Relay bypass mod to Ibanez and Boss pedals

[R.G.]

I had a PM question about converting Boss and Ibanez pedals to true bypass with relays.

If you don't need to run on batteries ever, the simple thing to do is to just use the discrete flipflop that's already there in the pedal that runs the LED and switching FETs. Just remove the FETS and solder jumpers to make the signal path always on, and connect up a MOSFET, diode, and DPDT relay to do the bypassing. This will be a NON-latching relay, of course, so it will use power all the time.

If you can stand to use a 14 pin chip and two transistors instead of an 8 pin microprocessor, you could use the circuit here: http://www.geofex.com/FX_images/ltchrly.gif on a baby board with the relay. That circuit's been at geofex for about 10 years now. Not as sexy as an 8 pin microcontroller, but works the same.

If you can stand doing a small surface mount board, the 14 pin SO14 package is about the size of an 8 pin dip, so it's not even at that much size disadvantage.

This is almost in the category of too simple to do a PCB, but the PCB is trivial too.

[Brymus]

Cool ,I dont like the bypass sound of my Ibanez PM-7
I will look into this for my pedal,thanks for sharing R.G.

[jkokura]

How much power will it use R.G? Also, can you show us a schematic of how this would work?

Jacob

[R.G.]

Power depends on the relay. You want a miniature "low signal" type relay rated at 9V. These tend to be about 200-600 ohms for the coil resistance, so at 9V they pull
15-45ma of DC. Mouser stocks the Panasonic TQ-2 9V, which should be a good one for this application. It's coil resistance is 579 ohms, which is nice and high, and it pulls 15-16ma of DC, which is remarkably small. That's not much more than an LED. They weren't this good last time I looked at relays.

Here's how to do the mod:
With reference to http://www.freeinfosociety.com/electronics/schematics/audio/pictures/bossds2.gif, which I grabbed as representative,
1. Remove Q3; short drain to source on Q4 and Q21. This makes the electronics board permanently on.
2. Wire the relay contacts as a DPDT bypass to input jack, output jack, and the input and output of the circuit board.
3. Look at Q1 and Q2. The LED indicator is on when Q1 collector is low. That means that when the LED is on, Q2 collector is high, pulled up by its 56K pullup resistor. You want the relay on when Q2 collector is high. Attach a to-92 MOSFET such as the BS170 or 2N7000 with its source at ground, its gate connected to the collector of Q2.
4. Connect the relay coil to +9V and the drain of the MOSFET.
5. Connect a diode across the relay coil, cathode to +9 and anode to MOSFET drain.
6. Enjoy.

[R.G.]

I should mention that all the other issues with relays are still there - clicking with the voltage change on the coil and current pulses in +9V and ground. The relay driver may need slowing down to avoid capacitive clicking and the power/ground leads may need special routing to avoid introducing a click. But maybe not. Depends on the relay.

[Mark Hammer]

The other day I saw someone posted a link to a small retrofit board that had a small latching relay and the support circuitry, plus a momentary switch, intended to convert Boss-type pedals to relay-based true bypass.  I forget whether it was posted here or somewhere else.

[R.G.]

It was posted here. It's the "Clickless Bypass" by a Deville Electronics.

By inspection of the pictures, the kits/boards both contain an 8 pin microcontroller, a voltage regulator to make a lower voltage from 9V so the controller will live, and a latching relay. The programming is such that the controller reads the momentary switch on the pedal, then flips the latching relay. There may be a driver transistor or two.  I didn't look that closely.

A PM made me think about this topic this morning, and I wondered what was wrong with using the existing discrete flipflop inside Boss and Ibanez pedals to work a relay. The obvious thing is that the relay current is (a) high and (b) continuous. This is the motivation behind using latching relays, and was the thinking behind my CMOS inverter latching relay driver, and the similar circuit at geofex from January 2002:

What's different since 2002 is that I went and looked at Mouser for what relays can be had now. It turns out that Mouser and presumably others now stock 9V rated relays. I believe this has happened in the last year or so. And some of those relays have a quite low coil current. The Panasonic TQ2-9V only takes a bit over 15ma, which is bigger than, but comparable to an LED's current.

This will still cause higher battery drain, but batteries are fast fading off of pedalboards as AC powered 9V adapters permeate pedal use. So the current drain issues are rapidly becoming moot.

Given that, messing with a driver logic chip at all, either a $0.50 CMOS hex inverter as in this:

or even using a $1.00 uC plus a $0.35 voltage regulator and a PCB gets to being something that may not be needed. If you can simply drive the relay from the pre-existing flipflop with a $0.50 2N7000 and live with the current drain, you can simply perfboard the relay and MOSFET and stick it in the box using the box's own flipflop and footswitch button.

Anyway, that's what I thought.  

[R.G.]

So I sketched up the additions and put them up on GEOFEX:


Added parts are the relay, MOSFET, R1, C1, and D1. D1 is there to prevent breaking the MOSFET by the relay coil's inductance when the MOSFET turns off. R1 and C1 are to slow down the on/off transitions to help in case the relay's internal capacitances couple switching ticks into the audio line. This will depend on the relay.

Because MOSFETs have a substantial gate-source capacitance, it may be possible to leave off C1 and just use a larger R1. The gate capacitance will slow down the gate voltage change then.

[jkokura]

wow... I never thought my simple questions would lead to all this awesome info! Thanks R.G.

I'm still struggling to understand though. I guess I understand the circuits of the Relay, now I just have to figure out a layout for them and then figure out how to actually install one. Is it as simple as adding the parts on a perf and inserting it between the switch and the circuit with power and ground?

[R.G.]

I guess I understand the circuits of the Relay, now I just have to figure out a layout for them and then figure out how to actually install one. Is it as simple as adding the parts on a perf and inserting it between the switch and the circuit with power and ground?

Pretty much, it's that simple.
-You rig the existing circuit to be always on by jiggering the FETs.
-Then you hook up the relay contacts like it was a DPDT switch (which it is!) by cutting the wire between input jack and effect board, then connecting input jack and board input to the relay.
-Same for the output jack wire.
- you find the internal flipflop transistor collector and wire that out to the gate of the MOSFET.
- You find +9V and Ground and wire those out to the MOSFET/relay board.

[Mark Hammer]

And as promised, here are the picks and the mod.
Here we have a plain unadorned Boss HM-2 with the bottom plate off.  You can see there is some space adjacent to the power jack.

here we have the same box with the board lifted up to reveal the underbelly of the momentary switch.  The switch has a positive and ground side.  The ground side in this instance is closest to the chassis, and is connected by a black wire.

I popped a hole in the backside to accommodate a standard mini phone jack.  I happened to use a stereo jack because I had bought a bunch cheap, but the mod only needs a mono jack.

Wire up the jack and install.

Connect the wires to the momentary switch, and away you go.

You can now insert a normal mini phone plug (1/8") and run two wires out to whatever sort of momentary switch you have.  For that matter, you can parallel two switches for remote purposes, one off by itself, and another snuggled up beside a switch for another pedal so that you can step on two momentaries at once and switch the state of two pedals simultaneously.  Pretty simple, huh?

I cannot vouch for the optimal location for installing the jack in other Boss pedals, but in most instances there should be a spot somewhere.

Enjoy!

[diydave]

Thank you very much Mark (and also R.G). 
I've been struggling with my pedalboard.
I've build a big multi-fx with 7 circuits. And I still use some boss or jacques pedals as well. Due to lack of space on my board, I have to put those boxes above my multi-fx. And when gigging, I have to use my heel to stomp on them, which sometimes can give some weird and funny acrobatic situations on stage.

But with what you've brewed up, I'm thinking off reinventing my multi-fx with added 'remote switching' so I can safely use and control other pedals as well.
Very smart indeed.

[The Tone God]

It was posted here. It's the "Clickless Bypass" by a Deville Electronics.

By inspection of the pictures, the kits/boards both contain an 8 pin microcontroller, a voltage regulator to make a lower voltage from 9V so the controller will live, and a latching relay. The programming is such that the controller reads the momentary switch on the pedal, then flips the latching relay. There may be a driver transistor or two.  I didn't look that closely.

Are you implying something here ?

Andrew

[R.G.]

It was posted here. It's the "Clickless Bypass" by a Deville Electronics.

By inspection of the pictures, the kits/boards both contain an 8 pin microcontroller, a voltage regulator to make a lower voltage from 9V so the controller will live, and a latching relay. The programming is such that the controller reads the momentary switch on the pedal, then flips the latching relay. There may be a driver transistor or two.  I didn't look that closely.

Are you implying something here ?

No. The statement is simply what it says.

I looked at the picture. There is an 8-pin DIP, a TO-92 or two, a couple of caps and maybe a resistor or two, along with a latching relay. The description of the unit says that there is a microcontroller in it, and that it reads a momentary switch and includes a latching relay.

Does that imply anything?

[RonaldB]

Hello R.G. and others.

Iám making al my pedals true bypass through relays. I was testing this circuit yesterday (used from the GEOFEX site) to switch a 5v relay but it does not work properly.

It switches but sometimes it doesn't and sometimes it will go on and off again. What am i doing wrong here?

hope some one can point this out.
RonaldB

[R.G.]

Iám making al my pedals true bypass through relays. I was testing this circuit yesterday (used from the GEOFEX site) to switch a 5v relay but it does not work properly.
It switches but sometimes it doesn't and sometimes it will go on and off again. What am i doing wrong here?

You're probably not doing anything wrong - there's just something you're not doing.

That 4013 can change state several million times a second. It is likely that your S1 switch is bouncing after making its first contact. If it makes an even number of bounces, the switch appears to have not worked at all. If it makes an odd number of bounces, it looks like it worked. If it has an uneven series of bounces it may appear to go on and off. And when I say "bounces" that translates to "moves through the sensitive voltage threshold on the clock signal multiple times even very very slowly".

Switch debouncing is a problem which will always arise when you are using mechanical switches to control logic. In theory, the R1-C1 network would debounce well enough. In practice, it may not. Replacing T1 with a CMOS inverter that has a Schmitt trigger input would help a lot. The CD40106, 74C14, or CD4584 would be good choices. The circuit as shown has the base of T1 always at the Vbe of the transistor until the switch makes. It is then pulled down by the switch and turns off at maybe 0.4V. But it only has to rise back to 0.5V when the switch bounces open to turn back on. A gate with hysteresis will sit at +12 normally, turn off when its input goes below about 4V, but not turn back on until its input goes above 8V, making it much more immune to bounces.

You could try making C1 be 0.1uF, or even 1uF. That might cure the symptom for this particular set of part values.

[The Tone God]

No. The statement is simply what it says.

I looked at the picture. There is an 8-pin DIP, a TO-92 or two, a couple of caps and maybe a resistor or two, along with a latching relay. The description of the unit says that there is a microcontroller in it, and that it reads a momentary switch and includes a latching relay.

Does that imply anything?

It may just be the wording of the original statement but it could be perceived that you are implying that one had copied the other's design. I just wanted you to have a chance to make sure you were clear with the intention of that statement so it was not miss understood is all.

Andrew

[RonaldB]

Iám making al my pedals true bypass through relays. I was testing this circuit yesterday (used from the GEOFEX site) to switch a 5v relay but it does not work properly.
It switches but sometimes it doesn't and sometimes it will go on and off again. What am i doing wrong here?

You're probably not doing anything wrong - there's just something you're not doing.

That 4013 can change state several million times a second. It is likely that your S1 switch is bouncing after making its first contact. If it makes an even number of bounces, the switch appears to have not worked at all. If it makes an odd number of bounces, it looks like it worked. If it has an uneven series of bounces it may appear to go on and off. And when I say "bounces" that translates to "moves through the sensitive voltage threshold on the clock signal multiple times even very very slowly".

Switch debouncing is a problem which will always arise when you are using mechanical switches to control logic. In theory, the R1-C1 network would debounce well enough. In practice, it may not. Replacing T1 with a CMOS inverter that has a Schmitt trigger input would help a lot. The CD40106, 74C14, or CD4584 would be good choices. The circuit as shown has the base of T1 always at the Vbe of the transistor until the switch makes. It is then pulled down by the switch and turns off at maybe 0.4V. But it only has to rise back to 0.5V when the switch bounces open to turn back on. A gate with hysteresis will sit at +12 normally, turn off when its input goes below about 4V, but not turn back on until its input goes above 8V, making it much more immune to bounces.

You could try making C1 be 0.1uF, or even 1uF. That might cure the symptom for this particular set of part values.

Thanks R.G.
Iwill try that and come back here to share the results.

ronaldb

[RonaldB]

So I tried the cap changes you surgestate but none of the cap changes made a good switching for the relays.
I tried 0.1uf(still debouncing), 0.22uf(still debouncing do less) and eventualy 1uf(Relays stays on afterswitch is pressed and deosn't go off on another switch press).

So I tried this idea off thetonegod and this work great for a relays swichting system.
[url]http://www.oocities.com/thetonegod/switches/switches.html[url]
I used the example with Momentary switch with inverter gates. and this is stable and works great.
I'll draw a schematic later.

just to let you all now,
ROnaldB

[jkokura]

I hope someone can get this working in a Boss pedal, and then it would be cool if we could develop a layout and a parts list for the project - something we could all use if we really wanted.

jacob