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SoundMods
PostPosted: October 25th, 2024, 1:20 pm 
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It came to my attention that there are a coupe of guys out there wanting build there own equalizer.

Designing an optical cartridge equalizer to provide superior playback beyond what the current market offers simply comes down to the critical path passive parts. Everything thing you think you know you don’t actually know. The most important parts in this equalizer are the parts ahead of the gain block.

My experience. The input coupling cap within the DS Audio product line ranges from .027-ufd to .1-ufd. I found that .1-ufd to be optimum. In terms of quality my findings were the use of a .05-ufd hermetic Teflon cap in parallel with a stacked-film polycarbonate. Musically speaking – polypropylene caps by any manufacturer will provide a disappointing result. The input 100-Kohm resistor is most important as part of the high-pass filter. Precision bobbin wire-wound resistors are optimum with Vishay bulk-film resistors as a good second choice. Go for the bobbins as they are plentiful on eBay. The 3300-pF (3.3-nF) high-pass capacitor I found to be almost more important than any other parts. After a lot of screwing around, some nice Russian surplus Teflon 3300-pf caps really brought the equalizer home to papa. The 33-Kohm shunt resistor as part of the high-pass filter is important and a nice Vishay bulk-film resistor gets the job done.

The gain block doesn’t work as well with IC op-amps unless you utilize the Burson “Vivid” V-7 discrete op-amp. They generate heat because of their class-A bias so ventilate. Performance wise? Their attempt at marketing is an understatement as these babies are music’s solid-state messiah. Please don’t entertain output coupling caps. Either provide a way to null out DC offset or incorporate a servo loop. Or -not – The Burson’s worst-case input offset is only .1-mv.

Any supporting resistors can be Dale metal-films (please – no Takmans) and small-value caps are well served with WIMA pulse caps. Output isolation resistors in series with the output can be served with Vishay 100-ohm bulk-films with a 35-Kohm shunt to ground. You don’t want the out-put to “float.”

Thinking of vacuum tubes? Don’t. Too many variables to deal with and the current choice of tubes other than mil-spec NOS just don’t get the job done. Plus, you have to deal with output couplers.

Has anyone thought of a passive gain block using a step-up transformer? Food for thought.


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dberning
PostPosted: October 26th, 2024, 12:17 pm 
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Location: Potomac, MD
Seems like 26 dB of gain would be straight forward to do with tubes. I remember doing a tube version of a strain-gauge cartridge amplifier years ago.
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SoundMods
PostPosted: October 26th, 2024, 12:44 pm 
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Location: Parkville, Maryland
dberning wrote:
Seems like 26 dB of gain would be straight forward to do with tubes. I remember doing a tube version of a strain-gauge cartridge amplifier years ago.

It would be. DS Audio has already introduced a tube model. But, holy cow! You need 5-vdc for the IR LEDs, 20-vdc for the photo-cell bias, 6.3-volts for the tube filaments, and 90 to 150-volts DC for the plates.

Building all of that for a basic equalizer circuit with a gain block just runs a tab $$$$$ and for what? Bragging rights?

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