Infact the most difficult thing is the metalwork for the casing.

Drilliing 16 holes for the switches and lining them up exactly takes some precision measuring. Luckily there is a program called Front Panel Designer that allows you to design a front panel layout for 19″ rack units. All it then takes is to print the design off and selotape it to the front of 19″ panel and use a centre punch to tap the holes for drilling. Make sure to start with a small drill bit and step up with a few different sized bits. Starting off drilling with too large a bit will certainly make the drill slip most likely ruin the front panel. You may then need a file to smooth out the inside edges of the drilled holes to get a perfect fit for the switches.

As though drilling out the front panel itself isn’t enough of a pain, cutting a hole for an IDE socket and 2 D-SUB types alongside a couple of holes for XLR sockets can be very awkward.

Depending on how thick your casing is you may get away with using a nibbler to cut shapes in the metal. Mine broke after much use so I had to resort to using a small drill bit to drill the shape out and then smooth the edges out with a metal file. What task.

I also drilled holes in the base of the unit so that I could place plastic PCB mounting pins to mount the PSU and the amplifier circuit.

Transformers were bolted on the inside of the case.

The plan was to build a 16 channel summing amplifier to sum the individual outputs from the PC DAW – Digital Audio Workstation – using two DOA – discrete operational amplifiers – as the output stage.

Why sum the outputs when I can mix internally and bounce the 2 track output?

To make good use of a rack of DIY Class A Line Amps that were built sometime ago. They were roughly based on the Neve 1272 line amp that used a stripped down version of a Neve 1073 Mic Preamp circuit.

One less gain stage and fixed at 55dB. As mic amps great on drums and guitars, but only really effective in close micing applications. The absence of the later gain stage meant they saturate the sound at higher gains. Not a nasty saturation at all, but certainly coloured. This can be good or it can be bad. Depends on the application and your taste in colouration. Recording ’sensitive material may need cleaner pres with more gain. As line amps though they’re perfect. Eight of them should give me a decent mix.

The Amplifier

16 inputs are fed to two banks of resistors, odd numbers left, even numbers right for eight stereo pairs.

As output pans are fixed either left or right 16 switches are incoperated to throw the L/R signal into the centre.

This makes sure we don’t waste a stereo pair if we only need a mono output. Just pan the signal hard L/R on the DAW output and throw the corresponding switch to centre it.

Inputs are terminated with two 25 way D-SUB connectors. As the unit housed in a 1u casing this squeezes the most amount of space from the crowded backplate.

The idea of hand drilling a hole for an IDE socket, plus room for the XLR outputs and 16 jack inputs would be impossible. The D-SUBs tidied things up a lot and cut expense.

There is no volume control. The was no room for volume control. The unit could probably do with a trimmer to drop the output a touch as once you send some tracks through it for mixing it can get quite hot on the output. (I often like to drive the line amps quite hard to get a bit of saturation.) Not a big issue if we use the input trim on the 2 track mix input, yet I may still rewire the transformer for a 2:1 step down and see if this helps.

Anyway

Here’s The Partslist

1u 19″ Case
1 IDE type socket
1 PSU 3 rail with adjustable voltage
2 D-SUB connectors female
16 SPST single pole single throw switches
32 100k input resistors
2 125uf capacitors
2 Op Amp circuits
2 feedback resistors
2 feedback capacitors
2 output transformers 1:1 600ohm
2 XLR outputs

After a small break from my DIY antics… mainly due to a recording studio evacuation and a couple of house moves, (the usual things) it’s time to get back on the DIY road.

This time though things are different. I have this site to catalogue my various projects and post nice pertty pictures when I finish them.

The first thing I will be posting is a new project I’m undertaking out of necessity. I ‘need’ to build a mix buss to sum the outputs from my DAW ( Digital Audio Workstation for the un-acronysed)

There is the never ending argument of ITB (In The Box) vs OTB (Out The Box) summing.

‘floating point integers mathematically….therefore ….. impractical ….summing …..digital domain….. satisfactory??’

Hmmm… did that make sense? None if it does thats why Nyquist remains theory.

All I know is that summing in the analogue domain makes mixes sound better.

Maybe our ears like errors. After all….crunch sounds good doesn’t it?

Back on track….

I’ve got loads of little bits floating around….rack cases, transformers, a couple of 2520 DOA (Discrete Op Amps), Neve BA283 circuits, a broken 1176 circuit and bucket full of resistors etc etc I might as well put it all to good use….

I’m sure you are as excited as I am to watch me start cutting holes in my fingers as I attempt to mount toggle switches in 2mm steel rack panels with nothing but a craft drill and a metal file….

Watch this space…. DIY is back

“There can be no spill between instruments as this will make mixing extremely difficult”.

I’m not sure where this train of thought originated, but I can guess it only became an issue with the rise of multi-track recordings and the need to keep things clean on their respective channels and to allow the ‘perfect mix’ to be created.

Sometimes though you actually want a bit of spill and other times…. you wont notice it anyway.

The ‘dreaded spill’ really only becomes an issue if you are doing multiple takes and overdubs and the remnants of previous takes may be left on the recorded track. And then this really only become’s an issue if the unwanted takes are out of time, out of tune or just plain wrong.

Granted this happens, but should you even be spending time in a recording studio if you haven’t practised the song enough to know what parts go where?

I’ll let you answer that…

So when does spill become a good thing, or even a necessity?

When you require some ambience.

You may wish to actually capture some of the room sound. And if you are doing your recordings with any thought then you will most likely will be setting up mics at specific sweet spots in a room just to add a little more vibe to the mix.

Sometimes isolation can kill your vibe. You make a room too dead and the drums loose that depth. You can try and add it back with a convolution reverb or whatever plugin, but you’re not really going to get a true sound of a live drum kit being thrashed in a room.

Of course you will want to spend time getting a degree of isolation between instruments, but this can be done with a careful mic placement and a bit of thought with the positioning between the band members.

I remember reading an article some years ago about how Pink Floyd actually ended up placing the piano next to the drum kit on a recording session as this was the only place it wouldn’t be so noticeable in the drum mics. I think this was to do with the length of the notes in that position and how the percussive action of the piano was masked by the drums… amazing stuff when you think about it. The fact was when both piano and drums were playing together, that’s all you noticed… piano and drums

But back to spill. Even if you don’t want pure ambience, some spill can give your mixes a special kind of sound that you wouldn’t always get had you kept everything in complete isolation.

For example you may track the guide guitars in the same room as the drums. With careful mic placement you keep the guitar sound to a bare minimum and it only bleeds into the overheads. Once you re-track the guitars and mix the drums you end up with a kind of double tracked heavily compressed distant guitar track that is present on the overheads. It adds depth and width to the newer guitar take. As long as there are no glaring mistakes in the original guitar you have created a unique effect that can give your recording a different natural ambience.

Of course this kind of approach has to be a controlled form of ambience. You couldn’t take it away if you had too much guitar in those overheads and then your drum take may be ruined.

Perhaps this is why people find it is easier to isolate everything and put it back together in the mix?

Obligitary picture of some 'Gear'

This site is going to provide resources on creating better recordings and mixes for musicians.

With the myriad of options available to musicians to produce and record their own music at home there seems to be a never-ending need for a better fnished product.

It’s not an easy task to begin recording an album, let alone finishing one. The music however will always be measured by the playing and the overall sound. Afterall it’s the sound that most often defines an album.

Hopefully this site can provide some insight into the recording process and how to get a better sounding record.