Wednesday, 11 March 2015

NonLinear Circuits - Dual OTA VCO - Build notes.

I was listening to a friend's NLC VCO the other day.
I loved it so much that I have decided to record the build of one.
What makes this particular  VCO so special is that it uses a slightly
different type of operational amplifier.
It's called a OTA or Operational transconductance amplifier.
Here is Andrew's blog relating to this VCO 
And his build notes & BOM.
This build is for the Eurorack version of the module.

 What the OTA  shares with your common Op-Amp is:
1. a single output.
2. They both have inverting & non-inverting inputs.
3. They both have power lines (V+ & V-)

What makes the OTA different is that it has 2 extra inputs (Ibias & Iabc)
and it's output is a current not a voltage.
So, to put it another way, a OTA is a voltage to current amplifier.

The OTA used in this module is a LM13700
"The  LM13700 consists of 2 current controlled OTAs each with differential inputs.
Linearizing diodes are provided at the inputs to reduce distortion."

There are loads of circuits that use the LM13700 in VCO, filters, Amps.
Here is the classic Triangular/Square Wave VCO:

Back to the NLC build. First instal all headers.

Resistors first.


Caps then Trannies.
There are two BC 547s & 557s which need to be in thermal contact.

Two 1K tempco resistors go over the transistor pairs. These are on back order along with the 20k trimpots, etc.
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23/06/2015
Finally resuming the build.
Instal the 20k trimpots and the tyco/Tempco resistors.

The Tycos & trannies need to be hugging one another.:-) Nice & tight.

My panel is only partly drilled.
So I'll install the two fine pots on the top first & the bottom jacks.
Make sure everything lines up.


Next the rest of the pots. By the way, they are all 100k linear (100K B).
The orientation of the jacks is different between bottom & top rows.
The bottom row of jacks have their ground tabs pointing downwards, 
the top row have their ground tabs pointing upwards. 
 
 
 You should be able to see the round holes on the pcb where you can solder a 
bit of wire (offcut lead) from the ground tab of the jack to the pcb


Right, we are almost there.
ICs & power cable in.


Looks & sounds great!



Extra Links relating to OTAs in Modulat Synths:
1. ElectroMusic.com
2. MuffWiggler
3.  A OTA based VCF - Scott Stites
4.  Youtube
5.  DIY stompboxes
6. DIY stompboxes 2

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Click here to return to the NLC Build Index:
http://djjondent.blogspot.com.au/2015/03/non-linear-circuits-ncl-index.html

Monday, 9 March 2015

The Boss DR-660 (Dr Rhythm drum machine)

This drum is very under rated.... and cheap too.
It hails from 1992 ... so it's over 20 years old.
Roland/Boss were by then using digitally sampled sounds.
Gone are those analogue days.

This was I feel the first digital drum where the sounds actually started to sound realistic.
Remember the DR 220 - I have both the acoustic & electronic versions.
Neither sound like the real deal. This was a weakness in 1986 but today I love their cheezyness.
The DR-660 has the same appeal.

The DR-660 has 16 velocity/aftertouch sensitive pads.....It's very easy to use.

There are 39 drum kits; 250 patterns; 100 songs.
The songs are created by combining patterns. Each kit was targeted at a particular style of music.
There are also memory spaces for the user to put together his/her own new kits.... Yes you can create your own new drum sounds.:-)
 For example, you can combine samples using the pad layer function.




There are 255 16-bit sounds. (The DR-220 was just 12-bit).
There are TR-808 and 909 samples (which in my opinion aren't spot on).
Most of the samples are however still pretty useable, with the 808 bass being fabulous. The snare is good. But the 909 kick in the 660 is pretty darn weak. You can though tweak this little puppy to create totally new sounds which is where I'm at these days.

So I wouldn't recommend the 660 if you want to emulate a 909.
On the positive side, the 660 has a built-in digital reverb, delay, chorus and flange.
The reverb & delay is pretty darn good.  The chorus and flange aren't too bad either.... a bit noisy maybe. Each of these effects are assignable per drum.



There are stereo outputs plus two individual outputs.


Though this does have its own sequencer its a bit fiddly to program. Using the RealTime Write function where you tap the rhythm in time to a metronome can be fun..... though if you make a mistake, editing is a pain in the arse. Luckily there is also MIDI in and out which make this very easy to sequence via your  DAW.





So probably the easiest way to see this is as a piece of history. ... a snap shot of the early '90s.
I generally avoid using the built in sequencer, and regard this as a tweakable bank of tones.
Its not a 909 or 808. If that's what you want, then buy a real 909 or 808. Nothing beats the real deal.
But if your looking for something different, then this could be what your looking for.

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For more info on the history of Roland Drum Machines click here

Sunday, 8 March 2015

Korg PS 3200 sequenced by a SQ-1 (patch 1)

What a awesome sequencer is the SQ-1
I'm totally in love with it.
This is the first in a series of videos using these two classic pieces of gear. Hopefully we
can come up with some finished pieces.

The unedited video is here:
https://www.youtube.com/watch?v=BXw92TosJPw






Saturday, 7 March 2015

Fatehpur Sikri - India

Fatehpur Sikri was founded in 1569 by the Mughal emperor Akbar.
It's in the state of  Uttar Pradesh. It's a short 40 km drive from Agra
The Emperor (1556-1605) decided to construct it on the same site where
the birth of his son was predicted by the wise & holy man, Shaikh Salim Chisti (1480-1572).
It's regarded as Akbar's crowning architectural legacy. The palaces, public buildings, gazebos, mosques, pavilions & halls were planned with great care for he intended FS to be his capital.

This only lasted between 1571 & 1585. Lack of water finally forced Akbar to move the capital to Lahore (in present day Pakistan) and then back to Agra (1598).

Akbar planned the complex around Persian principles that were derived from tent encampments.
The complex consists of independent pavilions arranged around central squares.


But the beautiful thing about all this was the fusion of styles. His adopted land of India, can be seen throughout.
Inner view of Buland Darwaza (Bulland Gate)

All the buildings here were made of the local red stone. And he used indigenous craftsmen throughout in the construction. One can see Hindu & Jain architecture mixed with Islamic elements.
The monuments at Fatehpur Sikri thus reflect the genius of Akbar. He successfully combined diverse regional architectural styles. This layout definitely influenced later town planning which can be seen in cities such as  Shahjahanabad (Old Delhi).

(Buland Darwaza) Bulland Gate, Fatehpur Sikri
Built to commemorate Akbar's victory against the Kingdom of Gujarat.

Bulland Gate (Buland Darwaza). This gateway is 55 metres tall. Completed in 1575, it's according to the locals the largest triumphal arch in the world. The Arch de Triomphe is 50m high. The Brandenburg Gate is 26m. The arch of Titus in Rome is 15m. One "gate" that is taller is the Arch of St. Louis, Missouri. It's 190m though it's debatable as to whether it's a triumphal arch or just a gateway. ???

Bulland Gate (Buland Darwaza)


The Horseshoe Gate at Fatehpur.
This is the central gate of the  Buland Darwaza. The horseshoes are nailed for good luck.


Tomb of Salim Chishti
A marble encased tomb for the saint who foretold the birth of a son  for Akbar. Beautiful Jali screens encircle the central room that houses the body of the saint.

The Tomb of  Shaikh Salim Chisti (1480-1572)
These screens are cut from single sheets of marble.



Anup talao (pond), the platform to the right was used for singing competitions

Anup Talao Platform

Panch Mahal
This is one of the most unusual structures of Fatehpur Sikri. It's a 5 tiered palace.
Also known as "The Pavilion of the Winds". This was used by ladies of the Royal Harem who were given privacy with Jali screens.

Diwan-I-Aam

Diwan-I-Aam - interior
The "Hall of Private Audience". It is here that Akabar had representatives of the different religions discuss their faiths in peace & friendship. The central pillar has 36 voluted brackets.