Tag Archive for electronics

Project Ryu Lagger – Guitar Effect

Lagger Slow Attack Guitar Effect facebooktwittergoogle_plusredditpinterestlinkedinmailby feather

Hello,

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:

Lagger slow attack pedal diagram
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.

Lagger Slow Attack Signal

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.

Speaker delay circuit schematic

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.

Lagger Slow Attack guitar pedal

 

Below you can find the schematic for the Lagger:

lagger slow attack guitar schematic

U5 shows as TL071 but you need an opamp with higher output current sink capability. Something like HA17358 with 50mA capability is good:

HA17358

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:

Lagger Slow Attack Guitar Effect PCBLagger Slow Attack Guitar Effect PCBLagger Slow Attack Guitar Effect PCB

Here are some pictures with Project Ryu Lagger:

Lagger Slow Attack Guitar Effect

Lagger Slow Attack Guitar Effect

Lagger Slow Attack Guitar Effect

Lagger Slow Attack Guitar Effect

Lagger Slow Attack Guitar Effect

Lagger Slow Attack Guitar Effect

Lagger Slow Attack Guitar Effect

 

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.

 

Balanced Line Attenuator バランスラインアッテネータ

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Hello,

In a home recording environment equipment often doesn’t come in a large variety because of either limited budget or limited space… or both. I am presenting here an balanced attenuator which comes in between fixed gain preamp and recording device/soundcard.

The purpose of this device is to adjust the level and monitor it to prevent saturation of the next stage in the recording chain. It uses a L-pad followed by a balanced buffer stage. The attenuation steps are 0dB, -3dB, -6dB, -9dB and -12dB.

The meter section uses a microcontroller with a 10 bit ADC. It monitors both polarities of the signal and detects the peak within a frame of 1000 samples. ADCs samples the signal every 12us.

Balanced line attenuator schematics バランスラインアッテネータ

 

In the schematics above J7 will be used later on future revisions to indicate symmetry in the balanced signal.

J3 will connect the attenuation selector.

There are certain modifications i did the initial schematic tho. R7, R8 must be of greater value. At least 100k. With 100k you will get a -0.8dB signal at 0 dB setting.

The circuit is pretty straightforward, you can use any quad opamp chip for U3 as long at it operates from a 9V single supply. I do recommend a FET input opamp if R7 and R8 >= 100k as they tend to have lower noise than bipolar with high input impedance.

U2 i used a LM324 as it allows operation at 5V single supply. U2:C is used to bias the ADC inputs at 2.5V.

I will explain how to rectify the signal with a PIC in a future project but you will find the hex file for this one at the end of this article.

Here are the PCB drawings:

バランスラインアッテネータ Balanced Line Attenuator

pcb top layer

バランスラインアッテネータ Balanced Line Attenuator

pcb bottom layer

Balanced Line Attenuator バランスラインアッテネータ

pcb top silk

 

Warning: NONE of the PCB images are mirrored!

Here is how the PCBs turned out:

Balanced Line Attenuator バランスラインアッテネータ

Balanced Line Attenuator バランスラインアッテネータ

Balanced Line Attenuator バランスラインアッテネータ

Balanced Line Attenuator バランスラインアッテネータ

I used a rotary switch to select the attenuation levels. For 0dB you can just omit R15. Use POT2 to calibrate 0dB on your meter. I usually set it to 0dBV.

Balanced Line Attenuator バランスラインアッテネータ

Balanced Line Attenuator バランスラインアッテネータ

 

After building the first unit i made some measurements. I used 5% tolerance resistors so i wanted to see if the attenuation levels are correct. Here are the results:

Balanced Line Attenuator バランスラインアッテネータ

 

-6dB and -12dB settings are about 1dB off and it seems -3dB setting is also a bit off. For -12dB i soldered a 47k resistor in parallel with the 6k8 one and for -6dB i soldered one 100k resistor in parallel with the 22k. For -3dB i soldered a 470k resistor in parallel with the 47k one. Results were much better:

Balanced Line Attenuator バランスラインアッテネータ

 

I will be making kits available for this device with PCBs and programmed microcontroller as well as fully built units. Please subscribe to receive more details about this offer in the next newsletter.

Below you can find the hex file:

PrjRyu Balanced Attenuator

Thank you for visiting

 

TRS to XLR Interconnect Cable

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Hello,

If you have been around audio enough you know that accessories, while many times ignored, can become really costly. Interconnect cables are easy to built and you can apply simple techniques to make them much better than the more expensive commercial alternatives.

In this article i will make a TRS – XLR balanced line interconnect. The connection follows the rules described below:

TRS      TO        XLR

Tip                   Hot

Ring                Cold

Sleeve            Gnd

In choosing the cable i recommend to look for braided shield and cloth layer. These features will help get a reliable cable.

TRS - XLR Interconnect Audio Cable  TRS - XLRインターコネクトオーディオケーブル

TRS - XLR Interconnect Audio Cable  TRS - XLRインターコネクトオーディオケーブル

The picture above depicts how i like to prepare the cable for the TRS plug. You can see the braided shield which will connect to the sleeve of the TRS plug.

TRS - XLR Interconnect Audio Cable  TRS - XLRインターコネクトオーディオケーブル

TRS - XLR Interconnect Audio Cable  TRS - XLRインターコネクトオーディオケーブル

TRS - XLR Interconnect Audio Cable  TRS - XLRインターコネクトオーディオケーブル

TRS - XLR Interconnect Audio Cable  TRS - XLRインターコネクトオーディオケーブル

In the picture above you can see my favorite way of securing the plug by using the cloth to tie it around the sleeve terminal.

TRS - XLR Interconnect Audio Cable  TRS - XLRインターコネクトオーディオケーブル

TRS - XLR Interconnect Audio Cable  TRS - XLRインターコネクトオーディオケーブル

I always use heat tube to isolate the shield connection of the cable when using XLR plugs. The XLR terminals are even in height so the shield will have a few mm of bare wire. I want to avoid it to touch the plug chassis on its own so i isolate it.

To solder the cable to the plug it is a good practice to hold the plug vertically like in the picture above.

TRS - XLR Interconnect Audio Cable  TRS - XLRインターコネクトオーディオケーブル

And the finished cable.

 

Thanks for visiting.

Monitoring Amplifier モニターアンプ P3: Speaker Coupling Delay

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Hello, こんにちは,

私の日本語があまり上手くありませんが許して下さい.

In this article i will present a simple delay circuit that will be used to couple the speakers to the amplifier after a certain settling time was allowed. The circuit also allows for to be controlled by an external 5V logic signal. This can be used to decouple the speakers in case a fault is detected.

これは、アンプがオンされたときにスピーカーを保護するためのDELAY回路であります。それが徐々にコンデンサを充電することによって機能します。コンデンサ電圧が一定値に達したときには、リレーを切り替えります。

The circuit schematic is presented in figure 1 and as you can see it uses just discrete components. It is a linear voltage ramp generator that commands a power transistor. The current charging capacitor C1 and the capacitor’s value are the parameters that set the ramp’s slope.

POT1は、時間遅延を調整します。

Speaker delay circuit schematic

Figure 1

In figure 1 Q3 forms a constant current source adjustable via POT1. R1, R2, D1, D2 set a voltage on the base of Q3 of about 5.4V and this means about 6V voltage drop over R6 and POT1 series connection. Assuming Ic3 = Ie3=Icharge,

Icharge = 6V/(R6+POT1)

Lets set POT1 at 90kohms for ease of calculation. This gives R6+POT1 = 100k.

Icharge = 60uA

Since Q3 is in saturation mode we can assume a voltage drop over C-E of about 0.5V so the voltage over the capacitor Vc1= 5.5V. The time for the capacitor to be charged to 5.5V is defined by the below equation:

T= (C1*Vc1)/Icharge = 0.91 second

上記の式は充電時間コンデンサを計算します。

Q2 buffers the voltage across C1 capacitor. It also provides a small delay until Vc1 reaches around 0.6V to bias Q2’s B-E junction. Q1 acts as a switch and when turned on via a 5V signal it absorbs most of the current from Q3 and capacitor will not be charged.

Q4 has the role to drive the relay. It is a small power transistor and it’s enabled via POT2. This variable transistor has the role to set the on/off steps based on the ramp voltage. If too low the relay will be on very fast and stay on if too high the relay will never activate.

Speaker delay circuit schematic

Figure 2

In figure 2 the time step is 200ms and we can see the ramp is about 1s long, very close to what we calculated. The blue trace is the Fault signal. When a 5V pulse is present the capacitor C1 is discharged very fast (pink trace) and speakers are decoupled (green trace). When the fault signal goes to logic low or ground the ramp generator shortly starts the process and enables the relay after about 1 second.

Speaker delay circuit schematic

Figure 3

 

Speaker delay circuit schematic

Figure 4

Figure 3 shows how the relay is activated faster if the POT2 is set too low in value and figure 4 shows a correct setting. The yellow trace represents power switched on.

Below you can see the circuit in the right side of the board.

Speaker delay circuit schematic スピーカ遅延回路図

 

Parts list does not contain the connectors in the schematic because the circuit most likely will be used as a part of something bigger:

Part Quantity
BC549 2
BC559 1
BD139 1
1N4001 3
R 12K 5% 0.25W 3
R 10K 5% 0.25W 2
C 10u 25V 1
POT 250K 1
POT 10K 1
RELAY DPDT 1

Thank you for visiting,

ご覧いただきありがとうございます。

LM13600: Noise Gate Project ノイズゲートプロジェクト Part 1

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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.

LM13600 noise gate project

 

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.

2SK30 FET noise gate module

2SK30 FET noise gate module

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.

LM13600 VCA schematic

LM13600 VCA schematic

LM13600 VCA Test

LM13600 VCA Test

Gain vs Control Voltage Plot

Gain vs Control Voltage Plot

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.

LM393 Dual Comparator

LM393 Dual Comparator

LM13600 Noise Gate Temp Schematic

LM13600 Noise Gate Temp Schematic

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.

LM13600 Noise Gate Module

 

Dual power supply

Dual power supply

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.

Scope view of pink noise through gate

 

Thank you for visiting.

ご覧いただきありがとうございます。