Brian Powell Audio

BPA Active Crossover

These crossovers are intended to be general purpose 2 way. The can be reconfigured for different speakers.

Initially the design has only been tested with the 1980 Mission 770. The internal crossover needs reconfiguring to be out of the circuit. A new connector plate has to be made with 2 pairs of connectors, one for each drive unit. In the prototype we have tested it with both the original and a Scanspeak tweeter.

The circuit is based around Linkwitz-Riley 24dB/octave system. The crossover has adjustable baffle step and LF EQ compensation. This can be adjusted with potentiometers.. The PCB also has a variable drive level for the tweeters. There is a built in time delay compensator set to 147uSecs for the Missions. Fo is 1.8kHz. The PCB has jFet muting for quiet power up/down transients.

The speakers and active crossover have been swept with a UMIK-1 and REW software with excellent results. These results will appear later.

Myself, my brother Clive Powell, and Stephen Bailey in November 2023 auditioned a pair of Mission 770s modified with Scanspeak tweeters and converted to active. They were superior to the passive speakers in every way, but especially in the detail and fast edges. Stunning.

As of Jan 2024 the retail price of the crossover is £200 including the PSU.

We are working on further updates for the original Mission 770s from the 1980s. We find the excess mechanical load of the heavy gauge speaker wires can pull the connector off the LF drive unit. It can be repaired ands improved (if not too damaged) by adding a through bolt with insulating washers. the wires can be terminated with an eye type connector for fastening to this sturdier mount. Great care must be taken when soldering the Litz wire to the coil to stop solder drips melting through the cone. Below is the new speaker connector plate:-

The damping on the cabinet walls was minimal to say the least and was noticeably live when tapped. An acoustic membrane was stapled all over the inside surfaces. Besides adding lot of mass this sheet material damps as well as the same mass of lead.

The port would benefit from flaring but is difficult to do. It was, however, possible to improve the air flow. The white plastic of the front was slightly smaller by about 1mm than the port tube, Careful filing has eliminated this turbulent discontinuity.

Sensible gauge flexible wire was used to wire the drive units directly to new connector plate. A fuse was not incorporated just 4 x 4mm sockets.

We shall be sweeping the finished speakers with a calibrated microphone and doing listening tests at the end of Feb ’24.

Above sweep result 4/10/23. These were Missions without the extra damping.

We tested the active crossover with Rogers LS5/9:-

Orange is the active version and blue is passive. The active is overall flatter especially in the 100-200Hz region.

Should you wish to hear these Active 770s then this can be arranged. Stephen Bailey is an Crimson aficionado who is happy to invite those interested to a listening session. Please contact Stephen Bailey stephenbailey@linc-medical.co.uk