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Old 19th April 2008, 03:08 AM   #1
obso is offline obso  United States
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Join Date: Apr 2008
Question Need help with stripping down onkyo reciever

First off sorry that my first post is one asking for help. Secondly I'm asking for direction more than in depth help (altho the latter would be appreciated).

What I have on my project bench is a broken onkyo tx-sr601. The best I can tell the board that controls the input switching/dsp/volume control is toast but the rest is in good shape. All I am trying to end up with is a simple amp with a set of inputs, a volume control, and a pair of outputs. Anything more complicated than that I can mess with after I get it working. What would be the easier route? Stripping the power supply and outputs out of it and starting from scratch there. Or leaving the amplifier/power supply sections intact and building my own input/preamp/volume control section (which involves deciphering how they are feeding the amp section).

The schematics/service manual are here if anyone wants to look at them and give me their 2 cents. Its for a sr600 and I have a 601 but it's the closest thing I could find.

As far as personal ability I have an advanced understanding of electronics and have everything to design and build my own circuit boards. My only audio experience is in 12v stuff (I run a car audio store).

Any help would be appreciated, even if its to tell me that it's more work than its worth and I should just break the thing down for spare parts.
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Old 21st April 2008, 03:17 AM   #2
obso is offline obso  United States
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Ok, I've got it working sort of. As long as I input a signal after the preamp I get output (albeit weak without any kind of preamplification) I never was able to get sound inputting a signal anywhere before the preamp section.

So what I have now is signal +/gnd/- x 5 channels. I thought about using some lm386's that I had left over from a previous project but its output is just +/gnd and it appears I need something similar but with +/gnd/- outputs. Is there something like this preferably all on a chip with minimal components like the 386? Or am I going about this the wrong way and there's a simple preamp circuit I could build to easily solve the problem. Not hugely concerned with high fidelity right now, I can always improve on it later once it's working.

Thanks again for any help.
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Old 24th April 2008, 03:58 PM   #3
obso is offline obso  United States
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Reposting this because after 2 days it never showed up .

What I have come up with so far is building something similar to this preamp design with a SSM2142 (and it's accompanying circuitry)tacked onto the end to give me a differential output.

Anyone see any inherent flaws with this? I'm not worried about super high fidelity or squeezing every last watt out of it. I have no idea what the actual voltage range the final amplifier needs so my plan is just ramp the preamps outputs up until the output clips and then back it off a little. Also if someone better at reverse engineering that me can spot an easy change to make the preamp above have a differential output without the added device at the end please let me know.
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