18 vs 22 vs 18 watts: Amp volume

My guess would be that it comes down to the output transformer.

 

Are you talking about a situation where the power stage was definitely distorting in all three amps?

Unless the power stages are reaching maximum power, volume comparisons are meaningless because the gain structure may be very different, and you can't tell what proportion of total power is occuring based on the knob settings. Although I'm guessing the the DR will be driven fairly hard at 7 or 8...

Also, what impedance are the Z speakers? A mismatch with either the Marshall or the DR (whose true match is closer to 16 ohms than 8 anyway) will substantially reduce the power.

And there is a huge difference between RMS power and 'peak' power. Two amps with the same RMS can have peak powers that differ by up to at least a factor of two - and perceived volume (at least for single-note playing) is more dependent on peak than RMS. That's one of the reasons solid-state amps generally don't sound anywhere near as loud as tube ones of the same power. The peak power is affected by a lot of factors including the power supply and OT, even given the same RMS.

If the Z has bigger transformers and filter caps than the others, it could sound much louder even if the steady-state power is exactly the same.

Yes, there is a lot more to 'volume' than 'wattage'.

 

I have experienced this same phenomena myself. I build a dual 6v6 parallel single ended Class A amp. It's supposed to be 9 or 10 watts at 2 on the volume dial (my amp guru designer will only measure the wattage output at 8 ohms, with a totally clean signal).

The difference between the 9 or 10 watts is the power tranny. That's right. The same amp with an old Gibson power tranny puts out 9.2 watts at 2. The same amp (the new models) with the same exact circuit, output tranny, tubes, wiring, etc. puts out 10.2 watts at 2. Freaky, huh? Something about the minor, and I mean MINOR (+/- 5 volts) plate voltages applied to the tubes does this.

After that, there's also a perceived volume and tone difference based on the tubes. I found the NOS 60's Sylvania's have a nasty Texas blues based tone, a little higher in the mids. More highs than say a vintage RCA/Sylvania from the 50's, which has a fatter, more bottom end based tone.

Then you get into the speakers, and their load with the output tranny. One thing I've learned, there's a bunch of small variables that make up a great sounding amp.

 

The other thing to note is that sound can "hurt" not because it's too loud, but due to other factors like frequency profile and light distortion. Maybe the Z sounds loud enough to hurt not because it's louder, but due to something like that. (?)

 

This site has some interesting observations that help to explain the volume differences you observed in these amps, especially the DR Z.


http://www.guitaramplifierblueprinting.com/doctorzamps3.html


-- Barr

 

I had a Carr Hammerhead, Z Maz Jr., and Fender DRRI, I noticed the same scenario. The Z flat out blew the other amps away volume wise. There was no comparison. I always thought that Michael must under rate his amps power output. I loved my Z, but it sure seemed to like to eat tubes.