Synthesizer Build part-31: NOISE MODULE with 5 TYPES OF NOISE + Random Gates.

A very easy to build noise module with 5 different sorts of noise, two of them being 'Grainy' noise with adjustable graininess.  Works on dual 12V so Eurorack friendly.

(The Random Gates section is located half way down the article)

This is a module I adapted from the MFOS Noise Cornucopia schematic by Ray Wilson. It's turning out to be quite a popular project because I'm getting lots of feedback from people who built it and are really happy with it. Especially the addition of the Grainy Noise.

So, I needed a good noise source in my synth and this one seemed perfect. The original schematic has a random gates section which I didn't need but which you can easily add on if you want it. But I left that out. (I made a separate layout for the Random Gates Generator section which you can find further down the article) I also changed the transistor used to generate the noise and I changed the way the transistor is integrated in the circuit. My way is simpler and generates 200mV worth of noise right at the emitter of the BC547. The transistor's Emitter-Base breakdown voltage is exceeded thus the transistor is operating in avalanche mode, creating nothing but pure noise.
This was a one day build for me. I spent the morning adapting the design and making a stripboard layout. Then I built it in the afternoon and by 8pm that same day I had a good functioning noise module built into my synthesizer. The layout I made worked right from the start. No troubleshooting needed.
In the layout below the transistor is shown as a schematic symbol, and not as it's normally shown in the TO-92 package, to make it clear that the collector is not connected. In fact, you need to cut off the collector leg completely to stop it working as an antenna. I've put the pin-out of the BC547 in the layout to make this extra clear. You might need to choose a BC547 that gives you the best noise results. I heared through feedback comments that there can be differences between transistors but you should get noise with any transistor. It's just that some transistors produce more noise then others. I myself put in the first transistor that I had, and didn't choose between them. It worked fine as you can se in the video. Should you experience hum or something, from the power supply, then you should resort back to the transistor arragement in the original design as shown in the original Noise Cornucopia Schematic. 

Here is the verified layout.

(Last revised 16-May-2020: Added grounding wires to output jacks and pinout to noise transistor.)

Stripboard only. 

For extra clarity: connect the 'Base [B]' of the transistor to copper strip 'I' and the 'Emitter [E]' to copper strip 'G'.

The cut on position D17 in the layout above, has been moved to position D21 to make it more visible.

Below is an overview of the cuts and the wirebridges alone. This is seen from the component side! As ever, mark the cuts on the component side with a black waterproof marker and then stick a pin through the marked holes and mark them again on the copper side. Now you can cut the copper at the marks with a sharp hand held 6 or 7mm drill bit.

Bill of Materials. Instead of the TL084 and TL082 you can also use the TL074 and TL072 opamps:

Here is the altered schematic, made from the original Noise Cornucopia design:

Btw, if the BC547 doesn't produce noise for you, try a 2N3904. Remember it has the opposite pinout of a BC transistor. E and C are changed around. Not all transistors are created equally and some produce more noise than others.

The noise output from the transistor goes through a highpass filter consisting of the 100nF capacitor and the 2 MegaOhm resistor. This creates a filter cutoff frequency of 0.8Hz letting through all the frequencies and rejecting any offset voltage. Should you experience an offset voltage after the filter then lower the resistor value from 2M to 1M. That will make the cutoff frequency 1.5Hz.

I changed the 500K trimmer, used to set the amplitude of the noise, for a 200K panel potmeter so you can use it as a level control on the front panel. In my panel I used a 500K panel potmeter but that really is too high a value. When I turn the potmeter 1/3rd open, the amplitude reaches it's maximum at 10V peak-to-peak and the rest is just maximum volume and starting to clip, so I think it's better to use a 200K potmeter. (However I haven't tested it with a 200K potmeter) .

If you only have a 100K potmeter you can try changing R5 from 10K to 4K7 to get the gain right, and then it should work with a 100K potmeter. I've had confirmation that this solution works just fine.

To be honest, you don't need a gain option in a noise module like this, so you can just as easily forget about the Gain potmeter and put in a trimmer, set it so the output of pin 7 gives +/-5Vpp noise level and leave it at that. That's also how it was intended in the first place. The gain option was just my own idea.

The opamps used here are not critical. The schematic says to use TL074 and TL072 but I used the TL084 and TL082. I think you could even use an LM324 instead of the TL074. The pinouts are all the same. 

This module is designed to work on a dual 12 Volt powersupply (so ideal for Eurorack systems) but it will work equally well on 15 V.

How Grainy Noise works:

The Grainy Noise consists of very short pulses with an amplitude of plus and minus 5V. The Opamps IC2 a and b are set up here as voltage comparators which are being fed on the non-inverting inputs with white noise and on the inverting input with a voltage that can be set with the Graininess Potmeter to between 0V to + or - 8.25V (roughly). Each comparitor has a diode on the output so handles only one part of the voltage phase (either positive or negative). So if the voltage on the negative inputs is very high, the noise will only occasionally go over it and we'll get only a few Grainy Noise pulses. When the opamps are not producing a pulse they are at rest in either full positive or full negative voltage on the output pins but those voltages are being blocked by the diodes. So only the Grainy Noise pulses are being fed to the output. As you lower the voltage, the threshold will become lower and the noise will tip over the boundary more often creating more and more Grainy Noise pulses.

The 'Grainy' noise is a real asset to have. It's very useful because of its harsh sound. It sounds a bit like the noise you get from old TV sets. If you look at the scope image in the video you can see that most pulses from the Grainy Noise go into negative voltage. The more you turn up the Graininess, the more pulses you get that go positive and that's what is used to create random gate pulses. In fact only the positive noise pulses are used in the Random Gates generator and the negative ones aren't used because that diode has been left out. See the original Noise Cornucopia Schematic for that. The Highpass grainy output is a bit low in amplitude. That's not just in my build but other example videos show the same thing. Maybe a different type of capacitor would make it better but to really change it you should put it through an extra opamp and give it some extra gain but I didn't bother with that. I don't think I will be using that output much anyway. If you change the resistor to ground you also change the highpass filter so I don't think that is advisable to make it louder.

Btw, the LowPass noise is not exactly the same as Pink Noise in my opinion. The LP noise has more rumble (bass) in it I think but you may have a different opinion on that. I leave that open :) I think to call it LoPass and HighPass etc is more intuïtive than to assign different colour-names to the noise. It's also a useful type of noise to have because a lot of people prefer mixing LoPass noise into the signal path instead of white noise because the LP noise sounds less muddy.

RANDOM GATES GENERATOR:

I've made a separate layout for the random gates section of the MFOS Noise Cornucopia design, for those interested in adding this on. The two 7 pin headers are there to provide a choise in randomness of the Gate signal. See the original Noise Cornucopia article for the schematic drawing. The signal has the most randomness if you place the jumper on the lower settings. The higher up you go the less random the Gates get. 

NB.: Place only one jumper on the pinheaders!! 

If you have a rotary switch with 7 positions you could use that, instead of the pinheaders, and make a feature of it by placing it on the front panel. That's up to you. Let me just say also that I have not built this random gates module myself but I've gone over the noise cornucopia circuit schematic with great precision and it's a very simple layout so it should work fine. If you have built this layout please send me some feedback about how it's working. I've had some feedback saying if it doesn't work like it should to put a 2,7MOhm resistor in parallel over the 10pF capacitor.

Personally I don't find this type of random gate circuit very useful. It's not synchronized in any way and you only get one output with a random pulse train on it. I would prefer the Yusynth 8 Random Gates project where each pulse has it's own output. What I would prefer even more is to pair a Sample and Hold circuit with a noise generator like the one above. But it's all up to you of course. 

(Check the comments below to read about Tim's findings when he breadboarded this circuit to test if he could build it with 7 outputs instead of one.)

Here's the layout I made for this section: 

Here's a demo video I made with sound samples of the different types of noise:

And finally some pictures of the finished product. As you can see the finished module is very small. In fact it is only 3 centimeters wide so it won't take up much space in your modular set-up:

To finish I want to direct your attention to a great video by Moritz Klein about building noise modules where he explains the theory behind it very well.  Click here to see the video on YouTube.

Okay, that's number 31 done. A very satisfying build because everything worked right from the get go. Any questions or remarks? Please put them in the comments below or post your questions on the EB Projects Discussion and Help Facebook Group.

Synthesizer Build part-3: TRIANGLE TO SINEWAVE CONVERTER

This article has been re-written at 11-11-2020.

After I had finished the VCO I wanted to add a Sinewave option to it. The first design I had posted here was a bit sketchy so I now present a new layout here. This layout has been made using the schematic of the Thomas Henry CEM3340 Deluxe VCO, which has a sinewave output. Btw, you can find that schematic in the 'files' section of the 'Synth DIY for non engineers Facebook Group'.

This circuit needs the Triangle input wave to be +/-5 Volt peak-to-peak. You can input a Trianglewave of 0V to +10Vpp but then the input must first go through the 1µF electrolytic capacitor to take away the offset voltage. The Triangle to Sinewave converter will not work properly if you input a 0/+10Vpp Trianglewave without first filtering out the DC offset voltage.

I altered the feedback resistor (Rf on layout) from 10K to 15K to get the amplitude correct with the waveform standard of my synthesizer project which is 0 to +10Vpp. This had the effect that the +/-5V output got a negative offset voltage. What I should have done is change the other 10K that goes from the + input to ground into a 15K also, so everything is in balance again but I put a 1µF capacitor in series with the output of the +/-5Vpp sinewave. The negative pole of the electrolytic capacitor is facing the direction the signal is coming from because I had a negative offset voltage to deal with. Make sure you match the 10K resistors so they all have the same value and if you change the feedback resistor to a 15K make sure you change the other 10K to ground also. Match the transistors too. (Matching them on hfe is good enough). If after all that you still have an offset voltage on the output (unlikely) then you can put a 1µF cap in series with the +/-5V output.

The output amplitude on a dual 12V powersupply is +/-4.2Vpp or 0 to 9.4Vpp. For a dual 15V power supply it is +/-5Vpp or 0 to 10Vpp.

Here is the new stripboard layout. This converter offers a +/-5Vpp output and a 0/+10Vpp output. 

Here is the schematic drawing. I did not include any de-coupling capacitors but if you want to include them then just add two 100nF ceramic capacitors to the voltage rails as close to the chip as possible. One going from +15V to ground and the other from ground to -15V.

Here are two pictures from the oscilloscope. One without offset from the +/-5Vpp output and one with offset from the 0/+10Vpp output. If you look closely at the pictures you see that the scope is set to 2V per division and therefore that the amplitude of the sinewave is 8V. But now that I changed the feedback resistor Rf, that has changed to 10V (even a tiny bit over):

As you can see they are beautiful sinewaves and you can set the symmetry and distortion very accurately with the trimpots on the stripboard. 

It will be easy enough to mount this little stripboard on one of the M3 bolts used to mount the print of the 'Really Good VCO' and thus add a Sinewave output to that VCO. You can tap the Trianglewave straight from pin 10 of the AS3340 (or CEM3340) chip or from pin 12 of the TL074 quad opamp chip. I think that will be even easier. On those pins the Trianglewave is not yet given a +5V offset voltage so it is still +/-5Vpp and therefore doesn't need to go through the 1µF electrolytic capacitor on the layout of the Triangle- to Sinewave converter. 

Okay that's the new version of this article done. If you have any questions please put them in the comments below or on the EddyBergman Facebook Group page.

Btw, all the comments below upto August 2020 refer to the original Tri- to Sinewave converter article and not to this one. So please disregard those comments.

A 'Brute Force' 15 Amp Power (Dummy-) Load. Easy to build!

Power-loads or Dummy-loads are expensive bits of equipment but if you need to test a powersupply or test a current protection circuit and need something that can draw a big current and is preferably regulated so you can dial in the current then this is the easiest and cheapest method.

The circuit below uses a BD182 transistor which I had lying around from an old audio amplifier. It is the equivalent to the well known 2N3055 and you can exchange the one for the other in this circuit without trouble.
The powerload needs no external power supply. It is a passive circuit but do make sure you use a big, and I mean BIG, heat-sink. The transistor will get hot very quickly.
Here is the schematic drawing of the circuit. I don't think you can make them any simpler than this.

I did away with the shunt resistor in the emitter to ground line because we don't need to measure the current at that point. We will use a Digital Multimeter in series with the Dummyload input. A shunt resistor is usually used for creating a feedback voltage to go into an opamp, In this case it only holds back the current so we leave it out.
I made my dummy load switchable. You can draw a big current and then by flipping the switch the current almost doubles. The lowest resistance I got from this circuit was 1.8 Ohms. That means with 12 volts connected you can draw a little under 7 Amps. and this transistor has no troubles with that (provided the heat-sink is up to it). Be sure to use a good heat sink and generous amounts of heat conducting compound around it.

Below are some pictures of how I build my power load. I build mine in an old Droste Chocolate can I had lying around. Previously I had built it in an old wooden cigar case so this is big improvement :)
Beware that the current-rise is exponential so when you turn the potmeter, the first few amps will go nice and smooth but at the end the current rises very quickly and even jumps to maximum just before the potmeter if fully turned. And yes, the potmeter I used is a linear type not a logarithmic one :)
The current fluctuates a little if you put an amp-meter in series with the load. The milliAmp digits will go up and down a bit as you read the amperes. But that's what you get when you keep it simple. The little 50nF capacitor is meant to suppress transients should they occur.
The maximum voltage from Collector to Emitter for the BD182 is 60 Volts so don't go higher then that and the maximum continuous Collector Emitter current is 15 Amps. That's a lot more then most of the circuits for powerloads you'll find online. They mostly go up to just 5 Amps. I try not to exceed 10 Amps with this design just to be on the safe side. I used a CPU heatsink on the 2N3055 which is not ideal but I mounted the transistor on a little copper sheet so that acts as a heat sink too and then I put the CPU heatsink on top of the transistor with heat conducting paste in between so the transistor can dissipate heat from the top of the TO-3 housing aswell. It's a very effective solution and works very well. If you need a power load that can draw even more current you can just put more transistors in parallel over the first one. Just connect base to base, collector to collector and emitter to emitter. (I haven't tested that btw, but it should work.)

That's it for this article. I hope you enjoyed it. If you did then have a look around some of the other articles on my website. There's loads of interesting electronics projects, mostly synthesizer related though. Please leave me a comment, because I always enjoy hearing from likeminded people. If you'd like to support my modest efforts you can do so by subscribing to my YouTube channel EdEditz

THANK YOU!