Berkel 77 Posted November 4, 2020 Share Posted November 4, 2020 Hello all, You may have seen my recent posts about obtaining an upgrade from my Pioneer PL15 R. Well, a couple of days ago I did buy a used Technics SL 10 with AT 81 CP cart. Unfortunately it has hum which I can't figure out how to eliminate. I've just been through all the usual suspects : changing power points, connecting and disconnecting TT leads ( incl. ground ) from various components, but still no change. My usual set up for phono is : TT - Denon AU 320 step up transformer - Cambridge phono stage ( 640 P )- line input on pre amp. This worked fine with my old Pioneer, but the Technics doesn't like it. I've connected the Technics straight to the Cambridge, then straight to MM phono on pre amp, without any change. Could some knowledgeable person ( s ) give me advice please ? Thanks, Dennis Quote Link to post Share on other sites
jack_b 78 Posted November 4, 2020 Share Posted November 4, 2020 This is just a stab in the dark, and other members might have better solutions to trial first - but have tried a different cartridge? I recently had a weird issue where it was the cart itself causing the issue (despite being properly connected). Quote Link to post Share on other sites
andyr 5,735 Posted November 4, 2020 Share Posted November 4, 2020 Dennis, looking up the AT 81 CP cart ... it is a MM (with an output of 3.5mV). So you certainly don't use a Denon SUT between it and your 640P phono stage. Am I correct ... you did run the AT 81CP straight into your 640P ... and have also run the cart into the MM input of your preamp? With no reduction in the hum? If so ... does the hum come from both channels ... or just one? Andy Quote Link to post Share on other sites
Berkel 77 Posted November 4, 2020 Author Share Posted November 4, 2020 1 minute ago, andyr said: Dennis, looking up the AT 81 CP cart ... it is a MM (with an output of 3.5mV). So you certainly don't use a Denon SUT between it and your 640P phono stage. Am I correct ... you did run the AT 81CP straight into your 640P ... and have also run the cart into the MM input of your preamp? With no reduction in the hum? If so ... does the hum come from both channels ... or just one? Andy Thanks Andy ; OK I won't use the Denon SUT. I don't think it had any effect anyway, as it was set for " through ". However, yes I ran the cart into the 640P ... no change, and I then ran it straight into the MM phono stage of the Rotel pre amp ..... also no change. The hum comes from both channels. Cheers, Dennis Quote Link to post Share on other sites
pwstereo 649 Posted November 4, 2020 Share Posted November 4, 2020 Check that there isn't a missing/broken/disconnected ground wire within the chassis of the turntable. Tonearm, chassis, sub-chassis, motor mount, etc. Check that there isn't an un-shielded portion of tonearm cable close to AC wiring or other PSU circuitry within the turntable chassis. Quote Link to post Share on other sites
Berkel 77 Posted November 4, 2020 Author Share Posted November 4, 2020 9 minutes ago, jack_b said: This is just a stab in the dark, and other members might have better solutions to trial first - but have tried a different cartridge? I recently had a weird issue where it was the cart itself causing the issue (despite being properly connected). Thanks for your suggestion, but I don't have another cart to fit. It's a P mount and brand new. When I auditioned the TT at the seller's place, I had to use headphones, as there were no speakers. Sounded perfectly OK, but maybe the phones don't pick up 60Hz, which I've read is the frequency of this type of hum. Dennis Quote Link to post Share on other sites
Berkel 77 Posted November 4, 2020 Author Share Posted November 4, 2020 1 minute ago, pwstereo said: Check that there isn't a missing/broken/disconnected ground wire within the chassis of the turntable. Tonearm, chassis, sub-chassis, motor mount, etc. Check that there isn't an un-shielded portion of tonearm cable close to AC wiring or other PSU circuitry within the turntable chassis. Thanks Peter. I'd have to take it to a technician for this, as I don't have the knowledge or skills. Dennis Quote Link to post Share on other sites
andyr 5,735 Posted November 4, 2020 Share Posted November 4, 2020 (edited) 9 minutes ago, Berkel said: Thanks Andy ; OK I won't use the Denon SUT. I don't think it had any effect anyway, as it was set for " through ". Aah, that's a new piece of information, Dennis. Sure, if it was set to 'through' then it shouldn't have much effect ... apart from a slight signal degradation from the extra switch contacts and RCA contacts. Quote However, yes I ran the cart into the 640P ... no change, and I then ran it straight into the MM phono stage of the Rotel pre amp ..... also no change. The hum comes from both channels. Cheers, Dennis Sounds like a wiring problem - as Peter suggested. Does the hum decrease if you clamp your finger & thumb on the base of the arm? Andy Edited November 4, 2020 by andyr Quote Link to post Share on other sites
andyr 5,735 Posted November 4, 2020 Share Posted November 4, 2020 (edited) error Edited November 4, 2020 by andyr Quote Link to post Share on other sites
Warren Jones 238 Posted November 4, 2020 Share Posted November 4, 2020 Hum can be difficult to isolate the source. Before trying anything. Does the SL10, PL15 and phono pre have 2 or 3 pin plugs? Quote Link to post Share on other sites
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.