xrk971 Pocket Class A Headamp GB

[xrk971]

New review by user on Head-Fi

This review just posted by a user on Head-Fi.org:

https://www.head-fi.org/f/threads/n...-as-complete-pcb.837656/page-14#post-13534374

This is my short review of my new " Pocket Class A Headphone Amplifier / Desktop Amplifier NHB Edition " Made custom by xrk971 Let me tell you I had a great experience with this purchase. This is one of those rare purchases where you get some of the man who built the product as well as this wonderful and magical amp.

Let me start by saying my review is only of my listening enjoyment and how I hear it. I have absolutely no idea of any technical aspects or any parts included with this build. He is welcomed to post any of the specs if he likes.

xrk971 asked for my listening preferences and gear I was using. It is Fiio X5 gen 3 DAP and Audeze LCD 2 headphones. Although many reviewers indicate the Fiio X5 gen 3 to be plenty strong to drive the Audeze LCD 2s, I did not. It seemed to me to be so much more there that wasn't being revealed. One day recently while trolling on Head Fi I came across what looked like a little jewel if 1/2 of what was being said about it was true.

I decided to try it and boy am I glad I did. xrk971
kept me up to speed continuously. He custom built it to my hardware and listening specs and he sure delivered. All in all from time I ordered, he built, shipped and delivered it was only about 5 days.

Short and sweet, these are my impressions. As always I try to remember to listen clean and mastered recordings. In this case I listened to the DSD recording of Christian Mc Brides " Live at Village Vanguard " This would be a sure workout for the bass. I'm a fan of " Steve Hoffman " masterings. I listened to some of his " Dreamboat Annie " Pee Wee Russell and his clarinet. And others.

Please be aware, this amp is very unforgiving in its reproduction of poor music source. This is clear evidence of not trying to color but to convey music as artist intended.

The sound stage was huge and wide. Most folks know LCD2S are well know for bass. The base this amp gave my setup was nothing less than articulate, good transit response, natural and detailed. I am a big believer in " It's not how low it goes. It's how well it goes low " . The speed of Mc Brides fingers up and down his bass is accurate. Who would ever believe this box could deliver so much bass. Next up instrument imaging and placement very distinct in height, width and depth. However vocals more up front in my face than I prefer. This may be unfair since I did not listen to very many recordings yet.

I could not believe the musicality this magical amp would provide me with. Here's how it was for me laying in my recliner listening Lincoln Mayorga and Distinguished Gentlemen on the Sheffield lable. " Limehouse Blues " toes are tapping relentlessly, shoulders rolling in and around and head rhythmically swaying side to side.

 

[yourownbuzz]

Hey, everyone who is using lithium rechargeables with the amp, what voltage are they?
I know there's no 9V spot on rechargeables so which ones are the most suited? (Personally was looking at LiFePO4 9.6V ~300mAh and Li-ion 7.4V ~600mAh)

 

[xrk971]

The Li-ions from EBL are about 8.4v fresh and run down to maybe 7v. They are true 600mAHr. The Okicell ones with USB charging are steady 9.0v thanks internal regulated DC step up. But they are maybe 300mAhr. Okcells don't have autoshutoff due to inrush current problem.

 

[yourownbuzz]

sounds like the 7.4 volt soshines I was looking at, think they're 8.4 fresh off the charger and 7.4 is depleted

 

[xrk971]

I find that 9v alkalines also work quite well if you are in a bind and need some instant power. They last quite a while too. Semi-depleted smoke detector batteries (the kind that cause them to give off the annoying "beep - better change me or I will drive you nuts" sound, are typically 8.5v and have a lot of life left for use in a pocket amp.

 

[babysupra]

Here is my latest unit designed to drive a 13.8ohm load with 115dB sensitivity (Andromeda's). With two 1000uF Oscons and a 10uF Silmic II on output and 10uF Silmic and 2.2uF Wima on input. With LTSpice sim I get 0.05% THD at 106dB SPL with 96% being H2 and balance just H3 and. Ofhing else. Frequency response is flat to 15Hz at -0.5dB. This unit is going out to Poland tomorrow after a 4hr burn in. The sound is perhaps the deepest bass impact Inhave heard on my 55ohm OB-1's. Actual test at 270ohm load and 700mV (about same drive level as 106dB on Andromeda's) measured only 0.02% THD and all H2, H3 almost non existent (-90dB).

Hi X,

Last time we went over output power calculation in private message on the standard version pocket amp, it was about 50mW for 250ohm, could you advise what changes over standard version needed to get that 700mV output at 250ohm?

edit: nevermind, i have mW and mV confused...

 

[xrk971]

Hi X,

Last time we went over output power calculation in private message on the standard version pocket amp, it was about 50mW for 250ohm, could you advise what changes over standard version needed to get that 700mV output at 250ohm?

edit: nevermind, i have mW and mV confused...

10v peak-peak is 3.54v rms, and (3.54v)^2/250ohms = 50mW

You would think 10v peak-peak is a lot but, watts wise, not so much into high impedance phones. But 700mV is a reasonably typical playing volume around 90dB loud on 96dB senstitive headphones.

 

[babysupra]

10v peak-peak is 3.54v rms, and (3.54v)^2/250ohms = 50mW

You would think 10v peak-peak is a lot but, watts wise, not so much into high impedance phones. But 700mV is a reasonably typical playing volume around 90dB loud on 96dB senstitive headphones.

gotcha, i was like "hmmm... 700mW at 250ohm?! hook a brotha up!" LOL, that kinda power would be giving Schiit's desktop Asgar 2 a run for its money, haha

 

[xrk971]

If someone has a Schiit Asgard SE Class A desktop amp to compare I would love to know how things pan out.

 

[yourownbuzz]

I find that 9v alkalines also work quite well if you are in a bind and need some instant power. They last quite a while too. Semi-depleted smoke detector batteries (the kind that cause them to give off the annoying "beep - better change me or I will drive you nuts" sound, are typically 8.5v and have a lot of life left for use in a pocket amp.

yeah haha ran my alkalines down to 6.5 =D had too much fun with the amp
It's still running fine with IEMs at 6.5v per battery but starting to have to crank it up. Got a couple more alkalines, but think rechargables would be the way lol.
Btw, received the two boards yesterday thanks!

I ordered some blank "altoids" tins off ebay as well, got sent something completely different, roughly double the size of an altoid tin and it has a window in the top. lol it's given me an idea for something like the Aune B1 lol. and I could prob fit huge caps AND the batteries in there to boot hahahaahah can't wait for the weekend

 

[xrk971]

A couple more amps going out the door this week. An NHB with dual 1000uF OSCONs and 10uF Silmic on output, and another with dual 390uF OSCONs and 1uF Wima with only a single 10uF Silmic on input (nonfilm cap bypass). They both sound wonderful. The dual 390uF OSCON has very low ESR for incredibly tight bass.

 

[stellarelephant]

Cranking em out!

X, how does removing the film from the input affect the sound?

YOB, please post a pic of your huge windowed tin when you get a chance! That does sound very fun to play with. Looking forward to seeing what you do with it...

 

[stellarelephant]

Just started board #2. Thus begins my adventure with the MicroMELF resistors. It'll be a miracle if I finish without dropping any and having them roll away forever. That said, I'm finding that they're actually very easy to solder. They're so small that there is a lot of extra room on the pads under the terminals.

For this build I'm going to substitute 51K (maybe 56K) for R4 to boost bias a little. I considered going higher but I would like to get at least 1.5 hours out of my OKCell USB batteries.

I soldered in 1K for RL this time around. It should load the output a smidgen more, and with the parallel load of my 50 ohm cans, I'll net 47R vs 42 with stock RL value.

Hopefully I'll finish tomorrow!

 

[xrk971]

You mean 51R for R4? K won't work. What are micoMELF resistors?

The no film input caps sounds very good - so good I don't miss the films. It seems the Silmic II 10uF 35v is the bomb of an audio coupling cap. I will replace all my current amps that call for a 10uF cap with this. The beauty is that they are much less expensive than a 10uF film cap which is bordering on boutique cap prices unless you get industrial caps or Chinese CBB's.

 

[yourownbuzz]

Cranking em out!

X, how does removing the film from the input affect the sound?

YOB, please post a pic of your huge windowed tin when you get a chance! That does sound very fun to play with. Looking forward to seeing what you do with it...

Haha, chances are that it'll be a while before I do anything with it, I have ideas, but I haven't even put my first amp into a tin yet, just been using it bare on my desk..lazy to go and search for my drillbits.

pics aren't great, snapped them quickly just to show the ebay seller he sent the wrong thing. The tins even came with foam inside, looks like product packaging.
Heres the link to the ebay listing I purchased if you are interested, no guarantee that you'll get these windowed tins: http://www.ebay.com.au/itm/272645535084?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

 

[stellarelephant]

Cool. Those tins look a bit less pocketable, but yeah for a desktop amp they'd look sweet. With the Aune B1 vibe like you said. You could probably fit big caps too.

You mean 51R for R4? K won't work. What are micoMELF resistors?

Good catch, X. 51R and 56R are what I bought.

They are all .2W Vishay MELF. I guess these "pro" ones aren't the exact "micro" line but same size. They are 1.1.x2.2mm SMT resistors that look like little perfect cylinders. I probably fell prey to the "boutique" hype. IFi Audio brags about using them in their flagship amps. Gave me the idea.

 

[xrk971]

0.2W rating is helpful for use at 470R R7 resistor array so that lets power dissipation go up to 800mW vs 500mW before. But a little known trick with flat SMT resistors is that you can stack two in top of each other in parallel easily. Could probably stack qnty 8 x 1k's to get 1000mW rating.

Round little cylinders do look very cool and boutique though.

 

[xrk971]

This is great for adding a LiPo and DC step up, Bluetooth module, and a graphic LED FFT spectrum display!

 

[abraxalito]

But a little known trick with flat SMT resistors is that you can stack two in top of each other in parallel easily. Could probably stack qnty 8 x 1k's to get 1000mW rating.

It would be jolly cool (pun intended) if that did work. Alas, the ratings for SMT resistors are for in free air at a particular ambient temperature. For a resistor sandwiched between other hot and sweaty bedfellows you'd need to apply fairly severe derating to the published dissipation figures.

 

[xrk971]

No free lunches. I am just talking about double stack so no sandwiches here but yeah, 1w is too optimistic I am sure. Clamping the resistors against silicone heat sink and proper sink works well.