Archive for the ‘Audio’ Category

Fixing Jeremy’s Ford Mach 460 Bass Amplifier

Saturday, October 2nd, 2010

Sometimes you get lucky.

Ford Mach 460 bass amplifier

My friend Jeremy has a 1995 Mustang that had the factory premium sound system in it when he bought the car used. The CD player was broken and he had the head unit replaced within a couple of weeks of owning the car. He later added a subwoofer.

I’ve always thought the stereo lacked clarity in the bass, and the head unit and EQ have had some quirks. Recently Jeremy pulled the head unit and found all sorts of interesting techniques used by the aftermarket installer that will be the subject of a later monologue … but one of the things we discovered is that the amplifier for the door woofers wasn’t working at all. Swapping it with the amp for the rear deck woofers caused them to go silent and the (shot) door woofers to work again (after resoldering their cut cables).

Turned out to be a delightfully easy fix.


Repairing a Crumar T1 Organ Swell Pedal

Friday, August 6th, 2010

Crumar stack

Both my Crumar T1 and T2 “portable” organs (the lower two cases in the stack) came to me without swell (volume) pedals. Each has a rotary potentiometer on its control panel for master volume, but I really want to be able to change the volume dynamically while playing. I’ve been using a Dunlop volume pedal (built into a rocker case identical to the CryBaby wah) on the organ’s output; but (at least when used with the organ) all of the pedal’s action is in about the lower quarter of its physical range, so it’s very finicky to use.

Crumar T1 organ swell pedal

I recently bought this original T1 swell pedal on eBay, listed as untested / project. That usually means tested / didn’t work / can get more money if I don’t admit that I already know it doesn’t work; but I figured I could fix whatever was wrong with it. And I have.

Crumar T1 organ swell pedal photoresistor enclosure


Repairing a Bad Horsie 2 Wah Pedal with Power Damage

Wednesday, July 7th, 2010

Bad Horsie 2 wah pedal

I recently ran across on Craigslist a

Bad horsie 2 that was plugged into the wrong power supply and messed up, and needs some minor electronic work.

I was intrigued by the challenge (I’m such a sucker for broken things, dang it) and bought it. When the seller and I exchanged the pedal for my cash, he remarked that he read on a forum that it probably just needed a resistor changed, and that if I were handy with a soldering gun I could probably do it myself.

Uh huh. Resistor.

Let’s dig in.

Bad Horsie 2 wah pedal circuit board

The circuit board has a hole in the top for a foam battery “cage” attached to the enclosure, something clever that I haven’t seen before. And it had no obviously damaged components.


Lacing the x0xb0x Wiring Harnesses

Sunday, June 6th, 2010

This isn’t part of a normal x0xb0x build so I didn’t throw it into my build notes, but I had fun figuring out how to route and lace the x0xb0x’s wiring harnesses. I know lacing is overkill for this; but without some kind of cable management, the individual wires of each cable wouldn’t even stay together. Had the kit included ribbon cables, I wouldn’t have bothered.

Planning the Paths

First pass at x0xb0x cable routing

Besides the obvious goal of keeping the wires tidy, my main goal was to position slack in the cables so that the back panel could be lifted out of the case and set to the rear, allowing full access to both circuit boards, without disconnecting anything.

Before doing any real lacing, I mocked up the cable path to make sure everything would work. My first attempt, here, had enough length for the J3 bundle from the lower right of the main board to the right end of the I/O board; but J7′s wires coming from the left edge of the main board looped around too much before heading to the I/O board and didn’t reach their destination.


Building the x0xb0x

Sunday, June 6th, 2010

As I noted previously, I recently got a x0xb0x kit. The x0xb0x is an open-source-hardware replica of the 1980s Roland TB-303 bassline synthesizer (and sequencer) that was influential in the development of acid house music. Limor of Adafruit Industries and a mysterious, anonymous German studied the TB-303 schematics and measured the behavior of its now-rare semiconductors and designed a replica with the same analog circuitry and new digital features, including MIDI I/O (supplementing Roland’s pre-MIDI “DIN sync”) and simpler sequencer programming.

Assembled x0xb0x, top view

Adafruit produced x0xb0x kits in batches of 100 as Limor was able to track down enough “rare parts,” order circuit boards, and assemble the common parts into kits. I’d been on her waiting list since 2008, so was terribly disappointed when she officially announced what we had all come to realize anyway — that tracking down the rare parts was becoming enough of a hassle, she wasn’t having any fun doing it and wasn’t going to produce any more kits.

Happily, Limor announced shortly thereafter that thanks to Adafruit’s open-source hardware license, James Wilsey of Willzyx Music in Taiwan has taken up the torch and would shortly be offering x0xb0x kits.


MIDI Looper?

Monday, May 31st, 2010

I’m starting to think I’d like a MIDI sequencer that behaves somewhat like a looper, doing the following:

  • Capture a short sample of a MIDI performance, including key velocity data.
  • Quantize to a tempo set by a “tap tempo” pedal continually and dynamically throughout the capture, rather than to an LED or click track.
  • Loop and play back, by default to the last tempo seen but honoring continuous “tap tempo” data from the same pedal.

Using a MIDI sequencer with these “tap tempo” features should give greater flexibility for capture and playback during a live ensemble performance than using a traditional audio looper, which requires the whole ensemble to play to the tempo recorded in the loop.

But my real motivation is to be able to play a pattern and then make gradual, multi-bar changes to the analog character of the sound without having to continue playing with one hand and turn knobs with the other.

Record a one-bar pattern on a MIDI keyboard driving a x0xb0x (or a real TB-303, if you’re filthy rich enough to have one and a DIN-sync MIDI adapter to go with it), then play it back and slowly tweak the knobs while everyone else jams on for a bit.

Am I going to find that all of this functionality already exists within the x0xb0x? (It looks like it might be close — MIDI ports; internal sequencer; variable tempo, although perhaps not that sophisticated.) Alternatively, are there MIDI sequencers that do all of this? Is this de rigeuer for every sequencer under the sun?

Repairing a Patch Cord

Monday, May 31st, 2010

Recently a couple of pieces of audio processing equipment I’ve bought used have had bad left channels. After recognizing the pattern, I finally thought to swap out the patch cord I had left plugged into the “test” channel on my keyboard mixer, and voila! Left channels fixed.

Audio patch cord, disassembled

I’ve always been curious about the construction quality of commercial patch cords — just how good are the connections buried under those lovely molded jackets and strain reliefs?

Naturally, the faulty end was the last one I disassembled. (Logic joke!)


x0xb0x Box!

Monday, May 24th, 2010

x0xb0x synthesizer kit, Willzyx edition

My x0xb0x kit has arrived from Taiwan!!!

x0xb0x synthesizer kit, Willzyx edition

Replacing a Broken Power Jack on a DBX 266XL Compressor

Sunday, April 11th, 2010

I recently bought a DBX 266XL audio compressor/limiter on eBay. The seller described it thus:

Has light scratches, small amount of rack rash, in perfect working condition- no issues whatsoever. Has been used in my guitar rig for the past several years with no problems.

Broken C-14 power jack on DBX 266XL compressor

It arrived oddly but adequately packed and … as you can see, not in perfect condition. I would go so far as to say it had issues. I suspect had I tried to use it, I would have had problems.

Well … I could complain to the seller, who would tell me it was damaged in shipping, and then I could try to deal with the USPS who I don’t think broke it, and I could spend a lot of time and frustration and maybe get some money back and probably end up with no compressor. Or I could just fix it myself and have a little fun in the process.


“New” Crumar T2 Organ Part 2: Easy Fixes and Investigation

Monday, January 4th, 2010

As mentioned previously, I recently bought a Crumar T2 organ manufactured in 1978 and started ascertaining its condition. Here’s what I’ve been able to fix so far and what I’ve been able to determine about the parts I haven’t yet fixed.

Crackly Volume Knobs and Stuck Master Tuning Potentiometer

Several of the volume knobs were pretty crackly.

Crumar T2 organ with control panel lifted

Most Crumar keyboards are wonderful to service because of how easy it is to get inside. After removing a few screws, the top panel lifts back on its rear hinge, without even having to take the knobs off all the controls.