I was given some very rough Goodmans Magnum K speakers when I went to collect a Goldring 88 deck.
The drivers worked but the sound was poor. Removed the stuck-on backs with the continuous-pull method. All the capacitors measured correctly at 10 and 4 uF, double checked by running 50Hz through them and measuring current. I replaced the 4 uFs with 2 * 2.2 Polyesters anyway. All four L-pad potentiometers were unserviceable.
The failure mode was high resistance between the moving wipers and the fixed centre terminals. The HF pots were easy to open but I had to get medieval with the MF ones. After all, the pots are otherwise scrap. Cleaning made no difference. Using some very flexible instrument wire I soldered to the wiper and to the terminal. 4 times. Very easy to do.
Result was surprising. The speakers go very low - I was hearing bass notes on the club-dance tracks I never heard in the clubs! This from 35 year-old metal cassettes.
They really are competent speakers for a mid 1960s design. If I want accuracy and realism use the 'statics. For trouser flapping use the Goodmans.
Incidentally the crossovers are similar to but not the same as the cct diagrams I've seen on this forum and others. The signals from the crossover filters go to the centre of the pots. Either the mid or the high - can't remember which, has a 15 Ohm load resistor to ground at one end of the pot's track and the driver at the other end of the pot's track. So you select between sending the signal to the driver or to the load or to a combination thereof. If anyone wants the details I'll open them u[p again.
The drivers worked but the sound was poor. Removed the stuck-on backs with the continuous-pull method. All the capacitors measured correctly at 10 and 4 uF, double checked by running 50Hz through them and measuring current. I replaced the 4 uFs with 2 * 2.2 Polyesters anyway. All four L-pad potentiometers were unserviceable.
The failure mode was high resistance between the moving wipers and the fixed centre terminals. The HF pots were easy to open but I had to get medieval with the MF ones. After all, the pots are otherwise scrap. Cleaning made no difference. Using some very flexible instrument wire I soldered to the wiper and to the terminal. 4 times. Very easy to do.
Result was surprising. The speakers go very low - I was hearing bass notes on the club-dance tracks I never heard in the clubs! This from 35 year-old metal cassettes.
They really are competent speakers for a mid 1960s design. If I want accuracy and realism use the 'statics. For trouser flapping use the Goodmans.
Incidentally the crossovers are similar to but not the same as the cct diagrams I've seen on this forum and others. The signals from the crossover filters go to the centre of the pots. Either the mid or the high - can't remember which, has a 15 Ohm load resistor to ground at one end of the pot's track and the driver at the other end of the pot's track. So you select between sending the signal to the driver or to the load or to a combination thereof. If anyone wants the details I'll open them u[p again.
Hi Antos' and welcome to the forum! I'm interested in the different versions of the Magnum K crossover circuit that you mention.
Below is a version which, like yours, includes a resistor. It is used in conjunction with what appears to be a simple wire-wound linear pot.
It looks like that is the tweeter level control.
Below is a version of the crossover which clearly contains two L pads (no resistor):
Goodmans may have alternated between the two versions depending on what variable controls they happened to have in stock at the time of production.
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...and there you see that the output from the small capacitor for the tweeter does not go to the end of the pot's track, but to its centre -it's not being used as an L-pad.
I expect the reason is to make sure that the audio power from the amp does actually go somewhere - either to the tweeter or to the load or part to both. This will maintain some semblance of constant load presented to the amp regardless of frequency.
I wonder if the difference is down to the 5 Ohm versions of the speaker v the original design which I believe was the 15 Ohm version. Mine is 5 ohm and the tweeter has a voice-coil resistance of abt 2½ Ohms.
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I expect the reason is to make sure that the audio power from the amp does actually go somewhere - either to the tweeter or to the load or part to both. This will maintain some semblance of constant load presented to the amp regardless of frequency.
I wonder if the difference is down to the 5 Ohm versions of the speaker v the original design which I believe was the 15 Ohm version. Mine is 5 ohm and the tweeter has a voice-coil resistance of abt 2½ Ohms.
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