Impedance quandary

[fauxpas]

Sorry for these newb questions, I'm just paranoid about blowing up the new amp.

I hooked up the amp to 2 sets of speakers, from years of experience, sound very similar. Anyway, when hooked to the slightly larger 8ohm speakers via the 8ohm output, the amp sounds gorgeous. When hooked up to the 4ohm speakers via the 4ohm output, they sound a little tinny and less controlled.

So today I go out and buy a set of Krix Equinox speakers and they are 6ohm. The Hi-Fi guy says to hook them through the 4ohm output as that will have sufficient current. So I get them home and via the 4ohm output they sound good, but I think they could sound much better via the 8ohm output.

Can I hook them up through the 8ohm? I never listen to my music loud if that has anything relevance.

Cheers,


Tony

[duderduderini]

Hi there
I would imagine that would depend on how low the impedence goes in the equinoxes and what kind of amp is driving them. I note they are 84db efficiency so i would assume you have either a ss amp or a push pull.
If the impedence dips too low(and by that I mean that speaker impedance is never 6 ohm but rather an averaged value.. it might pay to try and find out the lowest impedance the speakers might have and if it dips under say 4 ohms you will have to be careful no matter what tapping you use for the speaker connection) they may overload the amp but at very high power outputs..If it were me i would try at low volumes at 8 ohm
check the temp of the amp and compare and gradually increase the volume
Hope this helps
Nick

[fauxpas]

OK, so heat will be a giveaway its overloading. If it does overload, what's the worse thing that can happen? $$$ wise?

[duderduderini]

Hi Fauxpas
I am no expert by any means, I have just made more mistakes than a newbie!!!
If the amp is a ss state one it may well have thermall shutdown protection. If it doesnt it could blow the output stage(s) I mean you would have to run them quite hard I would say to blow them.
As i said I would try comparing the temp of 4 vs 8 ohm and look for distortion in the sound quality. I cant see it hurting at low volumes although that is not a qualified guess by no means.
Perhaps one of the many gurus on this forum could and will enlighten you further
Nick

[kevinkr]

Just use the tap producing the best overall sound with your new speaker system, since this the tube forum I am going to assume that this is a tube amplifier. Still a little more detail would be nice.

The amplifier isn't going to run noticeably warmer or colder on either tap. The only issue is running into a dead short where the output tubes will over dissipate, and into an open circuit where flyback effects can destroy the output transformer. (And this will only happen with audio present)

[fauxpas]

Yeah, she's a generic chinese amp that I've yet to build the courage (or breach warranty) to bust open and check out. Just wanted to know if I am safe going through the 8ohm at low/moderate levels without fear something will pop.

[dnsey]

Generally speaking, tube amps are in less danger when loaded with a lower than design impedence that they are with too high an impedence (in contrast to SS amps).
Go for it!

[fauxpas]

OK. Am running them through the 8ohm outs at the moment.

Bach Cantatas sound magical.

If 8ohm outputs have less current available, should the first sign of trouble be clipping?

Last night after hours of use from the 4ohm outs, even the aluminium case was nearly too hot to touch. Currently using the 8ohm outs, the square aluminium scallop covering the tube sockets is runinng about 41 degrees and rising slowly.

[duderduderini]

Hi
How did you go? Did the 8 ohm option sound better?
I have a chinese 300b and it ran soooo hot. I modified it a lot.. The supply voltages to the tuibes where above spec and some resistors where just too small a rating. I noticed a dropping resistor from b+ to the el34 driver had changed colour over a month for instance.. it looked like a 3 watter.. i ended up getting a 17watter in there and it was a bit warm but the original way way way hot.
I found the power tranny was always hot so i placed a pc fan on top of it blowing down.. Also 2 50mm fans underneath. All 3 fans powered by a wallmart type adapter.. It made a huge difference to the heat buildup.
If you dont know what you are doing under the bonnet dont as tube voltages are lethal.
Have you tried a small desk fan blowing across the amp?
Hope you sorted it all out
Nick

[fauxpas]

My thermometer hit 56c at that spot on the alloy cover. Ran it through the 8ohm outs all night at moderate volumes with no temp changes and it ran the same temp using the 4ohm outs the next night. I'm not sure if it sounded any better as I think I 'wanted it' to sound better. I'll have to get my partner to take a listen.

Will clipping be the first sign of problems?

Will be a while before I rip this amp apart to see how she's hooked up and make improvements. So much I have to learn about electronics.