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xrk971 Pocket Class A Headamp GB
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Old 12th April 2017, 08:59 AM   #561
twocents is offline twocents  South Africa
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Hi stellarelephant. I see you are doing some good research on caps, and I would like to hear your findings specifically relating to this amp. A year ago I was also fascinated by all the different caps and how they possibly affect final sound. A lot has been said about this topic already.

You might find this interesting regarding PPS caps – Wiki says: “The temperature dependence of the capacitance of PPS film capacitors over the entire temperature range is very small (± 1.5%) compared with other film capacitors. Also the frequency dependence in the range from 100 Hz to 100 kHz of the capacitance of the PPS film capacitors is ± 0.5%, very low compared with other film capacitors. The dissipation factor of PPS film capacitors is quite small, and the temperature and frequency dependence of the dissipation factor over a wide range is very stable. Only at temperatures above 100 °C does the dissipation factor increase to larger values. The dielectric absorption performance is excellent, behind only PTFE and PS dielectric capacitors.
Polyphenylene sulfide film capacitors are well-suited for applications in frequency-determining circuits and for high-temperature applications. Because of their good electrical properties, PPS film capacitors are an ideal replacement for polycarbonate film capacitors, whose production since 2000 has been largely discontinued.”

So, PPS caps are replacing Polycarbonate caps – but I found this interesting post on the ACA amp thread regarding the input caps, posted by the mighty Zen Mod: “so , 20uF solid cap , bypassed with 0u47 to 1uF, as I said - my fave are Icar motor run , bypassed with MKC (polycarbonat)”

No way you can use a motor run cap here, but the PPS might hold good possibilities although it looks like they mostly come in SMD.
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Old 12th April 2017, 09:11 PM   #562
xrk971 is online now xrk971  United States
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I have two ginormous 50uF motor run caps sloshing with oil inside. Brand new. I just might connect them to the big desktop version of his amp and take a listen. 50uF is enough for 250ohm cans all by themself to reach decent bass levels.

This PPS cap business is really interesting though.
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Old 13th April 2017, 04:10 PM   #563
xrk971 is online now xrk971  United States
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Testing the desktop version of this amp with a 19v laptop SMPS feeding a Linear Technologies LT1963A low dropout low noise regulator set at 18v. Amp runs at 113mA bias through IRF610 MOSFETs. Tested with 33ohm load parallel with 250ohm headphones in order to listen to effect of lowninpedanxe loading. Sound is very nice and bass is very good. No audible hum or noise at all. Amp is fitted with two massive 10000uF 25v rail caps and also using two 1000uF 16v oscons:

Click the image to open in full size.
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Last edited by xrk971; 13th April 2017 at 04:18 PM.
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Old 15th April 2017, 03:53 AM   #564
stellarelephant is offline stellarelephant  United States
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Quote:
Originally Posted by diyRookie View Post
Hi stellarelephant. I see you are doing some good research on caps, and I would like to hear your findings specifically relating to this amp. A year ago I was also fascinated by all the different caps and how they possibly affect final sound. A lot has been said about this topic already.

You might find this interesting regarding PPS caps – Wiki says: “The temperature dependence of the capacitance of PPS film capacitors over the entire temperature range is very small (± 1.5%) compared with other film capacitors. Also the frequency dependence in the range from 100 Hz to 100 kHz of the capacitance of the PPS film capacitors is ± 0.5%, very low compared with other film capacitors. The dissipation factor of PPS film capacitors is quite small, and the temperature and frequency dependence of the dissipation factor over a wide range is very stable. Only at temperatures above 100 °C does the dissipation factor increase to larger values. The dielectric absorption performance is excellent, behind only PTFE and PS dielectric capacitors.
Polyphenylene sulfide film capacitors are well-suited for applications in frequency-determining circuits and for high-temperature applications. Because of their good electrical properties, PPS film capacitors are an ideal replacement for polycarbonate film capacitors, whose production since 2000 has been largely discontinued.”

So, PPS caps are replacing Polycarbonate caps – but I found this interesting post on the ACA amp thread regarding the input caps, posted by the mighty Zen Mod: “so , 20uF solid cap , bypassed with 0u47 to 1uF, as I said - my fave are Icar motor run , bypassed with MKC (polycarbonat)”

No way you can use a motor run cap here, but the PPS might hold good possibilities although it looks like they mostly come in SMD.
Thanks for sharing. Not the first time I've seen PPS touted as the successor of polycarbonate. PPS has low dielectric absorption, which Cyril Bateman maintained was the most important spec that correlates with low distortion. Plus there's the high temp stability benefit you mentioned. The only suitable PPS caps I found on Mouser are Kemet SMR. The datasheet boasts "excellent sound quality in audio applications". I don't know much about dissipation factor, or how important it is to audio, but in that category they seem to be outclassed by WIMA MKS. (Just comparing data sheet specs.) But they win in the dielectric absorption category and have been praised for linearity, so I think they have good potential. I'm looking forward to tying them for myself!
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Old 15th April 2017, 10:55 PM   #565
xrk971 is online now xrk971  United States
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I'm going to look into these PPS caps myself. Does anyone have a part number for a 1uF and 2.2uF with similar footprint as the Wima's on this amp?
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Old 17th April 2017, 02:41 AM   #566
stellarelephant is offline stellarelephant  United States
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Here's the 1uF SMR. It is 7.2x7.2x13mm with 5mm lead spacing.
http://www.mouser.com/ProductDetail/...1e2hYXXKQKk%3d

I thought I had a suitable 2.2uF in my cart also, but now I realize it has 15mm lead spacing...
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Old 17th April 2017, 08:14 PM   #567
Morde is offline Morde  Finland
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Here's my version of the xrk971's Pocket Class A headamp as a desktop version.

Most of the case is filled up with LDR volume controller and it's power supply. The headamp itself is powered via 30 VA 230/2x15V toroid and user Mravlca's TPS7A4700 LDO board. Voltage is set to 16 V.

FETs are matched by X himself and the rail caps are 2200 uF/16 V. Otherwise it's a stock build and the bias is running at 57 mA in both channels. The FETs are connected to aluminum bottom plate via silicone pads. I still need to make some kind of aluminum bar on top of the amp board to squeeze it tighter to the base plate with M3 bolts and nuts.

I propably will make new version of the face plate by using clear plexi glass and replace the power switch with rotary encoder. Now I have only remote control.

The sound is sweet, though I'm poor at describing the details. Well worth the effort!
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Old 17th April 2017, 08:21 PM   #568
pcgab is offline pcgab  United States
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Awesome Morde, super awesome!!
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Old 17th April 2017, 09:12 PM   #569
xrk971 is online now xrk971  United States
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Morde,
That looks absolutely fabulous. Nice work! Amazing how little the amp itself takes up! I was looking at a similar TPSA power supply regulator myself. How do you like it? Specs are 4uV noise and -80dB PSRR at 100Hz. Very nice. If desktop use and fitted with silicone heatsink - you can boost PSU to 19v if you change our those 16v rated 2200uF caps for 25v ones. The 19v PSU should push bias up to about 75mA to 80mA. Total dissipation will be circa 3.2W. But dynamics will get a big boost.

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Old 18th April 2017, 05:21 AM   #570
xrk971 is online now xrk971  United States
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Quote:
FETs are matched by X himself and the rail caps are 2200 uF/16 V. Otherwise it's a stock build and the bias is running at 57 mA in both channels.
It's nice to see confirmation that my hand-matched FETs are really matched when you build the amp. 57mA is a great sweet spot as bias current settings go. At this setting you are getting classic -66dB H2 and H3 between -12dB to -20dB below H2, not much else in higher orders, and THD of about 0.05%.
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