Technical query re Speakers and impedance.

jimkehoe

Probably for @ICBM:

If I have a combo (valve 2 x 6v6 Class A) with a 16ohm internal speaker and the ability to have an extension speaker cab also plugged in, but it also specifies 16ohms, and my existing external cab has an 8 Ohm speaker, is there any way to safely use the 8 ohm speaker in the additional cab to augment or replace the existing internal 16 ohm speaker in the combo?
I hope that makes sense.

And whilst here Merry Christmas and best wishes for the coming year to all FB members.

ICBM

What amp is it? It would be very useful to know this, but it seems to be treated as confidential information whenever this sort of question comes up!

It’s rarely critical to the answer, but it would make it a lot easier to be sure.

jimkehoe

Incoming - Brunetti Singleman 16 combo.

ICBM

Ok, not familiar with that - does the extension speaker jack cut off the internal speaker, or does it add the second cab in parallel? (Or series, but that’s very rare.)

If it adds the extension speaker then it’s necessary to know if it switches the impedance of the amp - some do, many don’t.

*In general* a mismatch of up to 2:1 in either direction is safe with a valve amp, but there are some exceptions and it might be important to know whether it’s a good idea to push it close to the limit.

jimkehoe

It adds the cabinet.

From the manual:

AMPLIFIER: class A 16W (6V6GT tubes) 

LOUDSPEAKER: 12” cone Celestion V30 (16 OHM)

EXTERNAL SPEAKER: rear output, 16 Ohm for add-on speaker

Interested to know is there any box/gizmo/thing to add in line with the speaker via speaker cable(s) to convert the impedance from 8ohms to 16ohms?

ICBM

Yes - https://www.tedweber.com/z-matcher/ - but it might not be necessary. If the amp switches its impedance to 8 ohms when you plug in a second 16-ohm cab, it’s fine to just use the 8-ohm one anyway.

Are you going to be playing it loud? If you’re not cranking it into power-stage overdrive it's fine anyway, impedance matching isn’t at all critical.

There is a way of testing this even if the manual doesn’t say. Turn the amp up loud enough so you can hear the background noise/hiss - no guitar signal. Then put an unconnected speaker cable into the extension jack. If the noise stops, the extension speaker turns off the internal one. If it doesn’t stop and there is a brief interruption as the plug goes in or out, or a small change in the volume of the noise, it’s switching the impedance. If it doesn’t do either, it’s simply in parallel.

jimkehoe

ICBM said:

Yes - https://www.tedweber.com/z-matcher/ - but it might not be necessary. If the amp switches its impedance to 8 ohms when you plug in a second 16-ohm cab, it’s fine to just use the 8-ohm one anyway.

Are you going to be playing it loud? If you’re not cranking it into power-stage overdrive it's fine anyway, impedance matching isn’t at all critical.

There is a way of testing this even if the manual doesn’t say. Turn the amp up loud enough so you can hear the background noise/hiss - no guitar signal. Then put an unconnected speaker cable into the extension jack. If the noise stops, the extension speaker turns off the internal one. If it doesn’t stop and there is a brief interruption as the plug goes in or out, or a small change in the volume of the noise, it’s switching the impedance. If it doesn’t do either, it’s simply in parallel.

John as always you are the man. Thanks so much. I don't have the amp yet - I'm picking it up on Monday so will do as you advise to check. It won't be played flat out. 
Have a great Christmas.

Cirrus

@ICBM is one of those guys where you secretly wish he was your dad