Hi all,
Hoping someone might shed some light on how to retain good stereo imaging when cutting.
When i monitor the track to be cut with a plugin that allows me to hear the mono/sum and L/R difference - i can hear the image clearly, but when i do the same to the track after it's be cut (i record it back in) the image has almost disappeared.
The image has also changed when i review it with a Goniometer.
Im thinking i have a Phasing issue or something similar somewhere in my setup.
Any thoughts on how to test and solve this problem?
Cheers,
james
Stereo Image Depth
Moderators: piaptk, tragwag, Steve E., Aussie0zborn
You might want to check the pickup path (cartridge wiring, phono preamp wiring, etc..) to make sure that the gramophone is able to reproduce the signals recorded onto a pressed, test disc, which will have a 1 kHz sine wave recorded in stereo in phase, with no vertical modulation. How is this on the goniometer?
What system are you using? In the Ortofon GO741 and DSS732 package, you do have to establish polarity and feedback phasing. First, with Test and Power Limit engaged, you confirm that the 1 kHz input is playing back with equal intensity from the auxiliary outputs on the front of the amp. A Y-cable from the oscillator can feed both inputs with the same signal. The output of each amp feeds a dual-trace oscilloscope. (You could also feed a calibrated stereo ADC and use something like SpectraFoo metering.) You then make sure each amp has a properly applied negative swinging feedback coil signal, mixing inside the circuit of the amp along with the input signal before (re)output, by turning the feedback pot ever so slightly up.
{As long as the level goes down, you are feeding back negatively below resonance, which is good. It's canceling out some of the motional distortion. Feeding back positively is summing the motion to itself, and that easily causes oscillation (loud hum and hopefully cut off before release of magic smoke). Even if the phasing is negative below resonance, loud, very high frequency signals can create oscillation, too, since the complex impedance of the cutter head load twists the phase as frequency rises above resonance until the polarity of the negatively-wired Feedback signal is positive, in spite of the flipped connections.} Then you check that the other channel is also good. Each time the feedback for the channel under test is returned to 0 amps. Then, while playing a 5 kHz tone, Power Limit is removed and now acceleration is unfiltered and so both feedback pots (of the two mono amps) are very slowly turned up, at the same time, until the point where the peak in the 5 kHz range is pulled down to the level that 1 kHz was (through negative feedback cancellation of energy). Then you do a sweep and use the on board eq to tune the feedback for flattest response. This is the gist. Is there a manual with your system. That's where I got this information.
Not explained as to why in the manual, but encountered in the field, the two channels' feedback coil signals have to be phased (made identical in sensitivity and polarity) in the two mono cutting amps simultaneously because if you tried to do it one at a time, the results will tend to be lop-sided. The loading of the wiggling is one-sided if the other coil is silent while doing this adjustment. That's how it seems on the DSS head, anyway. Turning the two amps' respective Feedback pots up by the same amount at the same time makes the correction more balanced. Ymmv.
- Guy Rosecope
What system are you using? In the Ortofon GO741 and DSS732 package, you do have to establish polarity and feedback phasing. First, with Test and Power Limit engaged, you confirm that the 1 kHz input is playing back with equal intensity from the auxiliary outputs on the front of the amp. A Y-cable from the oscillator can feed both inputs with the same signal. The output of each amp feeds a dual-trace oscilloscope. (You could also feed a calibrated stereo ADC and use something like SpectraFoo metering.) You then make sure each amp has a properly applied negative swinging feedback coil signal, mixing inside the circuit of the amp along with the input signal before (re)output, by turning the feedback pot ever so slightly up.
{As long as the level goes down, you are feeding back negatively below resonance, which is good. It's canceling out some of the motional distortion. Feeding back positively is summing the motion to itself, and that easily causes oscillation (loud hum and hopefully cut off before release of magic smoke). Even if the phasing is negative below resonance, loud, very high frequency signals can create oscillation, too, since the complex impedance of the cutter head load twists the phase as frequency rises above resonance until the polarity of the negatively-wired Feedback signal is positive, in spite of the flipped connections.} Then you check that the other channel is also good. Each time the feedback for the channel under test is returned to 0 amps. Then, while playing a 5 kHz tone, Power Limit is removed and now acceleration is unfiltered and so both feedback pots (of the two mono amps) are very slowly turned up, at the same time, until the point where the peak in the 5 kHz range is pulled down to the level that 1 kHz was (through negative feedback cancellation of energy). Then you do a sweep and use the on board eq to tune the feedback for flattest response. This is the gist. Is there a manual with your system. That's where I got this information.
Not explained as to why in the manual, but encountered in the field, the two channels' feedback coil signals have to be phased (made identical in sensitivity and polarity) in the two mono cutting amps simultaneously because if you tried to do it one at a time, the results will tend to be lop-sided. The loading of the wiggling is one-sided if the other coil is silent while doing this adjustment. That's how it seems on the DSS head, anyway. Turning the two amps' respective Feedback pots up by the same amount at the same time makes the correction more balanced. Ymmv.
- Guy Rosecope
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jamesfabel
- Posts: 15
- Joined: Sun Jun 28, 2009 3:49 am
Hi Guy,
Thankyou for the detailed reply.
I failed to report in my first post - im working on a relatively simple cutting setup - one involving Souri's vinyl-recorder.
So i'm entry level - but keen to learn how to cut the best i can with what i have.
I have employed your test tone suggestions and this has helped already to balance the vertical signal and calibrate the playback stylus input.
I have been employing the use of 2 different solidstate amplification setups (not at the same time) - both New Zealand brands - Perreaux and the other Plinius.
Im not sure whether your suggestions for testing amplifiers can be applied to what i currently operate, but if there is any other basic methods you think i should employ to improve my imaging, im all ears.
Thanks again for your time and input.
Regards,
James
Thankyou for the detailed reply.
I failed to report in my first post - im working on a relatively simple cutting setup - one involving Souri's vinyl-recorder.
So i'm entry level - but keen to learn how to cut the best i can with what i have.
I have employed your test tone suggestions and this has helped already to balance the vertical signal and calibrate the playback stylus input.
I have been employing the use of 2 different solidstate amplification setups (not at the same time) - both New Zealand brands - Perreaux and the other Plinius.
Im not sure whether your suggestions for testing amplifiers can be applied to what i currently operate, but if there is any other basic methods you think i should employ to improve my imaging, im all ears.
Thanks again for your time and input.
Regards,
James
I see that Souri sells a Dynamic cutterhead and a Feedback type. The Dynamic is simpler. Polarity (aka "phasing") might be the culprit in either case. If the drive coil wires which go to the cutterhead are out of polarity with each other, but the feedback coil interconnects are still miraculously following the inverse of the polarity of the drive coils (becoming negative and therefore positive but flipping negative again, whew), or if the cutterhead is not relying on feedback coils but the drive coils are out of relative polarity, the phantom center image of the stereo mix will be nulled and you will only hear whatever uncorrelated sounds are in each channel. Image collapse. Hill & Dale cutting, only... No lateral motion. Is this the sound you are hearing/seeing?
When you cut a modulated groove that is being driven by a sine wave and you are already certain of the identical polarity of the two channels of the source (by using, say, a Y-cable from an analog oscillator's single output to the two inputs of the cutting amps) and of the interconnects between the amps and the cutterhead screw terminals and betwixt the cutterhead screw terminals and the cutterhead snake (pin 2 goes to LH, pin 3 goes to LL, pin 4 to RH, pin 5 to RL, etc...), then the stereo cutterhead should be able to cut a 7 cm/sec peak velocity (lateral-only) groove when each drive coil is moving at 5 cm/sec peak velocity (internally) and they are summing in phase. If you can cut 5 cm/sec peak vel. (aka 3.54 cm/sec RMS vel., as CBS describes it on their test record) on the inner wall while the outer wall is unmodulated and do the same thing on the outer wall while the inner wall is unmodulated, then, when you unmute both channels and cut, the velocity should be increased by 1.414x... (not by 2). Only, in the case of the single-channel stereo groove, that (modulation) velocity (5 cm/sec/peak) is 45 degrees off lateral (aka diagonal), right?
If you like, rather than using the interferometer or Buchmann-Meyer dual light source with telescope, you can determine the velocity of the cut in progress by comparing the voltage drawn on the oscilloscope by the output of the pickup stylus, as it tracks and traces the groove just cut (your tone arm needle is riding in the groove while you cut with the cutterhead during this test...) to that (voltage) which it draws when you cause the same pickup cartridge to play the test record (of stated reference velocity and frequency, and channel, and phase, etc...). Just make sure apples are being compared to apples, and not oranges. *\*
Also, if you are using a compatibility equalizer, such as an elliptical filter, the uncorrelated signals of left and right will be minimized. If the center frequency of the elliptical filter is high enough, it should sound like mono.
This type of image collapse is less unpleasant, but might also be what you are noticing.
Guy Rosecopic
When you cut a modulated groove that is being driven by a sine wave and you are already certain of the identical polarity of the two channels of the source (by using, say, a Y-cable from an analog oscillator's single output to the two inputs of the cutting amps) and of the interconnects between the amps and the cutterhead screw terminals and betwixt the cutterhead screw terminals and the cutterhead snake (pin 2 goes to LH, pin 3 goes to LL, pin 4 to RH, pin 5 to RL, etc...), then the stereo cutterhead should be able to cut a 7 cm/sec peak velocity (lateral-only) groove when each drive coil is moving at 5 cm/sec peak velocity (internally) and they are summing in phase. If you can cut 5 cm/sec peak vel. (aka 3.54 cm/sec RMS vel., as CBS describes it on their test record) on the inner wall while the outer wall is unmodulated and do the same thing on the outer wall while the inner wall is unmodulated, then, when you unmute both channels and cut, the velocity should be increased by 1.414x... (not by 2). Only, in the case of the single-channel stereo groove, that (modulation) velocity (5 cm/sec/peak) is 45 degrees off lateral (aka diagonal), right?
If you like, rather than using the interferometer or Buchmann-Meyer dual light source with telescope, you can determine the velocity of the cut in progress by comparing the voltage drawn on the oscilloscope by the output of the pickup stylus, as it tracks and traces the groove just cut (your tone arm needle is riding in the groove while you cut with the cutterhead during this test...) to that (voltage) which it draws when you cause the same pickup cartridge to play the test record (of stated reference velocity and frequency, and channel, and phase, etc...). Just make sure apples are being compared to apples, and not oranges. *\*
Also, if you are using a compatibility equalizer, such as an elliptical filter, the uncorrelated signals of left and right will be minimized. If the center frequency of the elliptical filter is high enough, it should sound like mono.
This type of image collapse is less unpleasant, but might also be what you are noticing.
Guy Rosecopic
Last edited by Serif on Wed Jul 25, 2012 7:55 pm, edited 1 time in total.
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jamesfabel
- Posts: 15
- Joined: Sun Jun 28, 2009 3:49 am
Thanks Guy,
I have the Dynamic cutting head.
Thanks for the clarity around phasing - I will perform tests on the coils. I would say the image has been 'nulled' or collapsing...but without an example i really cant say - the internet is a useful resource - im sure i can locate an example to compare!
Souri has been very helpful, but with a language barrier things are sometimes less clear than i would like. I agree with him that issues with the head are unlikely as it was working perfectly when he trained me. It may simply be the limitations of this type of head. The pickups provide a maximum 10dB of channel separation, which could explain why certain instruments or tones become more centered or mono in the cutting process.
I have also been using an Art Pepper Band Jazz piece as a cutting reference and the tone of the Saxophone provides a very clear image to A/B throughout the process. Of course i have been using a tone generator as well.
I also have a set of Tube amplifiers which i am employing as monoblocks. I have noticed the image to be preserved better with the tubes as opposed to the solidstate. If i could improve the image integrity a fraction more - i would say the difference would become only a matter of preference.
Thankyou for your suggestion of voltage draw comparison between the test record and a new cut - i will do an experiment with this.
And an elliptical filter. Again i will investigate. I dont think this is part of the kit supplied with Souri's equipment, i am familiar with the use and will look into employment.
Thanks again for your suggestions Guy!
Epic.
Cheers
I have the Dynamic cutting head.
Thanks for the clarity around phasing - I will perform tests on the coils. I would say the image has been 'nulled' or collapsing...but without an example i really cant say - the internet is a useful resource - im sure i can locate an example to compare!
Souri has been very helpful, but with a language barrier things are sometimes less clear than i would like. I agree with him that issues with the head are unlikely as it was working perfectly when he trained me. It may simply be the limitations of this type of head. The pickups provide a maximum 10dB of channel separation, which could explain why certain instruments or tones become more centered or mono in the cutting process.
I have also been using an Art Pepper Band Jazz piece as a cutting reference and the tone of the Saxophone provides a very clear image to A/B throughout the process. Of course i have been using a tone generator as well.
I also have a set of Tube amplifiers which i am employing as monoblocks. I have noticed the image to be preserved better with the tubes as opposed to the solidstate. If i could improve the image integrity a fraction more - i would say the difference would become only a matter of preference.
Thankyou for your suggestion of voltage draw comparison between the test record and a new cut - i will do an experiment with this.
And an elliptical filter. Again i will investigate. I dont think this is part of the kit supplied with Souri's equipment, i am familiar with the use and will look into employment.
Thanks again for your suggestions Guy!
Epic.
Cheers
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jamesfabel
- Posts: 15
- Joined: Sun Jun 28, 2009 3:49 am
Quick question you might be able to answer:
I am running a software plugin to assess the phase and image - gonoimeter - on both the input to the amps, and the output of the stylus as the head cuts.
If the image in the output looks by comparison to be UPSIDE DOWN on the vertical plane (left to right looks correct) then what do you think causes this?
Is there a test for this plane? Or will it be identified in techniques you have already suggested?
Best,
James
I am running a software plugin to assess the phase and image - gonoimeter - on both the input to the amps, and the output of the stylus as the head cuts.
If the image in the output looks by comparison to be UPSIDE DOWN on the vertical plane (left to right looks correct) then what do you think causes this?
Is there a test for this plane? Or will it be identified in techniques you have already suggested?
Best,
James
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Greg Reierson
- Posts: 198
- Joined: Thu Jul 29, 2010 1:31 pm
- Location: Minneapolis, MN
- Contact:
...you could need to include the knowledge of the polarity of the inputs and outputs of the converter which feed the goniometer (some converters invert absolute polarity without the manual saying, or if the manual is wrong - has happened with big name brands), as well as the pin-conformity (i.e., polarity) of the analog cables used to interconnect the converter with the lathe signals.jamesfabel wrote:Quick question you might be able to answer:
I am running a software plugin to assess the phase and image - gonoimeter - on both the input to the amps, and the output of the stylus as the head cuts.
Can you post a picture? Normally there is a strong degree of correlation seen in the summing direction and a lesser amount of random, chaotic energy in the difference directions.jamesfabel wrote: If the image in the output looks by comparison to be UPSIDE DOWN on the vertical plane (left to right looks correct) then what do you think causes this?
Does the goniometer you're using also show a correlation meter? -1 to +1? You don't want the bulk of the sound to be negative, if all other things are wired conventionally.
The part near the bottom about the special case of Lissajous, where A=B is pretty good, but it pertains mostly to the image seen on old school oscilloscopes.
http://en.wikipedia.org/wiki/Lissajous_curve
I have been using a Tektronics 465 which I got from someone out West. Dual trace with X-Y and a 100 MHz bandwidth. This is neat because it lets you see how far out the energy of clicks and pops go! Who said vinyl wasn't hi fi? (:
Guy "Ray" Schuhn
Nothing to do with this thread but the signature ending with Fable has me intrigued
There was a Record pressing equipment manufacturer in Belgium back in the days that was called Fabel
I have two of their steam heated extruders as well as the schematics and drawings of a manual record press they made and sold in the past
This press was a good copy of the Alpha Toolex mixed with the Italian made TCS press features of each was quite obvious on the Fabel press
They did made the best molds for very thin records which was the aim of every record manufacturer back than
It is amazing that this company has left no legacy behind it whatsoever
Nothing like SMT Finebilt Alpha etc
Is there any connection? or just coincidence?
Cheers
There was a Record pressing equipment manufacturer in Belgium back in the days that was called Fabel
I have two of their steam heated extruders as well as the schematics and drawings of a manual record press they made and sold in the past
This press was a good copy of the Alpha Toolex mixed with the Italian made TCS press features of each was quite obvious on the Fabel press
They did made the best molds for very thin records which was the aim of every record manufacturer back than
It is amazing that this company has left no legacy behind it whatsoever
Nothing like SMT Finebilt Alpha etc
Is there any connection? or just coincidence?
Cheers
Chris
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jamesfabel
- Posts: 15
- Joined: Sun Jun 28, 2009 3:49 am
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jamesfabel
- Posts: 15
- Joined: Sun Jun 28, 2009 3:49 am
Thanks Guy, i will investigate my hardware specs and check polarity and pin conformity.Serif wrote:
...you could need to include the knowledge of the polarity of the inputs and outputs of the converter which feed the goniometer (some converters invert absolute polarity without the manual saying, or if the manual is wrong - has happened with big name brands), as well as the pin-conformity (i.e., polarity) of the analog cables used to interconnect the converter with the lathe signals.
Guy "Ray" Schuhn
No i cannot provide snapshots of the input/output at the same exact time - The few screen grabs i have done alerted me to the possibility off polarity issues - but this is not accurate and could well be misleading.
Thanks for the curve comments and wiki link - will look further into understanding this better. I think if i can get my head round the basics and run some proper tests to ascertain wether i in fact have an issue here - from then on it should just be a routine.
Thanks again for your input!
Cheers
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jamesfabel
- Posts: 15
- Joined: Sun Jun 28, 2009 3:49 am
pure coinkidink mossman...mossboss wrote: Is there any connection? or just coincidence?
Cheers
I started a record label in 2001 and called it Fabel Music... moved into event production when CDs started to take a turn for the worse and have returned to this part of the business since the event industry bottomed out.
Nice to see i was on the right buzz tho...when i realised there was already a Fabel history out there in the world and that i had inadvertently tapped into it's ghost, it made me sm:)e
Cheers
mossboss wrote:Nothing to do with this thread but...in Belgium back in the days that was called Fabel
I have two of their steam heated extruders as well as the schematics and drawings of a manual record press they made and sold in the past
This press was a good copy of the Alpha Toolex mixed with the Italian made TCS press features of each was quite obvious on the Fabel press
...
Saw this, and also the Dead Weather video, which Aussie Cutter pointed out last year.
http://www.flickr.com/photos/verylastexcitingmoment/3345070971/lightbox/
- E. Sopp
Well Thank you for the reply as well as the good vibe you picked up
They had joint ventures everywhere in Europe and for some reason they did sell their gear in Australia But I have yet to hear any one else mentioning them
I have some original correspondence from them on Onion skin paper addressed to some plant manager or another
Their tone of "voice" certainly made my eyebrows raise
Any way that was way back I suppose another reason they left no legacy?
They extruders that I have still run with original screws and barrels
Quite amazing really they must have pushed out as a guess more than 10M records so far and still going
Quite excellent engineering one would say
Enjoy the name
Cheers
They had joint ventures everywhere in Europe and for some reason they did sell their gear in Australia But I have yet to hear any one else mentioning them
I have some original correspondence from them on Onion skin paper addressed to some plant manager or another
Their tone of "voice" certainly made my eyebrows raise
Any way that was way back I suppose another reason they left no legacy?
They extruders that I have still run with original screws and barrels
Quite amazing really they must have pushed out as a guess more than 10M records so far and still going
Quite excellent engineering one would say
Enjoy the name
Cheers
Chris
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Aussie0zborn
- Posts: 1825
- Joined: Sat Mar 11, 2006 8:23 am
- Location: Australia
- Contact:
Fabeldis SA went broke when the family who owned it squandered the company's money on personal spending resulting in the winding up of the very large number of companies in the group and the sale of the family's castle. A huge success story that just went haywire.
Only one Fabel press remains in operation today at United Record Pressing - what they call a "Belgian" press for test pressings. According to Flo, there is one sitting in Switzerland.
We have previously discussed Fabeldis SA here : https://lathetrolls.com/lathetrolls-post-5100.html
Welcome back, James. Good to see you finally took the plunge. Good luck.
Only one Fabel press remains in operation today at United Record Pressing - what they call a "Belgian" press for test pressings. According to Flo, there is one sitting in Switzerland.
We have previously discussed Fabeldis SA here : https://lathetrolls.com/lathetrolls-post-5100.html
Welcome back, James. Good to see you finally took the plunge. Good luck.