50W Amp project, no more cheapo. - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 26th October 2001, 04:49 PM   #1
diyAudio Member
 
Join Date: Oct 2001
I've asked around for information about transformers and boxing, and I've found some sites that have really good ideas. After looking at my old amp chassis, I found that it only accepts transformers 150VA to 300VA (that amp was an old class A design, pretty nice with elna audio caps). It seems a waste to spend 100 or so bux on 20W so I've decided to do the 50W project instead.

1) Interesting case idea. Plastic with foil.
I read somewhere that you could actually shield electromagnetic interference pretty well with a thin layer of aluminium foil stuck with spray adhesive covering a plastic box(these are pretty common) and attaching chassis ground to the aluminium foil. This sounds interesting, and I'll try it with the 20W amp at another time. the result can be sprayed, painted, whatever. So I think it'll save money.

2) I've run into lotsa problems with the layout of the board. An interesting idea was to solder the parts to the breadboard and use conductive pens to draw traces. Any comments on that? I think it'll save alot of time and effort. I probably won't even have to solder, a dab of superglue to hold the parts down and I can draw all the traces I want. Comments? Will it affect the sound?

Other interesting ideas were to point to point the circuit in free air and use casting resin to hold the parts together. It'll be very durable, although I don't know about heat problems. Mounting ICs and heatsinks are still a problem tho. Any ideas on that?

Oh I can pretty much order any transformer I want. Seems that a transformer winding factory is around my area. They only do EI types tho. Should I shield the transformer with heatresistant plastic covered with aluminium foil to prevent electromagnetic interference?
  Reply With Quote
Old 26th October 2001, 05:47 PM   #2
sonnya is offline sonnya  Denmark
diyAudio Member
 
sonnya's Avatar
 
Join Date: Oct 2001
Location: Denmark
Why use plastic coated with some kind of thinlayer of metal (From spraycan).
You will get better result with copperfoil or iron and it is cheaper.
You have to shield your transformer if is near your ampstage. It can be done by building wall's in your box with feedtrough for your cables.
If you want to draw a lot current (more than 100 mA) in the traces on your circuitboard then you have to do a real circuitboard. I would prefer min. 35um copper. but 70um or 105um is better.

Regards

Sonny
  Reply With Quote
Old 26th October 2001, 06:24 PM   #3
diyAudio Member
 
Join Date: Oct 2001
Thanks...
What if I just drew thicker lines?
I'm also contemplating real breadboarding... Buying a 1 inch thick chopping board and driving nails into it to hold down my transformer, using a nail as a star ground point, and nailing down my heatsinks. the circuit can be constructed by supergluing the components down, and connecting lead to lead or lead to wire. Sounds interesting? Probably looks wonderful too if I can glue it properly.
Thanks for the copperfoil idea, I have no idea where to get that tho. I was thinking fine wire mesh instead of aluminium foil, but if aluminium foil does the same thing, why bother shaping wire mesh.
I think the nails into wood idea is rather promising... can imagine binding posts superglued into position with nails for support. Really long and thick nails could also provide some sort of vibration dampening.
Wonder how hard chopping board wood really is tho, wonder if it'll splinter or crack. I'm thinking of getting them from IKEA, cos they're known for using lotsa soft pinewood for stuff.
  Reply With Quote
Old 26th October 2001, 06:50 PM   #4
diyAudio Member
 
kiwi_abroad's Avatar
 
Join Date: Sep 2001
Location: Wellington, New Zealand
Hi All,

Having been through the stage of thinking 'As long as it makes sound, who cares what it looks like', can I say, please please spend more effort on the construction. So much of the pride in building your own person piece of audio nirvana comes from the build quality, and being proud to show it off to others.

If you want to cut costs, do so where you can, but try to do the following:
Make the effort to layout and etch a PCB. All that is needed is the PCB blank, a permant felt tip marker, and the etchant. The result is physically more sturdy than anything else.
Alternativly, use the 'dead bug' method of construction. Get a peice of copper clad board and use that as your ground and solder components above it. hint: use 10Mohm resistors as stndoffs and supports. Mount IC's upside down (dead bug).

Simple tools for modifying casework can be brought cheap. A nibbler is one piece of equipment I find invaluable (although an aching hand usually results!). Don't glue heatsinks, that's just inviting disaster (most glues get soft when hot). Use screws and bolts.

Cheers, Adrian

PS I almost forgot, saftey must ALWAYS come first.
  Reply With Quote
Old 26th October 2001, 07:43 PM   #5
diyAudio Member
 
Lisandro_P's Avatar
 
Join Date: Oct 2000
Location: Argentina
Send a message via ICQ to Lisandro_P
Quote:
Originally posted by downhere

I read somewhere that you could actually shield electromagnetic interference pretty well with a thin layer of aluminium foil stuck with spray adhesive covering a plastic box(these are pretty common) and attaching chassis ground to the aluminium foil. This sounds interesting, and I'll try it with the 20W amp at another time. the result can be sprayed, painted, whatever. So I think it'll save money.
I did this a couple of times, and as long as you're tidy when laying out the aluminium foil, it works great. Just remember, if you're going class-A, you just can't forget the heat disspation. Most modern plastics take heat quite well, but i wouldn't be too comfortable...
  Reply With Quote
Old 26th October 2001, 07:51 PM   #6
diyAudio Member
 
Join Date: Oct 2001
Thanks, yeah I agree good looking stuff definitely makes you feel good. Remember the look of the tube amp kit they were selling at the electronics shop, machined aluminium with matching knobs and all.

Problem is, I don't have a workshop, and there aren't any workshops that'll do metalworking for you at a low cost. Last time I asked, labour was 40, price of materials extra.

I'll consider the dead bug method, but won't it look as bad as the gluing it to the board method? Sounds interesting tho, I can imagine using thick enameled copper wire to hold the board. Does the copper keep its shine? If it does then I'll definitely use it as ground.

I'm considering supergluing white plastic feet to the wood as a sort of mounting. Probably looks bad I noe, but it'll allow me to remove the board easily. Are there any other ways of mounting PCBs painlessly?

I was thinking that brass nails would match the colour of the chopping board, as well as the orangy brown of the transformer... Then I'll fine wire mesh the transformer, and then the entire chassis to block EMI. Or would a more cagey sort of barbecue mesh look nicer. (they all probably suck.) If you were me, and you'd be mounting it on a piece of wood, how would you shield the parts from EMI without spoiling the looks?
  Reply With Quote
Old 26th October 2001, 08:08 PM   #7
diyAudio Member
 
Join Date: Oct 2001
How many layers of foil did you put?
adhesive used?
pictures?
: ^)
  Reply With Quote
Old 27th October 2001, 12:03 AM   #8
paulb is offline paulb  Canada
diyAudio Member
 
Join Date: Jun 2001
Location: Calgary
So what kind of amp are you building?
I wouldn't mind seeing a real "breadboard" amp.
  Reply With Quote
Old 27th October 2001, 03:51 AM   #9
diyAudio Member
 
Lisandro_P's Avatar
 
Join Date: Oct 2000
Location: Argentina
Send a message via ICQ to Lisandro_P
Quote:
Originally posted by downhere
How many layers of foil did you put?
adhesive used?
pictures?
: ^)
Dunno if you asked me, but whatahell.. this is MY method, crude, slow, but it works Basically you lay a large piece of common, kitchen aluminium foil over the box and press it over the sides so it takes the internal shape, more or less. Now, you remove the foil, cut the excess material and (here's the tricky part), slowly and carefully, you glue it to the box, pusing it against the walls so it lays as smooth as possible. I use common superglue and this works very good, specially if you use the side of the foil feels like plastified (at least the one i use is this way). It might take more than one piece, but as long as all the pieces touch each other, the shielding works.

I did this on a couple of boxes and a guitar cavity and works wonders on almost any surface. Bear in mind that the foil is very easily scratched, so be gentle the whole process. AND, you can't solder over Al, so you'll have to come with some way of attaching a ground wire to it. Anyway, it's easy, cheap, and it works.
  Reply With Quote
Old 27th October 2001, 06:38 AM   #10
diyAudio Member
 
Join Date: Oct 2001
Paulb, i've looked at the transformer prices,found that the cost of building a 20W amp and a 50W amp is roughly the same, so I'm going for the 50W. It'll mean scrapping the 1 channel I completed, but it'll also give me a chance to try and think about the chassis before I construct the circuit.

Gonna cut excess LM3876 pins off with a lead cutter, and just tape, stick, wind wires to the leads. I saw them selling "Jumper wires" at the electronic shop, looks like 22/24 awg wire pre stripped and tinned , and it sells really cheap too, 2.50 for a rather large bag. Is that any good? the leads are about 4 inches long, 1 inch stripped at one side and half a cm on the other. I'm thinking of nailing the board with say half inch brass nails, and just winding the leads of the components together on the nails. any extra connections I'll just use the jumper wire + solder or conductive pens to connect it. I think I can make it look pretty much like the schematic this way. Trying to avoid soldering altogether... its bad for health.

I think aluminium foil would look cool, as well as copper foil. Aluminium foil is definitely easy to use, there's also a shiny side and a dull side. I think I'll use expanded polystyrene glue (Por by UHU).

For filter caps, any reccomendations? I'm using 2200uF x 4 and I can find Elna caps, Rubycon caps, Jamicon caps in my area. Which brand/type is the best? Should I get low inductance, long life, minature.... They probably be connected by enameled wire to keep the look... infact, won't clear enameled copper wire look the best for wiring my board? ... Any opinions on that?
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Cheapo Guitar Amp sorenj07 Tubes / Valves 9 9th May 2007 07:28 PM
Gc with cheapo components rs1026 Chip Amps 25 7th November 2004 08:46 AM
Cheapo amp project help pls downhere Solid State 47 28th December 2001 07:05 AM


New To Site? Need Help?

All times are GMT. The time now is 10:42 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2