Phase Linear 2000 Upgrade and Overhaul

From the Rain City Audio Repair Blog:

I recently got to work on another Phase Linear 2000 pre-amp. These well regarded components are a fantastic part of any stereo system with their high output rating, multitude of inputs and outputs, and low distortion – especially if they’re paired with a Phase Linear power amp. This particular one came from it’s original owner where he purchased it in the ’70s and variously used it as a stereo amplifier, a guitar pre-amp, and more.

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The owner reported it was sounding uneven between the channels and generally not working as well as it had. No wonder, it’s on all original parts!

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First up was a re-cap, and that did improve performance, it was still very uneven especially on the phono inputs and had an incorrect response curve. Phase Linear released a service bulletin a few years after these came out warning about the longevity of some of the early op-amp chips they used. While the chips in this particular model weren’t in the date range called out, they are known to have a reputation for failing, so it was time to purchase some new chips.

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The RC4136 op-amp is manufactured today, but the RC4739s have been out of production for many years, as they didn’t really fill a distinct niche and also had a non-standard pin-out. Fortunately, there are drop-in replacements available which use a very much improved NE5532A op-amp chip instead.

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In addition, I hand matched and replaced the passive components surrounding the phono pre-amp which delivered perfect channel balance and a correct RIAA equalizer curve.

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Both RC4739 chips got the same treatment. Time for testing:

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Testing showed that distortion was within spec, no doubt helped by even better op-amps than original, and the channels were balanced within 0.5 dB of each other through the full frequency range.

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Now it’s good as new!

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This entry was posted in Audio, Electronics, Hi-Fi, Stereo, Vintage and tagged , , , , . Bookmark the permalink.

One Response to Phase Linear 2000 Upgrade and Overhaul

  1. David DeRosier says:

    Nice job! You were lucky that replacement Op amps were available.

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