Little known fact: take a balanced (stereo TRS) 6.5mm to stereo 3.5mm jack to the amp. Wire a 3.5mm stereo jack so that tip wire goes to +ve of headphone voicecoil and right (ring) goes to -ve of voicecoil. Leave ground unconnected. You now have a single channel of balanced headphone amp that achieves double the slew rate, four times the power, and +12dB more dynamic range. But then you need two pocket amps, one for each ear. 
I am going to build a new PCB with both amps on one board plus the single to split phase converter circuit.
I am going to build a new PCB with both amps on one board plus the single to split phase converter circuit.
Lets down the road hear your feedback on that balanced setup
Had about an hour of listening into Behringer HSP5000 headphones which signature often reminds me of wesayso's line arrays when i place them a little stupid so that the hanger is in the forehead : )
I'm very happy your amp as configured sounds very nice clean and silky into this setup feeded from AP192 (M-Audio) using JRiver as player, i ended open up amps door so it can breathe a little better it gets some hot compared to OPAs used in other headphones amps i have : )
Have you ever tried use your VSSA v1.4 as dedicated headphone amp, maybe up bias settings a bit so it stay mostly into class A then guess its not bad for that task.
Had about an hour of listening into Behringer HSP5000 headphones which signature often reminds me of wesayso's line arrays when i place them a little stupid so that the hanger is in the forehead : )
I'm very happy your amp as configured sounds very nice clean and silky into this setup feeded from AP192 (M-Audio) using JRiver as player, i ended open up amps door so it can breathe a little better it gets some hot compared to OPAs used in other headphones amps i have : )
Have you ever tried use your VSSA v1.4 as dedicated headphone amp, maybe up bias settings a bit so it stay mostly into class A then guess its not bad for that task.
Hi Byrtt,
Glad you got to hear first sound from your NHB amp. It's one of the best ones I have made. Leaving the door closed is no big deal - it's designed for it. The door and underside of the tin is covered with Kapton tape which improves radiative heat transfer by about 5x versus bare metal. It changes emissivity from 0.2 to nearly 0.9. Temps on amp PCB never exceed 55C.
I have not tried the VSSA 1.4 with headphones but have tried jkeuterman's through hole VSSA - similar topology. It has too much audible hum with a conventional toroidal transformer and bridge followed by rectifier and cap banks. Whereas Aksa/Ranchu quasi amp does not have hum with same power supply. Which leads me to believe that the PSRR of the VSSA is not that great. It would need an ultralow ripple cap multiplier to be used as a Headphone Amp. Design is 180mA bias so I believe it would be indeed Class A for 99% of listening levels.
Glad you got to hear first sound from your NHB amp. It's one of the best ones I have made. Leaving the door closed is no big deal - it's designed for it. The door and underside of the tin is covered with Kapton tape which improves radiative heat transfer by about 5x versus bare metal. It changes emissivity from 0.2 to nearly 0.9. Temps on amp PCB never exceed 55C.
I have not tried the VSSA 1.4 with headphones but have tried jkeuterman's through hole VSSA - similar topology. It has too much audible hum with a conventional toroidal transformer and bridge followed by rectifier and cap banks. Whereas Aksa/Ranchu quasi amp does not have hum with same power supply. Which leads me to believe that the PSRR of the VSSA is not that great. It would need an ultralow ripple cap multiplier to be used as a Headphone Amp. Design is 180mA bias so I believe it would be indeed Class A for 99% of listening levels.
Hi X, I just googled balanced drive amp and was unclear if your approach here requires balanced source? Or the phase splitter takes care of that and we can use normal digital single ended source and get balanced output through your new design?
If you have a balanced source, then you can drive two of my amps to get balanced drive into your balanced drive capable headphone. I will design the new amp to accept balanced inputs, or usual (single ended) input like the kind on an RCA cable and the single to balanced phase splitter takes care of making a balanced drive. It's actually a very nice converter as it follows the mantra of simplicity in low parts count, and full Class A single ended, zero global feedback operation.
If I am understanding this correctly, with balanced source, just modify cable like you mentioned a few posts back into two PCA amps for balanced drive
But without balanced source, your phase splitter (using one or two of the splitter?) will take single ended source and feed into two PCA amp for balanced drive right?
This is pretty awesome!
For those of us building diy PCA amps, Will the phase splitter be available for DIY or only sold as complete board?
I just ordered a HD 6XX, and with my M1060, both will be easy to change cables, so I may try balanced drive if it is budget and diy friendly XD
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The phase splitter was just going to be the front end on a new desktop amp. I hadn't considered selling it as a separate unit to be used with existing pocket amps. It's only got two transistors but in fact is just as complex as the Pocket Class A amp. It will provide volume control and has similar Wima and Elna Silmic caps and a bunch of resistors. Almost the same complexity as the main amp. Just not as much heat output.
Its possible with very few passive components get a high quality balanced drive, at this ESP site link Balanced Transmitter and Receiver II see section "Hey! That's Cheating" and its figure-4, also at link Jensen Transformers Application Notes | Jensen Transformers application note 003 have same tip although it will need registration to be able to download those nice pdf's there.
The ESP method may have very few parts but each part is an op-amp with maybe a dozen transistors that the signal has to flow through. Also it's not pure single ended Class A. My method uses two BJT's and is SE Class A and the performance is actually very low THD - much less than the usual -66dB.
A5 is a nice amp - but not engaging. Just makes the headphone louder. The Pocket SE Class A amp (like most single ended Class A amps) sounds more expressive, dynamic, and open - the sound stage is bigger. The bass is more articulate and the mids are smoother. You want to listen more and it makes your toes tap along to the music. It's related to how natural the sound is. Natural sounds don't have odd order harmonics. So when your ear hears an amp with too much 3rd, 5th, 7th, 9th - it just doesn't sound as natural. Not having global feedback and not having higher order harmonic distortion is important. Sorry can't be more helpful - psychoacoustics is not an exact science.
Think what was meant got misunderstood here so will try explain further
real meaning was that most will feed your nice Pocket Class A Headamp from a DAC or soundcard that most probably use OPA as output stage and if that happen to be single ended output it doesn't need to have more active OPA's circuit to do quality balanced out, it is more clear to see that meaning in the Jensen application note than the ESP site therefor have redraw a possible circuit below because Jensen paper is copyrighted.Example of few passive parts (blue) added to existing circuit:
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Hi Byrtt,
I guess I don't understand how that passive leg connected to just ground is able to drive a second amplifier with opposite phase? If it was that simple, we wouldn't need balanced line driver IC's. For example THAT 1606/1646. Which was what I was about to use...
http://www.thatcorp.com/1600-series_Balanced_Line_Driver_ICs.shtml
I guess I don't understand how that passive leg connected to just ground is able to drive a second amplifier with opposite phase? If it was that simple, we wouldn't need balanced line driver IC's. For example THAT 1606/1646. Which was what I was about to use...
http://www.thatcorp.com/1600-series_Balanced_Line_Driver_ICs.shtml
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Hi xrk971,
Regarding THAT OPA's think they have many other special improved features build in compared to most normal OPA's, as example they over avarage up CMRR so as to be a semipro unit to replace the use of transformers.
If circuit is misunderstood suggestion to feed your amps is question but why not, output impedance is balanced and your inputs are floating and runs on its own batteri supply, will try to simulate in TI and get back tomorrow.
Regarding THAT OPA's think they have many other special improved features build in compared to most normal OPA's, as example they over avarage up CMRR so as to be a semipro unit to replace the use of transformers.
If circuit is misunderstood suggestion to feed your amps is question but why not, output impedance is balanced and your inputs are floating and runs on its own batteri supply, will try to simulate in TI and get back tomorrow.
Balanced Drive First Sound
It was a pain but I rewired my OB-1'a for balanced drive using two 3.5mm stereo jacks (taken by cutting a 3.5mm male-male cable in half) and then connecting that to the 4 wires from the OB-1 (luckily it is a 4 wire headphone and not 3 wire). I learned how to solder Litz wire for the first time.
So I have the single to balanced converters running of a stack of 4 rechargeable 9v EBL batteries for a Vcc of about 34v. Max output swing is 25% of that minus 1v or 7.5v p-p. More than enough to hit max SPL after 12dB gain on the power amps.
Source is the DAC from Focsrite Solo 2G playing high res FLACs. Power amps are NHB's running about 67mA bias with the works. Red amp is Right channel and Green amp is Left channel.
First impressions... WOW!!! It's a completely different ball game. The sheer dynamics, depth, crescendos, all kill a non balanced drive amp/phone combo. It appears to be much louder - probably 12dB? Volume knob is used sparingly.
First track played was Nils Lofgren's "Keith Don't Go" a song know well. The attack on the acoustic guitar is incredible.
Next up are some well tested tracks and all are amazing sounding. It sounds like a full blown desktop amp even though they are pocket amps.
Very very happy with the result. This is going to get made into a PCB for sure and probably is the one thing one can get to really change your listening sound quality to a whole 'nother level.
It was a pain but I rewired my OB-1'a for balanced drive using two 3.5mm stereo jacks (taken by cutting a 3.5mm male-male cable in half) and then connecting that to the 4 wires from the OB-1 (luckily it is a 4 wire headphone and not 3 wire). I learned how to solder Litz wire for the first time.
So I have the single to balanced converters running of a stack of 4 rechargeable 9v EBL batteries for a Vcc of about 34v. Max output swing is 25% of that minus 1v or 7.5v p-p. More than enough to hit max SPL after 12dB gain on the power amps.
Source is the DAC from Focsrite Solo 2G playing high res FLACs. Power amps are NHB's running about 67mA bias with the works. Red amp is Right channel and Green amp is Left channel.
First impressions... WOW!!! It's a completely different ball game. The sheer dynamics, depth, crescendos, all kill a non balanced drive amp/phone combo. It appears to be much louder - probably 12dB? Volume knob is used sparingly.
First track played was Nils Lofgren's "Keith Don't Go" a song know well. The attack on the acoustic guitar is incredible.
Next up are some well tested tracks and all are amazing sounding. It sounds like a full blown desktop amp even though they are pocket amps.
Very very happy with the result. This is going to get made into a PCB for sure and probably is the one thing one can get to really change your listening sound quality to a whole 'nother level.
Attachments
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