Switching between two sets of controls

[SolariEGO]

I'm planning to build the PT-80 delay from the GGG site, so I was day dreaming: "Wouldn't it be nice to be able to change between two presets, so I could have both 50's slap back and a more atmospheric 70's monster lead echo on the board, in one box and without fiddling with the controls?"

The two presets should be stomp switchable, preferably with indicator LEDs. My knowledge of switching (and electronics in general) is rather basic, but as I understand it, if the wire count was less, it should be easy to wire up two independent sets of controls and switch them with a 3pdt.

Now the problem (if I understand the wiring correctly) is that I need to switch four leads from the board; one for the time control, one for effect level and two for the repeat control (I guess there wouldn't be no need to switch the ground connections for the two sets of controls?).

What the (insert a four letter word to your liking) am I talking about? OK, here's the schematic and the outboard wiring layout:

http://www.generalguitargadgets.com/pdf/ggg_pt80_lo1.pdf

http://www.generalguitargadgets.com/diagrams/pt80schem.pdf

I know Smallbear has a 4pdt switch, but that would still leave me without indicator LEDs. So what are the options? A 4pdt switch AND a millennium switch? An adventure into CMOS logic? (I'm in way over my head now.) Take two aspirins and call my doc in the morning?

Steinar

[erick4x4]

I have only messed with it a litte, but it would seem like you are begging for relays.

One switch would trigger as many relays as you need to turn on/off. Usually just a matter of supplying the relays with the right voltage.

[Mark Hammer]

How much do you want to change at once?

If all you wish to do is select between one of two preset delay times, that is dead easy.  Simply replace the 50k delay-time pot with a 100k fixed resistor and use an SPDT section (either on its own or as one set of contacts on a multi-contact switch) to select between one of two alternate 100k variable resistances to ground.  When either pot resistance is placed in parallel with the 100k fixed unit, you'll have a resistance that is no higher than 50k.  If you craved more dialability for short delay times, you could have one of those pots be 50k and the other 100k.  The 50k unit in parallel with 100k fixed would achieve a max resistance of only 33k, which would essentially expand the portion of the pot's rotation that addressed short delays.

Selecting between delay-time and repeat intensity presets simultaneously is a little trickier, though not dramatically.  If you were to stick a fixed resistor between the 1uf cap coming off pin 6/7 of the 571 and the input lug of the 50k Repeat pot, this would be tantamount to turning down the Repeat pot.  So, if there were 10k in series with the pot input, the pot would behave like a 60k pot that can never be turned up completely.  So, if there were a 50k variable resistance in series with the input lug of the Repeat pot, you could adjust the "action" of the Repeat pot so that when the extra pot is set to zero K, the maxed Repeat achievs max repeat intensity.  When the extra pot is set to 50k, the Repeat control will never be able to achieve more than half even when maxed.

How do you use this?  Use a switch to shunt the variable resistance (i.e., place a straight-wire connection across it) on the input of the Repeat pot.  When shunted, the repeat control works as normal.  When the delay signal MUST pass through the extra pot, rather than the shunt-wire, the Repeat control and extra pot (we'll call it "repeat trim") will reduce the Repeat signal by some proportion dictated by the interactive nature of the two pots.  I must emphasize that these WILL be interactive.  If the repeat-trim pot is set for 10k, then a max setting on the Repeat pot will be 5/6 maximum.  If the repeat-trim pot is set to 25k, then the Repeat setting now drops to 2/3 maximum.  And so on.

My sense is that people use more Repeats for longest delays, so it makes sense to make the variable series resistance part of your "short-delay" preset.  That is, your stompswitch would flip over to the 50k delay-time pot and engage the repeat-trim pot in one setting, then flip to the 100k delay pot and shunt the repeat-trim pot in the other setting.  If you had a 3PDT stompswitch, you could go back and forth between shorter and longer presets and also have a status LED to tell you which was in effect at that time.

A BIG word of caution here.  Since the delay-time pot and the repeat control leads will be coming out to the same stompswitch, you will want VERY much to insure that the clock-related leads, and the repeat-related leads do not come close to each other or are shielded to prevent that, or both.

[rogerinIowa]

How much do you want to change at once?

If all you wish to do is select between one of two preset delay times, that is dead easy.  Simply replace the 50k delay-time pot with a 100k fixed resistor and use an SPDT section (either on its own or as one set of contacts on a multi-contact switch) to select between one of two alternate 100k variable resistances to ground.  When either pot resistance is placed in parallel with the 100k fixed unit, you'll have a resistance that is no higher than 50k.  If you craved more dialability for short delay times, you could have one of those pots be 50k and the other 100k.  The 50k unit in parallel with 100k fixed would achieve a max resistance of only 33k, which would essentially expand the portion of the pot's rotation that addressed short delays.

Selecting between delay-time and repeat intensity presets simultaneously is a little trickier, though not dramatically.  If you were to stick a fixed resistor between the 1uf cap coming off pin 6/7 of the 571 and the input lug of the 50k Repeat pot, this would be tantamount to turning down the Repeat pot.  So, if there were 10k in series with the pot input, the pot would behave like a 60k pot that can never be turned up completely.  So, if there were a 50k variable resistance in series with the input lug of the Repeat pot, you could adjust the "action" of the Repeat pot so that when the extra pot is set to zero K, the maxed Repeat achievs max repeat intensity.  When the extra pot is set to 50k, the Repeat control will never be able to achieve more than half even when maxed.

How do you use this?  Use a switch to shunt the variable resistance (i.e., place a straight-wire connection across it) on the input of the Repeat pot.  When shunted, the repeat control works as normal.  When the delay signal MUST pass through the extra pot, rather than the shunt-wire, the Repeat control and extra pot (we'll call it "repeat trim") will reduce the Repeat signal by some proportion dictated by the interactive nature of the two pots.  I must emphasize that these WILL be interactive.  If the repeat-trim pot is set for 10k, then a max setting on the Repeat pot will be 5/6 maximum.  If the repeat-trim pot is set to 25k, then the Repeat setting now drops to 2/3 maximum.  And so on.

My sense is that people use more Repeats for longest delays, so it makes sense to make the variable series resistance part of your "short-delay" preset.  That is, your stompswitch would flip over to the 50k delay-time pot and engage the repeat-trim pot in one setting, then flip to the 100k delay pot and shunt the repeat-trim pot in the other setting.  If you had a 3PDT stompswitch, you could go back and forth between shorter and longer presets and also have a status LED to tell you which was in effect at that time.

A BIG word of caution here.  Since the delay-time pot and the repeat control leads will be coming out to the same stompswitch, you will want VERY much to insure that the clock-related leads, and the repeat-related leads do not come close to each other or are shielded to prevent that, or both.

I am working on the same thing: Mark, forgive my ignorance (I'm trying to learn here)...Your reason for the caution concerning separating the clock and repeat leads, is that to avoid picking up "clock ticking", or what are you referring to?

[SolariEGO]

Hi guys,
And thanks a lot for your advice, especially to Mark for taking the time to go into such great detail – that's a true altruistic spirit! Now, at the risk of pushing my luck (and your patience):

How much do you want to change at once?

Well, in a perfect world, I'd like to change all three parameters simultaneously; delay time, delay level and repeats. I'd like the slap back echo to have the same level as the original signal (or almost), whereas in the "atmospheric" setting the volume drop between the original signal and the first echo should be approximately the same as between the second and third echo (etc.).

Use a switch to shunt the variable resistance (i.e., place a straight-wire connection across it) on the input of the Repeat pot.

OK, I read you – a second 50k pot to switch into series with lug 3 of the repeat pot for the shorter delay mode. Could I wire up another 50k pot in series from lug 3 of the repeat pot to lug 3 of the delay level pot and switch that one out of series in the same mode to set the echo level higher in slap back mode than in "atmospheric" mode? The interaction between the pots would make tweaking a bit of a challenge, but as these pots are voltage divider wired, I guess there's no way of getting around that one without going the relay or MOSFET route?

For delay time, I really like your idea with the two different pot values, the lower value pot giving more usable pot action for short delay mode. But why do I need the fixed resistance in parallel? To avoid pops when switching? I was thinking of just switching between the identical leg of two 50k pots and wire the other leg of the two pots together. I also considered using an Ohm meter to find the right value for the slap back setting and change the slap back mode pot for a simple resistor, saving a few bucks and some space in and on the box. Why wouldn't this work?

Since the delay-time pot and the repeat control leads will be coming out to the same stompswitch, you will want VERY much to insure that the clock-related leads, and the repeat-related leads do not come close to each other or are shielded to prevent that, or both.

Got your point – should the shield be connected to something at one end of the leads, then?

Best regards,
Steinar