Dear Upupa Epops,
I never had the intention to offend Dr. Sykora, as I haven't heard anything about the man and/or his designs. I have read many times on this forum that you, Czechs, invented so many substantial things in audio in the past, but - I didn't discuss your self-doubt.
I discussed phonobox as it was manufactured. In it present state it contains obvious engineering flaws.
The owner of the Project is in Austria and the production facility is in Czech. I once found the Czech factory web site, where they wrote that they produce automotive electronics for one German company and Project turntables, phono and headphone electronics as by-product.
I never had the intention to offend Dr. Sykora, as I haven't heard anything about the man and/or his designs. I have read many times on this forum that you, Czechs, invented so many substantial things in audio in the past, but - I didn't discuss your self-doubt.
I discussed phonobox as it was manufactured. In it present state it contains obvious engineering flaws.
The owner of the Project is in Austria and the production facility is in Czech. I once found the Czech factory web site, where they wrote that they produce automotive electronics for one German company and Project turntables, phono and headphone electronics as by-product.
To Dimitri : I take it only like explanation of all story around this preamp and I haven't anything agaist your name for it 
. It is only about how blatantly somebody ( and in this czech manufacture is sales manager " old bolshevic pig " ) know to stealed ideas of others. As I know, Dr. Sýkora don't get any penny. 
. It is only about how blatantly somebody ( and in this czech manufacture is sales manager " old bolshevic pig " ) know to stealed ideas of others. As I know, Dr. Sýkora don't get any penny.
You all probably know this already...
But if you open the phono stage you will find 3 sets of jumpers - 2 on either side at the top and one set at the bottom slightly to the left as you look at it.
The top 2 jumpers are for gain, the bottom one for selecting operation for either MC or MM.
If you are running an MM cart (or a high output MC design) you can move the top 2 jumpers and get higher gain for an MM cart.
Works very well and definitely improves the sound (even when you balance out the volume gain with the volume control on your amp).
I have tried this with a variety of cartridges (the standard K4 cart that comes from Project on the RPM4, the Blue Point Special and a Clearaudio Virtuoso 2) and all benefited.
Sharing - just in case there is anyone out there that does not know the trick.
But if you open the phono stage you will find 3 sets of jumpers - 2 on either side at the top and one set at the bottom slightly to the left as you look at it.
The top 2 jumpers are for gain, the bottom one for selecting operation for either MC or MM.
If you are running an MM cart (or a high output MC design) you can move the top 2 jumpers and get higher gain for an MM cart.
Works very well and definitely improves the sound (even when you balance out the volume gain with the volume control on your amp).
I have tried this with a variety of cartridges (the standard K4 cart that comes from Project on the RPM4, the Blue Point Special and a Clearaudio Virtuoso 2) and all benefited.
Sharing - just in case there is anyone out there that does not know the trick.
So...now I've done it!
Put sockets for fast opamp change. Tried both NE5554/TL071 and OPA2134/134, 134 preferred. +/- pins have 0,1uF to ground. Low noise opamps on the way.
Shorted out C7 elco and removed R9, R8 changed to 4k33.
R1 to 560 to give correct load to MC used.
I really wanted to get rid of all the ceramic caps close to the signal path, but didn't have proper sizes of values at hand.
The 4,7uF at the input gives me nightmares, but couldn't find anything better that was small enough to fit in...pointers welcome.
1000uF caps in the power supply as well as shottky diodes. Weird the the + and - sides of the psu aren't the same...
If there's any interest I'll report back what the owner thinks about the changes in terms of sound quality.
Put sockets for fast opamp change. Tried both NE5554/TL071 and OPA2134/134, 134 preferred. +/- pins have 0,1uF to ground. Low noise opamps on the way.
Shorted out C7 elco and removed R9, R8 changed to 4k33.
R1 to 560 to give correct load to MC used.
I really wanted to get rid of all the ceramic caps close to the signal path, but didn't have proper sizes of values at hand.
The 4,7uF at the input gives me nightmares, but couldn't find anything better that was small enough to fit in...pointers welcome.
1000uF caps in the power supply as well as shottky diodes. Weird the the + and - sides of the psu aren't the same...
If there's any interest I'll report back what the owner thinks about the changes in terms of sound quality.
@Dimitri : when investigating my Pro-Ject Phono Box,
it looks to me like C2 and C5 is pico-Farad instead
of nano-Farad.
Also in the pictures in the PDF they look like
ceramic capacitors, beeing physically to small
to be in the nanofarad-Range.
Especially for C2 in the input section, in series
with R2 /47 kOhm this would have some impact on
the calculations of the input impedance,
as a 47kohm in series with 27 pF will not have
too much effect in the audio band...
In my Phono Box C2 is labeled 27 (underlined),
C5 is labelled 12 (underlined), if they were nano-farad,
the labelling should be n27 or 273 AFAIK.
To me it looks that the purpose of the feedback servo loop
is to create a "virtual" cartridge loading, hence the terminology
"ACTI-DAMP circuit for automatic impedance adjusting"
(badly tranclated from german product description
found on the web).
regards,
Stephan
it looks to me like C2 and C5 is pico-Farad instead
of nano-Farad.
Also in the pictures in the PDF they look like
ceramic capacitors, beeing physically to small
to be in the nanofarad-Range.
Especially for C2 in the input section, in series
with R2 /47 kOhm this would have some impact on
the calculations of the input impedance,
as a 47kohm in series with 27 pF will not have
too much effect in the audio band...
In my Phono Box C2 is labeled 27 (underlined),
C5 is labelled 12 (underlined), if they were nano-farad,
the labelling should be n27 or 273 AFAIK.
To me it looks that the purpose of the feedback servo loop
is to create a "virtual" cartridge loading, hence the terminology
"ACTI-DAMP circuit for automatic impedance adjusting"
(badly tranclated from german product description
found on the web).
regards,
Stephan
Zombie, thanks for your reply. I will measure them
later because I have to unsolder them for measurement.
But I am quite sure they are pico-Farads.
OPA604 has FET inputs as opposed to NJM4580,
NE5532 etc. Many People advise against changing
BJT against FET Types. Did you try OPA604 in the Phonobox?
Also, im am very intersted in Opinions about NJM4580.
It has good-looking specs in my opinion. Some
posts above there was the advice to change them
to NE5532, to come back to the original design.
I have some thoughts that NJM4580 is somewhat
better than NE5532, from the specs.
Thanks,
Stephan
later because I have to unsolder them for measurement.
But I am quite sure they are pico-Farads.
OPA604 has FET inputs as opposed to NJM4580,
NE5532 etc. Many People advise against changing
BJT against FET Types. Did you try OPA604 in the Phonobox?
Also, im am very intersted in Opinions about NJM4580.
It has good-looking specs in my opinion. Some
posts above there was the advice to change them
to NE5532, to come back to the original design.
I have some thoughts that NJM4580 is somewhat
better than NE5532, from the specs.
Thanks,
Stephan
schnulli, I made the mods for a friend. The sound in MC was more detailed etc with OPA604 but noisy. He put in the NJM and the sound was "softer" and less defined but no noise. The best result was with OPA2227 (singel ver - wrote 2228 earlier), good sound, no noise. It's even better in MM mode.
Cheers
Cheers
Stephan wrote > when investigating my Pro-Ject Phono Box,
it looks to me like C2 and C5 is pico-Farad instead of nano-Farad.
Dear Stephan,
I could not check right now, as I don't have the Phonobox at hand.
May be other readers could check?
But R2C2 will be 47*10e3*27*0e-12=1.27us that corresponds 125kHz, so the cartridge will not be loaded at all in audio band.
Stephan wrote > To me it looks that the purpose of the feedback servo loop is to create a "virtual" cartridge loading, hence the terminology "ACTI-DAMP circuit for automatic impedance adjusting" (badly tranclated from german product description found on the web).
If you have the original design by Sykora, mentioned by Upupa Epops could you share?
With R7=330k and C4=0.33uF it will be only integrator, otherwise C6 and R5 are in the wrong place.
Stephan wrote > Also, im am very intersted in Opinions about NJM4580.
Try to add 2k2 resistors between op-amp outputs and –15V rail
it looks to me like C2 and C5 is pico-Farad instead of nano-Farad.
Dear Stephan,
I could not check right now, as I don't have the Phonobox at hand.
May be other readers could check? But R2C2 will be 47*10e3*27*0e-12=1.27us that corresponds 125kHz, so the cartridge will not be loaded at all in audio band.
Stephan wrote > To me it looks that the purpose of the feedback servo loop is to create a "virtual" cartridge loading, hence the terminology "ACTI-DAMP circuit for automatic impedance adjusting" (badly tranclated from german product description found on the web).
If you have the original design by Sykora, mentioned by Upupa Epops could you share?
With R7=330k and C4=0.33uF it will be only integrator, otherwise C6 and R5 are in the wrong place.
Stephan wrote > Also, im am very intersted in Opinions about NJM4580.
Try to add 2k2 resistors between op-amp outputs and –15V rail
Dimitri,
thanks for your reply.
Unfortunately, I do not have additional Information
nor the original design.
But what could be the purpose of having the
integrator in that place. Especially, it you reconnect
R9 as suggested, there will be no DC-Path to the next stage,
so DC offset removal is probably not the intention here.
DC-Removal would only make sense if R9 would be connected
to the output of NJM4580 in my opinion
What would we loose if we remove that TL061 and
all it's associated components at all ?
2K2-Resistors force the NJM4580 into Class-A, right?
Do you think a NE5532 would sound better ?
Thanks,
Stephan
thanks for your reply.
Unfortunately, I do not have additional Information
nor the original design.
But what could be the purpose of having the
integrator in that place. Especially, it you reconnect
R9 as suggested, there will be no DC-Path to the next stage,
so DC offset removal is probably not the intention here.
DC-Removal would only make sense if R9 would be connected
to the output of NJM4580 in my opinion
What would we loose if we remove that TL061 and
all it's associated components at all ?
2K2-Resistors force the NJM4580 into Class-A, right?
Do you think a NE5532 would sound better ?
Thanks,
Stephan
Stephan wrote > But what could be the purpose of having the integrator in that place. Especially, it you reconnect R9 as suggested, there will be no DC-Path to the next stage,
so DC offset removal is probably not the intention here.
I start to think, that the R6C5 network should be connected in series with C4, thus TL061 stage will have -1 gain at ac, so the input resistance will be R5/(1+R4/R3)=40kOhm.
Can you check R6C5 connection in your unit? In mine I checked it triple times.
Stephan wrote > DC-Removal would only make sense if R9 would be connected to the output of NJM4580 in my opinion
Why use R9 and C7 at all if R9 would be connected to the output?
Stephan wrote > What would we loose if we remove that TL061 and all it's associated components at all?
Nothing.
Stephan wrote > 2K2-Resistors force the NJM4580 into Class-A, right?
Yes
Stephan wrote > Do you think a NE5532 would sound better?
I wouldn't like to start a usual flame here but 4580 into class-A is more then enough
so DC offset removal is probably not the intention here.
I start to think, that the R6C5 network should be connected in series with C4, thus TL061 stage will have -1 gain at ac, so the input resistance will be R5/(1+R4/R3)=40kOhm.
Can you check R6C5 connection in your unit? In mine I checked it triple times.
Stephan wrote > DC-Removal would only make sense if R9 would be connected to the output of NJM4580 in my opinion
Why use R9 and C7 at all if R9 would be connected to the output?
Stephan wrote > What would we loose if we remove that TL061 and all it's associated components at all?
Nothing.
Stephan wrote > 2K2-Resistors force the NJM4580 into Class-A, right?
Yes
Stephan wrote > Do you think a NE5532 would sound better?
I wouldn't like to start a usual flame here but 4580 into class-A is more then enough
Hi guys,
the Phonobox / Actidamp II is quite old stuff. Nevertheless, there exists a new product, the CLEARAUDIO BASIC, which is made very similar way (from the same author), and this is assumed to be a flagship of the CLEARAUDIO phono preamp program.
Concerning the opamps: The very best is the AD745 for the MM, AD797 for the MC at the front end, but they are single ones in SOIC package - there is needed an adaptor. The absolute top among duals is Harris HA5222, but it is out of production yet. By measurement, the NE5532 has lowest distortion and very good noise, the JRC/NJM4580 is similar by noise and worse by distortion, but some say it sounds better. The OPA2227 is quite slow, but very good in respect of noise. The brand new AD8672 is very good, too, but it is produced only as SOIC, so again an adaptor is needed.
Concerning the ceramic caps - they introduce a lot of distortion, but some people like the resulting sound. Originally the polypropylene caps were used, the polycarbonates are even beter, but the good polyester work well, too, although they can be found some distorting pieces - probably due the weak winding of the foil.
And, finally, don't fear the bipolar elcaps - at the output voltage of the phono pickup they perform quite well.
By the way, you can follow the offer of Upupa Epops - take the original Actidamp II, although they are better things now, but not as an "open source"...
the Phonobox / Actidamp II is quite old stuff. Nevertheless, there exists a new product, the CLEARAUDIO BASIC, which is made very similar way (from the same author), and this is assumed to be a flagship of the CLEARAUDIO phono preamp program.
Concerning the opamps: The very best is the AD745 for the MM, AD797 for the MC at the front end, but they are single ones in SOIC package - there is needed an adaptor. The absolute top among duals is Harris HA5222, but it is out of production yet. By measurement, the NE5532 has lowest distortion and very good noise, the JRC/NJM4580 is similar by noise and worse by distortion, but some say it sounds better. The OPA2227 is quite slow, but very good in respect of noise. The brand new AD8672 is very good, too, but it is produced only as SOIC, so again an adaptor is needed.
Concerning the ceramic caps - they introduce a lot of distortion, but some people like the resulting sound. Originally the polypropylene caps were used, the polycarbonates are even beter, but the good polyester work well, too, although they can be found some distorting pieces - probably due the weak winding of the foil.
And, finally, don't fear the bipolar elcaps - at the output voltage of the phono pickup they perform quite well.
By the way, you can follow the offer of Upupa Epops - take the original Actidamp II, although they are better things now, but not as an "open source"...
Dimitry,
congratulations :
"I start to think, that the R6C5 network should be connected in series with C4" turned out to be true. Here is what I found in my
Phonobox:
R7 / 330 kohm sits directly between Output 4580, Pin 1
and negative Intput TL061 / Pin 2. C5||R6 is in Series with C4:
Pin 6 TL061 --C4 --(C5||R6)--Pin 1 TL061
Also, C5 and C2 are pico-Farad, not nanofarad. I unsoldered
and measured them to be sure.
What does that tell us ??
Regards,
Stephan
congratulations :
"I start to think, that the R6C5 network should be connected in series with C4" turned out to be true. Here is what I found in my
Phonobox:
R7 / 330 kohm sits directly between Output 4580, Pin 1
and negative Intput TL061 / Pin 2. C5||R6 is in Series with C4:
Pin 6 TL061 --C4 --(C5||R6)--Pin 1 TL061
Also, C5 and C2 are pico-Farad, not nanofarad. I unsoldered
and measured them to be sure.
What does that tell us ??
Regards,
Stephan
Stephan wrote > What does that tell us ??
This is no dc servo, this is so called 'electronic cooling'.
From Marcel van de Gevel EW paper: "When the input stage and feedback network are properly designed, the thermal noise of the 47k resistor shunted across the input is usually the largest remaining noise contribution in the RIAA amplifier itself".
Such connection will lower noise current spectral density from 47k resistor 1+R4/R3 times, but overall s/n ratio will improved 1-3 dB
This is no dc servo, this is so called 'electronic cooling'.
From Marcel van de Gevel EW paper: "When the input stage and feedback network are properly designed, the thermal noise of the 47k resistor shunted across the input is usually the largest remaining noise contribution in the RIAA amplifier itself".
Such connection will lower noise current spectral density from 47k resistor 1+R4/R3 times, but overall s/n ratio will improved 1-3 dB
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