Matchless Dirt Box | Part 5 : Ship in a Bottle

[@midtownunited9316]

I'm the owner of the pedal. It sounds absolutely amazing. It's just like Lyle said it would be: dead quiet, with no coloration when bypassed. He's worked on several amps for me over the years and they always come back sounding fantastic.

[@PsionicAudio]

Thanks Chris! I'll be getting to your Vibrolux next week!

[@shmert]

I've had one of these pedals in a box for 25 years. Just unearthed it, and the thing sounds pretty good (if noisy)! Who else is still using one? Happy to stumble across your excellent series!

[@breathtimebreath4934]

I’ve got an early 90s Hotbot 😊

[@breathtimebreath4934]

Wowowow!!!! Well done!!!!!👍

[@patricksrenaski3619]

Very nice work! The customer won't recognize the sound even in his bypass loop. I love the shoe on the knobs dexterity. I could NEVER get that skill to the point where I could adjust a pedal standing up. I'm impressed.

[@alexdeleon7135]

Well done!

[@sgt.grinch3299]

Fantastic reduction in hum. Did you have hair left after the goose chase?

[@lowdownfender]

AnalogMan buffers ! Got one

[@blubba4brainsfatnproud272]

Hey man, if you get to read this, what is the best approach to learn how to repair your own amps and pedals? Especially the older vintage circuits, not the newer smd ones. What kind of school teaches those things? Would it be a sound engineering school or would you recommend an associates in electrical engineering. I am not that interested in designing my products (even though that would be great), but I would definitely like to be able to build my own amps/pedals from kits, reverse engineer circuits and do my own repairs when needed.

[@PsionicAudio]

Like asking how to eat an elephant. One bite at a time. Start with making a tube screamer kit. Learn how to solder on that. When you get one that works and is quiet, figure out how that circuit works. Now ask yourself how to make it have more bass. Then less bass. Then brighter. Then darker. Then more gain. Then more mids. Then less. Then build a second one. Does that one work the first time? If not, practice more. Doing the above could take you 3-6 months or years. If you can get that far in 6 months or so you have a shot at it, at which point some community college electronics courses would be worthwhile. Once you have your soldering ability together (and I mean doing it well, not "sufficiently") and can make a tube screamer with no mistakes or issues AND YOU UNDERSTAND HOW IT WORKS, then build a Champ kit. And then learn that circuit the way you did the tube screamer. DON'T start with a large complex amp with high voltages.

[@blubba4brainsfatnproud272]

@@PsionicAudio thanks👍🏼

[@goodun2974]

Another usefull exercise: get ahold of a small 3-tube Champ-style Class A amp (12AX7, 6V6 or EL84, 5Y3 rectifier), handwired ---- no printed circuit boards! ---- for which you can obtain a printed schematic; examine the inside of the amplifier and compare it to the schematic, part for part, then set the schematic aside and hand-draw a schematic for the amplifier, using your eyes and an ohmmeter to trace the connections (use a pencil, eraser, and whiteout as needed). Compare your hand-drawn schematic to the factory schematic for accuracy, and learn how to draw and redraw the schematics so that they are more easily understandable. This will be easier if the amp is constructed with an eyelet board, tag board or turret board; true point to point construction can be tricky, especially for a newbie, to suss out. A typical 3 tube amp, like a Champ, might only have 15 to 20 caps and resistors, making it a good place to start. Then try this process again with a 4 tube amplifier, perhaps a Vibrochamp or similar which adds tremolo to the tube circuits you've already become somewhat familiar with; or a push-pull 4 tube amp with a 12AX7, two 6V6 or El84, and a rectifier tube. Tracing the circuits by eye and ohmmeter and drawing them out by hand will train your brain, and familiarize you with reading color codes, measuring resistor values for accuracy or "drift", and using the ohmmeter to check for continuity and power-supply flow. All of this can be done with the amplifier off and unplugged, therefore free from shock hazard (drain any stored voltage off of the filter caps before beginning). Once you've done this on two or three different amps, you can power them up and carefully make voltage measurements, comparing your measurements to those on the published schematics. Eventually you can work your way up the food chain to more sophisticated amplifiers with more tubes, perhaps point to point wired, or even amps which don't have schematics available. If you can hand draw a legible and understandable schematic for an amplifier with 4 or 5 or more tubes and for which a schematic isn't available, perhaps one that is point to point wired, congratulations will be in order!

[@retread1083]

That was quite the adventure, turning this PoS into something well behaved and useful. I think Matchless missed on the name. Dirtbag would have been less accurate since it's a box not a bag. But it would have been a more amusing name.

[@goodun2974]

Since this is an AC-powered device, I have to wonder if the now-reduced hum level is reasonably stable and consistent at varying AC input levels. Checking its noise-reduction performance with a variac, from say 105 to 125 VAC, might be a good idea. It's also possible that the current draw of the #47 lamps could be a factor in how it performs at the lower end of the input VAC range. Are the lamp filaments run off of DC, or AC ? Because the lamps are directly under the pots, and the lamp filaments might throw off a hum field, not to the same extent as the transformer, but I bet they can add to the hum. Plus, its a lot of additional heat in an enclosed space.

[@PsionicAudio]

I don't think you understand the constraints of billing by the hour. I already did much more than most techs would (or in all modesty, could) on this pedal. It's done and back to the owner. Not my job to fully redesign Matchless products.

[@douro20]

I would like to see a battery powered tube pedal using Russian rod pentode tubes. Their low-voltage performance is very impressive.

[@goodun2974]

@@PsionicAudio , oh, believe me, I got that part! I'm just asking questions in my head, as an exercise in remote problem-solving, a brain-teaser of sorts. I was curious if the lamps and tubes were heated from AC or DC and if they were being over-voltaged (those lamps were badly blackened). You certainly did more work than was called for, and no, you shouldn't have to reinvent the wheel; shame on those manufacturers who put repair techs in that position. Anyway, unplugging the lamps to see if anything changed, and playing the unit while adjusting a variac, would have taken less than 10 minutes. FWIW, I've seen plenty of tweaky audiophile amps with power supplies that wouldn't regulate at less than 110 volts, or above 125, and would hum badly at low or high wall voltages. Sometimes there was a practical fix, and sometimes not......

[@goodun2974]

@@douro20 , I have a few American made subminiature "pencil" tubes around here somewhere, but none that really cry out for audio applications. The other possibility for tube-based pedals that can run at very low voltages are "space charge" tubes that were specially designed to work efficiently at just 12 volts on the plates, in 1950's car radios. They are inexpensive as NOS because there's little demand for them nowadays. Prior to that, some radios needed a "vibrator", a mechanical forerunner to the pulse mode power supply, in order to generate 50 to 100 volts from a 12 volt car battery. Theres an article by Jeff Duntemann about space-charge tubes at junkbox [insert the usual punctuation symbol) com, as well as a great article about Compaction tubes that may be usefull for anyone with an Ampeg amp that uses a compactron, or the oddball Fender with a 6C10....