Thanks Reinhard for your analysys. I have not build anything so far and will use this schematic only as a starting point. I am not a tube specialist in any way, so this will be a learning experience. As far as i can see, single ended tube circuits have second harmonic mostly and this symmetric design could be able to supress second.
Some time ago i told you that i found an OPamp that is ideal to complement the Poket Phono to have a headphone amp on board. It is the National LMH6672.
It is designed as a DSL driver and can swing 500mA easyly. It has low distortion, low noise and has a slew rate of 135V/usec so it is very fast.
It is a double Opamp in an SMD package so it needs little space. That was also the reason why this little project was delayed so long. In the beginning a tryed to solder directly to this SMD part and destroyed my collection because i was unsuccessfull. I then had to order more and shipped them to Stefan Horwege that put them on adaptors.
Stefan is specialised in SMD soldering and did the usual good job. This Opamp has a restriction concerning PSU voltage and + - 6.5V is the maximum. This is ideal for the Poket Phono because it runs on + - 5V. When you need more juice you can build an INA and then it can swing double. This is a nearly rail to rail design so it has a maximum output of + - 4V. 8V into the 60 Ohm AKG701 gives 1W of power so it can drive this headphone really load. Cooling of the chip is then necessarry but with 1W on the AKG you land in hospital with Tinitus. This chip swings 20 times more current then the OPA134 in the popular C-Moy, a choice that i never really understood. The OPA134 needs a high impedance phone or it runs out of steam quickly.
I have now a system that i can take to the road with my lightweight Goldring table.
It can even drive a poweramp directly so i could fit a secound input that could be used for a CD player. There is some space left in the ELV cabinet.
I always take my Sennheiser PX200 with me that the Poket Phono drives with ease. I chose this headphone after listening to 20 alternatives at the Münster Media Markt and i liked this one the best of the foldable small ones. It has a surprisingly robust and dynamic sound.
The circuit shown has 10dB of gain and that is more then sufficient. I simply use DC coupling without a problem. Ideally i whould like to use a pot with say 47kOhm but i had some 5Kohm Vishey conductive platic pots lying around that fit.
It is designed as a DSL driver and can swing 500mA easyly. It has low distortion, low noise and has a slew rate of 135V/usec so it is very fast.
It is a double Opamp in an SMD package so it needs little space. That was also the reason why this little project was delayed so long. In the beginning a tryed to solder directly to this SMD part and destroyed my collection because i was unsuccessfull. I then had to order more and shipped them to Stefan Horwege that put them on adaptors.
Stefan is specialised in SMD soldering and did the usual good job. This Opamp has a restriction concerning PSU voltage and + - 6.5V is the maximum. This is ideal for the Poket Phono because it runs on + - 5V. When you need more juice you can build an INA and then it can swing double. This is a nearly rail to rail design so it has a maximum output of + - 4V. 8V into the 60 Ohm AKG701 gives 1W of power so it can drive this headphone really load. Cooling of the chip is then necessarry but with 1W on the AKG you land in hospital with Tinitus. This chip swings 20 times more current then the OPA134 in the popular C-Moy, a choice that i never really understood. The OPA134 needs a high impedance phone or it runs out of steam quickly.
I have now a system that i can take to the road with my lightweight Goldring table.
It can even drive a poweramp directly so i could fit a secound input that could be used for a CD player. There is some space left in the ELV cabinet.
I always take my Sennheiser PX200 with me that the Poket Phono drives with ease. I chose this headphone after listening to 20 alternatives at the Münster Media Markt and i liked this one the best of the foldable small ones. It has a surprisingly robust and dynamic sound.
The circuit shown has 10dB of gain and that is more then sufficient. I simply use DC coupling without a problem. Ideally i whould like to use a pot with say 47kOhm but i had some 5Kohm Vishey conductive platic pots lying around that fit.
Attachments
A lot of things are going on here but i virtually do not find time for DIY.
I visited Ward Maas from Pilgham Audio that now has the first run of PCBs ready for the FPS that i designed for Linear Audio Volume 0. A small problem apeared with the differential servo of the output stage. We found one solution that works and he is trying another option. As soon as we are 100% happy i will inform you about the revision.
The next day i visited the Utrecht X-Fi show. The VAT show is no more and the X-Fi show was held in the Plaza Hotel parallel to a bigger show in the Beatrix. What was obvious is the dominance of tube equipment. For example HAT was showing several preamps and no less then 4 phonostages. Two of them with Lundahl transformers, one had the top Jensen and one was with an AD797 opamp input stage. They played two very well restored turntables from Thorenz and EMT. Audio Note was showing the Baby Ongaku and Pink Faun had a plethora of amps, preamps. phonoamps and DA converters, all with unusual tube types and a lot of NOS parts. Thanks to Kaspar, the show organizer for inviting me for good food and interesting after hours discussions.
In the meantime i got the tubes for my tube phonostage, some 6C45Pi and i had some 6SN7GT in stock. Actually i changed my mind a bit. The ETF is very soon so i may not find the time to build the fully balanced stage i originally intended. Instead i will grind my teeth on a single ended stage with passive treble and active bass equalisation. The 6SN7GT is useless for that job so i decided on a EC8010 for the active bass equalisation.
It has more Gm and more mu and that is neccesary. Jaap of HAT promissed me that he has some good ones from Valvo. I plan to use LED bias and the T-Reg from Jan Didden.
I visited Ward Maas from Pilgham Audio that now has the first run of PCBs ready for the FPS that i designed for Linear Audio Volume 0. A small problem apeared with the differential servo of the output stage. We found one solution that works and he is trying another option. As soon as we are 100% happy i will inform you about the revision.
The next day i visited the Utrecht X-Fi show. The VAT show is no more and the X-Fi show was held in the Plaza Hotel parallel to a bigger show in the Beatrix. What was obvious is the dominance of tube equipment. For example HAT was showing several preamps and no less then 4 phonostages. Two of them with Lundahl transformers, one had the top Jensen and one was with an AD797 opamp input stage. They played two very well restored turntables from Thorenz and EMT. Audio Note was showing the Baby Ongaku and Pink Faun had a plethora of amps, preamps. phonoamps and DA converters, all with unusual tube types and a lot of NOS parts. Thanks to Kaspar, the show organizer for inviting me for good food and interesting after hours discussions.
In the meantime i got the tubes for my tube phonostage, some 6C45Pi and i had some 6SN7GT in stock. Actually i changed my mind a bit. The ETF is very soon so i may not find the time to build the fully balanced stage i originally intended. Instead i will grind my teeth on a single ended stage with passive treble and active bass equalisation. The 6SN7GT is useless for that job so i decided on a EC8010 for the active bass equalisation.
It has more Gm and more mu and that is neccesary. Jaap of HAT promissed me that he has some good ones from Valvo. I plan to use LED bias and the T-Reg from Jan Didden.
I have a 5U4GB rectifier NOS Soviet relabelled as ''RSD'' too. Same box art. There must be some rarity value at a point in future for things with East Germany Logo I guess. Sovtek are made in Saratov in the heritage Reflektor factory now run by foreign management and funds by New Sensor Corporation of N.Y. Electro-Harmonix fame. The old boxed anode RSD 6H8C could be originally coming even from FOTON of Tashkent or Melz of Moscow. Black ribbed anode, metal base Melz is the best 6SN7 I ever had listened with. Joachim is preparing to play CITY's vinyl if ''Am Fenster'' on the magazine is any clue. City are RSD original though.
HI mr. G
Joachim,
First of all, it was a pleasure meeting you at the X-fi in Utrecht.
I look forward to welcome you at my office, I'm very busy at the moment but I'm doing the best I can to make it possible to receive you within a few weeks.
Take care and thanks again for the great (audio) interaction / conversation of last weekend
Tjuus,
Audiofanatic
José
Joachim,
First of all, it was a pleasure meeting you at the X-fi in Utrecht.
I look forward to welcome you at my office, I'm very busy at the moment but I'm doing the best I can to make it possible to receive you within a few weeks.
Take care and thanks again for the great (audio) interaction / conversation of last weekend
Tjuus,
Audiofanatic
José
In the phono there will be surprises maybe. Some famous types in line level or amps can have inadequate hum to cathode from the heaters, out of spec en, many things. Different from sample to sample. Takes luck. Down to what theoretical Rn the 6C45Π can take the noise spec of the head amp? 1nVrtHz?
edit: I found some analytical spec. Seems like Rn=300R (en=2.2nVrtHz) if run at 10mA so not to create other noises. 2nVrtHz for 20mA, same 50V Va. I hope it will not need a grid stopper due to high gm, that would add up. Do ferrite beads work on tube base pins well?
http://www.triodeel.com/6h30.html
Joachim,
First of all, it was a pleasure meeting you at the X-fi in Utrecht.
Tjuus,
Audiofanatic
José
Me too Joachim.
Grusse, Loek
I do not intend to use the 6C45pi directly connected to the MC cartridge. I will use a Lundahl transformer before it. I plan to run the 6C45pi on 15mA with Led bias.
The first version will have a simple Anode resistor but i may try Anode chokes or constant current sources later.
Hi Loek, nice to meet you too.
The 6C45pi can stand more current so a Fet-Tube casode could be build like in the Athur Loesch circuit. I could then use 4 x 2SK369 on 40mA total. That whold be very low noise too. The Gm of that stage would be a massive 160mS.
The first version will have a simple Anode resistor but i may try Anode chokes or constant current sources later.
Hi Loek, nice to meet you too.
The 6C45pi can stand more current so a Fet-Tube casode could be build like in the Athur Loesch circuit. I could then use 4 x 2SK369 on 40mA total. That whold be very low noise too. The Gm of that stage would be a massive 160mS.
I build a Stereo Anti RIAA. Again i use a slightly modified Lipshitz Legacy network. This time i have optimised the final voltage divider for 300 Ohm loading. I use now 300 Ohm most of the time as input impedance of my MC stages. This Anti RIAA can also be put behind a CD or better SACD player with sufficiently low output impedance and then the player can drive the phonostage. I do not say that this is a fidelity test of any kind but a sraight wire bypass could be quite telling at least about the tonal balance.
