Mottlefeeder

Planning to arrive about 10 - satnav tels me it's about 90 minutes from home. David

I replied to James' wanted advert for a Zoom B1-4. The resulting sale was smooth, quick and stress-free. I'd be happy to buy from/sell to James again. David

Great, count me in please. I'm vegetarian too. David

Have you got room for one more body? I can bring - 5-string acoustic Ibanez EW205WNE 5-string fanned fret headless Ibanez EHB1265MS 5-string Hohner active cricket bat Home brew Eminence neo 10" in cab *2 Home brew briefcase combo Battery powered amps (and batteries) Vong variable HPF,LPF & DI David

Yes, that's the plan. Most of my busking is done on 240v from street furniture or battery power packs provided by the event organisers. For those I would use the Meanwell power supply. Where there is no 240v supply I would need a little under 2 × 7AHr batteries to run for the 5 hour set. For open mic nights, and / or Victorian pubs where the only power socket is on the wrong side of a gangway, I can play for a couple of hours on one battery. For 'acoustic' rehearsals and the like, the smaller amp and battery will reduce the weight by about a third. David

And finally, fully assembled, the slightly briefer briefcase:

If your band has a drummer, then your target is to be loud enough to be heard alongside him/her. If they can play quieter for rehearsals then one of the Elf/Gnome etc heads should be enough. If not, then you probably need the same wattage as your performance rig, and wear earplugs. David

Two more pictures: The back of the cab, with the amp connectors in the recess and the power connectors besides the battery compartment access. Amp and battery options - Top left: 90w per speaker Kenwood car amplifier Top right: 7AHr battery with fuse and one way only plug Middle right: Meanwell 12v 5A mains power supply. Bottom left: 15w per speaker ebay amplifier for home practice or 'jamming with a friend' - work in progress. Bottom right: 2.3AHr battery to power the smaller amp, giving a reduced weight rig for travelling - also a work in progress. David

Getting there... The preamp layout The preamp circuit The capacitor bank and acoustic foam on the back wall. David

I understand that some switching power supplies conserve energy by going into a burst fire mode on low loads, and the power-up / power-down is audible as noise on analogue circuits. David

Filling in some of the background, when I started the revamp I considered the electronics recess on the back of the Mk 1&2 and whether I could fit in 'Treble, middle and bass' on one row and 'variable HPF, swept mid-frequency & variable LPF' in a row below. But when I thought about it, I already have EQ on my basses, and I tend to leave the HPF set to suit the speaker, so I was able to curb my enthusiasm and go for a simpler option. - one hi-Z input stage with switched gain, followed by an 18dB/octave fixed HPF to suit the speaker, with a volume control between that and the amp. The only frills were a tuner out and a live/tune switch. Having made that decision, I then realised that the recess I built in for the electronics would be a tight fit for two jack sockets and the circuit crammed in between them, especially since I could not use the space under the overhanging control panel supports. To minimise the number of items on the control panel, I had to ditch the live/tune switch. The tuning jack socket is now always on, and can be used as an emergency 'DI', and you turn down the volume for silent tuning. I also opted for a combined power switch and volume control - a bit retro but it also solved another problem: the switch-off transient that blasted out from the Mk 2 is effectively muted by turning the volume down before switching off - simples. Another problem with the Mk 1 & 2 was that the peak current drawn by the amp was enough to pull down the voltage of the battery to the point where the amp momentarily tripped out on low voltage. Fitting a bank of 10 x 1000mfd capacitors in parallel with the battery seems to cure that problem. David

They are are gone- recycled a week after the first post. David

Thanks for that - I may have a problem that could be solved that way. My experience to date has been fabricated structures made from Plasticard. David

One problem with the Mk 1 & 2 was the positioning of the battery hatch, so this was the first thing to change. The original design had the battery in the speaker enclosure with an air-tight door (as PJ does in the briefcase). Keeping the battery outside the speaker enclosure, and allowing for a choice of battery depending on the required power and duration meant that the box would be bigger. Also, keeping the speaker enclosure volume the same as the Mk 2 but moving from 9mm Birch ply to 12mm Poplar ply also increased the volume. With the help of a spreadsheet calculating all the volumes, I found that the overall box size would increase by about 10mm in all three dimensions. The Mk2 layout - The Mk 3 layout - Battery access from below - One of the advantages of putting the battery outside the speaker enclosure is that I can have a cable route from the battery to the outside world without it having to be airtight. This will give me the option of using a mains power supply with an IEC male 'kettle connector ' on a short flying lead. One disadvantage is that all my battery packs have to be modified from 'fixed socket on battery' to 'flying lead socket on battery'. David

Having staggered to the end of this project in 2021, there were a few niggling problems - 1) The Mk1 was going to have a battery hatch on the back, and a class D amplifier module built in to a cavity on the back. The chosen amp module (Ebay) turned out to be very noisy, so I decided to replace it with a larger module hanging on the back, which preventing easy access to change the battery. This was the basis of the Mk2. 2) The Mk2 had a simple preamp containing a gain stage and an HPF, but it produced an annoying click as the compo was powered down. 3) The Mk2 was limited to battery power only, unless connected to an external mains 12-14v power source. The Mk3 is a rebuild intended to fix those issues and add some further benefits. David