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Old 3rd September 2010, 08:26 PM   #1
henryr is offline henryr  United States
diyAudio Member
Join Date: Jun 2009
Default multi room home stereo

I am building a multiroom stereo system. There are 5 pairs of speakers in 4 rooms, plus a sub-woofer. The speakers are all in place and ceiling mounted.
Required then is a pre-amplifer/audio distribution unit and 11 channels of amplification.
I have built a prototype of the preamp/tone control/audio distribution unit.
The pre-amp/tone control circuit is from The Audiophile's Project Sourcebook , 2002, by Randy Slone. The TL-084 data-sheet provided the distribution circuit.
The outputs from a sine wave generator input thru the pre-amp and tone control circuit are shown as perfectly reproduced sine waves.
The audio distribution op-amp circuit works sporadically, producing a square wave output, which I think is expected from this positive feedback comparator circuit. It seems to require a voltage threshold, as twiddling with the various control knobs might sometimes get me an output. Disturbingly, it also adds +10volts DC bias to the output.
My question is thus about the TL-084 op amp circuit. I don't know how to alter it to repair it, or perhaps there is another explanation.

Would a unitary gain negative feedback buffer circuit work as an alternative?
The op amps could cascade just like the diagram . Only one resistor would be needed in the feedback loop, if I match it to R source, something I also don't know theoretically how to do at this moment but emperical substitution seems safe enough.

There are already 8 control switches. I will need five more: one volume control for each pair of speakers. Could I use 100K ohm dual pots, put before the individual channel op-amps?

I need to determine the correct size transformer for this Pre-amp. The power supply is a split 15 volts with 7815/7915 regulators. It works with a 24 VC.T transformer, but the circuit( from the same book) calls for a 30 V C.T.
I haven't been able to find this- the closest is a 36 V C.T. What amperage rating for six ICs ( 18 total active op-
amps)? Could I put a resistor, say 2K at each op amp output, and then measure the current from my current bench top power supply? Would that give me a fair representation of the current draw under load?
i started a thread on this last April, but it took till now to get this far. I could not find the original thread so started a new one. I've had some misadventures- the shocking kind while building the power supply being the most exciting.
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