Inductor & Transistor Proximity in a Wah?

[davent]

Hi Folks,

Are any problems created by having them mounted close to each other on the pcb, weird interaction, strange behaviour?  OR... does it matter at all?

Thanks,
dave

[aziltz]

i'm modding some wah's right now.  dunlop doesn't keep much near the inductor, except maybe a resistor.  that said, get the inductor close to another one, in say a power supply and that's bad, very bad.  inductors can pick up a lot of noise.

[Paul Marossy]

AFAIK, it shouldn't matter at all. The biggest problem you'll have in an inductor wah is the inductor being sensitive to extraneous noises caused by EMI, in spite of being in a metal enclosure. Inductors act a lot like guitar pickups in terms of picking up noise. Just stick a wall wart in close proximity to a wah pedal and use something like a Boss Metal Zone with it and that will make a lot of noise!

I don't know why Dunlop doesn't have much near the inductor. If you look at vintage wah circuit boards, one of the transistors is pretty close to the inductor. They work fine, if you ignore the tone sucking in "bypass" mode.

[DiscoVlad]

I've noticed on the newer (on '90s ones at least) Dunlop boards that the board traces going to the inductor/q resistor snake around the board a good distance, whether this is to help prevent it from picking up RFI/EMI (which doesn't make sense... long traces are better antennae than short ones), or just because whoever laid the board out used the auto-router I don't know.

[Paul Marossy]

I've noticed on the newer (on '90s ones at least) Dunlop boards that the board traces going to the inductor/q resistor snake around the board a good distance, whether this is to help prevent it from picking up RFI/EMI (which doesn't make sense... long traces are better antennae than short ones), or just because whoever laid the board out used the auto-router I don't know.

I'm guessing that it's just due to the auto-router.

[davent]

Thanks guys! Sounds like i should be okay with my layout. Was trying to figure out why Dunlop would use such a big board for what is a pretty simple low part count circuit.

Take care
dave

[Paul Marossy]

Thanks guys! Sounds like i should be okay with my layout. Was trying to figure out why Dunlop would use such a big board for what is a pretty simple low part count circuit.

Take care
dave

It's probably just for ease of manufacturing. I know what you're saying, it does seem that the circuit board could be smaller.

[aziltz]

i mentioned dunlop just from what i've seen.  i never thought it was a noise-design aspect.  They just mount the inductor centered between the jacks, with the components mostly at the bottom of the pcb.  It is overly large, but from what I've seen, they use the same board for many of the different wah models.


on a side note,
in order to really pose a problem with EMI, something has to be "broadcasting" pretty well.  Coils are, well, lets just say that's how we make RF E&M fields in the lab. Hence the issue with proximity to transformer'd power supplies. 

Wires and traces on their own have a pretty weak field unless there's some serious current running through them, not something you're gonna find in a 100mA pedal.

[Paul Marossy]

They just mount the inductor centered between the jacks, with the components mostly at the bottom of the pcb.  It is overly large, but from what I've seen, they use the same board for many of the different wah models.

That's how I see it.

[aziltz]

That's how I see it.

off topic, I read about the "vocal" mod on your site paul.  I took the 33k to 47k in parallel with the inductor in my JH-1 and it kills now!  Went from dull to something I can actually use.

[Paul Marossy]

That's how I see it.

off topic, I read about the "vocal" mod on your site paul.  I took the 33k to 47k in parallel with the inductor in my JH-1 and it kills now!  Went from dull to something I can actually use.

Awesome! Wah on, dude.