My AX-84 "P1 Lite" Amp
If you want to hear what my amp sounds like, I made an MP3, recorded quickly in my home studio. A little outboard reverb was used, but what you get otherwise is pure P1 Lite, with not much else.
Bill Doggett's immortal "Honky
Tonk Part I" served as the basis for my demo. You can download the demo here.
(1.8MB--2min--128K stereo)
Here's my advice for anyone who wants to make a P1 Lite....
First you got to find the lite schematic. The bad news is the P1 site moderators have taken the schemo for the P1 off their site many years ago.
If you really want it, email me (see contacts) and I will see if I dig it up. Oh wait! I have it here! It's a varation of the AX84 design without tone controls.
For the amp you hear in the demo, I followed the AX-84 P1 REV 10 lite schematic exactly, except for
varing one cap value in the 1st preamp stage, which seemed to make the amp a bit less bright.
Specifically, C4 got changed to .03uF.
I also added the anti hum resistor/cap stuff from REV 10 full version, where you reference the heater
voltages to a voltage divider instead of ground. This is in the "regular"
version, not the lite, so go get that circuit fragment and put it into your
lite chassis. This wasn't in my original
build, but before I added this there was a pretty bad hum, and afterwards the
hum was gone. So plan on adding this.
There is a lot of talk on the AX84 site about using a star ground. Yes, you
will need this, unless you like the amp going awwaaaaaaaawwwaaa all the time.
Been there, done that.
I also used a Jensen Alnico-those expensive reissue ones...
and this made a big difference in how the amp sounded, having tested it with a
dogpoo 8" speaker I had in my junk box.
The biggest lesson I learned though, is that the cabinet makes a HUGE
contribution to this amp's overall sound. This of course makes sense, but I guess I never
realized the extent of this until I built this amp. My ex-wife built a nice little case out of
Poplar that she had an extra sheet of. Good to stay on good terms with your ex?
Pre-custom-cab, on the bench, the amp sounded cheesy. I was worried. Initially the cab made the amp sound pretty good but still too bright. I messed around with cap values inside the amp but the problem persisted.
Finally, I screwed around with the baffling on the back of the amp's cabinet,
The baffle made an
unbelievably huge difference in how the amp sounded and recorded. I tried
different baffles, using wood scraps and duct tape, until I found one that I liked sound wise. The winner covered most of the back
of the amp but not quite all of it (you have to leave some opening for the
tube's heat to get out...or else you will end up with a pile of charcoal.)
I noticed that a lot of old small Fender amps have
most all the back covered as well....hmmm, I guess those Fender guys knew
something that I am catching on to now.
Overall the amp is surprising quiet and very responsive to however you've set
volume and tone on the guitar. You can tell by the
recording that you can get a very wide range of sounds out of the amp, even
though it only has a single volume control. The crunch
sound is a bit harsh, and can be cold sounding, so I don't use it much. At
lower volume settings it's a surprisingly good sounding
amp. I had a great time building it, really a lot of fun, and
that's what counts. My hat is off everyone who has
contributed to the AX84 project, they have done a great thing: a newbie like me
can build a DIY amp that doesn't blow up.