So, needless to say, I'm thinking of soon buying either a single 2x15 or two seperate single 15's. I was checking out the booklet that came with the Fender BXR 200 amp head and it said 200 watts @ 4ohm mimimum.
Now, just out of curiousity, if I changed to either 2, 8, or 16ohm speaker cabinet, what would happen? Would the amp or speakers blow up? Would I be right in saying that the minimum ohm rating is the same as saying that it's the optimum speaker rating for that amp?
Speaker Impendence Question
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atomic_punk
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I think it means that the amp you have is not designed to run a speaker load less than 4 ohms. Some Ampegs can run at 2 ohms, and a few others. If you go with (2) 8 ohm cabs, you will have a 4 ohm load. If you run a single 8 ohm cab, you will not get the maximum power out of the amp. Increasing the load (in ohms) makes the amp more efficient, and therefore more powerful.
"They make great f***'n basses". - Lemmy, NAMM 2009
an ohm is a rating of resistance to current
efficiency and power of an amp are kind of abstract in your terminology and in my mind would rely on many variables.
generally:
speakers have efficiency ratings in dB/watt usually at 1 meter
amps have power ratings, but that is fixed (200 watts@4ohms in this case)
check out the last post on this page for a pretty good explain:
http://www.avforums.com/forums/archive/index.php/t-23324.html
I woudl call Fender CS and ask if the amp can work using an 8 ohm load.
I wouldnt go below the 4 ohms without someone smarter then me saying it was okay...
Philco is knowlegable in this area, but Im pretty sure if you have 200watts@4oms, you will end up with roughly 100watts@8ohms and assuming both speakers have the same efficiency, the 8 ohm speaker will produce less decibls
JP
efficiency and power of an amp are kind of abstract in your terminology and in my mind would rely on many variables.
generally:
speakers have efficiency ratings in dB/watt usually at 1 meter
amps have power ratings, but that is fixed (200 watts@4ohms in this case)
check out the last post on this page for a pretty good explain:
http://www.avforums.com/forums/archive/index.php/t-23324.html
I woudl call Fender CS and ask if the amp can work using an 8 ohm load.
I wouldnt go below the 4 ohms without someone smarter then me saying it was okay...
Philco is knowlegable in this area, but Im pretty sure if you have 200watts@4oms, you will end up with roughly 100watts@8ohms and assuming both speakers have the same efficiency, the 8 ohm speaker will produce less decibls
JP
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jwr2
If you run two 4 ohm cabs your load is 2 ohms ... this will damage many amps ...
my ampeg b2r is rated 350 watts at 4 ohms ... and 200 watts at 8 ohms ... the more resistance the less power ... but too little resistance will damage the amp ...
I think Steve meant to say increasing the load in ohms decreases the power output ...
my ampeg b2r is rated 350 watts at 4 ohms ... and 200 watts at 8 ohms ... the more resistance the less power ... but too little resistance will damage the amp ...
I think Steve meant to say increasing the load in ohms decreases the power output ...
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atomic_punk
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I just figured that whole thing out recently and may be a bit of a layman on it. I run 2 8ohm 4-10 cabs to get my GK head to a 4 ohm load. And it's LOUD. Two 8 ohm speakers in parallel will be 4 ohms, or in series they will be 16 ohms.
Do NOT run below 4 ohms if that is the stated minimum speaker load. Solid state amps will put out more power into lower impedance loads......up to a certain point. As the impedance decreases, the current increases. At some point, the power transformer can deliver no more current, and the voltage rails begin to sag in voltage, resulting in no more power increase and a clip point at a lower voltage. At some point, the output transistors will have their junctions fused sort or blown open by exceeding the absolute maximum current value......unless circuit/thermal protection kicks in or a fuse is blown to protect the amp. Figure 1 pair of output transistors at 4 ohms for every 100 watts as the absolute most power you expect from an amp......if the cooling fan works. Otherwise, about 50 watts for convection cooling if you have good sized fins on the heatsink.
Tube amps are a different beast. The output tranny is an impedance matching device. Any speaker impedance above OR below the optimum will decrease power. You CANNOT increase power in a transformer coupled tube amp by decreasing speaker impedance, but you will change the distortion characteristics and damping factor of the amp. Audiophiles use this characteristic to "loosen" or "tighten" the bass response of their tube amps. You could use an 8 ohm speaker on the 4 ohm tap to tighten the bass response and reduce distortion, with a slight decrease in power output, OR you could use the 16 ohm tap to loosen the bass response and increase distortion with a slight decrease in power output. You will hear a change in the character of your sound more than the slight loss of power. Many audiophile tube amps are wired at 5 ohms at the factory and will run 4 or 8 ohm speakers with no need to change transformer taps. Many tube guitar amps are supplied with different taps for different loads. My YCV40 is not, but that's mainly because it's a combo amp.
I found that my YCV40 could be a little monster of a tube bass combo amp if the back of the amp was a certain distance from the wall, forming what is known as a slot loaded radiator. Pull it away from the wall, and the speaker farts and breaks up at low bass frequencies. Disconnecting the internal speaker and plugging in an external bass cab will give you a fine 40 watt tube bass amp. I think I'll get an Avatar bass cab and do just that.
Do NOT run below 4 ohms if that is the stated minimum speaker load. Solid state amps will put out more power into lower impedance loads......up to a certain point. As the impedance decreases, the current increases. At some point, the power transformer can deliver no more current, and the voltage rails begin to sag in voltage, resulting in no more power increase and a clip point at a lower voltage. At some point, the output transistors will have their junctions fused sort or blown open by exceeding the absolute maximum current value......unless circuit/thermal protection kicks in or a fuse is blown to protect the amp. Figure 1 pair of output transistors at 4 ohms for every 100 watts as the absolute most power you expect from an amp......if the cooling fan works. Otherwise, about 50 watts for convection cooling if you have good sized fins on the heatsink.
Tube amps are a different beast. The output tranny is an impedance matching device. Any speaker impedance above OR below the optimum will decrease power. You CANNOT increase power in a transformer coupled tube amp by decreasing speaker impedance, but you will change the distortion characteristics and damping factor of the amp. Audiophiles use this characteristic to "loosen" or "tighten" the bass response of their tube amps. You could use an 8 ohm speaker on the 4 ohm tap to tighten the bass response and reduce distortion, with a slight decrease in power output, OR you could use the 16 ohm tap to loosen the bass response and increase distortion with a slight decrease in power output. You will hear a change in the character of your sound more than the slight loss of power. Many audiophile tube amps are wired at 5 ohms at the factory and will run 4 or 8 ohm speakers with no need to change transformer taps. Many tube guitar amps are supplied with different taps for different loads. My YCV40 is not, but that's mainly because it's a combo amp.
I found that my YCV40 could be a little monster of a tube bass combo amp if the back of the amp was a certain distance from the wall, forming what is known as a slot loaded radiator. Pull it away from the wall, and the speaker farts and breaks up at low bass frequencies. Disconnecting the internal speaker and plugging in an external bass cab will give you a fine 40 watt tube bass amp. I think I'll get an Avatar bass cab and do just that.
My Ampeg V-2 guitar amp head, which is tube, has a selector switch for I think 2,4, or 8 ohms. Now, why don't they put these on solid state amps? Or do some do? I always thought that switch was a great idea, since if your speaker cabinet is in the shop, and you need to borrow your friend's to play a gig, the impendence from his might be different. Hence, the impendence switch. Just switch to the impendence of whatever speaker you are using.
Rob the word is: impedance, haha!
Yes four ohms is the optimum impedance for your amp. Tube amps put out the same power at different impedances if they have the taps for it in the output tranny which is what the switches do and they also need to be matched to the load much more precisely, SS amps don't on both accounts except that they can't be run at lower than the recommended impedance so there is no need for an impedance switch. You can run any SS amp at a higher impedance (with less power out) but not at a lower impedance. The can fry easily. High power tube amps are more critical of impedance mismatches than lower wattage tube amps in my experience anyway.
Yes four ohms is the optimum impedance for your amp. Tube amps put out the same power at different impedances if they have the taps for it in the output tranny which is what the switches do and they also need to be matched to the load much more precisely, SS amps don't on both accounts except that they can't be run at lower than the recommended impedance so there is no need for an impedance switch. You can run any SS amp at a higher impedance (with less power out) but not at a lower impedance. The can fry easily. High power tube amps are more critical of impedance mismatches than lower wattage tube amps in my experience anyway.
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jwr2
some of the more powerful bass amps can handle 2 ohms impedance but most can't ...
it's like in an old band I used to play in the lead singer decided that 2 more monitors would improve the sound ... but he had no idea that it would also decrease the ohms ... well we didn't blow an amp but the sound was terrible ...
it's like in an old band I used to play in the lead singer decided that 2 more monitors would improve the sound ... but he had no idea that it would also decrease the ohms ... well we didn't blow an amp but the sound was terrible ...
[Tube amps are a different beast. The output tranny is an impedance matching device. Any speaker impedance above OR below the optimum will decrease power........ OR you could use the 16 ohm tap to loosen the bass response and increase distortion with a slight decrease in power output. You will hear a change in the character of your sound more than the slight loss of power.]
I'm no amp person, I think I've been told you can increase speaker ohms, but not decrease.
I'm considering changing the 15" 8ohm in a B15N with a 16ohm I have. The 16ohm is old and supposedly sought after. I'm reading the effect is a loss in power and increased distortion, which this amp doesn't need. Just to try out, will there be any damage to the output tranny. When jamming with guitar and drums, I'm already pushing the amp.
I'm no amp person, I think I've been told you can increase speaker ohms, but not decrease.
I'm considering changing the 15" 8ohm in a B15N with a 16ohm I have. The 16ohm is old and supposedly sought after. I'm reading the effect is a loss in power and increased distortion, which this amp doesn't need. Just to try out, will there be any damage to the output tranny. When jamming with guitar and drums, I'm already pushing the amp.
Actually you are better off to reduce the impedance in a tube amp rather than decrease it, which I just found out recently. Jess Oliver revamps his old B-15's with a 4 ohm speaker and says it increases the power, (I'm skeptical but he knows a lot more than I do) I'm sure he must do some other things too though. You can contact him, at OLIVERSOUND@aol.com if you like. he was the original designer for the B-15 and worked at Ampeg for many years, now has a shop in NY somewhere. He's a nice guy, he sent me a schematic for free for an old Ampeg that I had looked high and low for.
BTW you will find many different opinions on this subject and some amps are different. I play it safe and stay at the correct impedance in a high power amp. B-15's are built like tanks though as are most Ampegs.
BTW you will find many different opinions on this subject and some amps are different. I play it safe and stay at the correct impedance in a high power amp. B-15's are built like tanks though as are most Ampegs.
Well according to Jess Oliver he gets more power out of a B-15 with a 4 ohm speaker but I think he does other things with the upgrade also. I pretty much agree with Phil that a tube amp needs to be matched. I've never heard of getting more power out of a tube amp with decreased impedance before Jess Oliver said it.When I said you are better off, I meant if you can't avoid it and you have to go one way or the other, I wasn't very clear.
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jwr2