new system in anger...

I've just done a festival, gigs every lunchtime and evening for three full days. Mainly acoustic acts, but with one full band at the end of every night (Rachel Gittus Band, Seize the Day (9 of them now - had to add an extra battery powered mixer (Behringer UBB1002 - a nice flexible mixer, up to 5 mic inputs, 4 stereos, fx & mon loops - actually enough on it's own for a lot of gigs) and Magicfolk, who were suitably impressed with the new electric guitar amp, which proved to be more than up to the job.

I was running up to four generators, working across a battery into the sound system load. The battery has suffered greatly from neglect (was stored where I couldn't get to it and charge it for nine months) and is probably heavily sulphated and high impedance; it's showing 13.2 volts after not being in use for a couple of days, so most power was going straight to the amps, drawing as much as it needed from the bikes. When the bikes were going we generally breaking even, with surplus current going into the battery.

I've yet to document the new connection panel, but it basically has lots of input & output sockets (all now 4 pin XLRs) and a switch connection to the battery, with a circuit breaker (25A) and a 30-0-30A ammeter (from a scrapped old car) in series. No live voltmeter as yet, which will be more useful if I choose to run the system with the battery switched out (which should work fine, although I didn't get a chance to play over the weekend).

Note the lighting in the pic above (showing the lovely Rachel Gittus band). I used one of my 16W shaded flourescent lights on a marquee pole, and two LED spots (bought as a sound to light set of three for £15, I spotted they came with a remote 14v DC PSU, and gave them a go) to give the red & blue highlights. I also added blue LED fairy lights (each set run on 2 AA batteries for weeks) on some mic stands - they were bought in Wilkinsons, I think, last Christmas - a bit of forward thinking on my part. My camera was in a high senstivity mode (ISO800, perhaps) but there was enough for some decent pics, some a lot sharper than this one.

I should add a little about the power cabling - now everything is on 4 pin XLRs, outlets on sockets, inputs on plugs, I was able to be fairly flexible in connecting bikes & systems. For the bass amp, I wired in an extra small battery on a short cable to the bass amp to provide a local reserve to avoid volt drop being significant as the current increased on load which would happen otherwiswe. As I've tried to wire everything with both genders of connectors to give a pass-through, I was able to wire in the bike on the other side of the stage (rider just visible far right of the pic) though this too. This of course did involve using one cable in 'reverse', but since I'd put both genders on the generators too, this was fine - as long as gnd stays on pin 1 and +ve on pin 4, it's all fine, and almost acts as a ring main, current flowing to where it's needed. Connecting the batteries in parallel with varying states of charge wasn't ideal, but I did check the ammeter and very little current was flowing to equalise it... so yes, a successful revision of arrangements there, I think.

Guitar Amp

I've always avoided a specific 12v electric guitar amp, as I generally do acoustic acts, and anyway, electric bands are noisy and always want more power than is available... normally as mains, too. At least if I supply a guitar amp there's an alternative.

Also, the bright input of the bass amp has sufficed in the past, once we get past the teenage strops of the guitarist, in one case. I don't know who was more insulted, me or the bassist they refused to share with... admittedly it's not ideal.

I only built this as I realised I already had all the bits. The box - more or less a 12" cube with a partially open back - and the speaker, a 10" 50W Celestion guitar speaker were left over in the remains of a home built main amp from my active band days (the top of the box was replaced to allow for the preamp panel and the result repainted with blackboard paint, though). Amp was yet another smallish car booster amp - this one £3 in a car boot sale, I think - and the otherwise potentially hard bit of the preamp was solved by buying a cheap 10W amp from Thomann.de - it was a mains-only version of an amp they also did as battery powered (but a lot less, I was likely to be taking it to bits anyway) - the CG-10X - for £28 you got a 6" speaker, clean & dirty channels, and rudimentary chorus & delay. They'/ve even handily labelled the preamp PCB edge connector with everything I needed - amp, gnd, power - so it was almost trivial to wire all the bits together. I did need to add a capacitor in the audio feed from preamp board to the car amp - obviously unblocked DC, on the output, but that's not a problem.



It's quite an amp - loud, solid sounding, a decent clean sound, and of course the effects to play with - once you've done the Cocteau Twins & Ozric Tentacles impressions it's tempting to turn them off, but they're useful to have, along with the comprehensive EQ. They do a more basic version of the amp (CG-5), the preamp of which would probably do just as well, but this one wasn't much more. One thing I'd like to add is an isolated balanced output for PA use across the preamp output, but one day, one day.

I'm torn, of course, about making use of cheap electronics from China, and buying such things new - it's hard to avoid some times, but it's good to use what you already have sometimes. One alternative thought has been derived from a Laney practise amp, that used a +/-12v supply. Experiments proved that this could be bodged by using a car laptop supply to give +24; connecting -12 to the battery 0v, 0v to the battery 12 and +12 to the laptop supply 24, if that makes sense. Obviously any connections in & out would need to be referenced to the -12v rail (so that you're not shorting out the battery down the earth of an audio cable), but it could work. This way, though, I get more volume that just a practise amp...

new generator

freshly constructed - full details to follow to be part of the website eventually - but note connection box (4 pin XLRs of both genders to allow looping together, also car cigarette lighter socket which will be fed via a regulator, also ammeter on output), have also found some big U bolts to hold the motor down. All folds up neatly, with the motor & connection box tucking between the legs for transportation.

Basic size & construction info;

turbo trainers all from the same supplier on eBay (you'll work out which one if you do a search)

hinged base board approx 12" sq 18mm ply (existing, recycled from previous projects) - painted for neatness

hinges - 2off lengths of 16mm box section steel (sold in B&Q) - hinged on M8 bolts (Screwfix) held on with nylock nuts (ditto) - means they will stay on without being done up tightly (hence along hinge to move). Box steel then bolted to base board with four M6 screws (with large washers & more nylock nuts on the back).

The connection box is a diecast aluminium box from CPC, lid removed and bolted through the base board using M3.5 screws. All that really needs to be connected to each individual motor is a diode (so the current doesn't flow back in to the motor and turn the wheel), but on this one I've added a basic ammeter, which is useful. The connectors are my standard 4 pole XLR, both male and female so if necessary I can loop generators together. I've also allowed for a car cigarette lighter socket, which will be switch in along with a basic regulator - this would allow the unit to be used standalone driving equipment directly. I haven't thought about regulators yet - something about 14v would be useful for battery charging and equipent designed for car use (i.e. big amps), but a more precise 12v would be avisable for less robust equipment, such as radios or televisions that come with a 12v mains adapter, but aren't necessarily desisgned for coping with much more than that.

I've also added screw in eyes to neatly anchor the bungee cord that holds the bike wheel against the skateboard wheel; the board folds up neatly against the turbo trainer almsot flat, the motor & connector box sitting neatly between the turbno trainer legs.

Much respect to Louise & Wildfyre for a very productive day getting these done.

When I built the speakers mentioned in the previous post, I had mobile use in mind, as well as just being able to transport them by bicycle. Last Saturday's naked bike ride was the prefect application, so I loaded up with a sealed lead acid battery (12Ah, although the 7Ah battery I have may have gone to distance too) and a smallish car booster amp (MacAudio MP2095 2x 50W). The speakers facing outwards in opposite directions gave me a great stereo effect; I've inevitably no real idea how the stero worked for others, but I do know that the music was appreciated by everyone who spoke to me, the quality (and volume!) often being commented upon. A great success, I feel, and even playing some Philip Glass worked well (as well as egyptian belly dancemusic, some folk rock instrumentals, then Banco de Gaia & the reggae version of 'Dark Side of the Moon').

Not actually 'bicycle powered', then, but a relevant use of kit I already had. Some technical details of the speakers:

Plywood boxes (12mm front & back, 18mm sides) 14x12x6", painted in blackboard paint

main drivers - Monacor SP-202E (10.3980) 8" dia 50W rms 4 Ohm - SPL 91dB. A compromise on size, price & efficiency - in these applications speaker efficiency, which can vary greatly, as does the useful audio volume.

Tweeters - cheap piezo horns, wired in with a series 80 Ohm resistor.

I made simple metal hook brackets to mount the speakers at an angle on the pannier frame (visible below), one side more or less following the line of the frame down tubes, to give plenty of foot clearance when cycling.

These gave loud, clear sound, coping well with bass. How loud everything went before distortion was nicely surprising, certainly more than loud enough to make a bit of a splash on central London streets. I must have been fairly noticeable as there's a picture of me on flickr, if you know where to look. ;-)

Addendum - one possibility for speakers of this size would be to include an amp and battery inside - not only making them self-conatined, but getting the weight physically ower (the battery would sit in the bottom). The battery and stereo amp could go in one side only, or a more balanced way would be to have small batteries in both sides, and mono amps. Most small car booster amps cam be bridged to a mono output, but one possibility for a mono amp would be the Kemo M034 amp module available from Maplin & elsewhere. I've got one to try - it claims a power supply of 6-16v, mac output of 40W into 4Ohms at 16v, 20W at 12v - that's likely to be enough, actually, for many applications. A bit of electronics to make a simple mixer, CD, gtr, mic inputs and you have a small completely paortable PA. It's a thought.

turbo trainer generator progress

I've managed to get some adapter pins made up, that attach the roller (actually a skateboard wheel) to the generator unit (a motor sold as a replacement spare for a child's electric scooter). These were the only bit I couldn't fabricate myself, and that's only due to lack of lathe... ;-)



The prototype generator, minus bike - note simplicity of construction, the base is a piece of 18mmm shuttering ply, hinged on to the stand using two pieces of angled steel, bolted on, as is the scooter motor - no welding required. All other equipment seen in this and the nest picture is a temporary addition, putting the amp on the bike for a compact setup - normal generators will only have the motor and a tiny box of tricks including a diode (to stop current flowing back into the motor), possible a cheap ammeter, and an output socket.

(For the record - equipment mounted is a voltage limiter (stops output rising above approx 14v, to prevent damage to capacitor & amp, would also provide correct charging voltage for battery charging), smoothing capacitor that also acts as a power store. This is far bigger than required just to smooth the output of the generator, but also acts a power store for clean bass etc some parts of the music requiring more power than can be immediately supplied by the source. I'll be trying much smaller sizes for different applications). The capacitor is then connected to a smallish car audio amp that gives me around 50W rms into the speakers.

Whilst this is a temporary experimental system used for the event yesterday, it may be useful to have at least some generator units with built in capacitor & regulator, so they can be plugged directly into equipment rather than via a central regulator/power unit that will be part of the main PA system.

(having said all this only the regulator is really visible, the capacitor & amp are on the underside of the plywood).




With bike - wheel is held against wheel using bungee cord - low tech, and easily replaceable.



A long held ambition - to have a bike powered sound system I can get to an event by bike - and here we are. Speakers are under the covers on the front pannier, turbo trainer on top and everything else in the panniers. This was for Kingston Green Fair on the 26th of May, running sound (mainly a CD backing track, and also a mic) for the children's stage, for Pete Wintercrane of Big Top Mania.




And in use - one speaker mounted on the back pannier, the other is the other side of the stage. The bike mounts are deliberately off-square so give space for the feet when pedalling - these speakers are also designed to be useable on either side of the bike while in motion, running the amp from a battery. This gives a completely portable sound system for cycle demos - critical mass and the naked bike ride. ;-)

obligatory first post

A blog to be part of pedalpa.org.uk, my website about a pedal powered (actually audience powered, in theory) sound system/PA. Target audience is mainly myself ands those working with me, but all readers & comments welcome, especially technical suggestions/discussion...