10 common best practices and mods we should use in every circuit?

[tenser75]

I learnt few tricks that I try to apply to every build, so I'm wondering if I missing anything

for example

- 100uf cap connected to + to prevent ripple or interferences from outlet
- a 1M pulldown resistor to prevent the "clack"sound of the switch...
- a 22k resistor after a 100K volume "Better Volume Control"
etc...

I'm wondering is there is a list out there, or can you provide new ideas... thanks!

[thermionix]

Well?  What are the other seven?

[Derringer]

a "burst" function

[R.G.]

geofex.com
"Wrapper"

[amptramp]

Add an LC or RC filter to reduce any radio signals coming in that can upset bias points and modulate the signal.

A resistor on the output to protect the unit from the bozo who connects a battery there.

[Ben Lyman]

I also do the 100uF power cap on all builds.
I use the same power section on all my builds, a combo of components that I learned right here.
+9v goes through a series 1N5817 diode, then a series 47r then the 100uF to ground is also paralleled by a 100nF. Overkill? I don't know, I'm no EE 

I also include a big resistor to ground at the input but I also wire the footswitch to ground the board in and out when bypassed.

Also, I always use a clear blue super bright LED with a 47k resistor on all my builds, if i understand correctly, this maybe reduces a little battery use or something?

[beeltink]

Any chance to post small schematics of these ideas, please?

[feddozz]

I would include the stereo input jack switching malaki

[samhay]

>...we should use in every circuit?

While encouraging good practice in circuit design is to applauded, there will always be circuits where some/all of these 'maxims' will likely be inappropriate, or at least not best practice.

[Ben Lyman]

Any chance to post small schematics of these ideas, please?

I probably use this in 99% of my pedals.
Agreed, stereo input jack except for pedals with no battery.

[R.G.]

I would use an active device for polarity protection, as it's possible to get a lower voltage drop than even with a Schottky diode.

Having done that, I'd use the active device for power switching through the stereo jack by running a resistor to the stereo jack.

I'd use the OUTPUT jack for any stereo-jack switching, as putting it on the input jack runs all the device's current through the input ground, and inserts another place to introduce ground noise.  The active-device switching of power mitigates this by making the current through a stereo jack switch be much smaller and constant. A high gain bipolar or MOSFET switch may make input jack switching OK again.

I'd use active signal switching for routing of "bypass".

If I **had** to use mechanical signal switching, I'd use a DPDT and the Millenium Bypass.

[Ben Lyman]

I like those ideas RG. Especially the one about moving my stereo switching jack to the output side. I think I will try that next and see if i notice a difference. Is there any chance "introducing ground noise" will simply be carried over to the next pedal in the chain or to the amp? I guess i'll just have to try it.

I'm still very happy with the performance of my pedals without adding more components/time/money/etc. which is stuff I always weigh against the final goal.
After all, I'm not making Fuzz Faces for the government to use as navigational equipment on Air Force One! 

[electrosonic]

If you don't use batteries, why switch the power at all? My pedals are on until I unplug the power.

That frees up the circuit layout so the ground currents don't go through either of the input or output jacks. Check out proper tube amp grounding and follow that example.


Andrew.

[tenser75]

Add an LC or RC filter to reduce any radio signals coming in that can upset bias points and modulate the signal.

A resistor on the output to protect the unit from the bozo who connects a battery there.

@amptramp can you elaborate better this: I do happen to have a stompbox fuzz which actually seems to get radio signal (seems a local radio station maybe in AM)

I have to say i haven't tested the board in a grounded enclosure, but on the bench while i was soldering AND the pcb was connected to my amp i could hear songs form the radio ! haha..

[R.G.]

100R resistor in series with the input wire to the PCB, and a 47pf ceramic cap from input to signal ground after the 100R on the PCB.

Add a 0.1uF ceramic cap from +V to ground where the power comes onto the PCB.

With the circuit laying open on the bench, this may not be enough, depending on how far you are from the antenna farm.

[M.A.P]

I found this polarity protection and wanted to use it for all of my future builds. I didn't had the time to test it yet.
http://www.lothar-miller.de/s9y/categories/39-Verpolschutz
It is the 4th schematic from the top titled with "Verpolschutz für kleine Spannungen". Left side is voltage in, right side is voltage out. I will use IRLML6402 with an RDSon of 0,065 Ohm!

I was wondering if it would make sense to use a LM386 as an input buffer and for its self-centering feature on each pedal. With a voltage divider in front it would be possible to set the gain to 1 or use a pot for variable gain. This could also be done on the output.
Would this be an improvement or is this totally useless?

If we keep on collecting ideas maybe we can create a standard for the circuit around the effect circuit itself

[R.G.]

The MOSFET polarity protectors work. Those are variants of the same theme that I was using in "Advanced Polarity Protection" back in 1999: http://www.geofex.com/article_folders/mosswitch/mosswitch.htm

The LM386 is good for its self centering. That's been suggested and used here for quite some time. It works.

And as for collecting ideas for the standard for the circuit around the circuit itself, see "Effects Wrappers" from 2002 at geofex.
http://www.geofex.com/article_folders/wrapper/wrapper.htm

[Fndr8875]

R.G ....im just learning about the 386 thing, providing vref to ICs. I cant remember seeing a pedal its used in though. Is there a downside to this or are people just used to doing things in a certain way, or arent familiar with it. In my understanding its the only "ic" as its a power amp with ic package that will input 9 volts and output 4.5, with no other parts. Your thoughts?

[ashcat_lt]

I think mostly we just don't that often need such a stiff bias as you get from the 386, and people tend to be stingy with the active components.  A good resistive divider with capacitor decoupling doesn't actually take much less space or even much fewer welds, and probably doesn't even cost much less (at least until you're buying thousands), but it does usually work just as well, and is what everybody knows, so...

[PRR]

> LM386 as an input buffer and for its self-centering

It's not a good buffer. Input impedance is 50K, very low for guitar-chain interfacing. Gain is 20, which is way high for guitar level under a 9V battery.

There's usually some simpler smaller cheaper self-centering scheme. As someone who also dabbles in "good" audio, I wonder how "good" the '386 output is. With gain=20 it has significant hiss voltage on the output. Also it is prone to crossover distortion, which means it may slap 10mV either way before it really grabs-on and holds. Putting a cap on the output isn't a fix because it is liable to be unstable. You could do the strongly-suggested R-C network with a much larger C, and get a pretty stable output. Remember you also need the Bypass cap or power supply crap goes right through.