The 32.5 had (still has since I have it in the attic) 2 sets of BNC inputs (one set for MM and one for for MC). I only ever used MM (Shure M75ED). Eventually I moved to NAC82 and MC.
I think if you have both MC and MM cards in your 72 you can swap them around so that you have either the MC or MM card attached to the BNC sockets.
However, before you try this, check with the forum.
Unless you are using two decks or have a detachable headshell you really only need one phono input.
Long story short my 72/140 system is working perfectly now.
Long story -
I tried all the inputs again and found that I could hear audio albeit with background âmachine gun pop pop pop noiseâ. With no audio input the noise increased with the Volume knob turning louder when the CD input was selected , but not on any of the other inputs.
I opened up the 72 and removed the MC cards from their slots and all feedback noise ceased. Hurrah !!
I then replaced the MM cards feeding the BNC phono inputs with MC phono cards and hey presto that worked as well.
I reckon the MC boards were stored in those âCD ?â slots for safe keeping as the unit had been stored for some time. Those slots are now empty (as you can see : every thing works so I donât know what purpose they are used for).
See a picture of the empty slots
FWIW I still get a hum when the machine turns on and then after three seconds there are a couple of clicks and the hum disappears. It seems to happen when I turn the machine off, a thump then a hum , a couple of clicks . Can anyone explain this ?
Nice to hear itâs up and running. Free tweak - if youâre not using a tape player for recording, you can pull out the NA324 tape buffer boards. I find the sound is more focused, though some prefer to leave them in.
The CD input will work as next to the input wires (yellow/black & red/black) are the links that bypass any fitted board. What could be fitted there (with the links cut) was a variable input board which was designed to attenuate and filter the signal from early CD players but the general consensus is they are detrimental to the sound.
Hums and clicks are perfectly normal - the 72 has a mute relay which disconnects the 140 during power up and subsequently disconnects during power down. If you added a Hicap and kept the 72 powered on then you could turn the 140 on and off with no noises.
The hum can be reduced if you tie the signal ground to mains earth. Traditionally this would be achieved by connecting a naim source. (CD player, streamer). The other way to do it is an earth wire from the ground post on the back of the 72 to the earth pin of a mains outlet.
As said above - when you switch on, the main thump is from the power amp, followed by light hum as the power amp input is floating. The next couple of pops are each channel of the double pole output relay in the preamp closing.
When you switch off, the main thump comes from the preamp losing power, followed by the floating input hum, then the next couple of pops are each channel of the power amp discharging.
Iâve always viewed direct pre to power amp like this, as a bit of a stop-gap solution to get you up & running before adding a power supply.
Thanks Neil, thatâs very helpful - itâs reassuring to learn that the 140 is behaving itself and acting as should be expected, of which I wasnât sure.
I do realise that at some point I need to get her serviced but I would like to enjoy her first.
