[xrk971]

Hi Dbaldock9,
I thought you would like this. I'm going to modify my OB-1's tonight to be balanced drive. Then have a test listen in stereo. From the sims and oscope traces it should sound fantastic. Another Hugh Dean (Aspen Amplifier) design and collaboration. I was originally just going to make an all inclusive desktop amp with this converter and two pocket amps all on one large PCB. But it seems there may be interest in a standalone converter. Four 9v batteries will give about 32v to 35v rails which should be more than enough for most portable uses. It won't fit in an Altoids tin though. Bias current through the two BJT's is less than 7mA so 4 x 9v (600mAhr) batteries should run for a long time for 14mA combined - circa 40hrs.

 

[DBaldock9]

Sounds wonderful with good full range speakers too. Playing in the speakerlab: on the left is an XKi (Xrk's Karlson ab-Initio 6th order bandpass) with Tang Band W5-2143 and on right is tapered TL with Fostex FF105WK. Both are circa 89dB sensitive drivers with cabinets that give them bass extension down to about 55Hz,



Also note that you can plug in headphones in addition to listening to your 8ohm speakers simultaneosuly. It can handle it.

Back in the '90s, one of the companies I worked for, sent a group of us Techs to a training class taught by Sy Levine [ http://theconversation.com/profiles/sy-levine-126969 ].
During the break between sessions, the subject of loudspeakers came up - and he mentioned having some original Karlson enclosures.
I don't remember now, whether he said that he had known John Karlson, or had just bought the speakers because of the unique design.

 

[xrk971]

Karlson's are unique speakers. They are very efficient and have a clean dynamic sound. Wide dispersion via acoustic lens. I happen to be a Karlson fan and user. I have even developed a computational model of the Karlson and it's variants in Akabak (acoustic modeling and simulation software package).

Here are my threads in DIYA on the Karlson and variations (Karlsonator, Kazba, and XKi):

http://www.diyaudio.com/forums/full-range/237948-speaker-kicks-butt-large-spaces.html

http://www.diyaudio.com/forums/full-range/239338-mini-karlsonator-0-53x-dual-tc9fds.html

http://www.diyaudio.com/forums/full-range/271011-rockin-kazba-dipole-k-aperture-z-baffle-dipole.html

http://www.diyaudio.com/forums/full-range/268524-xki-xs-ab-initio-karlson-6th-order-bandpass.html

 

[DBaldock9]

Hi Dbaldock9,
I thought you would like this. I'm going to modify my OB-1's tonight to be balanced drive. Then have a test listen in stereo. From the sims and oscope traces it should sound fantastic. Another Hugh Dean (Aspen Amplifier) design and collaboration. I was originally just going to make an all inclusive desktop amp with this converter and two pocket amps all on one large PCB. But it seems there may be interest in a standalone converter. Four 9v batteries will give about 32v to 35v rails which should be more than enough for most portable uses. It won't fit in an Altoids tin though. Bias current through the two BJT's is less than 7mA so 4 x 9v (600mAhr) batteries should run for a long time for 14mA combined - circa 40hrs.

Is this circuit, which operates on twice the supply voltage of the NHB Class A amplifier - just an input / driver to connect to a pair of NHB boards, or is it a whole stand-alone Balanced Amp?
Also, is it one additional circuit card per pair of NHB Amps, or is it one new card for each amp?

If this new circuit is meant to drive a pair of NHB Amps, how many 9V batteries are going to be needed?
Is it 4 for the driver, and then 2-each for the amps?

I'm still awaiting the 18V @ 3400mAh Li-Ion Battery Pack & Charger that I ordered from SuPower Battery (there was a mix-up by the freight forwarder here in the USA, and they misdirected 3 packages).
If I had known that the input circuit would need twice the voltage, I would have ordered a pair of the battery packs.

 

[xrk971]

I am wiring up a 4 x 9v battery pack now and just tested it. Works well to power them. You need two converter boards for stereo. And two NHB amps. Basically one converter board and one NHB amp per headphone can. This just provides the NHB with balanced (180 deg out of phase pair of signals). The left and right of one NHB drive the +ve and -be phase of the headphone diaphragm in opposition.

I only came up with this circuit in past week and had no idea I would need 35v to 48v to drive it. Four 9v batteries is the cleanest way to do it. Very low noise and 40hrs is great life.

 

[xrk971]

First sound from Pocket NHB's and balanced drive converter.

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.

 

[DBaldock9]

First sound from Pocket NHB's and balanced drive converter.

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.

So, with the NHB amps running from their own pairs of 9V batteries - you're using a total of 8x 9V batteries?
Currently, I've only got 6x of the 9V batteries, and two dual battery chargers (1 at home, 1 at work).
How many batteries & chargers do you have?

 

[xrk971]

I have a lot of batteries and chargers. Probably 16 and 3 chargers. I have them on hand because some customers can't get their own in their country. This was just a test and by no means represents how this would be run in its ultimtate configuration. The phase converter is a relatively low current draw and there are plenty of IC's made for generating 48v phantom power via charge pumps. But really I think balanced drive is ultimately best realized with a new PCB that has everything on it: 2 phase converters and 2 amps, plus the necessary power supply system so that a LiPo battery can be used. But for now, it takes 8 batteries to power.

 

[xrk971]

Some more notes...

1. After a little more listening and tests I am finding that the interconnects between the phase splitter driver board and the power amps is critical. Use of 3.5mm stereo jacks is prone to noise as jiggling it can result in changes in background noise and a lot of popping if a disconnect occurs. Balanced drive is very very sensitive - essentially increases sensitivity of the headphones and makes them very resolving of low level detail. So I think this may not be practical to do with removable interconnects between balanced driver and power amp stages.

2. Because the output of the phase splitter is already capacitively coupled, there is no need to add more caps on the input of the power stage. Or vice versa, one can removed the caps on the phase splitter output stage.

3. If carefully matched FETs such as that used in the NHB are employed, and the bias of both +ve and -ve channels on each amp is carefully matched, then one can forgo output caps altogether as the voltage on each side will balance out for net zero current flow through the voice coil. Alas, about 7v DC will be sitting on each side of the voice coil but net DC offset of order 0mV to 5mV it can work. However, an uncomfortable proposition it will be should one side be inadvertently become unbalanced due to interconnect jostle or failure. But there will probably be increased resolution and dynamics possible in a DC coupled output configuration. It may be Ok to test and experiment with full knowledge one could destroy a set of cans with one false move. Hmm... I think I will leave the output coupler caps in place

I think this will be best implemented as a new fresh *integrated* PCB with all circuits on one board with small tight traces, full use of SMT components for the input phase splitter BJT's (vs TO92 through holes that I am now using). A delay turn on relay and possibly DC detect and protect output cut-off can also be added. This is all a lot of work though... but the resulting desktop amp can be very glorious sounding.

I may even switch to a CFP BJT topology for the output stage which will give even more resolution and better dynamics.
Attached Thumbnails

 

[xrk971]

Presenting a prototype PCB of the HyQu amp - a Class AB hybrid quasi complimentary amp with the ability to drive low impedance cans with authority while providing the harmonic distortion profile that resembles a low distortion SE Class A amp. Here is the first sound test of the amp with a single rail 24v power supply. Very dynamic, powerful, transparent sound with super resolution.

 

[xrk971]

Now in stereo. Wow!

 

[DBaldock9]

Now in stereo. Wow!

Is the green inductor part of the power supply voltage step-up circuit?

 

[xrk971]

The inductor is in parallel to a power resistor and is part of the Thiele network to ensure unconditional stability into any load. This is standard practice for Class AB amps with some global feedback (although very small as feedback amps go).

 

[jonmbarlow]

Ordered the uber NHB with rechargeable batteries.....really looking forward to the sound that this little device is reportedly capable of

 

[xrk971]

Measurements of the HyQu are very nice. 1.41vrms into 270ohms shows 0.003%THD with 28ppm H2 and about 9ppm H3 and monotonically descending higher orders. Flat -130dB noise floor (this is running of AC mains). Sound is exceptionally detailed and resolving. Data shown for 24v Vcc and 95mA bias current.