a.palfreyman
pfm Member
Well here goes....
I have had my amplifier (NCC200 based) and my pre-amp psu (an old Audio Alchemy dde linear psu) wired into the same plug for many years now as it saves room on the 4-outlet mains block I use. Anyway, despite much fiddling with my DIY speakers, I couldn't get past a certain point WRT reproduction. Middle image a bit ill-defined and what seems like a bit of a 'suck-out' in the upper-mids. Anyway, my B.I.L. gave me a couple of 'special' mains cables (# I'll tell you what these are later...) and on Friday I put the system on and played a couple of CDs. Sounded pretty much as-per normal. Removed the mains lead from the IEC at the back of the power amp and plugged in the 'special' cable. Much to my surprise / delight, the middle image was better rendered, the 'suck-out' was much improved, wider stereo image and a bit better depth rendering too (could be a bit all front-and-back before this change). Anyway, had a bit of a think overnight and realised that I’d effected two changes in one: different lead; and separated the supplies into two plugs.
After a bit of rummaging the following day (Sat), I found another plug. I separated out the original power amp mains lead and pre amp psu mains feed into separate plugs and tried this. Better than the original arrangement, but maybe not quite as good as the ‘special’ lead (would need to do more listening to decide on that one). Anyway after about an hour or so I thought I’d go back to the ‘special’ lead and the thought occurred to me that ‘If this makes an improvement, then I should try the power amp directly into the (double) wall socket and just use the 4-block for low demand stuff’ and sure enough this gave a further small but notable improvement, consisting of slightly more forward mid-range and a slightly wider more projected image. I wouldn’t have believed it unless I’d heard it with my own ears. (Play nicely Jez )
Anyway, I think there is still room for improvement, though I must admit I am very grateful for the ‘nudge’ that forced me into this as I probably wouldn’t have bothered otherwise and been stuck in 'limbo'. So where now? Not sure TBH. It is clear ‘something’ is going on but not sure what (fuse, tarnishing of plug terminals, etc etc)? There are no routers or similar in the house, although most of the lamps are low energy and the effects of these can clearly be seen by holding a ‘scope probe in the air: lots of 50kHz pick-up. However no need to use these in the (long) daylight hours so shouldn’t be causing any problems ATM. I also listen when the Wife is out, so no distractions or mains usage other than the cycling of the fridge.
A final thought / question about class A/B amplifiers: this mode causes ‘a rectified version of the output on the +/- psus’ i.e. positive output swings draw from the + supply rail and negative output swings draw from the – supply rail (my NCCs have separate transformers with the primaries paralleled after the mains switch) but I do wonder if this loading has any ‘strange effects’ WRT 0V plane voltages that could cause a variation of the 0V plane of one channel WRT both the other channel and the pre-amp where the 0V planes are commoned because each secondary half-winding of each transformer sees changing loading conditions that are different plus-to-minus as well as left-to-right? I know a transformer should be ‘fully floating’ but measuring (with a high Z DVM) from the 0V plane to the case earth where the 0v plane is not connected to case earth (e.g. my Farnell sig-gen which has 10nF from 0V plane to case earth as well as a removable earth strap on the output) shows a voltage swing. In fact this sig-gen swings +/-10Vp-p (yes, I did say Volts) at mains frequency so I wonder if this effect can cause earth currents in the 0V plane where the loadings of each winding vary particularly L to R and WRT the pre-amp which these pass through?
# it’s an older style RA ‘YellO’ cable. I used a 1m version on my amp, but was also given a 1.5m version.
I have had my amplifier (NCC200 based) and my pre-amp psu (an old Audio Alchemy dde linear psu) wired into the same plug for many years now as it saves room on the 4-outlet mains block I use. Anyway, despite much fiddling with my DIY speakers, I couldn't get past a certain point WRT reproduction. Middle image a bit ill-defined and what seems like a bit of a 'suck-out' in the upper-mids. Anyway, my B.I.L. gave me a couple of 'special' mains cables (# I'll tell you what these are later...) and on Friday I put the system on and played a couple of CDs. Sounded pretty much as-per normal. Removed the mains lead from the IEC at the back of the power amp and plugged in the 'special' cable. Much to my surprise / delight, the middle image was better rendered, the 'suck-out' was much improved, wider stereo image and a bit better depth rendering too (could be a bit all front-and-back before this change). Anyway, had a bit of a think overnight and realised that I’d effected two changes in one: different lead; and separated the supplies into two plugs.
After a bit of rummaging the following day (Sat), I found another plug. I separated out the original power amp mains lead and pre amp psu mains feed into separate plugs and tried this. Better than the original arrangement, but maybe not quite as good as the ‘special’ lead (would need to do more listening to decide on that one). Anyway after about an hour or so I thought I’d go back to the ‘special’ lead and the thought occurred to me that ‘If this makes an improvement, then I should try the power amp directly into the (double) wall socket and just use the 4-block for low demand stuff’ and sure enough this gave a further small but notable improvement, consisting of slightly more forward mid-range and a slightly wider more projected image. I wouldn’t have believed it unless I’d heard it with my own ears. (Play nicely Jez )
Anyway, I think there is still room for improvement, though I must admit I am very grateful for the ‘nudge’ that forced me into this as I probably wouldn’t have bothered otherwise and been stuck in 'limbo'. So where now? Not sure TBH. It is clear ‘something’ is going on but not sure what (fuse, tarnishing of plug terminals, etc etc)? There are no routers or similar in the house, although most of the lamps are low energy and the effects of these can clearly be seen by holding a ‘scope probe in the air: lots of 50kHz pick-up. However no need to use these in the (long) daylight hours so shouldn’t be causing any problems ATM. I also listen when the Wife is out, so no distractions or mains usage other than the cycling of the fridge.
A final thought / question about class A/B amplifiers: this mode causes ‘a rectified version of the output on the +/- psus’ i.e. positive output swings draw from the + supply rail and negative output swings draw from the – supply rail (my NCCs have separate transformers with the primaries paralleled after the mains switch) but I do wonder if this loading has any ‘strange effects’ WRT 0V plane voltages that could cause a variation of the 0V plane of one channel WRT both the other channel and the pre-amp where the 0V planes are commoned because each secondary half-winding of each transformer sees changing loading conditions that are different plus-to-minus as well as left-to-right? I know a transformer should be ‘fully floating’ but measuring (with a high Z DVM) from the 0V plane to the case earth where the 0v plane is not connected to case earth (e.g. my Farnell sig-gen which has 10nF from 0V plane to case earth as well as a removable earth strap on the output) shows a voltage swing. In fact this sig-gen swings +/-10Vp-p (yes, I did say Volts) at mains frequency so I wonder if this effect can cause earth currents in the 0V plane where the loadings of each winding vary particularly L to R and WRT the pre-amp which these pass through?
# it’s an older style RA ‘YellO’ cable. I used a 1m version on my amp, but was also given a 1.5m version.