Relay bypass mod to Ibanez and Boss pedals

[R.G.]

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.

I'll write something up and put it on GEO. It's one of those things where boards and layouts are almost parenthetical.

[323]

Hello, new guy here;)

I'm curious, is it possible to use 5V relays in that circuit because I only have 5V at my disposal? Also can this circuit be modified for using 5V relays?

EDIT: Can I use 12V relays, I've found that I can buy these too?

[R.G.]

I'm curious, is it possible to use 5V relays in that circuit because I only have 5V at my disposal? Also can this circuit be modified for using 5V relays?

You don't need to modify it if you have enough current gain in the driver transistors to pull the higher current that 5V relays need. You could also sub in to-92 MOSFETs for the bipolars and have that work.

EDIT: Can I use 12V relays, I've found that I can buy these too?

Yes.

Breadboard and get the circuit working to your satisfaction **first** before you go buy a lot of parts. It may need tuning depending on the relays.

[Fael]

Please excuse me if this question is stupid but how are we supposed to assign values to R1, C1 and D1 on the schematic for the true bypass using relays? (http://www.geofex.com/FX_images/relay%20true%20bypass%20with%20Boss-Ibanez.gif)

Mind you, this is coming from an economist, not an electrical engineer.

Is there some theory that I should read to be able to assign the aforementioned values? Are those values the same in every case?

[R.G.]

Please excuse me if this question is stupid but how are we supposed to assign values to R1, C1 and D1 on the schematic for the true bypass using relays?
Mind you, this is coming from an economist, not an electrical engineer.
Is there some theory that I should read to be able to assign the aforementioned values? Are those values the same in every case?

Sorry - use any silicon diode for D1. A 1N4148 or 1N914 is a common type, and works fine. You can also use any of the 1N4000 series, from 1N4002 through 1N4007.

For R1 and C1, you can start with 10K and 0.1uF. Really, you could put in 1K for R1 and leave C1 out and it would probably work OK. R1 and C1 are "slow down" parts, to make the MOSFET switch more slowly than the flipflop which drives. This helps in putting a slower voltage edge on the relay coil, and usually cuts down any clicking sounds which the coil may couple into the audio path. This varies from relay to relay; some are really bad, and some need almost no slowdown at all.

I guess the "theory" for that is to start with R1=0 and C1=0 and increase the R*C product until it quits making a [clik] when it switches - if it ever does.

It's not a stupid question, and there is some theory. But no, you couldn't be expected to know it already, it's not the same in every case. But it's also not hugely critical.

[jkokura]

Has anyone actually made this work in a Boss Pedal yet? If they could post pictures and describe the method that would be wonderful.

Jacob

[jkokura]

friendly bump to see if anyone has made this work in a Boss pedal yet.

Jacob

[R.G.]

friendly bump to see if anyone has made this work in a Boss pedal yet.

I'll get to it eventually, but my prototyping time is very limited.

[ocg]

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?

is that "clickless" thing.. the same as this: http://www.muzique.com/schem/bypass.htm  got any schem???

[R.G.]

is that "clickless" thing.. the same as this: http://www.muzique.com/schem/bypass.htm  got any schem???

They appeared similar to me, but I have been told they are different. No, I do not have the schematic of either one.

The schematic of most microcontroller circuits is trivial, simply a connection from the pin that does the work to what gets worked on. The complexity is entirely inside the programming of the uC, so a schematic of these is not particularly interesting. The programming may or may not be quite different.

[nexion777]

I would intend to try this schem, using two BS170 instead of BJT. But I would have some doubts:

1. With  MOSFETs is preferable to use very fast diodes (i.e. BAT41) or there is no difference, in practice, compared to 1N 4148/914 (or 1N4007)? And even choosing the best possible type of diodes, in this applications the life expectancy of the mosfet could be less than a more "rough" BJT?

3. R.G. mentioned the possibility of removing the slow down capacitors and increasing  the 10K resistors, because of the gate-source capacitance in  MOSFETs. But what is great in this capacitance? I read in the BS170 datasheet (Fairchild): "input capacitance," output capacitance" and "reverse transfer capacitance", which confuses me.  

[R.G.]

1. With  MOSFETs is preferable to use very fast diodes (i.e. BAT41) or there is no difference, in practice, compared to 1N 4148/914 (or 1N4007)?

In this circuit, it makes no difference. The diode is there to "catch" the relay coil, not the MOSFET. The catching diode needs to be very fast in power supply circuits which operate at high frequencies. In this circuit, it gets operated maybe once every couple of minutes, so it is not critical.

And even choosing the best possible type of diodes, in this applications the life expectancy of the mosfet could be less than a more "rough" BJT?

If it's done properly, the life expectancy of both BJT and MOSFET are the same - far, far longer than the relay. The only place where a MOSFET is more fragile than a similar-power-rated BJT is if there are transients on the gate that puncture the gate oxide. This can be prevented by adding a protection zener of about 12V with its cathode to the gate and anode to the source of the MOSFET. MOSFETs are actually more durable than BJTs in some cases because they have no second breakdown mechanism.

3. R.G. mentioned the possibility of removing the slow down capacitors and increasing  the 10K resistors, because of the gate-source capacitance in  MOSFETs. But what is great in this capacitance?

Just that it's already there, and you don't need to add another part.

I read in the BS170 datasheet (Fairchild): "input capacitance," output capacitance" and "reverse transfer capacitance", which confuses me.  

Input capacitance is the capacitance from gate to source, and is a simple capacitance. Reverse transfer capacitance is the capacitance from drain to gate which gets multiplied by the voltage gain or transient operation of the device. Reverse transfer capacitance appears to be much bigger than the actual number. Reverse Transfer Capacitance is like the capacitor I showed from collector to base, but it's built in inside the device.

Both bipolars and MOSFETs - and JFETs, tubes, everything that amplifies - have both of these capacitances, and they need to be understood for fast operations. Using a much larger capacitor makes the variation of the internal capacitor not matter.

[nexion777]

I sincerely thank you, R.G.
Now I have a bit less "fog" in my head .  

[Paul Marossy]

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

I believe that is Jack Deville. I've seen some of his posts at the Wampler Pedals forum. He seems to be pretty knowledgeable about electronics related things.

[nexion777]

I finally breadboarded the relay driver by R.G. using a 4069 hex inverter, a 5V latching relay  and a couple of BS170. Power is supplied by a 78L05 regulator. Well, the driver work, changing the state of relay.  

BUT... haem... There's a problem: measuring the voltage on the 10K resistors, I read 5V when a coil is engaged and 0V when disengaged. I suppose that is bad, the circuit should supply the needed voltage to activate a coil just for a little amount of time, right? Here the voltage is the same after 10 minutes ( ) in fact the regulator has become noticeably warm. I tried to connect the 100K resistors to ground instead of +V, and although the circuit still seem to operate, now the readings on the 10K resistors alwais show me 5V (engaging or disengaging the coils have no effects now)....

[R.G.]

I finally breadboarded the relay driver by R.G. using a 4069 hex inverter, a 5V latching relay  and a couple of BS170. Power is supplied by a 78L05 regulator. Well, the driver work, changing the state of relay.  

BUT... haem... There's a problem: measuring the voltage on the 10K resistors, I read 5V when a coil is engaged and 0V when disengaged. I suppose that is bad, the circuit should supply the needed voltage to activate a coil just for a little amount of time, right? Here the voltage is the same after 10 minutes ( ) in fact the regulator has become noticeably warm. I tried to connect the 100K resistors to ground instead of +V, and although the circuit still seem to operate, now the readings on the 10K resistors alwais show me 5V (engaging or disengaging the coils have no effects now)....

OK. Time for debug.

Measure the output pins of the two inverters which drive the ends of the two 10Ks. These two pins should sit near ground all the time, except when the switch is flipping states. If this is not true, if either one ever stays high. then look at the two input pins of the inverter. These must be pulled up to the power supply by the 100K resistors. They cannot be pulled down by the front part of the circuit if the two 0.1uF capacitors are inserted in the circuit properly.

Get out the DMM.

[nexion777]

In fact was a my (stupid) mistake: 100K resistors were connected in the wrong way... 
I have now corrected the error and the circuit works perfectly... true, the half of the  coin in diy is... the debug!
As alwais... thanks R.G. !

[R.G.]

In fact was a my (stupid) mistake: 100K resistors were connected in the wrong way... 
I have now corrected the error and the circuit works perfectly... true, the half of the  coin in diy is... the debug!
As alwais... thanks R.G. !

You're welcome. I know that mistake well - I've made it several times myself. 

[jimosity]

Sorry to drag up an old thread; but can someone explain what the MOSFET is actually used for in this relay switching?
It looks like it's used to slow down the relay so as to not 'click' as loud...is that correct?

[R.G.]

Sorry to drag up an old thread; but can someone explain what the MOSFET is actually used for in this relay switching?
It looks like it's used to slow down the relay so as to not 'click' as loud...is that correct?

It is the power element that switches the tens of milliamperes which are needed by the relay coil to work. That is its primary job. The other stuff is to slow the MOSFET down from the 100nS or so it would switch on its own to a few milliseconds to prevent the sudden voltage change on its drain from coupling through the parasitic capacitances into the audio path.

The CMOS stuff can't run that much current all on its own reliably.