well having replaced an old and dying amplifier with considerable hum with a nice clean one I can imagine it as you do at first feel you have lost something.
Looking at the lawson circuit that might be just about right at it gives -18dB at 50Hz. This is assuming that in reality by 150Hz the rumble is down in the noise anyway?
Is there any advantage into converting to sum and difference before the filtering in terms of removing component tolerance problems?
Looking at the lawson circuit that might be just about right at it gives -18dB at 50Hz. This is assuming that in reality by 150Hz the rumble is down in the noise anyway?
Is there any advantage into converting to sum and difference before the filtering in terms of removing component tolerance problems?
Hmmmm (hehe) !
Most amplifier circuit hum is at 100/120Hz with plenty of harmonics. And in any event the idea of filtering lf in such ranges would be at best controversial because there is plenty of genuine programme content there, down to subsonics really.
I think the issue is how to reproduce the content well, not filter it in that range. One could filter lf out-of-phase only which would remove the vinyl specific artfects, (along with any genuine programme content), and that is how the derumbleiser and the like seem to work. However, if Douglas and the OP article is right, those artefacts partly define vinyl sound..........
exactly, its killing the out of phase to see if that removes some magic as step one. And there shouldn't be any out of phase content that low, for a given value of shouldn't.
If anti-phase low frequency noise gives the feel of surround sound as said in initial posts; are there any examples vinyl albums where the low frequencies are kept as lower in range as possible in stereo ? It would be interesting to listen to those. Technically how low a stereo signal can be tracked for a well made excellent tracking phono cartridge ?
Thanks and regards.
Thanks and regards.
as said earlier I think it is also possible to increase the out of phase noise so that the difference would be even greater and so can easily be compared and distinguished.
Regards
OK, this is interesting.
So I took the 90 sec in phase (mono) sample of rumble/tone from the EMT950, low pass filtered at 500Hz very steeply so there was no audible 3kHz test tone. Used that as left channel and inverted it to create a right channel.
Now I have 90 sec sample of pure out of phase rumble/roar. Very vinyl it sounds too, very spacy. Very interesting. Try it !
So very hastily I just mixed trace of this phasy rumble sound into a track I happen to be mixing at the moment. One has to be super careful of expectation bias, but it seemed to add a certain warmth - but my tests are not blind and I definitely knew it was there, so I wouldn't believe me if I were you! Worth pursuing with interest though, I think !
I think Douglas might be on to something........
Any change of a blind A/B test that we can try? Or the rumble sample so one of us can make something up?
I thought the existence of 'CD rot' was utterly disproved except in a very cases of defective manufacture.
CDs are pretty resistant to damage. Just handle them by the edges.
I've got CDs that are more than 30 years old and they play flawlessly.
Perfect sound forever!
Why Compact Discs Sound Great
Ah Ken Rockwell. Where I go for a laugh. his section on Jitter on outboard DACs has raised a smile.
I'm probably missing the point utterly, but how can you measure out-of-phase stuff if the signal is folded to mono?
What turntable? How is the platter driven? Looks like there's a lot of motor noise there.
Are you sure about this? Pre-echo is very common on old LPs, and it doesn't seem likely that in every case the tape was stored for a long time before cutting the master. You've done the album, you want to get it out there!
I have always understood that pre-echo was caused by distortion of the adjacent groove when cutting.
Invert one channel and sum to mono, provides a mono channel of out-of phase (vertical stylus motion) content !
EMT 938 a well respected direct drive broadcast turntable from the 80's. They go for about £2000 now, but at the time were serious pieces of broadcast quality kit. The 938 is the little brother of the 948 which really was uber expensive.DouglasSelf said:
https://en.wikipedia.org/wiki/Elektro-Mess-Technik has some background and comments about the 938.
EMT TTs are a bit of a reference I suppose. Manual and spec is here : http://www.emt-profi.de/Dusch-pdf/emt938-e.pdf
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It comes down to good design an build quality for both media. Digital is even more complex than analogue techniques.. e.g. see the efforts ECdesign took in producing their products.
Understood. I see you added the bit about inverting one channel in Post #466
I have to admit I am not used to the acronym TT for TurnTable.
It certainly sounds like the right sort of gear for the test.
Trouble is, it's audible not least because of click/pops........ see PM for raw sample.
The trouble with the Lawson circuit is that the schematic doesn't make sense. There are two feedback paths connected directly to the inputs, so if they are driven from a low impedance (as usual) those paths will do nothing, as I mentioned upthread. If anyone can explain this I will be most interested.
This is a very good question, to which at present I don't have an answer. It sounds promising but maybe complicated.
I also remember tape print thru causing pre echo, and it didn't have to be stored for long. There's a cure for the beginning of the track, leader tape, which was quite popular, so there may be both causes. Not hard to figure out which is which from the delay time. Lp 60/33.3=1.8sec. Tape is unfortunately variable depending on which part of the tape your at. ( less tape=higher rpm. ). At the head of a 10"reel at 30ips. You get about 1 rpm or a pre echo delay of 1 sec. With less tape you get less delay. Unfortunately at 15 ips it's close to 2 seconds and at some point in the tape it will match the lp delay. The one thing that's different is that the lp delay stays constant tape is variable so it's still possible to figure out wich one is the usual culprit by taking the delay time of the first track and comparing it with the last track on a side.
I have some old Cds that have serious rot, to the point where you can see holes in the foil when held up to a light. Maybe that is defective manufacture, but it definitely exists. On the other hand I have Cds from the 80s that still sound great.
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