OHM confusion (i square i'm not wetodded)

[Empty Pockets]

So if you pay a little too much attention to my posts you've probably noticed the Peavey combo isn't in my sig anymore...sold it to the local shop today.

I think I can fill out all my amp needs with my Bassman head for now...especially if I grab the cool Gibson 4x10 bass cabinet they've got hidden in the back.

Anyway: My Bassman says 4 ohms, and i've been running it through a Sunn 4x12 that's 16 ohms. I haven't noticed any problems, so I'm pretty sure the 8 ohm Gibson 4x10 will be safe too. My only question is, would it be 'too much' to plug in the Sunn AND the Gibson? I would probably only do this when trying to sound REALLY heavy but if it works safely I could see it becoming my main rig for a while. I just don't want to blow up my vintage Fender.

If this IS as bad of an idea as it seems like it could be, do any of you electronics gurus know of a way to wire these cabs so that I can use them both with my Fender? Maybe a way to switch either the cabs or the head between 4, 8, and 16 ohms? I don't know much about this stuff and really need your help...I'd probably explode the head if I just tried this stuff on my own.

-X

 

[Rich_S]

Re: OHM confusion (i square i'm not wetodded)

The problem area with tube amps is when you drive a cabinet with higher impedance than what's set on the amp. I think driving a 4-ohm Bassman into the 16-ohm Sunn cab is too big of a mismatch. It may not have blown up yet, but you're stressing the amp.

The 8-ohm Gibson cab would be better. Still not a perfect match, but better.

The BEST setup would be to rewire the Sunn cab for 4-ohms. It most likely has 16-ohm drivers wired series/parallel to get its present 16-ohm overall impedance. Rewiring those same 16-ohm drivers in plain parallel would give you a 4-ohm load, and match the Bassman perfectly.

Using both cabs, you have a choice. The Sunn at 16 in parallel with the Gibson at 8 would give you about 5.3 ohms. A bit high, but not bad. The problem is, you'd need to add a toggle switch to the Sunn cab to select 4 ohms when its by itself, or 16 ohms when you're running it with the Gibby.. In this mode, the Sunn will get 1/3 of the total power from the amp, and the Gibson will get 2/3.

The other choice is simply leave the Sunn at 4 - in parallel with the Gibson at 8, you get about 2.7 ohms. Farther away from 4 than I'd like, but at least its on the low side, which is better. In this mode, the Sunn will get 2/3 of the total power from the amp, and the Gibson will get 1/3.

My advice is forget the Gibson. Rewire the Sunn for 4 ohms so as to take it easy on your amp. That rig should sound plenty heavy with the right stompbox in front.

 

[Empty Pockets]

Re: OHM confusion (i square i'm not wetodded)

Wow this is exactly the response I needed...thanks a lot.

I definitely see your point about forgetting the Gibson, the only reason I'm really interested in it is because it's technically a 'bass' cabinet and i just got rid of my bass amp...trying to keep it bass and guitar in one rig is probably a lost cause or at least a bad idea eh?

-X

 

[Rich_S]

Re: OHM confusion (i square i'm not wetodded)

I think your 4x12 will do just as well or better for bass. The biggest problem I see with that rig is the Bassman being underpowered for bass in this day and age, depending on what style you play and what the other players are using.

It's a great guitar amp. though. Years ago, I played with a guy who played a JB throught a '68 Bassman into a Sunn 2x15 cabinet. One day just for the heck of it, I tried his rig for guitar - it sounded great. I wouldn't mind having one as a big brother to my '68 Vibrochamp, but I'm beyond broke in the gear-aquisition budget.

 

[Empty Pockets]

Re: OHM confusion (i square i'm not wetodded)

Yeah I know a guy from the Stoner Rock site runs his Bassman head through TWO Sunn 2x15's and he always raves about it. The one time I tried it through a 15" speaker it got unbelievable crunch. heh maybe I should find a good cab with 15's in it...

 

[Rich_S]

Re: OHM confusion (i square i'm not wetodded)

Yeah, the Sunn cab I tried was a real bass cab; kinda like a small double-scoop cabinet turned sideways with big ports on the sides.

I saw a guy in a bar once who obviously had a thing for Blackmore. He was playing a blackface Bassman head through a Marshall 4x12 slant cab. He had the channels jumpered and it sounded great for "Highway Star".