[eonfire]

It will amp anything with an impedance between 30 and 600 ohms. If you are at the extreme low end of that range, you'll probably want to set the bias high for best dynamics and and put in at least 1000uF per channel for the output caps for bass performance. Otherwise the stock config works great.

Thanks for the info! Might be considering this amp in the near future but Im leaning towards the built-up unit as my soldering skills is quite next to nil! Thanks again and Good day!

 

[rellik]

Dont sweat solder skills. It isnt nearly as hard as it seems. Its just about keeping the tip clean. Like rewet a fresh iron with solder and a wet sponge after each joint. It will reduce frustration immensely.

Just dont do what I have seen sometimes by applying solder to the iron tip and paint it onto the joint. Its more like welding. The flux is necessary to get the bond. Just make sure to get the tip touching both/all pieces to be connected. If it doesnt flow on, then clean the tip again.

Getting the parabola shape is about getting the heat to wick solder into the thru hole. Otherwise the joint may resonate.

Bottlehead stocks a few amazing kits which may be more worth your while than a cmoy or its equivalents. Like I have been mentioning, if something breaks, just fix it or replace it. Dont sweat it otherwise you wont try again.

 

[xrk971]

IEM's work great and several amps out there are used primarily for IEM's and even earbud types.

For flying leads to improve ergonomics, be careful to keep leads from input jack to board as short as possible and twist the wires and use as thin of wire as possible. Shielded thin RG-174 is good. You don't want to pick up noise as this amp is silent.

 

[stellarelephant]

Elna Silmic II vs. Nichicon Muse KZ

I did some fun listening tests with different capacitor combos in this amp. Bypassing with a 1/10 value top shelf electrolytic does quite a lot for the sound--much more than a 1/100 value film!

After several hours listening back and forth between the 47uF Silmic II and Muse KZ on output bypass duty in the PCA amp, I can say with confidence that the two caps sound quite distinct in this application. Different beasts altogether.

I am not auditioning these caps on their own. They are bypassing my existing 470uF Nichicon KA output caps, so synergy is likely a factor. Also, the Silmic has the slight advantage of a 35V rating vs. the 25V Muse, but the caps are the same capacitance and have identical physical dimensions, so I feel the comparison is reasonable. I used both my xDuoo X3 DAP and Echo Audiofire soundcard as sources, using the Pocket Class A to power my Sennheiser HD598 headphones and also as a preamp, feeding my Tripath-powered Axiom Audio M3 speakers.



Silmic
As I explained in my earlier post, the Silmic tames the upper mids and low treble in a very smooth and musical way, by “damping” the resonances of the upper frequencies. The easiest way I can describe this sound is to say that notes with a lot of information in the midrange and low treble seem to buzz less and decay faster, lending a certain sense of control and wonderful transparency, as notes pop up and then sink rapidly into a dark background. This is nice and easy on the ears, but I notice that percussion can sound ever-so-slightly hollow and vocals a tad recessed in the mids as a result…smooth but perhaps harmonically incomplete. There is nice air on top, above the threshold of this effect. Synth pads emerge glassy and ghostlike from a cool, serene atmosphere in "Monument" by Robyn. Somehow this squeaky clean sound adds an amazing depth to the soundstage. I can listen "in" to the music more, and I can hear Amos Lee moving closer and further from the microphone as he sings "Bottom of the Barrel", creating a 3-D soundstage. What's more…his foot stomps in the beginning of the song sound convincingly deep. There is tight control, speed, and clarity in the bass registers, with superb weight all the way down to sub-bass. With complex and difficult material, like the rapid dynamic cliffs in the Futuristics remix of "Moonshine" by Bruno Mars, the Silmic keeps its composure, allowing the necessary breathing room in the mix for instrument separation and good dynamics.

Muse
The Muse lets everything through. In fact, my amp is subjectively louder with them in place. But volume isn’t the main difference…even if I dial it back, I can hear it. It lifts a veil and adds warmth. Presence, detail, and dynamics are off the chain. The snare drum in “The Bird” by Anderson .Paak simply hits faster and harder, with immediacy and sharp coherence. On top of that, I can now follow the long decay of its reverb tail all the way back down to the noise floor. Micro-details like the triangle “ting” in Daft Punk’s “Give Live Back to Music” come flying out of the mix…whereas I didn’t even notice them with the Silmic. Cymbals and chimes have a hyper-realistic timbre, with all their metallic harmonics beautifully apparent. Unfortunately this tizz carries over into vocal peaks and other sounds as well. While not the cleanest ever, the vocals are awesomely fun…in your face in a most engaging way with the KZ. Voices pop out of the mix with midrange presence, detail, and unabashed sparkle. The fat analog synth lead of Miike Snow's "Black and Blue" rips through the air like electricity…amazing. Bass is powerful, with more overall quantity than the Silmic, but sadly it is a bit less extended, and muddy in comparison. Every sound drips with texture and commands attention…it's like the notes are singing directly into my head. This can come off as compressed and fatiguing with complex material, but with simple arrangements, like Norah Jones' "Burn", the immediacy and realism of her performance is stunning.

Think of it this way:

The Silmic II is Gandalf's sword, Glamdring. Meticulously crafted, it has the heft to deliver solid bass thump and its sound is honed perfectly smooth, delivering balance and extension. Its enchanted blade cooly illuminates musical space, yielding a cool and calm atmosphere, even in the midst of musical chaos.

The Muse KZ is Kylo Ren's lightsaber. Red-hot, it hums with extreme harmonic texture and deals electrifying mids and treble. Every last detail cuts effortlessly through the mix with speed and warmth. But its brute resolving power can sound a touch unrefined (i.e. more distortion), and deep down, it's a little unsure in the bass.

I have actually had a hard time deciding which one I like more. They both bring out different nuances. My musician buddy who had a listen said he preferred vocals on the KZ but overall presentation with the Silmic. He joked that he wants me to build him an amp with a switch to toggle between caps! By the way, the green caps in the second photo are Muse ES bipolars. I left them out because they really didn't do anything audible as bypass caps.

 

[xrk971]

StellarElephant,
Thank you so much for such a detailed study and your carefully written reports. The Muse cap definitely sounds like it's worth trying. Wish I knew about your report before ordering my last batch of caps from Mouser. It will have to wait for the next order. Lately I have been having great luck with this combo:

Output with 1000uF 16v oscon and 100uF 16v Silmic II and 0.47uF 100v Vishay MKT.

Input with 10uF Silmic II and 2.2uF 50v Wima MKS

Bass, mids, highs are all well represented and smoothness is superb. 1000uF let's me hit some deep bass with 50ohm cans.

 

[stellarelephant]

Yeah I still keep going back and forth between the two. I think I'm going to leave the KZ in for a while and see if I get any burn-in improvements ( esp. in the bass) and then to be fair I'll do the same with the Silmic. If they stay exactly the same, I will probably end up going Silmic. It really is a nice high fidelity sound that never offends.

Your setup seems like it ought to sound very nice indeed. When I get around to my second board I'll have to try out a similar output combo. And I'm curious to experiment with an electro added to the input...to compare it with both the stock WIMA and my DIY PPS cap.

 

[xrk971]

A nice review of this amp by Michael of Headfonics.com just came out:

http://headfonics.com/2017/06/the-class-a-nhb-pocket-amp-by-xrk-audio/

The NHB unit I provided for the review used 1000uF Oscons + 100uF 16v Silmic II's + 1uF 63v Wima MKS on output and 2.2uF 50v Wima MKS + 4.7uF 35v Silmic II's on input.

I now bought a bunch of 10uF 35v Silmic's that are about the same size as 4.7uF so no point not to use.

But according to the reviewer, here is what he said about the treble:

"Sparkle factor is just incredible, at least to my ear. I can’t see anyone saying this amplifier is lacking treble density, response or substance. If you have a headphone geared for treble, you will adore this amp in terms of both quality and quantity offered. Yes, it does justice and then some to my $600 Audeze iSine20, as well as the Flare Audio..."

 

[rellik]

Panasonic FM and FC are more similar to typical real world applications for use in small and larger sizes. They retain a long life and have quite good extension without making things too quick. Similar to a Koss PortaPro headphone.

If you want to clean the addictive factor from the KZ yet retain some of its sonic qualities, consider Nichicon KX with power supply KA series. KG power supply will sound disparate without a more refined cap preferably a KZ due to frequency bandwidth range. KX and KA are similar to a small slit ported Sony MDR headphone such as Sony MDR-7502. Another great headphone.

Silmic are cloying and stuffy to my ears and alittle slick. Cerafine are much better from the Elna lines. Silmic are kinda like a cross between a Sennheiser and a Beyerdynamic where Beyerdynamic alone seperates from the pack with a lot of the KG note. High powered Sennheiser are like Silmic and high powered Beyerdynamic are line KG. If you want to use Silmic, please have a lot of current on hand. AKA not for CMOY imo.

Grado's are honestly more like Cerafines but can be tamed quite well using KZ, KZ are more like AKG K-701. Something I want from speaker vs portable "rare" headphone use.

My Master and Dynamic are a lot like a cross between KG with alittle Silmic depending on music but overdrive to really strange BHC Aerovox status where everything plays just fine but distorts on the diaphraghm alone vs the coil and magnet.

Here is an example of a well driven Silmic used in power supply you can hear the solen DC bypass and Mills Wirewounds when the Silmic power supply gets drained and relies on the LithIon:


This is the aforementioned design attached to a Sony PCM-F1 Betamax DAC and Sony SL-2001 Betamax (the Real Folk Blues) vs a Krell Foundation Processor and HifiMan HM-801 (be wary that the Krell Foundation is newish and lacks a discernible zipper note):


Here is an example of a well driven Silmic used in Coupling cap position don't know what power supply probably vintage Elna cerafine:

 

[stellarelephant]

Rellik, wow! That's a lot of great info to absorb. And exactly the kind of subjective interpretations I have been looking for. While opinions are easy to come by, this kind of detailed sound analysis is really hard to find. Thank you.

Since you've obviously done a good deal of cap rolling, what is your opinion about the "sweet spot" for bias voltage vs cap voltage rating? The output caps in this amp see about 6.5V DC. I have been trying to stick with a 25V or higher rated cap to minimize distortion, but if I opt for 16V, that opens up more options due to smaller sizes for the same capacitance.

 

[rellik]

Lower voltage caps will burn out faster. Bias is really dropping the full B+ to the bias caps. Honestly many of the caps can be a vareity of voltage ratings, check their can size.

Honestly dont know, depends on the amp and cap rolling especially when im trying to guess based on photographs from different capacitor sources. In sincerity, I dont have much experience with BHC Aerovox yet have seen a HiWatt british guitar amp. Straight up black hole.

Otherwise, my handle ("Rellik") looks quite stupid in text rather than on the side.

 

[xrk971]

Output caps are rated 16v, DC bias there is circa 7v. I doubt that level of DC will burn out an electrolytic designed to work at twice the operating voltage. On inputs the rating is 16v as well and DC bias there is about 1.5v.

 

[macky112]

I have had reports from a professional music producer who used this amp with HD600's and they rock. He had an O2 before this and he says the difference is amazing with this little amp. The music just sounds better.

I was reading up on O2 amp while I wait for my new pcb to arrive, because my monoprice m1060 is rec for at least 200mW at 50ohm (can take up to 2W at 50ohm) and the XRK PCA amp we calculated to be about 50mW at 50ohm. Glad I wanted to review both PCA amp threads before my next build attempt and came across this post, so scratch that O2 DIY idea! Now my question is, anyway to boost output power of PCA higher? Is running an 18v power supply making more output power compare to running two 9v batteries?

 

[xrk971]

You can make the desktop version of the amp - in DIYaudio thread I show a variant with 125mA bias and uses large IRF610 MOSFETs and large dual 3w 33R resistors in series for 66R source resistors. Voltage is at 19v. It may get a little more power but not in the watts range.

To do 2w at 50ohms will require a true desktop amp like the Silicon Harmony (still under development ). The SH puts out about 40w of heat per channel in pure SE Class A mode of operation. It runs 28v to 34v power supply. And to drive 50ohm cans, can make 1w rms and 2w peak.

Here is photo - I am testing and about to out it into a real case.

 

[macky112]

You can make the desktop version of the amp - in DIYaudio thread I show a variant with 125mA bias and uses large IRF610 MOSFETs and large dual 3w 33R resistors in series for 66R source resistors. Voltage is at 19v. It may get a little more power but not in the watts range.

To do 2w at 50ohms will require a true desktop amp like the Silicon Harmony (still under development ). The SH puts out about 40w of heat per channel in pure SE Class A mode of operation. It runs 28v to 34v power supply. And to drive 50ohm cans, can make 1w rms and 2w peak.

Here is photo - I am testing and about to out it into a real case.

Ok I'll try the desktop variant first

What is the purpose for 66R source resister? For protection or dissipate heat?

 

[xrk971]

Here is link to desktop amp.

http://www.diyaudio.com/forums/group-buys/302859-xrk971-pocket-class-headamp-gb-38.html#post5014544

Here is schematic:

R7 is the 66ohm source resistor in question. It serves as the "constant" current sink for the class A operation. You need something to draw the heavy bias load through the MOSFET. So for a 125mA bias at about 11v is about 1.4 watts. These run continuously hot so best to reduce the max load so spread over two 3w resistors so they can run forever without stress.