Joined: Wed Jun 06, 2007 8:29 pm
Location: The west's most mid-western town, Scottsdale, Arizona
Prior to getting my Sunfire TGP-III, I had a pretty long run to the amps that ran my mains (A-500x on the bass, and C-500 on the ribbons) where the Rane AC-22 was. So, I had a pair of long balanced cables from Monoprice that I could use. They happen to be terminated with TRS (Â¼â€ stereo phone) plugs on one end (to fit into the Rane) and female XLR (that fit into the Sunfire) on the other. So, the circuit I built begins with TRS inputs rather than XLR. From the re-build of my C-4000 by James Van Dyke (jvandyke_texas), I had three OPA2134PA opamps he sent me. These are very highly regarded modern amplifiers that have extremely low noise and exceptional linearity. The initial design I had used TL072s, but James convinced me that the 2134s would be much better in what he chides me as â€œthe worldâ€™s simplest circuitâ€. This circuit is shown below:
I had most of the resistors floating around, but they were all 5%, so I hand matched all the 1% resistors (actually, I hand matched them all to within 1 point in the third decimal place - 1 Ohm for a kOhm resistor). I had to buy the capacitors and the hardware, and a box to put it all in when I was finished.
As you can see from above, I used a wall wart for power. I found one floating around here that was used to charge batteries for a phone I no longer own. It puts out about 17.7 Volts, so my Vcc is Â±8.3V. I had a green LED floating around, so I just put it in the circuit as an ON indicator.
OPA2134 is a dual opamp. So, to complete the circuit, the three of three of them I had are required. I bought a couple of DIP circuit boards that can hold up to 20-pin DIPS. On one board I put two of the sockets for the 8-pin 2134s, and on the other, just a single socket. Because I had enough real estate on that second board, I built the voltage splitter onto it, as shown below.
You can see the ground routing around the chip carrier.
The input board carries the 0.1ÂµF caps and the 1MOhm resistors. The 22pF caps are carried directly on the TRS socket. Between the two chip sockets is where ground runs.
Because I ran out of real estate on both boards, I had to be creative in hooking them together. The 10kOhm resistors along with power and ground connect the two boards. Here is the unit ready for system test.
The TRS (Â¼â€ phone jack) sockets I used were THESE that I didnâ€™t know were switched until I wired them all wrong and wondered why (for a very long time) I couldnâ€™t get this circuit to work. The RCA jacks Iâ€™m using are THESE â€“ both of which I got at Parts Express. Finally, I got a not so small project box at Radio Shack, primarily because the width had to accommodate those two TRS jacks side-by-side.
Here is the box running the rear channels from my Sunfire TGP-III into an M-500. I was testing it using "party" mode that I have set up to run all my speakers except the center in stereo pairs.
It might be easier to just go ahead and get a CleanBOX, but I doubt it would have the quality opamps and hand-matched resistors. However, you would have balance controls (I eliminated the pots that were in the first design for simplicity (you'd replace the 10kOhm resistors that lead to the minus side of the output opamps with a 7.5kOhm resistor and a 5kOhm pot). It was a fun little project and it's a nice little gadget to have around.
There is a difference between hearing and listening...
Making life enjoyable through expensive electronics.
Carver: C-4000 & C-1 preamps, PSC-60 preamp/tuner, TX-11a tuner, M-400 (2), C-500, M-500, M-500t, M-500t Mk.II, A-500x, AL-III loudspeakers (2 pr.)
Sunfire:Theater Grand III processor, Ultimate Receiver, Cinema Grand Signature 400 ~ seven, True Subwoofer Mk. II, D-10 Subwoofer