Running two cabs off of one amp... ideas...

House53

My lead guitar player has a Fender Super Twin 212... yes it is one of the 180 watt monsters from the late 70s... loud as all hell... he wants it a bit louder...

he recently bought an old Bassman 10, with 410s... he wants to run the 410s as an extension off of the Super Twin, and run the internal 212 speakers.

Now, on the back of the ST there are two jacks(like most fenders) one labeled internal one external and it says total load 8 ohms.

The 212 internal speakers are 8 ohms total... the 410s in the bassman are at 8 ohms.

can he just plug into the extra jack at 8 ohms and be safe?

I am not sure. How are those jacks designed? It seems that if they put both an internal and external jack they would allow for both to be used... in that case how would those ohms add up...

one line with two speakers at 8 ohms and the other line with 4 speakers at 8 ohms... do they add to 16?

Any help is appreciated...

mccreadyisgod

The power outputs on the amplifier are PARALLEL outputs. If you plug into the internal speakers for 8 ohms and the external cabinet for 8 ohms, it will put a total load of 4 ohms on the amp. If the amp WANTS 8 ohms, and you GIVE it 4 ohms, bad things will happen. You are giving the amp less resistance than it expects, which is VERY bad. An amp will do alright seeing more resistance (higher ohmage) than it's rated for, it will just get worked harder.

Pacomc79

now what your buddy can do is replace everything with 16 ohm speakers effectively showing the amp 8 ohms in parallel. And I'm working on finding an attenuator at 8 ohms with two outs in series that may work but don't take my word for it until you look up what ohm load you get in series.

MIG is that right? I can't remember the ohm levels in series.

I'm pretty sure Andy Marshall at THD or Mr Weber could build him an attenuator or load box if this is the case, or Weber would be more than happy to help him replace all those speakers to 16 ohm loads

House53

That's what I was afraid of...

I recommended he split his input signal and run both amps... I am sure he will figure it out.

Pacomc79

Originally posted by House53
That's what I was afraid of...

I recommended he split his input signal and run both amps... I am sure he will figure it out.

sure. Run an ABY box. Run the thing in Y all the time or find out if he can slave the bassman 10 from the ST. Meaning only 1 preamp is controlling both power amps.

mccreadyisgod

Originally posted by Pacomc79
MIG is that right? I can't remember the ohm levels in series.

When you wire in PARALLEL, you split your resistance in half. When you wire in SERIES, you double your resistance. Parallel wiring is when you send the positive to both speakers, and receive the negative from both speakers. Series wiring is when you send the positive to one speaker, then from the negative of the first speaker to the positive of the next speaker, then from the second negative back to the negative of the amp. Or rather, parallel is a Y, and series is a loop.

I would second the recommendation to just use both amps. You can use an A-B-Y box (the best way) or just parallel the input jack of one amp to the other. I don't know if the Twin you mention has parallel ins, but I'm pretty sure that Bassman 10 does. That would drop your signal strength a bit, but would otherwise be fine.

Originally posted by Pacomc79
sure. Run an ABY box. Run the thing in Y all the time or find out if he can slave the bassman 10 from the ST. Meaning only 1 preamp is controlling both power amps.

If the Twin has a preamp output, or a direct out (same thing) you could just run that into the input of the Bassman 10. Without major modifications, you can't just wire directly into the Bassman power amp.