Thursday, 7 August 2014

Transistor Matching.

This page is part of my exploration re transistor matching.
Many synth circuits require matched pairs of transistors... often for differential amplifiers.
There are lots of transistor matching circuits and devices out there.
Many ways...... but the question is which to use. ???

Vbe (base-emitter voltage) matching is the most common type of matching done. It is what is used for matching transistors in an exponential converter for example. It can be done with a circuit like Ian Fritz's, or can be roughly done using the diode setting on a volt meter (Ian's circuit gives a more accurate result).
I like using a Atlas DCA Pro DCA75  




Why choose to measure Vbe ?
Taking a NPN transistor as an example, the main point is that the current passing through the transistor depends on the Vbe, the Ies & the temperature (Vt). This is according to the Ebers-Moll model:
 
Ie = Emitter current
Ies = the reverse saturation current of the base emitter diode.
Vbe = the Base-emitter voltage
Vt = thermal voltage

Ies depends on how the transistor is made and can be different from one transistor to the next.
It also changes with temperature.
The goal of transistor matching is to find pairs or transistors with the same Ies.

It's very difficult to measure Ies, but we can instead measure the Vbe if we pass a known current through the transistor. If we can keep the temperature constant, then matching Vbe is equal to matching Ies.

So the solution (if you are to build a circuit) is to have 3 things:
1. an accurate current source.
2. an accurate multimeter.
3. a constant temperature.

Whether you are using a circuit or the Atlas peak, remember that the temperature of the transistor will effect the measurements. I like to leave the transistors alone for about 5 minutes after handling them
and them carry out the measurements.
------------------------------------

The TTSH build required matched transistors in the filter section.
I matched them via hFE ... not by the usual the Vbe (base-emitter voltage).

I'm hoping I'll get away with it for that instance. However, the TTSH VCA section requires more matched trannies. So it's time I guess to bite the bullet.

Moog has a classic transistor checker schematic (from the mini-moog manual).
Here one current drives another current through the transistors and you need to measure the voltages between the base & emitter. It calls for a +/- 10V supply and needs a really accurate volt meter.

There is a variation of this circuit on DragonflyAlley.com
It uses a +/-15V supply, a 741 op-amp & 3 resistors.

 The Op-amp is a 741. (Pin 6 of the 741 connects to the base of the 3904)

 Here are some pics of the breadboarded circuit. (just for the NPN 3904 trannie).


It seems to work though there is lots of voltage fluctuation
Very temp sensitive.

Ian Fritz also has a transistor matching circuit.
You can download it here.

This is a breadboard of the Fritz transistor matcher.
The crossed resistors need to be matched as closely as possible. I guess a variable trim-pot could also be used to get a closer matching between the resistors.

I kinda like it more than the Moog circuit. It's definitely much simpler using just 3 resistors & a diode.

The voltage on the multimeter is the difference between the two transistors. In an ideal world of perfectly matched resistors & transistors the voltage would be zero.

This particular batch of 3906s seem to vary by 0.5 to 4 millivolts.

For completeness here are a few more links to blogs, websites which discuss transistor matching.
Hopefully you will find this useful.

Muffs has a cool thread for DIY Transistor matching if you finally wish to go down this path..
matching transistors - DIY
 
The famous minimoog tester of Dr. Robert Moog.

MFOS has a great page on how to build transistor matchers.
(MFOS Practical Transistor Matching)

I might try this MFOS matcher later if the earlier attempts aren't successful.

Links
+ Transistor - Basic info
+ JFETS - matching for synthesizers  
+ Muffs
+YATMA Yet Another Transistor Matcher

Wednesday, 6 August 2014

Dad Jokes

1. What does the Eiffel Tower and a tick have in common?
    They are both Paris-Sites (parasites)

2. Why do fathers take an extra pair of socks when they go  golfing?
    Incase they get a hole in one.

3. What did the ocean say to the beach?
    Nothing, it just waved.

4. What did one wall say to the other wall?
    "I'll meet you at the corner.

5. What did the zero say to the eight?
    That belt looks good on you.

6.  What did Baby Corn say to Mama Corn?
     Where's Pop-corn?

7.  Where do you learn to make a banana split?
     Sundae School

8. What has more letters than the alphabet?
    The Post Office

9. How do you get a squirrel to like you?
    Act like a nut

10. Why don't eggs tell jokes?
       They'd crack each other up.

11. Why shouldn't you trust stairs?
       They are always up to something.

12. When shouldn't you trust trees?
       When they look shady.

13. What do you call someone with no body and no nose?
      Nobody knows.

14. Did you hear the rumor about butter?
      Well , I'm not going to spread it.

15. Why couldn't the bicycle stand up by itself?
       It was too tired

16.  What did one hat say to the other?
       Wait here, I'm going on a-head

17. Why was the graveyard crowded?
      People were dying to get in.

17a. Why was the ghost so tired?
        He worked the graveyard shift.

18. What time did the man go to the dentist?
      2.30 (Tooth-hurty)

19. Why didn't the skeleton climb the mountain?
      It didn't have the guts

20. What do you call a snowman throwing a tantrum?
      A melt-down

21. What does a bee use to brush his hair?
       A honey-comb

21a. Why do bees have sticky hair?
        Because they use a honey comb

22. How did the penguin build its house?
     It glued (igloo) it together

23. Why are elevator jokes so good?
       They work on many levels

24. How can you tell if it's a dog-wood tree?
      By the bark

25. Why did the coach go to the bank?
       To get his quarter back

26. How do celebrities stay cool?
      They have many fans.

27.  What did the flowers do when the bride walked down the aisle?
       They Rose

28. Why did the man loose his job at the bank?
      Because he pushed a woman over when she asked him to check her balance.

29. How do you row a boat filled with puppies?
      You bring out the doggie-paddle

30.  Why were the utensils stuck together?
       They were spooning.

31.  What sort of music do chiropractors like?
      Hip-Hop

32.  What do you call a tooth-less bear?
       A gummy bear

33.  Why are spiders so smart?
       They can find everything on the web

34.  What does a house wear?
       Address

35.  What do you call an unpredictable camera?
        A loose cannon

36.  Why shouldn't you write with a broken pencil?
       It's pointless

37.  How do you weigh a millennial ?
       In instagrams

38. What do you call a fat psychic?
      A four-chin teller

39. What did the police officer say to the belly button?
      You're under a vest

40.  What do you call a company run by apes?
       Monkey Business

41. What did the baker say when she won an award?
      It was a piece of cake.

42. What vegetable is kind to everyone?
       The sweet potato

43.  What did the geometry teacher say when the class couldn't work out the problem?
       Lets try a different angle.

44. 



     

      
    

Arturia Beatstep & Microbrute with a Korg MS 20 mini

The Korg mini & Arturia micro are small in name but not in nature.
I have plenty of synths to play with but i keep coming back to these.



Sounds are all from the Korg.. The Arturia Beatstep is sequencing while the Microbrute is providing CV modulation via its patch matrix.

Sunday, 3 August 2014

Sabah - Malaysia

Sabah is one of the 13 member states of Malaysia, and is its easternmost state. It is located on the northern portion of the island of Borneo.

It's still very wild which is the reason for my visit (along with the great food).
Malaysia is the country of my birth.
Leave those synths at home and return to nature.


This is a Sabah Longhouse. It's a great way to experience the traditional Malaysian Borneo rainforest lifestyle.

Longhouses represent some of the earliest form of permanent structure in many cultures. Types include the Neolithic long house of Europe, the stone Medieval Dartmoor longhouse which also housed livestock.

This is a Rungus longhouse, where each family have their own separate quarters off a common hall.




The start of our hike through the jungle in Borneo. Cool bridge. This place was once the domain of the Iban tribes who once practiced head hunting.











Friday, 1 August 2014

TTSH Synth - Two Thousand Six Hundred - 4020 ADSR (DIY)

The envelope generator build of the TTSH synthesizer. 
This is part 8 of my TTSH (Two thousand six hundred) build which is an ARP 2600 clone synth.
You can see my full build thread HERE

There are two awesome TTSH threads in Muffs.
2600 clone - Two Thousand Six Hundred (TTSH)
and
Two Thousand Six Hundred (TTSH) Project General Build Thread

And of course the official build thread is here
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The ARP 2600 has two envelope generators: an AR & ADSR.

 The EG section of the TTSH faceplate.

Vintage 2600s use a 4020 submodule in the ADSR section.
The TTSH synth has this built into the main PCB.

These are pics of a vintage 4020 submodule from an old 2600

The large silver circular component is a LM301

The TTSH uses the modern version.




Trying to match up the TTSH BOM with the old schematics of the 4020.... they are pretty close.
(I've read there were some (intentional?) errors in the 4020 schematic... might be just a rumor though).

The TTSH BOM of Integrated circuits & semiconductors is:
       1N4148 x 8 (CR1-CR8)
       2N3904 x 1 ???
       2N3906 x 3 (Q1,Q5)
       2N4392 x 1  (Q3)
       2N5172 x 3 (Q2,Q6,Q7,Q8)
       2N5460 x 1 (Q4)
       LM301 x 1 (A1)

 Resistors
  • 120 x 1 (R20)
  • 1k x 1 (R12)
  • 1k5 x 1 (R24)
  • 4k7 x 1 (R15)
  • 9k1 x 1  ??
  • 10k x 2 (R7 & ?)
  • 12k x 1 (R23)
  • 15k x 1 (R5)
  • 22k x 1 (R2)
  • 33k x 1 (R8)
  • 39k x 1
  • 40k2 x 1 (R11)
  • 68k x 2 (R17 - 19)
  • 68k1 x 1 (R13)
  • 100k x 2 (R14 & ?)
  • 120k x 1 (R10)
  • 180k x 2 (R4,R22)
  • 270k x 1 (R1)
  • 470k x 1 (R18)
  • 1M x 2 (R6,R9)
  • 1M2 x 1 (R3)
In the ADSR section, at the input of the LM301 (A1), the resistor going to GND [R7] is 10K in the original schemo. The TTSH uses a 33k instead.


A work of art.


Maybe the envelopes on the 2600 could be improved ???
Without modifications, their maximum Attack, Decay and Release times are short (esp the attack ---> 1.5 seconds on mine). The Decay & Release were about 10 secs. This could be a good place to start future modifications.

Phil Cirocco of Discrete Synthesizer offers EG upgrades to 2600s.
He describes the ADSR in a stock 2600 as "quick".
His upgrade looks cool:

"ADSR: The ADSR is quick in a stock 2600. The 3 position switch we install gives you a x1(factory speed), a x2 and a x3 speed, providing much longer times previously unavailable on a 2600.
AR: Conversely, the AR generator in a 2600 is quite sluggish in certain situations. This mod now includes an upgrade of the AR circuit. In addition to the normal X1 mode, the high quality 3 position switch provides a new high speed mode for sharper attacks, as well as a X2 mode for longer attack and release times."
Anyway, below are pics of the TTSH (envelope section) PCBs before population with most of the components:

 The rear PCB.

The front PCB.

For now, I'll build the EG section to TTSH specs.

Resistors & diodes first as usual.

Caps next. The TTSH schematic uses a 30pF cap here in The AR section.
However the BOM specifies the 33pF cap from Mouser.
Hopefully it won't make too much difference.

The  2N5460 is a P-channel JFET.designed primarily for low level audio and general purpose applications with high impedance signal sources. In the TTSH it's used in the AR envelope section. 
It was also used in the early ARP2500 1004 VCO module.

 AR section. Two 1M sliders & the SPST Off(On) Pushbutton Switch.

The 2N4392
N-Channel JFET used in the ADSR section.It's identical to the JFET used on my original 4020 module.




The Decay slider in the ADSR is 100K linear. The rest are 1M Audio.

All components are in. Ready to test.


Wednesday, 30 July 2014

Native Instruments Master Class - Pro Sound & Lighting

This Native Instruments Master Class was held on the night of Wed the 30th July at Pro Sound & Lighting Studio in Wollongong, Australia.

Thanks to Claude of  Pro Sound & Lighting and Mike from CMI Music & Audio for organizing this event.


It was a great chance to trial out some of the latest gear that NI (Native Instruments) had on offer.
I was particularly interested in checking out the new MASCHINE STUDIO & TRAKTOR KONTROL S4




DJ Kuya demoed both the Maschine & the S4.
He is a 3x DMC Victorian Champion, 1x Australian ITF Champion!!
:-)

DJ Kuya explaining the Maschine & Traktor setup

Maschine looks like it's a solid host for VST/AU plug-ins and effects.
It's basically a hardware sequencer that hosts soft synths.

 Machine Mikro

Machine Studio (Pro version). 1 midi in & 3 midi out....so you can drive external synths or drum machines and even sync Maschine to external MIDI clock sources while at the same time being able to assess your arsenal of VSTs, plug ins & soft synths. 

Machine Studio - smaller than the Pro version. I think it would be great for live performance.