ampeg svt ohm question

[jpark]

I'm thinking about getting a custom cab from LDS, and the setup I want, 3 10's and 2 12's, run a little over 4 ohms. My amp is an ampeg svt classic and they will do 4 ohms and 2 ohms. Would it hurt my amp to run it a little above the 4 ohms?

 

[atoni]

As far as i know you can run SVT into 8 ohm cabinet safely when you have amp's ohm select switch at 4 ohms. Check the ohms FAQ here http://www.talkbass.com/forum/showthread.php?t=144244

Of course it is recommended to have ohms same at amp and cabinet.

 

[Espidog]

There's no risk at all in running the amp into a higher impedance than you have selected. All that will happen is that your max power output will be a bit less, and the sound will be a tad more "civilised" (the frequency response of the amp will shift a bit).

The dangerous things, especially with a valve amp, are running it into too low an impedance, and running it with no speakers plugged in at all.

You're safe.

 

[8mmOD]

There's no risk at all in running the amp into a higher impedance than you have selected. All that will happen is that your max power output will be a bit less, and the sound will be a tad more "civilised" (the frequency response of the amp will shift a bit).

The dangerous things, especially with a valve amp, are running it into too low an impedance, and running it with no speakers plugged in at all.

You're safe.

You definately dont want to run the amp below its rated impedence. but I always understood that running a tube amp above its rated impedence puts strain on the output transformer & is not recommended. I pretty sure I read a post (on talkbass) from Jerrold Tiers (of Ampeg) recommending against running an SVT CL at 8 ohm. Now running the amp "a little above" 4 ohms... well... I personally would stick within the impedence ratings, but I am funny that way.

 

[musicman swede]

I have a little question on this theme to, I see that you write that it could be dangerous to run youre amp with no speakers at all, does this apply to all kind of amps or just som specific...?

I use my ampeg 350h (not a tube amp but a transition or what ever it is called in english) without speaker as a preamp home in my appartment to praktice could this damage my amp?

 

[Espidog]

The risk only applies to valve amps. Solid state types aren't bothered by a lack of load on the outputs. If your 350H has a solid state output stage, you needn't worry.

 

[musicman swede]

Thanks it is a solid state amp, feels good to now there is no damage done.

 

[zachbass02]

what about a valve(or tube)/solid state hybrid? can that be run w/o load and not cause damage?

 

[BassIan]

For an SVT Classic, match the impedance. Do not go over or under the rating.

If you're getting a cab with 3 10s and 2 12s why not look at a Schroeder 310212? They're a 4 ohm cabinet, great sounding and the light version is very portable. Plus you have Jorg's awesome service behind you should you ever need it.

Be advised though that the "anything higher than minimum impedance" is applicable only to solid state POWER amps (this includes hybrid amps with tube preamps. For these, it is okay to have no speaker or shorting plug connected. For a tube amp, just match the impedance to the selected impedance on the amp. If you don't do this, you risk damage to the output transformer, which is an expensive replacement part. If necessary to use the amp's DI for recording or otherwise, either connect a speaker and turn the master all the way down, or leave the amp in Standby (my SVT-2 Pro's DI still works with the amp in Standby).

 

[jpark]

For an SVT Classic, match the impedance. Do not go over or under the rating.

If you're getting a cab with 3 10s and 2 12s why not look at a Schroeder 310212? They're a 4 ohm cabinet, great sounding and the light version is very portable. Plus you have Jorg's awesome service behind you should you ever need it.

I would but lds can make a cab to similiar specs for half the price.

 

[Herman]

As far as i know you can run SVT into 8 ohm cabinet safely when you have amp's ohm select switch at 4 ohms. Check the ohms FAQ here http://www.talkbass.com/forum/showthread.php?t=144244

Of course it is recommended to have ohms same at amp and cabinet.

I agree. The SVT classic owner's manual says to always keep the load at or above the rated impedance setting of the amp - you shouldn't have any problem.

 

[Psycho Bass Guy]

It's funny that this thread references the FAQ, but it appears that none of the people have actually READ the FAQ, especially in light of the responses given. I'll single out the most misleading of the bunch.

There's no risk at all in running the amp into a higher impedance than you have selected. All that will happen is that your max power output will be a bit less, and the sound will be a tad more "civilised" (the frequency response of the amp will shift a bit).

You are absolutely 100% WRONG!!! READ the FAQ.

The dangerous things, especially with a valve amp, are running it into too low an impedance, and running it with no speakers plugged in at all.

You're safe.

And just in case you missed it: this is NOT true, and VERY bad advice!!!

 

[Herman]

It's funny that this thread references the FAQ, but it appears that none of the people have actually READ the FAQ, especially in light of the responses given. I'll single out the most misleading of the bunch.



You are absolutely 100% WRONG!!! READ the FAQ.



And just in case you missed it: this is NOT true, and VERY bad advice!!!

Maybe you should re-read the FAQ - here's what it says about tube amps:

"Tube Amplifiers are a different animal, and many have switches to match the impedance of the cabinets to be connected to them. A given tube amp might be able to send a 400 watt signal to an 8 ohm, 4 ohm, or 2 ohm load, but the switch on the back must be set to the load being used). Generally it’s safe to be up to 100% off on the load hooked up to a tube amplifier from where it’s selected. For a tube amp set for a 4 ohm load that would mean that you could run it into anywhere from an 8 ohm load to a 2 ohm load and still be reasonably safe. The important difference between tube amps and solid state ones is that it’s dangerous to run tube amps above their impedance rating!! Running a tube amp set at 2 ohms into an 8 ohm load can dangerously raise the plate voltage of the amplifier and ruin it. Also, while most solid state amps will do ok with no speakers plugged into them (infinity ohms), tube amps need to have a load connected to them, or they will generally self destruct."

 

[Psycho Bass Guy]

Maybe you should re-read the FAQ - here's what it says about tube amps:

You've taken one sentence that completely contradicts the entire rest of the paragraph. I suspect it's just a typo with some omitted text that occured when the board got reformatted between the time of posting and now. One of my posts (which would enlighten you about this topic) in that thread had some of its text missing. Just to be clear, I'll highlight the rest of the stuff that's important and invite you to read up on things like reflected impedance.

"Tube Amplifiers are a different animal, and many have switches to match the impedance of the cabinets to be connected to them. A given tube amp might be able to send a 400 watt signal to an 8 ohm, 4 ohm, or 2 ohm load, but the switch on the back must be set to the load being used). Generally it’s safe to be up to 100% off on the load hooked up to a tube amplifier from where it’s selected. For a tube amp set for a 4 ohm load that would mean that you could run it into anywhere from an 8 ohm load to a 2 ohm load and still be reasonably safe. The important difference between tube amps and solid state ones is that it’s dangerous to run tube amps above their impedance rating!! Running a tube amp set at 2 ohms into an 8 ohm load can dangerously raise the plate voltage of the amplifier and ruin it. Also, while most solid state amps will do ok with no speakers plugged into them (infinity ohms), tube amps need to have a load connected to them, or they will generally self destruct."

 

[Jerrold Tiers]

PBG is correct.......

Think of it this way..... running a tube amp with NO load we can all agree is bad, right?

So.... running a tube amp with a much lighter than spec load (say 16 ohms on the 4 ohm tap) is "sorta like that, only less so...."

The question then comes up, "well how FAR can I go that way?" And I have no answer....

But you can go farther on a low powered guitar amp than with an SVT....

Now, a dose of reality... the "nominal" impedance of a speaker is just that... "nominal". It could easily be 20% , even 30% different from the "nominal". So "some" difference is not a problem, obviously.

And, the speaker impedance varies a bunch with frequency. That is another factor.

The problems start when you use a speaker with a "nominal" impedance different from the rating of the tap on the transformer, and then IT is ANOTHER 30% or so higher even than that. Now you are getting close to double the tap rating, PLUS it goes up proportionately MORE with frequency.

Again, how far can you go? I don't know an exact answer.

So how much is "a little over 4 ohms"? Maybe if you told us what the impedance was going to nominally be we could sort it out into "no way", "maybe" or "should be fine".

BTW, as far as lower than spec impedances..... remember that many amps have an extra contact on the jack shorting the outputs when no speaker is plugged in. Clearly that is regarded as better than leaving them open.....

 

[Herman]

You've taken one sentence that completely contradicts the entire rest of the paragraph. .

I don't think it does since two different situations are being discussed within the same paragraph. The first (which I underlined) is talking about a tube amp set for a 4 ohm load and how it should be generally safe to run that with a load +/-100% of that value.

"Generally it’s safe to be up to 100% off on the load hooked up to a tube amplifier from where it’s selected. For a tube amp set for a 4 ohm load that would mean that you could run it into anywhere from an 8 ohm load to a 2 ohm load and still be reasonably safe."

The second (which you underlined) is talking about a tube amp set for a 2 ohm load and how bad it would be to have an 8 ohm (nominal) cab connected to it - I agree, since that's 400% more than what the amp's output is set for.

If the "100% rule" discussed in the first part of this paragraph from the FAQ is incorrect, than it ought to be corrected.

 

[Psycho Bass Guy]

I don't think it does since two different situations are being discussed within the same paragraph. The first (which I underlined) is talking about a tube amp set for a 4 ohm load and how it should be generally safe to run that with a load +/-100% of that value.

There's also a whole slew of OTHER threads (not to mention the FAQ's subsequent posts) on this very topic, and in them, you'll find that while with MOST low-powered or guitar amps, 100% mismatch is OK, in amps like the SVT, a higher load is a VERY bad idea, regardless if it meets the "100% rule" or not.

The second (which you underlined) is talking about a tube amp set for a 2 ohm load and how bad it would be to have an 8 ohm (nominal) cab connected to it - I agree, since that's 400% more than what the amp's output is set for.

I didn't notice it said 2 ohms until later. The single FAQ post in itself is just general; that's why there's the rest of thread attached to it. This topic is tired and it's been discussed MANY times. if you want to blow up an SVT by running it at 8 ohms, I can't stop you.

If the "100% rule" discussed in the first part of this paragraph from the FAQ is incorrect, than it ought to be corrected.

In an of itself in general, the statement IS correct (most tube amps ARE guitar amps), but NOT for high powered tube bass amps, which is explained further in the REST of thread. If you don't believe me or Ampeg's own engineer, I'm not going to waste my time arguing semantics.

 

[Herman]

There's also a whole slew of OTHER threads (not to mention the FAQ's subsequent posts) on this very topic, and in them, you'll find that while with MOST low-powered or guitar amps, 100% mismatch is OK, in amps like the SVT, a higher load is a VERY bad idea, regardless if it meets the "100% rule" or not.



I didn't notice it said 2 ohms until later. The single FAQ post in itself is just general; that's why there's the rest of thread attached to it. This topic is tired and it's been discussed MANY times. if you want to blow up an SVT by running it at 8 ohms, I can't stop you.



In an of itself in general, the statement IS correct (most tube amps ARE guitar amps), but NOT for high powered tube bass amps, which is explained further in the REST of thread. If you don't believe me or Ampeg's own engineer, I'm not going to waste my time arguing semantics.

Chill out. Ampeg's own SVT manual says that the load should be kept at or above the selected output's impedance - maybe the manual needs an update as well.

 

[BassIan]

Chill out. Ampeg's own SVT manual says that the load should be kept at or above the selected output's impedance - maybe the manual needs an update as well.

It's not enough that an Ampeg ENGINEER (NOT a manual author) and the resident tube expert both contradict the Ampeg manual and tell you in exact electrical terms WHY this is wrong?

Do it then, and see what happens.

If I were you I'd smarten up and listen to the qualified people who are (thankfully) taking the time to reiterate this for you.

 

[8mmOD]

Chill out. Ampeg's own SVT manual says that the load should be kept at or above the selected output's impedance - maybe the manual needs an update as well.

Hey Herman

I dont personally know Psycho, but I know one thing about him and that is he is a stickler for the facts. I dont personally know Jerrold either, but I know he has been an Engineer at Ampeg for a LONG time & if he says its so, its so.

I also know that you are correct, it does state "the load should be kept at or above the selected output's impedance" in the manual & it probably should be changed for the SVT.

And lastly, I know this topic has been discussed many, many, many times here on TB. From these discussion and my own personal research, I can tell you that Psycho, Jerrold & all of the rest of us that are saying "dont do it" are correct. So dont take it personally, just chalk it up to learning something new.