Author: rt

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Voltmeter

I’ve just made a new addition to my self-made power distribution system- a small voltmeter (the display with the numbers on the left, by the recorder).  This allows me to see exactly how much battery power I have left  They’re available from a number of sellers in China on ebay

I just soldered the red and green wires (+ power and voltage reading point) to the positive pin and black to 0V) on my power distribution box and it all works

Here’s the distribution box and battery:

It’s essentially a load of locking DC connectors wired in parallel

 

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Selling Stuff

I’ve had a rummage through the cupboards and I’m looking to get rid of a few bits I rarely use, or have meant to get fixed and haven’t.  Open to offers on all

Doepfer Regelwerk Discontinued MIDI/CV sequencer/fader controller SOLD

 

Yamaha DX7S 80’s classic with a few tweaks.  New internal battery fitted £200

Panasonic NV-MX300 small 3CCD DV camcorder- doesn’t play nicely over FW with MS Windows (firmware bug) £200 SOLD

Commodore MK10 mini-key MIDI keyboard £15
Really light midi controller keyboard, great with small synths/samplers without keyboards.  And gets bonus retro points for saying Commodore on

Sennheiser ME3-ew Headset mic £50
Part of the Sennheiser ew135 system, as recommended by Alan Partridge.  Needs 5V plug in power.

Behringer Ultra DI800 8 way DI box £50 SOLD

Roland D-110 multitimbral sound module £40
Volume knob missing

Roland SP-404 (broken, won’t boot up) sampler good condition £50

AKG C535EB Condenser mic (broken, no signal + paint come off) Nice when working… £30

 

Mackie 1604 rackmount rails, unused £15 SOLD

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Clocker / Counter

Here’s a video of me performing an adapted version of Alvin Lucier’s Clocker at Bang the Bore X: Zone of Alienation

Instead of using a clock, we substituted it for a Geiger-Muller counter and radioactive source: Thorium 232.

Equipment used:

DIY Galvanic skin response sensor
Tapco Blend 6 Mixer
Roland SDE-3000 Digital delay (has control voltage input)
Coutryman B3 Microphone (to pick up the counter’s speaker output)

 

 

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Radio microphone comparisons

I’ve done a comparison of the various models of (reasonably) high end radio microphones available in the UK which will work with DC powering.  As a number of them work with 2 transmitters to 1 receiver, I’ve also made a cost comparison (most competetive I could find, including VAT) of 2 sets and put in the weight of the transmitters.

Transmission systems:

Analogue: Up until recently all radio microphones were analogue.  They use a compander circuit which compressed the audio signal on transmission and expands it in at the receiver.  The circuits need to be compatible on each end to match

Digital Hybrid:  Here a digital signal processor at both ends of the system looks at the incoming analogue signal coming in an compares it to a predictor algorithm, and sends any difference from this to the receiver as an analogue signal which will recreate the original.  They can also program in different compander algorithms, which can mean the receivers can work with other equipment.  The conversion and processing adds some latency (time in ms)

Digital:   With ‘pure’ digital systems, the signal is converted into a digital signal and compressed using a high-speed codec (like mp3 but faster to read/write and maybe better quality) before transmission.  This means they don’t use a compander at all and there are less analogue to digital conversions than with hybrid systems.  The conversion processes also add latency

Diversity:

This effectively means that the receiver has two goes at picking up the signal and picks the strongest, however the point where this happens depends on the receiver design (all receivers here have diversity in some form).  “True” diversity requires two separate receiver circuits, whereas antenna diversity switches between the signals from the two antennae.  In analogue systems it is often audible when switching between antennae, although I’m not certain with digital systems.  Also only two systems have true diversity in a dual channel receiver (4 receiver circuits), the Wisycom and Audio ltd EN2.

Bandwidth:

Although UK Channel 38, which we’re all supposed to be using next year is only 8MHz from 606-614Mhz, if you’re doing any work abroad or getting site-specific licenses you may have to be more flexible (or if things like ‘white-space’ devices start popping up).  The Wisycom, Sennheiser and  Audio Wireless systems have larger bandwidths (at a cost)

Remote:

Some of the systems have methods of remotely monitoring and/or controlling the receivers, and a number of them require buying a separate add-on or device.  Both digital systems will allow full control of transmitters from the receiver and the Sony system will allow you to name transmitters. The other systems require things like infra-red remote controls (which may not penetrate costume).  The Lectrosonics system uses audio tones through the attached microphone.

Output:

A few of the digital systems will allow digital output to recorders/cameras which have it, which can free up some more channels and reduce conversion processes.  Only the Sony system has word clock, so can be used in multiple instances in a system without sample rate converters.

Notes:

One of the main differences between the Zaxcom system and the others is that it can do some things which would require additional hardware.  The transmitters also act as 2.4GHz receivers so talkback and timecode transmission can be used with them if the receiver has the IFB option (or from a Zaxcom recorder).  Finally, some of the transmitters have recording facilities (for backup purposes) and will transmit in stereo.

Also, finally- if you are buying radio mics in the UK, make sure they’re Channel 38 compatible (606-614MHz), the current band, Channel 69 (854-863MHz) is probably going to be sold to mobile phone companies after the olympics.  Also the (otherwise lovely looking) Lectrosonics D4 isn’t available here as it uses a current GSM mobile band, so it won’t work.

System (RX/TX) Transmission system Diversity RX weight Dimensions (mm) Bandwidth (CH38) Remote Output RX cost TX cost Price: 2xTX+2xRX Notes
Lectrosonics SR / SMB Digital Hybrid
(3ms)		 Antenna (1ch true) 195g 68x89x18 25.5MHz All with RM (£462). Or phone app (£30) Analogue £1,650.00 £1,170.00 £3,990.00 Compatible with Senn HiDyn+, Shure, Audio ltd tx. Scan function
Lectrosonics UCR411a  / SMB Digital Hybrid
(3ms)		 True (1ch) 330g 82x120x31 25.5MHz All with RM (£462). Or phone app (£30) Analogue £1,250 £1,170.00 £4,840.00 Compatible with Senn HiDyn+, Shure, Audio ltd tx. Scan function. Front end tracking
Zaxcom QRX100 / TRX900LT Digital (3.6ms) Antenna
(1ch true)		 170g 83x133x32 30MHz All + IFB/TC – IFB board
needed £590 (2.4GHz)		 Analogue+ AES £1692
(£2282 w/IFB)		 £1,149.60 £3990 / £4580 Stereo transmission. IFB allows
2 way audio, TC, recording option on TX. Camera link TX. Scan
Wisycom MCR42 / MTP30 Analogue with digital expander
(1.3ms)		 TRUE (2ch) 180g 68x115x18 240MHz All (IR), (battery on emulations) Analogue+ AES £2,548.00 £1,978.00 £6,504.00 Compatible with Senn HiDyn+, HDX, Audio ltd  and most other analogue systems. Scan. 10mW circulator on TX. Moveable filters
Sony DWR-S02D / DWT-B01 Digital
(3.4/3.6ms)		 Antenna 280g 88x119x31.3 72MHz
/ 66MHz (tx)		 All + metadata (2.4GHz) Analogue + AES
(+Word Clock)		 £1,901.33 £1,278.84 £4,457.00 USB keyboard input. 7V power only. Scan, full remote control of TX from RX. TX power goes down to 1mW
Audio Ltd EN2 Analogue TRUE (2ch) 196g 63x139x20 24MHz Analogue whole kit £2,753.00 LCD on side. Scan. mini TX avalable
Sennheiser EK3241B / SK5212-II Analogue True (1ch) 200g (x2) 74x120x28 36MHz RX,
184MHz TX		 Battery (RF) Analogue £1277 (x2) £1,996.00 £6,546.00 RX can be reprogrammed within a 240MHz block. 10mW circulator on TX
Micron SDR550 / TX700 Analogue True (1ch) 200g (x2) 63x121x22 32MHz Analogue £1618 (x2) whole kit £3,236.00 no LCD display, New tiny TX
Audio limited DX2040 / miniTX Analogue True (1ch) 250g (x2) 64x147x20 24MHz All on separate IR device Analogue £1716 (x2) £960.00 £5,352.00 display on switchIR only (£50). Scan on palmpilot only. TX is Tiny
Audio Wireless Analogue True (1ch) 200g (x2) 62x114x20 32/64/120MHz Analogue £1275/£1700
/£2150 (x2)		 whole kit £2750/£3400
/£4300		 LCD on side
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Batteries

I’m really excited about a job I’ve got coming up, I’m off to France for a week to follow Team Strakka around for the Le Mans 24 hour.  Not only is it going to be taxing on me, especially for the race- but also for powering my kit.  So far I’ve managed to get by on AA batteries (bulk bought duracell procell from ebay or Kingsland waste market in Dalston), but it’s really not going to be practical for a week.

First of all I’ve found a way of getting a bit more from the AA’s- you can buy chargers which will get a few more goes out of alkaline batteries.  I’ve just had a couple of these arrive and they’ve got some of the spent batteries in them at the moment.  Both the mixer and recorder seem to give up when they get down to around 1.3V.  They’ll still be useful for the radio mics and as a backup.

For a while I’ve used a cheapo chinese Li-Ion 12v battery “6800mAh” designed for CCTV (with a polarity reverse cable) which’ll get a couple of hours out of the recorder. I think the 6800mAh quoted might be for something like 5V though (or just lies).  The connector is jut a 2.1mm barrel connector though so I really don’t trust it.

From having a look at what was available my choices were:

7.2V DVcam batteries- small, long lasting (although the equipment may drain more at a lower voltage, depending on the regulator), locking connector. Reasonable price

9V/12V consumer DVD player/CCTV batteries.  Cheap. Non Locking connector

Professional 14.4V NP1/V lock/gold mount etc. Big. Locking connectors.  Expensive

Unfortunately 7.2V wasn’t enough to power my recorder (even though it only gets 6V on AA’s), so that was out.  The consumer stuff would involve risky connectors and look cheap so I’ll see if I can do pro stuff.

I also found a full length NP1 doesn’t fit in my bag (I’ve got a couple of old ones).  The V-lock batteries etc were even more expensive and wider so that may not have been an option either.

Fortunately Hawk-Woods make a ‘Stubby’ NP1 style battery, the NP35 which will fit.  Shopped round a bit and got them for £70 each.  However they’re Li-Ion and my (broken) NP1 charger only recharges Ni-Cd and NIMH.

So, new charger.  They can get really expensive (up to £700…and they just recharge batteries?!?). Got a no-name chinese one off ebay (*hope it works*) for £80 which will recharge 4 batteries after just missing out on a 2nd hand PAG.

Finally to hook it up to my kit.  I’ve just bought a Hawk-woods NP1  shoe (rather than the full regulated distro) and I’m going to sort out a custom cable for it.

 

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Large Feedback Instrument #2

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

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DIY acoustic equalizers

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

 

 

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Large Feedback Instrument #1

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.

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Cabling and Commerce

Recently I’ve been making quite a few cables, including my own camera umbilical and tails. This has been a new adventure into soldering smaller connectors with more pins, but it’s no more difficult than putting standard electronic components onto a board really. The scary thing is paying over £10 per connector in some cases.

Anyway, after I’d bought 100m of mic cable and some connectors in bulk I thought I’d offer some to friends for a reasonable price. As that seems to work I thought there’s nothing to lose in offering it to the general public, so here’s my shop.

www.rtsound.vendder.com

It’s all good quality stuff (same that I’m using), Neutrik, Hirose, Switchcraft etc connectors, nice flexible cable

After a few requests I’m also doing contact microphones and coils. Contact Mics are sealed in Plasti-Dip (Nicolas Collins style), so should last a bit longer and be slightly waterproof (although I can’t guarantee this)

There should be most common configurations of cables and connectors up there as options, but please send me an email/DM for any custom requests. I’ve also got an IDC crimp so should be able to do replacement ribbon cables for things like Mackie mixers and Pro Tools TDM connectors