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JH. Subtle Chorus

The "Subtle Chorus" is a variable project consisting of 3 different PCBs that can be combined for various functions.

Subtle Chorus Main Board

Main Board Schematics, Page 1: PSU and LFO (HA1475 version not shown separately)
Main Board Schematics, Page 2: Input Section (HA1475 version not shown separately)
Main Board Schematics, Page 3a: Output Section (HA1457 + Transistors version)
Main Board Schematics, Page 3b: Output Section (general opamp version)
Generic Main Board Component Overlay as silkscreened on PCB
Main Board Component Overlay with reference designators

Building a version without exotic components, and 600 Ohms output impedance:
Main Board Component Overlay, TL072 OpAmp, AC Power Supply Version
Main Board Component Overlay, TL072 OpAmp, MOTM Power Supply Version
Main Board Component Overlay, TL072 OpAmp, Synthesizers.com Power Supply Version

Building a "Vintage Version":
Main Board Component Overlay with HA1457W OpAmps and Power Transistors
All SIL ICs are HA1457W.
Transistors marked "N" are 2SC495-Y (as in the vintage original - not tested by me!) or BD139.
Transistors marked "P" are 2SA505-Y (as in the vintage original - not tested by me!) or BD140.
(Versions without power supply not shown separately - similar as with TL072 opamp versions.)

Main Board Bill Of Materials (TL072 version)
Main Board Bill Of Materials (Vintage version)

BBD Board

BBD Board Schematics, Page 1
BBD Board Schematics, Page 2
BBD Board Component Overlay, Component Values
BBD Board Component Overlay, Reference Designators
BBD Board Bill Of Materials

Phase Delay (Tau) Boards

For the Dim T or Dim TD version, you need two PCBs from the Tau Phaser project.
You can either use two complete Tau Phasers - then you put them in Vibrato mode, where the direct signal isn't mixed to the all pass filtered signal in the (main) output.
Or you can build dedicated Dim T PCBs, omitting a lot of components on the Tau boards. (You don't need an LFO, no wet/dry mix, no resonance, no on-board PSU). Here's a component overlay for converting a TAU PCB into a Dim T PCB. The picture shows a CA3046 version. You can use SSM2210 or LM394 transistor pairs instead, just as in the ordinary  Tau project.

NEW:  Off-Board and Inter-Board connections

Connections necessary for all versions (except standalone BBD board)

Wiring of Mode switch (6 position Rotary), Bypass switch, Remote Bypass jack, and Bypass LED to Main Board
Audio Inputs and Outputs (Unbalanced outputs)
Audio Inputs and Outputs (Balanced XLR and unbalanced 1/4") - CAUTION: XLRs are not floating balanced outputs - do not connect to unbalanced inputs!
Audio Inputs and Outputs (Balanced XLR only) - CAUTION: XLRs are not floating balanced outputs - do not connect to unbalanced inputs!

Board-to-Board Connections for Dim D version

Connections for DC, LFO and Audio between Main Board and BBD Board in Dim D mode

Board-to-Board Connections for Dim T version

This describes the connections with modified Tau PCBs!
Connections for DC, LFO and Audio between Main Board and two modified TAU Boards

Board-to-Board Connections for Dim TD version

This describes the connections with modified Tau PCBs!
Connecting Main Board + BBD Board + 2 modified TAU Boards

Off-Board Connections for Dim T version with inset points for two external Tau Phasers

Only a Main Board with insert points for two external standalone Tau's

Board-to-Board and Off-Board Connections for Dim TD version with insert points for two external Tau Phasers

Main Board and BBD board internal; two standalone Tau's connected with send / return jacks

Make an ordinary true -stereo chorus from a single BBD board

voltage controlled Chorus Rate and Depth, pluse switchable phase inversion (should be able to emulate the classic Juno chorus sounds to some degree - not tested by me, though.)

Power Connections and Heat Sinks

As usual, I only give some general hints about power supply and heat sinks.
Current consumption depends a lot on what version you build: how many PCBs, and whether you use power transistors for the outputs on the Main Board or not.
I have used a 15V AC, 800mA wall wart to supply a Dim TD (4 boards),  TL072 version (i.e. *no* power transistors), using small on-board heat sinks for the LM317 and LM337 on the Main board, so you can use this as a good starting point.
The same wallwart will also work for a "Vintage" version, but you need bigger heat sinks in that case. (LM317 and LM337 are located close to the enge of the Main Board, so it's easy to fit a large heat sink here. But there must be electrical *insulation* between the regulators and the heat sinks in that case!
A "real" transformer with 2 separate 15V ... 18V windings is better - but I only recommend to work with transformators if you're skilled in working with mains voltage - mains voltage can be lethal.
In any case, when you're building something  using my PCBs and/or my descriptions, *you* are responsible for any risk and damage. Check that the regulators / heatsinks don't get too hot, for instance.
If in doubt, get a professional stabilized +/-15V DC power supply and build the "MOTM version" or the Main Board which doesn't have an on-board PSU. (The other boards are always powerd from the Main Board.)
General connection scheme for AC supply is shown here (3 options).


Prototype
Audio demo's were made under these conditions ...

Main Board detail view (Vintage Version)

Main Board, TL072 version (no power transistors etc.)

Open Prototype, "TD" Version (Main Board + BBD Board + 2 Tau Boards)

Audio Demos

Classic Dim D modes 1 ... 4, plus two extra modes 5 and 6
Oberheim OB-8 Brass sound
(starts dry, then Dim D modes 1 ... 6 are turned on, with switching back to dry between each mode)
Oberheim OB-8 Percussive sound
(starts dry, then Dim D modes 1 ... 6 are turned on, with switching back to dry between each mode)

Vocal demos:
Bypass mode
Mode 1 (switched on and off)
Mode 2 (switched on and off)

Dim T (with Tau boards instead of BBD boards)

CS-80 dry and then Dim T effect switched in (*.wav file; external link)
(Download 18MB *wav file with longer Dim T demo here.)

Demos with finished Subtle Chorus TD prototype

JH-3200 thru Subtle Chorus - bypass and Dim D Mode 4
JH-3200 thru Subtle Chorus - bypass and Dim T Mode 4
JH-3200 thru Subtle Chorus - various D and T modes


(will be continued.)

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