Newbie question: LM38xx based amp

[col]

Andrew, are you referring to the ESP chipamp projects? I was thinking more "general knowledge". There is a lot of good articles in the ESP site for someone starting out. I haven't built any of the chip amps as I only build class D at the moment

col.

[Tekko]

Now dont buy into esp 100%, much of his writing is to boost sales of his own boards.

[ChrisA]

Originally posted by Zoodle
Thanks everyone for the warm welcome and the info.

Netbug,
Fortunately, my S.Iron is a temp variable. I think it's fifty watts.

Mattmcl,
Looks like we're on the same road. I've realized I need a separate DAC, so I'll be looking at building one of those too. I was hoping that the vol control in my FLAC software (Rhythmbox) operated in the digital domain (prior to SPDIF). Wishful thinking?

John, Thanks for the advice (bulb tester), and I hear you on the safety issue. Luckily, I've got my pick of enclosures: the Sansui, plus two other amps (busted). I hope to cannibalize them for transformers and heat-sinks. I suppose using the P/S smoothing caps would be a false economy.

I may go with the 3886 because so many people have built amps using it, but I'm open to new ideas.

SPDIF is never scaled. It is always "full volume" so to speak. You really never shouod scale digital audio data. Volume control must be analog. The reason is simple, for every 6DB of volume reduction you in effect loose one bit of sample width. By the time you are down to soft, small room volume you have 68-bit sound that is "telephone quality" at best. Inside SPDIF the music is representy by a series a integers. When you divide (scale) integers you might get a fraction (3/2 = 1.5) but these get rounded back to integers so with digital audio 3/2=2. This leads to a 50% distortion which is unacceptable. So it's not done, volumes are analog.


It's odd how people say they are basing an amp on a "3886". Those parts sell for $5 and the amp cost $100 or more to build. Only 5% (or 10% if you build stereo) of the amp is "3886". When you listen to an amp what you are really listing to is the power supply. It's the PS that makes the big volume power, that "3886" is really a kind of throttle that sits between the PS and your speakers. Same applies to tube based amps. In all cases, tubes, transistors or chips that gbig exppensive parts are the PS and speakers.

If this is your first project, I'd suggest starting very small. Build two amps. make your first one very small. Maybe use a 12V power cube ("wall wort") as your power supply and build a 1/2 watt amp. Then later build the amp you really want. You can re-use the parts if need be.

[col]

Now dont buy into esp 100%, much of his writing is to boost sales of his own boards.

OK, I'll be a bit more specific, this area of Rod's site is very informative:

http://sound.westhost.com/articles.htm

I use a lot of Rod Elliot's PCBs I find them really easy to build and they always do what is claimed. I haven't tried any of his amp projects though.

One good thing about the ESP projects is that if you are living in Australia the designs keep in mind what components are readily and cheaply available. All of the boards I have made up Iv'e been able to walk into one of the 3 main electronics stores that are in every town here and buy all the components needed.

My first amp build was a 41hz amp9-basic. It probably wasn't the easiest to start with but being able to just connect it to a battery instead of using a mains powered transformer was a big plus.


col.

[Zoodle]

Mattmcl,
Yeah, I thought it was too good to be true. So I'll be looking at some sort of minimalist DAC and Vol control. I've also had a good look at audiosector - it's tempting to buy a parts kit from there and assemble it as point-to-point.

Col
I'll take a look at those articles. Americans and Brits are lucky - they don't know what a desert Aus can be for the DIYer. I thought DSE would have everything I need (wrong!)
I like the idea of battery power for audio (cleaner?)

AndrewT
Thanks for reminding me: Decibel Dungeon.

Tekko,
I'll be on guard!

Chris,
That's something I didn't know - SPDIF vol issues.
P/S: When I worked in hi-fi retail I remember how the best sounding amps always had P.supplies that seemed 'too big' for the job.

Thanks again all. You've saved me making some mistakes and wasting time/money.

[kscharf]

There are a few simple bare board kits for sale on ebay using LM3886 chips. Some come with a power supply PC, some are just the amplifier boards. If you have some surplus bridge rectifiers you don't want the power supply PCB's (and if you can't build a power supply using point to point wiring you shouldn't be building anything anyway).

I just finished a stereo gain clone using two of the simple ebay LM3886 pcb's. It came out great, sounds real good. I soldered the feedback resistor directly to the LM3886 pins rather than to the pc board because I thought the traces to it were too long, but it probably would have worked OK on the pcb. I will post some pic's on here later.

[john blackburn]

if you can't build a power supply using point to point wiring you shouldn't be building anything anyway

We all have to start somewhere and a kit gives the best chance of success for a first go.

I started with a 3875 kit, then a 3875 point to point, then a 1875 point to point with a couple of pre amps and a playstation in between. Not forgetting a couple of sets of speakers.....

Adictive? No I could stop anytime I want to, maybe just one more...........

John

[kscharf]

Originally posted by john blackburn


We all have to start somewhere and a kit gives the best chance of success for a first go.

I started with a 3875 kit, then a 3875 point to point, then a 1875 point to point with a couple of pre amps and a playstation in between. Not forgetting a couple of sets of speakers.....

Adictive? No I could stop anytime I want to, maybe just one more...........

John

My first gain clone built with ebay lm3886 amplifier pcb's sounds real good. The boards are not as nicely laid out as the BrianGT ones, but if you solder the feedback resistors directly to the chip, they'll do. Now I want to make a 3 channel amp for my HT, probably with 6 boards for 3 bridged channels. Later I'll add 2 or 4 more channels for the surrounds. (My Onkyo receiver is ok, but can't really drive all the speakers at once full bore.)

I like to build speakers too. I've built a pair with 6.5" woofers for my front channels, and later added a third for the center. Also a pair with 5.25" woofers for the surrounds. Also have an isobaric subwoofer almost finished (it still needs an active xover and a power amp ... another gain clone or two) for my PC.

Nothing wrong with kits for starters. Most PS boards are set up to use those T0-220 diodes intended for use in switching supplies (which are over priced IMHO). I have a load of common bridge rectifiers which are just as good if you add snubber caps. These won't fit the PC boards so I just point to point wire my PS. The PS circuit is so simple, a PCB simply isn't worth the cost. Guess if you have to cut your teeth on doing p-p wiring, the PS is the place to do it. (Just make sure the big caps and the rectifiers are not soldered in backwards!).

[col]

Iv'e been using these handy PCBs for power supplies:

http://www.altronics.com.au/index.as...=item&id=K3015

They have really fat tracks and are reasonably priced. Also, they look neat and tidy when mounted in the case, that and a chassis mounted KBPC3504 with some snubbers.

col.

[lanchile]

I recommend LM3875, it is simple and the sound is excellent.
just fallow some important safety tips. Good luck