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All JFET open-loop RIAA pre-amp
All JFET open-loop RIAA pre-amp
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Old 19th May 2018, 05:29 PM   #31
EUVL is offline EUVL  Europe
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Default Finally, the balanced version

Have been planning to build this for a few years now, and finally finishing this week.
Always want to build the balanced version only in order to get round the problem with low PSRR at the top rail.

Changes to the circuit are as follows :
+/-20V rails (battery powered, followered by 3x LM329, LP filtered to drive 5x BC327/337 follower in parallel)
Using 2SJ109 for 1st stage, 2SK389 for 2nd stage
2SJ109 is cascoded by 2x BC560C at -7V base voltage
R1,2,3,9,10 10k (Caddock MK132)
R5 2.5k nominal (2.7k S102//33k Beyschlag, fine trimmed for common mode DC)
Rv1 51R-51R//5k trimpot (for 1st stage differential DC)
R6,7 51R-51R//5k trimpot (for overall differential DC)
R4,C1 2.1k,147n (100n//47n)
R8,C2 880R,3.88n (887R//110k,2.2n//1n//680p)

After trimming, DC at the output before rumble filter is stable to within +/-5mV.
It is surprising stable considering the DC gain of 60dB.
A 10Hz rumble filter (15n/1M) was also added before the output followers, which are 2SK2145GR at 4mA.
The rumble filter will take care of any remaining DC after R9,10.

Gain at 1kHz is measured at 620x, which is as per expectation.
Still some final wiring to do.


Thanks for the nice and simple circuit.
Patrick

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Attached Images
File Type: jpg 180520 MEV Bal Phono C.JPG (263.8 KB, 318 views)
File Type: jpg 180520 MEV Bal Phono C Top 1.JPG (279.0 KB, 322 views)
File Type: jpg 180520 MEV Bal Phono PCB2.JPG (269.8 KB, 304 views)
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Old 19th May 2018, 07:32 PM   #32
Onvinyl is offline Onvinyl
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Wow, only 13 years later

I like your 3-D-thinking!

Do you have a schematic?
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Old 19th May 2018, 08:27 PM   #33
EUVL is offline EUVL  Europe
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Simplified form.


Patrick

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File Type: asc MEV Bal Phono Schematics.asc (7.0 KB, 136 views)
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Old 20th May 2018, 04:28 AM   #34
EUVL is offline EUVL  Europe
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Just noted a small typing mistake. R3 should be connected to -20V, and not +20V.


Patrick
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Old 24th May 2018, 12:19 AM   #35
Ejam is offline Ejam  Australia
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Default PDF Format

Patrick do you have the ASC file in PDF or JPEG format?
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Old 24th May 2018, 04:43 AM   #36
EUVL is offline EUVL  Europe
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Just download LTSpice.
It is free.


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