Dumb amp question #472

[Cheebatone]

I need to marry a 2 ohm amp to two 8 ohm speakers. I know I can wire the speakers in parallel to get them down to 4 ohms, but how do I make up the short-fall? Is there some way of including a dummy load in the circuit without affecting the tone?

As ever, many thanks for all help given.

[SatelliteAmps]

Nope. Adding a dummy load will affect the tone. The only possible way is to either add two more 8Ω speakers or use two 4Ω speakers.

[Cheebatone]

Bum.

I've read quite a bit on the subject and that was the conclusion I'd come to. I was hoping I might have missed something or there was a clever secret way of getting round the problem that one of TGP's more super brainy-types could enlighten me to. Oh well... :(

[MikeMcK]

Question: a 2-ohm amp? Nobody else seemed surprised by that, but I've never even heard of one.

[Blue Strat]

Question: a 2-ohm amp? Nobody else seemed surprised by that, but I've never even heard of one.

Anything that normally uses 4 speakers is a candidate. '59 Bassmans/RIs and Super Reverbs come to mind.

A 2:1 impedance mismatch isn't the end of the world. It will work ok but you'll lose a little power.

[smolder]

I was thinking some of the older fender amps were 2 and 4 ohm.

Weber makes an impedance switcher... it seems kind of expensive to me, but if it is what you need... it is available.

[SatelliteAmps]

A few of the old Oahu's, Supro's and other Valco made amps occasionally came with 2 ohm outputs. (usually the ones with the multiple oval speakers.)

[Cheebatone]

Anything that normally uses 4 speakers is a candidate. '59 Bassmans/RIs and Super Reverbs come to mind.

A 2:1 impedance mismatch isn't the end of the world. It will work ok but you'll lose a little power.

Correct Mike (as ever!), it's a Super Reverb that I'm trying to make a bit more portable.

Please tell me more about the, "2:1 impedance mismatch". How does this work, how does it affect the tone and will it do any damage to the speakers or amp?

Thanks.

[WaltC]

A super reverb will handle a 2x1 impedance (2 ohm into a 4ohm cab) with no problems and you probably won't notice the difference in tone or volume.

[Dave C]

Most amps will tolerate a 100% mismatch either higher or lower in impedance with only a a very small power loss (a few watts at most).

I have one of my Supers in an aftermarket 2x10 cab using 2-10" Webers at 4 ohms each in parallel for a 2 ohm load...very similar to a Vibrolux in size, weight and portability.

[mooreamps]

Question: a 2-ohm amp? Nobody else seemed surprised by that, but I've never even heard of one.

I don't think you have anything to worry about. Technically, you lose 3 db of sound volume level ; 2 ohm output driveing a 4 ohm load ; other than that nothing is going to burn up. Now, having said that, there may be some comments as how that will change the reflected impedance from the secondary coil winding from the output transformer back to the plates of the power tubes ; but the reflected impedance goes up instead of going down. Again, not a problem. As for the sonic perception in the change in tone, may not even be discernable.

-g