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Chip Amps Amplifiers based on integrated circuits

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Old 12th January 2006, 07:41 AM   #1
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Location: Wisconsin....what did you expect?
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Default Kit or DIY?

First, as you may have guessed, I'm a total newbie to audio in general. I'll leave it at that.
I was looking to build a Gainclone based off of 2 LM3886 IC's.
http://www.diyaudio.com/forums/attac...amp=1123974343
Would I be better off buying a kit (est. 40$, likely far more with PSUs) or making my own?

I found some for about 6$ each on Ebay; it looks to be a reasonable enough price for them. I'm familar enough with copper etching and have access to a ferric chloride bath and assorted other useful items, so making my own PCB is not a problem, so long as I can find a diagram. (That said, I would'nt say no to an inexpensive set of PCBs.) Would anyone know where I may find one of these? Also, what are the exact specifications of the parts? (I.E; do any of these have to be to specific tolerances, or will any random capacitor of the required value work? goldmine-elec.com has some rather nice 4700 uF capacitors for 4$.)

What are the differences between the LM3886 and LM3875? Audiosector has a rather nice looking 3875 kit w/ two PSU's for 50$; Chipamp.com appears to sell the PCBs used to make it for 12$.

Also, should I buy a PSU kit for each speaker, use two, or build my own? What advantages would I see from using two power supplies?
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Old 12th January 2006, 08:24 AM   #2
sangram is offline sangram  India
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If you want a challenge, nothing beats P2P. A small piece of veroboard should be enough for the 3886. There's somebody who's built 10 channels in one case using only veroboard, so it can't be THAT hard...

If you are a total newbie, nothing beats a Kit like the chipamp.com/audiosector ones (for minimalism; kits with more accessories like protection/high power etc. also available).

If you can make your own PCBs, then a good place to start is the PDF files from National, those have sample PCB diagrams also. Bill of materials is also a part of the files, and have all tolerances and values clearly mentioned, so...

As for caps, yes, any value cap is sufficient. I am only using the ones that came with the kit (2x1500 uF FC Panasonic) and they sounded great on my older speakers but now a bit too bright on my newer ones, so am going to experiment with more capacitance. 4700 uF should be fine for your use.
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Old 13th January 2006, 03:15 AM   #3
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Quote:
Originally posted by sangram
If you want a challenge, nothing beats P2P. A small piece of veroboard should be enough for the 3886. There's somebody who's built 10 channels in one case using only veroboard, so it can't be THAT hard...

If you are a total newbie, nothing beats a Kit like the chipamp.com/audiosector ones (for minimalism; kits with more accessories like protection/high power etc. also available).

If you can make your own PCBs, then a good place to start is the PDF files from National, those have sample PCB diagrams also. Bill of materials is also a part of the files, and have all tolerances and values clearly mentioned, so...

As for caps, yes, any value cap is sufficient. I am only using the ones that came with the kit (2x1500 uF FC Panasonic) and they sounded great on my older speakers but now a bit too bright on my newer ones, so am going to experiment with more capacitance. 4700 uF should be fine for your use.
I'd personally prefer to use Carlos Filipe's design. It's supposed to produce very good sound, and it's not too complex. However, I've yet to locate a list of reccomended parts, and I still can't find the volume pot. Also, is it capable of driving 8 ohm speakers without any problems?

Veroboard is availible locally, so I think I'm set there.
Here's a list of parts I hope to use for the 2 amps:
2x LM3886TF: 5$ ea., 10$ total.
4x 13,000 uF electrolytic caps (replacing 2200 uF caps): 12$.
(http://www.excesssolutions.com/cgi-bin/item/ES3463)
2x incredibly oversized heatsinks: Free. I already own them.

For the other stuff needed:
Are there any resistors/capacitors I should use? It seems that some parts give better audio performance than others.

I'm still not sure what to use for the PSU's. Carlos has created a rather nifty-looking regulated design, but I don't know where to get the transformers necessary at a low price.
Much thanks,
Spasticteapot.

EDIT:
I think I found Carlos' older PSU design. Not fancy, but I think it should work.
http://max8888.orcon.net.nz/LM3886GC.htm
Can I use the 13,000 uF caps on this, as well?
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Old 13th January 2006, 03:54 AM   #4
sangram is offline sangram  India
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If you plan to use Carlos' Design there is a PCB avilable from somewhere on the board, not sure where but people have built it. (I think it's called MyRef). I would guess that since there is an opamp in the feedback path, it would be nice to keep the path nice and short. In which case a PCB may work better than vero.

Though I'm not familiar with the PCB, it may or may not be accompanied by a parts list. I would think it is, and Carlos has also published the schematics on this board so adding it up to generate your own parts listing won't take much.

The 3886 can deal with loads down to 4 ohms without too much of a fuss, so I think you're in the clear there...

The PS design looks fine and should work with the 13000 uF. I see no problem.

As for the rest of the parts, yes, there are some supposed differences between parts from various manufacturers, but so long as you stay out of the bargain bins you should be OK. If you really want to get exotic you can use caddocks and rikens for resistors and Black gate caps, but those turn out to be very expensive... There'll be plenty of threads on the sound of caps and the sound of resistors, so you can read up a bit. I use ordinary Phoenix metal films that came with the kits, and I'm much more than happy.

The 3886 should be fine with a 24 volt transformer. You can find them now at Digi-Key, Plitron or Hammond. Down here in the third world I had to make do with locally made custom wound 22 volt 440 VA EI transformers. They work well but look very ghetto, and only cost me $40 the pair, so that isn't too bad.
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Old 13th January 2006, 02:12 PM   #5
Nordic is offline Nordic  South Africa
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As far as kit quality goes, you can also not go wrong with the TP Rev C LM3886 kits . Amazing attention to detail, with one of the best LM3386 topologies yet...
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