Author Topic: Auditory Bombardment (highly modified Hydra Delay, bomber plane control thing)  (Read 1211 times)

I should start by saying this is a really long post.  I had never built a guitar pedal before.  I have made many other synth-related gadgets and modules (mostly eurorack modular synth stuff) so it was about time I add a DIY pedal to my collection of retail pedals.  And why not challenge myself to try new things along the way like Fusion 360 and Eagle and general DIY pedal basics.  I thought it might be interesting to share the entire story behind this pedal:

In April 2022, I came across an auction for an interesting looking control panel thing.  It looked very industrial or vintage military equipment.  The auction didn't say what it was and it was randomly included in a lot of decorative gauges.  After some research, I learned that it was a near-complete camera intervalometer control panel from 1960s bombers such as the B-52 Stratofortress and B-47 Stratojet.  This type of intervalometer was a device used by the plane's navigator to essentially time the photos taken on a bombing run.  Pretty cool piece of militaria.  Not something I collect, but for a synth guy, the labels on the panel instantly made me think, "I need to turn this into a delay pedal". 

So the 2-month process began.  I researched many different available DIY delay pcbs and kits, originally thinking I may use a BYOC Analog Delay (it has three knobs, my panel has 3 knobs), but I was a little more interested in the sounds and potential of the PedalPCB Hydra delay.  Lots of switches and room for modifying!  Now, the fact the Hydra has 5 knobs meant I needed to get a bit creative.  In addition to that, the knobs of the intervalometer were not "knobs" in the traditional sense.  Each control "knob" had an intricate mechanism behind it (2-4inches deep) which included gears, PCBs, wiring, DC motors, etc, all part of the timing mechanism that controlled the interval at which the pictures were captured.

Once the internals were removed I was left with a hollow control knob which would freely and endlessly rotate on a brass collar which was bolted to the intervalometer's faceplate.  Still not a knob that would fit any potentiometer I could think of.

Bottom half of the control "knob" assembly: Rust removed and color restored gun bluing paste.

The solution to using these controls as potentiometer knobs was to design a 3D printed insert that would sit inside the hollowed out control knob, protrude through the mounting collar and attach onto a D-shaft potentiometer mounted below. 

Now where to mount that potentiometer.  The faceplate had large ~40 mm diameter cutouts for the control mechanisms to fit through.  Enter the adapter panel.  This would not only allow me to mount the 3 potentiometers under the large control knobs, it would give me the freedom to drill additional holes for enclosure mounting and PCB mounting.  One goal of this project was to keep the faceplate as original in appearance as possible.  Mostly, I did not want to drill extra holes or modify the panel in any way so this adapter panel idea solved many problems.

For the 3 large control knobs, I planned to use the Delay control for Level, the Interval control for Speed, the Exposure Limiter control for Swell/feedback.  Looking at the 2 amp fuse housing, I thought I could come up with a way to put a potentiometer in its place with a knob that looked like identical to the original fuse housing and use that for the Mix control.   

That left the Age control as well as the 4 toggle switches for enabling/disabling the delay heads.  I knew I needed to get a new enclosure to mount this faceplate onto (the original was far too deep), so I decided I would fit these as well as two other modifications onto the front of the enclosure.  This may not be a pedalboard-friendly option but, for my needs, this was more than adequate. 
Original enclosure that sat behind the faceplate (huge!)

With a little work (hours of grinding away aluminum), this enclosure from Digikey should work:

Since the intervalometer I had was missing the pushbutton switches, toggle switch, and a exposure counter, I figured I could make some use of those empty slots.  I knew I wanted the ON/OFF to be a footswitch and the Manual Exposure to be a instant-maximum feedback momentary footswitch.  The other two would make for a fun use of a toggle switch (with safety cover) to insert/remove the distortion circuit into the feedback path and a distortion bias knob could go right next to it in the Camera/Trip slot. 

The Ready and Operation indicator lamps were something I wanted to make functional for this project.  The yellow Ready indicator would illuminate when power is connected at the power jack and the green Operation indicator would illuminate when the delay effect is activated. These indicators used a bayonet halogen bulb which needed something like 26 volts to light up, so I decided to go with LEDs.  To do this I designed a 3D printed 5mm LED to bayonet bulb adapter to hold the LED in a way I could pop it right into the indicator housing and use the original two posts on the back for wiring.  Now I was then able to run the indicator [LEDs] from 9V with no lamp-housing modifications needed.

All that was left was to start working on the pedal's internals.
I had ordered the Hydra, intelligent bypass relay, and FV-1 clock module pcbs from PedalPCB and had to figure out a solid way of mounting them in the enclosure since I was not direct-soldering the potentiometers and switches as intended.  I decided to use a protoboard I had lying around since it had 4 mounting holes for standoffs and this could also be home to the Roland RE-150 preamp circuit I wanted to use as a fancy input level control and/or boost for lower signal levels, as well as the JTM distortion circuit as others have included in their Hydra builds.  The protoboard would also give me room to fit headers I could use with ribbon cables to connect all the controls and IO on the enclosure in a way that I could easily disconnect when fixes, or further modifications might be needed.  So using boardmount headers and sockets at strategic points on the 3 PCBS, I connected them to the protoboard.

breadboard testing the JTM distortion circuit (I believe)

and a last-minute modification of the JTM circuit to have 5 different pairs of diodes to choose from!

After a bit of troubleshooting the odd issue here or there, the wiring was complete.

The additional board with the 10-way dipswitch and 2-way dipswitch is for the diode selector distortion mod and the 100% dry mix mod.

More test fitting

Now to tidy things up a bit with labeling and wooden side panels for a vintage vibe that would suit the era of the intervalometer.  I went for the metal stamp labelling on the enclosure for a bit of a military aesthetic.  Since I didn't want to risk messing up too much, I designed a 3D printed jig to help line things up and keep even spacing between characters.

Many, many coats of gun stock Tru Oil on nice figured Maple.

Since venturing into resin 3D printing last year, I have been using Fusion 360 for a lot of custom designs and STL editing.  I decided early on to use this application to mock up the project once I knew I needed custom, precision parts.  Also it killed time while I waited for parts to arrive in the mail and made for a good learning experience to further develop my 3D-design skills.

Final mock-up in fusion 360:

So finally, about 2 months later and over 100 hours of research, planning and building, I present, Auditory Bombardment:


That is one hell of a build post. Thanks for sharing. You put in a lot of work on that one and it looks absolutely amazing!


Absolutely gorgeous. I have no notes. Brilliantly designed and executed project.
"Some people love music the way other people love chocolate. Some of us love music the way other people love oxygen."

Toy Sun

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  • ::: John S ::: Seattle, WA :::
Wow, absolutely love this approach. The one-of-a-kind sourcing of the chassis/knobs, the execution and attention to detail. Very inspiring. Thanks for the detailed report, too.