Dummy Loads: Possible solutions

[Bruce / Mission Amps]

Generally SS amps don't care as long as the load is greater than a a specified minimum load. You don't have output transformers. It is determined by how much current can be drawn from the output transistors. Most SS amps have a 4 ohm minimum but many have a 2 ohm minimum load. You can run an SS amp with no load at all all day. Just don't short the output. For SS amps you can always add a 2 ohm or so resistor in series with the load to bring it up to operational parameters. It's done all of the time.

You have to be careful when you say things like this "Generally SS amps don't care as long as the load is greater than a a specified minimum load."

A larger load means less impedance, not more.
I think you meant to say a greater "impedance" (numerically---ie 16 ohms vs 8 ohms) not "greater load", which would mean 2 ohms vs 4 ohms.
Statements like this could confuse someone resulting in some transistor damage.

[Bruce / Mission Amps]

Of course, it's best to match the impedance. I used an example of the extreme to make the point that the lower impedance load is the safer of the two. BTW, a 4 ohm load on a 16 ohm amp isn't more than 100% mismatch. 100% of 16 is 16.

Ha ha ha... I quit arguing that one after too many fights....
For those that don't understand 100%... it means 1.00 as a multiplier... or, 1:1.
100% of 16 ohms is 16 ohms, while 50% is 8 ohms and 200% is 32 ohms.
Thanks for bringing that up again!

[hasserl]

Thanks for bringing that up again!

It's a dirty job, but somebody has to do it.

[Steve Conner]

People use percentages in three ways. You're expected to figure out from context which is meant.

First is Bruce's way with the multiplier. But this rule doesn't always work: if someone says that the crime rate went UP by 50%, they can't mean that it's 50% of what it was, because then it wouldn't have gone up at all!

Here are the other two ways:

A 25% discount is a multiplier of (1-0.25) = 0.75 of the original price.
17.5% sales tax means that you pay (1+0.175) = 1.175 times the price before tax.

Thus 100% mismatch is either (1-1.00) = a short circuit or (1+1.00) = twice the proper impedance.

[MWJB]

A better, more universally understood way of expressing it (which makes me wonder why I didn't do this straight off) would be "either doubling or halving your original speaker load". E.g. the difference between 8 & 16 ohms is 8, or 100%. The difference between 4 & 8 ohms is 4, or 100%. The difference between 16 & 4 is 12, or 300%. It is assumed that you will always have a load on the secondary of a tube amp (open load blows tubes & transformers, short does the same thing given enough time, but can't produce any sound & therefore cannot be correct)...but as we are aware, assume makes an ASS of U & ME :-)

[Old Tele man]

...the "safe" OT range: Z/2-to-Z(optimum)-to-2Z

[hasserl]

The difference between 16 & 4 is 12, or 300%.

No, the difference between 4 & 16 (not the other way around) is 12, or 300%. The difference between 16 & 4 is 12, or 75%. Or, 4 is 25% of 16, 16 is 400% of 4 (4 * 400% = 16).

[Enzo]

When I put 2 and 2 together, I keep getting 22.

[Steve Conner]

Yup, 4 for parts, 18 for labor