I have an Onkyo DVD receiver, DR-UN7, which is part of a shelf mini-system that I bought in 2006. While most in hi-fi community would probably frown on this contraption, it can play SACD and DVD-Audio, among most other formats conceivable, and has 5.1-channel surround sound capability.
Shortcoming: while there are pre-outs for center, subwoofer, and surrounds, there is no pre-out for the main fronts (only the speaker-level terminals)! And there are no other outs I could use to get around this problem. The amp is only 16Wpc into 8 Ohms with THD 5% at rated power. This sounds really bad on paper, but in reality, I never heard it distort. Still, I want plenty of headroom to drive my main fronts.
Current set-up: for the main fronts, I use a line-out converter to step the signal down to line-level, then I use Onkyo A-RV401 (integrated amp, 100 Wpc) to drive my main fronts (Paradigm Mini Monitors v.4). For other channels, I use Yamaha DSP-E492 (integrated amp, DSP, 60 Wpc) to drive center (Polk CS2) and rear surrounds (Infinity US-1). It's a budget set-up, which is yielding satisfactory results.
First mod seems simple: I want to either bypass or incorporate a switch to bypass the built-in amp and obtain pre-outs for the main fronts (so that there's no need to use a line-out converter). I have a service manual for this unit. Would anyone be willing to have a look at the schematic with me to make sure I'm on the right track?
Second mod might be tougher, though looking at the schematics, I still believe it is doable. Ultimately, I would like to supply separate pre-amp boxes and use the DR-UN7 DVD Receiver only as Disc Player and Tuner. In other words, I would like to bypass its internal pre-amps but retain its DSP, such as Dolby decoding, DTS, and other nice goodies. Again, would anyone be willing to have a look at the schematics with me and answer specific questions to make sure I'm on the right track?
The schematic says that the built-in power amp is on a separate PC board of its own. The pre-amp and the DSP share a board, but they appear decoupled in the schematics. There is an IC chip at the heart of the pre-amp board, which I believe is designed to do the switching between different inputs (i.e., tuner, dvd) and different listening modes (i.e., 2-ch, 2.1-ch, 5.1-ch, DTS, DVD-Audio, etc). Basically, I need to consult about where the DSP signals end and where the pre-amp begins for each channel. The board seems pretty clear, but I do need someone with more knowledge of schematics.
Much appreciated and sorry for the long-winded first post. :-)
I did the separation of an integrated a long time ago. This amp had the power amp and preamp each on there own boards. I identified the jumpers from pre to main and did a snip snip / solder solder and it was done. Now, what I did was PURE LUCK. I had NO schematics but relied on simple reason. That it worked was great, 'cause I couldn't afford a real preamp, though in those days I had my eye on a few. Had I let the smoke out, that would have been it for a while.
If you can identify the power and pre boards, and are willing to have the darn thing go up in smoke, why NOT give it a try?
As for getting the DSP and other stuff out of the circuit, that is very dicey. I dare say this is not quite the right place for a DIY on this level, which amounts to reengineering the piece.
Even the least expensive HT receiver would 'best' this. As for SACD and other disc capabilities, most here would also probably say that even an entry player from NAD, Rotel or Cambridge and playing just the non-SACD layer from those discs would beat your all-in-one for sound quality.
Thanks for your post - I appreciate you taking the time to reply with your thoughts. I believe your post about decoupling a pre from an amp did come up in my searches while I was debating this project.
Basically, the service manual for this unit is pretty clear and shows not only the schematics but also clearly labels all PC boards and their arrangement in the chassis, including all interconnects. The amp and the pre-amp are on different PC boards, so I believe tapping these connections will be reasonable and not damaging to the original circuit design. I do have a detailed SM from Onkyo in PDF with full schematic.
Concerning the other objective - bypassing the pre-amp - I was not talking about getting the DSP out of the circuit at all! I'm not about to re-engineer this system. I meant I want to tap the signal out of the DSP *before* it goes into the pre-amp circuitry for each individual channel. So I would like someone to have a look at the schematic with me to confirm where those pre-amp sections are - I believe it's the ones with the transistor clusters (like what the amp board uses - it's just full of transistors), and those regions of the board are clearly visible because otherwise they use op-amps everywhere else.
You're right, I could get an excellent receiver for very low prices (<$100) on craigslist, but I'm after the player. I love this Onkyo - it has served me very well over 4 years I've had it, so I don't see a need to get another player at this time, when this system is fully operational. Plus, those players are $100 and above even used in craigslist.
Anyhow, it's a fun project, and I would enjoy taking on this challenge and see what I can dish out.
Would anyone be willing to check me on those circuit diagrams?
You're gonna need someone who is really good a sketch-o-matics. I would have no idea where to start. If you break a power trace, for example, downstream goes dead. Than, is it a broken part or what? ONE puff of smoke and you are DONE.
Unless you're absolutely broke or zero budget for stereo, I'd say to wander into Paramus or someplace and listen to a complete budget system at a stereo store...not a bigbox or multimart kind of place, a real stereo store.
Basically, I was just thinking about routing the outputs from the DAC to some RCA plugs, where an external pre-amp would plug in. Are you saying the design on these boards is so delicate that tapping a signal in such a way would wreak havoc downstream?
I know enough to know it's not like plumbing. You have all of the design to consider. Will the DACs sink enough current into whatever the input of the preamp is? And a dozen other things.