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Old 15th July 2005, 12:01 AM   #1
SGT is offline SGT  New Zealand
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Cool Which GC to build? Plus more...

Dear all ,

'having a hard time trying to decide which - of many - GC to build. I'm a noob in audio diy (apart from my speaker cable making "skills") and would appreciate educated suggestions (i.e. you tried it yourself) on following:

1. buy LM3875 kit or
2. buy LM3886 kit or
3. buy LM3886 kit with snubber PSU or
4. other - your suggestion here

What are the advantages/disadvantages of your suggestion?

Other part of my question is related to the possible combination of my Rotel ra-1062 and my new GC's-to-be. Are there any objections on using it as an pre-amp for GC's? I say it in plural, 'cose I'd build two and do bi-amping of Monitoraudio S8 speakers. Of course, I'd need some sort of bridge to link single pre-amp outs to two GC's.

Issues, ideas, suggestions?


Thanks and cheers,
SGT

p.s. Regarding GC's, it will have to be some sort of kit, because of my limited exposure to "all of this"
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Old 15th July 2005, 03:46 AM   #2
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BrianGT sells a wonderfull dual mono LM3886 kit which sounds ideal for you. You could do that with a passive pre, or with one of the many good ative ones such of the freebird I designed recently.

Check out Brian's kits at www.chipamp.com.


If you are adventurous and want to etch your own, checkout my thread on my tiny 3886 design which sounds quite nice. you could get a power supply from Brian for that board.

I really like the 3886. I think it sounds better than the 3875 personally, though some will differ.

I also tend to use 4-6 ohm speakers, and not 8. And the 3886 handles them quite well.

The 4780 is also quite nice (essentially two 3886s in one chip) but be prepared to solder some very narrow pin spacing. Its tight.


I any case all of national Semi chips sound good in my experience.

Still if I were to pick a winner of the beginner type kits it is the LM3886 with a snubberized PS.

You may also want to check out Mauros designs. Which are in another league altogether.

Cheers!
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Old 15th July 2005, 11:07 AM   #3
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Thanks a lot Russ,

kind of answer(s) I was looking for!

I did my homework and checked Brian's and Peter's sites early last month (after accidentally stumbling up on diyaudio ), then Carlos's snubberized solutions and finally by your posts/boards on Mauro's designs. But... still couldn't decide what's ok for my competency level and what can wait for later.

Yes, I think I'll go 3886, too. Are these based on latest snubberes or it's an earlier revision?

btw, my speakers are 8ohm - does it matter with 3886? Or would 3875 be better match here?

Right now I will avoid 4780 for not a lot of noobs kind of info on it (thanks Brian for those pictorial guides on his site! )

On the pre-amping from my Rotel's single pair of pre-outs to two GC's - any nick of advice how to do it? I'd really like to make two of these babes.

Thanks once more and cheers,
SGT
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Old 15th July 2005, 12:39 PM   #4
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You really cannot go wrong with the 3886, I have a wide range of speakers (my other hobby is speaker design/building) and these babies really sing on all loads I have thrown at them. I even have some 12-14 ohm speakers, which still sound great.

My opinion is (after hours of listening to both 3875 and 3886) that the 3886 just sounds better all the way around. I especially noticed/measured lower noise and distortion.

The snubberized supply brian sells is the initial version, which is very good. The new versions offer only very small changes in performance, and can be accomplished on the same boards, so no loss in getting them.

Quote:
On the pre-amping from my Rotel's single pair of pre-outs to two GC's - any nick of advice how to do it? I'd really like to make two of these babes.
Not sure your meaning here, do you mean two stereo amps, or do you mean two mono amps?

In any case just buy the appropriate kit from brian (stereo or dual mono) and then buy one tranformer for each case you want to build. 200VA is fine for a single channel. 300-400VA is better for a stereo pair.

Cheers!
Russ
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Old 15th July 2005, 03:15 PM   #5
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Another question:
which chips do you think sounds better, the isolated ones or the unisolated ones (generally, compared ex. lm3886T to lm3886TF)?

Michael
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Old 15th July 2005, 03:18 PM   #6
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There is no difference in sound, only in heat transfer. The safest bet is to get the TF package unless you know what you are doing, because you have to be sure you isolate the exposed back of the chip correctly in order to avoid catastrophy. Also, by the time you add good isolator to the T package thermal performance is probably no better than the TF package.
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Old 16th July 2005, 09:33 AM   #7
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Russ, once more - many thanks!

OK, I'm cooked and baked now and will place an order for 3886's ! I thought to go dual mono, but might not understand all the issues on dual mono blocks vs. stereo. Therefore will add the details to try to hopefuly clarify. Check it out, since it'll definitely prove my noobness, heh.

current status:
- I got ra-1062 (60Wx2, 8 Ohm, integrated)
- ra-1062 has single pre-amp output (one +; one -)

desired status:
- build two GC's based on this group Achievements (capital A )
- split ra-1062's single pre-amp output into two and feed GC's
- enjoy bi-amping with two GC amps and one Rotel pre-amp.

Does this make more sense... with monoblocks? Or I'll have to go stereo with this one?

"Splitting" of pre-amp out signal from ra-1062 is the unclear part you aksed clarification for in your previus post.

Now, as for toroids, I tought to buy two 300VA 25V (or 30V?) for each GC, but from your post I conclude I can go 200VA for monoblocks? That would certainly be cheaper, but please confirm.

Is there any particular reason why there are no "premium" kits on 3886 (as Peter D. has for 3875)?

Cheers and thanks,
SGT
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Old 16th July 2005, 02:55 PM   #8
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I wouldn't bother with the "premium" bits, as it is most likely a very subjective "premium" if you know what I mean.

Now lets get a couple of things established:

By amplifying is commonly defined as the pocess of powering a single speaker with two amplifiers.

Monoblocs are simply one channel amplifiers that have independant power supplys, so it takes 2 for stereo.

Now if you were to "biamplify" a pair of two way speakers you would need 4 monoblocs.

You would simply take a Y splitter from one channel on the preamp output and run each end to each power amp on that channels monoblocs which in turn are connected one ofthe speakers.

Is that what you mean to do?

In any case, please don't wast your money on subjective hocus pocas, keep it real. Save subjectivity for your own experiments when you get a chance, then you will not be dissapointed.

Look at the datasheets, they will shed a lot of light, and will be very helpful to you later.

I would use 300VA at least. 200VA will work alright though, just don't push the amps hard.

Cheers!
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Old 18th July 2005, 09:59 AM   #9
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Thanks Russ!

That's what I had in mind (see pic). Hence the need to order 2 dual monos... I wanted to use y-splitters, but wasn't 100% on do I need some other kind of crossover/splliter as some pre-amping designs suggest.

I understand what you say on "premium" kit...

300VA - that's for each dual monoblock (overall: 2 toroids 300VA each)?

One more question (I'm trying to dose this properly, heh):
- my pre-amp's output sensitivity/impedance is 1.0V/470 Ohm. Are 3886 signal inputs ok with this? Sorry to ask, but I couldn't find it elsewhere (tried Brian's pdf's, ...)

No more questions. I want to let you know that I'm *very* gratefull for your help and patience! Thanks.

Cheers,
SGT
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Old 18th July 2005, 09:59 AM   #10
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