[xrk971]

Gill has the Uber NHB with desktop option. It has an external input jack for DC power that switches off the internal batteries and uses 5.5mm coaxial barrel jack with external PSU. It's an unlisted option at the moment - let me know if you want it. It's a lot surgery on the amp to make it happen so cost of amp is quite a bit higher. Look back in this thread and you will see the amp Gill has with external jack. I will repost photo of desktop option here for you to see. Note that the desktop PSU needs to be the ultra-low noise/ripple super regulated variety. The kind they use for high end DACs. Ask for 16.5v, or in Gill's case, can be as high as 19v.

 

[gikigill]

The 19V input is a lifesaver or more appropriately a battery safer cause I'm getting about 5 hours of battery life on a set of 600mah rechargeables.

Make no mistake, this amp has nothing in common with your average Altoids CMoy and I own 2 of those.

 

[xrk971]

The 19V input is a lifesaver or more appropriately a battery safer cause I'm getting about 5 hours of battery life on a set of 600mah rechargeables.

Make no mistake, this amp has nothing in common with your average Altoids CMoy and I own 2 of those.

That's nice that you get 5hrs of life on a charge. Sometimes running for a few hrs at a time and then switching to desktop mode lets the batteries "rest" and sometimes they recover some charge naturally.

I am going to get some blank tins and offer that as an option. You can then paint or decorate it anyway you like to customize it.

The only thing in common with CMOY is the tin!

 

[funch]

And the knob. 

 

[xrk971]

Actually this amp has little in common with any other portable amp as it is the only SE Class A pocket amp.

There is indeed something very special about the sound of SE Class A amps given how many people are fans of SET tube amps, and larger SS amps by Pass.

Btw, the NHB amp with and without desktop option is now listed as an option on my shop.

https://www.etsy.com/shop/XRKAudio

 

[stellarelephant]

I finished a battery life test today with my OKCell USB LiPo batteries. Over four listening sessions I got two hours and ten minutes total.

Shorter than I hoped, but close to what I expected. An Amazon reviewer warned that the 800mAh rating was grossly exaggerated and that the real capacity was around 400mAh. This seems to be the reality.

On the bright side, these batteries have normal power-on behavior and keep their voltage over 9V til the bitter end. They measure 9.18V when freshly charged and I think the lowest I measured was 9.13V, circa 30 minutes before one cell quit. The weaker cell just switches itself off when it gets low, which is quite obvious, because volume drops a bunch and sound gets distorted. Out of curiosity, I charged the dead cell only and listened to the amp some more to let the stronger cell run its full course. It only lasted an additional 15 minutes.

For me, the convenience of charging my batteries in the tin, via micro USB, plus the steady, surprisingly high voltage these put out, makes them keepers. I can also confirm that these batteries have never gone into any sort of protection mode when charging up my amp's 1000uF rail caps (other users have reported having to switch on/off a few times for proper power up. These just work with the first click.

I wish they lasted a little longer, but I never really listen for more than 2 hours at a time, so for $11 shipped from AliExpress, I'm happy with these batteries. I plan to buy two more for my second build, and I hope they will give the same turn-on behavior with the larger rail caps I plan to try.

 

[xrk971]

Thanks for the update on those batteries. I might get some myself. The reason they are 400mAhr is that the rating is for the 3.7V native LiPo cell. It goes through a DC to DC step up converter (regulator) which is why it puts out a steady 9.1v. This means there is a high speed switch mode converter. I have done the same thing myself but use a 3000mAhr battery and step up to 16.5v. What I noticed is a broad white noise background at the -90dB level from DC to 1kHz. So even though the switch speed is 1.2MHz there was some background that increased the noise floor. We won't know for sure if these OK brand batteries exhibit same thing but I had to use a CRCRC filter to get rid of it.

 

[gikigill]

Which 3000mah battery are you using Xrk971?

 

[xrk971]

It's under development but I am trying to make an integrated rechargeable battery solution. It's a bare 3.7v 3000mAhr LiPo battery used on tablet PC's and then use a DC step up converter and a USB charger modlule. All separate components. The 50mm x 50mm x 6mm battery is actually 2600 mAhr.

 

[stellarelephant]

Possible switching noise? Ew! Would it be the kind of thing I could hear as hiss if I listened with no music at max volume? Just tried that and thankfully all I can hear is dead silence!

 

[hte80]

  Glad you liked the sound on high impedance cans gikigill.  Can you tell us which headphones you liked to pair with them (model and impedance)?
 
I will do my best to tweak the settings (bias current) and caps complement to get extended bass for your low impedance cans.  I am thinking boosting bias from 55mA nominal to 67mA and increasing output caps from 470uF to 1470uF - that should increase the bass extension by 3x or allow impedance 3x lower ( circa 16ohms) than 50ohms to have same bass extension.
 
The mods will be a 1000uF Panasonic OSCON + 470uF Nichicon AK + 1uF Wima MKS on outputs.  As long as I am at it, I will upgrade your inputs to 4.7uF Elna Silmic II's plus 2.2uF Wima MKS.  I will also upgrade your rail caps to 2200uF 25v rated ones so you can happily drive the system with a 19v desktop PSU for extended dynamics and power output to low impedance cans.  It should be quite the formidable Pocket Amp. 

 
Could you elaborate a bit more on how to tune the bias and output capacitorsfor lower impedance headphones?
[Nevermind, went back a few pages and found the post about capacitance. How should I adjust the bias current though? / Do I need to?]
I would be looking to use it with ~35-50 ohm headphones. May also use it with some IEMs for the heck of it, and the lowest of my bunch of IEMs would be around 12ohm.
(Also, how do you plan to fit 3 capacitors in the space allotted for the one output capacitor???)
 

I finished a battery life test today with my OKCell USB LiPo batteries. Over four listening sessions I got two hours and ten minutes total.

Shorter than I hoped, but close to what I expected. An Amazon reviewer warned that the 800mAh rating was grossly exaggerated and that the real capacity was around 400mAh. This seems to be the reality.

On the bright side, these batteries have normal power-on behavior and keep their voltage over 9V til the bitter end. They measure 9.18V when freshly charged and I think the lowest I measured was 9.13V, circa 30 minutes before one cell quit. The weaker cell just switches itself off when it gets low, which is quite obvious, because volume drops a bunch and sound gets distorted. Out of curiosity, I charged the dead cell only and listened to the amp some more to let the stronger cell run its full course. It only lasted an additional 15 minutes.

For me, the convenience of charging my batteries in the tin, via micro USB, plus the steady, surprisingly high voltage these put out, makes them keepers. I can also confirm that these batteries have never gone into any sort of protection mode when charging up my amp's 1000uF rail caps (other users have reported having to switch on/off a few times for proper power up. These just work with the first click.

I wish they lasted a little longer, but I never really listen for more than 2 hours at a time, so for $11 shipped from AliExpress, I'm happy with these batteries. I plan to buy two more for my second build, and I hope they will give the same turn-on behavior with the larger rail caps I plan to try.

 
What caps do you have on the power rails there (dimensions wise)? Wondering if I can get away with some 25mm tall caps and position them how you have yours.

 

[macky112]

Has anybody tried this battery in their build?

https://www.amazon.com/gp/aw/d/B00EJ4NJ7E/ref=mp_s_a_1_14?ie=UTF8&qid=1491737157&sr=8-14&pi=AC_SX236_SY340_QL65&keywords=9v+rechargeable+ebl

 

[hte80]

i think that's what x uses in his.

 

[xrk971]

Yes, but I have to warn folks that fhe qualify control on this brand is marginal. When fhey work, they work well. However be prepared for duds. Failure rate is maybe 30% to 40% out of the box. I have sent 3 boxes back. Amazon is nice for this. I get ones with charger for $21 with 4 batteries.

 

[xrk971]

Possible switching noise? Ew! Would it be the kind of thing I could hear as hiss if I listened with no music at max volume? Just tried that and thankfully all I can hear is dead silence!

It's very low level -108dB visible on an FFT with switcher I was using. I could not hear it - would not have known if I hadn't measured it. It looks like this.



I used a CRCRC with 2.2mF and 0.33R to clean it up.

If you can't hear it - don't worry be happy!