brundaddy Posted November 19, 2009 Share Posted November 19, 2009 The topic of expression pedals is coming up around here, and I have a burning question: How do I convert a simple volume pedal into an expression pedal? I have a Roland Space Echo pedal as well as a volume pedal (Goodrich model 120 I think, for a pedal steel that's collecting dust, I'm ashamed to admit). I would love to use the volume pedal as an expression pedal for the Space Echo! I heard an insert cable connecting the 2 would do the trick (single end into the Space Echo's 'expression pedal' jack & double end into the input and output of the volume pedal) but no such luck. That would have been too easy right? It seems like it would be just so easy to convert the volume pedal ... anybody have any experience with this? I am pretty handy with a soldering iron but not so good with schematics. I know there are some intelligent DIY guys in here. Advice is needed. Link to comment Share on other sites More sharing options...
Thundergod Posted November 19, 2009 Share Posted November 19, 2009 No easy way to do it IMO. Link to comment Share on other sites More sharing options...
brundaddy Posted November 19, 2009 Author Share Posted November 19, 2009 Yeah I hear ya. By all accounts, Roland's expression pedal is cheap plastic junk. I'd hate to buy one if I (potentially) already have a better one. It seems like, if I had to rewire, maybe a different pot and/or different jacks would do the trick ... but I am ignorant in this area. Link to comment Share on other sites More sharing options...
DrJustice Posted November 19, 2009 Share Posted November 19, 2009 Assuming that the volume pedal is a straight up passive one, the insert cable trick ought to work. Anyway, if you can solder, you can make it work. An expression pedal input normally expects to get a potentiometer connected via the three pins of a TRS jack. The wiper (middle pin) of the pot connects to the tip of the jack, and the two other pins connects to the ring and sleeve. A volume pedal will normally have a logarithmic potentiometer, whereas the expression pedals may have a linear one. You'll find out if you need to change if the response is overly abrupt towards either end of the potentiometer travel. DJ -- Link to comment Share on other sites More sharing options...
brundaddy Posted November 19, 2009 Author Share Posted November 19, 2009 Thanx for the input DJ- questions (I told ya, I'm seriously a dummy in this area): Assuming that the volume pedal is a straight up passive one' date=' the insert cable trick ought to work.[/quote'] It doesn't need a battery to work. Does that indicate that it's passive? I thought an insert cable would totally work too! Anyway' date=' if you can solder, you can make it work. An expression pedal input normally [b']expects to get[/b] a potentiometer connected via the three pins of a TRS jack. "Expects to get" - do you mean the pot is the next thing in the signal path? The wiper (middle pin) of the pot connects to the tip of the jack' date=' and the two other pins connects to the ring and sleeve. A volume pedal will normally have a logarithmic potentiometer, whereas the expression pedals may have a linear one. You'll find out if you need to change if the response is overly abrupt towards either end of the potentiometer travel. DJ --[/quote'] Seriously, thanks DJ. I'd love to sort this out. Link to comment Share on other sites More sharing options...
DrJustice Posted November 19, 2009 Share Posted November 19, 2009 It doesn't need a battery to work. Does that indicate that it's passive? I thought an insert cable would totally work too! Yeah' date=' that's passive. BTW I hadn't heard about the insert cable trick before you mentioned it, but this is simple stuff and I agree that it should work. "Expects to get" - do you mean the pot is the next thing in the signal path? Yes, an expression pedal is just the pot, no other electronics is involved. Here is a link to a Roland EV-5 pedal schematic. This is the pedal type recommended in the RE-20 Space Echo manual. If you look away from VR2 (used to set the minimum value with) it's just the VR1 pot connected straight to the jack. DJ -- Link to comment Share on other sites More sharing options...
brundaddy Posted November 19, 2009 Author Share Posted November 19, 2009 Hm. Maybe the pot is wired to the jack in a different configuration than you describe above ... wouldn't that be the only thing that would prevent the 'insert cable trick' (that's fun to say) from working? Link to comment Share on other sites More sharing options...
DrJustice Posted November 20, 2009 Share Posted November 20, 2009 Yep, that's right, brundaddy. You have to pop that volume pedal open and investigate now - I'm becoming curious about what's in there :- DJ -- Link to comment Share on other sites More sharing options...
brundaddy Posted November 20, 2009 Author Share Posted November 20, 2009 The volume pot: The input and 2 outputs: The whole enchilada: So there we are... I can't imagine it could be any simpler, what's the prognosis, Doctor? Again, I don't know what I'm talking about but it seems that there is some issue with the wiring configuration of either the pot or the jacks, or both (it's the only reason I could reckon that would prevent the insert cable from working - but like I said I really don't know my azz from my elbow when it comes to this stuff). Link to comment Share on other sites More sharing options...
brundaddy Posted November 20, 2009 Author Share Posted November 20, 2009 Sorry for the poor photography; circuitry and photography are not my forte Link to comment Share on other sites More sharing options...
DrJustice Posted November 20, 2009 Share Posted November 20, 2009 That looks logical. Plain and simple as expected. Does it still work as a volume pedal? If so, then I can't say why the insert cable trick fails here. Could be the Space Echo expression input in the worst case... If it fails as a volume pedal, then the pot could be bust (easy to replace). I also note that the output jacks have no ground leads soldered to them (would be the white lead), which means they must all make metal-to-metal contact with the pedal chassis so that the sleeves of the jacks are all connected - the chassis seems like it's painted so there it could be a bad contact there. An instrument, typically a "multimeter" for voltage, current and resistance, would be good to have if you get to the point of investigating this far. DJ -- Link to comment Share on other sites More sharing options...
brundaddy Posted November 20, 2009 Author Share Posted November 20, 2009 Ah, so concerning the ground leads: for the pedal to work properly, the sleeves of the jacks need to be connected to each other, with one chassis connection somewhere? Or connect each to the chassis? I didn't think of the Space Echo expression input. I don't know how to troubleshoot that, but it's certainly a factor to remember in this mess. Agreed, a meter would be super handy right about now... not that I'd totally know what to do with it... Link to comment Share on other sites More sharing options...
DrJustice Posted November 20, 2009 Share Posted November 20, 2009 Yes, the sleeves must all be connected somehow. In this construction it looks like the metal chassis is meant to make that connection, meaning that the nuts and washers of the jacks need to make contact with bare metal of the chassis (the nuts and washers also need to make a connection with the sleve of course, I assume the jacks have that type of construction). The first input jack has the white lead soldered to it's sleeve pin, and thus it should ensure that the pedal chassis is connected too via the sleeve/washer/nut. Of course, it's more than likely that this contact is OK, and that it's something else - but then again we don't know... Dis you test to see it work as a volume pedal? DJ -- Link to comment Share on other sites More sharing options...
brundaddy Posted November 20, 2009 Author Share Posted November 20, 2009 yep, perfect working order Link to comment Share on other sites More sharing options...
DrJustice Posted November 20, 2009 Share Posted November 20, 2009 Hmmm... Next up is measuring/testing the insert cable, then testing the Space Echo with a known good expression pedal (or just a pot + lead + plug). Then I'm near my wits end as far as remote diagnostics are concerned - sorry. If any readers spot some invalid assumptions or mangled/overlooked facts in here, please give us a shout! DJ -- Link to comment Share on other sites More sharing options...
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