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xrk971 Pocket Class A Headamp GB
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Old 20th July 2017, 12:55 AM   #1011
raptorlightning is offline raptorlightning  United States
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Originally Posted by xrk971 View Post
Look for a 51mm x 52mm x 7.8mm 2600mAhr LiPo batterymodel number 785251 on eBay. They are about $10. You will have plenty of room for a 3x2200uF RCRCRC (use 0.47R 1W) filter plus D.C. Step up plus USB charger module.
That's definitely an interesting option. I really like the fact that it allows micro USB charging for the amp, but the total stored energy is about the same as two 600mAH 8.4V batteries... and there's the added noise of the DC boost converter to deal with - which the gained room in the tin provides a solution for. Have you tried these little DC boost converters for audio, I assume they're pretty noisy, no?
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Old 20th July 2017, 01:15 AM   #1012
xrk971 is online now xrk971  United States
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I am using one now and it's dead quiet. Even without the RCRCRC it's not audible - I only have it to make the measurements pretty. The FFT is posted a ways back - it's essentially flat -123dB noise floor similar to regular batteries.

The DC step up is at 1.2MHz, so noise is easily filtered at band band.
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Old 20th July 2017, 03:00 AM   #1013
stellarelephant is offline stellarelephant  United States
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Thanks for the links to parts, X! You set your step up to 16.5V, right? And so your three caps in the filter are 16V rated? If I set mine to 18V, can I substitute, say, 1500uF 25V caps, or is the 2200uF value a critical spec?

And, a noob question: does higher voltage from the battery have the exact same effect as tweaking bias via R4 value?
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Old 20th July 2017, 11:20 AM   #1014
xrk971 is online now xrk971  United States
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Increasing Vcc does increase bias current but is different from changing R4 as that affects the balance of H2/H3 levels in addition to changing bias. But higher bias in general lowers overall THD. You can use 1500uF, not critical but bigger the better.
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Old 21st July 2017, 02:02 AM   #1015
stellarelephant is offline stellarelephant  United States
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Interesting. Thanks.

This amp is incredible. While cooking dinner tonight I hooked up my second PCA build as a preamp for my Tripath->Aurasound kitchen boombox. It has never before sounded even close to this good! Even my wife, who is known to roll her eyes at my audio endeavors and is constantly heckling me about my "flux capacitors" actually said..."This is the most I have enjoyed listening to music in a long time." When I took the PCA out of the signal chain and went direct from my DAP into the boombox, she said, "It sounds so flat!"

xrk971 Pocket Class A Headamp GB-img_2260-jpg

While my first build made substantial improvements to the same system in terms of dynamics and presence, this one makes strides across the board. Heftier bass, clearer treble detail and instrument separation, wider imaging (still not that wide...it's just a boombox!), and punchier dynamics than I ever expected to get from a 3.5" driver. Speed, presence and realism are all improved with this PCA in the chain.

I'm just astounded at the difference a clean, powerful Class A signal can make. X, you're the man for sharing this mighty little amp design. I encourage you to try out the stacked PPS & Panny FR cap combo. I think you'll agree that these transparent caps just get out of the way and allow the transistors to sing beautifully! At the moment I'm in the mood to build one of these for every audiophile I know...
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Old 21st July 2017, 02:17 AM   #1016
xrk971 is online now xrk971  United States
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I've been saying all along that I don't listen to my regular Class AB amps without this as preamp anymore. It makes a huge difference in sound quality. More bang for your buck than expensive interconnects that's for sure.
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Old 21st July 2017, 02:06 PM   #1017
stellarelephant is offline stellarelephant  United States
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Originally Posted by xrk971 View Post
I've been saying all along that I don't listen to my regular Class AB amps without this as preamp anymore.
Now I understand why... After I finish this portable build, I plan to build a SMPS-powered desktop version to live inside the boombox. Brings the thing to life!
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Old 21st July 2017, 02:37 PM   #1018
BYRTT is offline BYRTT  Denmark
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Originally Posted by stellarelephant View Post
Now I understand why... After I finish this portable build, I plan to build a SMPS-powered desktop version to live inside the boombox. Brings the thing to life!
Into these pre test stage think if its possible add a switch to drivers wiring that can switch their polarity to counter for PCA inverts, because some drivers in free air or in their final loading system end up when tested with advanced klippel-tests not to be perfect symmetrical in push/pull performance, admit for OB-1 that A/B tests for polarity was transparent for my ears but for some speakers have experienced noticeable difference whether polarity follow standards.
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Old 21st July 2017, 07:27 PM   #1019
stellarelephant is offline stellarelephant  United States
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I must have missed something further back. This amp flips the signal polarity? So I should reverse my speaker wiring?

Beginning my final round of tin-sized cap listening tests.
25V 220uF Cerafine / 16V 330uF Cerafine / 25V 470uF Cerafine / 16V 220uF Silmic / 25V3 30uF Muse

I should have also gotten the 16V 470uF Silmic that Funch used, but forgot that one. Even so, I think I'll get a good idea of the pure Silmic sound, just with a tiny bit less bass.
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Old 21st July 2017, 08:31 PM   #1020
BYRTT is offline BYRTT  Denmark
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Quote:
Originally Posted by stellarelephant View Post
I must have missed something further back. This amp flips the signal polarity? So I should reverse my speaker wiring?...
It inverts and that can be reason or not why she said "It sounds so flat!" without PCA, but it should be easy to experiment for in try without PCA and a flipped speaker wire, or with PCA and a flipped speaker wire.

Also to have PCA HD profile as into post 1 then don't load it lower than 270 ohms, myself tested it at 32 ohms and picture is very different then.

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Originally Posted by stellarelephant View Post
...Beginning my final round of tin-sized cap listening tests.
25V 220uF Cerafine / 16V 330uF Cerafine / 25V 470uF Cerafine / 16V 220uF Silmic / 25V3 30uF Muse

I should have also gotten the 16V 470uF Silmic that Funch used, but forgot that one. Even so, I think I'll get a good idea of the pure Silmic sound, just with a tiny bit less bass.
Nice arsenal there : )
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