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Old 2nd December 2009, 05:40 PM   #1
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Default Another Discrete BJT MC Preamp Design

Here is my latest design to throw into the ring. It is a 3-stage discrete MC preamp utilizing THAT304 matched PNP-NPN quad as input devices. The remainder of the circuit consists of a cascode VAS stage driving a 4-transistor output stage similar to that used in the OPA627 opamp. It simulates to the same En advertised by THAT Corp: 0.7-0.8 nV/sqrt(Hz). Distortion is in the -120 dB range. There are still a few tweaks to be done (like optimizing input stage resistances to minimize En). I have just about completed PCB layout and should be building the prototype by year's end.
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File Type: doc preamp.doc (43.5 KB, 540 views)
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Old 2nd December 2009, 08:48 PM   #2
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when i open your document i can not see the circuit values very well but i like what i see.
should develop into an interesting project. i ordered samples of the THAT304 but never got them, so i am very interested what you experience.
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Old 2nd December 2009, 09:25 PM   #3
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Default Difficulty Reading component Values

Joachim,

The file is a 2003 SP3 Microsoft Word document. When you open it in Word, go to the toolbar and increase the magnification to approx 150% (it is expressed as a percentage). That should fix the problem.

Jeff
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Old 3rd December 2009, 06:37 AM   #4
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i did that but still i could not read the values. the resolution is not high enough on my mac.
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Old 3rd December 2009, 06:43 AM   #5
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i opened it under windows xp and now it works fine. so mac users may have problems.
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Old 4th December 2009, 11:40 AM   #6
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Quote:
Originally Posted by analog_guy View Post
Here is my latest design to throw into the ring. It is a 3-stage discrete MC preamp utilizing THAT304 matched PNP-NPN quad as input devices. The remainder of the circuit consists of a cascode VAS stage driving a 4-transistor output stage similar to that used in the OPA627 opamp. It simulates to the same En advertised by THAT Corp: 0.7-0.8 nV/sqrt(Hz). Distortion is in the -120 dB range. There are still a few tweaks to be done (like optimizing input stage resistances to minimize En). I have just about completed PCB layout and should be building the prototype by year's end.
same circuit transfer to PDF
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File Type: pdf RIAA amp PP folded cascode.pdf (20.7 KB, 397 views)

Last edited by tiefbassuebertr; 4th December 2009 at 11:45 AM.
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Old 5th December 2009, 05:41 AM   #7
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Exclamation Correction to BJT MC Preamp Schematic

I noticed the V+ and V- pin numbers on the IC2 symbody are transposed. V+ should connect to pin 7, and V- to pin 4.
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Old 5th December 2009, 05:44 AM   #8
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Default .pdf Conversion

Quote:
Originally Posted by tiefbassuebertr View Post
same circuit transfer to PDF
Thanks for converting the image to a .pdf format. I don't have an Acrobat converter.
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Old 5th December 2009, 05:51 AM   #9
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CutePDF - Create PDF for free, Free PDF Utilities, Save PDF Forms, Edit PDF easily.
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Old 23rd December 2009, 05:00 AM   #10
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Default Chassis for Above Described Preamp

After a few days in the shop the chassis for the preamp is nearly complete. Lacking access to sheet metal bending tools I elected to use thick material for the front and side panels and then tap/thread to attach the other panels. I could not find knobs to my liking so I machened the ones in the photo. (It helps to have a vertical mill, a drill press and a lathe). Once all the electronics has been installed and everything tested I'll disassemble the panels and send them to an anodizing shop
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File Type: jpg preamp-chassis.JPG (147.2 KB, 661 views)
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