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Old 14th January 2015, 07:32 PM   #1
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Default A little nudge in the right direction.

Hi all, im new to this game and have a couple of quick questions.

I dont want to reinvent the wheel so to speak. In other words i want to stick with tried and tested design for a quality sounding pre amp using XLR outputs, as well as a quality sounding IC based (thinking LM3886) power amp. The system i have in mind would consist of the pre amp feeding two power amps.
Im looking for some thing in the region of 150W per channel to power a set of old Tannoy NFM system 8's and a set of Mission 702's (another project to replace them later).

Q1. Whats a good pre amp design?

Q2. Power amp wise i was looking at something based on the lm3886. Is the sound quality there or are the better ICs?

Q3. where is the best Uk based place to buy components? I have looked at ebay but most things seem to be US listed and not UK listed.

Q4. Is ebay worth it.

Construction wise i know how to use a soldering iron in anger but its a few years since i last used a scope although i do have one on the bench at work.

Cheers
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Old 15th January 2015, 06:23 AM   #2
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Quote:
Originally Posted by maiden fan 78 View Post
.... (thinking LM3886) power amp. The system i have in mind would consist of the pre amp feeding two power amps.
Im looking for some thing in the region of 150W per channel to power a set of old Tannoy NFM system 8's and a set of Mission 702's (another project to replace them later).
Q4. Is ebay worth it.....
LM3886 is a Chip-amp used in a lot of budget hifi. The 8Ω power is scarcely 50W however, so achieving 150W/8Ω would probably require several chips (like LM3875) that are capable of parallel operation and then bridging 2 pairs. That's 4 chips/channel - a bit ambitious for a first project, though no problem and more economical for a discrete design.

Read Ebay specs carefully - they usually quote high power wrt 4Ω or less. Sometimes this is impractical if you can't achieve all that you want without constraints like current and thermal safety limiters kicking in on some loads. Of course, if you really only need 1-5W as most people find at home, power like 150W is just an arbitrary, untested number.

Though there are higher power MOSFET chips like TDA7293 etc, there are physical limits to single chip output power. Bridging chips increases output level but the current demand also increases so your minimum speaker impedance becomes critical. Visit the Chipamp Forum threads for detail discussion.

Ebay is for people who simply want cheap, regardless of quality or likely fake parts. Google or the Yellow Pages finds local parts sellers quicker than waiting for forums members to type it all out for you though. Look around - Farnell, RS Components, CPC, Cricklewood Electronics, Rapidonline, Nikko-Dalbani etc. etc. For direct US products, Mouser Inc. & Digi-Key have vast catalogues of well priced genuine gear - noting the fixed freight charges.

In most cases though, you need to realize that Ebay imports have minimal customer support (often no legible schematics, BOM or guide to anything), craptanium quality electrolytics, nothing but the PCB and indicated components. everything else like fasteners, flex, pots, mounting hardware, external connectors etc. is excluded)

That's fine for many experienced DIYs with stocks of the extras required but it doesn't meet most beginners needs. Hence you see help threads opened here, seeking advice for all the stuff newbies didn't consider, such as soft-start, speaker protection, muting and overload limiter circuits as required. It's not simple when you look at the tiny package of bits and all you have is an iron, pair of tweezers and a blurry pic. or two.

In truth, the kits of amplifier-only electronic parts represent perhaps <10% of the overall power amplifier cost. The principal costs are your choice of the cases, power transformer, power supply components and heatsinks which for freight reasons, you'll probably seek closer to home anyway.
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Old 15th January 2015, 09:12 AM   #3
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Very good advice here!

Quote:
In truth, the kits of amplifier-only electronic parts represent perhaps <10% of the overall power amplifier cost. The principal costs are your choice of the cases, power transformer, power supply components and heatsinks which for freight reasons, you'll probably seek closer to home anyway.
You forgot the gold dust parts
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Old 16th January 2015, 11:17 AM   #4
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Thanks for the advice. I'm not very trustig of items on ebay or amazon at the best of times. you have just more or less backed up my concerns.

When i say im new to this game I mean DIY Audio. Electronics im just a little rusty and out of practice. My job moved away from componet repacement more item replacment. its cheeper!!
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