Tuesday, 26 November 2019

Synthesizer Build part-5: THE CABINET & TIPS.

How I made my synthesizer cabinets and tips concerning building the projects on my website.

My first synth cabinet:
I'm not going to get too deep into this because every individual will make their own cabinet or case to their own taste I think. This cabinet represents the vintage 70's look that I wanted for my synth and I'm very happy with it. 
If you are going to build all, or almost all, of the projects on my website you're going to end up with an amazing synthesizer (that I call the "Bergman-Berlin") that can rival the big Moog systems of back in the day and will cost you far less money. You can build as many oscillators as you wish (my system has five) and a variety of filters and other sound changers and noise generators and mixers that will make this an amazing sounding synth. There are examples enough in the demo videos on this site. Here is a picture of my synthesizer as it now is, at the end of October 2020:

Here are some pictures from different stages of building the first cabinet:

Almost finished, just one more panel to fit but already working very well:

I made no drawings and I measured everything as I was building it. That's the way I usually approach woodwork. The drawing is in my head. I did make two cardboard templates for the side panels to make sure I got those exactly the same. I measured the current draw with all panels that I have build so far switched on. All together it drew 250mA. That's less than an old fashioned bicycle lamp. :) I also installed a temperature sensor that is directly in contact with the heatsink of the LM317 that regulates the 15 volt output and it runs up to about 60°C. That's perfectly fine and normal. It can handle double that and the temperature stays at 60° and doesn't climb.

The panels I use are made from aluminium (or aluminum if you're in the States ^^ ). They are 20 centimeters high so you could say I use the LookMumNoComputer Kosmo format. I bought 2 sheets of 1 meter long and 1.5mm thick and they are powder coated in gray/black. This powder coating is something I can really recommend because it's hard to scratch. If you just spray-paint your panels they will scratch very easily. You can write on the powder coating with a white acrylic pen. The one pen I bought had too wide a tip and I sharpened the tip with a razorblade but in the end it was un-useable. I ordered a pen online with a 0.7mm tip and that works far better. But if you laser-engrave your panels then you don't need all this anyway.

One IMPORTANT TIP I want to give you is the following: When you make your front panels for the modules set up a standard for their measurements right from the beginning. What I mean by that is decide on a fixed width for all of them. Choose for instance, 10CM for the bigger projects like the VCO's and 5CM for the smaller ones. Use those widths throughout the synth and don't do what I did and make them just the smallest size they can be. 
Here is why: You're going to build more panels/modules (eventually) than will fit in your synth cabinet and if they have a standardized width you can easily exchange them. For instance you might need more LFO's so you can take out a VCA and put in an LFO panel because they are the same width. I can not do that as easily because all my panels are designed with different widths.  

Make sure the panels you are going to use are at least 1.5mm thick aluminium!! If they are any thinner than that they will bend or flex if you put a cable into a socket on the panel. So keep that in mind!
This cabinet is 1 meter and 11 millimeters wide, 38 centimeters high and deep. 
If you are building your own synthesizer I would be very curious to see some pictures so if you can link to that please leave the link in the comments. That'd be awesome!

When you're just getting into the modular synthesizer hobby you will hear/read terms like 'this module is so and so U high and so and so HP wide. What does that mean?
Well U stands for RU which means 'Rack Units'. It comes from the 19 Inch rack system. 1U equals one Rack Unit which is 1.75 Inch or 4.445 centimeters. Eurorack modules for instance are practically always 3U high which is 5.05 Inches or 12.85 centimeters. There are also horizontal modules in Eurorack that are 1U high. Some rigs have an extra 1U row to accomodate them.
HP stands for Horizontal Pitch and is a unit for width. 1HP is 0.2 Inch or 5.08 millimeters. 
So the Kosmo panels I use are 4.5U high and a 10 centimeter wide panel would be 20HP.

March 2020 the second stage:
Here are some pictures of the second stage of the synthesizer. This is a much simpler case and it is 20 by 20 by 100 Centimeters so it sticks out at the back a bit. This was necessary to accommodate the power buss system. I made some trunk locks on the sides so I can clamp the top section to the main synthesizer. This works just perfectly. I did have to solder these locks though because the locks themselves were connected to the main plate with the screwholes just by three flimsy bits of folded-over metal. So if you put any force on that they would bend and let loose over time. So I heated them with a blowtorch and soldered them from the inside. This worked really well because I used a bit of flux on the metal and this made the solder flow into all the little seems so it is very neatly soldered.

I made the width of the second stage too short by 1 centimeter so I had to use extra pieces of wood to connect the locks to.

For everything I build and publish on this website I use standard stripboards of 24 strips high and 56 holes wide. The layouts I make are 24 by 55 so you have one hole extra room in case you make a mistake. You can order those stripboards from AliExpress for a very reasonable price. However, sometimes the pre-drilled holes are not quite in the middle of the copper strips which makes it difficult to solder components but this doesn't happen often and is the compromise you have to be willing to make. I have built my entire synthesizer with these 24x55 stripboards and all the layouts I publish use this size as a starting point. That's 6,5 by 14,5 Centimeter. Here's a link to where you can order them:


Here are some extra tips about general topics, not necessarily relevant to my projects but just things I want you to keep in mind.

All the projects here require wire bridges to be soldered in. Don't make those wire bridges out of electrically insulated multistrand wire, because it will get messy very fast on your stripboard if you use that. The take in a lot of room and create big solder blobs on the copper side. Avoid doing that if you can. Instead use single core copper wire, like transformer wire. Use sandpaper to clean off the insulating lacker layer and reveal the bare copper and then you can easily solder them in place. I always neatly bend them to the right size too with a pair of neadle nose pliers. The picture below shows the stripboard for the Moog ladder filter (chapter 39) and imagine doing these wire bridges with normal electrical wire. It would be a mess.

Measure the value of every component before you solder it in place. Most multimeters these days have transistor, resistance and capacitance modes so this should be no problem. It might save you a lot of time in trouble shooting later on.

Get an oscilloscope if you don't have one already! You are going to need one very soon if you go on building modules. Get a cheap one from eBay like a DSO138 for about 20 dollars. You can also look at the second hand market. Very good analog cathode ray oscilloscopes can be had on eBay for very little money. I myself decided to invest in a good digital scope and at that time the Rigol DS1054Z was just coming on the market and was praised to the hilt by Dave from the EEVblog on YouTube so I got one of those. I've never regretted that because it's a tremendous help to me and it has 4 channels.

Don't use lead free solder. I know, environment etc etc. The stuff is CRAP! Get the good old 40/60 or 37/63 Tin/Lead solder at a thickness of 0.6 or 0.5 mm. You can thank me later ;)

Why is output impedance important? Output impedance is a combination of the normal DC resistance and the AC resistance of any module that outputs audio signals. This is usually determined by a resistor in series with the output socket. Why is the value important? If you have a high output impedance and you use long cables, the capacitance of this cable combined with the output resistance (impedance) forms a lowpass filter that can cut off some of your high frequency audio. Don't ask me for details, you will have to Google that but this is one reason why output impedance is a thing. Normally we have a HIGH INPUT impedance because the inputs go into opamps which have an infinitely high resistance and we have a LOW OUTPUT impedance around the 1K Ohm mark among other reasons because of what I mentioned above. Now long cables are not usually used between modular synthesizer modules but they are used in amplifiers. I just want you to know about this as part of you electronics knowledge.

Don't put those cheap Chinese Volt and Ampere meters into your power supply. I know these digital displays look cool and it's handy to know how much current your system is drawing but these meters introduce a shit-load of noise onto you powerrails. If you do want a measuring system in your powerrails, use analog meters with pointing needles instead. They look even cooler, especially when back-lit, and don't have internal circuitry that can introduce noise into your system.

Any questions or remarks? Put them in the comments below please. Comments containing links will be deleted!

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