The Maestro Filter Sample/Hold is a 1970s filter pedal that puts a synthesizer Voltage Controlled Filter module (an envelope filter, sometimes called an auto wah) and a Sample & Hold module in one stompbox, suitable for guitar and bass1. Its envelope follower mode sweeps the filter in response to your playing, while its Sample & Hold mode steps the filter to random settings for a stepped, synth-like effect that General Guitar Gadgets calls rare to find in a stompbox for guitar or bass1.
The pedal is a close twin of the Oberheim Voltage Controlled Filter. General Guitar Gadgets, whose DIY kit reproduces the circuit, states that it is exactly the same circuit, with the same PCB and enclosure but different graphics, and that both were released in the mid to late 1970s1. Pedal of the Day dates the Oberheim VCF / Maestro Filter Sample Hold to the early-mid 1970s and notes these effects are super-rare, with not a ton of information available2.
What Sample & Hold does, and how the two modes work
In its envelope follower mode, the pedal behaves like a voltage controlled filter or auto wah: the filter sweeps according to the dynamics of your picking. Guitar World describes the Oberheim VCF's mode switch as engaging either the sample-and-hold random-filter effect or an envelope follower, for autowah effects3. The two pedals being identical in every way except for their paint jobs, the same applies here3.
Sample & Hold is the main attraction. Instead of a smooth sweep tied to your attack, the circuit repeatedly samples a control voltage and holds each value, so the filter jumps between random-sounding settings at a rate you control. General Guitar Gadgets describes the envelope filter on the unit as excellent for guitar and bass, with the sample & hold being the rare part1.
The controls and trimmers
The original pedal keeps its control surface simple. Guitar World lists knobs for range (depth) and sample-and-hold speed on the Oberheim VCF3.
The General Guitar Gadgets kit documentation gives the equivalent component values:
| Control | Component | Value | Taper |
|---|---|---|---|
| Speed | R28 | 1M | Linear |
| Filter Range | R15 | 100k | Linear |
| S&H trimmer | R26 | 100k | Trimmer |
| S&H trimmer | R27 | 10k | Trimmer |
The two trimmers, R26 and R27, only affect the Sample & Hold function, and you have to set them by ear. As the kit documentation puts it1:
"You have to set the trimmers by ear. It takes a bit of time, but it's not difficult to tune it in."
A documented modification can reverse the filter's sweep direction. The Reverse Direction mod requires an extra IC and associated parts, built on a small board and wired into the main board, so it is a build-level change rather than a toggle1.
Power and connections
The kit's bill of materials (version 2018December30) and instructions (version 2019August25) list the connections as follows1:
- Input: J1, stereo 1/4-inch jack
- Output: J2, mono 1/4-inch jack
- Power: J3, DC jack
- Battery: B1, 9 volt battery, not included in the kit
- Switching: Sw1, heavy duty 3PDT footswitch
The circuit uses two CA3080 transistors in IC positions 1 and 2, three LM741 op-amps in positions 3 to 5, and a MAX1044 in position 61. For the noise-critical Q4 transistor position, the kit uses a BC182L, which General Guitar Gadgets calls the best transistor they have found for that slot1.
The Oberheim circuit behind it, and the DIY kit
Because the originals are super-rare, the practical way to get this circuit today is General Guitar Gadgets' DIY project. The kit reproduces exactly the same circuit as the Oberheim Voltage Controlled Filter, on the same PCB and in the same enclosure design, with different graphics1. If you buy the kit, the Ready-to-Solder Printed Circuit Board (RTS PCB) is included1.
The kit documentation also notes a toggle switch with S&H among its settings, so you can select the random-filter mode on the finished build1.
The circuit's lineage lives on in modern production pedals. Red Witch says that Oberheim and Maestro spring to mind when thinking of the great analog Sample Hold pedals of the past, and its Euphemia Sample Hold Filter is a 100% all analog Sample Hold Filter pedal built with hand wired, premium through-hole components4. Pedal of the Day reviewed the Yellowcake Pedals Psychotropia Sample/Hold Filter, a sample/hold filter whose Glide knob sets the amount of up and down slide for the sample/hold waveform and whose Level knob controls the overall output volume5. Pedal of the Day has also covered the Lone Wolf Audio Acetylene Nirvana VCF Sample/Hold, another analog pedal based on the 1970s Oberheim VCF / Maestro Filter Sample Hold2.
Videos
The Hue of Two
tablabol
Questions
Is the Maestro Filter Sample/Hold the same as the Oberheim Voltage Controlled Filter?
Yes, in circuit terms. General Guitar Gadgets, which sells a DIY kit of the circuit, describes it as exactly the same circuit as the Oberheim Voltage Controlled Filter, with the same PCB and enclosure but different graphics. Guitar World likewise calls the two pedals identical in every way except for their paint jobs.
What does Sample & Hold do on a guitar pedal?
Sample & Hold repeatedly takes a snapshot of a control voltage and holds it, so the filter jumps between random settings instead of sweeping smoothly. The result is a stepped, random, synth-like filter effect. On this pedal it sits alongside an envelope follower mode, which sweeps the filter in response to your picking for autowah sounds.
Can the filter sweep direction be reversed?
Yes, with a modification. General Guitar Gadgets documents a Reverse Direction mod that reverses the sweep, but it requires an extra IC and associated parts, built on a small board and wired into the main board. It is not a stock feature or a simple switch swap.
Does the kit include a printed circuit board?
Yes. If you buy the kit from General Guitar Gadgets, the Ready-to-Solder Printed Circuit Board (RTS PCB) is included. A 9 volt battery is not included, so you need to supply your own if you want battery power.
Sources (5)
- Maestro™ Filter Sample/Hold™ Clone: DIY Kit, PCB & Schematic, General Guitar Gadgets, 2014-05-14
- Lone Wolf Audio Acetylene Nirvana VCF Sample Hold, Pedal of the Day, 2017-06-02
- Weird Science: The 10 Strangest Vintage Effects of All Time, Guitar World, 2018-01-12
- EUPHEMIA Sample Hold Filter, Red Witch Pedals
- Yellowcake Pedals Psychotropia Sample/Hold Filter, Pedal of the Day, 2020-08-01
