Wednesday, March 23, 2016

1900ish Stainer Violin

After several months of watching low-priced violins on ebay I finally found this beautiful 100ish-year-old German-made violin! I've seen similar fiddles slip through the proverbial cracks on ebay many times before (attracting little attention and few bids), but this one looked particularly nice. The dramatically sloped top and bottom suggest that real effort and time were put into this instrument. I bid a maximum of about $165 and won it for $108!

(These three images are from the original ebay listing.)

When it arrived I was disappointed to discover that the fingerboard had cracked in transit! The seller took the bridge down for shipping, leaving the fingerboard vulnerable. He also accidentally missed the insurance option when shipping but offered me $60. I accepted the partial refund and decided to replace the fingerboard myself at the Appalachian Artisan Center luthiery where I apprentice.

I removed the old one and discovered that it wasn't the original and not even ebony, but a cheap replacement. It was a low quality repair job-- it was not well matched to the shape of the neck, was not well glued and was made of ebonized pearwood.

Doug Naselroad, the master luthier at the shop graciously supplied me with a fingerboard blank. It took three or four hours for me to sand and shape it... But hey, it was my first time! And ebony is some hard stuff!

We made up some hide glue, heated the neck and the fingerboard with a hair dryer, and then clamped it to cool and dry.

Then the neck and fingerboard needed to be sanded down to create a smooth junction where they meet. I also sanded away some of the neck joint around the body where it showed on the sides of the fingerboard.

After some nice 600-grit sandpapering, the back and sides of the neck really do feel smooth like silk. And some linseed oil helped blend the appearance of the new with the old.

The original bridge worked fine, but Matt over at WMMT gave me a bunch of old fiddle spare and junk parts and I decided to try some lower bridges. One made the D, A and E strings so much easier to play ...but the G buzzed a bit. I copied its contour onto a vintage Dresden bridge blank, but kept the G a little higher. After an hour of careful shaping, cutting and measuring I brought the strings up to tension and one of the bridge's feet snapped off, startlingly! ;( ;(

I was able to cut down the Teller bridge which came on the violin to a similar shape and it plays marvelously!

This chin rest needed some serious work (bending, sanding, gluing), and it had no cork to keep it from scratching the fiddle. I used two bits of leather with good results.

I found this old wood hardshell case at a thrift store in Hazard. I haggled to $15 for it and a vintage ukulele case!

Some piece was missing which secured the bow on one side, so I cut and sanded a scrap of wood to serve this purpose. I'll have to stain it tomorrow since Kate and Doug have both suggested it!

Monday, May 4, 2015

effects pedal DC power filter and photoresistor box

This tiny unit conditions the DC power from any generic 9V-13V adapter to provide a clean-sounding effects pedal power source. Hum is greatly reduced by a very simple one-resistor, three-capacitor filter circuit.

I use it with a very noisy, low-quality, ancient, hacked radio shack wall-wart adapter. The adapter plugs into the right DC jack, and a daisy chain cable powers my pedals from the left DC jack. The LED indicates that the DC filter is engaged. If no power adapter plug is connected to the right DC jack the internal 9V battery is utilized instead-- Great for emergencies!

The top of the enclosure has a photoresistor (LDR) connected to a stereo 1/4" jack. The LDR works like a variable resistor between the jack's tip and ring. This makes it compatible with stereo cables for 'expression pedal' connections or CV send/returns. This configuration is also compatible with mono cables-- in that case the LDR will work as a variable resistor between tip and ground.

Connecting the LDR to another pedal's expression pedal input, expressive filter sweeps, manual phase/chorus modulations, etc are created by blocking the LDR's exposure to light. The unit also includes a reverse polarity protection diode.

The biggest challenge was fitting a switch, two LED bezels, a 1/4" jack, two DC jacks, a tiny circuit board (including two radial electrolytic capacitors) and a 9V battery into the little case. Shrink tube came in very handy... :)

Sunday, August 12, 2012

versatile EH small stone

smallstone1 smallstone2 This Electro-Harmonix Small Stone phaser has components from eras of both the second and third Russian-made versions. The PCB layout seems to be the third version, though the schematic and part values are similar for either.

I've always thought it had a great sound.. but the major drawback is its extreme lack of flexibility. A stock Small Stone has only two controls- a potentiometer to vary the rate and a 2-position "color" switch.

First, I added a CV input- a switched 1/4" jack which interrupts the connection between the LFO's output and the inputs to the four OTA phase shift stages. Clamping diodes and a current-limiting resistor protect the OTAs. This modification allows the phase to be controlled by a synthesizer's LFO, an expression pedal, random S/H, analog sequencer, etc.

In the original design, engaging the DPDT "color" switch adds a lot of feedback, increases the depth of the LFO, and also slows its rate slightly. I disconnected the feedback portion of this switch, and installed a pot to vary the amount of feedback- from none to near-oscillation.

The other half of the original "color" switch (which affected LFO depth and rate) is now on the top left of the pedal and is labeled "deep/shallow". The switch on the upper right, which is labeled "phaser/vibrato" simply removes the dry input signal from the mix, creating a nice mild vibrato effect.

The four original OTA caps were all .0068uf. I replaced C4 and C5 with .022uf and .22uf. A DPDT toggle switches the third and fourth caps (C8 and C9) between the stock value and .00047uf / .0047uf.

My unit did have a very noticeable volume drop when engaged. On web forums, many people suggest replacing R42 (4.7k) with a 10k (or even 12k) resistor, however many also complain about reduced headroom and bad distortion once they've made this modification. R42 affects transistor biasing and will cause distortion if its resistance is greater than 8 or 8.5k. Based on my experience, an 8.2k resistor would be the most ideal replacement. I used a 10k trimpot (set to approximately 8.3k).

Also, that annoying 1/8" DC power jack has been replaced with a standard 2.1mm barrel jack.

Here are a few sound samples:
- smallstone1.mp3
- smallstone2.mp3
- smallstone3.mp3

All component names refer to these schematics (via
- ggg_smallstj_sc.pdf

And here is the documentation for all of my modifications:
- my_smallstone_mods.pdf

E-mail me if you'd like to have your Small Stone modified similarly!

Friday, April 24, 2009

moog VCF in vintage enclosure

Over the course of the past few years I've owned two Moog Prodigies. I got the first (keyboard-less) one about six years ago and modified it extensively. Eventually I sold it to buy the second one, which is covered in an previous post.

Of all the Prodigy's features, I've really just missed the warmth of the transistor ladder filter. But I've been so completely satisfied with the EML101's sound and versatility in every other regard that I decided it would be best to build a VCF module based on the Moog design.

I've never had much discipline for prototyping or PCB layouts so I arranged and soldered the parts on perf board and let the schematics guide me as I went. It's a challenging aspect of my electronics work.. but it's a good exercise in creative problem-solving.

While checking local thrift shops for an enclosure, I found this old electric shoe-shiner. The 'Regina'-brand "Electric Shoeboy." It originally had an industrial-type motor inside and rotating brushes protruding from each side.

After removing the motor and the shaft, dremmeling the case, and cutting, super-gluing and epoxying aluminum to cover the side holes, I had this finished enclosure! (The last image in this post was found on google to show what this unit looked like before modification.)

I based my circuit on yusynth's plans, but changed a few component values for a greater range of control. I also scaled the keyboard CV input for the EML101, with a SPDT switch to select between 1.2V/octave and 1V/octave.

Here are a few sound samples:

- moogvcf1.mp3
- moogvcf2.mp3
- moogvcf3.mp3
- moogvcf4.mp3
- moogvcf3.mp3
E-mail me if you'd like me to build a synth module in an enclosure of your choice!

Thursday, March 26, 2009

moog (modular) prodigy

This is a truly unique Moog Prodigy! I purchased it on ebay- broken- about a two years ago. After restoring all of its original functionality and its original appearance, I realized it held a lot of potential for interfacing with other modular equipment, including my EML101.

Luckily, this was the later model with the Sync Input, VCF Cutoff In, Oscillator In, Keyboard In/Out, and S-Trig In/Out.

I added a Gate Input, Gate Output, Oscillator 1 Output, Oscillator 2 Output, Mixer 1 Input, and Mixer 2 Input.

The 'Mixer Inputs' come before the Mixer potentiometers, so (one or two) external signals can be injected, attenuated, and mixed.

The Oscillator Outputs are interesting, too, because they can be used as effect send/returns. For example, one oscillator can be run through a phaser or vibrato effect, while the other is left dry.. and they both run through the VCF and VCA.

In lieu of drilling and adding a VCF FM control pot, the Oscillator Output jacks make it possible to patch the audio frequency CVs to the VCF CV Input with a simple attenuator in between.

I built an additional unit to serve as the Prodigy's second LFO, Noise Source, and patching Attenuator.

Due to financial constraints, I had to sell this Prodigy on ebay about a year ago. I vowed to one day build a clone of its VCF (so the EML101 could impersonate the Moog sound).

Here are some sound samples (recorded with the additional module for modulation, noise, and/or patching.. and some spring reverb):
- prodigy1.mp3
- prodigy2.mp3
- prodigy3,mp3
- prodigy4,mp3
- prodigy5,mp3

E-mail me if you'd like to have your prodigy modified similarly!

Thursday, February 26, 2009

modified poly-800 mkII [number two]

This Poly-800 mkII features the same modifications as my previous Poly-800, but it also includes the 2/4-pole filter switch.

The 2-pole VCF output sounds wonderful. If Korg (25 years ago) had me helping to make their big decisions, I would definitely have argued that the filter output must be switchable between 12 and 24 dB/oct.. I also wish they'd added this option on the DW-8000.

My control layout and labeling were also improved on this Poly-800. Additionally, the external input can now be used regardless of the setting of any parameter when the 'Noise+EG3' switch is turned "off." This causes the third envelope to have no effect on the external input level. So, to solo the external input, parameters 17 and 27 (Osc. 1 and 2 levels) simply need to be turned down.

When using my EML101 (or the Axxe I'm modifying for a local customer) to generate triangular LFOs, random S/H, or even envelopes to control the Poly-800's filter, I realize how lively the it can really sound. It takes on a much more antiquated and nuanced character. I think the 800's modulation generator just doesn't sound as smooth as a real analog LFO.

Recently, Kate and I have recorded a lot of material using the Poly-800 for its abilities as a synthesizer, but also as an effect processor for guitars. It appears on some of the new hushes and briefscenes songs.

This Poly-800 mkII was sold on ebay. ..including that cool original case!
I wish I'd kept that!

Saturday, December 20, 2008

modified korg poly-800 synth / processor

The Poly-800 mkII includes a wonderful, warm (stereo) digital delay (with modulation!), a great-sounding VCF, three envelopes (one for each of the two oscillators and one for the noise source/VCF), and an LFO to modulate filter cutoff or pitch.

I've also added several well-designed modifications on this unit. First, it now has a VCF CV Input, which allows the filter cutoff to be modulated by a modular synth, CV pedal, or other signal generator. The input is designed to receive 0-5V. Clamping diodes and a current-limiting resistor ensure that voltages outside of that range will not harm the Poly-800's circuitry.

Second, I added an External Audio Input to the Poly-800's VCF and digital delay. The modulation delay provides great analog-type echoes, flanges, and choruses. Modulated filtering can also yield some very interesting effects.

This input is designed to work perfectly with guitars or other low-level signals. An added circuit provides the right impedance and just enough gain to boost such a signal, and a pot allows for attenuation before the gain stage.

The Noise / External Audio Switch disables the white noise source, so that the external signal can run through the Poly-800 alone. The DPDT switch also holds the VCA level at maximum (regardless of the settings of parameters 61-65).

The Filter FM control pot adjusts the depth of Filter Cutoff Modulation from DCO1's audio. This allows for an extreme range of sounds- from growling synth bass to ring modulator-type noises. It should typically be used with Chord Memory in 'mono' mode.

And VCF Cutoff and Resonance pots allow the cutoff frequency and the amount of resonance to be tuned in real-time.

The program parameters (31 and 32) now set the maximum levels. The filter will self-oscillate, and the resonance pot offers its full useful range when parameter 32's value is set to 12.

Here are a few examples of this Poly-800's more unique capabilities:
- FMsyn.mp3 (FM, cutoff, and resonance settings are being tweaked.)
- SHgtr.mp3 (Guitar is being processed with a random S/H input to the VCF CV Input.)
- spacegtr.mp3 (The delay sounds beautiful as a guitar effect.)
- SHsyn.mp3 (Again, the filter is being modulated by the EML101's random S/H output.)
- warblegtr.mp3 (The filter is being modulated by the Poly-800's internal modulation generator.)

E-mail me if you'd like to have your Poly-800 modified similarly!