Frank Clarke's Zone of Distortion
Hotrodding the Tube Screamer:
Strangely, the Tube Screamer has an unusual frequency response and a limited range of gain. Luckily,
it can easily be tuned to
your personal needs.
Here is the TS-9 schematic:
One capacitor controls treble, one capacitor controls bass, one resistor controls gain. Excellent.
There is room around the knobs for a miniature toggle switch or two. A high gain/low gain switch is
probably useful. Possibly a
switch to change clipping diode configuration too. Or a bass boost. Or just make permanent internal
changes. Or use internal dip
switches. Or leave it the way it is.
Does "Mod X" really make a difference?:
If you want to know whether changing 2 resistors makes a real difference to the sound, use a DPDT or
rotary switch to switch the
changes in and out, assuming it is safe to to so. Listen to the difference (or the lack of it). No need
to take someone else's word
Many effects pedals contain cheap, inconstent components, with performance variation among "identical"
pedals, so modification
results may vary.
You can put the circuit in a larger case with all sorts of knobs and switches. You will lose the easy
battery change, and the result
my be less sturdy than the original. I wonder if you could put a stomp switch on the striped part beside
the battery compartment
of the original casing? It looks almost big enough.
- More Distortion
I changed the 4k7/0.047uF attached to pin 2 of the opamp to 2k4/0.1uF, and changed the 51k resistor
attached to the drive
control to 22k. This gaves me less drive at the lowest setting, and (almost) double the drive at the
highest setting, without
changing the frequency response.
1k/0.22uF multiplies drive by 4.7. I've tried that with the 51k resistor changed to 10k, and the drive
control is sensitive, but
useable. Noisy at the maximum position (gain = 500, like the SD-9), but fun. You can also add extra
clipping diodes for that
"SD-9 Sonic Distortion" sound which has a fuzz flavour when you turn the treble up. See Screamtendo
64. You could also add a
switch to put a 500k resistor in series with the 500k "Drive" pot. This doubles the drive
at the highest setting, without changing
the frequency response. See "Boost Mode" below.
There is increased hiss and squealing with increased gain, so you might want to increase the 51p capacitor
across the clipping
diodes to about 100p if this is a problem.
- Less Distortion
You could reduce the gain and use a low noise preamp for a clean "leave it on all the time"
boost. Havling the value of the 51k
resistor attached to the drive control halves the minimum gain without changing the frequency response.
It reduces the maximum
gain by 5%. You could combine this with the "More Bass" for a more hi-fi frequency response.
This sounds especially good to me.
To improve audio quality, replace the tone filter tantalum capacitors and 1.0u non-polarized with film
types. The replacements are
larger, and more expensive. The difference may be subtle, but electrolytic capacitors do cause more
audio distortion and noise
than film types. You could remove the clipping diodes completely to give a less compressed distortion
with more volume. I did
this when I had a DOD Overdrive Preamp 250 (I can't believe they are reissuing that) to make it sound
less unnatural. As a
compromise you could replace each clipping diode with two silicon diodes in series.
This produces less diode clipping (which I think sounds better) and less distortion with more volume
at low drive settings. Look at
the 4 diode group in this schematic:
GM ARTS generic distortion schematic
Conversely, you could take a SD-9 Sonic Distortion and add a switch to reduce gain and/or bass response
to make it sound more
like a Tube Screamer.
Gain-with-bass-cut knob.Replace the 4k7 gain resistor with a 5k pot in series with a 2.2k resistor.
As you increase the gain the
bass response is reduced, which makes chords less muddy (by reducing intermodulation distortions created
when a low
frequency modulates the gain of a high frequency - the human ear is very sensitive to this). The MXR
Distortion+ did this. At
lowgain you get more bass for a more natural "clean boost" sound. The ability to select this
mode using a footswitch would be
- More Bass
Change the 4k7/0.047uF attached to pin 2 of the opamp to 4k7/0.1uF or 4k7/0.2uF. Going as high as 4k7/0.47uF
but most film capacitors start getting physically big at this point. My favourite Tube Screamer mod.
This does not boost bass
compared to the clean signal, it just reduces bass loss. You could use an electrolytic or tantalum 1.0uF
if you were really stuck,
the sound quality wouldn't be so good. I tried a tantalum 2.2u, you do actually get a bass boost with
- More Treble
Following the clipping stage there is a 1K resistor leading to a 0.22uF capacitor to ground. Reduce
the value of this capacitor. By
half is as far as I would go, it increases hiss. You can have less treble by increasing the capacitor
value. Reducing the value of
the 1k resistor also gives a brighter sound.
Add a DPDT switch for both More Bass and More Treble at the same time. The mid range boost is popular
for single coil pickups,
the opposite effect might work well with humbuckers. Or electric bass. Scooped + More Distortion = Heavy
Put in a DPDT footswitch to remove all circuitry from the signal path when "off". Sometimes
you end up with switching noise, or
no sound if you hold the switch down. It will avoid the "switch squawking" problem, though.
DMZ True Bypass diagram
The little black switch inside the battery compartment gets dirty eventually, making its operation embarrassingly
up the battery compartment and blow compressed air into the switch. If using lungs, don't inhale. Some
cleaning/lubricant materials in and report good results, but some chemicals may dissolve or gunk up
your switch irreversibly. I
used air, then WD40, and my switch works very well now. You can take the switch apart, but it's risky.
See "Big Box" General
Tube Screamer Hotrodding: for a more permanent solution.
Update: I took the TS-10 switch apart with my fingernails. It contains a spring and a V-shaped tinny
springy bit of moving metal
contact, which explains the unreliability. It wasn't dirty so much as cheap. I suspect it didn't work
too well when it was new.
Anyway, it's worth opening up and checking for filth if you are having problems. Open it halfway to
see the orientation of parts
before the spring flies across the room. The TS-9 switch is different, I hear. So is the TS-5.
I drilled a hole in my TS5, put in a DPDT stomp switch for true bypass, and used one of the now-redundant
switching FET's for a
GEO - style Millenium Bypass. You can remove about 40% of the components on the PCB. Wierd.
A rotary switch changing the values of the 4k7/0.047uF would be useful, as would a clipping diode selector.
Have two, they're small:
Use two Tube screamers onstage, one with "Less Distortion", one with "More Distortion".
This is about the same price as one
Screamer in a Big Box with footswitches, and just as versatile.