Devil's Triangle Drone Sequencer

csj2k · Joined: Mar 10, 2019 Posts: 14 Location: UK

I have seen an image of a stripboard for the "Devil's Triangle Drone sequencer" by PStevenson. I would love to make it but the image is too small to see. The image links to paulinthelab.blogspot but when I follow the link it says you have to be invited to read the blog. I have an image for the related "Devils Triangle Drone Synth". Any suggestions please?

ps (I'm new to posting, I think I've followed rules/etiquette so sorry for any slip-ups in advance) & (Sorry, I tried to attach the image I'm referring to but nothing happened when I clicked on "Add an Attachment")

***If you build this circuit, look out for the hard to see cuts under under R10 & R17***

PHOBoS · Posted: Sun Apr 14, 2019 5:20 am Post subject:

did you try attaching a local file ? (doesn't work with urls)
maybe this is what you are looking for, just what I found with a quick search no idea if it is correct.

DTD stripboard.jpg

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DTD schematic.jpg

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csj2k · Joined: Mar 10, 2019 Posts: 14 Location: UK

I clicked on "Add an Attachment" and it just scrolled to the top of the page - I was expecting it would open a dialogue to upload a picture from my laptop?

Those are the pictures I wanted to upload as reference so thank you, but there is a version with an integrated sequencer that I'm looking for a larger image of. I'm going to try to work out how to post the image or a link so watch this space lol

csj2k · Joined: Mar 10, 2019 Posts: 14 Location: UK

This is the stripboard image I'm looking for a larger version of: This one (Link to google image search result)[/url]

PHOBoS · Posted: Sun Apr 14, 2019 5:57 am Post subject:

Yes, when you click on "Add an Attachment" the page reloads and at the bottom of the page a field will appear where you can actually attach an image (or music).

so this one ? (FYI I used tineye.com to find a larger version)

Devils Square Sequencer.jpg

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csj2k · Joined: Mar 10, 2019 Posts: 14 Location: UK

Yes, that's it! Thank you so much. I'm over the moon and a little embarrassed at the same time, I can't believe I didn't see how to post an image! Thank you also for the tineye link, a new addition to my search options.

PHOBoS · Posted: Sun Apr 14, 2019 7:03 am Post subject:

If you built it and it works you can use the attach function to upload a demo Wink

Do you happen to have a schematic of it, as I am interested to see what it does.
I couldn't find that with a quick search although I could reverse engineer it from the stripboard .
Guessing by the used chips I thinks it mutes/selects the outputs of the oscillators sequentially.
I also don't see a lot of pots needed for a sequencer that would control the frequency of the oscillators

csj2k · Joined: Mar 10, 2019 Posts: 14 Location: UK

csj2k · Joined: Mar 10, 2019 Posts: 14 Location: UK

PHOBoS, the image you found was titled "devils square sequencer" and I'd only seen it referred to as devils triangle

Using devils square sequencer as my search criteria I found a page with the schematic which I've attached to this post. The source is here

DD Sequencer.jpg

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PHOBoS · Posted: Sun Apr 14, 2019 8:35 am Post subject:

great! thanks Very Happy

That confirms my suspicion as to what it does.

csj2k · Joined: Mar 10, 2019 Posts: 14 Location: UK

PHOBoS · Posted: Sun Apr 14, 2019 10:23 am Post subject:

sure

The 4 identical circuits on the right side are oscillators that produce a triangle wave. The frequency/pitch of these oscillators can indeed
be adjusted with the 100K pots. (the way they are connected seems to be a little bit unusual though). The diodes on the outputs of
these oscillators are for mixing the signals together without shorting them out. The result is that the mixed signal will be whatever
oscillator output has the highest voltage.

Before the signals are mixed together they all pass through 2 switches. The first switch is the 4066 the second one is SW1. With SW1
you can manually mute each oscillator. The 4066 switches are controlled by a simple sequencer made with the 555 and 4017.
The 555 is used as another oscillator (squarewave) and the frequency of this one can be controlled with the 2M2 pot. With those
component values the range is somewhere from 3Hz~140Hz (you can use this online calculator).
The output of the 555 is connected to the Clock input of the 4017. This chip is a decade counter and it just makes one of its outputs high
in sequence. Everytime it gets a low-to-high signal from the 555 output it will advance one step. Because the reset input is connected to
the 5th output it will only count to 4 and then restart. The outputs of the 4017 is what controls the 4066 switches so only one of the
oscillators is send through to the output This actually makes the diodes redundant.

The opamp at the the right corner is used as a buffer. It's configured as in inverting amplifier which is a great way to mix signals together
but that's not how it is used here.

some modifications/improvements/suggestions:
- a 10K resistor between the output and GND, this wil prevent any loud pops when connecting the device to a mixer/amplifier/efx unit whatever.

- configure the output opamp as a voltage follower. This way you can eliminate the two 100K resistors (R20,R21).
you could also remove the diodes (D1,D2, D3, D4) and the 10K resistor (R22) but you'd need them for the next suggestion.

- make the connections between the 4017 outputs and 4066 control inputs patchable/switchable.
using connectors and patch cables would give you the most freedom and also make it possible to use something else to control them in the future.
you could also use four 10-position (rotary) switches between all the outputs of the 4017 and the control inputs of the 4066. You'd also need
a fifth switch connected between the outputs of the 4017 and its reset input.

- buffer V+ with another voltage follower.
This will make the oscillators more stable but it might not be so easy to adjust on the stripboard layout.

- use different capacitor values for the frequency of the 555 (C7).
I think it wil be great at high (audio-range) frequencies but low frequencies will be fun as well. You could add a switch to select different values.

- if you use a smaller value for the 2M2 pot the range will be smaller but also more precise.
It would work well together with a switch for different capacitor values.

- a binary counter (like a 4040) instead of the 4017.
Not something that is easy to experiment with unless you build it on a breadboard or make the circuit patchable with connectors/cable.

- you can also make the Clock (and reset) input(s) of the 4017 patchable so you can control the speed with something else.

- maybe some LEDs connected to the outputs of the 4017, blinkenlights are always fun.

- check out the Lunetta section of the forum if you haven't already. Wink

Most of these require some modification to the stripboard layout but some might not be that hard to do.

PHOBoS · Posted: Sun Apr 14, 2019 10:27 am Post subject:

blue hell · Posted: Sun Apr 14, 2019 10:43 am Post subject:

PHOBoS · Posted: Sun Apr 14, 2019 11:09 am Post subject:

Not sure, but I seem to recall having used them before and the circuit wasn't anything special but I could be wrong.
note that V+ is the Vgnd connection

JovianPyx · Posted: Sun Apr 14, 2019 11:48 am Post subject:

I wondered the same thing as Blue Hell wrote, thanks for pointing that out, PHOBoS. It's a rather unusual way to label rails.

That kind of labeling makes it more difficult to understand the schematic (again IMO). IMO +V should be labeled Vgnd and what is labeled with a ground symbol should be labeled -6v with +12v relabeled as +6v. This would IMO be more clear and allows for an easy implementation of the circuit with a true +6/-6 dual supply - for which there are already regulators.

This kind of drawing is a bit sticky because it starts with a 12 volt source and converts it to what is essentially a dual voltage supply by creating the virtual ground. I'd draw it with the 12 volt and "ground" input rails through lines to circles or dots and from that to the Vgnd and +/- 6v creation network. In other words - show that it comes from a 12 volt source and that it is converted to +6v / Vgnd / -6v.

I know it is to some a rather minor point, but it facilitates looking at the circuit and knowing what it's doing a bit easier.

Now that I can see what it's doing, it looks cool.

blue hell · Posted: Sun Apr 14, 2019 11:51 am Post subject:

Oh .. virtual ground - had missed that, that's better at least.

Thing is with the lm3900 the input voltages can not swing as far as for voltage input (regular) opamps .. the thing has a bit of an atypical low impedance input circuit.

Anyway. just wanted to let hear a word of caution, I'm not going to analyze the circuit to hypotize about what will happen.

PHOBoS · Posted: Sun Apr 14, 2019 12:14 pm Post subject:

I agree with most of what you said Scott but I personally would keep it as GND/+12V and relabel V+ to Vref.
The reason is that the left side of the circuit is single supply (it doesn't make any use of the Vgnd) so using
-6V/+6V might add some confusing. Of course you could label that side with GND/+12V. Also the circuit has
an audio output so you want to use GND for that. With an actual dual supply you could leave out the AC
coupling cap and use the actual GND instead. Relabeling GND/+12V to -6V/+6V might also add some confusion.

In the end it's just a voltage potential and it might aswell be -40V/-34V/-28V Laughing

I am actually slightly surprised it uses 12V instead of 9V (which should work fine) as this seems like a typical
battery powered circuit.

JovianPyx · Posted: Sun Apr 14, 2019 12:30 pm Post subject:

I can see using Vref instead of V+.

However, -112, -106 and -100 or whatever other numbers is just as confusing as the way it's currently drawn.

My problem with V+ is that there is no voltage associated with it at all. At least something like "Vref (+6)" would tell the builder what voltage should be there (for measuring in case the circuit isn't working).

The reason to use Vgnd for that rail is that for an opamp's functional summing node (which exists in the schematic), it makes sense to show an opamp's inverting input placed at (essentially) ground potential --- because that is what sets the summing node voltage. If you measure that referenced to Vgnd, then you will see zero volts.

I did write that I would have drawn it showing that the power coming in is 12v and 0v with a conversion network to what is actually a virtual grounded dual supply system with +6v and -6v rails.

Again, it's a minor point to some readers, but for people learning electronics, a clear and concise schematic makes that process easier. Heck - it confused me until I read what you wrote. Just sayin' Cool

csj2k · Joined: Mar 10, 2019 Posts: 14 Location: UK

Wow, PHOBoS, thank you so much for the time and effort you put in to explaining the circuit and improvements/modifications, I'm very grateful.

I think I'll end up making this circuit twice - once as is with the addition of the resistor on the output so I can see how it sounds/functions and then a second time with some of the more interesting & complicated modifications.

csj2k · Joined: Mar 10, 2019 Posts: 14 Location: UK

I've built this layout and can confirm it works perfectly. I'll try to upload a sample once I have more time. As I mentioned, I'm a newbie to DIY synth building but I think this may be my favourite synth so far. The lower frequencies give you a very pleasing percussive sound and when combined with the higher tones, you can create some really groovy loops on the fly.

I ended up using the IC's specified in the layout because by the time I got around to making it I had all of them.

c1rcu1t · Joined: May 04, 2020 Posts: 10 Location: EU

PHOBoS · Posted: Sat Jan 23, 2021 6:22 pm Post subject:

c1rcu1t · Joined: May 04, 2020 Posts: 10 Location: EU

PHOBoS · Posted: Sun Jan 24, 2021 4:25 pm Post subject:

yes just leave the capacitor in but I would reduce it to 100nF..1uF since there is practically no load anymore which is the nice thing
when using an opamp and the reaon it works. The problem with just using resistors without the opamp is that if the load varies it will
affect the voltage. And this can result in bleedthrough where you will hear an LFO while it isn't connected to anything or oscillators
syncing to each other which is generally not what you want for drones.

For a dual supply I would suggest using a wallwart one which takes a single AC voltage and converts it to a dual DC supply.
You can have a look at the MFOS one: http://musicfromouterspace.com/analogsynth_new/WALLWARTSUPPLY/WALLWARTSUPPLY.php
Normally I would recommend using adjustable regulators like the LM317/LM337 but for a simple circuit like this using fixed regulators
works fine. Adjustable is useful when circuits use the supply as a reference voltage for creating something like a 1V/Oct CV though
ideally those would use a seperate more stable voltage reference.