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Old 7th October 2011, 02:26 AM   #1
Thabto is offline Thabto  Italy
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Hi Guys,
I am a newbie and would like to build a low cost powerful amp with good sound quality. So I searched on the net and found this link:
600W Audio Amplifier
What do you think about this amp? Does it require improvement? Does it achieve promised results. Please help.
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Old 7th October 2011, 03:00 AM   #2
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Not recommended for a newbie - better for you to begin with a simple chip amp at a lower power level and work your way up. If you want to build a powerful amp straight off then find one available as a kit where the hard work of getting good layout has already been done for you.

The specific thing that worries me about this amp is the bias arrangement - seems to be handled by a 2N3055. But it does not show you that that transistor has to be kept on the same heatsink. Use of a TO3 type in this function is unconventional to say the least, there's also no pot shown for setting the bias up. All these missing details tell me you'll be best giving this design a wide berth.

<edit> Oh I missed that the '300W speaker' is being fed through a 400uF capacitor. You did say you wanted good sound? Steer well clear of caps in series with speakers, especially such low value electrolytics.
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Last edited by abraxalito; 7th October 2011 at 03:02 AM.
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Old 7th October 2011, 10:47 AM   #3
AndrewT is offline AndrewT  Scotland
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That 600W amplifier is fed from a 30-0-30Vac transformer.
The retailer lied.
The maximum power into an 8r0 load that this PSU will allow an amplifier to deliver is ~ 80W per channel.

If the retailer lies about the power rating then does that retailer have the integrity to offer adequate customer support if you run into assembly or operating problems?
regards Andrew T.
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Old 7th October 2011, 04:49 PM   #4
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Saw this schematic for the lm4702, and looks like an interesting new amp to build now my lm1875 amp is finished and up and running for a while. How does this chip compare to the gainclone lm's sound wise?

Thabto, i would start with an lm1875 or 3875 if you are a newbie, i did that too and you learn so much about everything really. This one has a separate output stage (if i am correct) which complicates things. Maybe you could built a power supply separate from the amp so you could reuse that one if you would like to scale up things. Power supplies are the biggest expense, on the component level off course.
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Old 11th October 2011, 03:00 AM   #5
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Given output power, tone, and chip-amps for input information, your request then matches with:

Decibel Dungeon inverting LM3886

For cross reference:
Inflate maximum usable music output power of these projects by 400% and also multiply the resulting figure by the number of channels if you want to compare to PMPO mass market rated products. For example, TDA7294, 600 PMPO watts in stereo.

Going forward, please use output figures that also indicate performance, such as:
65 watts per channel at 0.9% distortion
80 watts per channel at 10% distortion (same amp playing louder)
300 watts per channel PMPO (100% noise, no music at all, probability of smoke)
See? Isn't that more descriptive?
When distortion figures are absent, hide your wallet because they're talking about PMPO, not music.

Of course, distortion figures usually decrease considerably when you turn down the volume knob. Unfortunately, that makes smaller wattage advertisements.

Check out these options:
A 25 watt per channel amplifier with 93db efficient speakers or
A 50 watt per channel amplifier with 90db efficient speakers or
A 100 watt per channel amplifier with 87db efficient speakers or
A 200 watt per channel amplifier with 84db efficient speakers or
A 400 watt per channel amplifier with 81db efficient speakers
The sound pressure output level is exactly the same for all five of those examples (all five equally loud); however, the dynamic impact and overall quality from the first example is the best quality on just 25 watts. Its because of the speaker.
See, speaker efficiency is a lot more important than watts!

Last edited by danielwritesbac; 11th October 2011 at 03:03 AM.
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Old 11th October 2011, 03:18 AM   #6
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How can that schematic get 600W output? The power is only 112.5W even if you feed the 30V DC into the 8Ohm speaker directly!
I think the best starting point for a newbie is LM1875, or even LM386
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Old 11th October 2011, 06:26 AM   #7
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Default Peak ratings

Originally Posted by siliconray View Post
How can that schematic get 600W output? The power is only 112.5W even if you feed the 30V DC into the 8Ohm speaker directly!
Peak ratings only indicate what you should avoid
They don't indicate a power supply used in the maximum possible power surge rating that is further inflated by marketeers. Output of PMPO testing is smoke and ashes, not music.
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