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Old 10th July 2012, 12:01 AM   #91
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Richard Murdey
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The price difference isn't as great as I thought. 75 cents each for C0G vs. 25 cents for X7R (Mouser). Don't take that as an endorsement, mind you, just that people who are in the habit of paying $20+ for coupling caps might want to consider trying this "upgrade".

For bypass applications, I remain skeptical.
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Old 9th May 2013, 07:46 AM   #92
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Photo of a recent Sapphire build. The chassis ground is a heavy screw mounted between the L and R rectifier banks and the transformers. The circuit common is connected to the chassis ground from the COM pads on the board.

This seems to be the best way to do it.

Note that there are a pair of COM pads on the boards, but the are electrically bridged. You can use one or the other or both, it doesn't matter, I just included two to make it convenient to connect two bridge rectifiers per channel.

If you have one pad spare, you can use it to ground the boards to the chassis.

The reason there in no explicit "GND" pad like the Phonoclone/VSPS boards have is I imagined most people might be using headphone sockets which have the COM ring (gnd) in electrical contact with the socket housing, which, for a metal front panel, grounds the circuit by default. As it turns out most people use insulated sockets and make the chassis-to-circuit-common connection elsewhere - in which case, I suggest the COM pad.
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Old 10th May 2013, 12:36 PM   #93
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THD simulation for the BOM version of the J-Mo Mk. II, driving a 16 ohm load.

40 mW output at 1% THD (mostly second harmonic)
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File Type: png Jmo2 THD Circuit.png (43.1 KB, 369 views)
File Type: png Jmo2 THD Sim.png (26.9 KB, 354 views)
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File Type: asc J-Mo2 11m 5486.asc (3.0 KB, 6 views)
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Old 13th May 2013, 11:41 AM   #94
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Once again great work, RJM. Your stuff is very inspiring. Keep it up.

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Old 14th May 2013, 05:22 AM   #95
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Quote:
Originally Posted by rjm View Post
THD simulation for the BOM version of the J-Mo Mk. II, driving a 16 ohm load.
I mistakenly posted this to the wrong thread. It belongs in the J-Mo Mk. II thread instead, as a followup to this post.
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Old 26th November 2013, 09:07 AM   #96
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Default Revision 2.0

This looks to be about the final revision before sending off for fabrication.

The new boards are drop in replacements for rev. 1.4s, and the circuit can default back to the original if desired.

The main changes are the addition of a Zobel network on board, ceramic bypass capacitors on board, and an additional pair of resistors to increase the bias current through the output transistors. The parts numbering has been completely changed, however, and I will be updating the documentation to reflect that.

There will be 9 sets of boards available, and will do a limited edition kit if the interest is there.
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File Type: png Sapphire20f-brd.png (58.8 KB, 249 views)
File Type: png Sapphire20f-sch.png (37.2 KB, 265 views)
File Type: png Sapphire20d-lt.png (99.0 KB, 140 views)
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File Type: zip sapphire 20f.zip (76.4 KB, 15 views)
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Old 27th November 2013, 09:21 PM   #97
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Whats the story on the zobel on the output Richard? Have you found it particularly beneficial with any cans in particular or either end of the impedance spectrum?


Fran
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Old 28th November 2013, 01:51 AM   #98
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No, I can't say it makes any difference, but maybe it does. It's a comfort blanket, so you can rest secure in the knowledge you have that particular base covered.
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Old 29th November 2013, 10:19 PM   #99
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Updated links for the aluminum chassis I used to case up this amp.

Headphone Amplifier Aluminium Chassis 01 [Case 01] - $75.00 : DAC,Audio Amplifier,Hifi Amplifier,Tube Amplifier,Hlly Audio, Hlly Electronics
Headphone Amplifier Aluminium Chassis 02 [Case 02] - $75.00 : DAC,Audio Amplifier,Hifi Amplifier,Tube Amplifier,Hlly Audio, Hlly Electronics


AT $75 shipped the price is very reasonable, I would go so far as to say dirt cheap considering what you get.
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Old 30th November 2013, 06:30 AM   #100
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You night want to take a peak at this

Class B amplifier has automatic bias | EDN

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