# Magnetron Delay: Momentary Feedback Switch?



## ChrisSchwarzkopf

Hey, I built the Magnetron Delay and ist sounds great but I was wondering how difficult it would be to add a momentary switch that you can use to push the delay into oscillation? I found this, so maybe its a pretty easy mod: https://www.diystompboxes.com/smfforum/index.php?topic=110561.0

Any thoughts on this mod?


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## phi1

A couple options come to mind to get you started thinking.  I haven't tried them myself.  I sketched up quick schematics snippets.

*Option 1:*
Pros:
1. Soft touch SPST momentary switch
2. Simple mod to implement
Cons:
1. Feedback knob position affects oscillation amount
2. Delay Level could also be affected by the position of the Feedback knob
3. At low Feedback knob levels, the repeats could be shorted to ground entirely

*Option 2:*
Pros:
1. Oscillation amount is completely isolated from the Feedback knob
Cons:
1. DPDT momentary stomp switches usually feel clunkier than the SPST (at least the ones I've tried)
2. I'm not sure if there will be any click in the repeats sound when the switch is pressed


Admittedly neither of these solutions are perfectly elegant, so I assume there's a better way.  (Maybe a more complex transistor switching arrangement).  Option 1 should be easy to try out on your build with just alligator clips, Option 2 would require some more surgery.  Keep looking around the net for PT2399 solutions like you already have been.  Please report back if you find something or if you test out the above methods.


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## ChrisSchwarzkopf

Hi There, first of all sorry for the very late reply. Thanks for your answer. I did some research but unfortunately I wasn't able to finde useful information, but still want to do this mod  The one review for the pedal on the PedalPCB-Main site says "I added a havoc switch that sends the feedback into oscillation, which just made it perfect for my needs" so apparently there is an easy (!?) Way to do it


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## jjjimi84

I wrote that review! All I did was add a spst stomp switch with one side to the middle lug of the feedback pot and the other lug goes to a trim pot then attaches to lug 3. The oscillation is still dependent on the feedback knob position and the trimmer helps fine tune it.


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## phi1

Jimi is describing (functionally) my option 1. He reversed pins 2&3 of the fdbk pot compared to mine, but in this case that doesn’t matter, since you’re just switching in the trimmer as a smaller resistor between pins 2&3.


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## Jovi Bon Kenobi

jjjimi84 said:


> and the other lug goes to a trim pot then attaches to lug 3.


Really awesome mod. What value is that trimpot?


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## jjjimi84

25k


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## Dali

I'm not sure about the effect of the modification. Would it be possible to make a quick and dirty(!) video or send a sound file @jjjimi84 ?


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## jjjimi84

Yeah i can put together something in the morning.


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## jjjimi84

Here is a little demo showing off the delay mod, I completely over used it but I wanted to emphasis the effect. Every control is at noon on the Magnetron and I am using a strat into a VFE Tiger Comp into an Ice Cream into the Delay straight into the front of a Mesa Fillmore 50.


__
		https://soundcloud.com/dan-keclik%2Fmagnetron-2


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## zgrav

That is a fun demo.  Seems like a cool mod.


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## coccoslash

phi1 said:


> A couple options come to mind to get you started thinking.  I haven't tried them myself.  I sketched up quick schematics snippets.
> 
> *Option 1:*
> Pros:
> 1. Soft touch SPST momentary switch
> 2. Simple mod to implement
> Cons:
> 1. Feedback knob position affects oscillation amount
> 2. Delay Level could also be affected by the position of the Feedback knob
> 3. At low Feedback knob levels, the repeats could be shorted to ground entirely
> 
> *Option 2:*
> Pros:
> 1. Oscillation amount is completely isolated from the Feedback knob
> Cons:
> 1. DPDT momentary stomp switches usually feel clunkier than the SPST (at least the ones I've tried)
> 2. I'm not sure if there will be any click in the repeats sound when the switch is pressed
> 
> 
> Admittedly neither of these solutions are perfectly elegant, so I assume there's a better way.  (Maybe a more complex transistor switching arrangement).  Option 1 should be easy to try out on your build with just alligator clips, Option 2 would require some more surgery.  Keep looking around the net for PT2399 solutions like you already have been.  Please report back if you find something or if you test out the above methods.



Hi!
sorry to bother you  
I'm going to do this great mod to my Disaster Transport JR (Cataclysm Delay). I just try with alligator clips + 1k resistor and a momentary switch and it works! 

is there a method to increase the duration of the repetitions while I hold down the momentary switch?
Normally I use a short delay and closed tone (ala Carbon Copy style).

Thanks
Andrea


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## phi1

Hi. Do you mean make the time between repeats (controlled by the time knob)?

you could use a DPDT momentary switch. One part of the switch does the feedback like my “Option 1:” way. Then the other part of the switch toggles between the time knob and an internal trimmer.

but, I think there is a chance of some click sounds when the time is changed. Soyou could experiment, but I think that mod may have some problems.


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## Danbieranowski

jjjimi84 said:


> I wrote that review! All I did was add a spst stomp switch with one side to the middle lug of the feedback pot and the other lug goes to a trim pot then attaches to lug 3. The oscillation is still dependent on the feedback knob position and the trimmer helps fine tune it.



I’m interested in doing this. Can you help me understand the wiring a bit? So the SPST can be wired either way, just one wire goes to the 2nd leg of the pot and one goes to a 25k trimmer leg, while another of that trimmer’s legs gets soldered to the 3rd leg of the pot?

Does it matter which trimmer leg you solder the spst to and to the 3rd pot leg?

Thanks!


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## Mcknib

You can use any outer trimmer leg plus the middle wiper

You're using the trimmer as a variable resistor so the middle plus either outer leg or you can jumper 1 outer to the middle wiper as one side of your 'resistor' and the other outer leg as the other side


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## Danbieranowski

Mcknib said:


> You can use any outer trimmer leg plus the middle wiper
> 
> You're using the trimmer as a variable resistor so the middle plus either outer leg or you can jumper 1 outer to the middle wiper as one side of your 'resistor' and the other outer leg as the other side
> 
> View attachment 5513


Awesome thank you!


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## Danbieranowski

Mcknib said:


> You can use any outer trimmer leg plus the middle wiper
> 
> You're using the trimmer as a variable resistor so the middle plus either outer leg or you can jumper 1 outer to the middle wiper as one side of your 'resistor' and the other outer leg as the other side
> 
> View attachment 5513


Would this work on any delay circuit? Like the D3lay?


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## Mcknib

PT2399 delays it should work 

FV1 I  dont know enough about to know if you can manipulate it once it leaves the chip 

All you're doing with PT2399 delays is altering the resistance on the feedback pot lug 2


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