DIY Foot Drum

I am hatching a plan for a new pedal build, but something different this time.

I am thinking of picking up a cheap piezo transducer on eBay, and putting it into a wooden foot drum/stomp box sort of thing. I have seen people wire them as a passive circuit with just a volume pot which I will try first, but if I need to massage the output a bit more I will build a piezo preamp and wire it into the wooden box. This circuit might be overkill, but I have all the components and the volume, bass, and treble controls might be handy for shaping the sound.

I just wish my woodworking skills were up to making something fancy. I can probably manage something functional but ugly.


I only have one amp, and don't really want to use a mixer to blend this into my guitar signal so I am hoping that the preamp output will have a suitable level to go into the aux input on my THR. If not I could run a simple headphone amp after the pre-amp. Or I could build a 2 channel mono mixer, but I am worried about adding extra noise into my main signal.

Does anyone have any experience with this sort of thing? Any advice or suggestions?

DC

Cool project idea! I always wondering how these worked, but never got round to doing any research. I would have thought they would be better going into more of a PA rather than a guitar speaker. Something at least 12 inch, 15 inch being ideal as it is mimicking some of the sub frequencies of a kick drum.

I really don't get the description of the preamp. It says it's designed to work with electret condenser mic systems, but those need DC power supplied to them and a low input impedance. Whereas a piezo hates DC and needs a high input impedance. Ideally 5-10 meg ohms for most piezos for the flattest response. As the input impedance is stated as 2.2 Meg, then it looks like a piezo design, but with some wrong descriptive words.

Some piezos work best with 1-2 meg ohm input impedances, some are better at 10 meg. I have no idea what makes the difference. But too low an input impedance and the bass end will be missing, too high and you get a lot more bass (which is really what you want with a kick pedal).

I'd suggest looking for a preamp with a mid control as well, as that is very important for shaping the sound. For a bass drum sound, you need a fair bit of low end, around the 80-100Hz area, and some high frequency punch around 3kHz, and a bit of a cut in the mids.

The high impedance means that the output lead is very prone to picking up noise, and any capacitance will roll off the top end quite quickly. So any wire should be kept as short as possible.

I'm not sure a guitar amp is the best amp to use for such a pedal, as a lot of bass and a fast attack transient could give a lot more speaker cone travel than it's designed for if used at any volume.

Thanks Simon,
I agree the description of that particular preamp is a bit off. I think it was written by marketing not engineering. It's pretty much a piezo preamp with two tone controls as far as I can tell. I might be able to tweak the tone filter values to shift the bass control into the low-mid zone, or I could go with a simpler piezo preamp and run the output of that into a separate 3 knob tone circuit.

Simon and BD, you have me thinking my amp won't cut it. This was meant to be a cheap project, but I might end up needing a bass amp. Better build a bass kit too then! Although my THR has a bass amp channel, so it should be safe but I think it must attenuate the bass frequencies a fair bit.

And yes, I could just buy a Peterman Recession Buster for a bargain price, but where's the fun in that?

BD, I forgot to add that there are quite a few designs. Some of the pro models use piezo pickups but I am sure they have some sort of onboard processing, maybe digital in some cases, as well. Because I can't see how stomping on a box would sound like a snare, or hi-hat, or cowbells. The version I am thinking about is sort of like tapping on the body of an acoustic guitar fitted with piezo pickups.

Another interesting design uses bass pickups.

Simon, thanks also for the tip about preamp input impedances. I can tune that so will breadboard the circuit first to get the values sorted.

Sent from my moto g(7) using Tapatalk

Yeah that's the sound I figured you were going for. I did always presume they were made from pickups [emoji16]

You might want to see about including a high pass filter in your circuit so you can filter out subsonics and near subsonics which are major speaker killers.

It doesn't need to be a bass pickup. There's nothing inherently different between a guitar and a bass pickup except the number of coils and the coil spacing. Same magnets, same typical 42AWG wire. So a guitar pickup will pick up just as much bass end. Just use whatever's handy/spare/cheapest. Single coils will probably be better as they have less mid-range emphasis.

No need for a preamp or high impedance input then.

Most piezo-style kick blocks I believe are pretty solid as you really just want the 'thump' of the wood as your foot hits it. But a pickup style unit will need a thinnish top that can resonate - at least a bit. You don't want a long sustain and you don't want it so resonant that you get acoustic feedback when you apply a bit of volume.

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Originally Posted by JimC

You might want to see about including a high pass filter in your circuit so you can filter out subsonics and near subsonics which are major speaker killers.

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Good idea. I could do that in the tone control stage after amplification. And the circuit I am looking at using (the Barcus Berry circuit has some errors so will use something simpler) has a 0.1uF input filter cap, which combined with the 2.2m half of the voltage divider going to ground should act like a high-pass filter as well. According to Jack Orman's R-C filter calculator, it should attenuate below 0.7 Hz. Which is maybe a bit low. I think it's mainly intended as a DC filter. I could experiment with a lower value cap to raise the corner frequency perhaps. Or just handle it in the tone circuit.

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Originally Posted by Simon Barden

It doesn't need to be a bass pickup. There's nothing inherently different between a guitar and a bass pickup except the number of coils and the coil spacing. Same magnets, same typical 42AWG wire. So a guitar pickup will pick up just as much bass end. Just use whatever's handy/spare/cheapest. Single coils will probably be better as they have less mid-range emphasis.

No need for a preamp or high impedance input then.

Most piezo-style kick blocks I believe are pretty solid as you really just want the 'thump' of the wood as your foot hits it. But a pickup style unit will need a thinnish top that can resonate - at least a bit. You don't want a long sustain and you don't want it so resonant that you get acoustic feedback when you apply a bit of volume.

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Interesting. I do have a few spare pickups around. And I have an LM386 headphone amp that I built a few years ago that could maybe drive a speaker or the headphone input on my amp, at least for experimenting. And I found some piezo transducers for under $10 on eBay, so experiments seem likely.

Given my lack of a bass amp, I have a new idea. Make the wooden box large enough to house a small 386-based amp (like a noisy cricket or something modded for bass) and a speaker. A self-contained stomp box sub-woofer thingy.

Hmmm, I’ve all sorts of pallet wood, iron wood, blue gum, mahogany and ash scraps lying around the lab....if someone was to send me some dimensions for a box like thingy, Igor might be able to stitch, I mean, thtitch, something together....

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Originally Posted by FrankenWashie

Hmmm, I’ve all sorts of pallet wood, iron wood, blue gum, mahogany and ash scraps lying around the lab....if someone was to send me some dimensions for a box like thingy, Igor might be able to stitch, I mean, thtitch, something together....

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I like the cut of Igor's jib, or whatever that hump is called. Give me time to move this project beyond the embryonic stage and I might well take you up on that offer!

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Originally Posted by jugglindan

I like the cut of Igor's jib, or whatever that hump is called. Give me time to move this project beyond the embryonic stage and I might well take you up on that offer!

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Very kind of you to thay tho Marthter Dan, but it’th not my Jib. It belonged to my Couthin Igor and wath repurpothed after an unfortunate mithunderthtanding with an angry mob.

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Originally Posted by Ig0r

Very kind of you to thay tho Marthter Dan, but it’th not my Jib. It belonged to my Couthin Igor and wath repurpothed after an unfortunate mithunderthtanding with an angry mob.

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Can't .... reply ... too busy .... la la laughing...

I played in touring duos and trios that used a stompbox instead of a drummer. The best thing I ever heard was the Bigfoot by Wolftone. (now called Wild Dog following some lengthy legal issues)

My point is that (most) every other stompbox I heard, sounded real "clicky" with no real THUMP like you'd expect from a bass drum. The Bigfoot could sound huge and the guitar player ran it through a 10 band EQ into a 15" sub. We played pubs, theatres and festivals all around Australia and it always sounded great.
A lot of the DIY and old school stompboxes I saw were inconsistent in their performance, could be prone to feedback and as I said before, lacked big bottom.

I have no idea what the electronics were because the builder (from Byron Bay) would not tell anyone what the secret sauce was and drilled out all the screw heads after he assembled them.

I've heard the "Puck" ones and they still fell short of the Wolftone/Wild Dog brand.

Piezo trigger playing back a sampled kick sound maybe?

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Originally Posted by McCreed

I played in touring duos and trios that used a stompbox instead of a drummer. The best thing I ever heard was the Bigfoot by Wolftone. (now called Wild Dog following some lengthy legal issues)

My point is that (most) every other stompbox I heard, sounded real "clicky" with no real THUMP like you'd expect from a bass drum. The Bigfoot could sound huge and the guitar player ran it through a 10 band EQ into a 15" sub. We played pubs, theatres and festivals all around Australia and it always sounded great.
A lot of the DIY and old school stompboxes I saw were inconsistent in their performance, could be prone to feedback and as I said before, lacked big bottom.

I have no idea what the electronics were because the builder (from Byron Bay) would not tell anyone what the secret sauce was and drilled out all the screw heads after he assembled them.

I've heard the "Puck" ones and they still fell short of the Wolftone/Wild Dog brand.

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They don’t miss, 200 for a smaller one up to 400 for one of the bigger ones, yikes!

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Originally Posted by McCreed

I played in touring duos and trios that used a stompbox instead of a drummer. The best thing I ever heard was the Bigfoot by Wolftone. (now called Wild Dog following some lengthy legal issues)

My point is that (most) every other stompbox I heard, sounded real "clicky" with no real THUMP like you'd expect from a bass drum. The Bigfoot could sound huge and the guitar player ran it through a 10 band EQ into a 15" sub. We played pubs, theatres and festivals all around Australia and it always sounded great.
A lot of the DIY and old school stompboxes I saw were inconsistent in their performance, could be prone to feedback and as I said before, lacked big bottom.

I have no idea what the electronics were because the builder (from Byron Bay) would not tell anyone what the secret sauce was and drilled out all the screw heads after he assembled them.

I've heard the "Puck" ones and they still fell short of the Wolftone/Wild Dog brand.

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Anything I build is likely to be very inconsistent. But then, so is my playing, so at least Stompy and I will have that in common :)

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Originally Posted by Simon Barden

Piezo trigger playing back a sampled kick sound maybe?

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Or a pressure switch? But yeah, you might be right. Maybe a lot of them don't amplify the stomp but instead just trigger a sample. Maybe if I get an old midi keyboard, program it for drums, wire one key to the stomp and hide the keyboard somewhere...nah.

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Originally Posted by FrankenWashie

They don’t miss, 200 for a smaller one up to 400 for one of the bigger ones, yikes!

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Yikes indeed. It was looking at the prices that made me think DIY. That, and it sounds like a fun project to build. I can see two now. A small pedal, and something larger with the amp and speaker integrated. Maybe I could just buy an old combo amp and jump on that?

Lots of old drum machines with a trigger input out there!

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Originally Posted by Simon Barden

Lots of old drum machines with a trigger input out there!

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While that would take a lot of the mad scientist fun out of it, it would also be pretty cool having the ability to program in different drum sounds.

Out of this whole thread, I heard.....

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Originally Posted by jugglindan

I am hatching a plan for a new pedal build, but something different this time.

I only have one amp,......... Any advice or suggestions?

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You need to build another amp and experience that radness.

What size enclosure? I have some scrap timber which may be large enough and I have a possible solution for you for making the box.

Sent from my SM-G960F using Tapatalk

Thanks Woltz. I don't know what size yet, need to do some prototyping with books 'n stuff. Also trying to decide on the right profile. For playing seated I think a wide but fairly low box would work nicely, but should it be a wedge, or a flat rectangle?

This project will probably move fairly slowly since I have some other pedals and my tele to work on. I am getting very impatient with the tele, I really really want to play it! Oh, and I am also trying to find time for that other thing we do sometimes - playing guitar.

About the only other idea I have had for this one is the name. Either "Stompy", or "Monster Mash".

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Originally Posted by Andy40

Out of this whole thread, I heard.....



You need to build another amp and experience that radness.

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I was thinking about building one of the Lamington amps later this year, but it won't be for bass either.

I'd go for a wedge shape myself. Something reasonably heavy to stop it moving around, as well as rubber foam underneath for grip.

I just tested using a few books I have around, and found one that fits perfectly under foot, is a comfortable height, and is high enough for the potential electronics and wiring.
Attachment 35316

Two people have generously offered to help with the box construction, so please let me know if those dimensions are OK. Otherwise I am sure I can knock something together with BGS pine.

The generous size is so I can fit my whole foot on, and to leave room for a speaker.

Plan 1 for the speaker is to fit the piezo transducer, a small amp and the speaker all in the box, to see if an all in one solution can be made. I suspect the thump would be less than satisfying, but it might work for home use. Feedback might be an issue though. OK, ditch plan 1.

Plan 2 for the speaker is that some people have used a small speaker as the microphone instead of piezo pickups. Some claim they give a better thump. For example, here is a simple design that doesn't even use a preamp. Not sure if they have something off-board or run straight to amp or mixer:
Attachment 35317Attachment 35318

For the electrical side of things, if a speaker works well enough without a preamp then I would probably fit a passive tone and volume control, maybe something like the Fender Greasebucket - the high and low pass controls might be nice, but then it might be better to have separate pots for bass and treble.

If I use a piezo or if the speaker-mike needs an amp, then I will probably use a simple preamp on stripboard along either a 2 or 3 pot tone circuit and volume. The box dimensions should have room along the top edge (150mm) for 4 pots, DC jack, and 6.5mm output jack.

Or, I could keep Mr Stompy simple, and build a very cheap combo amp from this Ikea box and a noisy cricket:
Attachment 35319

And yes, I tested that box as a stomp. It's much too high for comfort.

Those dimensions are not an issue, JD. There’s a couple of options for it, I’ve a couple of blanks that could be hollowed out to suit, or a spec box built to house what you want.
are you going to stick with the flat format or did you want to wedge it a bit for ease of use?

A bit of taper might be nice. Even 1 cm difference would work, so 50mm at the back and 40mm at the front.

I had no specific plans for how the box would be constructed, beyond "box, with lid screwed on the bottom". I think in my mind it was sort of a wooden pedal enclosure. But I know almost nothing about building things out of wood, so please suggest whatever you think might work.

This is an excellent idea for a project. I have a whole box of cheap pickups kicking around in a box somewhere, and now I'm tempted to try the bass pickup version

[It seems my previous post vanished, so if you can all see two posts I apologise for the double post]

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Originally Posted by JohnH

This is an excellent idea for a project. I have a whole box of cheap pickups kicking around in a box somewhere, and now I'm tempted to try the bass pickup version

[It seems my previous post vanished, so if you can all see two posts I apologise for the double post]

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Just one post here. If you do build one I will be very interested in your results. This is pure experimentation for me.

I'm not sure how well standard volume and tone controls would work with a speaker as a transducer. You're looking at 8 to 16 ohm for the speaker impedance, rather than 6+k ohms for a guitar pickup. So a much lower volume pot resistance would be required and you'd have to look at the circuit maths as to whether you could get a standard passive tone control to work at all. I suppose it should do.

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Originally Posted by Simon Barden

I'm not sure how well standard volume and tone controls would work with a speaker as a transducer. You're looking at 8 to 16 ohm for the speaker impedance, rather than 6+k ohms for a guitar pickup. So a much lower volume pot resistance would be required and you'd have to look at the circuit maths as to whether you could get a standard passive tone control to work at all. I suppose it should do.

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Good point Simon. The output from the speaker will be so much lower than a pickup, so the voltage drop across 250k might be way too much. It is hard to see how it could work well without a preamp. And if I have a preamp I may as well do the tone controls in that (apart from a simple low-pass filter after the speaker), or in the main amp.

My plan has evolved now into stomp box --> piezo preamp (should work well enough for speaker transducer as well I hope) --> cigar-box amp.

If the cigar box amp doesn't have enough thump, I might be able to cook something up from an old PC speaker sub-woofer. But now I can't decide between a Little Gem, a Ruby, or a Noisy Cricket. Will have to breadboard all three and compare.

Not entirely correct.
Output to Input impedance matching is a subject not well understood.
Below is a link to a page on microphone impedance that may help you understand if you want to plough through it.

In a nutshell, low impedance output into high input works, high impedance output into low impedance input doesn’t.

It has more to do with the signal level presented to the input than the impedance of the output.

100K, 250K & 500K volume pots are better for matching small signals to a high impedance input than a lower value pot.

Here are some links.
https://mynewmicrophone.com/microphone-impedance/
https://sound-au.com/project01.htm

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Originally Posted by Cliff Rogers

Not entirely correct.
Output to Input impedance matching is a subject not well understood.
Below is a link to a page on microphone impedance that may help you understand if you want to plough through it.

In a nutshell, low impedance output into high input works, high impedance output into low impedance input doesn’t.

It has more to do with the signal level presented to the input than the impedance of the output.

100K, 250K & 500K volume pots are better for matching small signals to a high impedance input than a lower value pot.

Here are some links.
https://mynewmicrophone.com/microphone-impedance/
https://sound-au.com/project01.htm

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Thanks Cliff. That's why I love these projects and this forum: they help me learn things :)

I have used the sound-au pages for lots of other information, so I will start with that one.

DC

That's great, thanks Cliff. Everything about this is confusing for me, but honestly the learning is most of the fun!

A 500 ohm pot might work for volume. You don't want to add too much extra resistance in to the signal path at part-volume. If you keep a similar resistance ratio as a standard pickup e.g 8k to 500k, then 8 ohms to 500 ohms is about right. Whilst the pot acts as a voltage divider, and in theory the output voltage level should be the same with any pot, the current produced with a 500k pot compared to a 500 ohm pot will just be so much less, making it far more prone to picking up induced noise and making pot operation scratchy. The pot just needs to have a high enough resistance so that it doesn't 'load' the speaker, and a minimum 1:10 ratio is normally stated as being sufficient for that.

The pot resistance will form part of the input impedance seen by the speaker, but with a guitar amp impedance normally being around 1 meg ohm, the speaker will only really see the impedance of the pot.

A modern mic preamp will typically have an input impedance of between 1200 ohms to 3000 ohms. Older mic pre designs (and modern copies) tend to have impedances towards the lower end of the scale It would obviously be just as easy to make the input impedance a lot higher, but they don't.

A typical dynamic microphone will have an output impedance between 150 ohms and 300 ohms. So some dynamic mics may be slightly loaded by the lower input impedance mic pres, and in fact some stand-alone mic pre designs have adjustable input impedances so you can load the mic output for a different frequency response (less highs with lower impedances).

Speaker-based drum mics like the Yamaha Subkick (originally the LF driver from an NS-10M in a round enclosure), will run directly into the mic pre of a mixing desk, so will be running into that circa 3k input impedance. But that's a 7" speaker and the signal level produced by sticking that on a loud kick drum is going to be significantly greater than that made by a much smaller speaker resonating due to being given a small knock by your foot.

Personally I'd think about active controls, and look at getting say a cheap Behringer EQ700 pedal, stripping it down and mounting it in the enclosure. So you'll have level and tone shaping controls available. It won't take you to zero volume, but you won't need that. In fact you may welcome the ability to boost the output level!

I found this excellent article by Jack Orman that boils it down to voltage dividers and Ohm's law and finally it makes sense why low output and high input impedance is the way to go. The reverse leads to signal loss proportional to how large the mic impedance is relative to the input impedance.

Jack is talking about pickups and guitar pedals but that detail is irrelevant. It's really about a signal source and a sink. He also simplifies impedance to resistance by assuming it has a fixed value at all frequencies, but it still gets the concept across. And he indicates later how the effect is greater at higher frequencies.

As for EQ, building something is doable pretty much from parts I already have. I am not sure where to put the EQ, or how many to have. I can tack active 3-band EQ to the preamp built into the stomp, and the Noisy Cricket (or maybe a Ruby Tuby if I get extravagant, although reviews are mixed) will also have some EQ in the cigar-box amp.

DC

I probably need to start a different build diary for this, but I went shopping at The Green Shed (not the Big Green Shed) but a place in Canberra next to the landfill site that sells reclaimed stuff for next to nothing. I was looking for parts for the cigar-box mini amp that I am building for the foot stomp (or other things).

For the princely sum of $5 I got this old Sanyo speaker:
Attachment 35369Attachment 35370

It's as ugly as anything I can imagine, but paint can fix that, and it's the right size and the 6" 5W speaker is usable. It likely won't give anything like a solid thump, but this mini amp might end up being used for a completely different purpose anyway.

I also picked up the chassis of a Kustom Sienna 30W acoustic amp, again for $5:
Attachment 35371

It looks like someone let the magic smoke out of a cap in the power supply section:
Attachment 35372

While I can replace the cap and fuse, I would be worried about why it blew in the first place and whether there are other faults. I don't have a chassis, and if I went to the trouble to build one, I would want to put a homebrew tube amp in, not this. So I might strip it for parts. I can salvage all the pots, the knobs, jacks etc. Most passive components are not worth enough to desolder, but there is a nice JRC13700 opamp sitting on an adapter board that is just ready to use in a pedal. There is also a spring reverb unit that looks OK. Too large for a pedal but I might be able to use it somewhere else, like in the mini amp.