Maxon CS 505 true bypass mod

[BDuguay]

Hey all
I searched but didn't find any information on this subject. Has anyone done this before and would be willing to share some info?
Thanks,
B.

[BDuguay]

Was it something I said?
I'm figuring this won't be an easy task given the stereo outs. Thoughts?
B.

[BDuguay]

The owner of this pedal says he does not use the stereo out feature so this should make the true bypass coversion an easier mod.
Has anyone tried this and do they have any tips?
Thanks,
B.

[Mark Hammer]

Hi Brian,

From what I was able to find, the CS505 uses a sum vs difference output.  So, while your friend may not use it in stereo (i.e., both outputs at once), he may wish to be able to retain the option for using a clean+delay OR a clean-delay output.  If so, that would alter the manner in which any TB installation might occur.

What you haven't mentioned is whether it is the older style square momentary button, or the recent reissue stompswitch.

If it is the older style stompswitch, I would bet big money that the switch works in a manner identical to the stock CE-2.  That is, there is but ONE solitary FET that either feeds the delay signal to the mixer stage...or is turned off such that the mixer only has clean to work with.  In this instance, of course, there would be some sort of buffer or buffer/invertor since something needs to be able to feed a summing stage and a differencing stage at once.

If it does use the single-FET arrangement, all you really need to do for total bypassing is to:
a) wire a bridge across the drain and source of the FET so that it is always functionally "on" (easily done on the copper side)
b) run the wires from the input and output pads on the board to a stompswitch

[12bar13]

i was wondering if someone could clarify what a true bypass is exactly.  my assumption is that it cuts the effects circuit out of the loop entirely and delivers the signal straight to the output.  am i close?

[BDuguay]

Yes, that is what the majority, I believe, refer to as true bypass.
Mark, this  pedal uses the small SPDT momentary switch. I hope that helps and thanks for your reply.
Keep them coming please!
B.

[aron]

Maybe it would be best to use a True bypass box instead.

[Mark Hammer]

That assumes the context of use permits that flexibility.  Sometimes there ain't no more space on the pedalboard, dang it.

[BDuguay]

Shameless bumping for more info :icon_redface:please.
B.

[BDuguay]

Okay, I'll bite.
Am I over thinking this one possibly? Since the owner has assured me he does not use the pedal in stereo mode I finally realized that all I need to do is wire up the circuit switching to be permenantly 'on' and then add the 3PDT accordingly. Is that about right?
Is there anymore to it than that?
B.

[Mark Hammer]

There shouldn't be, other than deciding on whether he wants to use the sum or the difference output, or have a choice.  If the latter, then you simply rig the circuit to be permanently on, and run a lead from each of the two outputs to a SPDT toggle which then gets fed to the stompswitch.

[BDuguay]

Yeah, I was considering that too as a potential option for the owner. I'll have to look at the circuit to get a better idea of how that would work. Can you'splain further?
Thanks Mark!
B.

[Mark Hammer]

Why soy-tainly, Lucy.

The CS505 will have two outputs to produce its ersatz stereo.  One is dry plus delay and the other is dry plus inverted delay, also known as sum and difference.  Normally, the bypass simply cancels the feed of the wet signal such that, whether it is inverted or not, it doesn't make it as far as the mixer stage.  The mixer stages are most likely always available at the output jacks.  What you are planning is to have the stompswitch select between the outputs of the circuit itself (which will be the mixer stages) and the signal at the input jack (which is what true bypass does).  Since a 3PDT switch, if used to enable a status LED as well, can only permit selection between the routing of one output and one input, you will need to treat the pedal as if it only had one output jack.  Of course, since the sum and difference signals (complementary flavours of chorus) are normally only available from separate jacks, the toggle has to select between which of those circuit-related outputs you want for your audio output. 

Two people sit down in a diner booth.  One tells the server they just want water.  The other says they want coffee.  The server asks "Cream and sugar, or black?".  Customer says "I'll take it black".  The master switch selects between water (bypass) or coffee (effect). The toggle selects between cream and sugar ("regular" in New Yorkese, or "single-single" in Canadian  ) or black.

Since the switching will be done by a single FET (unless they use some scheme which involves a secondary FET used to adjust the gain to compensate for the notches and peaks), you need only bridge the drain and source of that FET to have it permanently "on".

[BDuguay]

The only thing clearer than that explanation is the weather we're having here in Burlington today. BTW, we brought this weather back with us from our tour of the Netherlands. Now, if only my head could be so clear.....
Thanks again Mark.
B.

[Mark Hammer]

Always glad to help out a buddy.  BTW, Bluesfest absolutely rocks this year.  Lotsa commercial big names, but dig deeper and there are more guitar gods than you can shake a stick at. http://www.ottawabluesfest.ca/en/  Do you have any idea how much it kills me to have to choose between Steely Dan, Richard Thompson, and Zappa Plays Zappa, who are all appearing simultaneously on different stages?

[BDuguay]

Lordy Lordy, Emory Gordy!
It's rarely famine and mostly feast at that festival eh?
B.

[davent]

Always glad to help out a buddy.  BTW, Bluesfest absolutely rocks this year.  Lotsa commercial big names, but dig deeper and there are more guitar gods than you can shake a stick at. http://www.ottawabluesfest.ca/en/  Do you have any idea how much it kills me to have to choose between Steely Dan, Richard Thompson, and Zappa Plays Zappa, who are all appearing simultaneously on different stages?

Whether with band or solo you could never go wrong with Richard Thompson 

Have fun
dave

[jakehop]

Shouldn't you be able to switch input, both outputs AND a LED with a contraption like the millenium bypass?

Jake