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PostPosted: Sun Dec 27, 2009 8:51 pm 
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Sorry guys, I have been really busy with the holidays! Ill try to get something up here tomorrow!


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PostPosted: Sun Dec 27, 2009 9:16 pm 
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I got 3 older pedals that bleed through and suck tone when bypassed that I want to "true bypass" using these relays. 8)
Hopefully they will work with no popping.

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PostPosted: Thu Feb 04, 2010 5:21 pm 
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Guys, please can we resurect this one and get a verified layout with part No's and values? I use the millenium BP - but occassionally still have some issues with it so I'd like to try this little feller out. Is the relay used available in the UK?

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PostPosted: Fri Feb 05, 2010 12:50 am 
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when I made this one ages ago I used this relay ...
http://cgi.ebay.co.uk/OKO-Pcb-Power-Rel ... 2a046cfca9

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PostPosted: Sat Feb 06, 2010 4:37 pm 
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Curt, any word on an "official" parts list?

I"ve got 20 of these things (or mayb 30, I can remember now) sitting there collecting dust.

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PostPosted: Sat Feb 06, 2010 5:57 pm 
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LED
1N914/1N4148 diode
100nF cap
4K7 resistor x 2
Relay 9V DC
NPN BJT (anything will work really, 2n3904, 2N5088, etc).

This setup is what RG has documented at GEOFX. Go there to find out more.

*Should also be a electro cap in there to slow the transistor transients when switching*

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PostPosted: Fri Mar 12, 2010 4:10 am 
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Hi all,

UK memebrs - I think the following link may be to the correct relay:

http://www.rapidonline.com/productinfo.aspx?tier1URL=Electronic-Components&tier2URL=Relays-Solenoids&tier3URL=PCB-Relays&tier4URL=Subminiature-relay-DPCO-1A&moduleno=35156&kw=DPDT+RELAY+1A#

I'm about to try the Millenium Bypass 2 (with shunt) circuit but this is not much more hassle and if it is more reliable/less picky then ace. I'm all for that.

I think the 12v ones are out of stock for 1-2months :shock: at Rapid. I'll keep an eye out. Maybe Bitsbox (thanks for the recommend Lochy) will have em in.

If I do get round to this I'll be sure to post my findings.

Cheers,
Ian

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PostPosted: Fri Mar 12, 2010 7:19 am 
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Hello again.

I've had a look over this. I'm feeling very noob-ish about this so i'm writing what I think and hopefully someone will be able to comment?

The switch (latching in this case [relay is non lathcing so needs to be 'fed', the LED is also controlled by this mechanism) completes the saturation of the 2n3904 by applying V+ across both the Collector and Base. This causes the 2n3904 Emitter to, well, emit i guess.

When this occurs the circuit across the relay coil completes causing the relay to actuate, thus flipping the relay from bypass to send/return.

At the same time the LED is fed from the same emitter, thus lighting when the switch is complete.

The 4k7 resistor is current limiting, set to preferred value.
The 1n4001 is a protection diode.
The resistor across the 2n3904 B&C controls the tranny saturation (I assume this means that the emitter will start to emit?!?) this should be set low enough to cause saturation.

I hope so far i'm in the clear. :?:

Right, now:

-What is the function of the cap across the base and collector? Stability?
-Should the LED be rotated by 180 degrees? It looks to me like the anode is connected to ground?

Image

The other question is regarding the coil voltage. Obviously 9v is the preffered option, however the 9v relays seem to be few and far between here. I have read a bit about relays being usable with a different coil voltage, i was thinking that a 5v relay could be used if the emitter volage was halved (a la biasing) using two equal resistors dividing between V+ and GND. I assume 4.5v is close enough to 5v to trigger it?

Thanks for any confirmation. Even after buying the relay and a good DPDT footswitch this is STILL cheaper than buying a 3PDT footswitch in the UK. Rediculous. :D :evil: :D

ian.

:D

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PostPosted: Fri Mar 12, 2010 9:15 am 
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Taking the ball and running with it here! :D

Ok, the 5v relays I'm looking at have a Pull-in voltage of 75% (so 3.75v) and maximum coil votage of 150% (7.5v).

So, the 9v supply is too much. BUT, dividing the voltage passed by the emitter will allow 5v relays to be used.


As you were gentlemen.

Ian
:idea:

As always critique welcome.

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PostPosted: Fri Mar 12, 2010 10:10 am 
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Nothing to add here except, Jolly Good Job Fella!!

I'm definately interested in giving this a go as neither the 3PDT or the MBP do the trick every time, all of the time. Tinkering with this idea has long been on the list of to-do's so thanks for moving it forward - you really are putting out some good stuff on here of late Ian, many thanks!!

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PostPosted: Fri Mar 12, 2010 10:51 am 
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Cheers! :oops:

To be honest I've been lurking for so long and just reading everything that is available that I finally feel like I'm in a posistion to give something back.

Even if it just pure enthusiasm! :shock: 8)

Ok. My reading so far indicates that we should simply be able to put a resistor of similar value in series with the supply from the emitter (after the LED tap) of the 2n3904. I will confirm with measurements later (sans relay :cry: :lol: :cry: ).

Rapid have the relays for about £0.93 or Bitsbox have them for £1.90. This plus the £1.53 for the footswitch (from Rapid) is way less than a 3pdt will set you back. Good times!

I can see me sacking off the MBP2. :wink: Good job this thing uses 2n3904's though! :shock: :roll:

More to follow.

Ian

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PostPosted: Fri Mar 12, 2010 11:21 am 
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Enthusiam indeed!

Next time i should re-read the spec sheet before writing. In all references above swap the Collector and Emitter.

:oops:

As my daughter would say:

:twisted: MEP! :twisted:

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PostPosted: Fri Mar 12, 2010 3:29 pm 
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So I've been getting my head around this circuit. And assuming my learnings are correct, it's been a really good learning experience!

OK – so this is how I understand it.

The fundamentals of the the circuit are the footswitch, the transistor and the relay.

Relay first

Simply the DPDT part is just like any other DPDT switch, the difference here is that rather than being switched by hand it is being switched by an electro-magnet. The electro-magnet in this case is the coil. Once the magnet is strong enough it 'pulls' the switch from its normal state to a switched state. In momentary relays once the electromagnet has no power the switch returns back to its normal state. In our case its normal state is hardwired bypass (In -> Out), our switched state is In->Send->FX->Return->Out.

Simple so far.

The power of the magnet is due to the current through it. As the coil has a fixed resistance (the exact resistance value varies from manufacturer to manufacturer, and relay model to relay model) the coil voltage can be determined to give the correct current through it. There are tolerances given in the spec sheet, such as the minimum voltage (and therefore current through the coil) to actuate the switch and maximum voltage (and therefore current through the coil) before it's switching-mojo is released...... The example I'm looking at gives a switching minimum of 75% voltage (and therefore... meh you get the idea) and a max of 150%. So the coil will be strong enough when 3.75v (=5v[coil rating]*0.75) is applied and will fail when 7.5v is applied (5v[coil rating]*1.50).

Still with me?

In this circuit the relay also has some protection across the coil, this is to stop voltage spikes when switching-off ruining the party.

I am not entirely sure if all relays share the same pinout. Check the spec sheet.

Here you can see the coil 'element' on the left, with the DPDT contacts on the right. Please note the wiper is shown in its normal state. In this case the pole is the left-column of the block of six, the normal is the middle and the switched is the right.

Image


Next up – The transistor

This is new ground to me, and makes me want to learn more about transistors. I think I'll have to read the Stompboxology article about this stuff!

Right, in this circuit the transistor is being used, like a power switch. The main principle being used is the saturation of the transistor. Look at the specs of the 2n3904, it gives a saturation voltage for the collector-emitter and base-emitter. At these voltages the transistor saturates, a useful feature of which is that the voltage across the collector and base is 0. If there is 9v at the emitter it will pass to the collector.

Ok so what? Well that brings me to the switch.

In this case the switch is completing a circuit from V+ to the base, a simple operation hence why a simple switch can be used. Please note that it must be latching as the relay is not. The completion of this circuit passes V+(ish) to the base causing the transistor to saturate, thus passing the voltage at the emitter to the collector (+9v -hurrah!).

Please note, the resistor in front of the base is to limit current. Without it the base would overheat and eventually fail.

So now we know what the switch is doing and that it causes the transistor to switch. What happens after that.

In this circuit the V+ serves two purposes.

First - You will all be familiar with the LED current limiting resistor and the LED. Right. Well when the switch is pressed, the transistor saturates, V+ then passes through, the LED resistor limits the current and the LED lights up. Yay. Indicator everywhere!

Second – The voltage is also applied to the coil in the relay (remember that? This turns on the electro-magnet and is 'pulls' the relay from normal to switched. In our case from bypass to FX.

The happy-happy-joy-joy bit is that they happen at the same time, and because our switch is latching it stays like this until we unlatch the switch. Nice!

OK – at this point if you have a 9v-coil relay you're sorted. In fact if you have a 12v-coil relay you're probably sorted too (as a quick justification, taking the earlier example of a minimum switching voltage of 75% - 12v*0.75=9v, therefore the switch will actuate. Unless you're using knackered batteries...).

If like me you're desperate to find ANY solution we are not out of luck. We can use a 5v-coil relay by using a series resistor to drop the voltage across the coil. The voltage passed by transistor is about 9v, this is supplied to the LED and coil in parallel. We don't want to touch the LED supply so we place the resistor between the LED resistor and the coil. This is placed in series.

Now stick with me here. My maths is pretty ropey (as may well be most of the above!).

We use the equation V=IR where V is the voltage, I is the current and R is the total resistance.

In this example V = 9v (collector supplied), I is to be found out and R is the resistance of the coil plus any additional resistance. Lets guess at a resistance bigger than the the coil resistance (so 210ohm)

So: 9 = I x 70[coil resistance]+210[limiting resistance]

Rearrange it to: 9/(70+210) = I

or more neatly I = 9/280 = 0.0321A

We can then use the V=IR again to work out the voltage across each element:

Voltage across limiting resistor: V = 0.0321A x 210 = 6.741v
Voltage across coil: V = 0.0321 x 70 = 2.247v

As a mathematical exercise: Voltage across limiting resistor + voltage across coil = 6.741+2.247= 8.988v

Not exactly 9v as I rounded the current value but you get the point!

OK. Looking at those we can see that the voltage across the coil is too low to actuate a 5v(75%) relay: 5v*0.75 = 3.75v the voltage calculated is 2.247v. No dice.

Looking at V=IR where I is constant, if we decrease R – V follows suit. We want less voltage dropped across the limiting resistor so there is more left for the coil.

I've done a couple of calcs to find it out but the resistor we need to get 5v across the coil is... 56R:

I = 9/(70[coil resistance]+56[limiting resistance])
I = 9/126 = 0.071

Voltage across coil = V = 0.071*70 = 4.97v

Tahdah!

OK. So there we have it. I will endeavour to test this as soon as possible. Probably should have done that instead of writing this!

Anyways, I hope it is all correct – PLEASE CORRECT ME IF I'M WRONG AS I NEED TO KNOW! - and I hope someone gets to learn something as I have.

Peace, love etc etc.

AND IM SPENT.

Ian.
x

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PostPosted: Mon Apr 26, 2010 1:04 am 
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irfrench wrote:
I'm feeling very noob-ish about this....


You went from noob to Master Jedi in less than half a day.

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PostPosted: Mon Apr 26, 2010 3:47 am 
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:lol: :oops: :lol:

I get a little involved with stuff when I get bored!

TBH the whole 3PDT thing will work a charm - however the current draw will be massive. Thats the main issue with relays, so, if you do try this (i've not yet as i'm engrossed in recording at the mo) you'd better do so with a hefty powersupply!

I'm pretty sure I drew up a stripboard layout for it, I'm happy to post it but it is unverified.

Cheers,
Ian

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PostPosted: Mon Aug 16, 2010 11:09 pm 
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Thread ressurection!

I'm looking at using this circuit to True Bypass some Boss Pedals. Thing is, the Boss pedal switch is a momentary one, and it looks like this needs a latching switch. I don't want to have to drill any holes to the outside, and I'd like to do as minimal 'damage' in doing the mod internally as I can. So, is there a source for a latching switch replacement for Boss type pedals? Does anyone have any ideas, or have the successfully used this in a Boss pedal?

Jacob

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PostPosted: Tue Sep 28, 2010 11:05 am 
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I still have a couple dozen of these damn things.

Has anybody actually built this and got it to work? If so, let us know a list of values please.

Thanks.

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PostPosted: Tue Sep 28, 2010 11:53 am 
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culturejam wrote:
I still have a couple dozen of these damn things.

Has anybody actually built this and got it to work? If so, let us know a list of values please.

Thanks.


Me, too. Have about 12.

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PostPosted: Fri Sep 20, 2013 12:12 pm 
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dcountry13 wrote:
culturejam wrote:
I still have a couple dozen of these damn things.

Has anybody actually built this and got it to work? If so, let us know a list of values please.

Thanks.


Me, too. Have about 12.


I *still* have like 20 of these things. :lol:

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PostPosted: Fri Sep 20, 2013 3:04 pm 
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Have you tried Chris' values above?

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PostPosted: Fri Sep 20, 2013 3:07 pm 
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jkokura wrote:
Thread ressurection!

I'm looking at using this circuit to True Bypass some Boss Pedals. Thing is, the Boss pedal switch is a momentary one, and it looks like this needs a latching switch. I don't want to have to drill any holes to the outside, and I'd like to do as minimal 'damage' in doing the mod internally as I can. So, is there a source for a latching switch replacement for Boss type pedals? Does anyone have any ideas, or have the successfully used this in a Boss pedal?

Jacob
Without the original schematic I'm kinda shooting in the dark, but based on some discussion here is sounds like this circuit uses a latching switch to engage a BJT when then turns on a non latching relay. In that case, you need to tap the output from the flip flop on the Boss pedal and use that to control the BJT and turn the relay on/off.

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PostPosted: Wed Apr 09, 2014 10:07 am 
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Does anyone have the image file for this? It seems to be lost.

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