Phase shifting (BD-Design)

by GC, Sunday, February 20, 2005, 11:23 (7004 days ago) @ GC

Hello Chris,

In my case reversing the polarity of the bass units gave only a small improvement so I decided to build a phase shifter. I finished it yesterday and gave it a first listening. The shifter inverts so the bass is put back to straight connection. When tuning the phase the lower midrange becomes fuller, male voices and instruments like tenor sax get more body. At the same time bass intruments get a faster respons and more overtones. The change is not dramatic but it is an improvement.

A shifter is easy to build as you can see on the image. I checked it on an oscilloscope and it works exactly as it should. The OPA27 is a high quality opamp, I don't hear a sound degradation or noise due to it. I do have a small hum now but I did not yet optimize all wiring. My filter now has three potmeters so it is not easy to tune it by ear to the optimum response. (I can tune it to my taste but that is not what HiFi is about.) I put the filter and its power supply in a separate box so it can easily be adapted. In case the filter is second or third order the first potmeter should be a fixed resistor. The shifter can also be used for additional gain if necessary by changing the ratio R1/R2.

Yours,
Eddie

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