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Nickou
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RIAA filter accuracy

Post: # 8225Unread post Nickou
Fri Mar 19, 2010 3:11 pm

Ok , i need some help here
any comment is welcome
I have a sal74 amplifier , probably build during 74 or 1975 , so the machine is 35 old .

I wanted to add a second RIAA curve for half speed cutting to the sal 74

So I unsold the original caps and resistor to measure there values .

I realised 2 things :
- the value of the caps have a difference of around 5 % between lñeft and right .
- The neumann RIAA filter does not match with the constant time of the official RIAA

Here some numbers
Left side

for the 3180 us
c =90700pF
r =40.1 K ohms

so the period is bigger than 3180 us, and not a bit

Right side
c= 93100 pF
r= 40,2 k ohms

for the 75 us it is the same ,
the resistor are equal but the capacitors shows differences of around 5 % between L and R

And again , the period is higher than the " official " RIAA curve, around 10 % .
I thought than my multimeter was ok to compare several caps and
bad to gives nominal values , so I bought a 0,1 % 100 nF cap ( 2,1 euros !!!!) and my multimetter gives 100047 pF , so the multimeter seems to be not so bad for nominal values
From that , I have several question , and would like to have serious answer ..

Question to the forum :

-the capas Neumann used are alumnium foils or polyester , they are now 35 years old or more ... (!)Is the age of this componement wich can make this change of values ?
I think no , but I am not sure ...

- Why Neumann Does not respect the frequencies of the RIAA ? Is it a deliberate choice ?



- I want to finisch my RIAA encoder for half speed : Do i work from the neumann value or do I do a new encoder also for normal speed with value matching as near as possible the RIAA "official curve ?

Writting this post , I am thinking than a encoder has sens with a decoder ,
so this WE , I ll check the values of the decoder of the sal and gives the values to the forum
Also I remember than EMT is still building a preamp with a a user interface wich permits to change those values.
So I can think than the choice of those values is "open", but at the same time the database of the RIAA curve is simple and clear , there is not so much interpretations to do ...

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mossboss
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RIAA Curve

Post: # 8232Unread post mossboss
Fri Mar 19, 2010 8:27 pm

Hey Yann
Why bother really This argument has been thrown around for years There is a long discussion about it at the ARCLIST (check it out) with a lot of scientific analysis on the ins and outs of the"Neumann curve" which as you rightly point out is slightly different than the published standard
I am not going to go to the ins and outs of all this it is all there any way
This discussion at the ARCLIST is from sound preservation exparts as well as archivists and discographers so it has nothing to do with the likes of us cutting producing etc
These people face the task of attempting to preserve recorded sound well before any standards where ever adopted with a plethora of variations as per record manufacturer at the time
They often have an active fully variable equilisation black box so as to get what they think the record would have sounded or should have sounded like
Some of them adopt a spectrum analyser and adjust according to known limits of cutting equipment at the time etc etc etc
The summary of this long flogged subject is this: Can any amplifier ever be able to reproduce what has been cut with the inverse curve which of course has to be the right opposite exact curve? even after standards where established? The answer is simply NO even the highest quality amps would have difficulty in that regard let alone gear that was made with a + or - 10% componenst that may even be 25% off if they happen to fall at the extremes of their tollerance
If this is really a case of purism than fine If it is parcticality? I would have thought it a waste of time and effort
Of course There lays the question! The devil is allways in the details
By the way Neumann had another cut-off point way up as well which was frowned upon at the time There was also an attempt of the European equivalent of the RIAA which attempted to adopt this standard with some other mods as well This was also somehow resisted by the industry based on the fact that reproducing equipment failed in this regard so what was the point any way since existing standards served the purpose quite well
Having said all of that I remember reading somewhere that amplifier manufacturers adopted the slightly different Neumann curve as it was the lathe of choice in most cutting houses so it become another Defacto standard I suppose (don't quote me on this)
It is like a comment that I come across when a client asked the guy that cut his music with sibilants being an issue for him He asked if it can be cut with out them The answer being "Sure I can cut it but can you play it?"
Good luck with it any way I would leave these components there if they are within the 5% tollerance allowed, Neumann was quite fussy in this regard and if my memory serves me well they where "selected" for them during production to fall within a certain range
They went a further "burn in" test at Neuman's works prior to assembly
Propobaly that is one of the reasons that this division of Neumann never made any money for the group as the historians tells us
I have personally tried to replace existing Neumann components at 5% tollerance with current 1% tollerance expensive ones and found that under working voltages the old ones stayed within their specs while the new stuff drifted to way past their designated tollerance ratings
It seems to me that the choice of components was such as they all drifted in unison if one can say that so the whole chain stayed within an acceptable range The choice of componentry there is quite specific as the manual not only specifies the value but also the manufacturer but it also says get your spares from Neumann by quoting the serial number of the unit I am sure you get the idea
By the way there is a long trail here in this forum as well in regards to this with CD4 cutter and Kevin Gray having a another go at it
It always makes an interesting topic regardless
Cheers
Chris

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cohearent
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Post: # 8296Unread post cohearent
Wed Mar 24, 2010 12:59 am

I think several points are being missed here.
First, the Neumann inverse RIAA is quite accurate, certainly within a half dB from 20Hz to 20kHz.
Second, on the Neumann schematics I have seen, 3 caps are paralleled for each cap to "nail" the value. They were also polystyrene caps which is about as good as they get.
Third the "so called Neumann fourth time constant" doesn't exist. It never did. Above 50kHz a two pole roll off was introduced to keep the RIAA from rising. You simply cannot continue climbing at almost 6dB per octave. Anyone heard of Radio Frequency Interference? Without it we'd all be picking up the bottom of the AM band like there was no tomorrow. And BTW every other manufacturer had a similar roll off. Why Neumann took the hit is beyond me, probably because they built far more systems than everyone else combined.
The NAB, IEC, and/or CCIR curve IS the RIAA curve. It is one of the few international standards. In the late '70s there was a proposed roll off in playback only, below 20Hz, but was never adopted.
Last, but not least you don't need to modify the RIAA curve to cut half speed. A fairly simple circuit can be built to go between the console and cutting rack. Gotham published a paper about this in the late 70s. You do need to modify the curves for the tape machine and any noise reduction, however.
PS...Half speed is a bad joke. It was needed for cutting high level 45s when cutting amps were 50 to 60 watts, and then in the 70s for cutting a 30kHz subcarrier for CD4 quad.
You can cut levels with an SAL/SX 74 WAY higher than can be played back. The limitation is in playback, not cutting. If the groove curvature is greater than the radius of the playback stylus the record will mis-track. The only way to prevent this is to HF limit until the resulting curvature is reduced. Half speed does NOTHING to help, let alone, prevent this. And try to make a HF limiter work with half speed...it don't! And this is assuming that the cutterhead head and tape machine are as happy an octave lower. They ain't!
The result is underdamped slop on the bottom and sibilants that will kill. But don't take my word for it, try it! I have.
Kevin Gray

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cohearent
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Post: # 8297Unread post cohearent
Wed Mar 24, 2010 1:11 am

Hi Yann and Mossboss,
I should change my middle name to RIAA...
I think several points are being missed here.
First, the Neumann inverse RIAA is quite accurate, certainly within a half dB from 20Hz to 20kHz.
Second, on the Neumann schematics I have seen, 3 caps are paralleled for each cap to "nail" the value. They were also polystyrene caps which is about as good as they get.
Third the "so called Neumann fourth time constant" doesn't exist. It never did. Above 50kHz a two pole roll off was introduced to keep the RIAA from rising. You simply cannot continue climbing above 20kHz at almost 6dB per octave. Anyone heard of Radio Frequency Interference? Without a roll off we'd all be picking up the bottom of the AM band like there was no tomorrow. Even Stanley Lipshitz, who published THE paper on all things RIAA in the AES acknowledged this. And BTW every other manufacturer had a similar roll off. Why Neumann took the hit is beyond me, probably because they built far more systems than everyone else combined.
The NAB, IEC, and/or CCIR curve IS the RIAA curve. It is one of the few international standards. In the late '70s there was a proposed roll off in playback only, below 20Hz, but was never adopted.
Last, but not least you don't need to modify the RIAA curve to cut half speed. A fairly simple circuit can be built to go between the console and cutting rack. Gotham Audio published a paper about this in the late '70s. You do need to modify the curves for the tape machine and any noise reduction, however.
PS...Half speed is a bad joke. It was needed for cutting high level 45s when cutting amps were 50 to 60 watts, and then in the 70s for cutting a 30kHz subcarrier for CD4 quad.
You can cut levels with an SAL/SX 74 WAY higher than can be played back. The limitation is in playback, not cutting. If the groove curvature is greater than the radius of the playback stylus the record will mis-track. The only way to prevent this is to HF limit until the resulting curvature is reduced. Half speed does NOTHING to help, let alone, prevent this. And try to make a HF limiter work with half speed...it don't! And this is assuming that the cutterhead head and tape machine are as happy an octave lower. They ain't!
The result is underdamped slop on the bottom and sibilants that will kill. But don't take my word for it, try it! I have.

Best,

Kev
Kevin Gray

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Post: # 8298Unread post cohearent
Wed Mar 24, 2010 1:15 am

Sorry for double post I got an error message that sending failed...
Kevin Gray

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Post: # 8299Unread post motorino
Wed Mar 24, 2010 2:05 am

Hi friends!

Thanks for the explanations about, this forum its great!

Kev, please, can you show in a pic the passive riaa circuit without the roll at 50 khz? I will like to made one and put in my riaa preamp selector.

Excuse me for my english.

Cheers

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mossboss
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RIAA

Post: # 8301Unread post mossboss
Wed Mar 24, 2010 3:40 am

Kevin
I am in complete and furious agreement with you mate
I do not think I have missed the point at all I was in actual fact telling the guy to leave it well alone
I also said that the 4th odd cut off point time constant was also flogged to death and I could not remember at the time the other "standard" proposed which was never adopted as I am pointing out and you do point out as well
I am also saying that it was the reproduction or play back gear that has shortfalls just like you
May be the point of the "Neumann standard" has thrown the whole thing out but there are references here and there about this as well
at the end of the day the Neumann has got it right no doubt about that
By the way about this half speed stuff once again I am with you and I do have an original of that Gotham paper somewhere here
By the way I wonder what Stan Ricker would have to say about all this than?
Cheers
Chris

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Nickou
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Post: # 8347Unread post Nickou
Fri Mar 26, 2010 9:50 am

Ok , if somebody can post this paper of Gotham Audio , I wll be very pleased to read it
Finaly I did a little circuit to dobble teh resitors and it works perfect .


Half speed a bad joke ? not so sure ... it will depend a lot on the music you are working on ... I have to do regulary cut of 22 min of contemporany electronic music per side wich are impossible to cut at normal speed because they have a lot of very high frequencies. If I use a deesser , I kill the music . If I don t use a deesser I kill the head , and at half speed it is perfect and sound so far better than with normal speed

no question of level , only bandwith and sound quality.

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Nickou
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Post: # 8348Unread post Nickou
Fri Mar 26, 2010 9:52 am

Ok , if somebody can post this paper of Gotham Audio , I wll be very pleased to read it
Finaly I did a little circuit to dobble teh resitors and it works perfect .


Half speed a bad joke ? not so sure ... it will depend a lot on the music you are working on ... I have to do regulary cut of 22 min of contemporany electronic music per side wich are impossible to cut at normal speed because they have a lot of very high frequencies. If I use a deesser , I kill the music . If I don t use a deesser I kill the head , and at half speed it is perfect and sound so far better than with normal speed

no question of level , only bandwith and sound quality.

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markrob
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Post: # 8363Unread post markrob
Fri Mar 26, 2010 6:41 pm

Hi Kev,

Can you explain why there would be any sort of underdamped response issues at half speed? I would think the feedback system would respond better if fed lower bandwidth source material. I can see issues at the low end in the form of reduced response. If the closed loop system has a -3db 20hz cuttoff, on playback you would be limited to 40hz.

Regards,

Mark
cohearent wrote:Hi Yann and Mossboss,
The result is underdamped slop on the bottom and sibilants that will kill. But don't take my word for it, try it! I have.

Best,

Kev

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Post: # 9227Unread post cohearent
Tue Jun 08, 2010 11:25 am

Frequency response isn't the issue, damping is. (The 68 and 74 are within 1dB to 10Hz)The reason is the cutterhead is running out of feedback control at the bottom octave. Neumann uses shelving Eq to correct for this. But when you feed in stuff an octave below this it gets unhappy. I can hear it on almost every 1/2 speed disk I've listened too. I had shoot outs with JVC and IAMC in the 80s and EVERY engineer who heard my full speed vs those half speeds picked the full speed.
Kevin Gray

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Post: # 9228Unread post cohearent
Tue Jun 08, 2010 11:37 am

Yann,

What cutting system are you using? If the amps are underpowered, yes, 1/2 speed is an improvement. If the amps are clipping the problems are not improved by cutting half speed. The problems are in playback and cutting half speed does nothing to improve the problems because the geometry of the resulting groove is exactly the same.
Kevin Gray

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opcode66
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Post: # 13839Unread post opcode66
Wed Mar 30, 2011 1:30 am

Nickou wrote:Finaly I did a little circuit to dobble teh resitors and it works perfect.
For real? That is all you had to do? Same circuit as in Neumann schematics but double the resistors?
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Post: # 13842Unread post Nickou
Wed Mar 30, 2011 5:14 am

I have electronic for half and normalspeed
in my system , the riiaa aencoder , the feedback preamp and the mixer are not from neumann , but from myself ... !!!!!!! I am joking , Yes they are from myself , but it is not a new design , it is the neumann design, I copied
normal speed , and did new cards for halspeed ...

so you can do that too , rebuilding the cards
but the solution is what gotham did, I think : a analog filter wich is correcting to half speed , I never found the schematic of that , so I built one , and Jvo Studer gived us the same solution in the digital domain ..


but all of that is not big mathematics ... it is just a serie of first order passive filter .. so you have to look how you can divide per 2 the cutting frequencie of a first order high pass filter , for example ... thats all

and if you look with big attention the neumann schematics , the solution is writted under your eyes , not everything , it is missing 2 or 3 values they don t give : and the fun is there

to go back to the topic , what I found is than the neumann filter was tune on a piano , I mean than the cutting frequencies were not 50, 500 , 2122 but very near frequencies you can play on a keybooard as musical note

If someboby has an idea about that .. a real idea , I will be very please to read it

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opcode66
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Post: # 13871Unread post opcode66
Wed Mar 30, 2011 2:49 pm

Do you have any schematics for the work you did on the filter? Or possibly can you elaborate on the digital domain solution?

Seems like you don't really want to divulge anything specific...
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Post: # 13905Unread post Nickou
Wed Mar 30, 2011 5:08 pm

flozki wrote:ok i think i got it with the images..
again the picture from my riaa encoder....

Image
it is that , with all the frequencies one octave down.
Certainly other members of the forum tried this design at half speed too .

Big up to Flozky for this input

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Post: # 13911Unread post opcode66
Wed Mar 30, 2011 6:11 pm

Thank you Nikou and Flo!
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Post: # 13922Unread post Nickou
Thu Mar 31, 2011 4:29 am

yes , big thanks to Flozky ...
big thanks in general to the forum , all those informations became so easy to find with it ! a bit too much easy and fast sometime ...
so now , look the neumann schematic , and ... Big surprise ! funny no ?
how the frequencies can be one octave down ? hmm ... brain storming ... let s go , I give it ! 1/2= 0,5... and 1 / (1/2) =2 :shock:

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Post: # 13929Unread post Nickou
Thu Mar 31, 2011 10:14 am

opcode66 wrote:
Nickou wrote:Finaly I did a little circuit to dobble teh resitors and it works perfect.
For real? That is all you had to do? Same circuit as in Neumann schematics but double the resistors?
for real ? do you want me to give the number of the part you will have to change and there values ?

make you investgation and understand how it works ... because , for real , if you ask that here and write there than everything is easy for you to design a new picht controler because you know everything about everything you already did so many things in your life ... it is sounding like a fake, it is a fake

yes for real , in RC filter , if you change the resistance , you change the frequencie of the filter !!!!!

http://en.wikipedia.org/wiki/RC_circuit some good informations ...

and you won t find anything else in this filter than capacitor or resistor , so you can change the values of the caps , or the values of the resistances , or BOTH !!! for real !"

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opcode66
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Post: # 13933Unread post opcode66
Thu Mar 31, 2011 10:58 am

Yann or Nickou or whoever you are. I am trying to do a lot of things at once. I am asking questions so I can do a lot of things at once. I have many projects going at once. I am not fake. Would you like pictures or video of me, my lathe, my workbench, my studio, etc?

There is absolutlely no need to be like this. Asking if you changed anything else about the circuitry other than doubling the resistors is valid. I'm only trying to save myself some time. You did the same thing not very long ago.

I saw that you posted on almost every board I read regarding this mod. Would you like me to quote you from other boards asking about it? You asked a lot of people how to do it. So, don't come off like you're an expert. You are working off the knowledge gained from other people too, including Flo. And, now you are acting like you are the supreme authority. Funny.
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