Meet Marvin, my pet Filigree Siberian Hamster!
BUILD REPORT:
I bought the L’il Mouse PCB probably a couple years ago or so. Last February’s Chinese New Year brought in the Year of the Rat, it behooved me to finally do something with the L'il Mouse. I gathered up all the parts needed, put them together with the PCB in a project box... and then the human race had a melt-down and the project was sidelined.
Nearly a year later, with the Year of John Entwistle looming on the Lunar Calendar, I decided to get my soldering iron and the project box out of mothballs.
I hand-drilled a cheapo-enclosure ‘cause my drill-press died, and I didn’t have time to head over to my friend’s Amp Atelier to use his press: so the holes are a little wonkey, but I managed to get it close enough to include all my planned mods that required drilling.
Mod All BehaviourAdded 2N5817 polarity protection
LEFT WHISKER: Clipping Switch SPDT on-off-on
> UP: Stock 1N914 /
> CENTRE: Turbo red LEDs (socketed so can try op-amp clipping or mixnmatch colours) /
> DOWN: Fat Rat BS170/BAT41
RIGHT WHISKER: Tranter Fat Mod Switch #2 (Retains Rat tone while retaining some bass!) DPDT on-off-on
> UP: Bass
> CENTRE: Stock
> DOWN: BASS-BASS
Meant to add a minimum gain resistor, but was halfway done when I remembered. This bummed me out when I was first testing it and got no sound... Then I remembered — the Gain has to be turned up a bit, idjit! Fuzzy Rattattatat!
More modding and testing… dead. Gain was up — clean sound but no fuzzy rat-droppings — Engaging the 3PDT helped (I didn’t have the LED installed yet.)
POTS:
1590A pot-helper daughterboard, made things extra tight when fitting switches.
— VOL: STOCK A100k
— TONE-POT (Filter-whatever) B100k
Swapped some tone wires around 'cause I wanted standard turn-clockwise for more treble-tone, but I got the wiring wrong. The easiest fix with the least amount of desoldering and re-soldering was repositioning one wire to make the circuit stock L'il Mouse. Well, worked just the way I wanted in the end! Clockwise giving more treble, and counterclockwise cutting treble.
Some mods call for 50k with an associated cap swap, I went with a B100k to the BYOC instruction's A100k.
— GAIN: Stock A100k, would've been modded but for the dagnabbed forgotten min-gain-mod-resistor. Didn’t want to try a 500k mod I’ve seen, will try that another time with more space in a bigger build. I've read 500k can be difficult to dial in.
CAPS
This build is for bass, so...
Bumped up the input 22n>220n, coupler before transistor 22n>220n and output 1µ>2µ2. I’ve read bumping the in/out/couplers is a waste of time, that the filter matrix is the place to tune the rat. Didn't want the Reutz Mod, as it supposedly changes the stock timbre of the circuit, so I when found the Tranter mod, that's what I went with.
C8 4µ7 Tantalum… I was going to make it a 2µ2 Film Cap for higher fidelity and it's still huge 'nough to let all the bass through. Someone else convinced me to put a stock value in. I used a tantalum to save space, and it's arguably better sounding than an electrolytic.
Caps for Tranter Mod #2: Tantalums to save space.
LM308’s slew cap: 33p with a 60p trimmer in parallel to experiment with.
C9 3N3 bumped to 4n7, wanted to go to 10n but was again convinced by my friend to stick closer to stock.
C6 stock is 1µ, but since it’s just some power filtering for the 4v5, I bumped mine up to 2µ2.
RESISTORS: Aside from the Tranter Sw, and the CLR I dropped to 2k2 from the recommended 4k7 — the rest is stock resistor values. I dropped the CLR because originally I was going to put in a Bi-colour LED (red=off/blue=on), but by the time I was done all the test-fitting, and testing and fitting and testing some more... I went with just a simple bright-white 5mm.
IC: stock LM308 — plastic DIP due to space constraints. I’ve got some of the metal-can LM-308H chips, but ... space.
Q1: stock 2N5458, but Socketed, so I can try a 5459 etc...
JACKS: notched the IN jack so the DPDT Tranter switch could fit.
Marvin’s Googly Eyes: From a bunch of different sizes leftover from decorating a pair of sneakers, I chose big as possible for Marvin, lest he look like a beady-eyed little runt.
Marvin’s Nose: Light-orange was meant to be pink, didn’t have pink and red just wasn't right.
SOLDER-MASK: before I started a trace looked like it was lifting, but turned out to be just the solder-mask (thanks again for the help I got here on the board for that). Nail-polished it (didn’t have any SuperGlue), so the trace wasn't exposed to whatever mods I was subjecting the project to. In the end, could've just left it.
Rat Fur: Donated by my Amp-Atelier friend, who gave me enough to breed a whole family of Siberian Hamsters. Marvin has a bit of a kilt, to hide the cover-plate. Can jam some pedalboard tape on his underbelly and stick him on my board now.
(Link for how to resize this monster was 404, and not in the FAQ for posting images.
First time I heard a Rat, I didn't like it — was on a friend's bandmate's board way back when. Times change, tastes change, and unlike that bandmate, knobs can be changed! Yeah, sounds really good when you adjust it to taste instead of 100% blasting every knob.
I thought my first Rat should be close to stock-sounding, albeit modded for bass. The 1590A doesn't give much room for mods and parts-value substitutions. Yet, I still went a little bass-crazy and every time I did my mentor-friend (amp-atelier) tried to reign me in ‘cause he thought I was building it for our guitawrist budday. No, it's
my Siberian Hamster.
Next time if there is one:
- Remember the minimum gain resistor;
- Use a lot less wire, it does NOT need to open like a book as shown in the instructions;
- Plan ahead better
- Don’t use thick-goopy adhesive that squeezes out the wrong end when applying it to the enclosure or Rat Fur (I couldn't find the adhesive I wanted to use, not for love nor money).
- Even out the volume between clipping positions; ie Add a resistor to the LEDs, but maintain enough forward voltage balance so the clipping switch still works.
Preferred modes: 1) Turbo LEDs, 2) stock 1N914s and 3) lastly the Fat Rat’s MOSFET and Shottky — co-inkydinkly the same order of volume loudest to softest.
To avoid angry-neighbours, I didn’t crank it in earnest. Normally, I test everything with my DoubleBass, which can howl with feedback when fed dirt. So I tested the Hamster with my YuBazz, and its completely hollow body wants to bay like a banshee, more than my DB. ;-D
The Tranter switch is subtle, possibly due to the neighbour-friendly feedback-fighting volumes used for testing.
The difference is audible, just not dramatic. The more the bass is bumped, you get more distortion and upper-order harmonics that comes with that extra gain. So bumping the bass seems like its bumping both upper mids and highs, too.
Gig at the end of the week, first in a lonnnnngggg time. Marvin will come with, see if he makes my upright howl...
Cheers,
Feral Feline.
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