[xrk971]

16ohms to 500ohms. Quite the range. Is the 3.5mm end the one that goes into the earphone? Let me know if you are still interested in running this amp in balanced mode.

 

[DBaldock9]

16ohms to 500ohms. Quite the range. Is the 3.5mm end the one that goes into the earphone? Let me know if you are still interested in running this amp in balanced mode.

 
This is the adapter that I'm using - https://www.etsy.com/listing/387459214/impact-audio-cables-ultra-mini-adapter
 
I would be interested in a Balanced Amp - but do you have another matched sets of transistors (which match the set in my NHB model)?

 

[xrk971]

Wow some of those cables cost as much as my amp. For balanced drive, it's important that the positive and negative phases of each channel be matched. But not critical that the left and right channels also match, as that is handled with the volume knob or level setting on each amp. So really all you need is another NHB amp. Although I can get you another one that will be close. It's just not critical. You will need balanced drive cables that terminate in 3.5mm on amp input and output. Also important is ring in is same as ring out and tip in is same as tip out. On the earphone and DAP side, it can be whatever your earphone/DAP uses.

 

[DBaldock9]

Wow some of those cables cost as much as my amp. For balanced drive, it's important that the positive and negative phases of each channel be matched. But not critical that the left and right channels also match, as that is handled with the volume knob or level setting on each amp. So really all you need is another NHB amp. Although I can get you another one that will be close. It's just not critical. You will need balanced drive cables that terminate in 3.5mm on amp input and output. Also important is ring in is same as ring out and tip in is same as tip out. On the earphone and DAP side, it can be whatever your earphone/DAP uses.

 
Would this be a Balanced Input to Balanced Output design, or could it also work as a Single-Ended Input to Balanced Output Amp?

 

[stellarelephant]

  Just to show you that the prototype system under development does indeed still fit inside the mint tin, here is a photo. It uses a 3.7v 2600mAhr LiPo cell that is 50mm x 50mm x 6mm thick.  The cell has built in smart protection circuit for over-charging, over-current, and over-depletion.  A DC-DC step up regulator takes that to any voltage but I set it at 15.5v for a good balance of long life and dynamics. A bank 2200uF 16v caps and resistors form a CRCRC filter to clean up the broadband residual switching noise.  An automatic USB charging circuit handles charging duties.
 
I am getting 3.5hrs per charge so far - that will also depend on your bias current setting on the amp.  The battery auto-shutdown is also tricky to deal with as the in-rush current to the caps on the amp tends to kick it into self-protect. Right now, use of a series resistor between the battery and the caps limits the current but wastes power as heat.  Similarly, the resistors in the CRC filter waste heat as well. Otherwise this amp should run close to 5.5hrs.
 

Wow, you did it.  Is it a lot warmer?

 

[xrk971]

The current limit resistor and CRC filter resistors probably burn off an extra watt. The amp is nominally 1.5w so yes it is a bit warmer. But not hot or uncomfortable. If you think about how much heat that is for 3.5hrs it's pretty incredible the energy density in a LiPo battery. Almost like TNT per weight.

 

[xrk971]

Would this be a Balanced Input to Balanced Output design, or could it also work as a Single-Ended Input to Balanced Output Amp?

The amp can work either as SE to SE or balanced to balanced but for balanced you need to give it balanced input (left and right channels out of phase by 180deg). But if in balanced connection phones and you give it SE input on one side it plays as if SE. If you give SE inputs to both sides and phones connected as balanced - the signals cancel and you get no sound (very very faint barely audible).

 

[DBaldock9]

The amp can work either as SE to SE or balanced to balanced but for balanced you need to give it balanced input (left and right channels out of phase by 180deg). But if in balanced connection phones and you give it SE input on one side it plays as if SE. If you give SE inputs to both sides and phones connected as balanced - the signals cancel and you get no sound (very very faint barely audible).

Ah, so I would need to come up with an analog SE to Balanced conversion stage, in order to drive balanced earphones using a single-ended input?

 

[xrk971]

 
Ah, so I would need to come up with an analog SE to Balanced conversion stage, in order to drive balanced earphones using a single-ended input?

I was assuming that you have a DAP or DAC that provides balanced outputs already - that is the ideal way to do it as the 180deg phase flip is done at the digital level with a simple sign inversion. Whereas doing it at the amp requires additional analog circuitry to do a SE to Balanced conversion (2 op amps). Linear Technologies makes a nice single IC one that I could add to a special balanced amp I suppose but that's a ways off.  However, you are getting away from the thesis of this amp: simple and pure 2 transistors for SE pure Class A.  Another option is a passive SE to Balanced signal transformer.  They can be very good but, impart their own harmonic distortion profile (usually H3 for transformers).  
 
Here is such a transformer - note that it has 600ohm impedance so meant to be driven by DAC with 600ohm drive capability:
http://cinemag.biz/output/PDF/CMOL-3x600T2.pdf
 
Most DACs that are designed for pro-audio usage have built in balanced XLR outputs - you can use these with cable converted to 3.5mm TRS to drive the amp directly in balanced mode.  I want to get the Focusrite  2i4 for this very reason.  An example is here - look at back panel it has two balanced outputs.  The DAC in this is very good. If you don't need a portable option, it's less than typical $500 balanced out DAPs.
 
https://www.sweetwater.com/store/detail/Scarlet2i4G2

 

[DBaldock9]

  I was assuming that you have a DAP or DAC that provides balanced outputs already - that is the ideal way to do it as the 180deg phase flip is done at the digital level with a simple sign inversion. Whereas doing it at the amp requires additional analog circuitry to do a SE to Balanced conversion (2 op amps). Linear Technologies makes a nice single IC one that I could add to a special balanced amp I suppose but that's a ways off.  However, you are getting away from the thesis of this amp: simple and pure 2 transistors for SE pure Class A.  Another option is a passive SE to Balanced signal transformer.  They can be very good but, impart their own harmonic distortion profile (usually H3 for transformers).  
 
Here is such a transformer - note that it has 600ohm impedance so meant to be driven by DAC with 600ohm drive capability:
http://cinemag.biz/output/PDF/CMOL-3x600T2.pdf
 
Most DACs that are designed for pro-audio usage have built in balanced XLR outputs - you can use these with cable converted to 3.5mm TRS to drive the amp directly in balanced mode.  I want to get the Focusrite  2i4 for this very reason.  An example is here - look at back panel it has two balanced outputs.  The DAC in this is very good. If you don't need a portable option, it's less than typical $500 balanced out DAPs.
 
https://www.sweetwater.com/store/detail/Scarlet2i4G2

 
Thanks for the info!
 
The one Balanced output device I've got (currently), is my DP-X1 DAP.
There are four separate wires, and the (L-) & (R-) cannot be connected to anything which would short them together.
So, if the Amplifier (-) inputs are at GND, and the GND is common between channels, that won't work for the output of my DAP.

 

[xrk971]

That is an amazing DAP btw, I am jealous.
 

 
 
http://www.onkyousa.com/Products/model.php?m=DP-X1&class=Accessory
 
 
I think you are fine with that DAP. Here is how you would wire it (whether ring or tip for +/- is not important, as long as consistent on output cable to phones):
 
Amp 1:
DAP Output  L+ to Amp1 input Tip
DAP Output  L- to Amp1 input Ring
DAP Ground to to Amp1 input Sleeve (GND1 on Amp1)
 
Amp1 output Tip to Headphone L+
Amp1 output Ring to Headphone L-
Amp 1 Sleeve unconnected
 
Amp 2:
DAP Output  R+ to Amp2 input Tip
DAP Output  R- to Amp2 input Ring
DAP Ground to to Amp2 input Sleeve (GND2 on Amp2)
 
Amp2 output Tip to Headphone R+
Amp2 output Ring to Headphone R-
Amp2 Sleeve unconnected
 
Note that L- and R- are never shorted or connected as on separate circuits completely. Monoblocks essentially.
 
If your DAP is 2.5mm TRRS connector, it looks like all you need is a 4-ring TRRS to a Y-split 3.5mm dual TRS cable?
 
All amp connectors are 3.5mm TRS
 
Note that GND1 and GND2 are not in common between Right and Left as they are two separate amps with separate power supplies. You have to be careful not to stack amp cases so they touch directly as case is at amp GND.  Use a silicone insulator sheet, etc.

 

[Slater]

  That is an amazing DAP btw, I am jealous.
 

 
+1.
 
Onkyo makes a lot of great stuff. I had a number of their old school components back in the day.

 

[DBaldock9]

BTW - What do we listen for, to know when the Amp's batteries need to be replaced (Alkaline), or recharged (Li-Ion)?

 

[xrk971]

Distortion crackling sound with regular batteries. Li-ions simply stop. The self over discharge protection kicks in.

 

[DBaldock9]

I paired the XRKAudio Class A NHB amp with my Cayin N3 and K's 500 (using an Impact Audio 3.5mm TRS Plug -to- 2.5mm TRRS Jack Adapter Cable), for a while at work today.
Sounds great together!