cabinets and mismatched impendances

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The internet is giving me mixed messages about this, so I want to see what the IMM panel of experts has to say. Is it never okay to mismatch the impedance betweeen a tube amp and speaker cabinet? I ask because, though I have a matched 8 ohm cabinet, it weighs a ton. I also have at my disposal a Fender cabinet containing 2 x 8 ohm Celestions, and it is currently unwired. It can be set up to be either 4 ohm or 16. Can I still use it? Which way is less likely to fry my amp?

― superultramega (superultramarinated), Monday, 16 January 2006 22:48 (nineteen years ago)

More relevant info: the amp (Sunn Solarus) has output jacks for an 8 ohm speaker or a 4 ohm 'external speaker', the latter of which I think assumes you are plugging in two cabinets at... 2 ohms each. I have a schematic here somewhere and will have to figure that one out. Not knowing for sure, I'd like to just use the 8 ohm output.

― superultramega (superultramarinated), Monday, 16 January 2006 22:52 (nineteen years ago)

I don't think your 4 ohm external speaker jack assumes anything except to be plugged into something with a resistance of 4 ohms. 2 ohm resistances are not so common with cabs... most are 4, 8 or 16. Also, it should make no difference how many cabs and what configuration is plugged into that jack as long as the final impedance is 4 ohms.

In the case of your 2x8 ohm speakers, if you wired that Fender cab to be a 4 ohm system, I don't see how it wouldn't make sense to connect it to the external speaker jack.

― martin m. (mushrush), Tuesday, 17 January 2006 00:21 (nineteen years ago)

If the external speaker jack is marked 4 ohms, I would assume that it's referencing the total impedance (i.e. 2-8ohm speakers). I could be wrong, but I know that I've run across plenty of 70's era amps that did such misleading thngs. (My Earth 2000, for one).

I would proceed with caution, however...if the amp has seperate taps for each impedance load, you could have a troubling problem ahead of you.

By the way, if I'm right in my guess about it expecting an overall 4 ohm load, all is not yet lost. Just wire each 8 ohm speaker to an independent jack, run seperate speaker wires to it, and presto, you've just created two 8 ohm cabinets. I just did this exact thing for a guy last week.

I'll see if I can find out more about the Solarus. Until then, don't be hasty. If you dump the transformer in that Sunn, it's probably amp shopping time...

― John Justen (johnjusten), Tuesday, 17 January 2006 02:41 (nineteen years ago)

Here's a schematic (the image is large so I've pasted the link). The output stage is in the middle on the right. My schematic-reading skills are marginal; what do you make of this?
http://www.dangpow.com/~sunn/solarus/solarus.gif

― superultramega (superultramarinated), Tuesday, 17 January 2006 03:42 (nineteen years ago)

Hang on, that schematic has it wired for 8 ohm speaker/16 ohm ext speaker which I think they did for other years. The 4 ohm tap goes to the external speaker on mine, according to the labeling.

― superultramega (superultramarinated), Tuesday, 17 January 2006 04:46 (nineteen years ago)

Alright, I got it sorted out. One 8-ohm cabinet, one 4-ohm cabinet or two 8-ohm cabinets. phew. Hopefully this thread becomes useful to someone else. I learned a bunch doing the research.

― superultramega (superultramarinated), Tuesday, 17 January 2006 05:37 (nineteen years ago)

from what i've learned, impedence mismatch in tube amps is fine when it's within +/- 50%. also, it's generally easier on the amp to use a higher speaker impedence than lower.

solid state amps are another thing, i guess no mismatch can be tolerated at all.

― AaronK (AaronK), Tuesday, 17 January 2006 15:17 (nineteen years ago)

All that for almost naught -- the Celestions I was going to wire up are both completely beat, which would explain the cabinet having been used as a studio table for the past 10-15 years.

― superultramega (superultramarinated), Wednesday, 18 January 2006 17:40 (nineteen years ago)

if the model is any good, consider reconing - could be worth the while.

― AaronK (AaronK), Wednesday, 18 January 2006 20:04 (nineteen years ago)

I think the coil is burned out (0 ohms across the terminals) so reconing is an option. I'll need to look into the model and cost. The cabinet itself is totally thrashed. Still has the angle-leg things and fender badge though.

― superultramega (superultramarinated), Thursday, 19 January 2006 17:04 (nineteen years ago)

oh, that sucks. i dont know, but it could be that if the cone is fine, the coil could be worth replacing? After all, the magnet would still be fine...

how is the cabinet trashed? if it's still solid/fully intact, it's definitely still worth keeping.

― AaronK (AaronK), Thursday, 19 January 2006 17:50 (nineteen years ago)

The cabinet is definitely still functional, it's just ugly and tattered. I think replacing the coil is part of reconing, no? The issue is now really what I want to spend my limited gear funds on, as always. We're not throwing it in the trash or anything (it's a good table), it just might be awhile before it gets repaired.

― superultramega (superultramarinated), Thursday, 19 January 2006 19:14 (nineteen years ago)

Reconing replaces both the cone and the coil. You could also have detatched or damaged tinsel leads (the leads going from the terminals into the speaker). Odds are, however, that reconing is your only option.

― John Justen (johnjusten), Thursday, 19 January 2006 22:07 (nineteen years ago)

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