Point to point LM4780?

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JojoD818

JojoD818

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Joined 2003
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Hi everyone,

I have a couple of 4780 chips just laying around and plan to build an amp out of them. I am thinking of doing a p2p build since the pins are too close for me to make a pcb and I don't know how to get a pcb for this chip. I'll run them in parallel so one chip per channel.

Has anyone tried a p2p build with this chips? How many amps is the recommended tranny?

I also need to ask this... are they any good/better than the tried and tested 3875?

Many Thanks
JojoD
 
M

Minion

Member
Joined 2006
JojoD818 said:
I am thinking of doing a p2p build since the pins are too close for me to make a pcb and I don't know how to get a pcb for this chip.
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Why can"t you make a PCB?? The pins are no closer than any other IC, actually they are quite a Bit farter spaced than say a 8 pin DIP and I make PCB"s with 8,14,16 Pin Dip IC"s all the time without any problems at all.....

I just etched a Simple Chip amp PCB for a LM3886 which is just as small or smaller than a LM4780 and there weren"t any problems at all .....

Maybe it is the method you use for makeing PCB"s?? I just use a PCB Drawing Program to design the Circuit Board, I then take a Screen shot of the Design and then Trace it out in MS Paint with Black lines and Dots and then copy it out on Photo paper and then transfer the design to PCB useing an iron and then Etch the PCB in 2 parts Hydrochloric Acid and 1 Part Muriotic acid and in 5 minutes I have a perfect PCB......


If you really want to try point to point then Just use a Piece of Perf Board and do the Point to Point wireing underneath the Perf board......


Cheers
 
G

Gcollier

Member
Joined 2003
Re: Re: Point to point LM4780?

Minion said:


Maybe it is the method you use for makeing PCB"s?? I just use a PCB Drawing Program to design the Circuit Board, I then take a Screen shot of the Design and then Trace it out in MS Paint with Black lines and Dots and then copy it out on Photo paper and then transfer the design to PCB useing an iron and then Etch the PCB in 2 parts Hydrochloric Acid and 1 Part Muriotic acid and in 5 minutes I have a perfect PCB......


If you really want to try point to point then Just use a Piece of Perf Board and do the Point to Point wireing underneath the Perf board......


Cheers
Click to expand...

You really should get a freware version of eagle, it is MUCH less hassle than what you describe to print your PCB layout. Secondly...Hydrochloric Acid and Muriatic acid are the exact same thing and will not etch a copper PCB...alone. I think that you meant a 2:1 mixture of Hydrogen Peroxide and muriatic acid (HCl). :) Just watch the fumes and the heat the reaction produces.

I agree that that the 4780 can easily be done on a DIY PCB (I have done it myself several times). The hardest part of using a PCB for the 4780 is the awful supply routing. I certainly admire the elegant simplicity of Mark Hennessey's and Peter's P2P efforts. If I were to build another one of these amps I wold likely forgoe the PCB and follow Mark's layout.

G.
 
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mhennessy

Member
Joined 2002
markhennessy.co.uk/
Leolabs said:


For me,at least 250VA is required.
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You can't generalise - it depends on the voltage of the transformer, and hence the output power you want to achieve.

I would agree with your suggestion if you were trying to extract the full 60 watts per channel from the IC. But for that project, I only wanted 25 watts per channel - any more would have required a bigger case with much more heatsinking. The 120VA device I used is generous in this application.

While over-engineering the power supply by using an over-large transformer might seem attractive, especially from a cost-per-VA viewpoint, be aware that it might bring other problems. For example, 250VA is getting close to needing an anti-surge circuit. It might have higher leakage current than the smaller unit, leading to hum problems. It might make more mechanical noise. The lower source impedance leads to higher peak charging currents. Etc...

Anyhow, just my opinion. Thanks for the compliments, and good luck JojoD with your P2P efforts. It's not that difficult, but you'll need good lighting, lots of time, and perhaps an eye-magnifier... There's some advice on my "construction" page about how I went about doing P2P - you may not choose to follow it all, but if you do, the finished result should last a lifetime. In a nutshell, get mechanical strength before adding solder!

Best regards,

Mark
 
JojoD818

JojoD818

Staff Emeritus
Joined 2003
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Hi there Mark,

Thanks for the encouragement and the tips. I actually have built some tube projects in the past so p2p is, in a lack of the proper words, a fun challenge for me. I also made several p2p 3875 gc many years ago.

I actually have 2 4780 chips, so I wanted to run them (each chip) in parallel but still would only like to extract about 40W from each chip, just enough to cleanly handle those loud passages from classical recordings.

Regards,
JojoD
 
M

mhennessy

Member
Joined 2002
markhennessy.co.uk/
JojoD818 said:
Hi there Mark,

Thanks for the encouragement and the tips. I actually have built some tube projects in the past so p2p is, in a lack of the proper words, a fun challenge for me. I also made several p2p 3875 gc many years ago.

I actually have 2 4780 chips, so I wanted to run them (each chip) in parallel but still would only like to extract about 40W from each chip, just enough to cleanly handle those loud passages from classical recordings.
Click to expand...

No problem ;)

40-50W is easily attained from a transformer with two 24V windings. It's good that you're using them in parallel mode because that'll help with heat sinking (LM4780s have higher thermal resistance than a pair of LM3866's). As an aside, have you considered bi-amping?

Now we know the power you're after, we can say that the 250VA transformer mentioned earlier is about right. Although, you might consider using dual transformers? Say, 120-160VA each... Makes certain things easier provided you have enough space. Worked well with my (old) LM3875 prototypes (which are still on a lump of wood!).

Looking forward to seeing the pictures. Send me a link, and I'll add it to my site. That goes for anyone else who's done a P2P LM4780 ;)

Cheers,

Mark
 
M

m8o

Member
Joined 2006
public.fotki.com/m8o/
where'd "edit" go? Would have done that. so, new post.

Please take the above with a grain of salt. I now notice the LM4780 pins are on 0.0394 centers. Additionally, if one doesn't want to bend leads to line the pairs up, you'd need a 54 or 52 pin socket and use 1/2 or them (52 can be used as pin-1 can float as it's a "NC" connection).

...but, I haven't found sockets to accomitate either however; either bending the leads to make pairs on a 28-pin socket with 0.394 centers or a 54 / 52 pin socket on those centers... so, ignore... :xeye:
 
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