How to cut a PCB trace?

[Steve Mavronis]

I'm going to mod my DOD YJM308 Overdrive pedal to 'grey' 250 parts specs and part of the mod involves cutting several traces and jumpering because replacing the Op Amp (from dual to single) means the pinouts change. The only parts change besides the op amp is replacing the input cap value and removing another that was not in the original circuit. What is the best way to cut a PCB trace?

[theehman]

Xacto knife or jeweler's very small flat blade screwdriver

[Steve Mavronis]

Xacto knife or jeweler's very small flat blade screwdriver

Thanks. So you just score it back and forth?

[jacobyjd]

Xacto knife or jeweler's very small flat blade screwdriver

Thanks. So you just score it back and forth?

If a well-placed karate chop doesn't work (my hands are very ham-like, so I don't usually have that kind of precision), yes, I usually just score out a small section--usually about 1/8"  worth of trace, then slice the unwanted copper off the board (this can be a pain with solder masks--just make sure you check to make sure there's no continuity with your meter when you're done).

Good luck! 

[Steve Mavronis]

(this can be a pain with solder masks--just make sure you check to make sure there's no continuity with your meter when you're done).

Yeah it has a mask or clear coating over the traces. Thanks for the tips.

[ayayay!]

I am very against using a blade for cutting traces.  Go to Harbor Freight and buy their Dremel multi-tool knock off.  You can cut a trace much more safely & cleanly with one of those, without jeopordizing nearby traces.  I think I got mine for $7.

[petemoore]

  Drill bit, slow, precise, could be hard to fit the drill inside the box though.
  Knife...don't slip !!
 

[Steve Mavronis]

 Drill bit, slow, precise, could be hard to fit the drill inside the box though.

The YJM308 (and the newer yellow re-issue 250) both use the same PCB (w/different component values) and are removable though a molex connector, so that should make things easier to deal with.

[ppatchmods]

not what you were asking, but you could just use the 1458 instead of the the single ic. it is the dual version of the 741.

[Steve Mavronis]

not what you were asking, but you could just use the 1458 instead of the the single ic. it is the dual version of the 741.

Yes, I know and then I wouldn't have to cut any traces. In readying Analogman's page on the mod, he said the 1458 had a bit more noise than the 741. I might end up trying a socketed 1458 first just to see how it sounds after removing the 25pF cap in the feedback loop and changing the input cap from .001uF to .01uF like in the original 250 specs. Anything is better than it sounds now with too much treble and not enough bass. Maybe I'll save the pure 741 thing for my 100% DOD 250 pedal clone which I'm going to make anyways and I'll have something to compare to at the same time.

[ppatchmods]

i have a 1458 if you need it. just pm me your address

[Steve Mavronis]

i have a 1458 if you need it. just pm me your address

Thank you for your kind offer. I'm lucky my dad works with electronics and says he can get me all or most of the parts I'd need for different projects. He had already mentioned he has some 741's and 1458's. None of the vintage brands though (like RCA) if that makes a subjective difference. He's supposed to make some pcb boards for me after I decide on a grey 250 layout to go with - either my own based on I hope an accurate schematic, one of your guys, or just make myself a cloned layout version of the grey PCB based on photos. I also used ExpressPCB to draw a modified layout of the YJM308/250 re-issue PCB for a 741 chip without altering the original by cutting traces and adding jumper wires. I'm kind of conflicted which project to concentrate on first but I really want an authentic clone of a '77 grey 250 to play with. I have a couple Hammond 1590B's coming to my house any day (one plain metal and one pre-painted black) and I'm eager to put something in them! If I mod my YJM308 first I'll probably redo the logo to say YJM250 instead, and who knows what I'll call my grey 250 clones, LOL.

[zombiwoof]

I have seen conversion boards on the net to change between single and dual IC's, but I don't have a link available right now.  It would make it easier to change from one to the other.

Al

[Steve Mavronis]

I have seen conversion boards on the net to change between single and dual IC's, but I don't have a link available right now.  It would make it easier to change from one to the other.

Hmm, very interesting idea! Like a little piggyback PCB socket adapter for the op amp!

[zombiwoof]

Well, I found those adapter boards, and while they have one to go from an SIL to a DIP8, they don't have one to go the other way!  I guess they think that would be a step backwards or something.  In case anyone is interested, here is a link to the adapter boards (I got the link from the "Build Your Own DS-1" document, he links to it in case you want to upgrade from the SIL IC in the DS-1 to a DIP8 IC):

http://cimarrontechnology.com/audioupgradeadapters.aspx

Still, maybe you could make your own adapter.

Al

[petemoore]

  I think it may be the other way round, the LM741 is the noisy one.
  If you want to call it that, there's 'better' but not necessarily for the DIST+ type circuit.
  Otherwise these opamps performances are, in terms of treble and bass balance of a circuit, very very close.

[Steve Mavronis]

 I think it may be the other way round, the LM741 is the noisy one. Otherwise these opamps performances are, in terms of treble and bass balance of a circuit, very very close.

From the Analogman site about his test results with the YJM308/250 mods:

741-"mojo" MOD
The most accurate at matching original gray (no surprise there). Tubey and round sounding highs with that low, slightly loose growling low end. Same noise levels as the original. Best YJM308 mod for authentic duplication of original grey

1458 "Reissue" MOD
Closer to original grey pedals than DOD's own re-issue series, but there are some noticeable tone differences.... There is a higher noise level. I test background noise by setting the studio noise gates to just barely cut sound when guitar volume is rolled to zero. When the gates are set to just go quiet with the 741 pedals, there is still a rush of HISS that comes out of the system with the 1458 pedals. I think this extra hiss may be from slightly higher gain as the pedal sounds a little TIGHTER but THINNER when set to the same positions as the 741 pedals.

It would seem the 1458 is the closest 741 dual amp equivalent out there but despite the specs, is NOT 100% identical in an Overdrive Pedal circuit.

[Steve Mavronis]

Still, maybe you could make your own adapter.

It shouldn't be too hard to create a simple PCB layout that re-routes the dual op amp pinout connections back to the single op amp pinouts. But accrording to my dad there are some dual op amp types that use different pinouts than these do so it may not work in a generic way for everything out there, but in this case it would be compatible to 4558 and 1458 pinouts going to a 741 pinout. You'd just have to watch how that second (B) of the dual op amps is wired up to itself (it's output to its + input, and its - input to ground) and not to the other main one (A) used in the circuit.

<- to ->
(graphics credit: gaussmarkov)

Would something a simple as this 2 sided PCB layout work, where red is for 741 and green is for 1448/4558? I probably have the top and bottom cooper colors backwards. I'm an amateur at this. The yellow text are the pins that are common between dual and single:



I guess too you have to watch out how much extra height a piggyback adapter would add to the board so it still fits in the case. Of course you could get around that by using a ribbon cable going to a separate IC adapter board instead.

[zombiwoof]

Just brainstorming here, but would it be feasible to use a DIP8 socket, solder some stiff solid wire leads to the pins and route them to the appropriate pads on the main board?  Then you could try different DIP8 IC's in the pedal, as long as they had the same pinout.

Al

[bumblebee]

I just use a razor blade of some sort, make two cuts and peel the little piece of trace off the board.