Super Simple Pedal Mod Question- delay time.

[Nyklus]

so ive been thinking alot about pedal mods lately,
and wondering specifically my guyatone flip tube echo,
what id like to do is add a switch that affects the delay time,

I'm just wonder if i attach it to the first and last lead on the potentiometer if it could theoretically put less resistance in the delay time, and act as it i turned the time down and back up again
or would the switch cause the delay time to drop below the resistance of the lowest setting on the potentiometer? would this ruin the pedal.

im asking because i love the sound of the distorted echos after you tweak the time.

maybe my answer lies in figuring out the lowest resistance of the pot and then putting that type resister on the switch.
lend any ideas to this beginner??

[Jdansti]

My understanding is that the Flip Tube Echo is a hybrid analog/digital circuit, but I don't know more than that. Do you have a schematic or can you tell what the pot is connected to on the board?  For example, if the pedal uses a PT2399, then the resistance at Pin 6 determines the delay. Without more information, I couldn't say how to affect the delay or whether your idea would harm the pedal.

If you could let us know what effect you're trying to achieve, that would help too. I have a premonition that you might get a reply from forumite Mark Hammer about the "Blind Urge to Mod". It sounds like you're trying to be cautious, and I'm not trying to label your idea as "BUTM" but, you should read the following quote from Mark (also presented to save him the trouble of responding ):

As the person who actually coined the term "B.U.M. syndrome" (Blind Urge to Mod), I guess I have to add some things here.

Many beginning modders will inadvertently end up wrecking something that could otherwise have resale value, but in the state they left it in, doesn't even have "for spare parts" value.  So, until a person acquires the chops to carry out a mod with some grace and skill, I would recommend purchase of a breadboard, and exploration of some very standard and simple circuits where it will be:
a) relatively easy to identify components that have known consequences/roles,
b) relatively easy to draw useful inferences about what kind of changes do what,
c) possible to do all that experimentation without requiring heat, solder, or destroying anything.

Once a person has some clearer ideas, understanding, AND appropriate tools (like a soldering iron suitable for tasks a little more refined than plumbing), THEN have at it.  Mods should be useful improvements or musically valid changes to circuits.  They shouldn't be a cause for exasperation or regret.  I've seen far too many "I modded it but now it doesn't work at all any more" posts.

If a person wants to learn about modding, I can't think of anything more fuly documented and explored than the venerable MXR Distortion+ and DOD250.  There are many things in there to play with that will let you learn what does what.

In addition to geofex, I would also recommend former forum regular Jack Orman's AMZ site.  The lab-notes section has a lot of very good and well-illustrated/explained ideas for mods to the familiar.

The only thing I would amplify on what Mark says, is to think about the "cost/benefit" of your mod idea, not in terms of direct dollars, but in terms of the value of your pedal as is. In other words, going out and buying a $15 Danelectro Echo and modding it for fun is one thing. Taking a pedal that is expensive, or you can't afford to replace, or is vital to gigging, and modding it for fun is not a good idea.  On the other hand, if you're a tech working for a big name act and you've got five spare pedals laying around, you can probably afford to turn it into a door stop if something goes wrong. 

[Nyklus]

right, i know what you mean, im trying to be cautious, thats why i'd get this question answered before ever trying to create this.
if the voltage change created by a potentiometer is changed with a switch and resistors within the parameters of the original potentiometer, then is there any damage that can be done?

and if the electricity is running in the direction of the least resistance, couldn't i attach the switch to the same place that the wires connect to the potentiometer.
 

[Jdansti]

Sorry to sound like Mr. negative, but your question can't be answered without knowing what the circuit looks like and without knowing what each lug of the pot is connected to.

It seems to me that you might not understand the internal workings of pots and how turning the shaft affects the resistance between lugs.



The resistance between the outer lugs A and B (normally called 1 and 3 respectively) and the wiper (center lug-normally called lug 2) varies as you move the wiper. Resistance across A and B is fixed. When the wiper is fully counterclockwise, the resistance between A and the wiper is approximately 0 ohms, and the resistance between B and the wiper is maximum, approximately the stated value of the pot. The reverse of the above is true when the wiper is fully clockwise.

You proposed shorting lugs A and B (1 and 3) using a switch to lower the resistance of the pot.  I don't think this would have the desired effect because the controlling resistance is the resistance between one of the outer lugs and the center lug.  Without the schematic, we have no idea what would happen if you shorted lugs 1 and 3.  

The affect of placing a switch between one of the outer lugs and lug 2 would be to make your pedal sound like you had turned the pot up or down. This alone would not harm your pedal provided you don't inadvertently damage something in the process. You could test the effect without installing the switch by using a jumper wire held with your fingers.

Placing a resistor on a switch connected to one of the outer lugs and lug 2 would be to place a resistor in parallel with the variable resistance of the pot, which makes no sense.

Again, if you or someone else can come up with a schematic, we could intelligently try to achieve the desired effect without damaging anything.  Aside from shorting between one of the outer lugs and the center lug (provided you possess the skills to do this), my recommendation is to not risk turning a $300 pedal into a doorstop.

[oldschoolanalog]

Walk before you start running:
http://www.diystompboxes.com/smfforum/index.php?board=6.0

[Nyklus]

Well,  yeah your diagram about how the pot works make perfect sense.
all i wanna do is have a momentary switch temporarily take the resitstance to 0ohms
the effect would be super short delay and the rush of it switching back to the origonal pot set delay time.

I've scoured and scoured but cant seem to find any schematics for the guyatone flip td-x tube echo.
its so frustrating.
I understand what your talking about, if i wasnt a novice this would be easy but i guess thats why i came to this forum so i can ask veterans if i can do tyhis simple mod with any damage.
what if i post some guts i found, only pictures i could find. 

[Jdansti]

Ok-I think I understand what you're trying to do. You want to flip or press a switch to momentarily short or place a fixed resistance between the wiper and the appropriate end lug of the delay pot.  Without a schematic, a) it's hard to say exactly how to do this, and b) whether this mod might damage your pedal.

If you can't find a schematic and feel lucky, here's what you can do. Connect a guitar or other source to the open pedal and place the delay knob in the middle of its range. Listen to the echo. Place a 1k resistor between the wiper and ground. See if this changes the delay the way you want. I recommended 1k because this is what other delays use in series with the pot to limit how low the resistance can go. One thing about the PT2399 is that if the resistance on pin 6 (the delay pin) is too low when you power up, the chip will lockup.

I think that the above is safe, but do it at your own risk!  I'm jut sharing my thoughts - you have to decide whether to risk damaging your pedal.

[Nyklus]

http://www.zimagez.com/zimage/img16646.php
http://www.zimagez.com/zimage/img16669.php
here are some pictures, thanks for your advice about the lockup that can happen when you let the resistance too low.

i guess i could find a ohmmeter and check the lowest point.

so once again your saying the pot arm/lead of the lowest value side and the middle arm of the arm/lead would accomplish this?

[Jdansti]

Ok-I don't see a PT2399, so anything I said about that chip is out the window unless it is one of the vertically mounted chips, but I doubt it.

If you measure the resistance of the pot with it completely rotated to it's lowest resistance, you will read a very low resistance, but you may be missing another resistor that's in series with the pot.

The more I think about it, placing a jumper (or a switch) between the middle leg and one if the outer legs should achieve the same results as manually turning the pot fully in either direction. In theory, this should be safe, but without a schematic, I can't guarantee that nothing bad would happen. It's up to you.

[Nyklus]

dudes, it works great. I took my ohm reader and it resists at zero, so i am confident in this mod, i've drilled the hole and have it ready for the momentary switch.

Now for another question.

This pedal uses 12v adapter only, no battery casing,

would it be stupid/ a bad idea, to add touch body contacts in between the momentary switch,

IE, is this going to shock me? since i now know that altering the value of this knob doesnt mess up the chip, make it lock up, or destroy anything.

[Jdansti]

What do you mean by "touch body contacts", and what is the desired effect of this mod?

[Nyklus]

the desired effect will be exactly what the momentary switch will be doing
but with body contacts, i will parrallel each lead to two metal nubs. so when i touch them both i can control
the resistance by touch.
flaring the delay time woth crazed occilations

[Jdansti]

I can't recommend making any part of your body part of the circuit for several reasons.

First, without a schematic, we don't know what the voltage would be across the switch. You could measure it, but the reading you get might not be constant depending on the settings of the various controls. Does the circuit boost the voltage above 12V? After all, there is a tube in there and it might be operating as high as 300V or more.  The voltage across the two switch terminals might (probably will) be different than the voltage between either one of the switch terminals and ground. You have your hands on the ground of your entire instrument/pedals/amp ground when you're playing a guitar.

Second, we don't know what the current would be at all times across your body contacts. Low voltage, high current can kill you.

Third, I'm not going to be responsible for your death should you fry yourself with this mod.  

If you want variable resistance across the switch contacts, use a variable resistor (pot). Figure out a way to put a pot operated by a treadle on there. If you could come up with a schematic, I'm sure that you'd get lots of help with this from the forum.

Another thought is to make a pressure sensitive variable resistor using a piece of antistatic foam that comes with some components. The foam is slightly conductive and it's resistance goes down as you squeeze it. Place flat pieces of metal (plates) on two sides of the foam. Each plate has a wire attached to it. Put the foam between two insulators and connect the wires as you would a pot. You might need to build a little hinged pedal with a spring to keep it open when you're not pressing on it. If the resistance is too low when you're not squeezing the foam, you might need to attach the upper plate to the underside of the pedal treadle so it doesn't contact the foam until you press on it.

Here's my patented idea:



Similar to this:
http://wiki.lvl1.org/Pressure_sensor_with_antistatic_foam

[Nyklus]

huh interesting idea i do like that foam concept. i guess it comes down to
the question of,
if this whole mod is manipulation of the resistance of the delay time pot
then how much voltage is a potentiometer usually able to handle?
is it usually very much, i know the bigger pots i see for light faders give a max voltage wattage amount
but what about this simple little pots?

[Jdansti]

I'm going by your statement:
>the desired effect will be exactly what the momentary switch will be doing
but with body contacts, i will parrallel each lead to two metal nubs. so when i touch them both i can control
the resistance by touch.
flaring the delay time woth crazed occilations

It sounded like you're trying to vary the resistance across the switch terminals, but maybe you're just trying to achieve an on/off state with your skin contact. If the latter were the case, why not just use the momentary switch?

>if this whole mod is manipulation of the resistance of the delay time pot
then how much voltage is a potentiometer usually able to handle?

Most pots we use are 1/2 watt. I don't know the power rating of the pots on your pedal.  The voltage a pot can handle is dependent on the current and the resistance. Without a schematic, we can't know any parameters affecting a given component.  If you can come up with a schematic we can help answer your questions better. Actually, I should say that someone smarter that I am about this stuff should be able to help you with the calculations that would answer your questions.

[Nyklus]

jdansi,
i am amazed you put up with all my misinformed questions,
i am a circuit bender first, a professional pedal moder somewhere way last.
i just know the beauty of cracking open a terrible distoring and touching the leads alligatir clips for wild sounds
what you said is correct, i just wanna play the resistance of the leads with my
fingers. it will sound crazy with my feedback looper.

is there a tool that could measure the wattage of this particular pot, since
you think one of the 300 or so post lurkers would have coughed up a guyatone flip td-x tube echo schematic by now.

[Jdansti]

I don't know of a way to measure wattage of a pot, but if it has some markings on it we might be able to tell.

My main concern with your idea is that I don't want you to hurt yourself.  If you are just going to use a finger or toe on these contacts, then the worst that can happen is you get a severe burn to an appendage and possibly lose it. Never allow electric current to pass across your chest or head. That includes from hand to hand.

[Nyklus]

interesting, even a 9 battery charge passin from accross the chest is bad news?

[Jdansti]

I don't know how many amps a 9v is capable of supplying, but under the right conditions (wet or sweaty fingers) I believe that it's possible to damage your heart even with 100mA or so. But what if you have a 9v, 1A wall wart?  That will provide a lot more sustained current than a 9v battery.

I'm sure we all have touched the + and - of a 9v battery or power supply while working on stompboxes without feeling any effect. I just don't recommend intentionally designing something that puts current across one's chest.

[timd]

@Jdansti - right on with the warnings.

@Nyklus - I have circuit bent things too. I see where it can be exciting to use the body contact bends and such...but just be wary and careful. I am not a big battery fan and I always use 9V with my bends (sometimes have to use voltage regulators to step down the initial 9V to 5V or 6V) so I never even think to do the body contact thing. Just be careful.