Compact Power Amp

[Alien]

This build came about after BC member [u]s u y *[/u] (Froilan) posted a thread about the lack of small, light power amps at reasonable prices. I reckoned that a digital power amp with switch-mode power supply would fit the bill.

After a bit of umming and aahing, and a couple of false starts, here's the build in progress.

The amp module is a BP4078, from [url="http://www.coldamp.com/opencms/opencms/coldamp/en/index.html"]Coldamp[/url]. It really is tiny, and very light. Here's a pic (with a pick)

[attachment=9065:Amp.JPG]

The amp will supply 400 Watts @ 4 Ohms, 240 Watts @ 8 Ohms.

OK, next comes the power supply - this is almost twice the size of the amp, but that's still pretty small, especially compared to a linear power supply, which would be 3-5 times the size and 5-10 times the weight.

[attachment=9066:PICT0373.JPG]

It's all going into an extruded aluminium case from [url="http://www.hammondmfg.com/"]Hammond[/url]. It's anodised black, with matching endplates and a slide out lid/base section. It's gonna be a bit tight getting the two modules in there!

[attachment=9067:PICT0374.JPG]

More details as the build goes on!

Andy

[s_u_y_*]

Looks like it's coming along nicely.

[7string]

Blimey, now that's a small amp

Be interesting to see how this turns out....

[Alien]

So, the build continues. Having (finally) received the last few bits from CPC, I can really start to make a go of it.

First, the case, with all the necessary holes (plus a few unnecessary ones - the filtered mains inlet took up more space than I thought, so I had to move the power supply right to the fromt of the case)

[attachment=9177:PICT0376.JPG]

Amp and power supply fitted. The mains inlet is the large silver block at the top left of the chassis. It's a Schaffner unit, rated at 6 Amps, with dual fusing and AC switching (ie. both live and neutral are fused and switched)

[attachment=9178:PICT0377.JPG]

You can see from this shot how little space there was between the filter and the power supply. It took a bit of persuasion to get it in!

[attachment=9179:PICT0379.JPG]

Next here's a shot of the back panel with the mains filter and Speakons fitted. Behind the unit are the 2 harnesses for wiring the Speakons to the amp, and to the right of the shot is the Neutrik XLR/jack combo which will be the input socket.

[attachment=9180:PICT0380.JPG]

Not much further to go now! More tomorrow with a bit of luck.

Andy

[Dubs]

looks like a fantastic little build. If you don't mind me asking - how much did all the parts cost? Not that I'm likely to build one myself but I'd just be really interested to know how much a build like this is likely to cost.

EDIT - Is this - [url="http://www.coldamp.com/opencms/opencms/coldamp/en/products/packs/active_speaker_30/"]http://www.coldamp.com/opencms/opencms/col...ive_speaker_30/[/url] - the 'kit' that you're using @ 250 Euros?

Edited May 29, 2008 by benwhiteuk

[Alien]

[quote name='benwhiteuk' post='209161' date='May 29 2008, 09:05 PM']looks like a fantastic little build. If you don't mind me asking - how much did all the parts cost? Not that I'm likely to build one myself but I'd just be really interested to know how much a build like this is likely to cost.

EDIT - Is this - [url="http://www.coldamp.com/opencms/opencms/coldamp/en/products/packs/active_speaker_30/"]http://www.coldamp.com/opencms/opencms/col...ive_speaker_30/[/url] - the 'kit' that you're using @ 250 Euros?[/quote]

Yup, that's the kiddie.

If there's sufficient interest, I may build a small batch of these amps. I haven't calculated a final price yet, but it's likely to be around £400.

Andy

[ahpook]

lovely bit of work, very tidy.

[Dubs]

[quote name='Alien' post='209176' date='May 29 2008, 09:17 PM']Yup, that's the kiddie.

If there's sufficient interest, I may build a small batch of these amps. I haven't calculated a final price yet, but it's likely to be around £400.

Andy[/quote]

Very interesting, it looks tiny and 400W @ 4ohms is very impressive for something of that size. Class D is definitely the way to go for keeping the size and weight down. I suppose you could do it a bit cheaper with a small PA amp that’s been bridged to mono and that’s likely to give you more power for less money, but obviously would be at least 3 to 4 times bigger, maybe more. My housemate recently bought a 2U PA amp that’s 1.3KW @ 4ohms when it’s bridged for £160 brand new. It’s not that big in general terms for the power output, but it’s about the size of an SVT3-Pro so it’s pretty gigantic in comparison to your amp.
I’d love to have a handy little amp that’s as powerful as yours, but at £400 it’s a luxury that I can’t really afford at the moment. It looks great though and I’d love to hear how it sounds when it’s finished. Are you planning on using it with a bass specific preamp of some description?

[Alien]

Other than for testing purposes, I'm not planning on using it at all I'm actually building it for Froilan.

Andy

[Dood]

I just wanna take an opportunity to say what an absolute diamond Andy is. This is a fantastic build to see coming along. Thanks for all the things you have done for me as well mate. My Bass Clef badge is still doing strong on my car it looks the proverbial t*ts! .. as is that wicked wrap stuff you let me have for my piles of cables. Dare I mention the nail varnish your good lady sent me??? ;o)


Take care mate! chat soon

Dan

[Alien]

[quote name='dood' post='209216' date='May 29 2008, 10:03 PM']I just wanna take an opportunity to say what an absolute diamond Andy is. This is a fantastic build to see coming along. Thanks for all the things you have done for me as well mate. My Bass Clef badge is still doing strong on my car it looks the proverbial t*ts! .. as is that wicked wrap stuff you let me have for my piles of cables. Dare I mention the nail varnish your good lady sent me??? ;o)


Take care mate! chat soon

Dan[/quote]

Cheers bud! [size=1]Cheque's in the post by the way[/size]

Andy

[s_u_y_*]

[quote name='benwhiteuk' post='209203' date='May 29 2008, 09:46 PM']Are you planning on using it with a bass specific preamp of some description?[/quote]

Yep... that's the idea for me. I use a EBS MicroBass II into a Mark Bass Little Mark II as a poweramp (I prefer the sound of the EBS). As much as the LMII is pretty small, I thought bringing a whole amp with me on the London Underground on the way to gigs is a bit pointless. Having this will definately lighten the load on my back.

Edited May 30, 2008 by s_u_y_*

[Dubs]

I’d imagine that this is absolutely perfect for carrying on the underground. Great solution to this problem as well. Maybe Andy needs to go into full scale production I reckon these amps could be very popular if the word spread that this was available. There’s got to be loads of people needing an answer like this to the woes of transporting gear on public transport.
It sounds like a great idea anyway and I’m eagerly anticipating some kind of review…

[clauster]

Might have to ave a go at one of these myself!

[Mottlefeeder]

A few points that spring to mind as I read this thread.

1) Hopefully the mains input unit has a two pole switch, but only one fuse. If it has two fuses, then a blown neutral fuse will give the appearance that the unit is dead, while parts of it inside are still live. This is not good practice.

2) In one of your pictures, you show a single insulated mains wire bent over the aluminium heatshik of the power supply. It would be better to route that wire somewhere else, or add some more insulation or sleeving to it. Since the other ends of those wires have screw terminations, you could find some space by soldering the wires at the filter end, and using heatshrink sleeving to insulate the joints.

I hope this does not come across as being picky, but if you build something for someone, you need to take some responsibility for the safety of the amp tech, hopefully several years down the road.

[Matty]

[quote name='s_u_y_*' post='209439' date='May 30 2008, 10:14 AM']Yep... that's the idea for me. I use a EBS MicroBass II into a Mark Bass Little Mark II as a poweramp (I prefer the sound of the EBS). As much as the LMII is pretty small, I thought bringing a whole amp with me on the London Underground on the way to gigs is a bit pointless. Having this will definately lighten the load on my back.[/quote]

Froilan mate, i'd still be interested in buying back the Little mark if you end up selling it.
Let me know if you do

Matty

[Alien]

Having read Mottlefeeders post, I've realised that I have approached this build as though it was a DIY project for myself. With that in mind, I've made a couple of changes and generally tidied up a bit.

First, the new tidier (and probably safer) arrangement of the mains leads.

[attachment=9287:PICT0384.JPG]

Next, amp power leads, speaker leads and input lead all tied off and tidied.

[attachment=9288:PICT0386.JPG]

The first end panel on.

[attachment=9289:PICT0387.JPG]

Nearly ready to go. Visible (just barely) in the foreground are the indicator LEDs for Power (blue) and Clipping (red).

[attachment=9290:PICT0388.JPG]

Once it's all together, it's time for a load test. I'm going to give it a couple of straight hours running just below clipping into a dummy load, wired with a speaker in parallel so I can listen for any odd noises. Hopefully, the case will act as enough of a heatsink that the amp won't need a fan.

Andy

[ahpook]

that is an incredible job you've done there alien.

very professional indeed.

can't wait to hear what it sounds like.

[peted]

That is very impressive indeed. Kudos to you.

[mcgraham]

May I ask what the exact final dimensions will be?

Mark

[alexclaber]

Very neat! Two of those amp modules bridged into my big 15"+6.5" as an active cab would be scarily loud and light.

Do you think you could run a simple preamp off that SMPS to give you a tiny head for non-tweakers?

Alex

[Alien]

[quote name='mcgraham' post='212586' date='Jun 4 2008, 04:19 PM']May I ask what the exact final dimensions will be?

Mark[/quote]

You may

The case is 220x165x51mm. Add on a bit for connectors, knobs and feet and you're looking at about 220x180x55. Haven't weighed it yet, but should be under 2kg.


[quote name='alexclaber' post='212604' date='Jun 4 2008, 04:50 PM']Very neat! Two of those amp modules bridged into my big 15"+6.5" as an active cab would be scarily loud and light.

Do you think you could run a simple preamp off that SMPS to give you a tiny head for non-tweakers?

Alex[/quote]

The SMPS has an auxillary output of +12/0/-12 V @ 500 mA, ideal for running a pre, crossover or pretty much anything else you might want to stick in there.

It would probably be possible to get a preamp section into the case I've used. A smaller AC input would allow the modules to move back a bit, which should leave room for a PCB up front. Might have to look into that :brow:

Andy

[Alien]

Time for the next episode boys and girls. Are you sitting comfortably?

I've closed up the case, and done a bit of testing. Before all that though, I decided to weigh the amp.

[attachment=9464:PICT0389.JPG]

1.6 kilos (thats about 3 1/2 lb in old money). Strange thing is, it feels heavier - probably because of the size of it.
If any of you are having difficulty picturing the size of this amp, have a look at this next pic.

[attachment=9465:PICT0391.JPG]

And then I fired it up for the first time...

[attachment=9466:PICT0396.JPG]

Christ that LED's bright, despite only running at 12 mA. It's like a spotlight. Well, Froilan reckons he likes blue LEDs.

Initial testing was done (not very scientifically) by plugging into a pair of PA cabs, and plugging a bass straight into the input. Houston, we have a problem. There's a high pitched whistle coming through at about 15kHz (I'm guessing here, but I know my hearing tops out about 15k, and it's right at the top of my range). It's not loud, but it is audible and would be very annoying, so I'll have a poke about in there with a 'scope later and try to find the source (my bet is that it's the power supply). Other than the whistle, it seems very quiet in operation, no buzzing or humming came through.

The other issue is heat. I had hoped that the case would be enough to act as a heat sink, but sadly that is not to be. I've sourced a tiny fan (40x40x10mm) and I'm going to fit it into the side of the case. I'd cunningly left enough room for this eventuality, so not a big problem. Looks like I'm going to be drilling some holes this afternoon!

Andy

[johnnylager]

Farkin genius mate, well done. Taking orders yet?

[Kiwi]

Hats off to you Andy