Magnavox s-8756 external crossover

External Crossover Top View

External Crossover Rear View

The 2-way external crossovers were constructed using Solen 1.2mH 14AWG air core inductors, Everwell 20uF motor run capacitors with Illinois .022uf bypass capacitors.

CTS 50 ohm 4W rheostats with 20 watt 8 ohm power resistors were added to complete the horn attenuation circuit.

The 1st order crossover frequency was lowered to 1KHz with the new parts values.

Subjectively, the Magnavox S-8756 with this external crossover sounds very relaxed and with no listener fatigue.

DT667 10/17/2022

External Crossover Rear View

5-way binding posts for woofer, input from amplifier, horn, and 50 ohm rheostat are mounted on aluminum angle brackets.

Rubber feet were added to the bottom of the wooden chassis to add acoustical damping and prevent slipping on top of the speaker cabinet.

The wood chassis was constructed from scraps of pallet wood that were finished in satin walnut spray paint.

Overall, DT667 was pleased with the outcome of this project.

Magnavox s-8756 crossover schematic

Original Magnavox S-8756 passive 1st order crossover schematic.

The horn section features an 8uF high pass filter and a 15 ohm resistor in series with the + terminal of the horn.

There is a 50 ohm rheostat in parallel with the +/- terminal of the horn that provides volume attenuation.

When the rheostat is rotated fully CW, a 50 ohm load is in parallel with the horn for NO attenuation/FULL volume from the horn.

When the rheostat is fully CCW, the horn is shorted out of the circuit.

Magnavox S-8756 2-Way Horn speakers

Upgrading Classic Magnavox Speakers

DT667 had acquired a set of Magnavox S-8756 2-way horn speakers off of a local EBAY seller almost a decade ago for $50.

These speakers feature a 15" 8 ohm CTS Alnico woofer and 10" x 4" 16 ohm Jensen midrange horn . The horn is an Alnico magnet type with phenolic diaphragm.

The crossover network was what appeared to be a 1st order with a 15 ohm resistor and 50 ohm rheostat for horn volume attenuation network.

To get the speakers going again, DT667 replaced both the 8uf high pass crossover caps and 50 ohm rheostats - they were blown.

The 16 ohm Jensen horns were replaced by 8 ohm Heppner versions of the same horn as one of the Jensen horns had a bad diaphragm.

After using these speakers for in a secondary system for years, DT667 wanted to upgrade the internal wiring , binding posts and crossovers to hear if subjective improvements could be realized with a modest investment of time and materials.

DT667 removed the woofers, horns, internal wires and crossover networks from both cabinets.

2 sets of Nakamichi style binding posts were installed on the back of each speaker.

Internal wiring was made directly from woofer and horn to binding posts so an external crossover could be connected. KnuKonceptz Kord 10AWG OFC stranded wire was used from this purpose.

Subjectively, the upgraded wiring and crossover parts made a substantial difference.

The vintage Magnavox speaker is efficient and smooth sounding with selected high resolution Qobuz audio streams.

DT667 has ordered some parts to build an upgraded passive 1st order crossover similar to the original Magnavox design. More on that project at a later time.

DT667 8/7/2021