non-PC Power amp project

[suicidal_monkey]

http://www.jamena.pwp.blueyonder.co.uk/amp.html

I've got a power-amp PCB soldered up but sitting in a cardboard box and
it really needs a casing of some sort. I imagine some of you might have
done some electronics DIY before, so maybe you could give me some
advice on a casing for my amp.


The equipment I have to cram into something is as follows:
-poweramp PCB + heatsink (BIG, should feel free air...)
-pre-amp, volume, tone PCB's (not made yet :s)
-Transformer and rectifier diodes/caps
-perhaps a cooling fan or two
-room for the same again as 2 amps can be bridged for a 400Wrms total...


It's approx 100W rms running off +-50V rails and the transformer weight
about 5kg so its quite a substantial piece of kit. I figured I might try and
mod an old PC case to house it or something. It'd need to be pretty hefty
to hold the transformers, although that might get replaced at some point
by a smps if I can be arsed to work out how to make one that powerful...

btw, if anyone has ever made any pre-amp circuitry for guitars (esp bass
guitars) I could use any advice going

[Gh0st Face Killah]

The first thing I would say is that if you are going to mount it into a pc case is get an aluminium one that way the heat generated will be disperced more effectively. You would probably be best bolting the transformers to the base of the case that way you haven't got to worry about then falling off the sides!! Other than that good luck and lets see some piccies on here when its done!!. Oh yeah you might want to invest in some silent case fans to help with the cooling.

[TeaLeaf]

Well it's beyond my electrical skills - so don't ask me  8O

TL.  

[Anonymous]

Have a look at http://www.maplin.co.uk as they have lots of cases available for electrical projects - they do a good range of handles too coz you'll need some to lift that mother!

Cases can be found under "components" then "enclosures"

[A Twig]

In my experience bridging amps is generally not a good idea, as you can get severe fluctuations of power output. Tis also a lot harder to trouble shoot a bridged pair of amps, as you have two lots of PCBs to go through.
Usually tis best to splash the cash on getting a more powerful amp in the first place???

Is the amp going to be a guitar style freestanding or a rackmounted? That will immediatly give you size restrictions if it is intended to be rack mounted, if not, the sky and your body strength (to lift it) is the limit.

PC cases probs aint too good an idea, ut again, depends on size of case. You'll need to wire up earths etc for your case, so normally a specific case is better.

Hope that helps in any way,

[suicidal_monkey]

cheers guys was wondering how many people would respond to this one

the amp is an old maplins kit amp (MOSFET power amp) and there is (or was) an available bridging kit to link 2 of them. seeing as the power supply is the most expensive part of the thing it might be worth a try when I have enough speakers to cope with 400Wrms of bridged mosfet power atm I have 2 big speakers. one was purpose bought for the 100Wrms output, the other was a freebie from a mate which I havent tested yet.

It's intended purpose is as an amp for my bass guitar. Hopefully something performace worthy, although 100Wrms is only enough for practice really...400W might manage smaller venues

Case-wise, the options are as follows:
1 - buy a case and try to mount the PCB and psu etc into it, cutting holes for the knobs and input/output bits
2 - find an old PC case and mod it as above
3 - but bits of wood/metal and construct a case, then mount everything in it...

I figure getting hold of an old rackmount or PC case on a junkpile will be easiest really. diecast and metal boxes cost quite a bit, and aren't going to be of any better or worse dimensions than an old PC case. The heatsink is quite adequate, so dispersing heat using the case isn't too important. I have some HUGE fans from an ancient "computer component" so I guess I could enclose the heatsink and use a fan to generate airflow.

I think I will set up a webpage for my amp progress :roll: and I will try to take some photos with my crappy webcam thing.

http://www.jamena.pwp.blueyonder.co.uk/amp.html

[Gh0st Face Killah]

If you are going for a twin speaker set up it would be wise to use a matched pair of speakers otherwise you will run into loading problems. If you have the brideged amp with too outpiuts you woulkd be making one side work more than the other which could cause you problems.

[suicidal_monkey]

yeah. atm I only own the one amp and the one speaker and they match pretty well.  Bass isnt very directional so stereo isnt exactly a concern.

The power amp can handle down to 4 ohm and possibly 2ohm speakers, I forget. My current speaker is a 15" paper-surround 8ohm impedance one, rated to 150Wrms or something like that. The other speaker I have is an 18" of unknown spec. The 15" is currently having its (home made) speaker box painted but that should be finished next weekend or so. It has no handles 8O but then the box used to be VERY big and no handles. I had to cut it down twice for transport reasons.

IF I ever get to the point when I can afford to get a powerful enough psu and the second amp plus bridging kit, I'd have to think also about getting enough speakers to cope with the power. I should be able to remember simple circuits so in theory I can match up all the stuff pretty well :n00b: and can I just say the new smilies ROCK

[Anonymous]

What every body seems to forget is it is not just how many watts you can pump out that is important. Certainly I always look at speaker efficiency (for a given number of watts, how many dBs do you get at 1m?) Efficient speakers on a low power amp will not only drive easily, they are less likely to get overdriven and damaged.

my 2p

[Gh0st Face Killah]

:stupid:

[suicidal_monkey]

I will check up on the speaker for you ...it's a "custom Fane KP15-150" 8 ohm 15 inch paper cone, paper surround rated at 150W rms continuous and 300W peak. It weighs in at around 6-8kg I think, and gets what I would rate (by ear/useage) as a pretty good dB gain. I've operated it with a similar amplifier before to great effect
0X
I can even feed my walkman phones output into it and get a decent volume out

In the meantime, I made a webpage for my project so you can all point and laugh at my seemingly endless supply of weird ideas...

http://www.jamena.pwp.blueyonder.co.uk/amp.html#2