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Why arent all amps 2 ohm stable?

dukeisdog

dukeisdog

Aug 2, 2005
2,740
156
33
Victoria, British Columbia
#1
Recently picked up an Ampeg 810e, and have been running the cab with a Peavey Tour 700. I've been wanting to pick up another 810e (overkill, I know, but they can be had for cheap, so I figure why not?)

I know I'm going to have to replace my amp to run two of these cabs at once. I'm mainly looking at Ampeg amps, specifically the Svt 3 pro and SVT 7 pro. Why would they make amps such as the 4 pro, CL, 2 pro, etc 2 ohm stable but not the others?
 
#2
Not all designs can be.

Why aren't all amps 1 ohm stable? Because they're not.

The 2 pro is a rackmount all tube SVT. Its output transformer has taps for 2 ohms and 4 ohms, only. It can't do 8 ohms, IIRC.

The 4 pro has a solid state power section like the 3 pro, and 7 pro, but these heads likely had different design goals. It may not have been possible to make the 3 pro and 7 pro stable at 2 ohms without screwing up some other aspect of the design.
 
#3
It all depends on the amplifier topology used and the price point you are trying to hit with your product. We use a class A/B power section in our amp, which @ 2 ohms is generating a lot of heat that has to be dissipated. Dealing with that much heat required a lot of extra engineering, as well as costly components such as a larger heat sink, larger fan, an aluminum chassis and all kinds of protection circuitry.
 
#9
The output devices in a SS amp are loaded by the speakers (the lower the number the higher the demand (load) on the amp). Tube amps the output devices (tubes) are loaded by the output transformer (OT) primary, the OT secondary matches the speaker load to to the designed primary tube load.

^ What R Baer said!
 
#10
I guess I just find it crazy that Ampeg would make amps that arent able to run two 810e's. I had my mind set on the 7 pro, now I'll have to reconsider. I'd love to get a 2 pro, I'm just not sure if I could afford to drop almost $2000 on an amp, which is why the 7 pro looked so great. What other options do I have now? I really liked the tone of the 7 pro, and would like to buy another rackmountable amp... Maybe the best route would be a power/Pre setup?

Also, I know that Ampeg uses 32 ohm drivers in their 810e cab to get a total of 4 ohms, but why wouldn't they use different drivers so they could offer the cab in both 4 and 8 ohm configurations? I know that Mesa offers their cab in both, and I would almost always get an 8 ohm cab (unless I had a tube amp that couldn't take 8 ohms).
 
#11
dukeisdog said:
I guess I just find it crazy that Ampeg would make amps that arent able to run two 810e's. I had my mind set on the 7 pro, now I'll have to reconsider. I'd love to get a 2 pro, I'm just not sure if I could afford to drop almost $2000 on an amp, which is why the 7 pro looked so great. What other options do I have now? I really liked the tone of the 7 pro, and would like to buy another rackmountable amp... Maybe the best route would be a power/Pre setup?

Also, I know that Ampeg uses 32 ohm drivers in their 810e cab to get a total of 4 ohms, but why wouldn't they use different drivers so they could offer the cab in both 4 and 8 ohm configurations? I know that Mesa offers their cab in both, and I would almost always get an 8 ohm cab (unless I had a tube amp that couldn't take 8 ohms).
Click to expand...
The new 810s can be split into 2 separet 8ohm cabs. As for the 7pro, you could use it to power 1 810 and simply get a small power amp for the second cab;)
 
#12
dukeisdog said:
I guess I just find it crazy that Ampeg would make amps that arent able to run two 810e's. I had my mind set on the 7 pro, now I'll have to reconsider. I'd love to get a 2 pro, I'm just not sure if I could afford to drop almost $2000 on an amp, which is why the 7 pro looked so great. What other options do I have now? I really liked the tone of the 7 pro, and would like to buy another rackmountable amp... Maybe the best route would be a power/Pre setup?

Also, I know that Ampeg uses 32 ohm drivers in their 810e cab to get a total of 4 ohms, but why wouldn't they use different drivers so they could offer the cab in both 4 and 8 ohm configurations? I know that Mesa offers their cab in both, and I would almost always get an 8 ohm cab (unless I had a tube amp that couldn't take 8 ohms).
Click to expand...

Why do you need 2 8x10's????? You could always add a power amp.
 
#13
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

In addition the whole "I want to maximize my amps output by running at the lowest impedance it will run" idea is not really sensible as a doubling of output (seldom achieved through halving the load) only provides a 3 db increase in sound pressure. And this is only if compression or heat limitations don't soak up part of that 3 db. Overall not a very realistic way to increase volume, most people in this situation really need a bigger amp AND more speakers. Further the best way to get more volume out of your rig is to replace your speaker system(s) with models with higher sensitivity. THIS will give you more volume with out another amp.
 
#14
dukeisdog said:
I guess I just find it crazy that Ampeg would make amps that arent able to run two 810e's. I had my mind set on the 7 pro, now I'll have to reconsider. I'd love to get a 2 pro, I'm just not sure if I could afford to drop almost $2000 on an amp, which is why the 7 pro looked so great. What other options do I have now? I really liked the tone of the 7 pro, and would like to buy another rackmountable amp... Maybe the best route would be a power/Pre setup?

Also, I know that Ampeg uses 32 ohm drivers in their 810e cab to get a total of 4 ohms, but why wouldn't they use different drivers so they could offer the cab in both 4 and 8 ohm configurations? I know that Mesa offers their cab in both, and I would almost always get an 8 ohm cab (unless I had a tube amp that couldn't take 8 ohms).
Click to expand...

The SVT has taps for 2 and 4 ohms, which is perfect for using one or two fridge cabs.

Very few people play through two 810s thee days, it makes sense they would make the 7 Pro more affordable and still be able to appeal to a large potential buying public.
 
#15
grendle said:
Why do you need 2 8x10's????? You could always add a power amp.
Click to expand...

What year did Ampeg start doing that? My current cab is a 2001 810e, and although lots of people say that 01 wasn't a great year for Ampeg, I love this cab. I suppose I don't need two 810's, but I'm young, don't mind the weight, and see a lot of big cabs going for cheap now. I also love the look on stage, and would imagine that my bass would sound so clear with two of these cabs.
 
#16
#17
bassmeknik said:
Another concern some (I) have is that for any design the lower the output impedance you run the higher the distortion level. If clean sound is your bag you DON'T want to run 2 ohms.
Click to expand...

not true. if an amp is proprely designed to run at 2 ohms then it will have no more distortion than when it's running at 4 or 8 ohms. an ampeg SVT for example has a specific transformer tap for 2 ohms and runs just as well (and just as clean) as it does when it's running at 4 ohms.

i've run my SS crown power amps at 2 ohms all night long (5 hours continuous), as well as my little Yamaha BBT500H, my Eden WT550-B, my acoustic 370 and my acoustic 320. i've never had a problem running at 2 ohms with any of them.
 
#18
dukeisdog said:
Recently picked up an Ampeg 810e, and have been running the cab with a Peavey Tour 700. I've been wanting to pick up another 810e (overkill, I know, but they can be had for cheap, so I figure why not?)

I know I'm going to have to replace my amp to run two of these cabs at once. I'm mainly looking at Ampeg amps, specifically the Svt 3 pro and SVT 7 pro. Why would they make amps such as the 4 pro, CL, 2 pro, etc 2 ohm stable but not the others?
Click to expand...

I've owned a SVT CL ( which WILL run 2, 8-10s @ 2 Ohms) for a few years now, and have tried the Traynor 8-10 with it. Switchable from 4 ( mono ) to 8 Ohm (stereo). Awesome sounding. Unlimited 2 year warranty (even if you drop it off the Bus !!!), and $600.00 LESS than the Ampeg. Built extra tough. Google it.
You'll only need one of these. If you need 2, you're playing too loud...lol.
 
#19
I have read a lot of spec sheets in my day and I have never seen any solid state amp with the same or less distortion at the lowest impedance. They are all slightly dirtier at lower impedance.

Don't misunderstand I'm not saying it won't work or that it will damage your equipment but the chance of damage is higher running lower impedance due to heat. Whether rated for it or not you are reaching the limits of the laws of physics here for any amp...

Like an earlier poster said "amps aren't rated for a one ohm load because they aren't" (can't and be reliable).
 
#20
billfitzmaurice said:
As a matter of fact unless you don't mind an eight foot high stack two will have less clarity than one. Read, learn:
http://www.talkbass.com/forum/f15/stage-cab-placement-812281/
Click to expand...

Thanks for the link, bill!

I know about stacking cabs to get the speakers close to ear level, and I would always stack two 410 cabs as opposed to putting them side by side, but is it really necessary to do so with two cabs that are already as tall as two 410 cabs stacked?
 

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