RF free Prefix
Posted by: Chris Bell on 13 March 2003
I just had a new prefix installed in my LP-12 which is RF free! Yes, RF free! Before, both the old Prefix (K) and Stageline (K) had terrible RF (Seattle radio stations). Now nothing but fantastic sound. Anyone who yerns for a Prefix but had terrible RF should run to their dealer. I am already contemplating a Supercap for mine.
Chris Bell
PS: Many thanks to Chris Koster for sending me the new improved Prefix...I was ready to buy a Groove or maybe that Boulder phono pre-amp (not).
Chris Bell
PS: Many thanks to Chris Koster for sending me the new improved Prefix...I was ready to buy a Groove or maybe that Boulder phono pre-amp (not).
Posted on: 13 March 2003 by Laurie Saunders
How is the new prefix different to the old one?
laurie S
laurie S
Posted on: 13 March 2003 by John
New prefix? you have my ears! Anyone with more info?
John
John
Posted on: 13 March 2003 by maxwellspeed
Chris,
I live here in Seattle also. On capitol hill to be exact and real near those darn 3 towers. I pretty much ruled out a prefix on the LP12 because of that. What has been changed? Any ideas? Heck, it is quite the chore whenever I change anything to arrange the cables just so, so that I do not get NPR coming through the SBLs.
I live here in Seattle also. On capitol hill to be exact and real near those darn 3 towers. I pretty much ruled out a prefix on the LP12 because of that. What has been changed? Any ideas? Heck, it is quite the chore whenever I change anything to arrange the cables just so, so that I do not get NPR coming through the SBLs.
Posted on: 13 March 2003 by Arthur Bye
Chris:
Could you tell us if there are any visible differences between the old and new Prefix?
Like maybe a Faraday cage or something.
Here's the link to Naim's current spec Prefix
Prefix
Arthur Bye
Could you tell us if there are any visible differences between the old and new Prefix?
Like maybe a Faraday cage or something.
Here's the link to Naim's current spec Prefix
Prefix
Arthur Bye
Posted on: 13 March 2003 by Chris Bell
Max,
I feel your pain. I went to school on Capitol Hill and I remember my car stereo was unusable due to the tv towers. I would be curious if the new Prefix could retard that much EMI.
Arthur,
As far as the design, I will have to defer to the folks at Naim. It looks just like any other Prifix to my eyes. All I know is that is sounds wonderful. A friend brought over a Supercap last night and both our chins it the floor. Its that good! I wonder if there will be a 500 series Prefix?
Chris Bell
I feel your pain. I went to school on Capitol Hill and I remember my car stereo was unusable due to the tv towers. I would be curious if the new Prefix could retard that much EMI.
Arthur,
As far as the design, I will have to defer to the folks at Naim. It looks just like any other Prifix to my eyes. All I know is that is sounds wonderful. A friend brought over a Supercap last night and both our chins it the floor. Its that good! I wonder if there will be a 500 series Prefix?
Chris Bell
Posted on: 13 March 2003 by John
Chris Koster,
Please announce on the Forum when it's available. It would also be nice to get some information on how it compares with old prefix.
Will it be sonically better than the old prefix/52? or will require a supercap to fully gain the potential gain over the old prefix. Will the main gain be in RF problems?
All vinyl heads would like to know!
John
Please announce on the Forum when it's available. It would also be nice to get some information on how it compares with old prefix.
Will it be sonically better than the old prefix/52? or will require a supercap to fully gain the potential gain over the old prefix. Will the main gain be in RF problems?
All vinyl heads would like to know!
John
Posted on: 13 March 2003 by Paul Stephenson
This unit is not yet available for sale, we are doing field tests around the world. So far the RF results are good, the performance has also been improved. More news later after ALL OF OUR TESTS ARE COMPLETE.
Posted on: 14 March 2003 by Philippe Dancause
Paul,
could these new developments one day be applied to NAP and NAC? Also, could the old components be upgradable?
I now it is a bit early but this is a very big issue in north america. I however understand that these developments take a long time to get on the market and that you may prefer to keep more reserved about these for the moment.
thanks you!
Philippe
could these new developments one day be applied to NAP and NAC? Also, could the old components be upgradable?
I now it is a bit early but this is a very big issue in north america. I however understand that these developments take a long time to get on the market and that you may prefer to keep more reserved about these for the moment.
thanks you!Philippe
Posted on: 14 March 2003 by Laurie Saunders
I know that the "old" prefix could be made immune to RFI by changing from "K" to "S". This simply added a low pass filter that did cure the RFI but IMHO also murdered the sound quality. Are Naim saying that they actually have a new design of phono stage that actually blocks RFI AND gives even better sound quality?
If true, that does seem to somewhat contradict the "conservation of energy" principle! i.e gains in one area not being accompanied by losses elsewhere. I am very curious. As it happens, I have effectively cured RFI problems on my K prefix/hicap/52 by ferrite clamping the EARTH lead to the preamp. Clamping the signal lead did cure RFI but also had a similar effect to the "S" boards....it ruined the sound.
My interest is not so much RFI immunity....I have solved that....I am much more fascinated by the (apparently) claimed better sound quality.
The current K prefix gives me astonishing sound quality. If I can do better......?!
More details please!
If true, I want one...quickly!
regards
Laurie S
If true, that does seem to somewhat contradict the "conservation of energy" principle! i.e gains in one area not being accompanied by losses elsewhere. I am very curious. As it happens, I have effectively cured RFI problems on my K prefix/hicap/52 by ferrite clamping the EARTH lead to the preamp. Clamping the signal lead did cure RFI but also had a similar effect to the "S" boards....it ruined the sound.
My interest is not so much RFI immunity....I have solved that....I am much more fascinated by the (apparently) claimed better sound quality.
The current K prefix gives me astonishing sound quality. If I can do better......?!
More details please!
If true, I want one...quickly!
regards
Laurie S
Posted on: 14 March 2003 by aht
To Chris Koster and other Naim luminaries--
Good news indeed! I have been using a MM Stageline with stepup transformer, as the MC-level Stagelines are more susceptible than ever to RFI. However, I hope that the new phono stage will not be limited to the Prefix configuration--many of do not use LP12 or ARO, and would prefer a more traditional stand-alone design that accepts RCA plugs. Thanks.
Good news indeed! I have been using a MM Stageline with stepup transformer, as the MC-level Stagelines are more susceptible than ever to RFI. However, I hope that the new phono stage will not be limited to the Prefix configuration--many of do not use LP12 or ARO, and would prefer a more traditional stand-alone design that accepts RCA plugs. Thanks.
Posted on: 15 March 2003 by Eric Barry
I live in upper Manhattan and had never had a problem with RFI until...
A few months ago my building had a cell phone transmitter installed on the roof. I live on the 3rd floor, and the building is six floors but...
there is some kind of box directly outside my window, with three big cables leading to the roof, literally on the other side of the wall that holds my tt. It's the only practical wall for mounting my tt wall shelf. I don't know what the box is, but it is killing my phono!
Now I get a high pitch tone on phono. In this location I have tried k and s prefix, k stageline, internal k and s boards on my 72, and mm boards.
I found no difference between k and s. I found the stageline possibly a tad less sensitive to the interference. The ability to move it around was it's biggest advantage as there are definitely peaks and troughs. But it was still too much for me (AT OC9 with .4mv output on the other end). With the volume high, it wasn't audible during the loud parts of an lp, but during the quiet parts.
With the internal mm boards, the tone is only audible with the volume up when the record is in between songs. I _can_ live with it, but I sure as hell don't want to. Nor do I want an mm in my main system.
By the way, the interference is bad enough that if I remove the case of the 72, it sounds like hell with all sorts of buzzing and chirping even on the line inputs. Ten feet away it's ok.
So, I humbly offer myself as a guinea pig for the new prefix.
And if anyone has any advice for me, please share.
--Eric
A few months ago my building had a cell phone transmitter installed on the roof. I live on the 3rd floor, and the building is six floors but...
there is some kind of box directly outside my window, with three big cables leading to the roof, literally on the other side of the wall that holds my tt. It's the only practical wall for mounting my tt wall shelf. I don't know what the box is, but it is killing my phono!
Now I get a high pitch tone on phono. In this location I have tried k and s prefix, k stageline, internal k and s boards on my 72, and mm boards.
I found no difference between k and s. I found the stageline possibly a tad less sensitive to the interference. The ability to move it around was it's biggest advantage as there are definitely peaks and troughs. But it was still too much for me (AT OC9 with .4mv output on the other end). With the volume high, it wasn't audible during the loud parts of an lp, but during the quiet parts.
With the internal mm boards, the tone is only audible with the volume up when the record is in between songs. I _can_ live with it, but I sure as hell don't want to. Nor do I want an mm in my main system.
By the way, the interference is bad enough that if I remove the case of the 72, it sounds like hell with all sorts of buzzing and chirping even on the line inputs. Ten feet away it's ok.
So, I humbly offer myself as a guinea pig for the new prefix.
And if anyone has any advice for me, please share.
--Eric
Posted on: 16 March 2003 by JeremyB
Eric,
Have you tried a "modern" phono cable? The one that came with my SME has two conductors carrying the signal, a screen for each channel with separate earth wires (SME phono plugs have isolated screen grounds and signal grounds) and a THIRD earth wire to ground the tonarm. I believe this is the optimum arrangement and should provide the most immunity from the common mode interference signals. Of course it's still not ideal since the isolated phono plug is not exactly a balanced connector like a DIN lead or a cannon (or a telephone jack come to that). I believe what we really need from Naim is an input stage with fully differential signal paths (hint hint!) to take advantage of this arrangement rather than the older, primative Linn/Aro etc single ended arrangement with BNCs and non-isolated phono grounds. If such an phono amp was available I would want to wire an unshielded twisted pair cable from the turntable all the way to the circuit board in the phono amp and forget about the screen altogether. This is after all how your telephone manages to work ok with miles of cable between your house and the phone company.
I could never understand why phono amp inputs aren't designed this way, using a DIN plug and socket instead of a phono plug and socket for the differential cartridge signals, since that is what the tone-arm uses anyway.
Have you tried a "modern" phono cable? The one that came with my SME has two conductors carrying the signal, a screen for each channel with separate earth wires (SME phono plugs have isolated screen grounds and signal grounds) and a THIRD earth wire to ground the tonarm. I believe this is the optimum arrangement and should provide the most immunity from the common mode interference signals. Of course it's still not ideal since the isolated phono plug is not exactly a balanced connector like a DIN lead or a cannon (or a telephone jack come to that). I believe what we really need from Naim is an input stage with fully differential signal paths (hint hint!) to take advantage of this arrangement rather than the older, primative Linn/Aro etc single ended arrangement with BNCs and non-isolated phono grounds. If such an phono amp was available I would want to wire an unshielded twisted pair cable from the turntable all the way to the circuit board in the phono amp and forget about the screen altogether. This is after all how your telephone manages to work ok with miles of cable between your house and the phone company.
I could never understand why phono amp inputs aren't designed this way, using a DIN plug and socket instead of a phono plug and socket for the differential cartridge signals, since that is what the tone-arm uses anyway.
Posted on: 16 March 2003 by Andrew L. Weekes
Jeremy,
A balanced, differential input phono stage (which is what you are suggesting) is a very good idea in principle.
The difference between phones and phono stages though is the bandwidth - you'd need a phono stage capable of rejecting any interference (common-mode signal) over the full audio band, possibly beyond.
Whilst not impossible (I have line receivers with 100dB of rejection flat to 20kHz, rising to about 70-80dB @ 200kHz), it's probably more difficult to do with the ultra low noise circuitry required for MC stages.
Interesting idea though...
What it doesn't help with is RF interference, for that shielding, and circuit design is the only way to eliminate it reliably. Bipolar stages need degeneration (worsening noise figures) or FET inputs (higher input capacitance, usually higher noise for MC).
RF is a bummer, nice to see that Naim are adressing the issue though - will old units be upgradeable I wonder?
At times of sunspot activity mine still gets a bit of radio Moscow, a few times a year...
Andy.
[This message was edited by Andrew L. Weekes on SUNDAY 16 March 2003 at 08:41.]
A balanced, differential input phono stage (which is what you are suggesting) is a very good idea in principle.
The difference between phones and phono stages though is the bandwidth - you'd need a phono stage capable of rejecting any interference (common-mode signal) over the full audio band, possibly beyond.
Whilst not impossible (I have line receivers with 100dB of rejection flat to 20kHz, rising to about 70-80dB @ 200kHz), it's probably more difficult to do with the ultra low noise circuitry required for MC stages.
Interesting idea though...
What it doesn't help with is RF interference, for that shielding, and circuit design is the only way to eliminate it reliably. Bipolar stages need degeneration (worsening noise figures) or FET inputs (higher input capacitance, usually higher noise for MC).
RF is a bummer, nice to see that Naim are adressing the issue though - will old units be upgradeable I wonder?
At times of sunspot activity mine still gets a bit of radio Moscow, a few times a year...
Andy.
[This message was edited by Andrew L. Weekes on SUNDAY 16 March 2003 at 08:41.]
Posted on: 16 March 2003 by kan man
Bugger
Only recently bought a Prefx/Armagedon. Will be feeling a bit shafted if I discover there's an improved Armagedon on the way as well. Faith will be restored if there's an upgrade path at incremental cost.
Regards
Steve
Only recently bought a Prefx/Armagedon. Will be feeling a bit shafted if I discover there's an improved Armagedon on the way as well. Faith will be restored if there's an upgrade path at incremental cost.
Regards
Steve
Posted on: 16 March 2003 by Eric Barry
I use an Ittok cable with BNCs with my SME. I have also tried a OL rewired Rega (no dif).
--Eric
--Eric
Posted on: 16 March 2003 by JeremyB
Andy,
I both agree and disagree:
Twisted pair has a first order pole at around 70kHz IIRC. If that was the end of the story, we may not have a problem. The problem is that after that there are pole/zero pairs which provide the sensitivity (zeroes) and selectivity (poles) to "tune in" RF signals which of course can be demodulated by the input stage band-pass characteristic. As you say the "RF" frequency may not be that high anyway and may be in the pass band of the phono amp. The Atomic Clock in Colarado transmits at 60kHz - happily I believe the modulation is too low to be audible!
What it doesn't help with is RF interference, for that shielding, and circuit design is the only way to eliminate it reliably.
I agree that the differential input configuration does not directly remove RFI (it could actually make it worse if the impedance to ground is very high). However, with reasonable component tolerances (1%) it should be possible to get 35-40dB CMR over the audio band. In theory the audio qualities would not be affected (no need to change the band pass for the differential signal). For eliminating radio station pickup, there is no need to have good CMR at higher frequencies since the signal cannot now be demodulated.
Bipolar stages need degeneration (worsening noise figures) or FET inputs (higher input capacitance, usually higher noise for MC).
I agree. Note that a fully differential cascode input configuration should mitigate these tradeoffs and enable reasonably low noise.
Ansy, when can you knock one together? (everything I ever built measured really well but sounded crap or visa versa...)
I both agree and disagree:
quote:
The difference between phones and phono stages though is the bandwidth - you'd need a phono stage capable of rejecting any interference (common-mode signal) over the full audio band, possibly beyond.
Twisted pair has a first order pole at around 70kHz IIRC. If that was the end of the story, we may not have a problem. The problem is that after that there are pole/zero pairs which provide the sensitivity (zeroes) and selectivity (poles) to "tune in" RF signals which of course can be demodulated by the input stage band-pass characteristic. As you say the "RF" frequency may not be that high anyway and may be in the pass band of the phono amp. The Atomic Clock in Colarado transmits at 60kHz - happily I believe the modulation is too low to be audible!
What it doesn't help with is RF interference, for that shielding, and circuit design is the only way to eliminate it reliably.
I agree that the differential input configuration does not directly remove RFI (it could actually make it worse if the impedance to ground is very high). However, with reasonable component tolerances (1%) it should be possible to get 35-40dB CMR over the audio band. In theory the audio qualities would not be affected (no need to change the band pass for the differential signal). For eliminating radio station pickup, there is no need to have good CMR at higher frequencies since the signal cannot now be demodulated.
Bipolar stages need degeneration (worsening noise figures) or FET inputs (higher input capacitance, usually higher noise for MC).
I agree. Note that a fully differential cascode input configuration should mitigate these tradeoffs and enable reasonably low noise.
Ansy, when can you knock one together? (everything I ever built measured really well but sounded crap or visa versa...)
Posted on: 16 March 2003 by Willy
Question is, are there plans to make a Prefix that would take full advantage of the multiple supplies in a Supercap?
Put my name down for one of those.
Willy.
Put my name down for one of those.
Willy.
Posted on: 16 March 2003 by Andrew L. Weekes
quote:
Andy, when can you knock one together? (everything I ever built measured really well but sounded crap or visa versa...)
Sounds like I don't need to anymore, Naim have beaten me to it...
I never get excited about topology either, just results.
Andy.
Posted on: 25 December 2003 by silklee
quote:
Originally posted by Paul Stephenson:
This unit is not yet available for sale, we are doing field tests around the world. So far the RF results are good, the performance has also been improved. More news later after ALL OF OUR TESTS ARE COMPLETE.
Hi,
is the new unit which solves the RF problems for sale now?
Posted on: 25 December 2003 by Mick P
I have one and it is very good.
Regards
Mick
Regards
Mick
Posted on: 25 December 2003 by Top Cat
Hmmm... very interested. How much does the new prefix cost (fitted, UK)?
It seems to be the obvious choice for an LP12/Aro/Armageddon, but my dealer tells me that the old Prefix (K?) might not be so suitable as I live less than a mile from a large radio or telly mast (don't know which). Not had any problems to speak of in the past, but I'd hate to get one in place to find it picks up a lot of interference.
One other question. If one hypothetically was looking to buy an olive-era Supercap, to run initially into an 82 and later into a 52, would powering a modern prefix this way sound better than dedicating the hicap that I currently have to it, and saving the Supercap for the preamp?
I know the answer is to try it, but it'll be a wee while before I'm in a position to go 52/SC, and I'd like to do a bit of research first of all...
John
TC '..'
"Sun went down in honey. Moon came up in wine. Stars were spinnin' dizzy, Lord, the band kept us so busy we forgot about the time."
It seems to be the obvious choice for an LP12/Aro/Armageddon, but my dealer tells me that the old Prefix (K?) might not be so suitable as I live less than a mile from a large radio or telly mast (don't know which). Not had any problems to speak of in the past, but I'd hate to get one in place to find it picks up a lot of interference.
One other question. If one hypothetically was looking to buy an olive-era Supercap, to run initially into an 82 and later into a 52, would powering a modern prefix this way sound better than dedicating the hicap that I currently have to it, and saving the Supercap for the preamp?
I know the answer is to try it, but it'll be a wee while before I'm in a position to go 52/SC, and I'd like to do a bit of research first of all...
John
TC '..'
"Sun went down in honey. Moon came up in wine. Stars were spinnin' dizzy, Lord, the band kept us so busy we forgot about the time."
Posted on: 25 December 2003 by Chris Bell
The RF proff Prifix has worked without fault for some time now. Seattle is a RF rich environment, so my guess is that it will work most cases. You can borrow a unit from your dealer and plug it into your 52 to test. It does not need to be installed to test for RF.
It sounds great as well.
Chris Bell
It sounds great as well.
Chris Bell
Posted on: 27 December 2003 by Brendan Price
To Paul Stephenson,
could you give us an approximation of how long it will take to have the improved circuit Prefix in production? I am in the market for one , but I live near some TV antennae , and I'd prefer to wait for the newer Prefix.
Brendan
could you give us an approximation of how long it will take to have the improved circuit Prefix in production? I am in the market for one , but I live near some TV antennae , and I'd prefer to wait for the newer Prefix.
Brendan
Posted on: 27 December 2003 by FangfossFlyer
How about a sound comparison between the old and new Prefix anyone?
Does thenew Prefix sound better or has the RF mod degraded the sound quality?
Richard
Does thenew Prefix sound better or has the RF mod degraded the sound quality?
Richard
Posted on: 27 December 2003 by John
Richard, I had my S prefix updated and the sonic improvements were significant. Lower noise floor, more transparent, more dynamic, etc. Well worth the $100.
John
John