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Old 27th September 2011, 06:37 AM   #1
50AE is offline 50AE  Bulgaria
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Default Quad 405 cheap kits on ebay

Hi,

I am a beginner and I need amps to assemble for my active system.
I've been recommended to make quad 405, I've been told it's a quite good amp for its price and availability.

I found sone cheap kits on eBay:

(link removed by moderators)
I suspect that after assembly, some components may be changed as caps and transistors. Could the transistors be fakes?
I've been also told that this amp requires a special launch procedure, a current value of few mA must be input or something.
 
Old 27th September 2011, 10:20 AM   #2
DF96 is offline DF96  England
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Is not a Quad 405 bought from anyone other than Quad a fake, by definition? Should we be encouraging this Chinese intellectual property theft? Has he paid royalties on the design?
 
Old 27th September 2011, 10:31 AM   #3
wahab is offline wahab  Algeria
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Quote:
Originally Posted by DF96 View Post
Is not a Quad 405 bought from anyone other than Quad a fake, by definition? Should we be encouraging this Chinese intellectual property theft? Has he paid royalties on the design?
That s in public domain now.
The only theft of property in this business is the use of the "Quad"
brand name in the PCBs...
 
Old 27th September 2011, 10:47 AM   #4
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After 5547 successfull eBay transactions, perhaps it is time now to correct the product description, like using the word "semiconductor" or "transistor" instead of "tube" ...
 
Old 27th September 2011, 11:05 AM   #5
DF96 is offline DF96  England
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UK copyright on creative work lasts 70 years from the death of the author, so I am surprised to hear that a 1970's design is now regarded as "public domain".

I suspect that what has really happened is that the patent on current dumping has expired, so other people can now make amps using the same idea. Calling such an amp a "Quad 405" is a copyright infringement. If it really is a copy of a 405 then the circuit is an infringement too, because the copyright on the circuit is still in force. If it is not a copy then it is misleading to claim that it is.
 
Old 27th September 2011, 11:20 AM   #6
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Quote:
Originally Posted by 50AE View Post
Hi, I am a beginner and I need amps to assemble for my active system. I've been recommended to make Quad 405, I've been told it's a quite good amp for its price and availability.
You say you are a beginner. Therefore you better not start with Quad 405 amplifiers. The Quad 405 amplifier is a very special design as explained by Vanderkooy & Lipshitz in their Wireless World June 1978 article you can download here Quad 405 Information Page

The same eBay seller has more appropriate items for you like a TDA7293 based dual amplifier here TDA7293 X 2 85W+85W +speaker protect upc1237 | eBay. It includes the bridge rectifier and the smoothing capacitors. You need to buy two such amplifiers for activating two 2-way speakers. You thus need to buy two mains transformers.

You also need a crossover. Do you know how to design it ?

If you want to build a nice 2.1 system, you may opt for the TDA7293 2.1 amplifier here, same eBay seller : NEW TDA7294 2X80W+160W(Subwoofer) 2.1 channe l Board | eBay. It includes the bridge rectifier and the smoothing capacitors. You need to buy one mains transformer.

If you are smart, you should be able to mod the circuit for a) customizing the crossover filter and b) adding a Linkwitz Transform (deep bass equalizer) in the subwoofer channel. I guarantee you that there is more science, satisfaction, and economy in such approach, than trying to appear smart or exotic in using Quad 405 clones as power amplifiers.

The Linkwitz Transform is detailed on point 9 in this webpage Active Filters
The same webpage contains a lot of info about crossovers, actually this is a "must read" document.

Enjoy !
 
Old 27th September 2011, 11:23 AM   #7
SY is offline SY  United States
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It's trademark theft, pure and simple. And if a company is happy to do that, one can raise some serious questions about their fidelity to the actual design, the quality and reliability of the parts, and their general sense of ethics- which is zero. If they'll steal from Quad, they'll steal from you.

Thread closed, and I am removing URLs to the crooks' website.
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