Hacker GP42 and AL42 - stereo connection with modern RCA plugs?

[qualityten]

About five years ago, a kind friend gave me a Hacker GP42 with the matching AL42 amplifier. At the time I gave them both a basic service and somehow got them connected for stereo. I say 'somehow' as I didn't then understand that longer RCA plugs are needed to activate the switching from mono to stereo. Thinking the old sockets were faulty, I replaced them with newer RCA sockets. I did keep the originals, but they have since been lost in a house move. A further complication is that I subsequently replaced the original ceramic stereo cartridge with a cheap Chinese one. At present, both units work correctly on their own, but the record player only plays one of the channels from the stereo cartridge.

I am now in the process of checking the units before passing them on and I wonder (a) whether the switch sockets used by Hacker are still available, or (b) whether others have found a workaround that allows for use of standard length RCA plugs to to achieve Hacker's mono/stereo arrangements? They really found a rather elegant way of playing a stereo cartridge with both channels combined when using the GP42 alone, but separating the channels when using the GP42 with the AL42 amplifier.

I appreciate that the simplest solution would be to follow Hacker's design -- if their clever 'switch sockets' are still available.

[Edward Huggins]

Yes this can be done. You will be highly unlikely to source those old switched sockets these days so suggest a RCA plug arrangement. These can be added at the rear of both units where the existing connections are so it would not be too unsightly. You will then have dedicated, clean signal path, LH and RH leads - but this arrangement will need a bridging switch.

[qualityten]

Thanks Edward, so I need to add a switch to bridge the stereo signals from the cartridge when playing a stereo record on the GP42 alone. And then switch out the bridge when sending one of the signals to the AL42 via the Output Stereo Amp socket?

Can I just sum the LH and RH signals from the ceramic cartridge, as Hacker does, or should I add resistors, as per the attached diagram? The diagram is from https://www.instructables.com/Simple-Way-to-Convert-Stereo-to-Mono/

[Uncle Bulgaria]

It's time for another outing of 'Why not Wye? Or, 'Successful Monoing of your Low End' (attached). The principle being as you show in your drawing - the outputs drive the input rather than each other, as could happen if they were directly connected together.

I will add the caveat that I have no experience in ceramic cartridges, but understand they work with a very high input impedance in the order of megohms, so can presumably provide a reasonable output which I would have thought wouldn't be ideal to appear on the other channel's output. How they react to direct connection may be OK if Hacker did it, or it may simply be tolerable and things would be improved if you made up a proper summing cable. I've done it for connecting stereo inputs to my various mono tape recorders.

[Edward Huggins]

Originally Posted by qualityten

Thanks Edward, so I need to add a switch to bridge the stereo signals from the cartridge when playing a stereo record on the GP42 alone. And then switch out the bridge when sending one of the signals to the AL42 via the Output Stereo Amp socket?

Can I just sum the LH and RH signals from the ceramic cartridge, as Hacker does, or should I add resistors, as per the attached diagram? The diagram is from https://www.instructables.com/Simple-Way-to-Convert-Stereo-to-Mono/

Yes, a switch to bridge the channels when you use the GP42 on its own in Mono mode.

[qualityten]

Thank you Edward, and to Uncle Bulgaria for the helpful copy of 'Why not Wye?'. As ever, I always find it helpful to air a problem here when I get stuck.