480 stereo/mono weirdness

[rogerroll]

After finding a few songs sounding odd, I realized there is a stereo issue. When playing a record with obvious left-right separation (I used The Beatles version of Twist and Shout) I can barely hear John singing. When played on my Technics TT, he comes out mostly on the right channel. What’s weird is when putting my ear to the JB speakers, I can hear the music evenly left and right, but his singing is nowhere.

There is a stereo/mono switch on the amplifier box (52280-A) that is set to “stereo”. When I try to switch to “mono”, the sound cuts out altogether.

Questions:
- is this an amplifier issue? If so, is there a good place to start the troubleshooting?
- is this a needle/cartridge issue?
- is this a cross-over issue?

Any advice is appreciated!

[Ron Rich]

Could be anyone, or all of them-- Ron Rich

[jukenorman]

Hi Roger,

Disconnect one channel of the cartridge and play your Twist and Shout with the switch firstly in stereo and then in mono - you should have sound from one channel and then from both. Do the same with the other cartridge channel disconnected. That should give you a fair idea what's going on.

It would be worth checking that the cartridge is wired correctly before you start - the 3 pin connector at the amplifier has the centre pin as ground and the two cartridge negatives are paralleled at the cartridge.  Originally a Shure M44 would have been fitted.

Norman.

[rogerroll]

Thanks Norman, I will check there ASAP!

Confirmed, the cartridge is a Shure M44MR.
Looking at the back of the cartridge, from top to bottom, it’s labeled L, R, LG, RG (the RG appears to be part of the casing shield)
The black wire, which I believe should go to the 2 “grounds”, ie LG and RG, was connected to the L and LG. That seems wrong.
I’m going to connect that black wire to LG and RG and the red to R and white to L unless advised otherwise.

Thanks!

[rogerroll]

Update/setback:
When re-wired to black on LG/RG and white on L and red on R, John came back. However, he was now on both channels and switching to ‘mono’ cut sound altogether as before.
Flipping the 3-prong plug that goes to the amplifier had no effect, John was still on both channels.

Theory: amplifier has been tinkered with to play left or right signal on both channels, as if permanently on ‘mono’.

Setback: when swapping red and white wires on the cartridge I appear to have snagged the black wire and it is no longer connected to the awful solder job someone had previously done. I have removed the wire harness and will attempt to resolder all 3 of those incredibly dainty wires. Wish me luck.

To be continued...

[jukenorman]

Hi Roger,
There is something very wrong there! Yes you are correct, that is how the cartridge should be wired. Incidentally, you shouldn't be able to flip the 3 pin plug at the amp., there is a wider gap at two of the pins! It does sound as if someone has tinkered to mono up the channels somehow, but if John's voice is vanishing when you switch to mono, it would appear that something is out of phase (the speakers?). Are you lacking bass? You might need to do some serious wiring checks, I fear!
Norman.

[rogerroll]

It’s not just John, switching to mono results in no audio at all, in any configuration. Very strange, indeed.

The 3 pin plug is nearly symmetrical, but you’re right, there is a subtle difference, but it slips into the socket just as easily either way. If the ‘common’ is the centre pin, I guess it’s not critical. But if the pin out isn’t what I thought, that could possibly explain this anomaly, right? I will double check the manual.

I’m just taking a break from trying to solder those teenie tiny wires to repair the cartridge connections. My eyes are crossing. Time for a snack!

Thanks

[jukenorman]

Yes the centre pin is the ground on the 3 pin phono input. Some guesswork, if there was a fault on a pre-amp channel, then maybe it has been commoned up at the 3 pin input socket? Otherwise the mono switch could have been used! But something must be out of phase somewhere for the mono switch to cancel the sound. These amps are quite prone to poor solder joints if you were looking for a broadbrush approach - otherwise it's one step at a time.
Norman.

[rogerroll]

I found a schematic diagram for the 52280-A. The stereo-mono switch basically shorts the 2 outer pins of the input socket. That’s pretty straight forward, or at least it should be.
Once I get the cartridge reconnected I’ll have to open up the amplifier to confirm a few things.

Once again, thanks for your help!

[jukenorman]

Hi Roger,
Good news then, it would look like the tinkering has been done at the 3 pin socket and since you are getting sound from both channels, the amplifier should be OK!
Norman.

[rogerroll]

Long story short: the fine strands of wire are proving to be beyond my skills when it comes to soldering.

I have never dealt with wire so small and flexible. To top it off, I lost one of the brass connectors (it’s in the JB somewhere...). I got it working again by shorting the LG and RG with a strand of wire and connecting one pin only. i’m not convinced the cartridge is okay, but the stereo/mono switch now seems to do what it’s supposed to, ie John sings on one channel when set to stereo and comes out both channels when set to mono. I’m afraid to swap L and R pins at the cartridge for fear of breaking a weld again. Once I have a replacement dual input cable, hopefully with connector pins already attached, I will try swapping L and R to verify the cartridge.

The reason the cartridge wiring is in such bad shape to begin with may be due to the needle brush being set way too high and brushed the wiring as it stroked.

Thanks!

[jukenorman]

Hi Roger,
I feel your pain! One fairly easy way to resolve this is to buy a set of phono cartridge leads (you can find them on ebay). The set of four already has connectors at each end so you can cut them in half and then you only have wire to wire soldering to contend with. You can simply twist the wires together and hold the base of the connection with small long nose pliers while you solder (the pliers conduct heat to prevent damaging the insulation). Cover the joints with heat shrink insulation. And you still have a set of phono connectors left for your next jukebox!
Norman.

[Ron Rich]

Hi Norman,
Where( under what category) can these be found -- on the UK eBay, or the US eBay ? Ron Rich

[jukenorman]

Hi Ron,
Yes you can find them on both UK and US ebay - do a search on "phono cartridge headshell leads". There are sellers both in the US and Canada. And many in China, if you can wait a couple of weeks or so!
Norman.

[Ron Rich]

Hi Norm,
Waiting is no problem-- getting the flexible wire 14 inches long is a problem-- I will search "headshell leads"-- just never thought of the headshells before -- Thanks ! Ron Rich