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Old 17th June 2009, 03:13 PM   #1
Zoodle is offline Zoodle  Australia
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Default Newbie question: LM38xx based amp

I'm looking at building an inexpensive power amp. It will be first electronic project. I've been recommended a LM3886 based design - based on National's example.

A kit site is offering a LM3875 based design. National's site is pushing the LM4780. Would anyone comment on these?

I'm looking for something 'musical' (pace, tune, timing). Anyone familiar with the 'Flat Earth' cult will know exactly what sort of sound I'm after.

I have a soldering iron and a $5 multi-meter. Not much gear, but it's all I can afford. My knowledge of electronics is very basic. I mean, I can follow a schematic, but that's it.

My current source is FLAC through a sound card (a little hissy, but okay for now). My current amp is an old Sansui receiver, which I found on the street. I managed to mod it into a power amp. It sounds quite tuneful, but the tone controls are annoying (bypassing them seems to be beyond my ability). So, that's why I'm looking at starting from scratch.

So, what do you think? Are any of the above mentioned parts suitable for me? Am I barking up the wrong tree completely? Would much appreciate your advice.
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Old 17th June 2009, 04:39 PM   #2
netbug is offline netbug  United States
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I think a 3875 or 3886 kit would be a great first project. I built a 3886 kit and really love the sound. You really donít need to have any great understanding of electronics to build a kit from chipamp or audiosector, as long as you pay attention.

What kind of soldering iron do you have? A 30-40 watt fine tip iron would work best. Too much power or too large a tip and it will be tough to solder the pcb.

Donít forget to include the cost of a transformer/Potentiometer/RCAs/Binding posts/case/wire/Ö. in your budget. About $100.

One word of warning, projects like this are like crack. Once you finish one itís really hard to stop.
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Old 17th June 2009, 05:04 PM   #3
mattmcl is offline mattmcl  United States
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I'm in the same position Zoodle. I'm looking at doing two monoblocks, probably the LM4780 from audiosector.com. I can do crossovers, but that's the limit of my experience. From what I've gathered, construction for any of the chip kits at chipamp or audiosector require only basic skills.

I've been reading everything I can find comparing the chips, and it's all very subjective. My plan is to jump in and do it.

I'll also be doing FLAC through the sound card, though after the amps I'm considering a DAC/preamp combo.
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Old 17th June 2009, 05:10 PM   #4
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For a first try I would also say go with a reputable well known kit as plenty have been built. That way if you have a problem with it, the answer will most likely be out there. You can get adventuous with the next if you want, but keep things simple for a first go.

If you are using a pc as source be aware that they can have a lot of DC on the output. If this means nothing to you, search on "DC offset" and "input capacitors". Also have a look for "lightbulb tester" and put one together before you start your amp build.

What enclosure are you thinking of using? If you are making your own this will be a bigger job than assembling the circuit boards. Read up on safety grounding, it's vital you don't electrocute your loved ones as they are seldom happy about it.

Have a browse at Decibel Dungeon for answers to many questions and maybe some inspiration in the gallery pages.

Netbug is right about it being an addictive hobby. If your first one works and sounds as it should it's very pleasing. If you take your time and be careful you are in for a very pleasant surprise, and a grin from ear to ear.

John
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Old 17th June 2009, 05:34 PM   #5
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by john blackburn
have a look for "light bulb tester" and put one together before you start your amp build.
A new champion to the cause?

I like the build order you recommend.
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Old 17th June 2009, 08:29 PM   #6
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Hi Andrew

I never said thanks to you for pointing it out when I first started here. It saved me from killing the linear power supply I did for my playstation when a whisker of solder causing a short went undetected. The bulb shone brightly instead of my stripboard.

Cheers Matey

John
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Old 18th June 2009, 02:00 PM   #7
Zoodle is offline Zoodle  Australia
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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.
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Old 18th June 2009, 02:11 PM   #8
mattmcl is offline mattmcl  United States
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Quote:
Wishful thinking?
Yup. My preamp plans are volume, built-in DAC and subwoofer out.

Peter Daniels from Audiosector has an excellent step by step walkthrough in the chip amp section, that was a big factor in my decision, plus he's very open to questions.
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Old 18th June 2009, 02:22 PM   #9
col is offline col  Australia
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Having a read through the ESP website is a good place to start too:

http://sound.westhost.com

col.
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Old 18th June 2009, 02:26 PM   #10
AndrewT is offline AndrewT  Scotland
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or go to decibel dungeon (Nuuk).

I cannot recommend a partially DC coupled chipamp that has few if any of the "National optional" components fitted, to any newcomer to DIY amplifier building.
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