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Simple High Performance DC Coupled Class A HPA with sub PPM THD
Simple High Performance DC Coupled Class A HPA with sub PPM THD
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Old 14th June 2018, 03:49 AM   #41
xrk971 is offline xrk971  United States
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Simple High Performance DC Coupled Class A HPA with sub PPM THD
Desktop amps generally have RCA inputs and 1/4in TRS outputs, but we have JST connectors so you can wire your favorite connectors with leads. To have it on the board will force people to drill very exact holes on their panels and will be too restrictive.

One thing we are considering is to make the PCB a perfect fit for the $36 Aliexpress case with all holes precut (except for Xfeed bypass). That would force everyone to get that case but it would be a nice integrated "turn-key" solution.
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Old 14th June 2018, 04:04 AM   #42
yourownbuzz is offline yourownbuzz  Australia
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I was thinking along the lines of having it as an option (JST and 3.5mm) like how there were multiple holes for caps on the DCA. But yeah I get your point
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Old 14th June 2018, 12:30 PM   #43
xrk971 is offline xrk971  United States
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Simple High Performance DC Coupled Class A HPA with sub PPM THD
We have so many options right now built into board that we may need simplify by removing some features. For example, switchable cross feed is sort of hard to implement with switchable AC coupling. This amp’s raison d’etre is really the fully-DC-coupled topology, so I think we may leave AC coupling as some solder pads for installing a small box film cap and leaving out a wire jumper for DC-coupling. Even adding passive cross-feed upstream of pot requires forcing pot to a specific value (10k) in order to fix the input impedance of amp to ensure stable slope and frequencies of the cross feed filter.
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Old 14th June 2018, 05:42 PM   #44
xrk971 is offline xrk971  United States
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Simple High Performance DC Coupled Class A HPA with sub PPM THD
More progress on integrated amp from JPS64. Note how JPS64 maanged to stuff a cap Mx onto the bottom side of the already full PSU board via use of SOTR223 MOSFETs.

Some amazing work there JP, simply beautiful and professional layouts never before seen on DIYA. We really are lucky to have you spinning boards for us.

Simple High Performance DC Coupled Class A HPA with sub PPM THD-tims-integrated-update-bottom-cap-mx-png

Simple High Performance DC Coupled Class A HPA with sub PPM THD-tims-integrated-update-top-cap-mx-png
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Old 14th June 2018, 05:55 PM   #45
pinnocchio is offline pinnocchio  Canada
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looks cool!
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Old 15th June 2018, 05:07 AM   #46
stellarelephant is offline stellarelephant  United States
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Click the image to open in full size.

The FFT makes me think of this cool article on distortion harmonics.
Adventures in Distortion
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Old 15th June 2018, 05:21 AM   #47
xrk971 is offline xrk971  United States
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Simple High Performance DC Coupled Class A HPA with sub PPM THD
The amp that resembles Bob's Blender is the DLH, which has a pot that can control relative H2/H3 and absolute THD.

DLH Amplifier: The trilogy with PLH and JLH amps

From here:
Click the image to open in full size.

To here:
Click the image to open in full size.

To here:
Click the image to open in full size.

With a twist of a knob.
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Old 15th June 2018, 02:43 PM   #48
stellarelephant is offline stellarelephant  United States
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Nifty. I wasn't referring to the adjustability so much as this amp's low distortion with H2 dominance. Bob sez:
"No distortion sounds better than a little bit of bad distortion, but moderate, well-distributed distortion sounds better, too!"
This amp seems to nail it on both counts. Although I guess with ultra low THD, we will get very little H2 to magically "mask" the higher harmonics, so the overall sound becomes heavily dependent on the sound sig of the source.
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Old 15th June 2018, 04:43 PM   #49
xrk971 is offline xrk971  United States
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Simple High Performance DC Coupled Class A HPA with sub PPM THD
Quote:
This amp seems to nail it on both counts. Although I guess with ultra low THD, we will get very little H2 to magically "mask" the higher harmonics, so the overall sound becomes heavily dependent on the sound sig of the source.
This can tweaked to user's desires by setting bias current and/or putting asymmetric Source/Drain power resistors, and also by choice of feedback resistor materials, and bias current setting. 400mA is smoking hot (14w per channel) and THD is <1ppm, whereas at 100mA bias current it will be closer to 0.005%THD (all H2). 100mA is plenty for most headphones and only 3W dissipation per channel.
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Old 15th June 2018, 11:52 PM   #50
stellarelephant is offline stellarelephant  United States
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Well, I've got these darn power-hungry Fostex planars. So lowering bias will probably not be a good option for me...as it would increase not only the H2 of the amp's output signal, but also probably significantly increase distortion of these 50 Ohm, 92dB sensitivity drivers.

My LingDAC has a SE Class A buffer, so hopefully I'll have a good distortion profile from the get-go, and this amp will simply "do no harm"
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