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Ohms FAQ

#881
TOHARROV said:
Relative newbie here. Readily acknowledge my ignorance with regard to "ohms".

Just told by Gallien-Krueger tech that I can't operate my new combination of cabinets simultaneously without damage to amp, cabinets, or all, due to impedance issues.

I would sincerely appreciate advice on what (if anything) I can put between my bass guitar and my two cabinets in order to operate all at full potential (meaning all speakers, not full volume)

Cabinets: Ampeg's SVT-810-E and PN-115HLF

SVT-810E specs show "Mono 4 Ohms (8x10); Stereo 8 Ohms 4x10)" There are separate 'stereo' input jacks for the top four 10s and the bottom four 10s.

PN-115HLF specs indicate simply "8 Ohms"

Amp: GK's MB500 has two speakon outputs and the manual indicates that it can run "one cabinet at 4 ohms or two cabinets at 8 ohms", with "350W @ 8 ohms" and "500W @ 4 ohms".

Willing to replace the GK - that's no problem - I just don't know what to replace it with.

Thanks!
Tom
Click to expand...
You really shouldn't bother as flat out the 15 won't be heard with the 810 wound up even a little.

If you really have to try you need a power amp with two channels.
 
#882
^^^This

I don't think you will notice much, if any difference if you add the 15. It just can't compete with 8 10" speakers. If your goal is to get the full available wattage from the amp, why not just run the 8 x 10 in stereo mode? 350 to 500 watts is not as big of jump as you might expect. I would just run the 8 x 10 in normal mono (single cable) mode and let the amp live the easy life. Note the wattage ratings of the amp are "nominal" and not a guaranteed maximum output. The actual wattage out of an amp can exceed the nominal ratings, so if you find you have to dime all the knobs to be happy, it would be good to get a more powerful amp to avoid doing that.
 
#883
Downunderwonder said:
You really shouldn't bother as flat out the 15 won't be heard with the 810 wound up even a little.

If you really have to try you need a power amp with two channels.
Click to expand...


Hey, Downunderwonder - sincere thanks and hello from prairie of the north central Texas! Wasn't aware of a two-channel option, so will want to pursue this before giving up on being able to use both cabs at the same time. Our 'thing' is that we have been running a casual get-together of mostly older musicians who want to play "geezer rock" with others purely for the fun of it. We do this every Saturday afternoon and are just into our fourth year. Our studio space is in an old factory building that is now home to more than three dozen art studios - meaning that we have to keep our volume 'tenant friendly'. I share this only to let you know that at our low volume, the 115 does indeed make an appreciable difference. Again, thanks for the helpful info!
Tom
 
#884
BadExample said:
^^^This

I don't think you will notice much, if any difference if you add the 15. It just can't compete with 8 10" speakers. If your goal is to get the full available wattage from the amp, why not just run the 8 x 10 in stereo mode? 350 to 500 watts is not as big of jump as you might expect. I would just run the 8 x 10 in normal mono (single cable) mode and let the amp live the easy life. Note the wattage ratings of the amp are "nominal" and not a guaranteed maximum output. The actual wattage out of an amp can exceed the nominal ratings, so if you find you have to dime all the knobs to be happy, it would be good to get a more powerful amp to avoid doing that.
Click to expand...


Much appreciation here for sharing your thoughts. I find that trying to convey my intent sometimes gets lost in my unfortunate choices of words. Definitely NOT trying to get full wattage. (Please see my reply above, to Downunderwonder)
We play in a large room with doors closed, needing only to hear one another - and trying to avoid causing nuisance to other tenants in the building. A typical session includes three or more guitars, keys, drums, a sax - and me, with the bass - along with a couple of small PAs for our singers. Again, thanks!
 
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#885
TOHARROV said:
Relative newbie here. Readily acknowledge my ignorance with regard to "ohms".

Just told by Gallien-Krueger tech that I can't operate my new combination of cabinets simultaneously without damage to amp, cabinets, or all, due to impedance issues.

I would sincerely appreciate advice on what (if anything) I can put between my bass guitar and my two cabinets in order to operate all at full potential (meaning all speakers, not full volume)

Cabinets: Ampeg's SVT-810-E and PN-115HLF

SVT-810E specs show "Mono 4 Ohms (8x10); Stereo 8 Ohms 4x10)" There are separate 'stereo' input jacks for the top four 10s and the bottom four 10s.

PN-115HLF specs indicate simply "8 Ohms"

Amp: GK's MB500 has two speakon outputs and the manual indicates that it can run "one cabinet at 4 ohms or two cabinets at 8 ohms", with "350W @ 8 ohms" and "500W @ 4 ohms".

Willing to replace the GK - that's no problem - I just don't know what to replace it with.

Thanks!
Tom
Click to expand...

If you ran both cabinets, chances are it would actually not be as loud. With two cabinets of equal load, half the power goes to each. So you'd be cutting power to the 8x10 in half. There is so much more speaker surface with 8x10, robbing half of its power could result in more db loss than the 115 would add.
 
#886
kiat said:
. . . is there any way I can add something electronic on the path, that would make the speaker a matching 8Ω?
Click to expand...

Technically? Yes. Practically? No.

The issue is that any resistance you add in the circuit, is going to . . . well . . . resist! Whatever you add "uses" half the power. That is, if you added resistors to bring the load to 8 ohms, your speaker would get half the output and the other half would be dissipated as heat by the resistors.
 
#888
Chasarms said:
Technically? Yes. Practically? No.

The issue is that any resistance you add in the circuit, is going to . . . well . . . resist! Whatever you add "uses" half the power. That is, if you added resistors to bring the load to 8 ohms, your speaker would get half the output and the other half would be dissipated as heat be the resistors.
Click to expand...

Thanks, Kiat! Will be checking out the earlier suggestion of a two-channel amp, to see if that provides any hope. Meanwhile, I'll maintain the balance at 8 ohms by running with only the top half of the 810 and the 115.

Thanks again to all who've posted on this!
 
#889
TOHARROV said:
Thanks, Kiat! Will be checking out the earlier suggestion of a two-channel amp, to see if that provides any hope. Meanwhile, I'll maintain the balance at 8 ohms by running with only the top half of the 810 and the 115.

Thanks again to all who've posted on this!
Click to expand...

You don't need a two channel amp.

If you like your GK and just want to tinker, pick up any power amp and run it as a slave. Drive the 8x10 with the GK and run a line from the GK lineout to the other power amp to drive the other cabinet.
 
#894
TOHARROV said:
It definitely is! Our sessions have helped me to hang on to what little bit of sanity I still have - for sure!
Click to expand...
That's very cool! I'm very new to bass, BTW, and goal is to be able to do just what you do... play for fun. I have probably at least five years to go, then relocate overseas, then hope to play with new friends and relatives.

Sanity? Yaaaaah, I think I remember something about that thing. I think my faded away over the last ten or so years. In case you didn't know, we have a "Grumpy Old Fart" thread/club thingy: Amps...Get off my LAWN! "Grumpy Old Farts" You may enjoy the company (self excluded). It's just there for fun and fellowship. I would be honored to learn from you if you would like to check in. We mostly complain about health issues and which body part has stopped working, fallen off, or is expected to fall off soon, but it is oddly therapeutic and we all mostly get along, at least whenever I'm not posting... It would be my honor to learn from you... and believe you me, I have plenty to learn!
 
#896
TOHARROV said:
Our 'thing' is that we have been running a casual get-together of mostly older musicians who want to play "geezer rock" with others purely for the fun of it. We do this every Saturday afternoon and are just into our fourth year.
Click to expand...

Watch who you call geezer!! Many of us are up in that range and are grumpy to boot! :(

Edit: To welcome Tom to our ranks!
 
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