Build the LushOne EchoThe LushOne Echo is straightforward to build but it does have quite a high component count. It is recommended that you have some experience in building electronics before starting on this kit. The instructions show all the building steps but don't explain basic techniques like how to solder.
The LushOne Echo build instructions are provided as a PDF file.
Schematic diagrams (PDF)
Notes on the Design
The following images show where the main functional blocks of the LushOne Echo appear on the schematics.
The "DelayAmps" sheet contains the voltage controlled amplifiers (VCAs) for the Echo and Feedback as well as the buffer amplifiers for the input and output.
The VCAs start with a voltage-to-current converter which then drives an LM13700 acting as a current-controlled amplifier. The voltage to current converters use positive feedback from the control-current input pin on the LM13700 to make the operation independent of the negative supply voltage.
The "Delay" sheet contains the digitial delay based on the PT2399 and the circuit to allow the delay to be controlled using a CV. The circuit around the PT2399 is pretty much straight from the datasheet with the exception that the resistor on pin 6 that normally controlls the delay duration has been replaced by the leg of a voltage-to-current converter with an exponential characteristic. The exponential characteristic allows a more natural feel to the control.
The exponential converter is a standard design that uses the charteristic of a transistor response curve. The exponential converter is fed from an opamp that sums the control inputs and also deals with the PT2399 power-on issue. The PT2399 has an odd feature that it can be damaged if it is powered on with the delay control set in a low range. Some designs avoid this problem by not allowing the lower part of the PT2399 range to be used, but I wanted to make the fullest use possible of the chip. To avoid the power-on problem the circuit around Q403 will override the normal control inputs and force the PT2399 to a long delay for about half a second after power-on. Because the Q403 circuit shares the same power supply source as the PT2399 we know they will both be powered on together.
The envelope generator is on the "envelope" sheet. The main constraint with the envelope generator was that I wanted to use only the two "spare" op-amps left after implementing the rest of the circuit. In the end I picked a design from a synth published in the magazine Electronics Today International (ETI) in the 1980s. For my purposes the circuit worked OK as-is.
The circit is constructed as a precision (zero offset) rectifier followed by a buffer/low pass filter.
Use the LushOne Echo