Anecdote about "loudness" vs. power

[jamesmafyew]

So I had a guy who asked me to mod his JCM900 2500 to more-or-less JCM800 2204 specs. He also specifically asked me to put in Mercury transformers and a choke, which I did (he had the all-too-common blown 900 OT anyway). The amp sounded great in my opinion and put out 48W before clipping before the modifications and 55W before clipping after. Not an audible power increase by any means, but enough to indicate to me that the Mercury iron was probably more efficient. Whatever.

Dude loves the sound of the amp, but tells me that it's "not nearly as loud as" his bandmate's DSL 50, which is unmodified. He thinks there's something wrong with his amp. I asked him about cabs, speaker efficiency, etc., and all that stuff had been matched and controlled for.

Finally I asked him about settings. He told me that their settings were roughly comparable, and made a particular note that both guys had their presence controls at zero.

Well the 2204 circuit has a 20k presence pot with a 100n cap. The DSL, on the other hand, has a 5k presence pot with a 220n cap. So the DSL guy basically had a 6dB boost in his midrange, at the most sensitive spot of human hearing, and his amp wasn't farting out in the lower frequencies until it was perceptually quite a bit louder than the guy with the modded 900. So I just changed the cap on the 900 to 220n and told the guy to set his presence control at '8'.

Called me later and told me that his amp now stomped all over the DSL, volume-wise. Far as I know, both amps were putting out within 5W of each other.

[Jazz P Bass]

Cool post.
Thanks!

[Chuck H]

I can back this up. I try to be especially sensitive to the things that make OD tone exciting. So a few years ago, when I did a twenty watt amp design for a big cootie that was going to be presented at NAMM 2009, I pulled out the stops. I was obviously up against some heavy hitters like the Orange Tiny Terror and the Suhr Badger!!! "I" thought I did pretty well. But that's another story. What I wanted to reflect was that the only complaint I got about my design was that it was too loud!!! A twenty watt amp! It actually only puts out about fifteen truely clean watts! But the voicing and gain structure really take advantage of whatever jumped out during listening and adjustment. The OD wattage is just over twenty. But I would put my amp next to any 50W 1X12 combo when over driven. Huge exciting tone to the ear. Which, after all, is what we listen with!

EDIT: Power supply sag is a big factor in this. Sustained attack reduces the dynamics on sustained runs. But even the bass notes can be tuned into the more audible low mids for initial note attack for effect while still getting good compression on single note runs. But it's heinously tedious!