Month: April 2011

From last time I’ve now managed to get some new IDC headers to replace the broken ones, so went about reconstructing the ribbon cable.

I also gave up on the idea of getting an A-gauge patchbay and soldered in the aux sends to the back of a 96way bantam patchbay as shown here:

as there was only one 0V reference I had to get a wire and bridge it across all the other connections.

I also wired in 8 jacks to feed back the signal into the mixers inputs.  I decided to leave the connections open too, although I considered having them normalled (see this article for patchbay configurations) which would be mental (all signals would be feeding back all the time).

Now to fire it up again and see if there is audio…

Unfortunately I’ve only got 2 bantam patch leads (this might get expensive to remedy). But running 2 channels and 2 auxes it sounds like this (go to the end for animal sounds):

 

Large Feedback Instrument: Test 1 by richard-thomas

In February I recorded a fantastic concert (review from The Watchful Ear) put on by Bang the Bore in Southampton.  It was located in the Castle Vaults, under the town centre and consisted of a performance of Alvin Lucier’s classic, I am sitting in a room and a top form set from John Butcher who does things with a saxophone which must be heard to be believed.

As a large part of what was going on in this gig was reacting to the space (John Butcher has an ongoing ‘Resonant Spaces‘ project), I thought I’d try and record as much of the room without it getting too muddy.

Omnidirectional microphones, pickup the most room sound but need to be placed within the critical distance (closer than the with directional microphones) to receive more of the direct sound from the performer rather than reflected sound from the walls of the room.  I was looking at recording outside the critical distance, in the diffuse field (where there is more sound reflected from the room) so needed to improve the directivity of my microphones but retain the flat frequency response down to low frequencies that the omni’s have.

You can do some of this using EQ on a mixer.  Alternatively you can affect what happens to the sound before it gets to the microphone by creating a reflective baffle around the microphone, which I intended on doing.  DPA already make these for their microphones, but they’re £75 each (ow!) and don’t fit my AKG’s.  So went out to the local shops in search of foam balls…

I came back with a pair of ‘Dog Balls’ from “Magic Prices at Just Jeff’s” (yes, it’s really called that) and an apple corer.  Total cost was under £3. And lighter than a mixer 🙂

Unfortunately the apple corer wasn’t the best tool for the job:

however (with some pain and awkwardness) did get through the balls *ahem*.

and managed to squeeze a microphone through:

although they did look a bit silly they did do the job, however the room wasn’t as reverberant as I expected.

I’ll see what’s happening with the recording- if it gets put up somewhere I’ll add a link

 

 

I do quite a bit of mucking about with no-input mixer setups, it’s usually my little Tapco Blend 6, but started running short of Aux sends (independent outputs from the main output on a mixer) and started thinking of what you could do with more…

I had a look round and the only mixing desks you could readily get with this were desks designed for monitor engineers and they were big, or there’s the A&H Mixwizard 12M which looks just about ideal, apart from the price. I had a look into matrix mixers (which are essentially just aux sends) and found either were no longer available in the case of the Mackie/Oz Audio HMX-56 or again expensive (Midas XL-88)

Looks like it’s a homemade job then…

I’d been looking up matrix mixer schematics and experimenting on breadboard until I came across some input modules on ebay (NOS) for a DDA CS12 monitor console, for not much money at all (and the schematics are online).  Ended up buying 2 of them (8 channels each). They have 12 aux sends per channel (more than enough).

Then looked into sourcing the stuff to make them work which was quite a bit more difficult.  Found each channel is connected up and powered with a ribbon cable, which happen to be the same connectors as on a floppy drives (great!). But I needed at least 8 nodes and a way of hooking them up to a power supply (needing +18V 0V -18V and +48V rails).  DIY job. Bought an IDC crimp, some lovely retro rainbow ribbon cable  and some IDC headers (which took 3 months to get here from China and most parts were already broken…)

And I needed to power the thing. Replacement linear power supplies for mixers like this are big, heavy and expensive things and I wanted the desk to stay portable.  You can’t usually get switching power supplies with two rails (or at least I couldn’t find any), so instead I bought 2 18V PSUs and wired them so 0V on one and +18V on the other were soldered to the same plug, making that 0V, so 0v on the ‘low’ power supply was now .  An XLR seemed to be the only 3 pin connector I had handy so soldered them to this (let’s hope I don’t ever plug this into a mixer or similar.

 

 

After counting (and double checking) the number of each strand on the ribbon cables (the rainbow effect was very handy), I separated out all those connected to power and put them on another XLR.

After also crimping on 8 IDC headers and plugging them into the PSUs they started making a bad clicking noise.  Something was shorting out.  After going through the XLR connections multiple times to make sure something wasn’t touching it turned out one of the crimps wasn’t in line and was shorting out adjacent cables.

After the cable was taken apart and put together I found most of my IDC headers were now completely broken…  Fortunately one was left so I plugged it in.

It’s alive!

Next steps are (when I’ve got more headers) sorting out the outputs.  I’d got hold of a Mosses and Mitchell B-Gauge patchbay I was going to use for this (with patches going back to the line in), but on second thoughts everything it’ll be plugged into will use A-Gauge jacks so might get one of those instead.