Ohms and Tone

[satyr]

Tube output amps..(not valvestate) use different O/P transformers.Solid state is pretty forgiving, BUT...old tube amps are not...Set your Marshall at 16..or 8..but DO NOT hookup cabs that total under 8.Setting at 16 with an 8ohm cab. will make it work harder..I use a Tom Shultz Power soak, which uses an 8ohm output(speaker16ohm)...as you turn it down, the overdrive increases, the dynamics decrease.By the way...more than 1 cab decreases the impedanece..eg:2 X 16 = 8, 2 X 8 = 4!!!
By the way... I bought my Master volume 50W Marshall in '77, and have changed nothing but the tubes!!Lots of years on the road...awesome workhorse!

[Robert Burns]

VHT told me, just to make sure that i have the amp settings lower than
the actual speaker impedance. So my left channel on the VHT is at 16
ohm setting on the 2/90/2...with a 16 ohm load on the cab. B' Channel is set (the amp) at 4 ohms, with the Crate speakers actually showing 6.5 ohms on
a digital meter. So as long as the amp settings are lower than the ohms
of the cab... your fine. Just not good to have the amp set at 16ohms,
with a 4 ohm speaker cab attatched to it.

[DonP]

Safer how? Safe from what?

In case of a speaker failure.

[toejam]

VHT told me, just to make sure that i have the amp settings lower than
the actual speaker impedance. So my left channel on the VHT is at 16
ohm setting on the 2/90/2...with a 16 ohm load on the cab. B' Channel is set (the amp) at 4 ohms, with the Crate speakers actually showing 6.5 ohms on
a digital meter. So as long as the amp settings are lower than the ohms
of the cab... your fine. Just not good to have the amp set at 16ohms,
with a 4 ohm speaker cab attatched to it.

Exactly. Mesa/Boogie's site also has amp handbooks which have diagrams of safe mismatches for amps and speakers.

[MSGfan]

The cab or speaker can be of higher impedance than the amp, so running your amp at 4 ohms into an 8 or 16-ohm speaker load is fine, at least that's how I remember it. The 4 ohms will indeed give you more low end.

That's what I thought for a long time but that is NOT true, it is the opposet of that with tube amps. I read an old question/answer column that Mike Soldano use to host that someone asked this question. His answer was as follows:.......

"If the load is lower than what the amp is set for, like using a 4 ohm cab. with the amp set at 16 ohms, the power tube will be worked harder and will run hotter. This, of course, will shorten the life of the power tubes. However, if the load is higher than the amps setting, like a 16 ohm cab. with the amp set at 4 ohms, the voltages in the output transformer will be higher than normal. These excessively higher voltages increase the risk of arcing, which can destroy the output transformer and/or tube sockets. I'd say tubes are easier to replace, wouldn't you?"

[toejam]

That's interesting. Then why would Steve or whoever at VHT state the opposite to Robert Burns? Where's Pete when we need him?

Then again, I usually play through a THD Univalve that's got a switch for 2/4 ohms and 8/16 ohms. Its transformer has a higher level of tolerance to withstand whichever settings I decide to use.

[Rupe]

That's why you match your impedance...then there are no worries

As was mentioned, mismatching can be done in certain instances but usually to the detriment of the amp's tone. Why bother?

[Stinkbug]

My Mark IIc+ manual reads that it is ok to mix and match 4 and 8 ohm jacks and cabs. There is one caution that in the 100W mode and using the 8 ohm jack will increase headroom, but if distortion is used the increase in power may cause speaker damage. It ends by saying "No harm can be done to the amplifier by mismatched speaker loads and we encourage you to experiment...". So it appears that the amp is safe, but your speakers may suffer.

The mesa site has lots of great articles on amps. I have learned a lot from that site over the years.

[CharvelRocker]

My Mark IIc+ manual reads that it is ok to mix and match 4 and 8 ohm jacks and cabs. There is one caution that in the 100W mode and using the 8 ohm jack will increase headroom, but if distortion is used the increase in power may cause speaker damage. It ends by saying "No harm can be done to the amplifier by mismatched speaker loads and we encourage you to experiment...". So it appears that the amp is safe, but your speakers may suffer.

The mesa site has lots of great articles on amps. I have learned a lot from that site over the years.

Odd. The resistance is for transformers afaik. Speakers are pretty tough from that standpoint; the only harm that can be done is either by putting more juice into them than they can take, or using them for something they aren't designed.

[Shawn Lutz]

mismatching can give you some cool tones, rule of thumb is x2 so 8-16, 4-8 etc unless you like the smell of fried transformers or the soukd of blown speakers