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#1 |
diyAudio Chief Moderator
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Hi all, this thread is about a JFET & MOSFET preamp I am cooking for sometime now. Its two stage single ended Class A circuit.
It was developed on the bench involving much experimentation with topology and a range of active parts. Simulations came second. Some speakers are insensitive, some amps also, or a source is relatively low output like a phono stage. So a line preamp with gain is good to have. Its named DCG3 because it has DC servo and three MOSFETS. Its standard gain setting is also times three. The main schematic is attached* Click for circuit description Some THD plots when driving 1.5kOhm line input and various headphones are also attached. *(12 Oct 2016 updated and build guide/bom pdf added) erratum: C6,C7 should read 4x in the BOM. J3 in preamp's schematic is named Q5 on the actual board. About J3/Q5 possible IDSS tolerances and a matching R3 value: post#452 V1.03 boards have split ground between channels (can be bridged) and the relay is reconfigured to rest at ground: post #3207 |
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#2 |
diyAudio Chief Moderator
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Some pictures
There is also a simple series DC stabilizer I designed for it |
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#3 |
diyAudio Member
Join Date: Sep 2009
Location: Catalonia - Europe
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Subscribed!!!!!!
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#4 |
diyAudio Member
Join Date: Sep 2009
Location: Catalonia - Europe
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Is suitable for high impedance headphones?
What are the rail voltages? Power consumption? Etc.... |
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#5 |
diyAudio Chief Moderator
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Beta build samples by friends. Thanks for the good early feedback to Michael V and Tham C especially.
![]() And clips by Tea tampering away in his basement following no particular order of instructions ![]() https://www.youtube.com/watch?v=QSQSrmGxBAY https://www.youtube.com/watch?v=URX2...ature=youtu.be |
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#6 |
diyAudio Member
Join Date: Sep 2009
Location: Catalonia - Europe
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What are these lights at the psu?
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#7 | |
diyAudio Chief Moderator
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Quote:
Rail is +/- 17.3V. DC power consumption about 7W for two channels (when with 100mA output stage bias) |
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#8 |
diyAudio Member
Join Date: Sep 2009
Location: Catalonia - Europe
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What about the SQ?
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#9 |
diyAudio Chief Moderator
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Bargraph Leds. No need to match Vref Leds for DCG3 because it does not care about exact same +/- rails. Bar Led packs are compact, straightforward to solder, looking great.
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#10 |
diyAudio Member
Join Date: Sep 2009
Location: Catalonia - Europe
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Thread | Thread Starter | Forum | Replies | Last Post |
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