Remote Volume Pedal with LED/LDR combo?

[DiamondDog]

Hi,

Before you ask, yes, I have searched- such as this

I have a remote wah, using the circuit from RG's Technology of Wah pedals (thanks, RG!) What I would like to do now is apply the same LED/LDR concept to a volume pedal.

My breadboard is occupied with a disemboweled Rat at the moment so I can't start prototyping yet. (Only one breadboard? Yeah, I know...  ) What I would like to do is ask some questions so I'm facing the right direction when it becomes vacant again.

0. I'm not into reinventing the wheel. Does anyone already have such a circuit?

1. I'm seeing as a basic building block the Anderton volume pedal descratcher, and replacing the the pot resistance a LDR + resistor. The pedal end will be what's needed to drive the LED at the LDR end. Yes, lift-and-drop the concept from the remote wah circuit.

Is this too simplistic an approach? What Obvious Thing have I overlooked?

2. While I'm doing that, is it possible to sub a lm13600 for the CA3080/071 combination without major headaches?

That should do for now... 

[R.G.]

0. I'm not into reinventing the wheel. Does anyone already have such a circuit?

Yes, the Anderton volume pedal de-scratcher.

1. I'm seeing as a basic building block the Anderton volume pedal descratcher, and replacing the the pot resistance a LDR + resistor. The pedal end will be what's needed to drive the LED at the LDR end. Yes, lift-and-drop the concept from the remote wah circuit.

I'm confused. Why do you need to do anything else with the pedal end other than what Craig did? Is there a good reason I just can't see?

2. While I'm doing that, is it possible to sub a lm13600 for the CA3080/071 combination without major headaches?

Y es. That's what the darlington buffer on the LM13600/13700 is for.

By the way, the LM13700 has a fixed bias for the darlington buffer, the LM13600 has a buffer bias that's proportional to the Iabc. The 13600 is therefore good for low power applications as the buffer does not burn constant power. The LM13700 is better for audio, as the buffer does not telegraph the change in amplifier bias, so has lower thump and control noise.

[DiamondDog]

1. I'm seeing as a basic building block the Anderton volume pedal descratcher, and replacing the the pot resistance a LDR + resistor. The pedal end will be what's needed to drive the LED at the LDR end. Yes, lift-and-drop the concept from the remote wah circuit.

I'm confused. Why do you need to do anything else with the pedal end other than what Craig did? Is there a good reason I just can't see?

Yes. It will integrate into the system I already have. There is a distance issue involved. Anyway - looks like I'm on my own!

Thanks for the reply, RG- I appreciate it! 

[Ben N]

I think RG's point is that the VPR already allows you to isolate the pedal from the signal--that is what the CA3080 or whatever does. You can just put the VPR in your signal chain where you want it and run a cord out to the pedal, and there you are (or as the Queen's subjects like to say, "Bob's your uncle"). LED/LDR is another way to possibly accomplish the same purpose, assuming you can get the right range of resistance out your LDR, but you need one or the other, not both. Trying to sub an LDR for the pot in the VPR is adding unnecessary complexity for zero benefit.

[R.G.]

Thanks, Ben! I just gotta get back into those "English as a second language" courses! 

That is what I meant. I always saw that one could remote the pedal from the controlled amplifier. In fact, that is one of the chief virtues of the volume pedal circuit.

[DiamondDog]

I think RG's point is that the VPR already allows you to isolate the pedal from the signal--that is what the CA3080 or whatever does. You can just put the VPR in your signal chain where you want it and run a cord out to the pedal, and there you are (or as the Queen's subjects like to say, "Bob's your uncle"). LED/LDR is another way to possibly accomplish the same purpose, assuming you can get the right range of resistance out your LDR, but you need one or the other, not both. Trying to sub an LDR for the pot in the VPR is adding unnecessary complexity for zero benefit.

I think we all could take English courses sometimes. It's not my first language anyway!

I respect the replies I have received- I do appreciate the time that you have taken to explain it. Thanks specifically to Ben and RG. However, mine is not a normal situation.

My main issue is that I am not in a city in the US (for example). I have to deal with several different voltages at once- some of which will spike and turn an IC into a egg fryer. To make it even better, when they say that mains is good for x volts, it's more a guideline than a hard and fast rule...

The use of LED/LDRs allows some hookup with a safety margin built in. Bitter and expensive experience has taught me that I have to isolate as much as I can. Or in other words, your "zero benefit" is my rig saver. So, whilst it may seem needlessly complex at Madison Square Gardens or Wembley, it's in my personal interests to use such a setup in a woolshed miles/kilometres from anywhere that makes its own electricity. I hate to think what Pete Cornish would make of it all!

So with that in mind, I will still investigate the LED/LDR setup. It's a protection thing.

I hope that makes it a bit clearer. If not, you've just got to trust me! Wish me luck!

Thanks for your patience.

[R.G.]

Yes, that does make the issue clearer.

The real problem is that you have electrical supply problems and are trying to use opto-isolation to avoid them.

It's an interesting problem. Can you describe the several voltages you're dealing with simultaneously, worst case if possible.

I *like* problems like this. My first pro job was as a power supply designer. 

[DiamondDog]

Yes, that does make the issue clearer.

The real problem is that you have electrical supply problems and are trying to use opto-isolation to avoid them.

It's an interesting problem. Can you describe the several voltages you're dealing with simultaneously, worst case if possible.

I *like* problems like this. My first pro job was as a power supply designer. 

Thanks for the offer RG. Please don't go to any trouble, and excuse any incorrect terminology and my tiredness. I think I may have decided on a course of action, and the following is for completeness. Read this in the context of touring in the countryside. And I mean countryside. Power source is something I have little control over.

Imagine going into a town that has been physically and economically devastated. Sure, they have a community hall or whatever, but money is better spent on other things than making sure the visiting band has access to phase 3 power. In fact, the main competition we have for power is from refrigeration. Drinks make profit; we're the excuse to get together and be social, so I know who gets priority....

So while sometimes I get decent power, often I'm being fed what is really 'domestic' 240v (I'll call that 'nominal mains'), which often is closer to a very dirty 230v, sometimes 220. It's not so much the supply to the venue, it's inside the venue. Assuming there's a venue to start with and it's not a space with a generator of unknown heritage and a couple of tents.

The following came about from a nasty incident which also gave the vocalist burns on his hands from the mike.

Mains is fed into what started off as an old server uninterruptable power supply to try and 'condition' the supply. The idea was that hey, computers like clean power too. The goal is to minimise ripple (let's be honest, tsunami), absorb spikes, with a battery that can help during those leaner seconds. It's not meant to run off battery- let's just call it a lead acid capacitor. A large compressor (refrigeration, not a Ross-type ) kicking in plays havoc. The "UPS" doesn't seem to cause any issues. I had little to do with it's making, and since it's not broken, I'm not looking at the specs too hard!

From there, I run my amps @ 220v and effects at 18VAC, 16VAC, 18VDC and 9VDC (yes, if they were all @ 9V I would be using batteries...) They are physically together with the amps. I have tried to 'encapsulate' it to reduce cable runs (and noise in a filthy environment).

I also run a remote switching pedal board, 18VAC, knocked down to 12VDC internally. You might recognise it if you saw the inside of it. That includes a remote wah. To date volume has been solely by knob on guitar or fingers on dials.

The idea with the LED/LDR was not to so much to get around these issues- it was as another line of defence against spikes, and 'noise soak' which is why I don't run a 'live signal' cable out.

However, I think I overlooked the obvious- if it's a volume pedal descratcher, any noise ain't gunna get through, and if it's powered internally...

I do overdo it sometimes, but I have lost an entire rig before, so I get nervous. As does my wife. And the bank manager.

[R.G.]

A couple of things come to mind.

First, I actually did two articles on "gigs on generators" and how to keep your rig alive. They should be in the archives at Premier Guitar. If not, I can send you a copy. You mention exactly some of the issues I talked about, including the refrigeration. Generally it's worse when they turn off. That gets you a jump in AC line and a big inductive spike at the same time.

Second, you are the prime candidate I can think of for carrying your own (a) small generator, 1-3KW, or (b) ferroresonant/constant voltage  isolation transformer.

(A) will give you the usual problems with generators, but it will be YOUR generator, not whatever is knocked together at the "venue" so you can control your own fate. I have a 1KW generator in my workshop that's 50x40x35 cm roughly. 3KW is not much bigger. They're heavy, but then so is losing all your gear.
(B) is also heavy, but it is probably less so than the generator. There are transformers which take in, say, 200-260Vac 50Hz and turn out 230Vac +/-5% sine waves. They were a mainstay of the large computer industry (i.e. IBM) back when there was a large computer industry, and for the same reasons.

But back at your specific, as opposed to general, problem. The nice thing about Anderton's volume pedal solution is that the "bandwidth" of the human foot is so much slower than the human ear. You can deliberately make that foot pedal slow by putting capacitors across it - and zeners and transient spike absorbers to ensure it doesn't get out of bounds. Or you could just add another layer of LED/LDR as you thought. That does not solve the issue of your power and ground lines running out to the pedal itself acting as a noise spike antenna. That may be the biggest issue.

Of course, your guitar is a major sensor of noise in that environment, and I don't know any way to get around that.

Given how hard you're struggling with power issues, why not simply choose only effects which run on 9Vdc? There aren't many types of effects where there is not at least one possible pedal that runs on 9Vdc. The only good example I can thing of is a high-current-drain digital delay. I grant you it may not be possible to choose the most tonally sophisticated pedal, but then the acoustic environment is not the best either.

[DiamondDog]

A couple of things come to mind.

First, I actually did two articles on "gigs on generators" and how to keep your rig alive. They should be in the archives at Premier Guitar. If not, I can send you a copy. You mention exactly some of the issues I talked about, including the refrigeration. Generally it's worse when they turn off. That gets you a jump in AC line and a big inductive spike at the same time.

Second, you are the prime candidate I can think of for carrying your own (a) small generator, 1-3KW, or (b) ferroresonant/constant voltage  isolation transformer.

(A) will give you the usual problems with generators, but it will be YOUR generator, not whatever is knocked together at the "venue" so you can control your own fate. I have a 1KW generator in my workshop that's 50x40x35 cm roughly. 3KW is not much bigger. They're heavy, but then so is losing all your gear.
(B) is also heavy, but it is probably less so than the generator. There are transformers which take in, say, 200-260Vac 50Hz and turn out 230Vac +/-5% sine waves. They were a mainstay of the large computer industry (i.e. IBM) back when there was a large computer industry, and for the same reasons.

But back at your specific, as opposed to general, problem. The nice thing about Anderton's volume pedal solution is that the "bandwidth" of the human foot is so much slower than the human ear. You can deliberately make that foot pedal slow by putting capacitors across it - and zeners and transient spike absorbers to ensure it doesn't get out of bounds. Or you could just add another layer of LED/LDR as you thought. That does not solve the issue of your power and ground lines running out to the pedal itself acting as a noise spike antenna. That may be the biggest issue.

Of course, your guitar is a major sensor of noise in that environment, and I don't know any way to get around that.

Given how hard you're struggling with power issues, why not simply choose only effects which run on 9Vdc? There aren't many types of effects where there is not at least one possible pedal that runs on 9Vdc. The only good example I can thing of is a high-current-drain digital delay. I grant you it may not be possible to choose the most tonally sophisticated pedal, but then the acoustic environment is not the best either.

Thanks, RG. I appreciate you input here!

1. I think the easiest way around the problem is shooting the guy who got us the gigs! It may not solve the problem- but it sure will be satisfying...
2. The more I think about it, yes, the own generator idea is worth exploring. Band meeting, fellas!
3. I checked out Premier Guitar. The archives only go back to 2007, and I couldn't see the articles there. However, the Immortal Amplifier is now on the list of things to do...   (You have PM)
4. The two AC pedals are a Neovibe and 12AX7 overdrive. The neovibe, well, pass the Hollis Easyvibe schem will you dear, but the overdrive... You know how stubborn we guitarists can be. Ah, the old artistic integrity versus "will they notice?" question...!
5. The remote switcher is based on your very own- the 2/27/03 lisitng on your front page- two boards running 9 switches (that include amp switching, etc) That's also coming off the 18V AC, down to 12VDC as per your design. What sort of current draw would that be? If I dropped the LEDs at the effect end to minimise draw... I think you can see where I'm going here.
6. I'll do an Anderton for now, and once everything settles down I'll revisit it. Your suggestions are as always sensible!
7. The guitars are as you said an issue. My favorite's about 1 lb heavier from all the shielding (maybe, well, you know! ) I also use the sound check method of interference reduction. (Walk around the stage during sound check with some tape- yellow for stand here, grey for don't stand here.) Sometimes the simplest solutions are the best.

Many thanks, RG! I really appreciate it. You've gone far beyond the call of duty here!