REVIEW: ELECTRO-HARMONIX HOT TUBES PEDAL
Lord Valve
I just got one of the new Electro-Harmonix
"Hot Tubes" distortion/overdrive pedals,
and of course the first thing I did was
take it apart and lick all the pieces. It
looks pretty good inside, aside from the
fact that it was a bitch to take apart and
an even worse bitch to put back together.
It uses two tubes, described in the "manual"
(half a page) as "12AX7EH," but the ones
installed were Sovtek 12AX7WB. (Not my
favorite by any means.)
THE OUTSIDE:
It's a pretty cool-looking gizmo, 7-1/2" X
4-3/4" X 1-3/4", made from two C-shaped pieces
of brushed aluminum which fit together to form
the box. The tubes stick right up out of the
top of the pedal through a couple of holes,
around 2" from the stomp switch. In order
to keep them from getting smashed, the tubes
live under a little gazebo (this word is
really the best name for it) made from a
half-cylindrical piece of pretty stout
aluminum with a bunch of holes drilled in
it; it sits on two hexagonal standoffs,
and goes all the way across the pedal.
While it looks pretty cool, I don't like
the fact that the tubes stick up through
holes in the top of the pedal. Plenty of
dirt from the player's shoes is going to
find its way inside the pedal, and I'm the
dude who's gonna hafta clean all that crud
outta there when the pedal finally croaks.
Can't have everything, I suppose.
THE TONE:
It has five controls: Master, Gain, Drive,
Bass, and Treble. The tone controls are the
peaking type, with a fairly sharp Q, and a
sweepable band center point. As far as I
could tell, the Bass control has a range of
around 2-1/2 octaves, starting at around 60 Hz.
I used a pink noise generator and my ears to
eyeball this, so I don't know how accurate it
is. (Probably dead solid perfect, but then...
I *am* Lord Valve. Somebody stop me...)
The Treble control (also sweepable) has a
less pronounced effect than the Bass knob.
Both of these controls were *extremely*
interactive, and a tiny adjustment of either
would often produce a huge difference in the
tone. The instructions mention that for some
settings of these controls, oscillation will
occur. No shit. These filters are *hot*;
whenever I encountered oscillation, a tiny
tweak of either tone control was usually
enough to get rid of it without radically
altering the effect I was trying to achieve.
Since there is a lot of boost occurring in
this pedal, there is a noticeable amount of
tube noise ("blow") present. It uses DC
heaters (more on this below), so there isn't
much 60 Hz hum happening in the pedal itself;
of course, "guitar" is probably the Swahili
word for "hum," so you'll get plenty of that
when you plug yours in, especially if it has
single-coil pickups. Guitar hum is inevitable
when using the amounts of gain the Hot Tubes
can provide, especially with the more extreme
settings...and this thing is *extreme*, no
doubt about it. 120Hz hum, however, is
present in larger amounts than I would have
thought. There's a workaround for that one,
though...the "Gain" control appears to use
a stage which is out of phase with respect
to the "Master" control, so if you tune it
right, you can null most of the 120Hz off
the output. I may experiment with using
some larger caps in the HV supply later on.
I found the "Drive" control to be much more
useful than the "Gain" control; extreme
settings of the "Gain" control just sounded
buzzy to me. Of course, I'm a *terrible*
guitar player (and I don't use distortion
on my Hammond, since I'm a jazzer) so I'm
going to have to wait until my fearless
assistant Scooter Barnes is finished getting
laid or high or bailed out or whatever it is
he's been doing instead of showing up for work
for the last three days to hear what this
gizmo can really do. One thing I can tell
you, though, is that the Hot Tubes pedal
has one serious *shitload* of sustain, more
than damn near anything I've ever heard
before. It's *smooth* sustain, too...not
the kind that jumps from level to level as
the string decays. Nice. Good crunch, too.
I can't wait to hear a real geetah-picker
through one.
THE GUTS:
It comes packed in one of those nifty-looking
finger-jointed plywood boxes, with a slide-
off top. The box is way bigger than the stuff
inside, so I have a suspicion that the box was
spec'd at some earlier phase of the design
process, when they thought the pedal was going
to wind up being a lot larger than it is now.
No matter, plenty of bubble wrap was used to
keep things from slamming around in the box.
The Hot Tubes runs on a 12VAC 1000mA wallwart,
two-prong type, which has a piece of 20-gauge
zipcord hanging off of it with a strange-looking
(and probably completely unobtainable) two-pin
connector on the end. This connector has one
large rectangular pin and one smaller round one,
sticking right out of the plastic with no shell
around them. I know for a *fact* that a lot of
these warts are going to croak from being shorted
out when someone kicks the wire out of the pedal
and those exposed pins hit metal. It's a 1-amp
wart, so it's gonna spark real purty when this
happens. And it *will* happen, guaranteed. If
I was going to take this pedal on the road, I'd
chop that bogus connector off the end of the
wart's output wire and replace it with a standard
low-voltage power connector, the coax type found
on most effects pedals, the kind that can't be
shorted accidentally if it pops out. Since it's
an AC wart, polarity doesn't matter. Inside the
unit are some very good quality parts. They used
a clever trick to obtain the HV for the tubes;
instead of using a diode ladder (like many of the
"tube" pedals which run on 12-volt wallwarts) they
used a little encapsulated toroidal power tranny;
this is a PCB-mounted device with two 115V primaries
and two 9V secondaries. The slick trick they
pulled with it was to wire the secondaries in
parallel and put the primaries in series, and then
operate the tranny BACKWARDS by putting the 12VAC
from the wallwart into the paralleled 9V secondaries
and obtaining a 238VAC output from the seriesed
primaries. The 238VAC is then input to an inline
fullwave bridge, which gives around 280VDC at the
input to the filter section. The 12VAC from the
wallwart is also fed directly into another bridge,
to provide raw DC for a 7812 regulator which is
used for the filament supply. Interestingly, the
regulator has a small bi-pin lamp soldered from
its output terminal to ground, right between the
two tubes. I could determine no reason for this
lamp to be there, other than to make it look like
the tubes were lighting up a lot brighter than they
normally would. Egad. Anyway, the plate voltages
on the four triode sections are 125, 160, 117, and
132 VDC, with three 220K plate resistors and one at
150K. The tubes are in PC-mounted ceramic sockets.
Most of the resistors are carbon film type, with
a few metal-films here and there. All the signal-
path caps appear to be 400V Mylar or Poly types.
The PC is standard green fiberglass. The pots
feel really good; I couldn't tell who made 'em,
as there was no logo or lettering of any kind on
them anywhere. Imported, to be sure. Two were
duals, the other three were singles. They are all
mounted to the the chassis, with flying leads going
down to the board. (This is part of why the pedal
is so hard to take apart and put back together...
once you have the PC out of the chassis, you have
5 pots waving in the breeze on the ends of a whole
mess of wires.) They elected to drill some small
holes next to each pot to take advantage of the
antirotation studs, which most manufacturers clip
off; a nice touch. Lockwashers, too. The knobs
are push-on type, which fit *really* tightly on
the split/knurled pot shafts. There are two LEDs
on the pedal; one for power-on indication and
another (marked "status") to indicate whether
the effect is engaged or not. This pedal is
TRUE BYPASS (yay!), accomplished by means of
a 12VDC DPDT relay operated from the 12V filament
supply. As far as I could tell, the operation
of the relay was noiseless. I confirmed true
bypass by taking a direct reading from tip-to-tip
on the input and output jacks with an ohmmeter.
BTW, the jacks aren't labeled, so you have to
guess. I guessed wrong, and thought the damn
thing wasn't working at first. Boo. Here's the
*best* part, though...NO SAND IN THE SIGNAL PATH.
I mean nil point zippity-shit, nada! The whole
thing is 100% tube from input to output; the only
sand in it is used for rectification and regulation.
Probably why the thing sounds so damn good.
HEADS-UP:
There's a typo in the instructions. They tell you
to make sure that you get a 100mA 12VAC wallwart
if you need a replacement; this should be specified
as a 1000mA (or 1 amp) device. If you hook a 100mA
wallwart up to the Hot Tubes, it'll melt in a few
minutes. The one it comes with is a 1000mA type.
THE BOTTOM LINE:
If I were a geetah-pickah, I'd probably buy this.
I'm going to carry it in my store, that's for
sure. The overall build quality is very good,
it looks great, it sounds *killer*. (If it sounds
good with *me* playing, imagine what *you* could
do with one... ;-) This one's a winner. It'll
probably be selling in the under-$200 range soon.
Lord Valve
VISIT MY WEBSITE: http://www.nebsnow.com/LordValve
I specialize in top quality HAND SELECTED NOS and
current-production vacuum tubes for guitar and
bass amps. Good prices, fast service.
QSC amps, RNC compressors, lots of other good stuff!
NBS Electronics, 230 South Broadway, Denver, CO 80209-1510
Phone orders/tech support after 1:30 PM Denver time at 303-778-1156
VISA - MASTERCARD
"I'm not an asshole, but I *play* one on the Internet." - Lord Valve