Members Zappacat Posted May 3, 2009 Members Share Posted May 3, 2009 I'd like to build a combo 2x12 stereo amp that has balanced stereo sends(to send to the PA). It doesn't need much(if anything) on it for a tone stack. The more power the better. It just needs to be uncolored sound. I guess what I'm looking to build is very similar to a stereo Tech 21 power engine. Could any of you point me in the right direction. I'd really appreciate it. I'm seriously considering trying this amplifier http://sound.westhost.com/project27.htm 100W Guitar Amplifier Mk II. Have any of you built this amp? The only thing I see that it lacks is stereo. Outside of that it seems to be well documented and I like the way he explained it. Link to comment Share on other sites More sharing options...
Members tedmich Posted May 6, 2009 Members Share Posted May 6, 2009 You are in EXCELLENT company with Rod Elliott; his designs are exceptionally well though out and he is an invaluable resource when building them, he has been ripped off a TON by weasels with a fraction of his talent. I am building his preamp now (http://sound.westhost.com/project88.htm) to go with a ~135w stereo chip amp from Marchand electronics. Rods amp uses discrete transistors and likely works very well. Another option is to build a chip amp/gainclone, I just built up a Marchand PM21 (shown here:http://www.marchandelec.com/pm21.html) its a dual LM3886 (National Semiconductor) which puts out 2X~68 watts of clean power into ~4ohms with a +/-24VDC powersupply. The components are ~$30-$50 depending on how much surplus you use. Other ChipAmps/Gainclones are cheaper to build, some use very simple PCBs. See this page for cheap toroids for the power supply and a simple build: http://www.apexjr.com/miscellaneous.html#Toroids they have cheap LM3886s too ( the Ebay ones are inflated) and National will sell you them cheap if you register for "samples" With a line level input from the Pod you may be able to skip a preamp as you don't want a tone stack etc. the PM21 has 32db (40x) gain and can amplify w/out a pre (dual 10k can work for volume in control) Link to comment Share on other sites More sharing options...
Members Zappacat Posted May 6, 2009 Author Members Share Posted May 6, 2009 You are in EXCELLENT company with Rod Elliott; his designs are exceptionally well though out and he is an invaluable resource when building them, he has been ripped off a TON by weasels with a fraction of his talent.I am building his preamp now (http://sound.westhost.com/project88.htm) to go with a ~135w stereo chip amp from Marchand electronics. Rods amp uses discrete transistors and likely works very well.Another option is to build a chip amp/gainclone, I just built up a Marchand PM21 (shown here:http://www.marchandelec.com/pm21.html) its a dual LM3886 (National Semiconductor) which puts out 2X~68 watts of clean power into ~4ohms with a +/-24VDC powersupply. The components are ~$30-$50 depending on how much surplus you use. Other ChipAmps/Gainclones are cheaper to build, some use very simple PCBs. See this page for cheap toroids for the power supply and a simple build: http://www.apexjr.com/miscellaneous.html#Toroidsthey have cheap LM3886s too ( the Ebay ones are inflated) and National will sell you them cheap if you register for "samples"With a line level input from the Pod you may be able to skip a preamp as you don't want a tone stack etc. the PM21 has 32db (40x) gain and can amplify w/out a pre (dual 10k can work for volume in control) Thanks so much for your advice. I'm new to this sort of thing and your help is greatly appreciated. I don't understand how to connect the the stereo outs of the POD(or any processor) to the inputs of this amplifier. Is the ouput signal of the POD running in the same levels/frequencies as it would be for a standard CD/tuner/tapedeck input? It seems as though all these amp circuits are designed for home stereo systems. I thought the signal levels were entirely different. Am I missing something here? What are you going to do for speakers? I thought since this circuit has 2 LM3886s that you could drive 2 8 ohm speakers like Celestion seventy 80s. Why are you going to use 4 ohm speakers? Also, why do so few of these circuits take advantage of the LM4780. It seems like that would be the "cats meow" for this type of application since(from my understanding) it's basically two LM3886s? Thanks for your time! Link to comment Share on other sites More sharing options...
Members tedmich Posted May 6, 2009 Members Share Posted May 6, 2009 a good rule of thumb, if the output has a volume control, its not a "line level out" so the ipod headphone jack is not, but the ipod dock output is a LLO. The signal loading and impedance mismatch can degrade the typical high gain signal going into a LLO input, thus Mr. Anderton's famous "guitar buffer" op amp circuit to allow you to play through your home stereo. To some degree you can use the POD output with a 1/8 stereo jack to dual RCA converter cable available at Partsexpress.com as long as you keep the volume low. I used the 4 ohm spec because it maxes the watts output, 8 ohms works fine as long as the power supply requirements are met. The LM4780 is two LM3886s and newer, much discussion here:http://www.diyaudio.com/forums/showthread.php?threadid=50504 and that group has a TON on the designs its the impedance matching you need to pay attention to, to be sure the nice clean amplification these chips provide is fully realized; Rods design will be optimized, and though shipping from Aus can be slow his kits are top notch Link to comment Share on other sites More sharing options...
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