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Old 31st August 2011, 09:44 AM   #2581
brianco is offline brianco  Ireland
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Location: Scottish Borders - Kelso; on the famous Tweed River!
And also reasonably similar to the front end of a (built) Yamamura prototype. That sounded excellent......even the power amps which I had at home for a few months were battery powered!
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Old 31st August 2011, 09:57 AM   #2582
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As far as i can see the photo diodes do not deliver enough current. The LC Audio MC stage runs on 1mA as far as i can see. For a bipolar this can be enough because Gm is 10 times higher at the same idle current a Fet consumes. I could imagine that we use a solar panel though. For example the ASI-F2/2 delivers 12V, 125mA and i can get it for 19,95€ each.
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Old 31st August 2011, 11:53 AM   #2583
MiiB is online now MiiB  Denmark
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Solar power....I like..) that will also leave room for some Super filtering....
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Old 31st August 2011, 12:05 PM   #2584
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Michael, the circuit is a constant current source so does not need tight filtering. Anyway, i have seen Hiraga Pre-Pres with a PSU as big as a power amp. Thats the way we build in the old days. Was a lot of fun.
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Old 31st August 2011, 12:46 PM   #2585
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Quote:
Originally Posted by Joachim Gerhard View Post
Unfortunately i can not get the DC offset stable so you have to insert a 1uF cap after the trimmer when the next stage input impedance is 47kOhm. I have noticed that Euvl thermo couples the Fet`s. I have not tried this and it should stabilize the DC offset. If that is good enough for DC coupling i do not know but i will try.
Jim Williams (RIP) addressed this in an application note: "775 nanoVolt Noise Measurement..."
http://cds.linear.com/docs/Applicati...ote/an124f.pdf
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Old 31st August 2011, 01:45 PM   #2586
MiiB is online now MiiB  Denmark
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I am currently making PCB's,, for my One shot RIAA....Getting 10 boards made....Do you want some for fun...??
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Old 31st August 2011, 02:07 PM   #2587
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Thanks Jacki, i will read it.
Michael, sure, that would be nice. I think the circuit is very promising.
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Old 31st August 2011, 02:36 PM   #2588
MiiB is online now MiiB  Denmark
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I also think i holds some promise, but like with all new things and concepts.. you never know... but for sure simulation did show some promise....

Fun to see a practical implementation. the boards are with an lot of R-C filterings which off course ca be left un-populated...like the input which is with 4 parallel Jfet sets, can be built with a single set..
the circuit currents can be adjusted with resistor values.
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Old 1st September 2011, 05:56 AM   #2589
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Michael, i am sure i can make it work. I use RC filtering a lot too. I like passive or non feedback filter solutions. I have not fallen in love yet with shunt regulators though. On some of my designs they worked well, on others i ran into oszillation but when it comes to PSU i am a bit challenged.
I worked a bit more on the PEN pre-pre. I am now back to Euvl´s AC coupled design and i found out that the Fet´s have to be matched well to make the circuit work. i hope i find the time today to make something satisfying.
I also have not given up on the balanced transimpedance phono. I think i have an idea that works. The input stage is now reconfigured for very low DC into the cartridge and i have added an inverted INA to make use of both inputs. An even better solution would be to use a fully balanced OPamp like the OPA1632 as the second stage and also include the RIAA there.
Attached Files
File Type: pdf Balanced Transimpedance Pre-Pre.TSC - TINA.pdf (7.7 KB, 95 views)
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Old 1st September 2011, 06:15 AM   #2590
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Here is the version with balanced RIAA.
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File Type: pdf Balanced Transimpedance Pre-Pre with RIAA.TSC - TINA.pdf (10.0 KB, 103 views)
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