Has anyone modded the silver Marshal pedals for TBP?

[Ben N]

Having just learned that the "passive bypass" touted by Korg is the same as the old MXR bypass, I just opened my ED-1 to see about modding it.  Although I was hoping to find a switch with wires, what I did find was only slightly more complicated:  a separate switching board, with the small DPDT stompswitch and jacks soldered onto it, and pretty widely spaced traces.  It struck me that it couldn't be that hard to design up a TBP PCB, either for a 3PDT (if it fits--I didn't remove the board yet to se), or for a Millenium or Rat bypass on the board--there looks to be plenty of room for that.  It may even be possible to do it with perfboard, if the holes are spaced right for the jacks.

So, before I start trying to reinvent the wheel, has anybody done this yet.  Anybody who actually knows what they are doing want to take it on?  And JD, FP, Brian, et al:  I would be happy to buy a RTS board for this purpose, and I'm pretty sure others would, too.  These are good pedals for the $$ (ED-1, BB-2, GV-2), and converting to TBP would take them the last yard.

Ben

[O]

What would also be cool is to have a schem of the ED1 (I had one and stupidly sold it)...

Those are great boxes... and you're right, TB would really be cool for those pedals.

[Ben N]

PM me your email, and I'll send you the schem I have (no guarantees as to accuracy).

Ben

[O]

You've got mail!  :wink:

[Mark Hammer]

I'm not about to give the pendulum a big push in the opposite direction, but the material posted by Pete Cornish on his site, the various related threads here in recent years, and the assorted interviews (and sound samples) in Dave Hunter's recent FX book, have persuaded me that TBP is not the be-all and end all.  Personally, I *like* it because it is easy as pie to wire up, dependable, consumes no current, and works when my on-life-support-already batteries crap out.  But that being said, if the input buffer is decent enough (and we have no reason to assume it isn't), other switching forms which take the output signal from the buffer rather than the input jack can deliver audio quality just as good, and occasionally better.  Even if all your other effects use TBP, having the first thing in line be "hard-buffered" (i.e., even in bypass mode there is a buffer between guitar and the rest of the signal path) would appear to make audio sense.

So, without wishing to trash your intentions (because they might be irrefutably logical), WHY do you want to convert the pedal to TBP?  That is, what added advantage do you expect to gain?  Are the advantages of conversion significant enough to offset the disadvantages of rehousing?  Consider this like a little "Are you sure? Yes [ ]  No [ ]" pop-up window on your computer.

[cd]

MH makes a good point but I'm fairly sure the Marshall pedals use one half of the DPDT to switch the output, leaving the high impedance input always on (doesn't load down the bypass signal that much).  The other half of the DPDT is used for the LED indicator.  If that's the case, there's no buffer in line when in bypass mode, and it should be trivial to re-wire.

[TheBigMan]

I've never looked in one myself, but I have heard that at least some of these Marshall pedals use Milennium Bypass.

[Ben N]

Mark:

I'm not a TBP fanatic--I have three Boss pedals on my board, and lots more in the dugout, and I always want some buffering at least at the input and output of the pedalboard, and before potential tonesuckers.  Although too much duplicative buffering can be a bad thing, I'm not one of those that goes and sticks a Carling in the top of his TS9--ick!  

But, as cd stated, I believe the bypass of the Marshall is not buffered, unlike a Boss, Ibanez or DOD type, more like an MXR, which just switches the output jack between the input and the effect output.  Thus, even if the input of the effect itself is high impedance, meaning that the input is connected, in effect, in parallel with the input of the next pedal in line (and maybe others), so the potential for tone sucking is quite real, depending on where the pedal is placed on the board.  I try to make sure I have buffered pedals before and after, so that minimizes the problem, as you pointed out.  But I'd rather not have to worry about it.  Because it is a passive bypass, I don't have to worry about the battery dying, but I use a wallwart anyway, so that is really not an issue.  And, as I stated in my initial post, converting these to pedals to TBP looks to be a very simple thing, with no downside, if it done right.  I'm surprised that none of the commercial mod-meisters out there have marketed such a mod yet.

Big Man, I did not pull the switching board to see what is on the other side, so I cannot say for sure that there is no Millenium, but there didn't seem to be much going on in that board.  The schematic also doesn't show that.  I guess I'll just have to pull the damned board out tonight and settle it!

Ben

[O]

Ben, thanks for the schem. If you do yank out the board, please remember to take pics.

[Ben N]

Didn't get to it--too much kid homework.  I'll try again tonight.

Ben

[O]

Didn't get to it--too much kid homework.  I'll try again tonight.

Ben

No hurry... I have my hands full with my 4mo old too...

[vanhansen]

Didn't get to it--too much kid homework.  I'll try again tonight.

Ben

No hurry... I have my hands full with my 4mo old too...

Just have to chime in here.  I feel for both of you.  I got a breadboard for Christmas and haven't had a chance to really do to much with it.  I have a 2 year old (2 just this month).  I have the Easy Drive and an LPB1 on it and haven't been able to even test them out.  I still have to make my alligator clips and get a test enclosure together.  :roll:  It's at least comforting to know I'm not the only one in this situation.

[TheBigMan]

Ben, it was just something I heard.  It may well be that someone has opened the pedal and seen that the bypass switch, as well as triggering the LED, is connected to a p-channel FET which appears to mute the first opamp stage and assumed that it is part of the LED switching circuit therefore the pedal is TB.

[Mark Hammer]

Sensible attitudes all round.

If the pedal *benefits* sonically from having either improved buffering or a complete bypass of *bad* or insufficient buffering, then "Thunderbirds are go!" in my books.

My own "mission" here is to encourage folks to think about context, rather than pursue any particular switching scheme IN SPITE of context.

Note that when manufacturers design their switching scheme or make choices between switcing schemes, one of the things they factor in is that they have absolutely NO idea what you're going to do with the pedal, so they try to design around a worst-case scenario.  Sometimes what suits such a scenario is not the best choice for a more hospitable context.  The best advice one can offer here is to understand your signal path and do what assists the signal path GIVEN YOUR USE.

As an addendum, Marshall seems to have adopted the one-set-of-contacts-for-LED-switching strategy on other pedals as well, judging from the schematics for the original Guvnor, Shredmaster, et al.