Tag Archive | werkstatt

Synthfest UK 2019: my DIY modular gets screen time!

For the last three years I’ve been working hard on a complete modular synth system (which is partly why this blog has been so quiet lately), and at last the graft is starting to pay off!

I took it to Synthfest UK 2019 last weekend to give people a chance to see it, hear it, and more importantly to play it. Happily, it went down very well, and to my surprise the crew from Sound on Sound magazine asked me for an interview! Of course I was excited to oblige, and here (unscripted, unprepared, and with terrible hair) is my 6 minutes of fame…

As outlined in the interview, the synth itself is currently two cabinets. The upper cabinet contains:

  • VCO
  • VCF (24dB low pass)
  • VCA (transistor design with lots of colour)
  • ADS(R) envelope (Decay and Release share a control)
  • Dual lag processor
  • White & pink noise
  • Dual LFO (with waveshaping)
  • Passive ring modulator
  • Passive filters (Low and High pass)
  • Passive attenuators
  • Passive multiples
  • PSU

The lower cabinet contains the following, at the time of writing:

  • Dual VCA
  • AR & ADSR envelopes
  • Envelope follower
  • Gate delay
  • Audio (log) mixer
  • Attenuverting linear mixer
  • CV sources and inverters
  • Dual Sample & Hold
  • Headphone output and extra gain control
  • Buffered mults & inverters
  • PSU

I was ill for a couple of weeks leading up to the show, so I didn’t get chance to complete and install the High Pass VCF (24dB) that I had working and half-built, so that’s going in next. That leaves one slot in the lower cabinet which will become a Dual VCO.

The synth as it was for Synthfest UK 2019:

Photo of my DIY modular at Synthfest UK 2019

Photo of my DIY modular at Synthfest UK 2019

There’s a long way still to go. Once the lower cabinet is complete, I’ll be making another cabinet of sequencing and control modules – clock converters, triggers, all that kind of thing. I’ve also got plans for various units that I think will become separate devices, and which are at various stages of development. I’m trying to keep the focus on finishing this pair of cabinets first, and taking things one step at a time.

My aim is to turn these into modules you can buy. That’s also in progress, but it’s not about to hit the streets just yet. Hopefully something will start to appear in 2020, but the most important thing is to get this right, so releases of any kind will happen when they’re ready. There’s a lot of work in turning an idea into a product!

Watch this space, anyway. Meanwhile, I’ll try to keep posting a few synth DIY circuits, and maybe some details about vintage synths, but I have had to focus my time and energies on the design and testing for now. This blog is definitely not done yet, I will keep it going as long as I possibly can, but posts will be more widely spaced than they were in, say 2014-16, when I was dissecting the Lambda and modding my old Werkstatt. I haven’t forgotten those people who message me here and ask questions, either! I still try to answer as many of those as possible, where it’s appropriate and I am able to find the time. Please do keep asking, I’m very happy that my little blog gets such an audience!

I wish you all the best, and hope to continue seeing you here for a long time to come!

Nathan

 

 

Moog Werkstatt: improving the VCO and VCF direct outs

There are three ways to get audio from your Werkstatt: the VCO direct out, the VCF direct out (both on the pin header), and the main audio out (the 1/4″ jack on the rear panel).

The VCO Out signal is a sawtooth or pulse, depending which wave the VCO is switched to, at 0-5V. This is pure, dry VCO with no further processing, though of course it will be pitch- and/or pulse-width-modulated, depending on your modulation routings. The VCF Out is taken directly from the output of the filter, bypassing the VCA, and is nominally -2V to +2V. The main audio out is at typical line level (a couple of volts peak to peak), and comes through the filter and VCA.

If you want to use the Werkstatt as an extra oscillator for a modular, for example, you’ll probably want to use the VCO direct out. If you’re running the filtered sound into an external VCA for more varied amplitude modulation or to use with a high-pass filter maybe, you will probably want to take the Werkstatt’s audio directly from the VCF out. If you’re using the Werkstatt as a standalone expander, the main audio out will do just fine.

If signal levels were the same all the way along, none of this would be a problem. However, as with other aspects of the Werkstatt’s design, it needs some tweaking to integrate perfectly. Here’s how.

VCO direct out

Let’s say you’re using the VCO direct out. Eurorack has typical VCO signals of 10 volts peak-to-peak (see Doepfer’s Signals in the A-100 section, for example), centred around 0V (that is, -5V to +5V). To get the closest match sonically we want the Werkstatt’s output to match the other oscillators you’re using. Not all modules with mixers on board will boost as well as cut their inputs, so we can add a small circuit to give a true -5V to +5V VCO Out on the Werkstatt. The schematic below shows both the VCO and VCF mods. More on the VCF shortly.

Schematic for improved VCO and VCF direct outs on the Moog Werkstatt

Schematic for improved VCO and VCF direct outs on the Moog Werkstatt

How It Works

The VCO out mod is a basic non-inverting amplifier with an offset to make the positive-only signal bipolar. The gain is set by the two 20k resistors (1+20k/20k = 1+1 = 2) and the unity-gain reference point is at 5V. That is, 5V in gives 5V out. 0V in would be a difference of -5V from this reference point, so this is multiplied by the gain of 2 to give a difference of -10V, which taken from the +5V reference gives -5V out. In this way, the 0-5V input becomes -5V to +5V out. You can see it in action at this link. Below is a screenshot of the simulation.

Simulation of the improved Werkstatt output mod in Falstad

The improved Werkstatt output mod  demonstrated using Falstad’s online simulator

VCF out

Likewise, if you want to run the Werkstatt’s VCF output into an external module, boosting the signal to match requires just a small circuit, almost identical to the first. The signal level drops as resonance is increased, but to keep our circuit simple we won’t worry about that. The schematic is on the same sheet as the VCO output, posted earlier on this page.

How It Works

This is also a non-inverting amplifier, but this time with no offset as the VCF signal is already bipolar – all the amplification happens around a 0V centre point. Positive signals get more positive, negative signals get more negative. The VCF direct out is normally about 5V peak to peak at maximum, so we just double that to get the more useful 10V range. The gain is set the same way as the previous circuit, and we get an output of -5 to +5V maximum.

Installing the mod

I built both these circuits onto a small piece of stripboard mounted onto the panel with one of the minijacks. There’s just enough room, as can be seen in the photos. This allows the use of both halves of a dual op-amp so nothing goes to waste. There’s also plenty of room on the experiment pads at the top of the Werkstatt’s PCB, though you may find it a bit cramped if you’ve already got a couple of mods in there like I have…

The photos show the locations on the PCB of the various supply rails you’ll be wiring up to: -9V and +9V to power the op-amp, +5V for the VCO amplifier reference, and GND. These are all labelled on the top side of the PCB anyway so it’s easy to find them. I shared the ground that my existing mods were already using, which is connected to the nearby screw post via a solder tag. See my CV mod for details.

Werkstatt VCO and VCF direct out mod wiring

Werkstatt VCO and VCF direct out mod wiring

 

Werkstatt VCO and VCF direct output mod installed

Werkstatt VCO and VCF direct output mod installed

 

Werkstatt VCO and VCF direct output mod external appearance

Werkstatt VCO and VCF direct output mod external appearance

 

Before and after: VCO and VCF direct outs. Top image 1V scale, bottom image 5V scale

Before and after: VCO and VCF direct outs. Top image 1V scale, bottom image 5V scale

Parts

U1: TL072 or equivalent
R1, R5: 10k (1/4W 1% Metal Film used here, but it’s not critical)
R2, 3, 6, 7: 20k
R4, 8: 1k
jacks, wire, stripboard: as per your own choice

Moog Werkstatt: adding a VCA CV input jack

I’ve already blogged about the reasons you might want to mod your Werkstatt, and have posted a list of mods here, so to complete the VCO/VCF/VCA trio, here’s the VCA input at last!

How it Works

This is a very simple mod, and just replicates the existing patch header input. All you need is a 10k resistor, some wire, and a jack socket.

Werkstatt VCA CV input mod schematic

Werkstatt VCA CV input mod schematic

The easiest point to solder to on the board is JMP62. This is located just above the Decay pot. This point is where incoming VCA CV signals are passively mixed. It’s probably best to solder the new parts to this jumper on the underside of the PCB, which you can see on the photos of the wiring:

Werkstatt VCA input JMP62 location

Werkstatt VCA input: JMP62 location

Werkstatt VCA input JMP62 on underside of PCB

Werkstatt VCA input: JMP62 on underside of PCB

Werkstatt VCA input soldering

Werkstatt VCA input: soldering

Werkstatt VCA input panel

Werkstatt VCA input: side panel

Parts

10k resistor
Jack socket
Wire

Further thoughts

As the Werkstatt already has a pin for VCA modulation on its patch header, you might think this mod seems less immediately useful than the VCO or VCF CV inputs. The main issue is that there is no way to simply switch off the Werkstatt’s own VCA – you can select EG shaping, or ‘on’ for drones, but you can’t bypass it for use with an external envelope. What does this mean in practice, and why bother adding a CV input for it?

If you’re using the Werkstsatt with a modular, you’ll have more interesting envelopes than the attack-decay type on the Werkstatt. You might well also have something that will give an offset. It should be possible to use a negative offset to counteract the Werkstatt’s ‘on’ VCA CV, and mix in a more interesting envelope signal; setting the Werkstatt’s VCA to ‘on’ and feeding this CV input with that mix will then allow you to contour the Werkstatt’s VCA as you like.

It would also allow you to use the Werkstatt’s own patchbay to feed the VCA with its LFO, and simultaneously blend another LFO in with this CV mod. Mixing different LFOs gives a lot of movement to a sound, and can be very enjoyable to play with. You can also sequence the VCA level this way, while retaining other modulation via the pin header.

As always, my mods are not definitive – the best thing to do is experiment, and adapt, and find out what works for you and this excellent little synthesizer. Enjoy!

Envelope Circuits: a simple discrete AR design

As a companion to my simple op-amp AR envelope circuit, here’s a discrete version. It has the same basic functionality – gated input, variable attack and release times – but is made with transistors instead of integrated circuits. Power consumption is very low (just a handful of mA), and it runs from a positive supply of your own choosing. Like its op-amp cousin, it could be powered with a battery, or in a Eurorack system, or you could add it into an existing synth like the Moog Werkstatt as a mod.

The main difference between this and the op-amp circuit, aside from it being discrete, is that I have included a very simple way to set the level of the envelope output (see below for details).

RV1 is Release, RV2 is Attack. The Gate input can be anything over a couple of volts. Negative-going inputs (eg., from a bipolar LFO) will be removed by D1. The output goes to nominally 0V when fully off (closer than the op-amp version, in fact).

Discrete AR envelope schematic

Discrete AR envelope schematic

Parts List

R1, R2, R6, R7, R10: 100k
R3, R4: 47k
R5, R8: 560 Ohm
R9: 24k
R11: 10k
R12: 1k
RV1, RV2: 1M linear pot
C1: 1µ non-polarized
D1, D2, D3: 1N4148 or equivalent
Q1, Q4, Q5: BC549C or equivalent
Q2, Q3: BC559C or equivalent

*

How it works

Compare the first pair of transistors with my discrete gate buffer circuit. A positive voltage on the input turns on Q1, taking the base of Q2 low. This turns on Q2, taking its collector high. This is how we drive our envelope.

Now compare the diode and potentiometer arrangement with my op-amp AR. Once you’re past the transistors, it works in basically the same way.

Q3 inverts the output of Q2, so when Q2 is on, Q3 is off, and vice versa. When the collector of Q2 is high, the capacitor charges through diode D3 and pot RV2 (Attack). When the gate input goes low, the transistors Q1-3 switch off, off, and on, respectively. In this state, the capacitor discharges through RV1 (Release) and D2.

Note the two 560 ohm resistors: one on the emitter of Q2, the other on the collector of Q3. When the gate input is high and the capacitor is charging, current flows through Q2’s emitter resistor; when the gate is off and the capacitor is discharging, current flows through Q3’s collector resistor. These two resistors put a lid on the current flow and limit the fastest times for Attack and Release. The value is a trade-off between current and snappiness. With the values shown, maximum current through these resistors is around 16mA and the fastest rise and fall times of the envelope are around 2ms.

The final two transistors in the circuit after the capacitor are the output buffer; notice the two resistors between them, forming a potential divider. With the values shown, if you run this circuit on 12V, the envelope output will be around 8V max.

There are better ways to set the peak level of an envelope, but my aim here is to keep things simple as a base for experiment.

Changes

The most obvious things to tweak are the envelope times and the output level.

The values of the two potentiometers affect the attack and release times, but the envelope can be substantially stretched by using a larger capacitor. It would be easy to add a switch that connected, say, a 4.7µF or 10µF capacitor in parallel with the existing one, which would multiply the envelope’s times substantially (use perhaps a 25V electrolytic, with its -ve terminal to ground).

The two resistors between the output buffer transistors can be adjusted to suit your requirements. If you want full-scale output (ie., envelope peak closer to the supply voltage), remove R9 and R10, and connect the emitter of Q4 directly to the base of Q5. In fact, this circuit will also work with just a single NPN as a buffer (miss out Q4 and the divider resistors, connect the cap to the base of Q5), but amongst other things the ‘zero’ value is less close to actual zero; if you want to experiment with a single transistor here, setting the level of the output can be done by replacing the 10k resistor on its emitter with a pair of resistors as a potential divider, or even a 10k trimmer with the output taken from the wiper.

Feel free to experiment with the circuit in Falstad’s handy online simulator.

 

Envelope Circuits: a simple AR design using op amps

A very simple Attack-Release envelope generator can be built with a dual op amp and just a handful of extra components. The input stage is basically the same as my op amp gate buffer, with only its output resistor changed; the rest is a simple low-pass resistor/capacitor setup with an output buffer. Here’s how it works:

The input acts as a comparator. When the gate input goes high, the comparator output goes high, and the capacitor is charged up via D2 and the Attack pot RV1; when the gate goes low, the comparator goes low, and the capacitor discharges through the Release pot RV2 and D3. The diodes directionalise this process, so the attack time is governed only by the Attack control, etc. The output is a very simple unity-gain follower.

 

Operational Amplifier Attack-Release Envelope

Operational Amplifier Attack-Release Envelope Schematic

 

With the values shown, attack and release times range from just a couple of milliseconds to around 5 seconds. Larger values for the pots and/or cap will extend the times proportionally, smaller ones reduce them. The 560 Ohm resistor sets the minimum time against a given capacitance.

With an op amp such as the LM358, the output will swing between 0V and approximately 1.5V below the positive rail. If a lower output level is desired, add a potential divider of resistors in the low-mid single Ks after the output buffer amplifier, taking the overall output from their junction.

Supply voltage is not critical, but as mentioned above, the LM358 op amp will swing to around 1.5V below supply at maximum. It does, however, swing to ground too, which when operated on a single supply is necessary in obtaining a correct ‘gate low’ output. If you cannot find a 358, use another op amp which will swing rail to rail, or ground to near-positive.

*

A circuit like this makes a nice addition to synths with only one envelope, such as the Moog Werkstatt and Mother 32, or Arturia Microbrute. It will run from a 9V battery and is small enough to build into the Werkstatt itself, or indeed any small external box of your choice. You could easily build one for a Eurorack modular system too, and it will run happily on +12V or +15V.

For details of how to modify the Werkstatt, take a look at my Werkstatt page.

*

Op Amp AR, parts list:

U1: LM358 or similar
D1-3: 1N4148 or equivalent
C1: 1µ poly non-polarized
R1,2: 100k 1/4W resistor (I use 1% Metal Film types, but 5% Carbon are also fine)
R3: 82k —”—
R4: 18k —”—
R5: 560Ω —”—
R6: 1k —”—
RV1,2: 1M linear pot
Input and output connectors as desired.

Moog Werkstatt: adding a proper Filter CV input

Note: I make reference to the Moog Werkstatt schematics throughout. Copyright prevents me reposting them here; they can be found on Moog’s website.

After the VCO Frequency CV and Gate inputs, perhaps the next most useful control we can modify is the VCF cutoff frequency. The Werkstatt already has switches to select either LFO or EG filter modulation in positive or negative amounts. Many synthesizers also have a Keyboard Tracking control which routes the CV generated by the pitch control source to the filter cutoff, allowing the filter to open up as higher notes are played. The amount of this modulation is often governed by a pot — giving continuous variable control — but is also often implemented with a switch — giving either preset amounts of modulation, or at its most basic just on/off (that is, 100% or nothing). At 100% Keyboard Tracking, a self-resonant filter can be used as a sine wave oscillator, the pitch of which will follow the keyboard.

Various filter tracking controls

Various filter tracking controls

 

The Werkstatt’s filter has a CV input on the header, which is fine for simple self-patching, but two problems show themselves when you want to control this parameter from an external source: firstly, the necessity of hacking a cable together as described previously; secondly, the accuracy of tracking. The Werkstatt’s existing filter CV input point does not, in my experience, give accurate 100% tracking from an external V/oct CV, which spoils sounds that require the resonance to boost harmonics that are locked to note pitch.

The mod below overcomes these problems by giving the Werkstatt a separate, tunable Filter CV Input that can be trimmed to give suitably accurate pitch tracking.

How it Works

As with the Pitch CV Input mod, we’re going to simply duplicate the existing control input and make a slight alteration. The existing header input for cutoff control mixes its CV via a 47.5k resistor. In order to be able to give tunable tracking, this mod is going to use a 43k resistor and a 10k variable trimmer in series. 100% tracking should be somewhere towards one end of the trimmer’s range.

Werkstatt filter CV mod schematic

Werkstatt filter CV mod schematic

 

Solder the two extra components to the board, take the third leg of the trimmer to TP17 (purple wire in the photos below), and take the outer leg of the resistor to the input jack, which is mounted and grounded exactly as for the CV and Gate jacks.

 

Werkstatt filter CV input mod PCB top

Werkstatt filter CV input mod PCB top

 

Werkstatt filter CV input mod PCB rear

Werkstatt filter CV input mod PCB rear

 

Werkstatt filter CV input mod rear wiring

Werkstatt filter CV input mod rear wiring

 

Werkstatt filter CV input mod jacks

Werkstatt filter CV input mod jacks

 

Fine Tuning

Tuning the tracking is similar to tuning the pitch (a process described in the manual) — with the Werkstatt open, connect the external CV and play as normal, using full resonance on the filter, with the cutoff tuned so you can hear the pitch of its self-oscillation. Adjust the trimmer so the filter’s resonant frequency scales up the keyboard at the same rate as the note pitch — that is, two notes played an octave apart should give a resonant filter peak an octave apart.

Because the Werkstatt’s VCO cannot be silenced without modification, it might be easier to disconnect the pitch CV control while tuning the filter; alternatively, if you have a way of multing the pitch CV, connect it to both pitch and filter. You might try setting the filter to resonate at an obvious harmonic such as a 5th above the pitch, as any deviation in the tracking will result in some noticeable sonic artefacts.

More Ideas

Of course, you might not want a simple fixed 100% tracking filter. It would be possible to add a pot to allow the user to vary the tracking amount; you could install a switch to select between different resistors to give preset fixed trackings; you could route the pitch CV to a break-contact on the filter CV input jack so that it tracks by default unless a jack in insterted to over-ride it. My own mod is simple and quick and functional, and hopefully will provide a point of departure for your own experimentation.

 

Werkstatt filter CV input mod in use

Werkstatt filter CV input mod in use

*

Parts used:

43k 1/4W 1% MF resistor
10k trimmer
1/8″ panel mount jack socket

Moog Werkstatt: adding a proper Gate input

Note: I make reference to the Moog Werkstatt schematics throughout. Copyright prevents me reposting them here; they can be found on Moog’s website.

In its original form, the Werkstatt’s own keyboard generates the Gate signal to trigger the envelope, and there is no obvious ‘Gate Input’ on the header. The existing Gate Out can be (ab?)used as a Gate In, but it’s not ideal, because as with most of these header points, anything coming in here isn’t buffered from the internal signal.

Adding a proper Gate In to the Werkstatt is straightforward enough, though a little more involved than the CV input; my approach doesn’t require the cutting of any traces, the only hack-work being the hole in the enclosure for a jack socket. It does require the end of one wire to be soldered to rather small SMT (surface-mount) components though, so you’ll need a suitably fine tip for your iron and a steady hand.

Werkstatt gate mod schematic

Werkstatt Gate Input mod schematic

 

How it Works

The Werkstatt’s keyboard scanner outputs a logic high at U19 pin 3 when it detects a key press. As well as stopping the scan and loading the current key value into a latch (which feeds the VCO CV), this signal is buffered to provide a Gate, and differentiated to provide a Trigger. The Key On signal is buffered inversely by the Schmitt trigger of U14-F before being flipped back positive by U14-D. In order to add our external gate without affecting any other part of the keyboard circuit, we only need to bring the input of U14-D low. In this way, we can use both the Werkstatt’s own keyboard and an external Gate without having to switch between control sources.

The solution is to use a simple NPN in saturation to take U14 pin 9 to ground when its base is taken high. In other words, a positive external Gate will take the gate inverter input low, just as does the keyboard gate detector. Because there is a diode in the way (D14), our added transistor is isolated from the keyboard scanner clock and data-bus, so there won’t be any accidental mis-readings of the keyboard CV.

Another advantage of this solution is that the Werkstatt’s own envelope retains its Gate/Trigger operating modes, as our external Gate also gets differentiated; we are activating the Werkstatt’s envelope, not over-riding it.

The modification takes just four components and a socket, and fits easily on the PCB. The hardest part is soldering the wire from the collector of the transistor to the appropriate point on the Werkstatt’s circuit – I chose to solder it across the connection between R89 and C64, as the two solder points make a convenient place to lay a thin wire and give it a firmer purchase.

I presume you’ll be doing both CV and Gate input mods; the socket ground can be wired to the CV In socket ground, which I wired to a solder tag around the nearby PCB mounting screw (see also the CV Input page).

Werkstatt gate input mod smt solder point

Werkstatt Gate Input mod SMT solder point

 

Werkstatt gate mod extra components highlighted

Werkstatt Gate Input mod extra components highlighted (PCB top)

 

Werkstatt gate mod PCB rear highlighted

Werkstatt Gate Input mod extra components highlighted (PCB rear)

*

Parts Used:

33k 1/4W 1% MF resistor
100k 1/4W 1% MF resistor
1N4148 signal diode
BC549C NPN transistor
1/8” panel mount socket
wire

These parts are what I had handy. Pretty much any NPN with reasonable gain can be used here, and the signal diode is a generic one.

Moog Werkstatt: adding a proper CV input

Note: I make reference to the Moog Werkstatt schematics throughout. Copyright prevents me reposting them here; they can be found on Moog’s website.

The existing header on the Werkstatt allows for a VCO pitch CV to be patched in. Although the pitch can already be modulated by either the LFO or the EG (selected using a panel switch), the patch header input means you can use both modulation sources simultaneously – or an external CV, if you can cable it up.

When you start wanting to connect control sources to the Werkstatt, one problem is pretty obvious: the patch pin header provides a signal path, but there’s no ground. The user manual suggests hacking cables together, taking a ground from the cable to a screw on the case (or the ground on the audio output jack), but this isn’t a very neat solution. Better to add a proper CV input jack so you can directly and simply hook up your external CV source using standard cables.

Moog themselves (at the time of writing) do sell an add-on jack board, which provides both a row of minijacks and a signal ground, but I decided against buying it for two reasons: 1) it still doesn’t offer a true Gate input, which I felt necessary; 2) the jack board replaces the patch pin header – adding mods like mine means you can use them and the patch pins simultaneously, giving more possibilities.

How it Works

The circuit is very simple. Looking at p.2 of the official schematic, we can see the existing header CV input is mixed in via a resistor R46 and trimmer VR5. This trimmer can be carefully adjusted to give a 1V/octave response for your external CV.

It would be super-easy to simply wire a jack to the CV point on the header, but this has the disadvantage that inputs are not isolated from each other. Better (and still easy) is to replicate the two passive components and route them to the same mix point.

Here are my additions to the circuit:

Werkstatt CV modification schematic

Werkstatt CV modification schematic

Here is the mod in situ:

Werkstatt CV input mod (top)

Werkstatt CV input mod (top)

Werkstatt CV input mod, rear

Werkstatt CV input mod (rear)

The handiest solder points for connecting the extra components to the existing circuit are TP14 and TP10. Either will do:

Werkstatt CV input mod routing

Werkstatt CV input mod routing

The jack is wired to be brought to the side panel beneath the header. In this photo the Gate mod jack is also in place. The jack grounds are wired together, and then to a solder tag that connects to the nearby screw post. The existing screw is long enough to accommodate a washer or two:

Werkstatt mod ground point

Werkstatt mod ground point

Drilling the hole in the case is simple and quick, and a label finishes the job:

Werkstatt with CV and Gate mods

Werkstatt with CV and Gate mods

The accompanying Gate Input mod is also detailed on this site.

*

Parts Used

68k 1/4W 1% MF resistor
100k trimmer
1/8” panel mount socket
3mm solder tag
3mm washers (x2)
wire

%d bloggers like this: