SP – Peak Selector

Buy the PCB:

Steiner Peak Selector
Steiner Peak Selector
Available Qty: 25
Price: $30.00







This module generates a trigger when the input signal exceeds a preset level set with the Threshold control. The trigger will remain active while the incoming signal exceeds this threshold with a minimum of about 30 milliseconds. The LED indicates the trigger and remains illuminated while the trigger is active.

From the Synthasystem manual:

The peak selector will provide an output trigger at output jacks whenever a signal input or DC level input fed into the input jack exceeds a preset level controlled (set) with the threshold knob on the front panel.

The duration of the trigger lasts as long as the signal or DC voltage stays above the threshold level, but has a minimum duration of approximately 30 milliseconds. A red light on the FP indicates when the peak selector has been triggered and stays on for the duration of the trigger.

A few typical uses of this module include: Triggering the synthesizer in sync from sounds (or “Ticks”) already recorded on a tape recorder.

Production of triggers by blowing into an amplified microphone fed into the peak selector.

Production of triggers by human touch. Simply attach a metal pad to the hot conductor of a shielded cable and feed directly into peak selector. when body touches pad, it feeds in stray 60 Hz A.C. hum (which triggers the peak selector). the input amplifier may be necessary in some locations where low levels of A.C. fields are present.

Finally, you can produce random trigger rhythms by feeding in white noise and adjusting the level to the appropriate level.

A chain of triggers can be produced from a low frequency oscillator fed into the peak selector input.

Signal to filter to peak selector could for example produce triggers only on a bass line, etc.



This module has one input and one output:

  1. Signal in – A DC or AC voltage/signal
  2. Trigger out – An S-Trigger (V-Trigger) which can be used at any gate or trigger input such as the Envelope generator. This trigger can be wired as an S-Trigger, V-Trigger, or you can connect both to separate jacks and have both available.


This module has 1 knobs:

  1. Threshold – This knob sets a threshold above which the Peak Selector will output a trigger.


No switches


Hooking it up is pretty simple. Connect a signal to a Signal In jack. Set the threshold to your liking. Connect the trigger to a module to control.

The original documentation suggests some interesting connections:

  • Triggering the synthesizer from a “click track” on a tape recorder(very old school)
  • You can connect a microphone (you may need a the pre-amp module) and produce a trigger from breathing or tapping the mic.
  • Connect a metal pad to the hot conductor of a piece of shielded cable and feed the other end into the Peak Selector. When you touch the pad, stray 60Hz hum will trigger the Peak selector.
  • Feed some white noise in and set the threshold appropriately.
  • You can create a trigger chain using an LFO.
  • A low pass filtered signal could produce triggers only on a bass line. High passed, on a high frequency line.



This module was originally built with carbon core, 5% resistors with one or two 1% metal film resistors. So, you have a wide range of options here. I recommend using 1% tolerance, metal film resistors everywhere, but the critical resistors are R37 and R38, input summing resistors. These should ideally be hand matched or purchased to 0.1% tolerance to insure consistent response between the inputs.


There are probably a billion different ceramic capacitors at a place like Mouser. Pick a capacitor that can fit the hole easily, typically 0.1 inch on centers.

Pick good quality electrolytics where designated. The 1.2 u will be hard to find. Use a Tantalum or a 1.0u electrolytic.


The original used 2N5172 NPN and 2N5138 PNP transistors. These are still available, but I could only find a “PN5138” which I think is the same transistor. In any event, you can use any standard NPN or PNP transistors and they should work.

For Q2 and Q7, the schematic shows two PN5138 transistors. The PCB is setup to accommodate either two discrete transistors or you can use a monolithic pair, like an SSM2220. Matching them isn’t critical, but it won’t hurt either. The discrete pieces are really fine.


Nothing special, 1N4148s are fine. Use any appropriate panel mount LED.


Your choice for your panel. If you use the panel I laid out, the holes and spacing will work for the Alpha 12 and 16mm pots. You can probably use nicer BTI, Bourns, etc. 9mm pots with “pot chiclets”


Use good trimmers, please. A good Bourns multi-turn trimmer like Bourns 3296Y series will fit the pad layout and work well.


For the panel I laid out, a good 3.5mm or 1/8 inch jack will work. I use the Switchcraft 42A Tini-Jax true 1/8 inch jack. These are switched jacks and they work with 1/8 inch plugs and 3.5 mm plugs.


I’m using an Electroswitch C5P0112N-A Mouser number is: 690-C5P0112N-A for the rotary switch. It can be set to any number of throws from 1 to 12.



I assume you know the basics of soldering. I like to insert the low lying parts first, like resistors, diodes, etc. After these, I install the IC sockets. Next capacitors, transistors, connectors. Use a good solder, either an organic flux, which you should wash regularly, or a no-wash flux.

Take a break every so often, wash off the flux if you are using a flux which required cleaning. Double and triple check orientations, pins, and solder joints.

Power Supply Regulation/Filtering:

Some additional comments here. These modules are tested to run on +/-12 VDC. The original power supply in the Synthasystem was +12/-10 VDC due to how Nyle designed the -10 volt section of the power supply, not for any magical requirement to have -10 volts.

The power/regulation section has 2 voltage regulators on it which can be set to +12/-10 (or +/-12 volts) depending on your needs. If you are coming from +/-15 volts, you need both regulators and you may as well set one to -10 volts.

If you are coming from +/-12 volts, technically you don’t need the regulators, but if you want, install the negative one and set it to -10 volts. The LEDs are not strictly needed. They are there to establish a base current draw so the regulators will work.

Important… if you don’t install the regulators, you have to install a jumper between pins 2 and 3 as shown on the Power/Regulation PCB or you won’t get power.



This PCB has four holes to allow flexible mounting configurations. The FPE Euro panel is setup to allow this PCB to be mounted parallel to the panel using some 3/4 to 1 inch (typical) standoffs. The mounting holes are connected to ground. The Power Regulation PCB will mount to this PCB using standoffs.


There is no calibration

Panel Notes:

There is nothing too special. I suggest using connectors on the PCB and jacks on the flying wires. The spacing and holes are setup for Alpha 16 mm or 12 mm pots. The jack holes are 0.25 inch in diameter.