Later I heard a pair of Apogee full-range ribbons and I was again mesmerized by what a linearly-driven diaphragm could do that dynamics could not. A friend of mine has a pair of Martin Logan CLS-3z driven by four huge Audio Research monoblock tube amps, something that took my breath away. But as all humanmade things go, one of them died. So he sent his boxes off to be repaired and 5 months later with zero work accomplished, he insisted they be returned. Frustrated, he asked me (paraphrasing), "You want to give it a go?"
Never one to turn down a good challenge and to see what was under the hood of the CLS, I agreed and we arranged a trade: I repair his speakers and he builds me a new satellite box. Both he and I were waiting to do something for the other and willing to put that little extra touch on what friends do for friends.
I got the boxes and boy was I surprised. I heard these speakers and they indeed sounded fantastic but once I looked at the circuit board, I was - in a word - shocked. The primary side of the transformers, the side connected to the amplifier via speaker wires, was what one would not consider to be the best design. Because of the high current delivered to these transformers, not one but several parallel traces ran from here to there but instead of converging at a large circular trace, the converged on a single small trace and then to a small circular trace. Now if you don't understand what impact this has, think of using #22 wire as speaker wires and you'll get an idea of this faux pas.
So further investigation showed that resistors were used in the path between this transformer and the speaker terminals on back. What I found unusual was that these were inductive-type resistors, something that most engineers avoided in the high-end realm years ago. So I decided that rebuilding this part of the circuit would be highly beneficial and so I did.
After a few hours of tracing out the circuit, I was very surprised by the simplicity of its design. And as many have pointed out in other DIY groups and forums, there are many things that one can do to just swap out components and replace them 1:1 for higher quality devices. While a definite sonic benefit will be reaped, unfortunately this will only solve half of the built-in issues with this box.
My friend encouraged me to take a no-holds-barred approach at redesigning this unit and so I did. They will be finished (parts still on order) some time next week. After I stuff everything back into place, I'll let you know what we hear.
Here is a picture of the one of the boards before modifications:
Note the use of multiple traces on this side of the board (there are even more on the bottom side). So, let me explain a little about what you see. The large rectangular gold things are resistors and they - along with the red coil called an inductor - electrically connect the speaker wires to the transformer (there are actually two transformers but both are used as one) I spoke of earlier. The black and yellow wires run to these transformers and the speaker wire connections to this PC board are barely visible in the lower RH corner.
See if there is anything else you can spot that could be remedied and when I post the results of the mods in my next article you can see if you are correct.
BTW, what these multiple resistors do is to double the power handling capacity of the resistor but reduce the overall resistance by half. The two top resistors are 2 ohm 50Watt so they actually become a 1 ohm 100Watt resistor. The two on the lower RH corner are 12 ohm 50W so they become 6 ohm 100W. The one on the lower LH side is used when the NORMAL/SOFT switch is in the SOFT position only.
Put on your thinking caps. If you've read all of the things I've written about over the years, you may be able to guess correctly as to what I am about to do. Stay tuned...
Yours for higher fidelity,
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© 2015 by Philip Rastocny. All rights reserved.