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Old 28th June 2010, 11:45 AM   #1461
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I tryed the LC Audio Low Noise Supply and the Twisted Pear Placid. Both work fine.
I use 27mH coils behind the LC Audio but this is not absolutely neccesary.
You can use between 12 to 15 V. I always try my prototyps with 2 x 12V lead acid batteries.
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Old 29th June 2010, 09:01 AM   #1462
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Here is another example of a Transimpedance RIAA Stage. This time it is a common base stage with input offset cancelation. Noise impedance is around 17 Ohm when the current in the input transistors is set to ca. 3.5mA. You can double or quadruple the input transistors for even lower noise. You have to raise the iddle current by a factor of two or four in the input stage when you do that.
I like that stage and will build it.
Attached Files
File Type: pdf Common Base Transimpedance RIAA.TSC - TINA.pdf (93.2 KB, 206 views)
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Old 4th July 2010, 12:11 AM   #1463
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Some cartridges really need a transformer because the output is so low that even the best active solutions have too much noise. For example the original Audio Note IO Ltd. with 0,04mV @5cm/s. The new Kondo IO-M has some more output with 0.12mV but still it is a challenge for active MC stages. Some time ago i presented a Zero Field ballanced input that was not fully worked out. After discussing with Holger Barske i made a unbalanced version with inductive RIAA. This stage is hard to beat in noise rejection and puts even 0.3nV/qHz stages to shame due to the extremely low DC input impedance of 0.75 Ohm. I talked to Lundahl and Sowter and they can make me transformers to spec. I now have the choice between MU-Metal, Nickel and Amorphous core. I do not know yet what to take. The Zero Field technology cancels the effect of the secondary winding and extents the response of the transformer to nearly DC and cancels distortion.
P.S. : I build the Common Base Transimpedance RIAA and it works.
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File Type: pdf Transformer Coupled Inductive RIAA.TSC - TINA.pdf (59.0 KB, 116 views)
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Old 4th July 2010, 04:37 PM   #1464
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Several people are now building my USAIG phonostage so i fell responsible to extract the best posible sound from that circuit. I gave one stage to Frank Schder and he gave the following commend: Sounds very clean but could have a little more deep bass, noise is a little high for low output MC, should have a switchable Neumann pole.
So this is what i did: I substituted the LME49720 with two single LME49990 on an adapter made by Stefan Horwege for me. The LME49990 is much more quiet with MC, has lower distortion, higher bandwidth and better PSU rejection. I prefer it over the AD797 or LT1028 i used before. I recalculated the RIAA and put an RC filter at the output that makes the RIAA curve flat over 20kHz. The old values gave the following time constants : 75.2 usec ( 0.3% off ), 291.8 usec ( 8% off ), 3000 usec ( 5% off ), that does not sound as bad as it looks because it gives only a small lift ( ca. 0.5dB ) in the fundamental tone area. The new values give : 75.2 usec ( 0.3% ) , 306,6 usec ( 3.5% ), 3200 usec ( 1% ). It is no problem to get the 75 usec and 3180 usec time constants but the 318 usec is much harder with standart values. Considering that i do not use exotic values i am satisfied with the result. I raised the 2200uF elcap to ground to 4700uF plus a 2.2uF foils cap for lower distortion and more extention in the deep bass. The Neumann Pole was added. It is switchable.
Circuit diagram with commend, picture of LME49990 adapter and a photo of a deluxe version of the USAIG 2.0 is added.
Attached Images
File Type: jpg LME49990 single to dual.jpg (85.2 KB, 581 views)
File Type: jpg USAIG 2.jpg (100.3 KB, 581 views)
Attached Files
File Type: pdf USAIOG 2.0.TSC - TINA.pdf (69.4 KB, 147 views)
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Old 8th July 2010, 03:46 AM   #1465
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My first experiment with Zero Field technology was successfull after some playing around with values. As transformer i used a 600 Ohm - 3.2 Ohm transformer that a friend of mine bought at a Ham Fest. It must have been used for talkback to transform 600 Ohm to a little loudspeaker. The specs say 200 Hz to 6kHz +-1dB. I use it "up side down", so i use the secondary as primary and the primary as secondary. That way, the primary DC impedance is around 0.15 Ohm and the secondary is 27 Ohm. You can imagine that this gives a really worst case szenario because this transformer has very little "primary" inductance so without the Zero Field trick it gave vitually no bass. I have a little hum problem but otherwise the sound with Zero Fied was surprisingly good with decent bass and treble extension so i am really looking forward to use this technology with a better transformer. I use a cap in series with the transformer to avoid DC through the coils. In fact it was not that bad. One channel measured 27mV, the other 3.5mV so the "bad" channel gave 1mA through the transformer. This is not much and i could jumper the cap but i have not tryed that.
Theoretically i can use now a very small transformer and the OPamp compensates for any low frequency distortion. Lets see how this develops.
Attached Images
File Type: jpg Experiment with Zero Field.jpg (77.5 KB, 496 views)
File Type: jpg Talk Back Transformer.jpg (80.4 KB, 485 views)
Attached Files
File Type: pdf Experiment in Zero Field.TSC - TINA.pdf (43.8 KB, 79 views)
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Old 12th July 2010, 06:14 PM   #1466
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Today the PCB boards of the JOSI discrete OPamp arived. The JG Trio ( me, Sigurd Ruschkovski and Jan Didden ) has worked silently on perfecting the design. It is now version 2.81 Rev.2 so a lot of hard work was put into it. I came up with the fundamental design, Sigurd simulated and optimised the circuit and choose most of the active and passive components and Jan did the layout and the servo design.
We got the following performance : GBproduct 40MHz, Open Loop Bandwidth 40kHz, Voltage noise 1.5nV/qHz, Open Loop Distortion up to 100kHz 0.01%, Supply Voltage +-15V to +-24V, Max Bias Current in the output stage 70mA.
The circuit can put out more then 3W in Class A in theory. To make that posible the board is quite big ( 60mm x 83mm) and we use strong and fast Sanyo video transitors at the output that can be bolted to a heat sink.
This is the first PCB i hold in my hand since i started this thread, so it needed over one year to get something finalised. In fact the first circuit i designed that got a PCB was my discrete INA. It will be available from Pilgham Audio but so far i have only seen a picture and the artwork. In fact several people are working on PCB boards for my designs. I keep you posted if there is any news.
In use the Josi is very flexible. It can do what an integrated OPamp can too but also much more. A phonostage could be made for medium output MCs and it can also be used for MM work because the double input Fet does not only have low voltage noise but also low current noise. This could be nice for the top Grados.
A headphone amp can be build, so does a line stage or a line buffer. An INA can be made from 3 JOSIs. Active filters and equalizers come to mind too.
Attached Images
File Type: jpg Josi 2.jpg (113.1 KB, 400 views)
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Old 15th July 2010, 08:02 PM   #1467
jason12 is offline jason12  United States
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Quote:
Originally Posted by Joachim Gerhard View Post
I slept well, thank you very much.
I put more thought into the BJT INA.
The current sourced caskode did not work so well with BJTs so i simplified a bit.
They are now fed by a capacitance multiplier and the feedback goes directly from the collectors.
Circuits like that proved to work in designs by Douglas Self and Burkhard Vogel but they used them unbalanced.
Idle current in my design is adjutable for minimum DC offset and optimisation for an MC with higher impedance like the Denons and Clearaudios.
When i use 4 x 4 input transistors and reduce the feedback resistor to 1 Ohm i could get 0.3nV/qHz in a balanced design.
Hi,

I have few questions regarding this BJT schematic posted here few month back.

Please correct me if I am wrong, but it seems that the cartridge will see approximately 1.5V DC. Either that or (in case of 0 Ohm cartridge) 1.5 VDC has to be applied across R1 with resulting current of 600mA. The latter seems is not going to happen because of the servo opamps keeping the output voltage of the OP1 and OP2 close to 0VDC. As a result T1-T4 will be turned off.

Hopefully I am wrong and missed something else here.

Another question - is it possible to convert this schematic into single-ended similar to shown in post # 814 in "Intrumentation Headamp Unbalanced.TSC - TINA.pdf" file.

Thanks
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Old 15th July 2010, 08:37 PM   #1468
jason12 is offline jason12  United States
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It looks like the system did not include the attached schematic. I was referring to the schematic in the post 1022.
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Old 15th July 2010, 09:38 PM   #1469
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Yes, you are right, the schematic from post 1022 needs input caps. This input stage can be converted into single ended. I will post a circuit later this day that should work.
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Old 15th July 2010, 11:15 PM   #1470
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This circuit is straight out of Burkhard Vogels book "The Sound of Silence". I only changed the OPamps to more modern and better performing types. It should fullfill your request.
It is a single ended, all in one go MC RIAA, itself an elaboration on the well know D.Self design from the 90th. You can use other BJTs at the input and i have given many choices here earlier. I noverdays design parallel symmetric BJT transimpedance circuits with DC offset cancelation or paralel symmetric FET transconductance circuits because they can be DC coupled to the cartridge, have cancelation of second harmonic and a 3dB noise advantage.
Attached Files
File Type: pdf Burkhard Vogel Single Ended BJT MC Phono.TSC - TINA.pdf (74.4 KB, 155 views)
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