Trying the Sitar

Posted: May 19, 2015 in Uncategorized
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I’ve always been entranced by the sound of the sitar, and wanted to try it for myself. If you do some research on beginner sitars, you will find a lot of people pontificating in a most discouraging way, e.g. by saying that it’s incredibly hard and painful to play, that every sitar costing less than $1000 is rubbish, and so on. You get the picture.

Casting these admonitions aside, I ordered a 1/2 size sitar on Amazon. It’s probably about 3-4 feet total length.


The 1/2 size sitar. This has 7 main strings, and 11 sympathetic strings. There are two toombas: one at the base (the big, round object that is made from a gourd/pumpkin), and the one on the neck, which looks a bit like an upturned salad bowl. Never rest the sitar as shown!

Although it was advertised as “blemished”, what I got was an unblemished model. It arrived well packed, inside a soft carry bag, and complete with a set of new strings, some mezrabs (the little wire things you put on your forefinger to pluck the strings), a learning sitar book, and another soft cloth bag.

There are seven main strings that are played, and a set of 11 “sympathetic” strings, which lie underneath the main strings, and aren’t played, but vibrate in sympathy with the main strings. I spent quite some time tuning *all* the strings to the Ravi Shankar C# settings, which you can find online. I used an Android tuning app to do this. Take extreme care, as it’s easy to over-tighten a string when tuning it, and thus create a crack around the tuning peg hole (I did this on the third main string, and had to repair the crack using wood glue and clamps overnight – now it is fine). Another thing that can happen is that a string can break – this also happened on mine, just after I started tuning one of the main strings. Replacing it was easy, but make sure you replace the string with one of the correct gauge (I used a micrometer to measure the snapped string diameter, and then selected a new string of the same diameter from the set sent with the sitar).

Another tuning tip is to remove each tuning peg carefully and rub some pavement chalk on it, before carefully reinserting it – this helps to avoid the peg slipping. After tuning all the strings, the effect is striking – if you pluck any of the main strings, the whole instrument resonates and produces that very characteristic buzzy sitar sound. With the strings un-tuned, the sound is dull and lifeless.

What is great about beginning the sitar is the fact that it sounds good even when a novice is plucking it, unlike most other instruments (the violin is a particularly bad offender). So, you can sit plucking and strumming and bending notes randomly on the sitar and it actually sounds very pleasant.

One other issue I’ve found is that the strings dig deeply into your finger ends, when you press them against the fretboard. It’s like playing an egg-slicer! The first main string (tuned to F# in the Shankar tunings) is the one that sees most finger pressing action, and it is thin! After a while of playing, it becomes almost unbearable, so I’m hoping that I develop some callouses soon.

This is an LT-70 that at one time was part of the Mitsubishi “Audio Intelligent System Model DA-L70/LT-70”. I am trying to get it to work standalone.


On the back panel, there are phono outputs for the cartridge, and an 8-pin DIN plug that connected to the rest of the system.

DIN plug

The wiring is as follows:

  1. Pin 1: Yellow -12V
  2. Pin 2:  N/C
  3. Pin 3: White (“AF”?)
  4. Pin 4: Orange +12V
  5. Pin 5: Black (“SYNC”?)
  6. Pin 6: Braid 0V
  7. Pin 7: Red (“STP”?)
  8. Pin 8: N/C

This plug is marked “TO CACEIVER” J106 on the following schematic for the turntable:

LT-70 schematic (part)

The same plug is marked “PL CONT” on the schematic for the main unit:

DA-L70 Schematic (part)

Working from the schematics, I saw that the turntable uses a -12 0 +12 power supply, which I’ve duly connected to pins 1-6-4 on the plug (29,28,27 on the turntable schematic). Sure enough, the unit powers up, the track indicator 7seg LED lights up, and I can operate the tray using the “Open” button on it, the fwd/rev buttons that move the cartridge left/right, and the various programming buttons on the tray (track select, program, etc.)

However, the turntable never spins, the “Start” button has no effect. I think this is because I am not providing the correct signals on the pins marked “SYNC”, “AF” and “STP” (shown on the main unit schematic).

Two of these three pins (24 & 25) are connected to IC151, a BA612 quad driver, on the turntable circuit board: 24 seems to be an input signal to the turntable (since it goes to a BA612 driver input, pin 2). The other, 25, looks like an output signal from the turntable to the main unit, and measures +12V when the turntable is powered up. Finally, pin 26 also looks like an output, some sort of current source from Q221?

EDIT (April 2016): I don’t know what I was doing wrong above, but I just checked three years later, and the unit works fine using the connections specified above. I was able to play and listen to an LP without problem.

Summary: open the DIN plug connector on the cable coming out of the unit, and connect the following wires to a 12-0-12 power supply.

  • Yellow to -ve 12V
  • Orange to +ve 12V
  • Braid to Ground

Connect the RCA plugs (left and right) to your amplifier.

The red wire, if touched to +12V, will stop playback, but it’s not required.

Swedish Crepes, courtesy of IHOP.

Posted: September 25, 2013 in Uncategorized
Untitled by snigfargle
Untitled, a photo by snigfargle on Flickr.

Before the days of integrated circuits …

The Tek 575 Transistor Curve Tester can be used to measure tubes like the twin triode 12AX7 (which has a 12V heater requirement) and the 6DJ8 (which uses 6V at the heater). The 575 can sweep collector (plate) voltage between 0 and 200 Volts, which is a useful range for these tubes. All the 575 is missing is a heater supply, and a suitable tube socket.

I constructed a tube adapter that can plug in to the banana plug sockets on my 575’s DUT panel, using a panel from a parts 575 I acquired years ago (to replace the bad CRT tube in my original 575). The angled faces on the panels combine to result in a horizontal surface, which I used to mount the tube socket (B9A), a pair of terminals for an external heater supply (I used a 6VDC wall wart adapter rated at 300mA), and a single pole double throw (SPDT) switch to select between 12V and 6V tube types.

Here is the completed adapter, measuring the transfer curves for a 12AU7A dual triode.

Tektronix 575 Tube Adapter

One convenient aspect of the wiring in the adapter is that the tube’s two triodes can be compared easily by flicking the 575’s transistor A/B select switch. This allows an instant comparison of the transfer curves, and shows how well (or badly) they match.

This is a quite rare device I picked up on Ebay some years ago, for testing transistors and diodes, including tunnel diodes.

SECO Model 250 Transistor Tester

 SECO 250 Transistor Tester

The instructions are on a label pasted to the inside of the cover, and are unfortunately in a sorry state.

SECO 250 Instructions

Here’s a better image from a recent (2012) Ebay auction for the same type of tester:

Instructions (found elsewhere)

Instructions (found elsewhere)

This is a project I’m working on: a six-footed robot controlled by an Arduino processor.

The Arduino is a Duemilanove with a BMA180 accelerometer shield attached (this is used for dead-reckoning of the robot’s movement). There are six “legs” using twelve servos (HobbyKing HK15138 rated at 3.8kg @ 5V) arranged radially in pairs around a central platform. The upper servo on each leg is mounted horizontally and controls the leg twist. The lower servo is mounted vertically and has a short dowel foot that can rotate in the vertical plane.

The servos are powered from a separate 5Volt high current supply (from an old Sun desktop workstation) that can deliver several amps. The servos are attached to a servo board made from a small piece of Veroboard which shares a common ground with the Arduino.

The Arduino code uses the servos.h library to position the servos. Here is the code:

// Control code for the hexapod
// JJB 2012


Servo legServo[6];
Servo footServo[6];
// angles for each foot servo so that the foot is vertical
int zeroFoot[6] = {60,90,100,95,95,95};
// angles for each leg servo so the servo arm is at right angles to the platform
int zeroLeg[6] = {120,100,95,90,110,100};
int maxangle = 45;
int NLEGS = 6;

void setup() {
Serial.println("Attaching servos:");
for(int i=0;i<NLEGS;i++) {
int ileg = 2*i+2;
int ifoot = ileg+1;
Serial.print("Leg ");
Serial.print(" Leg servo pin ");
Serial.print(" Foot servo pin ");

void centreServos() {
Serial.println("Centre servos");
for(int i=0;i<NLEGS;i++) {

void crouch() {
for(int i=0;i<NLEGS;i++) {

void stand() {
for(int i=0;i<NLEGS;i++) {

void liftFoot(int i) {

void rotateLeft() {
Serial.println("Rotate Left");
for(int i=0;i<NLEGS;i++) {

void rotateRight() {
Serial.println("Rotate Right");
for(int i=0;i<NLEGS;i++) {

void liftFootSet0(int dir) {
// dir = +1 forward, -1 backward
void liftFootSet1(int dir) {
// dir = +1 forward, -1 backward

void lowerFootSet(int i) {

void swingLegSet(int i) {

void rotateLeg(int i, int dir) {

void tripodWalk(int nsteps) {
// align first tripod feet
// align second tripod feet

for(int i=0;i 0) {
int inbyte =;
switch (inbyte) {
case 't':
case 'c': // crouch
case 'i': // init - centreServos
case 's': // stand
case 'r': // rotate left
case 'R': // rotate right

Here is a video of the hexapod walking. It’s not very efficient!