It’s a mod, mod, mod, mod world

I think it’s the curse of the engineer. Or maybe it’s because I’m so cheap. But somehow when I buy audio gear, I immediately start devising a plan to modify it. I must improve its performance, or quality, or appearance within reasonable limits of budget and time. My first rig was a JC Penny combo unit with AM/FM receivers, a cassette recorder and that master of all media formats, an LP record player. I played the hell out of those old pressed wood cabinets. But soon the mod bug hit. Bigger speakers led to a bigger receiver, which led to getting yelled at by my parents. So I transferred my efforts to my car stereo, the mod-crazy teenage boy’s badge of honor. Mine started humbly with a pair of Jensen 6x9s and culminated in a tri-amped system with multiple amps and custom door panels to hold the carbon fiber cone speakers in the optimum position.
My mod-craze has led to a hobby. While I’m traveling on tour, I keep my eyes open for certain vintage mixing consoles – those with nice sounding preamps or EQ’s or those that would sound good in a recording studio. A few weeks ago, though, I was sitting at home, not even thinking about vintage consoles, and came across an ad for not one, but two of one of my personal favorites, the Yamaha PM2000. With the help of some dedicated friends with a truck, I acquired both of these 32 channel beauties. Yamaha debuted the PM2000 in 1978 and continued production until 1988. It’s a “litigation era” console that borrowed its technology heavily from other, established console manufacturers. They’re built like tanks, hand wired and chock full of tasty transformers and discrete opamps. Some time ago I racked up just the microphone preamps from a PM2000 that once belonged to Radio City Music Productions. With careful modification, they made a nice copy of an API312C circuit and they sound outstanding. The rest of the console is a good design, but because of the use of noisy opamps, it just can’t keep up with newer models. While waiting on cross-country delivery of my most recent pair, I’ve started formulating a plan to rebuild and update one of the consoles and use the other for parts.
Some background: an opamp is an integrated circuit (chip) that is used in audio gear to control audio signals. Everything from gain to tone (EQ) to dynamics to routing. They’re like an audio swiss army knife. They began to enter the pro audio market in the mid 1970’s and Yamaha embraced their use. Some sound great, like the API2520 and its Yamaha cousins the NE80100 & NE80200. My console has 96 of those. Some sound just ok, with noticeable distortion and noise characteristics, like the Hitachi HA1457W. My console has 282 of those. That just won’t do. So I did some cross referencing and determined that the Texas Instruments OPA604AU is a great modern replacement with almost no distortion or noise figures. Unfortunately, there is a catch. The HA1457 is a “thru hole” SIP (Single Inline Package) opamp, but the OPA604 is a “surface mount” SOIC (Small Outline Integrated Circuit) – in other words, a square peg in a round hole problem.

ha1457_vs_opa604

Technology to the rescue. Thanks to the proliferation of online circuit board manufacturers who make prototype boards at cheap prices, I can get custom made circuit boards to solve the problem. I surfed over to ExpressPCB.com, downloaded their free software and got to drawing. In less than 20 minutes, I drew up a schematic for a single adapter board. This adapter board will allow the small modern surface-mount device to fit in the “pin thru hole” designed originally for its more archaic cousin. I’ll be able to fit 96 of these tiny boards on a single PCB then cut them apart as needed. They should cost about 40 cents ($0.40) each. The opamps are about $2.50 each. The noise floor should drop considerably and the entire console will sound more musical. This modification will accompany a complete recap and replacement of all the old incandescent bulbs with LEDs.

HA1457_to_OPA604_adapter

Such are the daily ramblings of someone with endless modification syndrome. In the end, it’s all about the result. And with any luck my newest obsession will sound better for it.

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2 Comments Add yours

  1. Gregor says:

    And? Does it sound better now?

    Like

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