Need help daisy chaining relays for a Marshall clone amp project

[Mike_J]

I am in the process of planning a Marshall clone build.  The amp would require a large number of relays to switch from a 1968 model Plexi to a 2203 using one footswitch button.  I just don't know if my idea of daisy chaining relays would work.  (What I mean by daisy chaining relays is sending the 5V or 12V power to the cathode side of relays one after the other in series and the same for the anode side of the relays daisy changed essentially to one footswitch button.

I have used relays in a couple of Dumble clone builds but I am not certain if my idea for daisy chaining relays like this will work.  Thankfully I know which side of the diode to run power to and what com, nc and no mean and where they can be found on the relays but I am still far from an expert in their use. 

The only power source I have used for relays is Dumble's voltage doubler circuit going into a 12 volt voltage regulator and 12 volt relays.  Doug's relay system appears to require fewer parts than Dumble's, so I would like to use Doug's system if at all possible.

The relays I think I will need are as follows:
   -  One DPDT relay to switch between the Plexi and 2203 preamps.  The other side would switch the .68 cap out of the tone stack when the 2203 side is selected.
   -  Two DPDT relays to switch between the 2203 pair of 220K resistors in the PI and the Lar-Mar circuitry for the Plexi.  I will need another half of a DPDT relay to disconnect the 2203 master volume pot when the Plexi side is chosen.
   -  If I am going to go this far I should probably have a DPDT relay to choose the NFB resistor value and corresponding OT secondary tap.

My hope is to pair this amp with the Steel String Singer hybrid amp I made.  It is great for creating one of my favorite tones which is Texas Blues / Fender Twin clean based.  My other favorite tone is 60s and 70s British Marshall crunch and overdrive.  If I could AB between them I will hopefully have created Strat tone nirvana in one nice little 250 pound package.

Someone has already put together a layout of a Plexi / 2203 circuit that uses a SPDT switch on the front of the amp to switch between the preamps of each amp.  It appears to just use the 2203 master volume.  I hope somebody knows if my idea of daisy chaining the relays will work.  Any suggestions would be greatly appreciated.

Thanks
Mike

[PRR]

> What I mean by daisy chaining relays is sending the 5V or 12V power to the cathode side of relays one after the other in series and the same for the anode side of the relays daisy changed essentially to one footswitch button.

Please draw a sketch. Basic relays don't have cathodes/anodes and your description could be read several ways.

[Mike_J]

I am referring to diodes commonly placed across the coil of the relay (from pin 1 to 16 or 16 to 1).  The diodes are used to protect the relays if the footswitch is repeatedly and rapidly stomped on and off.  From my understanding and usage you can run them across the coil in either direction.  However, the power from the voltage regulator must go to the cathode side of the diode or the diode will fry immediately and become useless.  If any of what I just said is incorrect please correct me.  From my understanding the diode is not a necessity.

I learned to use relays making a few Dumble ODS clones.  It is my understanding he used them to prolong the life of the relays.  Since diodes are cheap I did not question that theory and just went with it.  Again, if I am wrong I am here to learn and hopefully pass on the little bit of knowledge I have about building amps.
 
I am not trying to skirt your request for a schematic but I am woefully ignorant when it comes to doing anything other than handwriting a schematic.  I could do so and scan it as a pdf file if you still think it is necessary.
 
I have managed to learn how to make and finish my own cabinets.  I also make my own faceplates and nameplates using Inkscape and can get them made pretty inexpensively which provides a lot of flexibility in amp design.  I also silk screen my own nameplates on mirror finished stainless steel and drill out many of my own chassis after I have them custom made.  However, I do not have the faintest idea how the people here make such nice drawings and schematics on this forum.  It is something I am looking forward to learning.

The last and only time I have appeared on any amp forum was this one about six or eight years ago.  I was making a revibe and just torturing Tore T because I couldn't figure out how to get rid of the hum in my revibe.  Turned out it was a poorly soldered ground that once fixed made the revibe absolutely dead quiet.  He was very nice but would have been in his right to tell me to hang it up and try a different hobby as I did torture him with my ignorance.  My apologies if you are still out there Tore T.  Your revibe mod is outstanding. 

[Mike_J]

Here are two of the probable relays I would use.  They are both made by Omron Electronics.

5VDC Relay Part No. G5V-2-DC5
    Coil Current = 100mA
    Power Consumption = 150mW

12VDC Relay Part No. G5V-2-DC12
    Coil Current = 41.7mA
    Power Consumption = 500mW

If I wired the coils of five 5VDC relays in series would they draw 500mA (5 x 100mA coil current)?  What impact does power consumption have on the other secondary's in the power transformer?

[rzenc]

If I wired the coils of five 5VDC relays in series would they draw 500mA (5 x 100mA coil current)?

If you wire them in SERIES:

1) the same coil current will flow thru all of them, meaning, current consumption will NOT multiply;
2) you will need 25Vdc, meaning, each coil will need 5Vdc across it's coil.

I have used multiple relays switching together in many amps I built. IMHO, it should be wired in parallel. In the event of a relay coil goes dead it will be easier to spot, since this stage won't be switching it's pins.
If you wire them serial, in the event of coil failure, your whole string of relays will stop working. It will take longer to identify the problematic piece.
Apart from the mentioned failure, I believe both methods, series and parallel should provide the same end result. However, I never tried it serial.


Hope it helps.
Best Regards,

R.

[sluckey]

If I wired the coils of five 5VDC relays in series would they draw 500mA (5 x 100mA coil current)?

You won't be wiring the relay coils in series. They will be wired PARALLEL (see pic). They will draw a total of 500mA.

What impact does power consumption have on the other secondary's in the power transformer?

Probably none, unless you have a wimpy PT.

There is a much simpler way of doing this that will only require one relay. You could build a complete Plexi preamp and a complete 2203 preamp and use a single relay to switch the two preamp outputs to the PI. Or, and this would be my choice, take a look at this PDF and see if it doesn't give you some ideas.

     http://home.comcast.net/~seluckey/amps/misc/Marshall_Dual_50.pdf

[kagliostro]

Ciao Steve

Nice trick, ingenious, simple and effective 

Franco

[Mike_J]

Could someone please tell me how you do the quote boxes.  I want to respond to sluckey's comment but don't know how to do the quote boxes.

Thanks
Mike

[HotBluePlates]

Go to his post, and click "Quote".

Or, if you've already clicked "Reply" then scroll down to his post and click "Insert Quote".

[Mike_J]

sluckey

It was your schematic and layout that inspired my idea to look into this project.  My primary reason to add more relays is to give the Plexi the PPIMV.  If I was going to go that far then I might as well make the changes to the two circuits to make the Plexi a complete Plexi circuit and the same for the 2203.  It would take probably five relays to do that.
 
Any advice you can give me is appreciated.  Your drawing is what I was calling series.  I often get the two confused.

Thanks
Mike

[Mike_J]

Go to his post, and click "Quote".

Or, if you've already clicked "Reply" then scroll down to his post and click "Insert Quote".

Thanks HotBluePlates, I will get a lot of use out of this tip.

[Mike_J]

I have been using the Fairchild Semiconductor LM7812CT voltage regulator.  It's output current is rated up to 1A.  I see Doug sells 7812's for about one-half of the price I have been paying for the Fairchild's.  Anyway, presuming Doug's voltage regulators are rated up to 1A I see no reason why Doug's relay power supply board wouldn't work well.  With an allowance of 150mA for a footswitch LED I would have power to spare running five relays.

Using sluckey's relay.gif schematic above I would hook the positive side to the voltage regulator and the negative side to a manual/pedal switch on the back of the chassis.  Run a wire from the manual/pedal switch to the ground side of the voltage regulator and I am home free.  Put a footswitch jack in next to the switch and I am in tone nirvana.

On the last amp I built I had a 6-0-6 1A secondary tap added to the power transformer.  Does anyone think it would be wiser to install a separate power transformer in order to protect the amp from a fried coil in one of the relays?

[sluckey]

On the last amp I built I had a 6-0-6 1A secondary tap added to the power transformer.  Does anyone think it would be wiser to install a separate power transformer in order to protect the amp from a fried coil in one of the relays?

A separate winding dedicated to the relays is a good idea. I wouldn't bother with a separate PT though. If you use 5V relays you won't need a 6-0-6 secondary.

As long as you use that 7812 your amp will be protected from even a dead short on the relay coil circuit. The 7812 will gracefully shut down in the event of a short on it's output.

[Mike_J]

On the last amp I built I had a 6-0-6 1A secondary tap added to the power transformer.  Does anyone think it would be wiser to install a separate power transformer in order to protect the amp from a fried coil in one of the relays?

A separate winding dedicated to the relays is a good idea. I wouldn't bother with a separate PT though. If you use 5V relays you won't need a 6-0-6 secondary.

As long as you use that 7812 your amp will be protected from even a dead short on the relay coil circuit. The 7812 will gracefully shut down in the event of a short on it's output.

Thank you for your response.

I presume that would also apply to a 7805 as well.  One thing I left out was power to the LED in the footswitch.  Can I run the positive along with the negative to the back of the amp and connect it to the footswitch jack to power the LED?  Did you build the amp in the layout and if so did you like it?  Do you think it would make any sense to separate the master volumes?

Thanks
Mike