DOD FX80 (not B) Compressor. Adding "Attack" knob ?

[Jamforthelamb]

Hello All,

I recently aquired a DOD FX80, and after doing a little research on it I found that DOD had an FX80-B model that had an "Attack" knob. Is there any way I could add one to my pedal, or would it not be that simple ?

Thanks,
-Kevin

[Mark Hammer]

I don't know that pedal specifically, but the chances are pretty darn high that it simply uses the same simple circuit mod seen in a wide variety of pedals using the same sort of rectifier circuit.  This involves replacement of a stock 150k fixed resistor with either a pot or a toggle that selects presets.

[Jamforthelamb]

Ok, cool.
I have to take it apart to change the battery snap anyway, so I figured I'd look for some mods. Haven't been able to source a schematic yet, so I will likley try to just compare it to the more common compressors out there.

Thanks!
-Kevin

[Jamforthelamb]

Hi Mark,
Is this the resistor I should replace with a pot? I measured it, and it showed to 150k.

[George Giblet]

> Is this the resistor I should replace with a pot? I measured it, and it showed to 150k.

I think so.  The 150k is the MXR dynacomp value.

If you want to be absolutely sure:   One end of that resistor should go to +9V and the other end goes to: the base of the transistor to the right of it,  the collectors of the two transistors above it and to the 10uF cap to the left of it.  I'm assuming that is a 10uF cap?

For FX80B attack replace that with a 33k in series with a 500k pot.

[Jamforthelamb]

Great! I'll do the mod this weekend!

Thanks!
-jftl

[Mark Hammer]

Just don't expect miracles when you do the change/mod.  Many folks here have a hard enough time telling if their compressor is on or off, let alone small differences in the recovery time.  Moreover, the differences will not be audible if yo pick slowly.  The change in response to faster recovery (which is all you will be doing) comes with faster clean picking using moderate compression.  If you're a Paul Kossoff kinda slow finger wagger (and absolutely nothing wrong with that), faster recovery time will do nothing for you.  If you pick a Tele by the bridge, and your distortion is not always on, then you may benefit from the mod.

Personally, I can't see a need for anything more complex than 3 presets (slow, medium, fast).  I originally installed a variable control on a Dynacomp clone way back, and I gotta tell you that it is hard to discern audible differences simply by moving the pot over 20 degrees.  One tends to end up with the pot set at either 7:00 or 5:00 (i.e., stock recovery time, or much shorter).  A buddy, who makes the Retro-Sonic Ross clone, implemented the 3-way switch I suggested to him, but after a while he said that customers just seemed to want a variable control.  Though the term "security blanket" was never used in our discussions, I think it applies.  If it was something like a tone or blend control, where small differences are reliably heard, then a variable control makes sense.  In the case of the recovery-time mod, the audible outcome depends so much on your picking speed and dynamics that you need BIG differences in setting to be able to reliably hear the difference.  Why take up valuable chassis real estate?  In most instances, a toggle is cheaper and easier to install than a pot with a knob.

[Jamforthelamb]

Hi Mark,
I agree with your thinking. How do I implement a switch instead of a pot ? I assume it would need to be center off switch with fixed resistor to set the slow and fast with off being medium ?

Thanks!
-jftl

[Mark Hammer]

Yep, you essentially start with the stock resistance value (150k) and add in one of two parallel resisors to achieve the minimal (10k) and an intermediate (in the vicinity of 40k) resistance value.  A 56k in parallel with 150k gets you 40k, and 12k in parallel with 150k gets you 11.1k.  Close enough for rock and roll.  I picked 40k as the medium value because it's just under 4x the minimal value and 150k is just under 4x of the medium value.  So, an equivalent proportional change.

[Jamforthelamb]

Thanks Mark!

And I assume that those resistances don't have to be dead on ?

-jftl

[Mark Hammer]

Correct.  Something in the neighbourhood is likely good enough.  Max and min recovery times are easy enough to hear.  The goal is to make the "medium" setting audible.  So try to keep the proportional change from min to medium to max in the ball park.

[Jamforthelamb]

Got it all sqaured away with a spdt center off in between the two knobs. There is an audible difference between the setting, so it turned out great! Now I just have to get used to using it (I've never had a compressor before).

Thanks again Mark and Everyone !

-jftl

[Mark Hammer]

De nada my friend.  Glad it worked out well.

Subtle, eh?  One of those things that if you didn't know you were supposed to hear it, you might not be able to hear it, or at least able to identify what the specific difference was in what you were hearing.