TWIN PEAKS TREMOLO

Build Guide for v3.1

Revision 3.1 David Rolo 2017

Reference Quantity Value Description Switches Multiplier 1 1 pole 6 pos. rotary switch Shape 1 1 pole 8 pos. rotary switch Trem Type 1 2 pole 4 pos. rotary switch Tap Switch 1 Normally open Momentary Switch single pole NO Capacitors C18, C19 2 22p Ceramic Capacitor C5, C8 2 270p Ceramic Capacitor C4 1 4n7 Film Capacitor C3 1 6n8 Film Capacitor C1 1 100n Film Capacitor C10, C12, C13, C16, C21, C22, C23, C24, C25, C26 10 100n Ceramic Capacitor C20 1 470n Ceramic Capacitor C9 1 1u Film Capacitor C6, C7 2 10u Non Polar Electrolytic Capacitor C17 1 47u Electrolytic Capacitor C11, C14, C15 3 220u Electrolytic Capacitor IC's U1 1 TL074 OpAmp U2 1 LM358 OpAmp U3 1 TAPLFO Microchip Diodes D1 1 1N5819, 1N5817 Schottky Diode D2 1 1n4001 Diode, optional, see notes Tap Led 1 LED Light Emitting Diode LED1 2 LED with max. 2V fwd voltage Light Emitting Diode Misc T1, T2 2 78L05 Fixed Voltage Reg. XTAL 1 20 Mhz Crystal OPTO1, OPTO2 2 VTL5C1 or self rolled LED/LDR Optocoupler Resistors R13, R14, R15 3 33 Resistor R47, R48 2 100 Resistor R21, R22, R23, R24, R25 5 1k Resistor R9 1 3k3 Resistor R32, R33, R41 3 5k1 Resistor R18, R19, R20, R27, R28, R29, R30, R31, R34, R35, R36, R37, R38, R39, R40, R42, R43, R44,R45, R46

20 10k Resistor

R3, R4, R5, R6 4 15k Resistor R11, R12, R16, R17 4 22k Resistor R26 1 24k Resistor R7, R8 2 56k Resistor R1, R10, R2 3 1M Resistor Potentiometers Tone 1 10k lin Potentiometer Rate 1 10k lin Potentiometer Depth 1 10k lin Potentiometer Symmetry 1 10k lin Potentiometer Volume 1 50k Trimmer Offset 1 20k Trimmer Bass 1 20k Trimmer Treble 1 20k Trimmer

The pots best suited are Alpha 16mm Right-angle PCB mount Pots:

And the mini rotary switches should be this type:

However, the PCB was laid so you could use a potentiometer instead of the 1p6t and 1p8t rotary switches, which are a little harder to find. If you go with that solution, use 10k lin pots like the other ones in the parts list. Use a 3k6 for R26 instead of 24k and do NOT populate these resistors: from R27 to R41. Of course you can use other parts and not mount them on the PCB. Then you will probably need a bigger enclosure.

Notes:

Use sockets for the IC’s, at least for the TAPLFO

Populate the boards with all parts, starting with the smallest to the tallest. Solder in the pots and rotary switch last.

D2 can actually be bridged, unless you feel that the non-modulated parts in the Bass only and treble only modes are too loud compared to the modulated signal.

R19 is the current limiting resistor for the Tempo indicating LED. The indicated value of 10k is what I am using with white super-bright LED’s. Choose the value that will be best for your particular LED. I would recommend a super-bright as they will draw less current and reduce the chances of inducing ticking.

C26 is used to smooth out the sharp corners of the LFO signal and remove some spikes that can produce audible clicks especially with sharper edged wave shapes. You might not necessarily need it. It depends on your particular Optocoupler and whether you like the signal to be chopped real hard or not. I suggest socketing that cap, trying without it first and then start with a low value like 20n until you find a value that removes the tick but does not round off the square wave too much.

C3 and C4 define the High Pass and Low pass cut off frequency. If my calculations are right, with the values indicated in this document, the Low pass cuts at 664.3 Hz and the Hi pass at 780.6 Hz. You can of course experiment with other values.

LED1 is there to increase the output of the voltage regulator (5V + the Forward voltage of the LED). Try to find a LED with no more than 2V FWD voltage to make sure the voltage regulator still has enough drop out voltage to operate correctly.

The IN and OUT pads on the top and bottom of the PCB’s are just to route the input and output from your jacks. You don’t have to necessarily use them, I just find it convenient.

C6 and C7, for safety’s sake these should be bipolar/non polar electrolytics. Though on my unit I am using regular caps for a while and nothing happened (yet)

Biasing:

1) Turn the DEPTH pot fully counterclockwise, SYMMETRY and TONE in middle position

2) Start with the Offset, Bass and Treble trimmers fully counterclockwise Leave the volume trimmer at midpoint for now.

3) Start by measuring the supply voltage at measure point B1

4) Now measure the voltage at B2 and B3 and adjust the Offset trimmer until you get half of the voltage you

measured on B1. This action will center the LFO signal (originally 0-5V) around the bias voltage of U2.

5) Now adjust the Bass and Treble trimmers to have a good balance between bass and treble. As you turn clockwise, the optocoupler gets more current and the signal gets louder. But increasing the current also increases the chance of getting audible clicks, especially with sharp wave shapes. So it’s best to be conservative and compensate for the volume with the volume trimmer.

6) Adjust the volume trim pot T1 to have the same level between effect OFF and effect ON (or any level you like).

That’s it! Now trem’ away ;-)

Controls:

Rotating from CCW to CW, the rotary switch selects the tremolo modes:

Bass and treble modulated in phase (normal tremolo)

Bass and treble modulated out of phase (Harmonic tremolo)

Bass modulation only, with fix treble

Treble modulation only, with fix bass

Tone : adjusts the balance between the bass and treble portions. Turn it fully CCW and only the bass comes out. Turn it fully CW and you get only treble. In the middle you get both. If you turn down the depth completely you can use the tone knob as a sort of EQ

Depth: Allows setting the depth of the modulation

Rate: Sets the speed of the modulation

Symmetry: Allows changing the ratio between the upper and lower wave of the LFO signal For example, when using the square wave, you can set whether the “off” or the “on” periods are the longest.

This diagram shows the effect of the symmetry pot on some wave shapes:

Source: http://www.electricdruid.net/datasheets/TAPLFO2Datasheet.pdf

Shape: This knob allows selecting one of the 8 available modulation wave shapes:

Source: http://www.electricdruid.net/datasheets/TAPLFO2Datasheet.pdf

Multiplier: allows to select the multiplier that will be applied to the tapped tempo Source: http://www.electricdruid.net/datasheets/TAPLFO2Datasheet.pdf

This is a drill template I have been using but take your own measurements to make sure everything fits (before committing to drilling your box … ;-)