee (QSC)]

the bit about 2Ω operation creating more distortion with solid state amps is true (check any straight-up power amp spec sheet).

Any? Power amp spec sheets usually include only a simplified, perfunctory THD spec at one or maybe two load impedances. More descriptive distortion specs are actually the exception; I suspect it's because in most cases they would only prove their insignificance to the knowlegeable and confuse the others.

 

[Bob Lee (QSC)]

there are many amps today that have the same distortion specs at 4 and 2 ohms, so on those amps it doesn't matter. even on the ones that don't, their distortion specs comes into play when running them at full rated power, and since the power often doubles when switching from 4 to 2 ohms, having more power makes it less likely that you'll drive the amp to its limit. so in that the case, it's possible that you'd have less distortion running it at 2 ohms.

Distortion specs are not useful at full rated power, because that's the onset of clipping. True distortion specs are taken well below full rated power.

 

[BassmanPaul]

Another concern some (I) have is that for any design the lower the output impedance you run the higher the distortion level (SS amps). If clean sound is your bag you DON'T want to run 2 ohms.

Also due to the aforementioned heat concerns I don't like to run any amp at 2 ohms whether it is designed for it or not. Just my .02

I, on the other hand have no compunction running my amps into 2Ω. I've done it so many times I've lost count. If a modern well designed amp is designed to operate into 2Ω it will do so without problem. Yes it will generate more heat but the cooling will have been designed with that in mind. As for distortion, the difference in THD between operation at 4Ω and 2Ω will be inaudible.

 

[Thexawakening]

My best recommendation would to not buy cheap inefficient cabs and get something with much higher sensitivity. Running an amp designed for 2 ohms is fine. Barely noticeable distortion and you have more power on tap. The ampeg 7 pro has a very small, universally designed power section, and an OK switching power supply. If paired with something efficient and high quality, there's no reason to need more than one 8x10. Unless you want the look, then I would say buy a dummy cab. The SVT-810 was designed for the big 300 watt tube amp. Which you want inefficient speakers for, because you can get that grind without blowing them.

 

[dukeisdog]

Man, I love talkbass. You guys are awesome.

I was really set on the Ampegs, but I'm going to consider other cabs right now. Maybe I don't need a new amp. I really love this Peavey Tour 700, and it sounds great with my new Spector LX5. I'm gonna go out and try as many cabs as I can (most interested in the Mesa PH cabs) and see what I think. I'll bring my bass and my amp, and maybe I'll be able to figure out this situation.

 

[Korladis]

The 810 isn't designed to be inefficient. The whole point of the 300 watt SVT in the first place was getting clean headroom, not grind. The reason it was built was to get stupidly loud.

 

[TheNightLife]

Op. I would just save up for an svt cl. I own an svt cl and 2 810s and its not worth getting another 810. The svt cl on the other hand is definitly worth saving up for the things a monster and sounds great. I didn't notice much of a difference running mine at 2ohms with 2 810s either. Not enough to warrant purchasing another cab.

 

[B-string]

The 810 isn't designed to be inefficient. The whole point of the 300 watt SVT in the first place was getting clean headroom, not grind. The reason it was built was to get stupidly loud.

The original 810 was designed with a roll off of 80Hz (or cps in those days). All 300 watts projected (punch) instead of stage rattle. We were naked in those days, we didn't have 5000 to 25000 watt PAs to DI through. Thus the legion is born.

 

[Korladis]

Indeed so.

Most of the speakers of the day couldn't really do really deep lows at any appreciable volume, plus such frequencies take up power that could be better used for volume. The idea that it was purposefully designed to be inefficient so as to get a 300 watt tube amp to distort is silly, though. If you wanted the amp to distort, there were plenty of lower wattage tube heads around at the time.

The SVT came about for playing to large audiences in the days before everybody had a really good PA system. Both the head and the cab were meant to have the ability for very high volume.

 

[AlexanderB]

A lot of the "old school" boat anchor PA amps will power 2 Ohm loads without any problem. Since QSC dropped in, the RMX series comes to mind. I use RMX 5050 for medium duty 2 Ohm subwoofer use and it works great.
EBS also make a lot of conventional PSU heads with 2 Ohm capability.

A more powerful amp than the SVT would also give you more SPL out of that 810. Increased risk of speaker damage will follow...

 

[One Drop]

Indeed so.

Most of the speakers of the day couldn't really do really deep lows at any appreciable volume, plus such frequencies take up power that could be better used for volume. The idea that it was purposefully designed to be inefficient so as to get a 300 watt tube amp to distort is silly, though. If you wanted the amp to distort, there were plenty of lower wattage tube heads around at the time.

The SVT came about for playing to large audiences in the days before everybody had a really good PA system. Both the head and the cab were meant to have the ability for very high volume.

They did most definitely have distortion in mind as well when they designed the SVT. They wanted lots of clean volume and the ability to overdrive nicely, too. There's an interesting read in 'Ampeg: The Story Behind the Sound' about the designers' internal battles with the founder during the late '60s, and their desire to embrace distortion as a design feature rather than as a flaw, as Hull saw it.

 

[Bob Lee (QSC)]

A lot of the "old school" boat anchor PA amps will power 2 Ohm loads without any problem. Since QSC dropped in, the RMX series comes to mind. I use RMX 5050 for medium duty 2 Ohm subwoofer use and it works great.
EBS also make a lot of conventional PSU heads with 2 Ohm capability.

A more powerful amp than the SVT would also give you more SPL out of that 810. Increased risk of speaker damage will follow...

A lot of the "old school" boat anchor amps won't do 2Ω loads, too. And among amps with switch-mode power supplies, some do 2Ω and some don't.

 

[TheRealKong]

Why not looking for a used Peavey TMax? With it's tube in the preamp it is IMHO the best non-Ampeg Ampeg - sound I ever heard. BTW it's 2-Ohm stable.

I have a TMax, and an Ampeg SVP Pro, run into a power amp wit 2 x 700 W @ 4 Ohm, 2 x 450 W @ 8 Ohm, bridged it will deliver 1.400 W @@ 8 Ohm. So there is power enough. If pushed by the Gain-Knob and the Distortion-Knob the SVP Pro sounds verry nice. But the TMax sounds similar to the Ampeg. A nice, tubey tone with a lot of grind.

TMax has one knob for Pre-Gain and one for Post-Gain. You can push this lonsome little tube, a AX7, I think, so gently or so hard, it sounds like an real Ampeg.

For this price this is one possibility to get the tone - and goes down to 2 Ohm.

Last, not least: The Peavey TMax is IMHO the most flexible amp I found since I started playing 34 years before. Nice, warm Solid State - sound, and a tubey grind that is good enough to eat. It delivers 250 @ 8 Ohm, 350 W @ 4 Ohm and 500 W @ 2 Ohm. This is helpfull, because I run it with two Peavey TVX - cabs, one 410, one 210, both 4-Ohm. So I have a beautiful 610 full-stack with more flexibility than a SVT CL - but I have the Sound of a SVT CL - at a much lower ammount of money. Look on second hand market, you will find one shortly. 150 - 250,-- USD will be a good price.

Have fun everybody!

 

[Korladis]

They did most definitely have distortion in mind as well when they designed the SVT. They wanted lots of clean volume and the ability to overdrive nicely, too. There's an interesting read in 'Ampeg: The Story Behind the Sound' about the designers' internal battles with the founder during the late '60s, and their desire to embrace distortion as a design feature rather than as a flaw, as Hull saw it.

I sit corrected.

 

[derridiandrift]

I, on the other hand have no compunction running my amps into 2Ω. I've done it so many times I've lost count. If a modern well designed amp is designed to operate into 2Ω it will do so without problem. Yes it will generate more heat but the cooling will have been designed with that in mind. As for distortion, the difference in THD between operation at 4Ω and 2Ω will be inaudible.

Back in the 90s I had an SVT4-Pro and a pair of 4 ohm Eden D410XLT cabs. I was playing large venues, mostly outdoors, and I ran the amp quite hard. When I ran that amp bridged into both cabs (making the load 2 ohms), it sounded a bit more distorted than when I ran one 4 ohm cab from each side of the amp in dual-mono mode. After trying it both ways for many nights, I decided to stick with the dual-mono setup over bridged. Both sounded great, but the dual-mono was better. My experience seems to contradict what lots of people are saying about the difference being inaudible.

Maybe there was something wrong with my amp? Or maybe the sonic difference is simply related to bridging the amp, and not at all related to the comparison of 2 versus 4 ohms?

 

[georgestrings]

I *used* to think that 2 ohm capability was a big deal - then, I came to the realization that if you're going to bother to drag along 2 big cabs, it really isn't much extra effort to bring along a 2nd "slave" amp to drive the 2nd cab...


- georgestrings

 

[babebambi]

Bridging the 4 Pro into 2 ohm, you are running each side at 1 ohm

no wonder you would hear distortion :scowl:

 

[derridiandrift]

Bridging the 4 Pro into 2 ohm, you are running each side at 1 ohm

no wonder you would hear distortion :scowl:

No, that's now how it works. Two 4 ohm cabs in parallel is 2 ohms. Always. You can't get 1 ohm resistance from two 4 ohm cabs.

But the point is moot anyway because now that I think about it, I was describing the whole situation incorrectly.

When I used two 4 ohm cabs I would run each one from it's own power amp in the 4pro. It was only when I ran one 4 ohm cab (club shows) that I tried to figure out the difference between running that one cab from the bridged output, or from only one of the power amps in the 4 pro. That was the only time I ran it bridged, and I remember thinking that it wasn't quite as clean sounding.

 

[jastacey]

Why not looking for a used Peavey TMax? With it's tube in the preamp it is IMHO the best non-Ampeg Ampeg - sound I ever heard. BTW it's 2-Ohm stable.

I have a TMax, and an Ampeg SVP Pro, run into a power amp wit 2 x 700 W @ 4 Ohm, 2 x 450 W @ 8 Ohm, bridged it will deliver 1.400 W @@ 8 Ohm. So there is power enough. If pushed by the Gain-Knob and the Distortion-Knob the SVP Pro sounds verry nice. But the TMax sounds similar to the Ampeg. A nice, tubey tone with a lot of grind.

TMax has one knob for Pre-Gain and one for Post-Gain. You can push this lonsome little tube, a AX7, I think, so gently or so hard, it sounds like an real Ampeg.

For this price this is one possibility to get the tone - and goes down to 2 Ohm.

Last, not least: The Peavey TMax is IMHO the most flexible amp I found since I started playing 34 years before. Nice, warm Solid State - sound, and a tubey grind that is good enough to eat. It delivers 250 @ 8 Ohm, 350 W @ 4 Ohm and 500 W @ 2 Ohm. This is helpfull, because I run it with two Peavey TVX - cabs, one 410, one 210, both 4-Ohm. So I have a beautiful 610 full-stack with more flexibility than a SVT CL - but I have the Sound of a SVT CL - at a much lower ammount of money. Look on second hand market, you will find one shortly. 150 - 250,-- USD will be a good price.

Have fun everybody!

Another Peavey 2 ohm stable amp is the Pro Bass 500, it basically has the same power section, as the T-max, but it has a full parametric EQ, and it also has a 12AX7 tube in the preamp section, I just recently aquired this amp and have used it on a kinda loud Icehouse gig and was very pleased with the ability with the performance with a 2 ohm loading, these amps were designed when 4 ohm cabinets were the so called norm, so if you had 2 of them and you hooked them up in parallel the amp be able to handle the load