Category Archives: Electronics

DIY Anodizing

Hi there!

To finally round off a good solid month or two of building audio electronics studio stuff for the album ( in this case some gorgeous pre-amplifiers for recording vocals ), I decided, just before handing over the final product to Lee Safar, to try my hand at DIY Anodizing….

So it was off to the wonderful Sydney Hackerspace ( Robots and Dinosaurs ), to get some help.  Macca, an already competent Anodizer ( 😉 ) gave me a hand understanding the process.

First we mixed the active ingredient ( an acid ) with demineralized water, sitting inside of a PVC tube that contained a cathode ( a piece of aluminium ), and then the anode ( the front panel of the pre-amplifiers itself ) was connected to complete the circuit through a constant-current 2.5Amp power supply.

We let this do it’s anodize thing for an hour, then immersed it in a very string mix of red clothes die and more water ( this time regular, but warm, tap water ).

From there, around another hour later, it was straight into a boiling water bath for around 10minutes, to fix the die within the molecular structure of the metal, and then BOOM, you go a red piece of aluminium….!

So enough nerd speak, here are some crazy-cool images of the final result – a DIY “red”(ish) coloured set of pre-amplifiers:

ClassicAPI VP26 and Sound Skulptor MP73 Preamps are finished!

Well, what a project!

For those who haven’t been following my progress lately, I built ClassicAPI VP26 and Sound Skulptor MP73 microphone pre-amplifiers ( pre-amps ) to use on the album I am currently producing for Lee Safar.

Whilst the pre-amps themselves were fully self-contained kits, the processing of putting them into a 1u rack case, along with some of my own customizations, was a much more time-consuming and complex project than I originally expected.

I am happy to say that as I type this, they are completely working and racked up beautifully in a case I cut with my own hands ( no CNC machines were used this time, just a good old drill press and a bunch of manual labour! ).  The next time I undertake such a project, I think that I’ll be relying more on automation, but I wanted to get my hands dirty this time.

Picking up from my last pre-amp post, I rounded up the last part of the build by assembling everything roughly, and running through the MP73 calibration procedure for a few hours, running a bunch of test tones to and from the unit, and calibrating things like the clipping LEDs etc.

At that point in time, the whole thing looked a little like this:

Here you can see the test tones are being fed in to the MP73:

Since the MP73 is designed for a custom Sound Skulptor case, I had to improvise on some of the wiring:

I also had to ensure that the VP26 kept working with the MP73 running simultaneously, since the JLM Audio Powerstation power supply I used was providing all of the various voltages I needed:

Here was the first image I took of the clip lights on the MP73 operating correctly.  That was an exciting time!

From that point, all that was remaining was the hefty final wiring, which included an extremely cool customization feature that I added for the specific purpose of being able to get a bunch of different tones for the recordings we are going to do of Lee’s vocal.



The Customizations:

Basically, you can see here, an unlabelled little switch just to the right of screen:

When it’s sitting “up”, which is the “off” position – it has no effect.  but when you flick it down to the “on” position, it does something pretty cool.  It turns on a relay that bridges the two inputs ( if we label the VP26 circuit as pre-amp A, and the Sound Skulptor MP73 as pre-amp B ) so that the inputs for A and B are connected.  This means that with the switch down, plugging a single microphone into input A, drives BOTH the preamps A & B, and produces distinct, isolated outputs from both the A & B channels.

This is an intentional cost-cutting feature, designed because we decided not to buy two microphones.  Instead, I wired in this bridging mechanism, allowing us to get the phase-accurate sound of BOTH the API and Neve-style pre-amplifiers at the same time, from one source.

This allows us to then record the two different flavors of sound to the Left and Right inputs of a standard sound-card.  Cool huh? 😉


The second customization again relates to the bridging swtich, but allows you to still safely use phantom power.  With the bridging switch in the “off” position, channels A and B have separately controlled independent phantom power switches.  However, with the bridging switch “on”, the phantom power is disconnected from the B channel, and instead, the phantom power from channel A is used only.  Since the inputs are bridged, this just means that you get the correct phantom power, controlled by channel A’s phantom power switch, without the hassle of having to worry about the current setting of channel B’s phantom power switch.

It’s basically just a safety feature that allows phantom powered microphones to be used in the bridging confuguration.

I can’t WAIT to use this feature and be able to blend two independent colours of Lee’s voice together to find the right tone.



The Final Images:

Here it is, completely finished, but with the lid off:

And here are the carefully wired internals:

Followed by some close-ups, that show some of the features I’ve discussed:

Here you can see the relay driving the bridging input configuration.  It sits right near the inputs to keep the length of cables as small as possible.  I didn’t want to run audio cable all the way from the rear inputs, to the front switch, and then back again, so this was a good alternative solution:

And here are the rest of the internal pics:

Since Lee needs to take this back to LA with her, I’ve included the ability to switch between 120V and 240V input power:

Looking good!

And here it is, trying out a rack space for size, alongside my previous build, an SB4000 SSL-style Bus Compressor ( thanks ruckus! ):


For any details about this, please let me know and I’ll give you whatever information I can.

It was a really fun and challenging project and I can’t wait for Lee to arrive in Australia to start recording the vocals for her album through these.

Sound samples coming soon….

Updating a Legend – SEM transplant

I’d like to tell you all a little story about a recent experience I had with Synthesizer legend Tom Oberheim.

As you’d know from this website, I purchased an Oberheim SEM Pro synthesizer from him a while back.  I had issues with it interfacing with my modern MIDI gear ( namely an RME Fireface 800 sound card ), which it just would not recognize.

I actually wrote directly to Tom about this, also mentioning that I’d figured out that running the Fireface MIDI out to my Yamaha s90ES keyboard, out through it’s MIDI Thru and THEN into the SEM actually fixed the issue.  This got me thinking that the problem was to do with the fact that the original MIDI spec specified 18V signals.  Most modern gear can only output 5V max due to USB power restrictions.  After a few e-mail exchanges, I explained the issue, let him know that I had a theory on signal strength and the SEM being too correct in it’s MIDI implementation ( i.e. to spec, but therefore not working with modern gear ) and was only half expecting a response.

Well, it turns out I DID get a response.  It was a very detailed and lovely e-mail, the first of a few I received from Mr. Oberheim.  I went on to explain that I have significant electronics experience, and, a few months later, he told me that he’d organized a fix for me.  The fix was a replacement Printed Circuit Board ( PCB ) for the entire Input/Output ( IO ) board.

Not only did he tell me in an e-mail that he was in the process of sending this replacement board to me, but that he also was including a screwdriver as it was the only tool required to perform the replacement.  WHAT a guy.  There are so few people around with such a kind soul.

Since this synthesizer is going to be used on the album I’m currently producing with Lee Safar, I sent Tom a link to our first single, I’m Here – evolutionary theory Remix featuring Lee Safar, and here was his response:

Great!  I love your track! Now I want to hear more.


…. Well, as the photos below show, the transplant of the new IO board was a success, and I documented and photographed the internals during the process.

What a lovely device it is!  Really well made.  You can see also in the photos ( the last few especially ), the old board sitting outside the case, with the new board having been transplanted to it’s new home.

The last photo is the SEM now all fixed, and working perfectly, interfacing beautifully with all of my modern MIDI gear, posing with Tom’s screwdriver ( which I still have BTW, it’s a freaking awesome screwdriver! ).

So, I hope you all enjoyed that little experience, and soon, you’ll also be able to enjoy the sound of this newly fixed synthesis legend.

If you have any questions about this please feel free to ask.

ClassicAPI VP26 Built and tested

Hi there!

For those following my studio exploits I’ve been 1u racking ClassicAPI VP26 and Sound Skulptor MP73 preamplifiers in a custom drilled and layed-out case.  A big thanks to the Robots and Dinosaurs Sydney hackerspace for the use of their equipment.

Two days ago I tested the VP26 ( successfully I might add – it worked first time! 😉 ).

Here are the shots of the resulting installation of the VP26 board into the 1u rack case, and also some of the PSU wiring.  You should also be able to make out some “more complex than usual” wiring around the rear panel near the transformer.  That’s due to the fact I’ve wired this box to support 240V and 120V inputs, to make it compatible with most countries in the world ( it will be traveling regularly between LA and Sydney for the album I’m currently producing ).

I used a JLM Audio Powerstation power supply to derive the 0V, +16V, -16V, +24V, -24V and +48V rails required to run both of these pres in the same space ( including Phantom Power ).

The VP26 is visible as it was wired for the sound test in the last image.  Next up ( hopefully tonight ) will come the MP73 final wiring and testing.


Boxing an MP73 and a VP26 – Part 1

Well, it’s been some time since I’ve used a drill press…. Probably year 10 at school, which was some time ago now….  However, harking back to my days of old, I managed to get some pretty good results.

Those who have been keeping up to date on this blog will know I just finished soldering together Sound Skulptor MP73 and ClassicAPI VP26 preamp kits.  This post is about how I’ve been able to successfully fit them into a 1u rack case.

I got the rack case from Altronics in Sydney:

Working at the wonderful Robots and Dinosaurs Hackerspace in Sydney, the first step suggested to me by my mate talsit, was to put tape ( it’s green! ) across the front of the aluminum panel.  This was so that if(/when) I slipped, I wouldn’t need to shed a tear, as underneath it would be protected.

With previously acquired Ninja hack-sawing skills ( and a really cool hacksaw he had ), talsit helped by cutting to size an Aluminium L-panel that I found at Bunnings to fit as a divider and as shielding protection between the power-supply and sensitive pre-amps, along with helping to mod the case slightly to allow room for the preamp front panels ( which involved some brutal tearing out of screw-flanges with a large pair of pliers – kind of like going to an Aluminium dentist…. )

Next I took the two front panels and laid them to the left middle of the panel.  This was to make room for the power supply that’s to sit to the right of the case, along with a linked/independent toggle for running the pres both from input A, or independently from A and B ( it basically will bridge input A to preamps A and B so that one source can run separately through both preamps ).

I then proceeding to mark with pen all of the holes.  From there I used a digital caliper to measure each and every hole interior diameter.  Unfortunately the Hackerspace did’t have the extremely strange drill sizes I needed – but this was very much a blessing in disguise.  Since I had to mark the centers of all the holes by eye, I knew I’d be out all over the place with sizes.  So I rounded up to the nearest bigger size.  This allowed me to have the play across the whole panel I needed, and the accumulative error was spread out.

Much to my surprise, after drilling it, everything fit perfectly, first time, with no modifications or tears.  Amazing considering how inaccurately I thought I was drilling everything….

I’m still waiting from element14 for some key parts to ship, but, the front is basically done ( sans power switch ), and the rest of the case can be drilled in another Hackerspace session.

Here are some photos of the results and the anticipated case layout – including the lovely green tape ( which will be removed and replaced by a bright red front panel, which I’ll send to be anodized when it’s fully finished ) 😉

Stay tuned for Part 2 where I hope to finish preparation of all of the holes, then Part 3 where I’ll solder it all together and test it….

Sound Skulptor MP73 – Build

Hi there!

For those who haven’t been following so far, I’ve been building some equipment for a high-quality DIY home studio for an album I’m working on for Lee Safar.

This post is about the second of two microphone preamplifier builds.  The first one ( in an earlier post ) was about the ClassicAPI VP26 ( which has a classic old 70s thick API tone), and this one, is about the Sound Skulptor MP73 ( a Neve 1290-style preamp with a warm gooey character ).

The package arrived from Sound Skulptor, so I proceeded to unwrap it:

Here is the top and bottom of the included PCB:

I started to populate the board with the diodes first, as per the excellent included instructions:

After this point however I deviate a little from the provided instructions cause I felt I had a better construction order, however, next came the resistors:

Next came the ceramic caps:

Then the film capacitors:

Then the tantalum capacitors:

Then some transistors:

Then the trimmers:

The header:

The relays:

The small electrolytic capacitors:

The terminal block connectors:

Then the main front panel switches:

Next came the potentiometers:

Then the heatsink clips were applied to the power transistor and voltage regulators:

The large electrolytic caps went in next:

The Carnhill input transformer went in next with some tricky manouvres to seat it into position:

Now the Carnhill output transformer goes in:

So then I trimmed and soldered the output transformer leads, and whacked in some IC sockets ( even though the instructions didn’t mention them, I put them in cause I have a bad track record with destroying static sensitive chips…. ):

I used the front panel, held on by the other components, to help me correctly line up the LED before soldering it, and I’m glad I did, cause now it lines up PERFECTLY.  A slight deviation from the original instructions, but easy, and accurate:

And that was it, finished!  Now I just have to do some careful cleaning of the underside of the board to remove the flux I used on the ground-plane connections ( they had to be HOT to solder properly due to the thermal dissipation…. ), but here are the shots of the final construction:

Now all that is remaining is building a power supply, casing this MP73 preamp with the VP26 one in a 1u rack case, and then, some testing.

But so far it’s looking good – not long to go now!

Catch you all soon!


ClassicAPI VP26 – Build

As I’ve mentioned previously on this website, I’ve been organizing a minimal home recording studio for Lee Safar for the album I am currently producing for her.  In order to save money and also get the best possible sound we can, I’ve decided to DIY a lot of the recording equipment.

Jeff Steiger, owner of the ClassicAPI company was amazingly friendly with all of the questions I had for him when deciding to purchase this kit.  After putting in the order, about a week later, the box arrived:

Everything was beautifully packed, and the initial reaction was “wow, this is one seriously professional piece of kit….”.

Here you can see the silk-screened front panel ( which was shipped in the wrapping it’s sitting on ):

Here is a glimpse of the input transformer, output attenuator and input gain control and associated mounting hardware:

These are the main front panel switches for Mute, Phase reverse and Pad:

Here is the wrapping for the main mounting frame:

The gorgeous input transformer:

A close up of the switches including the 48V Phantom power switch:

Here is the top and bottom of the PCB that comes with the kit:

Here is the whole lot on the table:

The first thing I did was set up the workspace ( yes, I am using a Country Road magazine as a work mat – that’s how I roll – I’m not quite as well setup as when I was working at talsit‘s house! ):

Then I put in the resistors:

Followed by the diodes:

Then the latching push switches:

Then the blue Murata ceramic capacitors:

Then the large capacitors, radial and standard electrolytic went in.  The Mill-Max sockets also went in at this stage.  You’ll notice the botch job of the large 470uF capacitor with it’s horrible soldering.  A note to those building this kit – use flux!  I didn’t and it made soldering to the ground pads exceptionally difficult due to the massive thermal inertia of the exceptionally thick PCB.  I bought some flux the next day and used it to fix up that area ( which you will see in later photos ):

The input transformer went in next:

Then the output transformer ( also note the cleaner solder joint on the large axial 470uF capacitor that I cleaned up by application of flux and re-soldering ):

You can see the output attenuator now after being added:

Next the 48V Phantom power switch went in, and I started to assemble everything into the main frame, along with the front panel:

Next the knobs went on to the potentiometers:

And that was the end of the basic ClassicAPI VP26 build.  A preamp isn’t much without an amplifier now is it?  So the next part was building the gar2520 Discrete Operational Amplifier (DOA) – which performs the actual amplification task.  It’s a compatible physical layout to the original API 2520 units ( which can also be used in this kit as DOA’s ).

The first part of the gar2520 build is the pins for insertion into the Mill-Max sockets of the main VP26 board:

Next go in some resistors and capacitors:

Then the diodes:

Next are the main transistors:

Now we add some more resistors and capacitors:

And more:

And more:

And more:

And more:

And more:

And then, finally, the last parts go in to finish off the gar2520 DOA:

Now the DOA can be inserted into the main board:

And now it’s time for some modelling shots of the finished ( but untested ) product….

And now for some close-ups:

And there you have it.  Next up, the Neve-style Sound Skulptor MP73 build.  Stay-tuned for that, and the testing of this pre.

SB4000 Bus Compressor – Build – Finished

Well, we finally did it;  talsit and I finally finished building the SB4000 compressor.

Here are some images of our handiwork.  The meticulous wiring layout is mostly due to talsit.  Firstly you can see the heat-shrink applied to all bare terminals – here the compression engage and side-chain switches, and even heat-shrink also applied to cable bundles for support:

Next you can see some of the XLR wiring at the back, which uses a star-grounding scheme, that means each pair of XLR’s ( left and right ) is returned to ground separately ( which helps reduce noise and hiss ):

Next you can see the mains switch which has been hot glue-gunned for protection to remove any possibility of direct exposure to a bare live mains voltage ( should you feel the need to stick you face inside of the box whilst it’s on…. ) and the cable-ties for strain relief and rigidity to movement and bumps – it’s all about safety:

We also made sure that for future possible tweaks, things would be tied down, but not TOO much so – hence the plastic clip is used with a cable-tie, since the cable was too thick to fit through it directly and it means easy less fiddly access later on – you can also see the ribbon cable that feeds the display here too:

Red and Blue cabling was used for a consistent colour scheme throughout – to match the blue capacitors and the red circuit board – attention to detail was important to everyone involved:

For those who bought a kit of parts from diypartssupply, you would all have the same meter.  It is marked with + and – slightly indented into the white plastic, which took us a while to find…. Noting that throughout Red is + and Blue is – we hope that these images might help some other people figure out how to wire it.  We also checked this with a diode checker ( which can verify the LED on the meter – the small tabs ) and the diode check on your multimeter can move the meter also to verify it’s polarity and orientation – which we verified before soldering:

And here it is, in all it’s finished glory – waiting only for some better and sexier pot and switch knobs, and some testing and calibration – which I’ll write about next time.  It has been switched on and neither exploded nor got hot, and the switch lights and start-up procedure seemed perfectly fine.  The voltages also check out perfectly – so hopefully that means we have a fully functional compressor!:

Sound Skulptor MP73 Preamp – Kit Arrived

As a part of working with Lee Safar on her up and coming album, I’m also helping her build a studio in her home, so that as and when ideas come to her, she can record them, completely professionally, right then and there.

In order to aid this I’ve suggested she use a Shure SM7b microphone and an Apogee Duet 2 sound card.  One of the missing parts of that chain however, is a big, classic, beefy sounding preamp.  The two types of tone I wanted to give her in particular are the smooth sound of a Neve 1073 and the forward mid-biting rock sound of an API 70’s pre.  I wanted both types of sound extremes to be recorded simultaneously each time she records, so that I’m able to blend them how I want during the production stage.

In order to give her these two sounds within a small budget, I decided to build them myself from kits.  The two kits I decided upon were the Sound Skulptor MP73 and the ClassicAPI VP26 with a gar2520 discrete opamp.

Today the MP73 arrived.  It was beautifully packaged, and didn’t take very long at all to ship to Australia.  I’m very impressed with every facet of the kit, from how thorough it is ( ALL nuts and bolts, the front faceplate and even the pot knobs are provided…. ) and I can’t WAIT to start building it.  You can see in these photos the large heavy iron transformers, which impart the warm sound of this pre:


When finished, it should look a little something like this: