Purposely mismatching speaker loads on valve amps

pintspiller

The power amp that we use for our subs is busted. I was wondering if I could one sub as an extension cab to my bass amp and have it out front.

My Carlsbro has 16, 8 and 4 ohm outputs. If I selected 4 ohms I could have one output to my 8 ohm bass cab and another output to my Powerbreak set at 8 ohms and connected to the 4 ohm sub. Would this work?

My Sound City does not have a 4 ohm output. Would I have to select 8 ohms and run amp to Powerbreak to cab to sub?

ICBM

pintspiller said:

My Carlsbro has 16, 8 and 4 ohm outputs. If I selected 4 ohms I could have one output to my 8 ohm bass cab and another output to my Powerbreak set at 8 ohms and connected to the 4 ohm sub. Would this work?

You're better just to connect both cabs to the amp set to 4 ohms. It will be a mismatch, but safe. If you use the Powerbrake, you need to set it to at least 3dB down (1 click), preferably 6db (2 clicks), to 'hide' the cab impedance from the amp, and then you'll reduce the volume from the sub which may defeat the point of using it.

pintspiller said:

My Sound City does not have a 4 ohm output. Would I have to select 8 ohms and run amp to Powerbreak to cab to sub?

That's likely to be too much of a mismatch.


Why not just use both amps? Carlsbro (4 ohm) to sub, Sound City (8 ohm) to main cab. Problem solved.

ecc83

So you are using a valve amp for bass? Too much up there for this old brain. Bottom line for valve amps..

SIZE is everything. Well the size of the signal that is. You can run a valve amp quite safely as a rule with a 50% "mismatch"* either way (but lower is a bit safer than higher) SO LONG as you are not driving the bllx off it. Many amps will tolerate even that but some won't!

But you seem to be saying you will set the amp to 4Ohms and run 2 eights in parallel? Happy amp if so.

Transistor amps will blow if the load is even fractionally lower than rated and even some cheaper ones though rated for 4R can still fail and NEVER connect any kind of transformer to a transistor amp. It is often said sstate amps can be run open circuit. In theory yes. In practice don't do it especially if again driving the bllx sort of thing..

*We don't of course "match" audio kit no, not even valves and speaker but that is a whole other can of worms.

Dave.

pintspiller

Worked like a charm. Thanks chaps.