BassBusker - DIY 4W battery/practice/headphone/DI/acoustic-gig thingy

[sandy_r]

hi all, just going to share a long-term DIY amp project for the archives…

 

As we all know, playing the bass usually involves a number of compromises on the gear:-

better bass/projection => bulkier, heavier gear

easier carrying => poorer bass

 

Also, there are are some events where more power is required (eg. bands including drum kit), but also many where a small amp is quite sufficient

 

I've tried, over the years, to DIY smaller setups which i can use for practices, busking, acoustic-oriented events, and personal practising

 

In the past there wasn't a great choice of components to optimise power, quality and battery life - but when Class D ICs became more readily available i felt it was time to get on board with that tech

 

So, trying to distill as many useful features as i could, based on my decades (ouch!) of bass wizardry (hah!), i drew up a wishlist for a custom small amp:-

• 3-5 Watts
• internal 12V rechargeable battery
• several hours battery capacity
• external 12V power adapter input
• stereo headphone output
• CD/mp3 stereo input
• DI output
• internal charging circuit for battery
• compact case
• reasonable cost for going DIY

 

After consulting my pal Google, and doing a bit of headscratching, i found i could buy or make all of that and have a decent amount of change from £50 (batteries not included!)

 

I bought:-

• 10+10W Class D Amp module (pre-built);
• TDA2822 headphone amp kit;
• components for DIY preamp & charger;
• connectors & controls
• 6x4x2" extruded aluminium case

(already had 12/18V 300mA mains adaptor)

 

Since i only wanted 3-5W ouput, i only used one channel of the amp module (grounded the other input)

 

When i started getting involved in busking, in Brighton in the '80s, i trialled a range of bass cab types made from layers of cardboard - all bulky, still too heavy, and poor output.  Eventually i realised that a tube would be perfect from a weight, strength and performance point of view

 

i made two speakers: 'Tube' and 'Son of Tube' - one with an unbranded 10" driver in a telescopic cardboard tube, approx 4' long extended; the other is a 12" Fane driver in a plastic 'cardboard-type' board, rolled into a tube, approx 2' long (still going strong after 40+ years)

 

The tubes have been really great - each only slightly heavier than the driver on its own, easy to carry, good bass response, and surprisingly sturdy (the 12" tube has even been fine with a 30W amp at some practices including drums)

 

(had to laugh: one time, mid 80s, a tech student interrupted our busking to tell me my bass cab was a useless shape and it would never get anywhere ...not many years later, bass tubes were on sale in Maplins, and popping up in the car-boots of boy-racers everywhere!)

 

Edited August 18, 2023 by sandy_r

[sandy_r]

Details of my 'BassBusker' posted here, if of any interest…

 

Preamp

High-impedance, single JFET gain/buffer stage with trim pot gain control (accessible through front-plate), feeding into Bass/Treble control (centred on bass mid-range); input jack switches-on power

 

Amps

PAM8610 (now superceded with improved part) module, single-channel (incl Volume control) operating up to approx 4W max; TDA2822 stereo headphone amp mixing centre-panned instrument with stereo CD/mp3 input; balanced feed for low-impedance DI connection; switch-select for power to main or headphone amp

(Schematic shows generic op-amps for main & phone modules)

 

DC Power

Internal 10x AA rechargeable NiMH cells configured as 12V battery,  recharge circuit supplies 0.1C charge (ie 10 hours) from 18V 300mA mains adaptor; optional external power: 12V 300mA

(i use switchable 12/18V adaptor).  Fully charged battery lasts 6-8 hours at 3-4W, or approx 100 hours on headphones

 

The amp is compact and light enough to carry in a small backpack with my folded guitar stand; i can lift the cab+speaker easily with my little finger (wouldn't want to carry it far like that, though!)

 

 

 

 

 

Edited August 18, 2023 by sandy_r

[Mottlefeeder]

Interesting - Small amp and efficient speaker. I went for small speakers and a bigger amp, and my rig looks a lot heavier than yours.

Is that EQ a tilt control or a mid boost/cut control?

David

[sandy_r]

hi David

actually small speakers + bigger amp can make sense when main power available, too, for smaller or acoustic-led events. I guess you can get some good-quality low-end sound with your rig.  Batteries ok for this, but presumably could get heavy?   Perhaps LiPo is good here?

 

My tone stage just a simple wiper between Bass cut and Treble Cut to compensate somewhat for room/location acoustics - i sometimes use tube placement to create a natural bass-reflex horn with the ground or corner reflection

 

Loose Change Buskers looks good - fun & entertainment for worthwhile cause - good man!

 

sandy

 

 

[BillB]

Very cool. I'm trying to build a tiny combo into a 50Cal ammo can at the moment. Small class D amp based.  Not sure if to go mains or battery (or swappable between the two) as its only really a home practice amp.

 

You can get cardboard tubes for casting concrete pillars into, Google 'sonotube' if you want more info.

[sandy_r]

Wow - i don't think my setup is as cool as a 50 cal. ammo can!!  If you could make the controls look like a WWII Radio or Tx as well that would be something!

 

Looks like plenty room for a small Class D module, preamp & speaker in there - you could leave room for a battery later and power initially from an external mains adaptor, maybe?  Those cans might need some serious attention to rattles and vibrations

 

Thanks for the heads up on those sonotubes (from a weightlifting point of view, cardboard=good, concrete=bad - from a home hifi PoV, its t'other way round, i think!) 

 

All the best with your mini combo project - looking forward to seeing the results

sandy

[BillB]

Yeah rattle and vibration wise I'm thinking of a thin wall (9-12mm) wood enclosure that is bonded with a flexible adhesive to the inside of the ammo can to give stiffness and damping, hopefully that would stop any ringing. I've a little bass driver from Tangband that should hopefully fit for wobble duty, thinking about the pre-amp side of the amp and tone controls at the moment. Should all run off about 24v, so lithium battery or mains adapter is all possible, I would like to get the lid back on and everything in there if possible for storage/transportation. Once I get somewhere I'll post some pictures.

 

I'd love to do the whole retro chicken head knob thing and keep the looks all period, but I fear space may be an issue.

[sandy_r]

Ooh,  i hope you don't lose too much of it's natural acoustics with the damping - me, i'd start with the obviously clangy bits and work outwards from there

 

sounds like it's all under control, though - those Tangband drivers look unusual, will be interesting to see/hear how this all pans out

 

(PS.  if you were able to keep the supply to 20V ish, you may be able to use a replacement mains adaptor for laptop)

[BillB]

Looking to use a TPA3106 class d amp which runs off 10-26v so scope there. A 6s lithium battery would work nice if I want portable. I have various power supplied, I'm an electronics tinkerer/hoarder.

 

I doubt it will be too damped, I don't want ringing, and a box in a box should seal up nicely.

 

This is the driver combo I have, there may be issues getting the passive radiator in too:

https://www.soundimports.eu/en/tang-band-pr14-b.html

 

It may also lack top end, so all could change yet...

 

Will have to have a play and see what I can do.

Edited August 18, 2023 by BillB

[sandy_r]

 

From a quick look at the specs, the driver appears to have a more or less flat response up to 1 or 2kHz, so you may be ok with top end, depending on your preferred bass sound.  The drivers are presumably optimised for quality over efficiency, so it looks like you'll need plenty of drive.  The IC has a low THD up at 20W output but it increases somewhat rapidly at higher levels, so hopefully 20W will be sufficient

 

Neat - a meaty project to head into Autumn with!

[BillB]

Driver is optimised for low bass in a tiny (7-8l) box. Hoffman's iron law, 'low, loud, little, you can have any 2!) It going to have poor efficiency, for a practice amp I can live with that. There may be a better amp chip out there for that driver actually. I'll probably start with TPA3116 as I have those on a nice pcb already to play with.

[BillB]

So the Tangband does not fit into the ammo can, too wide, very annoyed, might build it into a tiny combo style amp with a wooden cabinet...

 

However, I have found some Peerless SDS-135F25CP02-06 drivers I bought for another project years ago, and one of those will physically fit, need to get the driver into Hornresp or bassboxpro to model the driver/box combination and see if it will work. They are recognised as a subwoofer on the datasheet and do 50Hz-5kHz I think.

[Mottlefeeder]

43 minutes ago, BillB said:

So the Tangband does not fit into the ammo can, too wide, very annoyed, might build it into a tiny combo style amp with a wooden cabinet...

 

However, I have found some Peerless SDS-135F25CP02-06 drivers I bought for another project years ago, and one of those will physically fit, need to get the driver into Hornresp or bassboxpro to model the driver/box combination and see if it will work. They are recognised as a subwoofer on the datasheet and do 50Hz-5kHz I think.

If the Peerless does not model well, you might consider the Faital Pro 5FE120 - 5" 80W  Loudspeaker from Blue Aran - £23.44 +p&p It's available as a 4 ohm as well as an 8 ohm.

I use a pair of them, driven by a stereo class D amp and they sound pretty good.

David

[sandy_r]

8 hours ago, BillB said:

So the Tangband does not fit into the ammo can, too wide, very annoyed, might build it into a tiny combo style amp with a wooden cabinet...

However, I have found some Peerless SDS-135F25CP02-06 drivers I bought for another project years ago,

...

. They are recognised as a subwoofer on the datasheet and do 50Hz-5kHz I think.

sorry to hear about the size issue with the Tangband, Bill - hope the Peerless pans out.  Another approach for the ammo can might be to use 2 smaller drivers?

 

the Faital drivers look useful, David, i like the way that Faital provide a decent amount of spec, to help with the cab design

 

 

[BassmanPaul]

May I be so bold as to give you a nod for your ingenuity. Nice one Brother.

 

[sandy_r]

On 22/08/2023 at 21:26, BassmanPaul said:

May I be so bold as to give you a nod for your ingenuity. Nice one Brother.

 

Apologies Paul, I was away for a while and somehow missed your post 😯  Many thanks for kind words!

 

There are some amazing skills in evidence on the BC site, I hope I can learn a lot here

 

Cheers Bassman!