Volume pedal with needless complications for fun

[MrStab]

hi guys,

at first i just wanted to make a buffer to keep my new Korg Pitchblack tuner on all the time and to allow for a killswitch of sorts (a pre-manufactured pedal! i feel dirty!), but then i thought "buffers are really boring, why not use a charge pump and a Burr Brown opamp to pimp it out?", and today i picked up a nasty, plasticky Bespeco volume pedal at the charity record shop i volunteer at, so it's all set: i'm making this pointless monstrosity.

here's what i'm after (and have built some of): two dual opamps, one for a unity-gain boost and a post-pot output buffer (as suggested here: http://www.diystompboxes.com/smfforum/index.php?topic=85422.0 ) and another "utility" opamp for tuner out and whatever else. i want this configuration in order to be able to prioritise the signal path and maybe use a lower-current IC on the tuner out opamp. in the likely event i'm not making much sense:

input > opamp A boost+opamp B tuner > volume pot > opamp A buffer > output

i thought it would all be straightforward, but then i realised:

because of the biasing difference, where should i split the input signal, if half is going to a boost and the other to a (tuner) buffer? maybe another opamp before all that, but is there any way i could avoid it? as i'd really like to keep it to just one dual opamp for boost & buffering of the signal. would splitting pre-input cap be bad?

ofc, judging by the sturdiness of this shell, expect this thread to change title to "boost pedal...!"

cheers!

[MrStab]

see, most of the schematics i came across had the boost before the pot & buffer, or the boost between an input and output buffer. except this one, which uses an LDR (sourced from http://0xdfx.wordpress.com/2012/05/29/solar-lifeforce-ldr-volume-pedal-schematic/ ):



...but is buffer > pot > boost okay because that circuit uses an LDR? does it really matter if it's all unity gain (altho the option for an actual boost wouldn't go amiss)?

[MrStab]

it's just dawned on me that it doesn't really matter if i just use a buffer for both input & output instead of a boost,  and would probably be preferable, so consider this thread null and void. guess i need to type stuff out to fully comprehend it! lol

thanks anyway, unless someone has anything to add

[brand0nized]

I'm very interested in this circuit you're building! I'm currently working on building my own volume pedal shell. I'm trying to think ahead to what circuit I would use, but unfortunately, I barely know anything about building pedal circuits.

[MrStab]

despite all the madness of my above posts, i've had the pedal up & running for about a week now and it seems fine. i just opened it up to reduce the input cap, actually, as it just wasn't offensively trebly enough.

i'd be happy to make a schematic for you, Brandon, but it's just a bunch of (probably imperfect) buffers built around an effects loop, with a volume pot at the end. and a charge pump to double the voltage. and a VU meter. and a tuner output. lol

conceptually, it's not too different from this, except without a blend control and with a volume pot: http://seanm.ca/stomp/bblender.html.

here's my build, before i added 2 more jacks to make it FX-loop-based:

[brand0nized]

Nice build, MrStab! How do the lights work?

[MrStab]

Nice build, MrStab! How do the lights work?

thanks! i just used the LM3916, and the schematic on the datasheet (except just 1.2k to ground instead of a voltage divider):
http://www.ti.com/lit/ds/symlink/lm3916.pdf

[duck_arse]

leds that bright must keep your foot warm, surely.

[MrStab]

incidentally, we just switched to LED bulbs at my house and even the lowest available option is far too bright. i'm getting melanoma just sitting here. maybe i should just leave a guitar feedbacking into this pedal and just use that to light the place.

[deadastronaut]

Nice build, MrStab! How do the lights work?

thanks! i just used the LM3916, and the schematic on the datasheet (except just 1.2k to ground instead of a voltage divider):
http://www.ti.com/lit/ds/symlink/lm3916.pdf

..

[R.G.]

This brought back some fun memories. Many of those "needless complications" and a few more are inside the Visual Volume 10th Anniversary volume pedal, although implemented a bit differently.

We had a similar issue with LEDs. The first prototype had LEDs so bright that they made a blue spot on the ceiling. I had to dial that back quite a bit to avoid blinding the user looking at the volume pedal. 

[deadastronaut]

sunglasses help..

R.G. while your here....i have an issue with the 3916 coud you take a peek..

http://www.diystompboxes.com/smfforum/index.php?topic=108853.new#new