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Discussion Starter #1 (Edited)
Hey guys I need to pick your brains a little and tell you a story!

And I hope this is posted in the right spot!

So my wife's cousin's husband and I both have a love for music ( as we all do here) he and I will often cobble together instruments when they visit or sit around and jam all day. He's a very rootsy leather tramp banjo playin, while kickin a wash tub for a bass drum kinda guy. While I'm more of a turn the amp up till my ears bleed kinda guy. Anyways... He lives in Kingston and I live in ptbo so we only see em a few times a year, that's not really relevent to the story I guess, but he was taking some brush to the dump a few months back and while he was there spotted a cardboard box with patchcords hanging out of it. Upon further inspection under the cords were a bunch of pedals. Him being a musician of the non amplified persuation and not knowing what the pedals were thought hey Cory might like these for knobs and parts and stuff. Fast forward to this weekend when they come to visit. He hands me a handwired mxr distortion plus script logo, a Piedmont aluminum falcon 2, line 6 dl4 delay and a tc electronic flashback delay. All of them were pretty dirty and he had just taken for granted they were all pooched. All but the mxr worked flawlessly. The Piedmont has a sticker on the inside that says 12 of 200, from what I've read it's a very accurate repro of a klon. Anyways HOLY SHIT WHAT A SCORE. I can't imagine the reason they ended up at the dump???
Anyways here's the question part. So the mxr was the only one with filth on the inside, and someone had left a battery in it that exploded over time. At first no signal came through. So I pulled it all apart cleaned all the gnarly acid garbage as best I could and resoldered in a new 9v supply as the old one was rotted to dust. Signal comes through now but only when the volume and distortion knobs are cranked and it sounds thin. Are the pots the culprits here. They are both quite rusty? Any thoughts or ideas on what's causing these symptoms.
 
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The AF2 may have some issues. I bought one of those and it has some issues. He changed the board or something after the first run.. I got a replacement from him during the internet s**t storm over it. I remember the buffer doesn't go to bypass with the bypass switch, and there is a ground hum on it if I touch the pedal anywhere with my finger. But the pedal is still quite usable. I don't think it makes a hum on it's own, and buffered. Enjoy!
 

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Cool find--hopefully others here will be able to help out some...

Enjoy!
 
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Discussion Starter #5
The AF2 may have some issues. I bought one of those and it has some issues. He changed the board or something after the first run.. I got a replacement from him during the internet s**t storm over it. I remember the buffer doesn't go to bypass with the bypass switch, and there is a ground hum on it if I touch the pedal anywhere with my finger. But the pedal is still quite usable. I don't think it makes a hum on it's own, and buffered. Enjoy!
This AF2 seems to be mint. I have a homemade fuzz that sounds totally different for whatever reason if it's placed after a buffer pedal. And AF2 has this affect on it. It's got a little handwritten thank you message on the back cover too!

Any ideas on the mxr?
 

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The early Distortion+ design did not have a lot of output, partly due to the use of a volume pot value that was too low. Changing it from 10k to 100k improves things. As well, the design has a bass cut that moves steadily upward as you increase gain, resulting in a thinner sound as one approaches the sorts of output levels that a hard-rockin' guitar-player would want. The Ibanez Tube Screamer has a similar bass rolloff frequency, but since it also includes a lot of treble-cut to counterbalance, it doesn't sound shrill. The Dist+ lacks any such balancing treble-cut so it sounds thin/shrill/tinny. I suspect, but don't "know" that MXR did this because the pedal came out well before there were very many hum-reduction solutions for single-coil guitars. One of the side benefits of their gain control was that 60hz hum was amplified less as gain was increased. But like I say, I'm just speculating here.

In addition to changing the value of the volume pot (which MXR later did), the sound can be improved by replacing the .047uf cap connected to the gain control with a larger value, like .1uf or .22uf. It's a dirty distortion, so I wouldn't fuss over what type of capacitor to use.

As a sidenote, the op-amp chip used - a 741 type - provides its own clipping without needing any diodes. Many builders have commented that they can't get any clean sound out of it. So, in some respects, it is a "double clipper" (i.e., clips the signal twice, once via headroom limitations, and a second time via diodes).

In any event, VERY nice score. Having both of those delays is a pretty big deal.
 

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Discussion Starter #8
Nothing to add here except this find would not happen to me.
This doesn't happen to me either. But the afformentioned cousins husband seems to have a knack for picking. This isn't the first time he's showed me something begotten for free from places unknown. And before anybody says it. Lol. He's very law abiding (when it comes to people's personal property) salt of the earth kinda guy. He's totally a societal fringer but a good honest guy non the less.
 

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This AF2 seems to be mint. I have a homemade fuzz that sounds totally different for whatever reason if it's placed after a buffer pedal. And AF2 has this affect on it. It's got a little handwritten thank you message on the back cover too!
Actually, there are a great many fuzzes that don't sound all that great if preceded by a low-impedance source (which the buffer would present). It's a common complaint. That's why more recent licensed Klon Centaur clones have a switch to deselect the buffer, and enable true bypass. Some things - e.g., the old Dallas Rangemaster - expected to be fed the guitar directly and also feed a tube amp directly. In other words, its "sound" depended on the right kind of loading.
 

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Discussion Starter #10
The early Distortion+ design did not have a lot of output, partly due to the use of a volume pot value that was too low. Changing it from 10k to 100k improves things. As well, the design has a bass cut that moves steadily upward as you increase gain, resulting in a thinner sound as one approaches the sorts of output levels that a hard-rockin' guitar-player would want. The Ibanez Tube Screamer has a similar bass rolloff frequency, but since it also includes a lot of treble-cut to counterbalance, it doesn't sound shrill. The Dist+ lacks any such balancing treble-cut so it sounds thin/shrill/tinny. I suspect, but don't "know" that MXR did this because the pedal came out well before there were very many hum-reduction solutions for single-coil guitars. One of the side benefits of their gain control was that 60hz hum was amplified less as gain was increased. But like I say, I'm just speculating here.

In addition to changing the value of the volume pot (which MXR later did), the sound can be improved by replacing the .047uf cap connected to the gain control with a larger value, like .1uf or .22uf. It's a dirty distortion, so I wouldn't fuss over what type of capacitor to use.

As a sidenote, the op-amp chip used - a 741 type - provides its own clipping without needing any diodes. Many builders have commented that they can't get any clean sound out of it. So, in some respects, it is a "double clipper" (i.e., clips the signal twice, once via headroom limitations, and a second time via diodes).

In any event, VERY nice score. Having both of those delays is a pretty big deal.
Super good score after some more in depth looking this morn. The mxr is an origional 1978 model. Regrettably somewhere along the line somebody drilled the side of the case for a 9v power supply. It was rotted
The early Distortion+ design did not have a lot of output, partly due to the use of a volume pot value that was too low. Changing it from 10k to 100k improves things. As well, the design has a bass cut that moves steadily upward as you increase gain, resulting in a thinner sound as one approaches the sorts of output levels that a hard-rockin' guitar-player would want. The Ibanez Tube Screamer has a similar bass rolloff frequency, but since it also includes a lot of treble-cut to counterbalance, it doesn't sound shrill. The Dist+ lacks any such balancing treble-cut so it sounds thin/shrill/tinny. I suspect, but don't "know" that MXR did this because the pedal came out well before there were very many hum-reduction solutions for single-coil guitars. One of the side benefits of their gain control was that 60hz hum was amplified less as gain was increased. But like I say, I'm just speculating here.

In addition to changing the value of the volume pot (which MXR later did), the sound can be improved by replacing the .047uf cap connected to the gain control with a larger value, like .1uf or .22uf. It's a dirty distortion, so I wouldn't fuss over what type of capacitor to use.

As a sidenote, the op-amp chip used - a 741 type - provides its own clipping without needing any diodes. Many builders have commented that they can't get any clean sound out of it. So, in some respects, it is a "double clipper" (i.e., clips the signal twice, once via headroom limitations, and a second time via diodes).

In any event, VERY nice score. Having both of those delays is a pretty big deal.
Super good score considering I just found out it's a 1978 model!!!! Regrettably at some point it was drilled out for a 9v input jack which was rotted. So then( before I realized it was origional and not the reissue) I drilled the hole a little bigger to replace the jack...I know...I'm a bone head.
 

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Discussion Starter #11
Actually, there are a great many fuzzes that don't sound all that great if preceded by a low-impedance source (which the buffer would present). It's a common complaint. That's why more recent licensed Klon Centaur clones have a switch to deselect the buffer, and enable true bypass. Some things - e.g., the old Dallas Rangemaster - expected to be fed the guitar directly and also feed a tube amp directly. In other words, its "sound" depended on the right kind of loading.
I dunno man. I copied the bazz fuss circuit for my homemade jobby. And it rocks way better with any boss pedal stuck in front of it
Edit: I wasn't disputing your statement. Sorry if it came across that was
 

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I can't imagine the reason they ended up at the dump???
Parent or ex.

Anyways here's the question part. So the mxr was the only one with filth on the inside, and someone had left a battery in it that exploded over time. At first no signal came through. So I pulled it all apart cleaned all the gnarly acid garbage as best I could and resoldered in a new 9v supply as the old one was rotted to dust. Signal comes through now but only when the volume and distortion knobs are cranked and it sounds thin. Are the pots the culprits here. They are both quite rusty? Any thoughts or ideas on what's causing these symptoms.
How did you clean it? Just wiping with a rag may not be enough, it is safe to use 99% isopropyl alcohol in there (if not on the shelf at the drug store ask for it at the counter). Go at it with a toothbrush. You need to get all the battery acid out of there. I had my studio flood so been there. Managed to save everything except possibly a friend's multi-effect thing, which I still have to take a second shot at.

If the pots are rusty, change em. Probably a lot of dirt inside them anyways and not worth trying to clean. Also note the value change Mhammer suggests. That's cheap and relatively easy.
 

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Discussion Starter #14
Parent or ex.



How did you clean it? Just wiping with a rag may not be enough, it is safe to use 99% isopropyl alcohol in there (if not on the shelf at the drug store ask for it at the counter). Go at it with a toothbrush. You need to get all the battery acid out of there. I had my studio flood so been there. Managed to save everything except possibly a friend's multi-effect thing, which I still have to take a second shot at.

If the pots are rusty, change em. Probably a lot of dirt inside them anyways and not worth trying to clean. Also note the value change Mhammer suggests. That's cheap and relatively easy.
Yup I lightly did the isopropyl thing but I'm gonna change the pots today and report back .
 

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You didn't do anything to compromise its "value" by installing a wallwart jack. I don't consider it a particularly great design. Its real strengths lie in being a terrific platform for learning about, and how to do, mods. I have a zillion of them if you're game.

BTW, if you're game, both the Flashback and DL4 have stereo capabilities. Many musicians ignore them because they figure "I don't have a stereo rig". But most such pedals allow for "re-processing". That is, you can plug into one channel, and feed its output back to the input of the 2nd channel, providing a different twist on the same effect. What's ultra-cool is "re-reversing" reverse delay. Since many such pedals assume the user will be feeding it a mono signal, even if using two amps, they often provide two slightly different outputs at the output jacks. So, when you patch an output back to the other input, you get a fascinating combination of forwards and backwards delays. Try it, but remember to call in sick, because you won't be showng up for work that day.
 

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Discussion Starter #16
You didn't do anything to compromise its "value" by installing a wallwart jack. I don't consider it a particularly great design. Its real strengths lie in being a terrific platform for learning about, and how to do, mods. I have a zillion of them if you're game.

BTW, if you're game, both the Flashback and DL4 have stereo capabilities. Many musicians ignore them because they figure "I don't have a stereo rig". But most such pedals allow for "re-processing". That is, you can plug into one channel, and feed its output back to the input of the 2nd channel, providing a different twist on the same effect. What's ultra-cool is "re-reversing" reverse delay. Since many such pedals assume the user will be feeding it a mono signal, even if using two amps, they often provide two slightly different outputs at the output jacks. So, when you patch an output back to the other input, you get a fascinating combination of forwards and backwards delays. Try it, but remember to call in sick, because you won't be showng up for work that day.
Yeah once I have it working properly I'd be game for some tasteful mods. I don't wanna bastardize it too much though
 

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Discussion Starter #18
Not at all. Just things to smooth it out and give it a little more oomph.
Well I'm always down for more oomph. Do tell.
I do enjoy the semi fuziness of it though. I have a boss ds1 and a tc dark matter for distortions (and I like em) but the mxr has some durrrt and I like it. )
 

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Discussion Starter #19
Well I was wrong. I just dated all the guts of the pedal and it's all 1975,76... Do I have something rare or special here? The board has a set of initials on it and does not say built by guitar players for guitar players as I've seen other boards say. Inside the case it says mxr innovations and the box has a sticker with 413676 on it. And like I said earlier it's like all point to point wired but utilizing a board.
 

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AFAIC, nothing special or rare, though I'm not the world's greatest fan of mojo, and don't frequent reverb.com. Given just how many dead mint early-issue distortion+ units are out there, a beat-up one would require waiting a while for the right sucker to come along.

How to improve it.

1) As noted earlier, the volume pot needs changing. In tandem with the 10k resistor before it, the stock 10k volume pot functions like a 20k volume control that can never be turned up above half. Installing 100k regains a big chunk of the missing level, allowing for even medium gain settings to provide a volume boost. Use a log pot.

2) There's a lot of fizz in the unit. If your speakers can't convey the difference between SC and HB pickups then its no problem, If they have any treble response, then you'll want to tame the fizz. There is a 1000pf (.001uf) cap in parallel with the diodes, but it only provides a rolloff starting above 15khz, which may stabilize the chip but does buggerall for the fizz. Bump that up to 3300pf to provide a rolloff starting around 4.8khz. The rolloff is shallow (6db/oct) so you won't lose the bite. That can, and should, be supplemented by a second cap - 47pf is probably appropriate - in parallel with the 1M feedback cap between pins 2 and 6 of the chip. That will yield a rolloff starting around 3.4khz. Again, that sounds low, but is shallow and keeps the bite. Remember that the clipping diodes will add more harmonic content than they are fed with. Nobody really likes harmonics of harmonics. Clean 'em up early. You won't miss 'em.

3) As noted earlier as well, the .047uf cap tied to the gain pot trims bass as you increase the gain. You can keep more bass by increasing it to 100nf-220nf (0.1uf - 0.22uf). The larger the value, the more bass at max gain. Cap type doesn't matter.

4) The DOD 250 - an equally-liked overdrive - uses silicon diodes, where the Distortion+ uses germanium. Silicon has a higher forward voltage, resulting in a higher clipping threshold. That means less distortion for any given gain setting, but much more output level, making medium gain settings, for a hint of grind, robust enough to push an amp or stack with another overdrive pedal. Germanium will have a lower clipping threshold. So, more dirt, for the same gain setting, but noticeably lower output, even with the volume-pot change. Some folks like the one and some like the other. Neither are "better", just better-suited to different purposes/goals. If you replaced ONE of the germanium diodes with a silicon type, you would have a version of asymmetrical clipping, and a bit of a volume boost over a stock unit. A reasonable compromise.

There. That'll get you started.
 
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