Here it is, the pedal version of Project Ryu Lagger. For more details on this pedal check the first article Ryu Lagger.
Tag Archive for guitar pedal
Do you remember BOSS Slow Gear pedal? If your a guitarist you most likely do or at least you’ve heard of it. It was a great pedal sold from 1979 to 1982 and it was made in Japan. The pedal would cut the attack of your notes giving a swelling sound. It god famous for making the guitar sound kinda like a violin.
I always liked that effect and i even made a clone a few years back. It is based on a 2SK30 JFET and it was a pain getting these transistors. It was a lot of fun though and i though i should make a Project Ryu swell effect pedal and so LAGGER was born!
Recently i worked on a few projects with LM13600/LM13700, one of them is a nice noise gate / compressor unit which i will present at a later date, and i really like the VCAs that can be built with these chips.
To cut the attack of a note and then swell the volume basically we need a triggered fade in effect. This means that we need to control our VCA with a rising voltage using what i call a ramp generator.
In a previous article (Monitoring Amplifier モニターアンプ P3: Speaker Coupling Delay) i described the circuit of such a ramp generator and it even has a command input. I will use this circuit with the LM13600 VCA all controlled digitally with a PIC18f1320.
Below you can see the block diagram of the Lagger:
The input is fed into an ADC channel to be rectified and averaged in order to detect when a note is played. Once it is detected, the ramp generator is triggered and provides the control voltage for the first VCA.
Since LM13600/LM13700 is a dual amplifier the second one is configured as a VCA with manually set control voltage. In the picture below you can see how the circuit works. The top signal is the input signal, the middle signal is the output of the ramp generator and the bottom signal is the trigger.
There is a problem with using the ramp generator circuit this way. The capacitor is discharged too quickly when the trigger is interrupted and this causes an audible thump noise when trigger goes off. Looking below at the schematic we can see the discharge current goes through CE junction of Q1.
We can lower this current by inserting a resistor between ground and Q1’s emitter but in our specific application that will cause an offset and the output will not be totally silent in absence of input signal.
Another way to solve the problem is by paralleling a capacitor with R3 (Q2’s emitter resistor) This will cause a fade out effect and eliminate the thump noise.
Below you can find the schematic for the Lagger:
U5 shows as TL071 but you need an opamp with higher output current sink capability. Something like HA17358 with 50mA capability is good:
Trigger for the ramp generated is created when the microcontroller detects a signal from guitar. In my last article i have explained a way to rectify and average an analog signal using ADC and software. If the input level is higher than a set threshold level then ramp generator is triggered.
In the first units the middle pot was used to set a sustain period but that was changed to sensitivity control as it proved to be much more helpful.
J1 is a push-button which will generate an interrupt for the microcontroller and provide a true bypass via the SPDT relay.
You will notice some unusual supply voltages. For example the microcontroller’s Vdd is set to GND and Vss to -5V. This is done in order to provide correct trigger levels and avoid using other active components to shift the level.
Below you can see the PCB for the unit:
Here are some pictures with Project Ryu Lagger:
Here is a short video with the unit in action:
I will be supplying the hex file for the PIC18f1320 microcontroller in my next newsletters so if you want to built the unit and your not a subscriber yet please use the top right form to subscribe.
Also in my newsletter you will find offer for kits and complete units for those who don’t do well with electronics.
Thank you for visiting.
Here is a noise gate module built around LM13600. You can use the newer and better LM13700, i chose LM13600 because i already have a few of them from National Semiconductor. I use these modules to clean up sound in audio surveillance applications but also can be used with music instruments like electric guitars.
In the past i was using a FET transistor, mostly 2SK30, as a variable resistor and create a voltage controlled… voltage divider hehe. However better performance comes from using a VCA (Voltage Controlled Amplifier) not to mention the versatility of having the entire module in the form of a integrated circuit.
In LM13600 we have two operational transconductance amplifiers giving the posibility to varry the current through the input stage long tail pair. Its input will be a voltage and output will be current so you can find these devices named OTA (Operational Transconductance Amplifier) or VCCS (Voltage Controlled Current Source). They are very handy when you need to adjust gain of an amplifier dynamically.
In a noise gate we want to pass all signal with an amplitude higher than a settable threshold and block all signal with lower amplitude. What we’ll do is take the input signal rectify it, compare the result with our threshold and then modify the gain of the amplifier based on the comparator output.
As a first step i built the VCA around LM13600 as i wanted to check how the amplification works. You can see the schematic (pretty much the one from datasheet) and construction. I was able to trace the gain vs control voltage plot and it shows a pretty linear function.
Looking at the above chart we can see that if our input signal amplitude is below noise gate threshold then we need to set the control voltage to -15V (with +/-15V supply) and if it is above threshold ideally we will need 15V control voltage.
To rectify the input signal i use a two opamp schematic fairly common discussed on ESP website and other materials. The DC voltage is then compared with our threshold with a LM393 dual comparator. Supply voltage for the LM393 is +/-15V so output will swing close to these values providing the control voltage.
Before the rectifier you can see an amplifier, this is used to adjust sensitivity. Threshold is set by R16. C3 C4 are very important as they reduce artifacts caused by ripple in the rectified signal. Even so as it is there are a few issues when the signal level is equal to the set threshold level but solution for this will be presented later.
The voltage from the LM393 output can be passed through and integrator and thus adjust the attack time. This can be a very cool effect for musical instruments as it provides a swell effect similar to a volume pedal.
Circuit works of course will be improved pretty much in next articles so hope you will visit again. Below you can see a scope trace with TrueRTA (the scope feature is free). You can see pink noise signal and only peaks with an amplitude higher than my threshold are passing through.
Thank you for visiting.