Introduction
Over the last few months, I've
been spending a lot of time playing around with
small wattage guitar amplifiers. The concepts of
small amps has fascinated me for quite a while.
Most of my playing time is spent in my home
studio, with some occasional recording. Not
quite the environment to crank up a 100 watt
amp. (Or a 50 or 15 watt amp for that matter).
Then there is the portability issue--I like the
idea of a battery powered amp that I can plug
into any cab no matter where I am. And finally,
there's the challenge part: fitting amplifier
circuits in small boxes is quite fun.
As I've been designing and
building small amps, I've learned a couple of
very interesting things that seem
counter-intuitive to my thinking as a guitarist:
-
Solid state amps can
be made to sound very good in a small form
factor
-
Less than 1/2 of a watt can
power a 2x12 cabinet
-
Hybrid tube/solid state
amplifiers yield some interesting
opportunities
-
For consumers, the choices
for low-wattage amps are either cheezey $30
fake-stacks, or super high-cost boutique
amps. Hmm....there has to be something in
the middle.
This all started when I built a couple of Ruby
low wattage amps from runoffgroove.com. This is a
fantastic little solid state circuit that puts
out less than a watt of power but will nicely
drive a 2x12 cabinet. The Ruby has a character
all its own. (More about my Ruby builds
here).
The Noisy Cricket Schematic
In playing with the Ruby, I
found two things:
-
If you put a boost pedal in
front of the Ruby, it saturates very nicely.
-
Wouldn't it be nice to have
a tone control?
This lead me to break out the
breadboard and start playing with the circuit. I
created some ideas and posted them over on
DIYStompboxes.com and got some fantastic ideas
from the folks there. What I learned is that
adding a standard passive tone control to a
circuit is going to suck some of the power out
of the Ruby. So I need to add a boost stage
(which also addresses finding #1 above). Second,
there are tons of tone controls to try.
During bread-boarding, I played around with
substituting different values to get a
better understanding of the circuit. The first
interesting find was what I call the boost. A simple cap change (value and position)
yields a nice boost in gain. You can play around
with the values, but at 100nf values sounded
best to me. Additionally, I added a very simple
tone control using a 250 audio taper pot and a
couple of 100nf caps.
For the latest schematic, view the
Mark II Build Guide PDF.
Here's the first prototype build of the Noisy Cricket with
the just the Grit boost switch: (This pedal is
now in the collection of Richard Guy at
www.guytronix.com super nice guy and awesome
amp kits!)
Production Noisy Crickets
The next exercise was to engineer the design to
a point where it would be easier to build ten
production units. I quickly learned that
building 10 of something requires a lot more
forethought than building just one :) Here
is serial number 0001:
And the insides:
The first run sold out in one day. I was
surprised and pretty stoked at the same time.
Production
Run 2
Having shown the one of the
production units to some local dealers, and
based on emails from folks about missing out on
the first run, I decided to do a second
production run. This time I'll do 20. The only
change is that replaced the power on/off toggle
switch with a more intuitive switch/volume knob
combination. As with the previous run, there
will be lots of color/finish/knob variations.
Here's the prototype for production run 2:
The indomitable Adam at
Swankbox has provide me with a set of
beautifully painted enclosures. A run of ten of
those will also be part of production run 2. The
following pictures don't do justice to these
boxes--they are simply fantastic.
The Pico Cricket
I also wanted to build a
super-duper-small version. Something that I
could drop in my guitar case and always have on
hand. Various web searching yielded a
dirt-simple schematic for the original "Smokey"
amp:
In creating the Pico Cricket, I wanted to fit
everything, including a nine volt battery in a
Hammond 1590A enclosure. This was a challenge,
but left enough room for a simple mod: a
switchable output cap on C2 between the stock
47uf value and a somewhat bassier 200uf value.
This switch is labeled Lean/Fat.
Here's another version--this one adds a gain
control:
Here are some pictures of the enclosure
work and the strip-board of the circuit:
The Tube Cricket
I decided that the next evolution in the Cricket
line would be the addition of a full tone stack
with knobs for bass, mid and treble. I settled
on the famous Fender three knob stack. The only
problem is that such a circuit cause quite a bit
of signal loss. So I looked at various
gain-recovery circuits that would make up for
it. After looking at all the various options, I
came across a great circuit for an all-tube
boost using two halves of a 12AT7.
So the Tube Cricket will have an all tube
pre-amp, a full tone-stack, and hopefully
support up to 16vDC operation. I'll post more
information on the Tube Cricket as it gets a bit
further along. |
