G'day all, I'm gauging opinions on the desirability or otherwise of the so called 'Allen Wright' 50 KHz additional time constant as used in the RIAA eq network of the VSPS and several other fine phono stages.
I have read extensively on this subject and I'm just not sure about this 'modification' to the RIAA network. Some say it's worthwhile and others are vehermently opposed to it.
For what it's worth, I have built the VSPS and I find its sound rather musical and pleasant, and I really like it. Any thoughts or comments? Regards, Felix.
I have read extensively on this subject and I'm just not sure about this 'modification' to the RIAA network. Some say it's worthwhile and others are vehermently opposed to it.
For what it's worth, I have built the VSPS and I find its sound rather musical and pleasant, and I really like it. Any thoughts or comments? Regards, Felix.
Last edited:
From what I recall reading some time ago,not all cutters used the 50 Khz time constant ( 3.18uS). So how do we know if the album was cut with that or not ?
It might be a good idea to incorporate it in a passive equaliser scheme where you can switch it in or out. You might end up using it to get what you prefer to hear rather than if it was really required for that album !
It might be a good idea to incorporate it in a passive equaliser scheme where you can switch it in or out. You might end up using it to get what you prefer to hear rather than if it was really required for that album !
Yes, at least make it switchable. While one may like the way it "sounds" it´s completely wrong from a technical standpoint:
- The Neumann SAL 74B for example has a roll off at 49.9 kHz, but it´s a second order filter, so you can´t compensate that with a single pole.
- Other lathes made by Neumann and other manufacturers might (and do) have different roll off points
- The recording electronic might already compensate for the phase and amplitude error that is
introduced by this roll off in the audible frequency range. Using this additional 3.18 µs will actually
worsen RIAA accuracy at 20kHz
- The Neumann SAL 74B for example has a roll off at 49.9 kHz, but it´s a second order filter, so you can´t compensate that with a single pole.
- Other lathes made by Neumann and other manufacturers might (and do) have different roll off points
- The recording electronic might already compensate for the phase and amplitude error that is
introduced by this roll off in the audible frequency range. Using this additional 3.18 µs will actually
worsen RIAA accuracy at 20kHz
Or it could be that you won't hear any difference. Allen claimed that there was a huge difference but never offered any real evidence that this was the case. I tried it with my His Master's Noise and (qualifying this because my ears are old, but younger than Allen's were!) have to admit that I couldn't hear a blessed bit of difference. Perhaps if I were 19 and female, but if that were the case, I wouldn't be building tube preamps...
I'm a little lost on this.
IF the cutters already had a rolloff, and/or the masters had nothing much above 20kHz, much less anything out at 50kHz (likely) then what is the point of rolling off something that is not there?
Not many phono carts have response out there either... save some that were designed for "Quad"?
Perhaps it reduces some noise, including RFI?
_-_-bear
IF the cutters already had a rolloff, and/or the masters had nothing much above 20kHz, much less anything out at 50kHz (likely) then what is the point of rolling off something that is not there?
Not many phono carts have response out there either... save some that were designed for "Quad"?
Perhaps it reduces some noise, including RFI?
_-_-bear
Ah ha! He put "nothing" there! 
So he put a boost in... oh.
Ah, ummm..., oh... don't know what to say.
So he put a boost in... oh.
Ah, ummm..., oh... don't know what to say.
Last edited:
Well, speaking from an academic point of view, the extra energy at 50kHz will mix with the lower frequencies, even if it is uncorrelated "extra noise". Could have some sort of sonic effect, possibly.
_-_-
_-_-
Inserting a filter that has an F-3dB @ 50kHz affects many other frequencies, not just @ 50kHz.
If you read the Salas RIAA Thread you will find Members who are claiming to hear changes due to tiny resistor and/or capacitor changes that theoretically should not be audible.
If you read the Salas RIAA Thread you will find Members who are claiming to hear changes due to tiny resistor and/or capacitor changes that theoretically should not be audible.
Hi Felix,
I think Allen gave us a valuable "tweak" for LP playback when he wrote about the 50KHz boost (to counter the roll-off which cutting amps implemented, to stop them burning out the cutting head) in the late 80s. IMO, he is a "guru" ... so I use his 50KHz pole as a matter of course in the passive-RIAA, JFET-based phono stages that I build.
I found it interesting when I built Hugh Dean's AKSA "GK-1" phono-equipped preamp, about 12 years ago, that one particular owner of this pre (who has deep technical electronics knowledge) implemented the 50KHz boost - which wasn't in Hugh's original circuit - and enthusiastically posted about the improvement in HFs. I know this guy has a pretty good ear - so that confirmed to me that Allen was on the right track. 😀
BTW, what's the "VSPS" phono stage? I thought you were wedded to your ESP P06? 😉
Regards,
Andy
Last edited:
G'day mate, all noted. Yes the P06 is my reference phono stage but the VSPS is the nicest sounding full feedback op amp stage I've ever built or heard. The VSPS is very popular here and there is a very long thread on it, and also information here. RJM Audio - The Very Simple Phono Stage Regards, Felix.
Last edited:
Hello all,
I guess I'm the first to activate this thread in a while :/. I've gone over the Neumann cutting amp manual and it is a 2 pole sallen key filter at the input which has a corner of 49khz but a breakpoint of 34.659 kHz. All the zeroes I have seen apply that initial breakpoint of 50khz, but shouldn't this zero start at 34.659 kHz for somewhat close to proper compensation?.
Colin
I guess I'm the first to activate this thread in a while :/. I've gone over the Neumann cutting amp manual and it is a 2 pole sallen key filter at the input which has a corner of 49khz but a breakpoint of 34.659 kHz. All the zeroes I have seen apply that initial breakpoint of 50khz, but shouldn't this zero start at 34.659 kHz for somewhat close to proper compensation?.
Colin
Hah - you may well be correct, Colin! 😉
I just implemented what "the guru" suggested. 😀 (And I am very pleased I did.)
Andy
A 2-pole filter is characterised by corner frequency and Q. What do you mean by breakpoint? -3dB point?vynuhl.addict said:
You can't compensate a 2-pole filter with a 1-pole filter. The phase and amplitude cures are just different. The best you can do is correct one of phase or amplitude at one frequency, and approximately at adjacent frequencies.
Df96,
Yes breakpoint is essentially the corner or -3db. The corner is not the pole, a zero is there to try and cancel a pole. Yes a single zero may not fully cancel a 2 pole lpf, but it should help regain some proper phase linearity. We also must remember that vinyl by nature simply cannot be cut flat to 20khz so a little boost can't hurt in the highs. Moving coils have a very high frequency resonace which seems to help null the roll off. My apologies for the mistype, corner of 34.659khz, pole of 49.9khz.
Colin
Yes breakpoint is essentially the corner or -3db. The corner is not the pole, a zero is there to try and cancel a pole. Yes a single zero may not fully cancel a 2 pole lpf, but it should help regain some proper phase linearity. We also must remember that vinyl by nature simply cannot be cut flat to 20khz so a little boost can't hurt in the highs. Moving coils have a very high frequency resonace which seems to help null the roll off. My apologies for the mistype, corner of 34.659khz, pole of 49.9khz.
Colin
Last edited:
So which is it? The corner frequency and the -3db point only coincide for a Butterworth filter (Q=0.707?) (and, of course, all 1-pole filters).
If it is -3dB at 34.659kHz, but with a 49.9kHz corner, then it is a rather low Q 2nd-order filter. A low Q 2nd can be roughly approximated by a 1-pole filter, at least for lower frequencies. So the 50kHz corner which some add is wrong, and it should be a 35kHz corner? That would be more audible, but the main effect would be to add more noise - which may then be confused with extra detail.
Df96 ,
Try it, until then this is all just....talk. Extra detail?, let your ears be the judge. I've tried no zero, 100k zero, 50k zero and this 35 k zero and the 35 k had the best sound too to bottom. Noise wise, actually it has cut surface noise by an audible margin go figure 🙂.
Colin
Try it, until then this is all just....talk. Extra detail?, let your ears be the judge. I've tried no zero, 100k zero, 50k zero and this 35 k zero and the 35 k had the best sound too to bottom. Noise wise, actually it has cut surface noise by an audible margin go figure 🙂.
Colin
- Status
- Not open for further replies.