I just want to be sure on this one before I plug in, but would an 8 ohm amp jack (fender hot rod deluxe) to a 16 ohm 4x12 (laney - GS412A i think) definately be ok?

It is just the one step and the right way round, but the words 'typically safe' bring a slight element of doubt.

thanks

There are no definites with valve amps.

That mismatch is not extreme and many people get years of happy service from equipment in similar configurations.

To get the best output, tone and reliability from your amplifier you need to match impedences where possible. It is rare that an amplifier is so sensative that a single step mismatch causes an immediate failure, but such amplifiers do exist.

If I were to suggest a rule of thumb it would be 'output should equal input'.

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I've digged through this thread a bit, and I dont think I found something quite applicable to my dillema, maybe someon can help me out.

I bought a '68 Fender Bass 15 cab (2X15) today, each of the speakers is rated at 8 ohms, put together for 4 ohms. I'm slightly worried... Here's the deal. I have a Traynor YCV 40WR. Now, the speaker in it is a Vintage 30, 8 ohms. But, the Traynor has an extension speaker jack. The manual says you can hook up another 8 ohm cabinet to it. So... there's a 1/4 inch hookup for the original speaker, and then another 1/4 inch hookup for another cab. Hook up two 8 ohm cabs, you get 4 ohms right? So my worry is, this 4 ohm cab, hooked up to one of the connections, will be mismatched in a bad way. Technically, it should work just fine, but what worries me is that I'm just plugging this cab into one of these jacks. Does having two different speaker jacks make a difference in the end ohmage?

Also, right here, in the specifications it says the minimum impedance (ohms) is 4 ohms. What exactly does that mean? Basically, to sum things up... will I **** up my amp only using this cab (disconnecting the Vintage 30 that comes with the combo amp)? Sorry for the huge long post, pretty specific...

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I have a couple questions.

I have a 50 watt Peavey Classic 50 2x12.

Now, it says in the manual that "speaker outlet jacks are provided fo 16 and 8 ohms. When both jacks are engaged, amplifier impedence is at 8 ohms".

Now, would this not run the signal to the 2 12" speakers in the combo?

Also, how can I find out the impedence of an cab? I picked up a 1x15 cab second hand, but I don't know the brand and I accidently deleted the e-mail with the wattage it can handle and its impedence. I want to use it as an extension cab with my combo.

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I would say that you can disconnect the internal speaker and plug in the cab to the extension cab jack. it should set the amp to 4 ohms and it should work fine.

in any case, from 4 ohms to 2.66 ohms (4 paralleled with 8) isn't even a 2:1 jump. you can be pretty sure (especially with a quality amp like a traynor) that you won't hurt the amp.

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take the back off the cab and look at the speaker inside... it should say right on it what its impedance and power ratings are.

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I'll have to remember to do that when I get back home.

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This is all too much. Let me just tell you what I have set up.
I have a Hartke VX2510 combo amp w/ optional ohms inputs
4ohms=250 watts
8ohms=175 watts
So a minimum of 4 Ohms. There are two outputs from the amp.(for your cabs).
One output is use to power the 2x10. The 2x10 are both 8 ohms, I know this beacause I have removed them to add some foam to the cab( bad vibration W/ lower end tones).
So this tells me its wired in a parallel.

1/8+1/8=2/8=4ohms.

I'm sure they(Hartke) would wire it to get the most out of the amp.(250watt@ 4ohms) right?

Here's the meat of my question. What is happening to the impedance if I add a single 8ohms speaker cab to the other output on the amp?

Welcome to Guitar Geek!

If I might just correct your equation so it is mathematically correct.

1/(1/8+1/8)=1/(2/8)=1/(1/4)=4ohms.

Without wanting to complicate matters further doesn't the combo also have a horn?

Assumming that the combo speakers are 8 ohm and are still wired in parallel:

Plugging in another 8 ohm speaker would result in

1/(1/4+1/8)=1/(3/8)=2.7ohms

This is LESS than the stated minimum output and as the Hartke has a solid state power amplifier this would cause it to fail.

Wiring them in series 8 + 8 = 16 would enable you to connect a 16 ohm extension cabinet in and get 1/(1/16+1/16)=1/(2/16)=1/(1/8)=8 ohms or even an 8 ohm one to get 1/(1/8+1/16)=1/(3/16)=5.3 ohms which would also be OK.

Because I am not familiar with the amp I may be making assumptions which are incorrect. Coupled with the issue of the horn I suspect you need to get local professional assistance to answer this properly.

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Thanks for the response.
I guess that I'm gonna have to do more research on the amp. My set up is sounding alright, but 2.7ohms is dangerous. I did forget about the horn, but I believe the end result is that the combo cab is wired by Hartke to have 4 ohms impedance.

To the internet I go!!!....

Thanks for responding.

thought id try here too. umm. i have a powerblock, two 4 ohm outs in stereo, can i only use one of the at a time?
and i have a mesa with an 8 ohm out and then two 4 ohm outs. i want to run one 4 ohm out into a 4 ohm cab and have nothing else connected. is this safe?

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down and down the spiral we go..

Unlike most amps the powerblocks 2 stereo/4ohm outs are series instead of parallel. That means that you can plug in two 4ohm cabs to the powerblock, one in each output. The two outputs are summed together instead of divided, so 4ohm + 4ohm = 8ohms. Don't just plug one 4ohm cab into the powerblock because that may cause it damage.

sorry i dont know for sure about the mesa.


i have even plugged 3 seperate 8ohm cabs into the powerblock (using all of its outputs) with no bad events.

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cool. thanks man.

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down and down the spiral we go..

great post on impedance, I'm a newbie when it comes to that stuff. Quick question, I don't think you answered this specific arrangement (unless I missed it). I just picked up an avatar 4 ohm cab that I'd like to use with my rig, but I'm learning I might not be able to...here's the setup:

Laney GH50L --->mesa 4x12 (4 ohm stereo or 8ohm mono) --->avatar 2x12 4ohm mono.

I saw in your post that if I run it 8ohm mono through the mesa, that will create a load too low. But, if I run the mesa 4 ohm stereo, then daisy chain that to the avatar, would the load still be too low?

Thanks so much!

The 8 ohm and 4 ohm cabinets run in parallel would be 2.6 ohms. Two 4 ohm cabinets run in parallel would be 2 ohms, even lower. in addition, you'd only be using half of your 4-12.

ou're kind of stuck using one cab or the other. Even if you got a box to run them in series, the total load would be 12 ohms, which is not quite on for 8 nor 16, though you could probably run the 12 ohm load with the amp set to 16 ohms with no real problems.

Cheers!

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