Here is Vogels Cap Tester. He claimes that he can not hear a 1000uF 25V Pannasonic FM in that position. The OPA627 is excellent but expensive. You can use an OPA134 or the better OPA1641 here. The OPA827 is even better then the OPA627 and less expensive. Still the OPA627 is hard to beat in speed and this is important because the gain is 1000 here and with lower the bandwidth of the Opamp by GB:1000.
The king whould be the Analog Devices OPA627 substitute ADA4627. It comes in at about 10,- € and has linear output current of 45mA, nearly double then the OPA627.
When you listen to headphones make sure you do not overdrive the Opamp. An AKG701 will not work well here. You could use a buffer like the BUF634 of cause or any other good headphone amp modified for a gain of 1000 provided you are left with enough bandwidth.
The king whould be the Analog Devices OPA627 substitute ADA4627. It comes in at about 10,- € and has linear output current of 45mA, nearly double then the OPA627.
When you listen to headphones make sure you do not overdrive the Opamp. An AKG701 will not work well here. You could use a buffer like the BUF634 of cause or any other good headphone amp modified for a gain of 1000 provided you are left with enough bandwidth.
Before i build the Transformer-Inductive RIAA with the Josi i made an OPamp version as proove of concept. I chose the Lundahl LL9226 because it as 4 primary and 4 secondary windings so a lot of options are posibe. It has an amorfous cobalt core and after a discussion with Brian Sowter i am convinced that it does not have any technical advantage over a mu-metal core but a lot of people i respect tell me that amorfous core sounds more transparent. Anyway, a good Sowter whould do as well i think and i will compare a similar model from Sowter with mu-metal core in the future. I use the Lundahl with 1:10 gain with my Lyra Titan i. Then the Lundahl has an input DC impedance of slightly under 5 Ohm so will worsen the SN of the Lyra alone by only 3dB.
In noise voltage that means it goes up from 0.3nV/qHz to 0.4nV/qHz and that is excellent. For the Audio Note IO i whould use the 1:20 connection. Then the DC input impedance is slightly over 1 Ohm and that whould worsen the SN of the IO alone again by only 3dB. See a photo of my prototype. I will post the circuit later today. Sofar i do not use a zobel at the secondary, only a 47.5Kohm resistor. I may try something like 6.8kOhm and 200pF.
In noise voltage that means it goes up from 0.3nV/qHz to 0.4nV/qHz and that is excellent. For the Audio Note IO i whould use the 1:20 connection. Then the DC input impedance is slightly over 1 Ohm and that whould worsen the SN of the IO alone again by only 3dB. See a photo of my prototype. I will post the circuit later today. Sofar i do not use a zobel at the secondary, only a 47.5Kohm resistor. I may try something like 6.8kOhm and 200pF.
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I am listening to the Transformer coupled RIAA and the sound is downright amasing. Very transparent and dynamic. Of cause hum and hiss are no issue here. I can hear no treble loss whatsoever. This Lundahl is the first transformer i heard that can compete with my electronic stages in terms of treble resolution and i had some very expensive ones here.
They all had an audible loss of transient behavious but not this time. I asume that the Lundahl must go over 100kHz in the 1:10 connection, a point where the cutter head is already 15dB down when i can trust the Neumann manual. It is not inexpensive at 207,-€ a pair i payed including shipping but it is worth the money. Other transformers cost even much more and are no better. At least i have not heard one. If the Sowter 8055 is any better i do not know but i will find it out. This listening experience was quite a shock after the Phonoman AC and i was seriously considering to build in a pole at 20kHz. When i looked again at the RIAA components i saw the desaster. I had connected two caps wrong so no wonder it sounded dark. Frequency response is the most important issue in High End design and when your Phonostage sounds sharp or dark it may not by the Opamps or choise of Components but simply a bended frequency response. I do not say that all components with flat response sound the same but it is a very important ingredient plus exact level matching when you compare the sound of two electronic stages. I am happy that i could trust my ears.
They all had an audible loss of transient behavious but not this time. I asume that the Lundahl must go over 100kHz in the 1:10 connection, a point where the cutter head is already 15dB down when i can trust the Neumann manual. It is not inexpensive at 207,-€ a pair i payed including shipping but it is worth the money. Other transformers cost even much more and are no better. At least i have not heard one. If the Sowter 8055 is any better i do not know but i will find it out. This listening experience was quite a shock after the Phonoman AC and i was seriously considering to build in a pole at 20kHz. When i looked again at the RIAA components i saw the desaster. I had connected two caps wrong so no wonder it sounded dark. Frequency response is the most important issue in High End design and when your Phonostage sounds sharp or dark it may not by the Opamps or choise of Components but simply a bended frequency response. I do not say that all components with flat response sound the same but it is a very important ingredient plus exact level matching when you compare the sound of two electronic stages. I am happy that i could trust my ears.
After repair the Phonoman AC sounds much more balanced. The circuit diagram is correct.
I had calculated successfully of a lot off various shunt feedback stages and they all worked perfectly well. How whould i rate the soundquality ? A difficult question. If you have not heard circuits like the High Z and Low Z MPP, the discrete INA, my latest Transconductance or Transformer-Inductor stages you may find nothing wrong. There is no colouration. The sound is lively and dynamic with no audible distortion. Where it is lacking is in the finer details. For example the track " Maybe You´ll Be There " from the fantastic Diana Krall Album " Life In Paris". There is a problem on this track that sounds like misstracking on lesser stages. She sings and you hear a strage noise at two incidences delayed by maybe 1/4 of a second. On lesser stages this simply sounds like noise from misstracking. The Phonoman AC is two notches better and you can hear that this is a distorted echo of here voice. You start to understand parts of the text a second time delayed and slightly distorted. On the Transformer-Inductive or TI as i will call it you clealy hear a delayed version of her voice including perfectly understandable text. The delayed voice is strangely thin because some harmonic content in the lower reaches are missing but does not sound distorted any more. More like it was elctronically modified and delayed not much different then the computer voices you hear on early startreck movies but without the rustling " roboter voice". Deleniated and resolved that way it is much less objectionable. Also on the TI it is clearly audible that this delayed and manipulated voice of hers does not come from the same space. In fact it is some meters to the right, a bit up and smaller in size. You may ask me what pill i have taken to be able to describe this. Well nothing. I can show the effect to anybody that has some experience with judging sound or even a totally naive person that has the ears intact. Without me telling what to listen for this person would be of cause totally lost or overwhelmed.
I am very happy that my frontend is that stabe since over one years. I only made a small adjustment to the downpreasure some weeks ago and that is all. I am really surprised how robust the Titan i is. I have really abused it many times when i developed the early Transimpedance stages with considerable DC into the catridge but it never gives up and shows me new extremely delicate information virtually every time i improve my system. Mishima San, Jonathan and Stig, this is a masterpiece. I am very happy that i count such brilliant creators as my friends. Also thanks Allen, for building such a warship of a table and thanks to Try for supplying me with the Triplanar. Herb Papier, the creator is long dead. He was my friend too and i am very happy that the legend lifes on with your fantastic craftsmenship that even improved the finish of the older versions. I am a happy man.
I had calculated successfully of a lot off various shunt feedback stages and they all worked perfectly well. How whould i rate the soundquality ? A difficult question. If you have not heard circuits like the High Z and Low Z MPP, the discrete INA, my latest Transconductance or Transformer-Inductor stages you may find nothing wrong. There is no colouration. The sound is lively and dynamic with no audible distortion. Where it is lacking is in the finer details. For example the track " Maybe You´ll Be There " from the fantastic Diana Krall Album " Life In Paris". There is a problem on this track that sounds like misstracking on lesser stages. She sings and you hear a strage noise at two incidences delayed by maybe 1/4 of a second. On lesser stages this simply sounds like noise from misstracking. The Phonoman AC is two notches better and you can hear that this is a distorted echo of here voice. You start to understand parts of the text a second time delayed and slightly distorted. On the Transformer-Inductive or TI as i will call it you clealy hear a delayed version of her voice including perfectly understandable text. The delayed voice is strangely thin because some harmonic content in the lower reaches are missing but does not sound distorted any more. More like it was elctronically modified and delayed not much different then the computer voices you hear on early startreck movies but without the rustling " roboter voice". Deleniated and resolved that way it is much less objectionable. Also on the TI it is clearly audible that this delayed and manipulated voice of hers does not come from the same space. In fact it is some meters to the right, a bit up and smaller in size. You may ask me what pill i have taken to be able to describe this. Well nothing. I can show the effect to anybody that has some experience with judging sound or even a totally naive person that has the ears intact. Without me telling what to listen for this person would be of cause totally lost or overwhelmed.
I am very happy that my frontend is that stabe since over one years. I only made a small adjustment to the downpreasure some weeks ago and that is all. I am really surprised how robust the Titan i is. I have really abused it many times when i developed the early Transimpedance stages with considerable DC into the catridge but it never gives up and shows me new extremely delicate information virtually every time i improve my system. Mishima San, Jonathan and Stig, this is a masterpiece. I am very happy that i count such brilliant creators as my friends. Also thanks Allen, for building such a warship of a table and thanks to Try for supplying me with the Triplanar. Herb Papier, the creator is long dead. He was my friend too and i am very happy that the legend lifes on with your fantastic craftsmenship that even improved the finish of the older versions. I am a happy man.
There are various recording clues in that Krall's live. You can also clearly hear the breathing of the noise gates opening with some keystrokes in her solo piano & vocal Joni Mitchell fellow Canadian's cover* in that album. Listen to that through different systems.
Also the cavernous hand clapping in Blue Eyes's Under My Skin cover. Not as many individual hands through all systems etc.
*That one Mitchell song in the video, not the same performance as included in the album though.
YouTube - A Case of You: Diana Krall
P.S. Yes the front end is the key and I was fortunate I could a few times test my contraptions through a friend's system that has this little beast in the photos, but I have also seen there that the phono stage can make or break the investment if it masks. I think that this German cart in the photo could hold its own right before a Lyra Titan**, although I am not sure because I have heard them in different systems. I also liked the Transfiguration on an Avid Reference with Dynavector DV507MK2 arm as well as MySonicLab Eminent cart on a VPI HR-X.
**Brand name and carts all got Greek names when no obvious relation, what's the story?
Also the cavernous hand clapping in Blue Eyes's Under My Skin cover. Not as many individual hands through all systems etc.
*That one Mitchell song in the video, not the same performance as included in the album though.
YouTube - A Case of You: Diana Krall
P.S. Yes the front end is the key and I was fortunate I could a few times test my contraptions through a friend's system that has this little beast in the photos, but I have also seen there that the phono stage can make or break the investment if it masks. I think that this German cart in the photo could hold its own right before a Lyra Titan**, although I am not sure because I have heard them in different systems. I also liked the Transfiguration on an Avid Reference with Dynavector DV507MK2 arm as well as MySonicLab Eminent cart on a VPI HR-X.
**Brand name and carts all got Greek names when no obvious relation, what's the story?
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I really enjoy DK's performances and have most of her CDs/SACDs. I have "Live in Paris" in DVD...is the noise also present on this version or the CD?...I take it you are listening vinyl? Where exactly on the song will I listen to for this anomaly?...I'll listen tonight when it is quieter.
I love that song. I have all Joni albums until she got on CD. I have a few CDs too.
Tomorrow i will publish the most important parts of the schematic of the TI. I plan to make the Sowter coils available but they are very expensive because i can only afford that Sowter makes them piece by piece. I tryed other coils with varying success but only the Sowter was dead quiet. That Mu-Metal is an amasing material and got also very expensive over the last years. I not only need perfect shielding but also tight tolerance in DC value and inductance and they did a great job on that too.
i will also try to explain why this stage sounds so amasing transparent even with IC Opamps. One clear reson i can tell you right away. Burkhard Vogel build two MC Phonostages. One with a Jensen transformer at the input and one with low noise bipolars. When i look at his noise plots i can see no difference until 100 Hz. Then the transformer really comes into it´s own and has a 7dB advantage there. The reason is the low DC impedance in the transformer. Even the best transistors have some 1/F noise in the lower reaches and the transformer is simply a 5Ohm resistor ( in this case ) and the impedance rise at higher frequencies has only an imaginary part. There are other reasons and one the the inductive input stage. I will explain more tomorrow.
Tomorrow i will publish the most important parts of the schematic of the TI. I plan to make the Sowter coils available but they are very expensive because i can only afford that Sowter makes them piece by piece. I tryed other coils with varying success but only the Sowter was dead quiet. That Mu-Metal is an amasing material and got also very expensive over the last years. I not only need perfect shielding but also tight tolerance in DC value and inductance and they did a great job on that too.
i will also try to explain why this stage sounds so amasing transparent even with IC Opamps. One clear reson i can tell you right away. Burkhard Vogel build two MC Phonostages. One with a Jensen transformer at the input and one with low noise bipolars. When i look at his noise plots i can see no difference until 100 Hz. Then the transformer really comes into it´s own and has a 7dB advantage there. The reason is the low DC impedance in the transformer. Even the best transistors have some 1/F noise in the lower reaches and the transformer is simply a 5Ohm resistor ( in this case ) and the impedance rise at higher frequencies has only an imaginary part. There are other reasons and one the the inductive input stage. I will explain more tomorrow.
It reflects a higher Z that helps the NF-Signal Source Resistance curve of the input devices particularly under 1/F in other words.
You can see it that way. Transformers are complicated animals and i have great admiration for people like Lundahl, Jensen and Sowter who do wonderfull work.
By the way Diana Krall sings "Each time i see a croud of people" and then shortly after you here the echo. Diana is maybe 2 meters right before my ears, bigger then live so i asume that her voice was recorded with a nearfield microfon ( no, i am sure, you can see it on the DVD). The strange echo comes shortly later. It is 2m to the right, slightly higher then here voice, around 3 to 5 m away, around 10cm in diameter. I can not exactly hear how deep it is, it is a function of my rather shallow room that does not allow as much cavernous depth then my old room and does not differentiate the depth dimension as well.
By the way Diana Krall sings "Each time i see a croud of people" and then shortly after you here the echo. Diana is maybe 2 meters right before my ears, bigger then live so i asume that her voice was recorded with a nearfield microfon ( no, i am sure, you can see it on the DVD). The strange echo comes shortly later. It is 2m to the right, slightly higher then here voice, around 3 to 5 m away, around 10cm in diameter. I can not exactly hear how deep it is, it is a function of my rather shallow room that does not allow as much cavernous depth then my old room and does not differentiate the depth dimension as well.
Probably a side-fill stage monitor that they faded down after they heard it could be picked up.
Okay 3rd's the charm with "crowd"
I went and listened to this song several times including the first 4 she sang just to listen and get the feel of the stage/performance. It is obvious that there is some very subtle echo but more apparent when she talks to the audience in between songs. On "Maybe You'll Be There" she speaks before singing (probably not on vinyl and cd) and the echo is there but not as you described with delay. So is at the start as the orchestra comes in softly and DK begins the song with "Each time I see a crowd of people..." I don't hear echoing as bad as you described. Maybe it was cleaned up on the mastering of the DVD?
By the way, the stage is quite intimate with the performers bunched up close. Her right side to the audience, DK plays an open Steinway with a mic right close to her lips (breathing/lips and mouth sounds between lyrics captured); to her left and slightly behind are the drums; left and behind is the guitar; behind this guitarist are the percussions; immediately to her left is the stand-up bass; left and front is another acoustic guitar; behind the bass is the conductor and the orchestra with it being 3-4 rows deep; the back of the orchestra is thick floor to ceiling stage curtains about 15-18ft high; there's also a pair of mics hanging above the orchestra seen on the 4th song as the camera pans from above and front. Overall the performance, music and sound are first rate, IMO. I've seen it over and over so I was quite surprised I missed the anomaly you described...maybe on vinyl only?
Well, then this is an artefact of the vinyl. I will now try to get the digital version and do a comparison too.
I promissed to explain the TI circuit more. As i already mentioned the transformer coupling has the advantage of better SN under 100Hz. When you look where the inductor is placed you can see that it has the same kind of advantage. In most stages you find a resistor where the coil now is and that resistor i usualy between 200 and 400 Ohm. Noise wise it is in series with the signal so worsens SN by it´s Johnson noise.
The inductor on the other hand has only several Ohms at DC so again has the edge in SN at lower frequencies. The TI stage has also a totally diffent gain structure then more conventional solutions. I do the 50Hz breakpoint in the first stage and the treble shelf in the second stgae. So the first stage has a gain that falls by 6dB/octave over 50Hz. First it has the advantage that the feedback factor of a typical Opamp will be maitained and constant up to high frequencies because the open loop gain of an OPamp also falls by 6dB/oct. Second it makes the slewrate of the incomming signal really slow so that the second stage sees a very easy to handle signal, even when the input contains high energy, wideband spikes from scratches and dirt on the vinyl.
I put a servo into that stage because it has a lot of DC gain. To not desturb the accuracy of the shaping action of the coil, the resistor in series with the servo has to be as big as posible because the coil sees it virtually in parallel to ground. I found that values over 100kOhm do no harm but it is a delicate game now. You have to use an OP with good DC precission or the servo does not have enough authority. The OPs i show in the schematic worked well. After the first stage is an R-C combination that sets a pole at 2.2usec compensating for the forth time constant that comes from the fact that a series feeback stage can not have gain under 1. That time constant is shifted higher and higher when the DC gain of the series feedback gets up so circuits with high gain have less of a problem here then circuits with low gain. Anyway, that pole can be perfectly handled by the R-C combination. When you take out the 2.2nF and substitute it with a 10kOm resistor you have the infamous Neumann pole handy.
The putput stage simply does a shelf in the treble to restore the resulting frequency response. That stage does not have much to do and i did not use a coil here because you can get very high quality 0.1uF caps even Teflon that do the job perfectly well.
What i also like as a side effect is that the cap is in series with the OPamp to ground,
so makes the DC gain of the output stage 1 so with a precession Opamp a servo or a coupling cap is not necessary. I use the LME4913 here, one of the few current feedback amps that work well in a non inverting circuit. It has he advantage of high speed and can shift of to 100mA clean so you can also connect a headphone at the outpt or drive very long cables. In case of a headphone i whould use a 10 Ohm resistor in series. You could also try a potmeter, somewhere between 200 and 500 Ohm for volume control in front of the headphone.
I promissed to explain the TI circuit more. As i already mentioned the transformer coupling has the advantage of better SN under 100Hz. When you look where the inductor is placed you can see that it has the same kind of advantage. In most stages you find a resistor where the coil now is and that resistor i usualy between 200 and 400 Ohm. Noise wise it is in series with the signal so worsens SN by it´s Johnson noise.
The inductor on the other hand has only several Ohms at DC so again has the edge in SN at lower frequencies. The TI stage has also a totally diffent gain structure then more conventional solutions. I do the 50Hz breakpoint in the first stage and the treble shelf in the second stgae. So the first stage has a gain that falls by 6dB/octave over 50Hz. First it has the advantage that the feedback factor of a typical Opamp will be maitained and constant up to high frequencies because the open loop gain of an OPamp also falls by 6dB/oct. Second it makes the slewrate of the incomming signal really slow so that the second stage sees a very easy to handle signal, even when the input contains high energy, wideband spikes from scratches and dirt on the vinyl.
I put a servo into that stage because it has a lot of DC gain. To not desturb the accuracy of the shaping action of the coil, the resistor in series with the servo has to be as big as posible because the coil sees it virtually in parallel to ground. I found that values over 100kOhm do no harm but it is a delicate game now. You have to use an OP with good DC precission or the servo does not have enough authority. The OPs i show in the schematic worked well. After the first stage is an R-C combination that sets a pole at 2.2usec compensating for the forth time constant that comes from the fact that a series feeback stage can not have gain under 1. That time constant is shifted higher and higher when the DC gain of the series feedback gets up so circuits with high gain have less of a problem here then circuits with low gain. Anyway, that pole can be perfectly handled by the R-C combination. When you take out the 2.2nF and substitute it with a 10kOm resistor you have the infamous Neumann pole handy.
The putput stage simply does a shelf in the treble to restore the resulting frequency response. That stage does not have much to do and i did not use a coil here because you can get very high quality 0.1uF caps even Teflon that do the job perfectly well.
What i also like as a side effect is that the cap is in series with the OPamp to ground,
so makes the DC gain of the output stage 1 so with a precession Opamp a servo or a coupling cap is not necessary. I use the LME4913 here, one of the few current feedback amps that work well in a non inverting circuit. It has he advantage of high speed and can shift of to 100mA clean so you can also connect a headphone at the outpt or drive very long cables. In case of a headphone i whould use a 10 Ohm resistor in series. You could also try a potmeter, somewhere between 200 and 500 Ohm for volume control in front of the headphone.
