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Old 17th August 2006, 01:43 PM   #1
morbo is offline morbo  Canada
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Default newbie to DIY amps needs suggestions

I am in need of some new amplification for some speakers I've just built. Currently they are being powered by a low powered (late 70's Yamaha receiver, not sure of RMS, model is CR400 which I've always liked, but I suspect they would really like some more power, as they are fairly inefficient). Specs on the speakers (FR, Impedance curves) can be found here:

http://www.htguide.com/forum/showthread.php4?t=13154

I would like to upgrade to something that can put at least 100w into 8ohms, more would be better. The speaker above will be the load for the forseeable future, but of course I would like the amp to work well with more difficult loads if/when I upgrade. The rest of my system is decidedly 'mid-fi', using a Pioneer HT receiver as the pre/pro, sources are a stock marantz CD63, Panasonic DVD player, and modded Xbox. At some point I will be moving to a better CD player, maybe a modded PSX. I would also like to do this as cheaply as possible, within reason. I'm willing to part with the ~$179USD for a Behringer A500, so I'll set that as my budget, say $200USD.

What I am would like advice on is whether I can DIY something of better quality than the A500 for the same money using the kits from audiosector.com (the closest DIY kit vendor to me). I should also note that I have no DIY electronics experience beyond soldering crossovers, and am not particularly interested in getting into amplifier DIY as a hobby, I just want the best value amplification I can get for my $$$. Any advice you can provide me would be much appreciated.
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Old 17th August 2006, 04:56 PM   #2
araven is offline araven  United Kingdom
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Hi,

The yamaha CR400 looks like it delivers about 16-24watts.

I'd recommend the parallel LM4780 kit, delivering about 120watts per channel, but it won't like speaker loads below 8ohms (you could instead not use it in parallel and get 60w per channel and it will be able to use 4ohms then).
The LM3875 kit is a good one too, deliverying about 56watts per channel, again only really for 8ohms.

Although those kits contain the bulk of the electronics, overall costs can vary according to your ability to source a nice enclosure, filter capacitors, transformer, heatsink etc..
You do not need to have any electronics experience, as long as you're willing to read the many helpful forum posts on this site which will cover in detail every part of the construction of the kits (also i notice the guides on audiosector are very well written).

The behringer looks like it will do about 130watts per channel in 8ohms (250w 4 ohms), so it looks like it'll suit your needs more, though i'd be very surprised it if yields particularly good sound quality. It's a "studio" power amp (probably more designed for a DJ) and so is bound to be a bit crude, plus it's very cheap for what it is so i wouldn't expect quality parts to be used inside. I'm almost certain a well made amp using either the LM3875 or LM4780 would be miles ahead of it.

Hope this helps a bit
Alex
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Old 17th August 2006, 05:27 PM   #3
morbo is offline morbo  Canada
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Thank you for your comments araven. I have read some of the chipamp threads, and I'm fairly confident I can do it, especially with the excellent help I've seen given in those threads. I'm not sure about the sound quality of the behringer, I know audio critic tested it and gave the following specs:

Quote:

Signal:Noise: -99dB

Crosstalk: -55dB

Frequency Response: -0.3dB @ 10Hz, -0.1dB @ 20Hz, 0.0db @ 1000 Hz, -0.2dB @ 10kHz, 0.6dB @ 20kHz,-2dB @ 40kHz

138 watts @ 8 ohms @ 1000Hz @ 1.000% THD+N, both channels driven

120 watts @ 8 ohms @ 20Hz @ 0.030% THD+N, 1 channel driven

120 watts @ 8 ohms @ 1000Hz @ 0.025% THD+N, 1 channel driven

120 watts @ 8 ohms @ 20000Hz @ 0.045% THD+N, 1 channel driven

220 watts @ 4 ohms @ 1000Hz @ 1.000% THD+N, both channels driven

180 watts @ 4 ohms @ 20Hz @ 0.056% THD+N, 1 channel driven

180 watts @ 4 ohms @ 1000Hz @ 0.050% THD+N, 1 channel driven

180 watts @ 4 ohms @ 20000Hz @ 0.050% THD+N, 1 channel driven

Harmonics of THD are primarily 2nd order, with subsequent harmonics approaching or under -100dB.

Power output was tested from 0 degrees phase resistive load(results given above) and into other phase angles up to +/- 60 degrees. Little variation of output voltage occured, regardless of phase angle.


Here's some images of the internals:


http://forums.audioholics.com/forums...5&d=1155146363

http://forums.audioholics.com/forums...6&d=1155146373

Not sure if any of that helps at all WRT sound quality. Audio critic is an objectivist magazine, so they had no real sound quality comments, just measured performance.
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Old 17th August 2006, 05:59 PM   #4
sreten is offline sreten  United Kingdom
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Hi,

$180 = 90, you haven't a hope in hell of building anything better than
the Behringer A500 for that sort of money being totally inexperienced.

TBH you couldn't buy the parts for the A500 for 90.

The chip amp kits :
you need at least 4 a side, maybe 6 for decent power.
That is 2 or 3 paralleled and then repeated to be bridged.

The most expensive parts of an amplifier is the casework, heatsinks,
feet, knobs, socketry and the transformer i.e. the hardware, and this
is before you get to the circuit boards and the components.

/sreten.
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Old 17th August 2006, 06:48 PM   #5
araven is offline araven  United Kingdom
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I agree with sreten, for what's in that amplifier it's amazingly well priced. It doesn't look too shabby inside (not that you can tell what the quality is going to be like from that).
For that sort of money, and that sort of power, that amp is probably your best bet.

Alex
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Old 17th August 2006, 06:48 PM   #6
preiter is offline preiter  United States
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Commercial wattage ratings need to be taken with a large grain of salt.

If your desire for 100 watts is based on your experience with commercial amplifiers, I think you will find a 50 watt gainclone to be more than satisfactory.

For $200 you can build a gainclone that looks and sounds quite nice. If you are clever about scrounging parts, or don't care too much about what it looks like you can do it for a lot less.
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Old 17th August 2006, 07:16 PM   #7
morbo is offline morbo  Canada
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Thanks for your input sreten and araven, I'm starting to think the same. I've been a little doubtful about the behringer, but most negative comments I've read come from non-technical folks who don't neccesarily evaluate it on the design/build quality or any listening experince, but on the behringer name and the low price tag.

preiter - thanks, I know today's commercial wattage ratings are grossly exaggerated... for example the Pioneer receiver I have is rated at 100wpc into all channels , yet it has truly sad dynamics and was never able to drive a simple mid-efficiency 8" 2way to its limits in stereo.. whereas my 60wpc Carver receiver will have them bottoming at 1/3" gain.

My 'true' wattage references are the Carver receiver mentioned above which was rated as follows

Quote:
Magnetic Field Amplifier Section
60 watts RMS per channel (8 ohms) 20-20Khz with less than 0.05% THD
90 watts RMS per channel (4 ohms) 20-20Khz with less than 0.05% THD
and the old Yamaha receiver, mentioned above which I think puts out an honest ~20-25 WPC. So I don't think my references for 'real' power are that far off.

Perhaps 50watts would be enough, but I'd rather err on the high side, at the last Canadian DIY get together we ran a similar speaker to mine off a 100wpc Bryston and its clipping indicators were coming on from time to time.
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