Hi
Hans, this is why I would better prefer to damp the cart-arm to reduce amplitude of the resonance than to add a high-pass filter with high slope.
Intermodulation is not appearing in the amp (except a bad one) but at the cart level IMO.
And, IMO, it is difficult to add 15 or 20 dB loss at 10 Hz by filtering without altering the amplitude or phase of the audio signal at 20 or 25 Hz.
Furthermore, I have no problem with warps or things giving 1 or 2 Hz vibrations and rumble (I consider parasistic signals coming from the turntable) above 20 Hz can't be filtered.
So, for me, the best is to cancel mecanical resonances but not to use electrical filtering, if possible.
Jacques
Hans, this is why I would better prefer to damp the cart-arm to reduce amplitude of the resonance than to add a high-pass filter with high slope.
Intermodulation is not appearing in the amp (except a bad one) but at the cart level IMO.
And, IMO, it is difficult to add 15 or 20 dB loss at 10 Hz by filtering without altering the amplitude or phase of the audio signal at 20 or 25 Hz.
Furthermore, I have no problem with warps or things giving 1 or 2 Hz vibrations and rumble (I consider parasistic signals coming from the turntable) above 20 Hz can't be filtered.
So, for me, the best is to cancel mecanical resonances but not to use electrical filtering, if possible.
Jacques
I remember in the 70's high compliance cartridges were very popular. One I remember was Ortofon's VMS20E - I think Shure were leaders in this line of development.
There is a discussion of various factors (moving magnet and moving coil types) at Tonearm/Cartridge Capability
OK,
The test was first run with ‘normal’ anti-skate and then with ‘zero’ anti-skate, with the unexpected result that the noise floor about 1000HZ went down. So, anticipating the other shoe to drop, what would happen if the anti-skate were set excessively ‘high’? Should the noise floor about 1000HZ then go up or down? Was there an observable deflection of the stylus when operating with zero anti-skate? Could there be some proportional relationship between the noise floor of a ‘bias deflected’ or ‘bias neutral’ stylus and arm offset angle like, what effect might a 12” arm or linear arm have on the 1000HZ noise floor under the same conditions?
Ray K
Thanks for the link mjona. With so many variables affecting tonearm cartridge interaction, it is difficult for me to comprehend. As seen by some measurement even bias weight has effect on noise. So I was wondering if compliance is a factor for low level noise (Not resonance which we can lower with arm cartridge matching).
Regards.
Regards.
Sorry Hans, I forgot to answer your last point.
With no anti-skating, I can hear distorsion ( no identical on the L and R channels ) on high levels sounds. I absolutely need to put some anti-skating.
jacques
Well, I'm interested in seeing it...
I think that might be aimed at me. You do not want to propagate the JLH Oct 1991 article because it is a sea of errors. This was pointed out by many people in the letters pages at the time, though I don't think I joined in. One more voice would have been redundant.
Just a few examples. There is no such thing as a 'bootstrap filter' as Google will show you. JLH's configuration is not a filter because with increasing attenuation the slope degrades from 12dB/oct to 6dB/oct. This occurs just below the -24dB limits of Fig 17 which is why they were chosen. Note that these are sketches not simulations and they do not properly show the irregular responses in the passband.
Figs 15a and 15b are described as 'Butterworth-style' filters (a vagueness that should at once ring alarm bells) but they are not Butterworth filters. 15a has a Q of 0.871, and 15b a Q of 0.882, whereas the Q for a Butterworth response is 0.7071. That is not hard to accomplish; you just make one component twice the size of the other, as any textbook will tell you.
I'm afraid most of the article is at that level of inaccuracy.
I am not here to belittle JLH's overall work, but it really must be said that he had no clue about filters, and that article is best forgotten.
De mortuis nil nisi veritas.
I'd be very glad indeed if you could give me the 1961 reference. I failed to find anything that early on the idea, though as I said it seems to be a fairly obvious one.
Probably because it's hard to design (see my Linear Audio article just out) and requires three extra opamps.
Are they? Look at the number of them that omit tone controls, and some even omit balance controls.
Well, that's what this thread is about. The Devinyliser design is now available, so anyone can do experiments to decide the matter.
Apart from your posts there has been no response. That is not unexpected since the article is nearly 25 years old and Hood was a contemporary in your field at the time.
I did not get the issues of Electronics World after the article in question so I was not aware of the letters to the editor you refer to. This publication had lost in popularity here due to ongoing increases and I stopped buying it in favour of Silicon Chip magazine which has a down to earth approach.
I knew you had investigated filters for your book on active crossovers and would be able to judge the value or otherwise of the approach.
I thought the way I drew attention to Hood's article was low key and the fact I did not post the circuit in the first instance should have spoken for itself.
Your reply was blunt and deprecating to say the least and I felt you were attacking me as much as the late author of the article.
If I had raised this circuit at lecture you were giving and you had responded in that way that would be equally as unacceptable as someone making an obscene gesture.
Hi
A friend of mine has a Shure M91eX. This cartridge has a little damped brush at its front, applying on the record.
I was wondering if it could damp a little bit the 10-12 Hz big cart-arm resonance I have.
The answer is YES !
I borought this cart this morning and I ran the same process I did with the OMB40 cart.
The output level of the Shure cartridge is 2 dB less than the one of the OMB so I adjust the recording level to have the same amplitude at 1 KHz.
We can see that in the range 3Hz to 30 Hz the level of noise is 6 or 7 dB less than with the OMB40.
The amplitude of the resonance is nevertheless still to high but it shows that I have not enough damping with the OMB40.
Jacques
A friend of mine has a Shure M91eX. This cartridge has a little damped brush at its front, applying on the record.
I was wondering if it could damp a little bit the 10-12 Hz big cart-arm resonance I have.
The answer is YES !
I borought this cart this morning and I ran the same process I did with the OMB40 cart.
The output level of the Shure cartridge is 2 dB less than the one of the OMB so I adjust the recording level to have the same amplitude at 1 KHz.
We can see that in the range 3Hz to 30 Hz the level of noise is 6 or 7 dB less than with the OMB40.
The amplitude of the resonance is nevertheless still to high but it shows that I have not enough damping with the OMB40.
Jacques
Attachments
The ideal rumble filter, for me at least, consists of a DIFFERENTIAL 2nd order Bessel filter with a cut-off of 150Hz to remove the vertical rumble as no musical information is present in the stereo difference below 150Hz, followed by an 18Hz 3rd order Butterworth filter to remove the lateral rumble.
Once you remove the vertical rumble, a 3rd order filter is perfectly sufficient for attenuating any subsonic common mode rumble to acceptable levels.
If anyone's interested, I'll post a schematic of my 'Super Deluxe Phonostage' that I am developing for my website that features this filter.
Once you remove the vertical rumble, a 3rd order filter is perfectly sufficient for attenuating any subsonic common mode rumble to acceptable levels.
If anyone's interested, I'll post a schematic of my 'Super Deluxe Phonostage' that I am developing for my website that features this filter.
Good to see that you made a big progress and proved that more damping does a lot.
Hans
Well, I don't know why. My only intention was and is to warn people off that train-wreck of an article, which should never have been published. Brian Pollard ripped it to bits in the Letter pages the next month more thoroughly than I could have done, and I did not get involved.
Oh come on now, I think that is exaggerating a bit.
That's a very interesting idea; filtering in both modes. Why a Bessel though? Group delay issues?
That's just the point I deal with in The Devinyliser article. (out now: Linear Audio Vol 11) I use Butterworth filters to set the crossfeed, with phase compensation. I don't know if that is optimal (this whole subject seems to be in its infancy) but it seems to work nicely.
Yes please!
There is nothing wrong with the idea of reducing rumble in preventing unwanted side effects, and as a bonus, below 100Hz rumble is out of phase.
The only reason to remove rumble can be to avoid (large) woofers from making large movements, leading to production of IM speaker distortion.
All the harm that rumble does to the signal has already been done and cannot be reversed by a rumble filter.
The amount of rumble suppression that is needed depends on:
A: The amount of rumble the phono preamp produces in relation to a reference, for instance 1Khz@0dB.
B: The speakers you have.
Looking at the graph that Hyperman just sent for two different elements, the rumble is resp. -21dB (Ortofon) and -28 dB (Shure) ref 1Khz@0dB.
Below I have added a complete set of frequency plots coming from my Pick Up.
What you see are the spectra from 10Hz to 2Khz for 3 different situations.
The upper set at 1Khz are both channels when playing a 1Khz@0dB tone.
Going down you see both channels when playing an unmodulated groove, and the set at the bottom is when the element is not resting on the disk, but the motor is running.
Everything mounted on the same scale.
The rumble ref 1Khz@0dB is now -39dB.
So compared to the Ortofon this is a difference of 18dB, probably more than a rumble filter can achieve at 10Hz.
When changing both channels below 100Hz to mono, I might achieve another 10dB, bringing the figure to -49dB, and you could go on and on.
But less than enough does not make sense, so what is enough, we have no clue.
So selecting the ideal rumble filter is not : One Size Fits All.
If your hands are itching to build something, it is a great hobby that can give huge amounts of satisfaction and let nobody stop you.
But if you want to solve a problem, there need a goal to be set to start with.
And as the originator of this Thread, I think it makes sense that Douglas Self will be the generator of proposals in that direction.
Hans
The only reason to remove rumble can be to avoid (large) woofers from making large movements, leading to production of IM speaker distortion.
All the harm that rumble does to the signal has already been done and cannot be reversed by a rumble filter.
The amount of rumble suppression that is needed depends on:
A: The amount of rumble the phono preamp produces in relation to a reference, for instance 1Khz@0dB.
B: The speakers you have.
Looking at the graph that Hyperman just sent for two different elements, the rumble is resp. -21dB (Ortofon) and -28 dB (Shure) ref 1Khz@0dB.
Below I have added a complete set of frequency plots coming from my Pick Up.
What you see are the spectra from 10Hz to 2Khz for 3 different situations.
The upper set at 1Khz are both channels when playing a 1Khz@0dB tone.
Going down you see both channels when playing an unmodulated groove, and the set at the bottom is when the element is not resting on the disk, but the motor is running.
Everything mounted on the same scale.
The rumble ref 1Khz@0dB is now -39dB.
So compared to the Ortofon this is a difference of 18dB, probably more than a rumble filter can achieve at 10Hz.
When changing both channels below 100Hz to mono, I might achieve another 10dB, bringing the figure to -49dB, and you could go on and on.
But less than enough does not make sense, so what is enough, we have no clue.
So selecting the ideal rumble filter is not : One Size Fits All.
If your hands are itching to build something, it is a great hobby that can give huge amounts of satisfaction and let nobody stop you.
But if you want to solve a problem, there need a goal to be set to start with.
And as the originator of this Thread, I think it makes sense that Douglas Self will be the generator of proposals in that direction.
Hans
I am sorry, I have read dozens of papers, patents etc on the subject, but I cannot retrieve the two earlier proposals from 1961 and 1967, published before Macaulay, Langvad and Oldfield.
When I come across them I will let you know.
May be you are interested in the following list with over 150 references, all having to do with Record Players and their specific problems.
https://dl.dropboxusercontent.com/u/18462778/Pick-Up.docx
Concerning your other points, I am more a believer of "Less Is More", so I am in support of those manufacturers that have abandoned enabling too many options.
I see tone control and to a lesser degree balance adjust as Symptom Fighting.
Taking away the cause, if possible, is much better.
If everything is properly positioned, you probably won't need it.
Hans
A Bessel differential filter seems to be necessary to avoid a significant dip in the response of the individual channels, which can be rather disconcerting. I found that 2nd order Bessel is best.
Differential filtering makes a real difference IMO, no nasty 'road noise' that seems to plague most of my LPs.
I'll post a quick copy of my circuit at some point tomorrow.
BTW, Douglas, I remember reading that you had devised a way of significantly reducing high frequency distortion caused by input clamping diodes on pre-amplifiers. Care to share it with us?
Differential filtering makes a real difference IMO, no nasty 'road noise' that seems to plague most of my LPs.
I'll post a quick copy of my circuit at some point tomorrow.
BTW, Douglas, I remember reading that you had devised a way of significantly reducing high frequency distortion caused by input clamping diodes on pre-amplifiers. Care to share it with us?
You recently updated your Wireless World Archive to include rumble filters.
Part 1 of the Williamson Amplifier is in there but Part 2 "Design of Tone Controls and Auxiliary Gramophone Circuits" did not make the grade ( possibly in view of Baxandall's later landmark work).
In that part 2 article there was an unusual steep slope rumble filter which was level down to 20 Hz and -30 dB down at 10 Hz. What do you know about this one?
Nothing. But I will. Can you give me the issue date?
Likewise, could you let me have the issue date of the Elektor filter?
It has set me thinking...
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