Help with Bud Box Dynacomp

[Erlend]

Hi!

Could I maybe get some help in salvaging an old Bud Box MXR Dynacomp?

When I got this thing on my desk, it had holes drilled for an LED mod, and it wasn't working. So I've tried my best to get it going, with a true bypass mod as well. I almost got it, but it's distorting quite a bit.

I've tried to finesse the bias, with things like turning the dials all the way up, not strumming the guitar and setting it where it's the most noicy. This is somewhere pretty close to the middle, but not dead center.

Here's a sound example:

1. Clean sound
2. Sensitivity at eight
3. Sensitivity at elleven

Any ideas? It looks like it has quite a few bits changed on the PCB, so don't know how easy it is for you to help me, heh.

Thanks!

-Erlend

[TomCarlos]

Hi Erland....

Level 1 tech here. I did a Google Search for this device. You can do the same. You might find a schematic and photos of the PC board - both sides. I am attaching photos I found on the net. I also found a schematic. Let's look at the obvious first.

When I compare the PC board pic to what you have, I noticed a few things.

1) Your device has a new switch so that an LED will lite up when the device is on.

2) Your device has electrolytic caps - are they installed correctly?

3) I may be wrong, but if your device has the original transistors, are they installed where the flat edge is facing down?

4) I would see if you can restore this back to the original design for now. You'll need to figure out what changes where made for the true bypass.


See if what you have looks like the sample photos and schematic.

[Helmholtz]

What does bud box mean here?

[TomCarlos]

What does bud box mean here?

I believe "Bud" refers to an all metal enclosure. If you look on the removable lid, the word "Bud" might be stamped there.

[Helmholtz]

So what does the "bud box" case tell us about the unit?

[mozz]

Just that it was a early unit.

[DrGonz78]

So what does the "bud box" case tell us about the unit?

Or I could make something up. Like it was a metal box that some hippie electronics dude used to hold his pot. Then one day it became the Bud Box when he built an effects pedal using it as the case. Balderdash!!

[Mark Hammer]

The 3080 is known to not handle hot signals very well. This graph from a Jan 1980 article in POLYPHONY by Jim Patchell - who has probably studied the chip more than most - compares the distortion at different input amplitudes for a CA3080 and CA3280. Indeed, Craig Anderton used the 3080 for a voltage-controlled distortion module. So the pedal comes by the distortion honestly. For some player's it's a feature, not a bug. More recent Dynacomps use more recent OTAs. like the LM13700, which are a little more robust. What happens when you turn the bass's volume down a bit?

Incidentally, you'll note that, despite all the chatter one runs into about cap types, that pedal elied fully on cheap ceramic disc types, plus one tantalum People tend to overlook the fact that the big pots and footswitches tended to leave little room in those enclosures - whether Bud Boxes or Hammond - .between the circuit board and the bottom plate of the enclosure, so MXR made it a practice to use components that could be easily bent over flat. Not just transistors, but capacitor types as well. The dimensions of those enclosures have not changed in the last 50 years, but the pots and footswitches have gotten smaller, , leaving a little more clearance for electrolytic caps that stand upright.

[Erlend]

Thanks for your reply, guys!

I will test some more in the next week, and get back to you. But will provide some answers here now as well:

From/to TomCarlos: (Is it possible to mention users on this forum?)

1. Your device has a new switch so that an LED will lite up when the device is on.
   • Yes, I installed it. When I got it, it had drilled holes for LED and DC Jack, but they weren't installed.
2. Your device has electrolytic caps - are they installed correctly?
   • Heh, I don't know. Any tips on how I can check? I haven't done any adjustments to the PCB.
3. I may be wrong, but if your device has the original transistors, are they installed where the flat edge is facing down?
   • Same answer as on number 2! ☺️
4. I would see if you can restore this back to the original design for now. You'll need to figure out what changes where made for the true bypass.
   • In addition to the LED and DC jack, I also installed the footswitch. But I didn't touch the PCB (just followed a true-bypass guide), and if I remember correctly, it had the exact same issue before that change.

My best guess is perhaps that it has something to do with the components on the PCB that has been swapped out through the years..?

----------

To Mark:

Yeah, I noticed that it was pretty tight up against the backplate! Do you have any advice on things I could try and swap out to see if the distortion can be reduced? Or is it simply normal that I have to have the sensitivity almost at 0 to not have distortion?

Later I can try to bring down the volume of my bass - but it's a 1961 P-bass (with original pickups), so I wouldn't think it's a very hot signal. But I guess it might be hotter than your average single coil guitar..?

[g1]

(Is it possible to mention users on this forum?)

Use the @ symbol with no space after it. Once you type the 3rd letter of the user name a list will drop down and you can select, or just continue typing full user name.
Erlend