Hey guys. I've got a Belton reverb pedal i built from their schem that I added another reverb pot to switch between, but I get that popping noise when i do. I think there's a cap to ground thing you can do to get rid of the popping, but i don't quite understand how it works and what exactly to do. Can someone explain it to me or give me another suggestion? Thanks fellas.
Please post your schematic.
(https://mail.google.com/mail/u/0/?ui=2&ik=76ee25e868&view=att&th=121b258756ab978c&attid=0.1&disp=thd&realattid=f_fvlezpff0&zw)
This is basically it. The two switches are really just one DPDT footswitch. What do ya think?
ok, i'm seeing that this layout is not very helpful at this size, let me see if i can make it bigger. :P
(https://mail-attachment.googleusercontent.com/attachment/u/0/?ui=2&ik=76ee25e868&view=att&th=121b258756ab978c&attid=0.1&disp=inline&realattid=f_fvlezpff0&safe=1&zw&saduie=AG9B_P-FkiK9fU5bGstzGhRlJ7h7&sadet=1374262657545&sads=tvbLF7cPBsuDzpjXZulmk9Mpk2E)
Looking at the path to your image, it looks like you're trying to post a picture from a Gmail account or similar? I can't see anything. Can anyone else? You may need to put it somewhere else (e.g. dropbox).
I can't see it.
Sorry about that. Try this.
https://www.dropbox.com/s/7idmn9l814hb3e6/Reverb%20board%20Layout%20%28TL074%29.gif
That's better! :D
It didn't pop at first, and I've switched out the switch before and it temporarily fixed the problem, so it might be as simple as i need to put a better switch in. Plus, I've got a dual looper i built that has that same basic switching circuit that doesn't pop. There's a cap to ground, or something, trick i've heard of, though. I just don't quite know what it is and i wanted to try and see if that was the answer.
I can't follow your layout. Can you post the full schematic? (Not just the app note, which is incomplete.)
Also, is your 78L05 output tied to ground?
1M resistor between where one/both of the pots connect to the switch and ground? probably a cliché answer, but why not! lol
This is the schem i used. It only shows the half of the switch that switches the pot, the other half of the switch just goes from the 9v to the ground of the TL074.
https://www.dropbox.com/s/d1s3ms2kc0jgevh/reverb%20schematic%20with%20two%20switchable%20pots.jpg
the 78L05 output is goes in to one of the lugs of the Belton unit. It looks weird on the layout, but the 3 and 4 hole jumpers on the bottom are really the lugs of the reverb unit.
The switch can pop for mechanical problem or cause there's some voltage inside that
Are younsure there are no bridge? Could you try with some pull-down resistor
The pull down resister is the 1M to ground between the switch and the pot, right? I'll totally give that a try.
Try adding a 1M-2.2M pulldown resistor to ground on the common lug (center lug) of the switch.
(https://dl.dropboxusercontent.com/u/53299166/DIYstompboxes/reverb%20schematic%20with%20two%20switchable%20pots.jpg)
This is a virtual-ground circuit, it's running on a single supply, convincing the opamps that 1/2 that supply (Vref) is "ground". Probably better to hook the 1M to Vref, that's where that bit of circuitry is DC biased. Grounding the 1M won't slam it all the way from 4.5V to ground (since the next opamp is forcing it to Vref via the 10k feedback resistor and the 39k next to it, while the split second the switch is open the large 1M is attempting to pull to ground) but it won't help. A small difference in voltage during the switching cycle WILL result in a pop. A voltage divider of 1M and 49k (10k+39k) makes the switch lug sit at 4.3V. If you have one of the two pots at max, it will force that point to 4.5V. Difference 0.2V, big pop.
if the cmos inverter is doing nothing but powering the led, I'd ditch it, and use a proper millenium bypass setup (or a 3pdt footswitch, if you lean that way), and run that from the 9V with a series resistor and supply bypass cap.
both the 100nF at the input (1M) and the 10uF at the output (100k) already have pulldown resistors. I don't think there is many maore places within this circuit that needs pull-downing.
Quote from: duck_arse on July 22, 2013, 11:27:54 AM
both the 100nF at the input (1M) and the 10uF at the output (100k) already have pulldown resistors. I don't think there is many maore places within this circuit that needs pull-downing.
Take a look at the Roland Jet Phaser schematic.
There is a switch to choose between "Jet" and normal phasing in the middle of the circuit. Pulldowns are used in the same fashion as what was suggested here.
duck_arse - I actually did use a 3PDT switch for that LED
Mike Burgundy - is the "Vref" your talking about "REF" on the schem?
I'll answer for Mike.
Yes. vref is REF.
I think Mike might be right about tying the pulldown resistor to vref. If it still pops......try ground.
I tried both and i think they both work. I'm gonna keep it at running to Vref and put it back on my board, see if i have any problems on stage (where it will go wrong if it's going to go wrong!). Thanks guys!
Good to hear!
So...I lied. It didn't work, though I did realize that running it at 18v, as I've been doing, makes the pop much louder and I keep thinking it's fixed at home until I put it back on my board because at home I test it with a battery and on my board I've got a power brick. I tried changing switches ans that didn't help at all, so I think i'm gonna try moving that ground thing we talkked about to actual ground and not vref, see if that helps. If not, i could really use some suggestions!
no dice. nothing has worked so far. If I run it at 9v, the pop is there, but bearable. is it just an issue of not running it at 18v? How can I get it not to pop at 18v? I tried a 1M to ground and someone mentioned 2.2M, would that make a difference?
Also noticed something else. I was gonna put a bigger resister behind the LEDs to lower the brightness of them (they are clear blue ones) and I noticed that I put a 22k resister behind the both of them. I'm surprised I can see them at all with that big a resister behind them, does them. Could that have something to do with something?
I should really say that the resister is in front of the LEDs.
I might have made a mistake putting that resister in. I might have meant to put a 2.2k and put a 22k instead. It looks like I also put a 22k in front of the bypass switch LED too. They're real bright, though. does that make sense?
Quote from: simpleobserver on August 01, 2013, 02:12:55 PM
They're real bright, though. does that make sense?
Nope. Sure it's a 22K and not 22
ohms?
Yeah, I'm sure. Red, red, orange, gold.
What about this anyi-popping mod? anybody tried this?
http://s440.photobucket.com/user/devnulljp/media/ANTI-POP-1.png.html
I'm worried about trying too much before I figure out this LED thing first. I really don't understand what the deal is with the 22k resisters before all my LEDs. plus I want them dimmer. Do I just try bigger ones?
nope, anti-popping mod didn't help.
Quote from: simpleobserver on July 21, 2013, 07:07:25 PM
This is the schem i used. It only shows the half of the switch that switches the pot, the other half of the switch just goes from the 9v to the ground of the TL074.
Can you explain the bolded part a little better, or put it on the schem? I'm having a hard time picturing what it means.
Never mind. You're using an led to indicate which pot you're switched to.
Two ideas:
1. Temporarily disconnect that led. Does it still pop?
2. Instead of the pulldown on the switching node (39K resistor), try one pulldown each to the nodes being switched to (the wipers of the pots). Try 1M each to start, and they should go to Vref, not ground.
Sorry, yeah. What i meant to say was the other side of the dpdt switch switches between two ultra bright blue LEDs to ground. I don't think it really matters but I grounded them at the ground of the TL074, on the 11th lug or whatever. Sorry, I don't really know how to draw it on the schem, but it shows it on the layout (though i was having trouble posting the layout before). I think it must be the LEDs with the pedal running at 18v. i can just run it at 9v and the pop is ok, but i'd rather figure out how to use it at 18v if i can.
Still pops after the LEDs are disconnected. Trying the pulldowns on the pots to vRef.
no dice. neither helped at all. Any other ideas?
How about switching the pot inputs (lugs 3) and outputs (lugs 2) at the same time? If it works you'll need a 3PDT to include the leds, but you could try it without the leds to see if it helps.
nope. no help.
Ok. Sorry, that's all I have for now. Good luck.
Have you tried the pedal with a different guitar and amp just to eliminate them as contributing to the problem?
Yeah. Tried it with a couple combos including different power sources and instruments.
on your led brightness problem, if 22k is too bright at 9V, it will nearly blind you at 18V as it will have more than 2x the current through it. increase the value of your in-series-with-your-led resistor, often known as a CLR or current limiting resistor, until you get enough dimness to suit your taste. it really shouldn't affect your popp problem one way or another.
is the pedal popping in all instances, or does it not popp when connected to a particular pedal or chain of pedals?
Three more ideas:
1. Try another switch.
2. Measure the DC voltage at pin 1 of the belton and at Vref.
3. Try moving one of the pots to pin 2, instead of having both on the same output pin.
Quote from: duck_arse on August 02, 2013, 10:33:59 AM
is the pedal popping in all instances, or does it not popp when connected to a particular pedal or chain of pedals?
It pops when it's in my signal chain and it pops when I test it on it's own.
Quote from: induction on August 02, 2013, 11:08:50 AM
Three more ideas:
1. Try another switch.
2. Measure the DC voltage at pin 1 of the belton and at Vref.
3. Try moving one of the pots to pin 2, instead of having both on the same output pin.
I'll try moving one of the pins. I seem to have misplaced the probes to my multimeter, not that I really know how to use it anyways, so i might have to get back to you about the voltage on pin 1 of the brick.