Tuesday, 17 September 2019

Noise, LC Filters, Inductors, etc

noise, Noise, and MORE NOISE.

Filtering noise is really important when building your synth.
Lots of ways to do this and the method may vary depending on the scale ... does the noise effect the whole synth (the PSU) or a small part of a circuit.
Decoupling capacitors, Ferrite beads, Inductors, LC Filters ??

I guess before you do this, you need to ask the questions;
  1. Are you better off filtering the noise, or preventing noise in the first place?
  2. Is there actually much noise to begin with?
  3. Is any LC filter you might install making more noise than it is removing?

On the macro level, a common method is to use something like a LC filter.  This often is found in the psu (the main power supply). An LC filter consists of inductors ( represented by the letter L) connected in series with the power flow and capacitors (represented by the letter C) from the filtered voltage to ground.


Ferrite Beads
A ferrite bead and capacitor is another form of LC Filter. It is often used to filter power for specific power pins on an IC.  They are frequently used on sensitive parts of a circuit like PLL’s & analog sections.

 LC filters are used to keep noise in one section of the circuit from getting to another section.

Decouplig Caps.
A decoupling capacitor is a capacitor used to decouple one part of an electrical network (circuit) from another. Noise caused by other circuit elements is shunted through the capacitor, reducing the effect it has on the rest of the circuit. (Wikipedia)

Also known as bypass capacitors.
They act as energy reservoirs ... you will often see them close to ICs ... they help to smooth out any voltage fluctuations.

You can also use decoupling caps on your main power distrobution board.
Here is an example for eurorack:
NLC power distro board


Below is a LM7805 voltage regulator.
Notice the two decoupling capacitors:
The capacitors are placed between the power line & ground.
The 0.33uF helps to smooth out any low-frequency changes in an input voltage. 
The 0.1uF helps to smooth out any of the high-frequency noise at the output.
Combining these two caps helps to deliver a smooth uninterrupted voltage to your circuits.


As mentioned earlier, decoupling are often used with ICs. Logic circuits tend to do lots of sudden switching ... between on & off with not much in between..So decoupling caps help to smooth  and stabilize the input voltage..... absorbing excess voltage if the voltage spikes suddenly, and providing more power to the IC should the voltage suddenly drop.   

The decoupling capacitors are connected between your power source, whether that’s 5V or 3.3V, and ground. (Generally it's recommend to use a 100nF ceramic capacitor and a larger 0.1-10uF electrolytic capacitor for each integrated circuit).

Inductors
These are also called coils or chokes.
They are passive two terminal components.
Like capacitors, they store energy.


 However, in this case, energy is stored as a magnetic field.
They are usually made up of a insulated wire, wound round a core (magnetic ... iron or ferrite).

We measure inductance in units of Henry (H).
1Henry = 1 volt of EMF across the inductor with 1 Amp of current.
The larger the number, the higher the inductance.
The higher the inductance, the more energy we can store and provide.
It will also take longer for the magnetic field to build.

 

This is a inductor from a Metromodular Eurorack PSU
The inductor will remove any voltage ripple .
Notice also the diode> this eliminates voltage spikes if the power is suddenly switched off.
 
Here is another inductor - Its SMD


Ferrite Beads.
Also called Ferrite chokes, cores, rings, blocks, EMI filters.
These are passive components that suppress high frequency noise.
They are often wrapped around cables to  prevent the cable from acting like an antenna and receiving interference from other devices.


These are snap on ferrite beads. The upper pic shows one used at the end of a USB cable.

Ferrite beads convert Radio Frequency (RF) energy to heat. They are like a filter.
(Contrast this with inductors, which by design do not convert RF energy to heat, but rather offer a high impedance to RF.) 

 On the left is an inductor. To the right is a PCB ferrite bead.
You will probably have seen many of the PCB ferrite beads in DIY synth modules.

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Splitting ground planes.


I recently read a great article from Texas Instruments re splitting ground planes as a way to reduce digital noise.
http://www.ti.com/lit/an/slyt512/slyt512.pdf
A ground plane is an electrically conductive surface, usually connected to electrical ground.
On a PCB this is a large area of conductive material which is connected to the power supply ground terminal and serves as a return path for current from different components on the board.

 Hoikka1 [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]

Placing the ground planes below the relevant components and signal traces is also helpful. ...
maybe on a seperate layer of a multi-layer PCB .
This should help reduce electromagnetic interference, cross talk & ground loops.

I often see single ground planes on pcbs (with just analog components).
But if there are both analog and digital circuits on a single PCB, best practice seems to be to:
"separate the ground plane on the back layer into a digital section and an analog section, but leave the two planes connected near the return to the power supply. This ensures that digital signals do not follow a return path beneath sensitive analog components....

It is a bad idea to completely split a ground plane and try to bring the sections to the same potential using something like a ferrite bead, as this creates more EMI and noise problems ." (Altium resources)


I've always wondered why Don Buchla used two grounds on his power distro busses.



This may be the reason.
Two separate grounds for analog and digital.???
He never used this on the earlier 200 series.
This type of distro was first used in the 200e which of course uses digital components.

Other ways to reduce noise:
+ Use two separate supplies .. one for the analog & the other for digital
+ keep the analog & digital components separate & don't let their grounds touch.

But I think splitting your ground planes is a really neat idea.

Links
+ Altium
+ Texas Instruments

Saturday, 14 September 2019

ARP 2500 - modular jamming 070919

Some more jamming on the old arp.


Vitals on the keys


Just playing around with ideas for a future track.



Video is just from a mobile phone


Modular Jamming 070919 - buchla 100

My friend Mitch (Vitals) visited the other day.
Had some fun jamming with the old gear.

Nothing polished ... working with ideas... hopefully one day something from here will find its way onto an album

 Mainly Buchla 100 .. mixing vintage & new



The audio is just from a mobile phone (sorry)



Friday, 13 September 2019

1/n - NLC Build pics

Some build pics as I put together this module.
The 1/n by NonlinearCircuits is a eurorack format module.
It's a clock divider.
Andrew says this circuit is straight out of the Lunetta playbook.
https://docs.google.com/document/d/1V9qerry_PsXTZqt_UDx7C-wcuMe_6_gyy6M_MyAgQoA/edit


These pics aren't official ... just my personal notes to help with troubleshooting.
The official build notes are here:
+ Official build notes
Andrew's old blog documents this here:

+ NLC blog

It's wafer thin :-)


 
One of my favourite Monty Python movies

 sOME  pre soldering pics

The 1/n is similar to the divide & conquer module
The main difference, is that you can program your own clock divisions.
You do this by patching.


The NLC 1/n is simply a CMOS 4018 with buffers on all of its inputs and outputs, along with a 4081 to enable further divisions.
The CD4018 is a presettable divide by n counter.
 J1 to J5 on the module refer to JAM 1 to 5 on the IC
CLOCK, RESET, DATA and PRESET are your inputs that enable you to program divisions.
The CD 4018 allows you to divide by 10, 8, 6, 4, or 2..... this is done by feeding Q5, Q4, Q3, Q2, Q1 back into the DATA input.

For interest sake, a CD 4011 should also be able to enable further divisions
Andrew has added a CD4081 to enable further divisions.

A high signal on the RESET will clear the counter to an all zero condition.
A high signal on the PRESET ENABLE input causes the JAM inputs to preset the counter.


i LIKE to put the ICs in first.










jACKS in first.
Line up everything.



tHE shrink wrap is to prevent shorts between the LEDs and jacks.






Nice !

How to use this
The module can be patched to supply a division of the clock signal. 

To do simple clock divisions
 1. patch a gate into CLK (eg a LFO) and select a desired division from the right side column.
    (numbers 4 to 10)... these can be used to trigger external modules ... EGs or drums etc.

To do more complex clock divisions:
1. patch a gate into CLK and select a desired division from the right side column.
    (numbers 4 to 10)
2. patch this into IN. The /4 is pre-patched to the IN jack via internal switching.
3. The 1/n jack is your programmed clock output (the divided clock signal)

Using the JAM & PRE-SET inputs
The J1-J5 (jam) and the PRE EN (preset enable) inputs, enable greater variation in your clock divisions.
1. Patch various signals to J1-J5 (jam)
2. Patch a signal to send PRE EN (preset enable) high.
    This will rest the count to whatever jam inputs are high at the time.
    Something like a Pico RND (erica Synths) or the NLC 2xLFO is good for this.
3. Patch signals into the RESET & IN for even more  interesting patterns

    "This is a good way to develop complex gate patterns but is also very interesting at audio rates too.
     When used at audio rates, the 8 output signals from the right column will all be related
     to each other but different. It is possible to get many interesting effects using this
     module as an audio processor." (NLC build notes)



Links:
+ NLC blog
+ Official build notes
+ CGS 36 - Ken Stone's Pulse divider


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You can find more NLC builds here.
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Thursday, 12 September 2019

LED Wiring

Some very basic info re LEDs
Light Emitting Diode orientation.
The earliest LEDs seem to have appeared around 1962
Before this there were incandescent lamps (you will see these used on early Buchla 100 modules... eg the 123 sequencer)

Anode - positive, long lead
Cathode - flat side, short lead


Note: If there is no flat side marked on the PCB use a multimeter to find the ground.
Usually, the ground is the round pad = .cathode (though I have seen the reverse being used).

In my experience, LEDs usually follow the same convention as used in electro caps.
Most aluminum caps come with the positive lead longer than the negative and when inserting them I aim the longer lead for the square hole.

So with LEDs, usually this holds:
The square pad represents POSITIVE
The round pad represents NEGATIVE

But, to be sure, use your multimeter to locate ground which connects with the cathode.
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Multi colour LEDS


Bi-polar LEDs

These are two colour LEDs
Actually, there are two LEDs in the one case connected to the same two leads
Current flowing in one direction emits one color, and current flowing in the opposite direction emits the other color.

You will probably see these used a lot in synths.
Like regular LEDs, they have just 2 pins : Anode & Cathode
but they also allow two colours (red & green for example) .
Only one colour will appear at a time.... this is determined by the polarity of the connection.

This feature is very useful if you are trying to identify the polarity of a voltage 

I used this type of LED when building the NLC sloth.

The most common colours are red/traditional green, however, other colours include amber/green, red/green, red/blue, and blue/green.

Tri- colour LEDs

 

LED's that provide three or more colours can have two, three or four pins allowing for a wide range of mixed colours. Some have a common Cathode. With other types, the anode is common.
There some types with only 2 leads (anode + Cathode) ....  here, the colour is determined with a built in electronic controller.





Two LED Tri-colour
These have 3 pins but contain just 2 LEDs (red & green) in the one package.
When both the red and green LEDs are turned on, the LED appears to be yellow.
 

The common cathode is the centre leg, which is where the resistor should be fitted.
The outer leads are both anodes. .... allowing the LEDs to be lit separately
Green is the shorter leg.

 RGB LEDs
These contain one green, one red and one blue LED in the single package.
They however have 4 Leads with a common cathode (usually).
This allows simultaneous use of all the LEDs. If you illuminate the different LEDs to different levels you can achieve almost any colour.


These are sometimes called multi-colour LEDs since more colours than just RGB can be achieved.

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The LED Drive circuit

LEDs are current dependent and thus it is necessary to protect them from excessive current with a resistor. You attach the resistor in series (Rs).
To determine the required resistance use this formula:

Rs = (supply voltage - LED voltage)/LED current.

You can usually find the LED voltage from its data sheet.
Eurorack will have a supply voltage of 12V.
You just need to work out the current.

Links:
NLC nonlinearcircuits Sloth


Bahai Hanging Gardens of Haifa - Israel

These are  Terraces of the Bahá'í Faith, also known as the Hanging Gardens of Haifa.


You can see the garden terraces around the Shrine of the Báb on Mount Carmel in Haifa, Israel.



 The gardens rest in the neighborhoods of Wadi Nisnas and Hadar HaCarmel.





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