Starting my first LM4780 Gainclone amp

[duelbox]

Well I have done a lot of reading in this forum and I have decided to build my first amplifier. I have decided on a gainclone. I guess the thing that got me onto the trail of these amps was researching the Phoenix speakers on www.linkwitzlab.com and his talking about chip amps. I am an ex-Air Force avionics tech and working on electronics has always been enjoyable to me, I think this will be a fun 'first' amp to build.

I am on a very tight budget so it may take a while for me get done but I went ahead and bought the first piece of the puzzle a few days ago. I got the heatsink off of eBay and it should be arriving within a few days. I thought the price was fair and it is probably overkill but to me that is usually a good thing. With shipping it was $9.25. From the pics it appears to already have the proper mounting holes for the LM4780 but only time will tell. I have access to only basic tools so that would be a nice bonus.

I plan to use it to drive my modded Optimus LX-5 Pro speakers and will probably also build another to drive my diy T-Line sub. Of course in the long run I plan to build some new speakers and it will be a real challenge for me to pick a design; Phoenix, full-range driver (Fostex), or maybe just some MTM's.

I have not nailed the design down yet but I plan on an unregulated ps and point-to-point construction for the amp (I think I have an idea that may make this both easier to contruct and more durable, I'll see).

I plan to update this thread as work progresses but with an 18-hour load this semester, free time will be a bit of a luxury.

Thanks to everyone for all the great information that is being shared in this forum!

[duelbox]

Well I finally have the power supply design nailed down (not my own design or anything, just thrown together after sifting through many different designs). I can always modify it later if need be. I will be ordering the parts within a day or two.

All components are from Parts Express:

1ea - Avell 25-0-25 330VA Toroidal Transformer
2ea - 400V 25A Bridge Rectifiers
2ea - Dayton Film & Foil 400V 5% 0.10 uF Capacitors
2ea - Jantzen Metalized Polypropylene 400V 5% 10.0 uF Capacitors
1ea - Power Connector
1ea - 250V 15A DPDT Toggle Switch
1ea - AGC Fuse Holder (2-3A Slow Blo)
16-Guage stranded copper hookup wire

I will also be using 2ea 'Panasonic FC 1500-1800 uF 50V Capacitors' connected directly to the p2p power rails on the LM4780 along with 2ea 'Dayton Film & Foil 400V 5% 0.10 uF Capacitors'. I am still researching these components but they are not a part of the power supply physically although the are electrically. I may also add a few resistors to drain the capacitors during power off situations but I am not convinced that they are needed.

Plugging along...

[lineup]

You can compare with parts of BrianGT LM4780 Kit.
See http://www.chipamp.com/

LM4780 Dual Mono Kit Contents
1 PCB set, consisting of 2 amplifier and 2 rectifier boards.
2 LM4780
6 22 kohm 0.5w compact metal film resistors
4 1 kohm 0.5w compact metal film resistors
4 680 ohm 0.5w compact metal film resistors
2 10 kohm 0.5w compact metal film resistors (mute)
4 0.1 ohm 3w Dale LVR3 power resistors (output)
4 2.7 ohm 2w Panasonic metal film resistors (zobel)
4 0.1 uf BC polypropylene cap (zobel)
4 1500 uF 50v Panasonic FC Capacitors
16 MUR860 On Semiconductor Diodes
4 10 uF Panasonic FC Capacitors

[duelbox]

Side note:

I did in fact receive my new heatsink. I prefer the natural aluminum versus a black anodized finish so I removed it with sodium hydroxide. Now the problem is that the person whom I got it from had touched up the bad spots with a permanent marker of some sort. Anyone had this problem and found a solution, or just some ideas to try? It isn't going to make or break the project but it would be nice to remove the marks.

I have tried normal dish soap with brush, hydrochloric acid, and sodium hydroxide; not all at once of course

Thanks.

[Nordic]

maybe try some automotive rubbing compound or toothpaste...

[Hugh M]

Try a bit of acetone.
Hugh

[jackinnj]

you can use this tool at Aavid's website to calculate the thermal impedance of the heat sink:

http://www.aavidthermalloy.com/technical/thermal.shtml

unless you are using forced air, put 32 LFM in the box for air velocity.

bookmark that link -- you'll find it very helpful. i think you scored a real bargain with that heat sink.

[duelbox]

lineup, thanks for the link. It has already come in very handy.

Nordic & Hugh M, I will give both of those ideas a try this weekend. Thanks.

jackinnj, wassup in NJ? I lived in Wrightstown (middle of nowhere east of Philly) a long time ago. Your link did come in handy to calculate the heatsinks C/W. Thanks.

[jackinnj]

Originally posted by duelbox

jackinnj, wassup in NJ?

NJ is a political disaster -- corruption is now rivalling Rhode Island -- the state is facing a $4bn deficit and they want to raise our taxes again. I am in Short Hills, about 40 min from NYC btw.

[duelbox]

Nothing ever goes as planned. I ran across some transformers on eBay and I just had to buy them. I got 6ea NOS 24VAC/75VA transformers for 23.60, that is shipped by the way. I will use four of them for my amp to give +-24VAC@6A and keep the other two as spares/future project. I think he has 11 of them left so if you want some better jump quick. eBay Item number: 7584210717. I am not affiliated in any way with the person selling these, just giving out the info.

I also have four Panasonic FC 63V 1500uF capacitors on the way too.

Plugging along.