buffer is good but...
This circuit can be useful if, for instance, your cd player (or preamp...) has a high output impedance and/or only one op-amp with no buffer.
Let me explain.
I tweaked a Marantz cd-player and one of the mods was changing the two series 100 ohm (for a total of 200) resistors on the output, after the op-amp, by one 47 ohm resistor.
You would not believe the improvement.
The player stays much less sensitive to the quality of the interconnect.
Naim cd players have 10 ohms of output impedance, they shure know what they are doing.
There are cd players and preamps with output impedances of hundreds and even 1k - 2k ohms!
In these cases this circuit may work very well indeed.
But you may not notice anything on a well engineered high-end product like a top of the range cd player with variable output like the top Wadia, or even Mark Levinson.
Do you know why?
Because they have on the ouput OPA2132 and BUF634.
This circuit can be useful if, for instance, your cd player (or preamp...) has a high output impedance and/or only one op-amp with no buffer.
Let me explain.
I tweaked a Marantz cd-player and one of the mods was changing the two series 100 ohm (for a total of 200) resistors on the output, after the op-amp, by one 47 ohm resistor.
You would not believe the improvement.
The player stays much less sensitive to the quality of the interconnect.
Naim cd players have 10 ohms of output impedance, they shure know what they are doing.
There are cd players and preamps with output impedances of hundreds and even 1k - 2k ohms!
In these cases this circuit may work very well indeed.
But you may not notice anything on a well engineered high-end product like a top of the range cd player with variable output like the top Wadia, or even Mark Levinson.
Do you know why?
Because they have on the ouput OPA2132 and BUF634.
terminating resistors
No. I have done many and many listening tests, blind tests, switch-box tests. Low output impedance is not enough. The terminating resistor at the second end of output cable is a must. All of the effect disappears in case you do not use it. The best result is: 50 Ohms in series with cable (R10, buffer output resistor) and 50 Ohms as a terminating resistor (R12). Omitt R12 and everything has gone ..
Also 0 Ohms (direct buffer output) without terminating resistor at the cable end gives no sonic result.
No. I have done many and many listening tests, blind tests, switch-box tests. Low output impedance is not enough. The terminating resistor at the second end of output cable is a must. All of the effect disappears in case you do not use it. The best result is: 50 Ohms in series with cable (R10, buffer output resistor) and 50 Ohms as a terminating resistor (R12). Omitt R12 and everything has gone ..
Also 0 Ohms (direct buffer output) without terminating resistor at the cable end gives no sonic result.
Hi PMA,
Does it have to be RG58 network cable?
Is there an explanation for this?
I mean, that cable has a 50 ohm impedance (I used to work with that many years ago ), but would a 75 ohm cable and resistor give the same effect?
Have you tried other cable types?
You could use a T BNC plug in the end, and a BNC 50 ohm terminator.
That's how it's done in computer networks.
Well... not anymore.
Now it's UTP, SFTP...
Does it have to be RG58 network cable?
Is there an explanation for this?
I mean, that cable has a 50 ohm impedance (I used to work with that many years ago
), but would a 75 ohm cable and resistor give the same effect?Have you tried other cable types?
You could use a T BNC plug in the end, and a BNC 50 ohm terminator.
That's how it's done in computer networks.Well... not anymore.
Now it's UTP, SFTP...
fmak said:
Yes, that is perfectly right until you start to use the buffer. All of that commercial electronics is terribly influenced by the components you have described. Not by the foil cap, but input capacitance of power amp etc. But as I said, nobody who did not try believes. I am sorry guys, this is just waisting my time.
--------------------------------------------------------------------PMA said:
I have exactly the circuit built into the output stage of my DAC. I don't actually find that it sounds that good comapred to other DACs and there are suggestions by others (review magazines) that you should jump it and take the output straight out of the output opamp. The unit is the Assemblage 3.1 Platinum.
Active cable
Just a comment with no intention to criticize.
Why are you calling this project an active cable? It is really a preamp/buffer which feeds a cable as it should with little or no loss.
An active cable is something different, as far as I know. It's a cable that is polarized in some way using a battery or supply.
Right now I can't seem to find the files I had downloaded on such projects, to mention some URLs.
Synergistic Research manufactures some active cables and charges a lot for them.
Carlos
Just a comment with no intention to criticize.
Why are you calling this project an active cable? It is really a preamp/buffer which feeds a cable as it should with little or no loss.
An active cable is something different, as far as I know. It's a cable that is polarized in some way using a battery or supply.
Right now I can't seem to find the files I had downloaded on such projects, to mention some URLs.
Synergistic Research manufactures some active cables and charges a lot for them.
Carlos
Carlmart:
Demian Martin has a patent on a DC biased-shield cable. One of Demian's principle goals was to bias the dielectric so that it never changed polarity.
Patent link:
http://patft.uspto.gov/netacgi/nph-...,307,416.WKU.&OS=PN/5,307,416&RS=PN/5,307,416
Bootstrapped (driven) shielding is occasionally discussed in opamp and buffer amp data sheets and application notes, and these can be seen in the data sheets from IC manufacturers such as TI
http://www.scanti.ru/docs/datasheets/sbos003.pdf , Figure 13,
and National Semiconductor
http://www.national.com/ds/LH/LH0033.pdf , page 10.
hth, jonathan carr
Demian Martin has a patent on a DC biased-shield cable. One of Demian's principle goals was to bias the dielectric so that it never changed polarity.
Patent link:
http://patft.uspto.gov/netacgi/nph-...,307,416.WKU.&OS=PN/5,307,416&RS=PN/5,307,416
Bootstrapped (driven) shielding is occasionally discussed in opamp and buffer amp data sheets and application notes, and these can be seen in the data sheets from IC manufacturers such as TI
http://www.scanti.ru/docs/datasheets/sbos003.pdf , Figure 13,
and National Semiconductor
http://www.national.com/ds/LH/LH0033.pdf , page 10.
hth, jonathan carr
DRIVING THE SHIELD.
Hi,
Yes, and I can show work of L'Audiophile for which magazine I contributed for a number of years that explained these principles well before this got patented...our mistake.
The active cable driver does more than that however but unless you need to deal with severe impedance mismatches between sender and receiver I feel it's rather superfluous.
The idea behind it is to treat the interlink as a transmissionline, I've explained my thoughts about that in the " Blind Listening test" thread at great length and have been told a few times that this shouldn't be an issue at audio frequencies.
I disagree, it does and here is one reason why cables do sound different: diferent transmission line will give you different sound, all else being kept equal.
Cheers,
Hi,
Yes, and I can show work of L'Audiophile for which magazine I contributed for a number of years that explained these principles well before this got patented...our mistake.
The active cable driver does more than that however but unless you need to deal with severe impedance mismatches between sender and receiver I feel it's rather superfluous.
The idea behind it is to treat the interlink as a transmissionline, I've explained my thoughts about that in the " Blind Listening test" thread at great length and have been told a few times that this shouldn't be an issue at audio frequencies.
I disagree, it does and here is one reason why cables do sound different: diferent transmission line will give you different sound, all else being kept equal.
Cheers,
Hi Frank:
Don't worry about the patent. I don't think that Demian has enough money to successfully prosecute any infringement case.
Regarding the rest of your post, I do use bootstrapped shielding on occasion, but my main reason is not impedance matching, but rather to null out load capacitances.
regards, jonathan carr
Don't worry about the patent. I don't think that Demian has enough money to successfully prosecute any infringement case.
Regarding the rest of your post, I do use bootstrapped shielding on occasion, but my main reason is not impedance matching, but rather to null out load capacitances.
regards, jonathan carr
Patent
"Don't worry about the patent. I don't think that Demian has enough money to successfully prosecute any infringement case. "
I am waiting for them to sue manfactures of phantom powered microphones. I did sell an AES/EBU digital cable with a biased shield that sounded very good. There was actually an optimum bias voltage for the cable. It used a topology outside the scope of the patent. One could drive the shield with an amplifier with a DC offset to acheive both the usual objectives for an "active shield" type cable.
Many metalized film caps also sound better with a bias voltage, even on a SPDIF digital interface. It maybe that the electrostactic force creates a more stable capacitance value from the plates not moving as much with signal. This is about ten year old technology for the audio tweakers by the way.
"Don't worry about the patent. I don't think that Demian has enough money to successfully prosecute any infringement case. "
I am waiting for them to sue manfactures of phantom powered microphones. I did sell an AES/EBU digital cable with a biased shield that sounded very good. There was actually an optimum bias voltage for the cable. It used a topology outside the scope of the patent. One could drive the shield with an amplifier with a DC offset to acheive both the usual objectives for an "active shield" type cable.
Many metalized film caps also sound better with a bias voltage, even on a SPDIF digital interface. It maybe that the electrostactic force creates a more stable capacitance value from the plates not moving as much with signal. This is about ten year old technology for the audio tweakers by the way.
Re: DRIVING THE SHIELD.
Cable impedance is not usually an issue at audio frequencies but is a real factor at FR frequencies. Source termination of the cable driver is one approach and terminating the cable with its characteristic impedance is another. I use an RC load termination for the cable at high frequencies without having to drive 50 to 100 ohms at audio frequencies. This also filters RF out of the input to the amplifier. The load of a cable can have a serious effect on the phase margin of the circuit driving the cable. Many people fell that the best bass response and dynamics are achieved by diving cables with a very low impedance. RC load termination has an advantage over source termination in this respect.
http://www.intersil.com/data/elantec/d40954.pdf
http://www.analog.com/UploadedFiles/Application_Notes/180434159AN257.pdf
http://www.analog.com/UploadedFiles/Associated_Docs/362551532.pdf ( page 12)
fdegrove said:Hi,
Yes, and I can show work of L'Audiophile for which magazine I contributed for a number of years that explained these principles well before this got patented...our mistake.
The active cable driver does more than that however but unless you need to deal with severe impedance mismatches between sender and receiver I feel it's rather superfluous.
The idea behind it is to treat the interlink as a transmissionline, I've explained my thoughts about that in the " Blind Listening test" thread at great length and have been told a few times that this shouldn't be an issue at audio frequencies.
I disagree, it does and here is one reason why cables do sound different: diferent transmission line will give you different sound, all else being kept equal.
Cheers,
Cable impedance is not usually an issue at audio frequencies but is a real factor at FR frequencies. Source termination of the cable driver is one approach and terminating the cable with its characteristic impedance is another. I use an RC load termination for the cable at high frequencies without having to drive 50 to 100 ohms at audio frequencies. This also filters RF out of the input to the amplifier. The load of a cable can have a serious effect on the phase margin of the circuit driving the cable. Many people fell that the best bass response and dynamics are achieved by diving cables with a very low impedance. RC load termination has an advantage over source termination in this respect.
http://www.intersil.com/data/elantec/d40954.pdf
http://www.analog.com/UploadedFiles/Application_Notes/180434159AN257.pdf
http://www.analog.com/UploadedFiles/Associated_Docs/362551532.pdf ( page 12)
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.