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xrk971 Pocket Class A Headamp GB
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Old 16th June 2017, 03:51 AM   #811
abraxalito is online now abraxalito  United Kingdom
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Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
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Originally Posted by xrk971 View Post
You can even try this as a preamp from your DAC to your power amp driving your big speakers: it will sound better, every time.
In my experience headamps such as these sound better when used as 'preamps' into poweramps because they have a higher input impedance than typical poweramps. Plus the JFET input helps a lot with RF rejection, DACs are rather noisy in ultrasonics typically.
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Old 16th June 2017, 05:09 AM   #812
xrk971 is offline xrk971  United States
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No, it's not not double amping. People use preamps all the time as a volume controller or source selector in one. Some power amps like certain Class A amps have very low gain of 15dB and need a preamp to get to 27dB or so in order to be able to hit clipping levels. But if you have a plain power amp with no volume control, and you feed your CD player RCA out tonyiur pocket amp as a preamp, you now have a volume controller that can drive multiple power amps with a fan-out as long as combined impedance of all amp inputs is >60ohms you are good. Most amp inputs are 47k to 10k.

This will imbue your power amp with a SE Class A harmonic signature.
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Old 16th June 2017, 07:13 AM   #813
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Another NHB going out to Singapore. This one is tuned to dig deep with LCD-2. Dual 1000uF 16v OSCONs + 10uF 35v Silmic II's on outputs, and 10uF 35v Silmic II's + 1uF 63v Wima MKS on inputs.

Click the image to open in full size.

Measured FFT:
Click the image to open in full size.
Attached Images
File Type: jpg NHB-SN017-Photo.jpg (98.5 KB, 318 views)
File Type: png SN017-FFT-3dB.png (7.0 KB, 313 views)
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Last edited by xrk971; 16th June 2017 at 07:15 AM.
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Old 16th June 2017, 04:06 PM   #814
xrk971 is offline xrk971  United States
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In case anyone is looking for a budget priced but great sounding headphone to go with my amp, I can highly recommend the SM-OB1 from Status Audio (I don't get anything from this recommendation, if you are wondering). I just like how it sounds. And a recent price drop on Amazon to $55 makes it a steal. I just got another set for backup or for converting to balanced drive (perfect for it as it has two wires - one for each side). They are extremely sensitive above their rated 96dB and the bass has a visceral punch. Nice mids and highs, although the highs on my DT880's are "more refined", for all around listening, I think they are great. The (Innerfidelity measured) 70ohm impedance is a nice match for the Pocket Class A.

https://www.innerfidelity.com/images/StatusSMOB1.pdf

Same company is also offering a 50% off web coupon code for their foldable over-ear HD-1 model. Code is in attachment and only works from the manufacturer's wbsite. I don't know how these will sound but the price is right. They say it has a V shape enhanced bass/treble response so probably good for commuting or hip hop etc.
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File Type: txt HD1-Code.txt (7 Bytes, 14 views)
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Last edited by xrk971; 16th June 2017 at 04:16 PM.
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Old 17th June 2017, 03:05 AM   #815
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I fired one of my amps up today, and can confirm that those little heat sinks that I posted about on page 77 do work. I can only hold my finger on one for about two seconds.
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Old 17th June 2017, 04:47 AM   #816
babysupra is offline babysupra  United States
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Hi X, the stock build aims for 55mA bias current for a good balance of battery life and dynamic, and desktop variant aims for 125mA bias for pure performance. What about the NHB version, what is the bias you aim for?
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Old 17th June 2017, 05:13 AM   #817
xrk971 is offline xrk971  United States
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About 65mA in NHB.
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Old 17th June 2017, 07:58 AM   #818
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Silicon Harmony casework is a PITA. A 24mm Forstner bit goes through 8mm thick aluminum plate well (for headphone jack).



It's mostly together and listening and checking temperatures. Heatsink is reaching about 50 deg C at the middle where the MOSFETs are located. Sound is still great. Very quiet, no noise or hum. Super powerful sound.
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File Type: jpg SH-Casework-1.jpg (380.2 KB, 186 views)
File Type: jpg SH-Casework-2.jpg (406.5 KB, 1076 views)
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Old 17th June 2017, 08:50 AM   #819
prasi is offline prasi  India
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I was wondering mate!, as to what happened to Silicon Harmony..
BTW nice case, and controls, yummy!
lots and lots of work!
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Old 17th June 2017, 12:04 PM   #820
xrk971 is offline xrk971  United States
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Thanks, Prasi! You did a beautiful job on the layout for this board. Looks and sounds great. I didn't know what a PITA casework is until I had to hog-out a big hole in aluminum. Noisy, messy, time consuming. But it had to be done. Soldering is so much more fun

I am always amazed when I plug in a 112dB/mW sensitive headphone into an amp that is plugged into the wall mains and hear no hiss or hum or noise of any sort. Headphone amp designs have to be absolutely silent when no signal playing. It's a lot harder that it seems. This is the same as measuring 0.0mV AC volts on the outputs with the Fluke.
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