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iBasso PB-2 Pelican fully balanced portable, DB-2 Dac . . HiFlight recommended op amps page 16. . - Page 6

post #76 of 1424

I don't know if I would say that the cost of recabling with an expensive cable is worthwhile, but it is very easy to balance the stock cable by just adding the appropriate connector.   That only costs a few dollars.   As the HiRose connector is not real easy to work with, I would just buy the iBasso pigtail connector and use a standard XLR 4-pin connector on your KSC75. 


I can't answer if it is worth it though.  I like mine balanced but I have lots of time to tinker and play with wires and gadgets.  The TWag cable on my KSC35's was a joint experiment between myself and Craig with the wire first was introduced. 

Originally Posted by estreeter View Post

Originally Posted by HiFlight View Post

I don't have my KSC75's balanced, but I do have a set of balanced KSC35's with TWag cable and they sound superb, more like multi-hundred dollar phones.

Ron, I'm always up for a challenge, but is it seriously worth the cost to have a pair of KSC-75s balanced ? I have a pair on the way, but they cost me $39 delivered - I guess its different if you can do this stuff yourself, but for me it would be serious overcapitalisation :)

post #77 of 1424
Originally Posted by HiFlight View Post

The Hi-C as provided by iBasso is not the maximum wideband, but rather about halfway between low and high bandwidth.  The does have the effect of lowering the input impedance of the buffer stage and providing better square-wave response of low-signal inputs.  This arguably can result in improvement of low-level detail while the lower impedance allows an increased, albeit farly small, current flow from the LR opamps.. 


When driving my HE-6 to my normal listening level using high gain,  the stacked buffers running Hi-C get only slight warm to the touch.  Although my cellphone is in fairly close proximity to my PB2, I have not experienced any RF interference while using the Hi-C configuration. 


I do have some of the LME49990 opamps that I will try.   The specs do look very good, but I have been somewhat unimpressed by some of the other LME49xxx opamps, so they kind of gotten placed on the back burner. 


I will say that my current configuration is really making my HE-6 sing sweetly!

erm Ron, the point of RF oscillation (notice I didnt say interference) is that its in the RF, we cannot hear RF so you cannot 'experience it' to do that it would have to be down in the audio band which is a factor of 3 lower bandwidth (kHz vs MHz) what you hear with mobile phone interference is sidebands of the main signal that exist down in lower frequencies. it may instead manifest itself in oscillation,


opamps are designed to drive MASSIVE impedances like other opamps, which generally have extremely high inputZ so they are capable of driving a wide range of loads. I cannot see how this better dealing with low level will effect anything much audio related, except a chance of a phono preamp or something with really massive gain on very low level signals, not on a 4-5v output from a balanced dac which is then amplified by in this case how many opamps?


the buffers are inside the feedback loop so outputZ of the circuit should be close to nil. thing is though and this is why I recommended the national chip (only if heatsinked) instead of stacked buffers, that these DIP8 and SOIC8 packages are designed to use the PCB for heatsinking, using stacked dip8 packages in a socket...well you should see where i'm going. if they are only just warm, you are not using high current


dont get me wrong the BUF634 can and does often sound very good, i've used them for years and have been very happy with them, but a single heatsinked package like the LME49600 or even a to220 buf634T is IMO a much better choice, shorter feedback paths, better dissipation specs, lower inductance etc etc. so if possible I would try it and this amp provides enough room for it.



oh and I totally agree re the sound of most of their chips until now, to use a term I hate; they sound too 'HiFi' technically brilliant, but boring as hell and lacking any substance.


not this one so try it LME49990 I mean

post #78 of 1424

Hi Ron, How is the PB2 compare with P4 for the SE part? Is the PB2 also have a G/V channel to roll?

post #79 of 1424

there is no ground channel in a balanced amp. in fact there is no signal ground at all in a properly balanced amp, Vground or not. the only connections to 'ground' are in the power supply. so the only way they would possibly have a signal ground channel amp would be if they installed this specifically to drive the single ended outputs

post #80 of 1424

Not only is this thing sexy (I really like this matte black finish!), but sounds fantastic right out of the box...Ill have to wait for A/B comparisons but WOW!

I love balanced amps now, the HD-650s never sounded this good before I got the PB1/2

post #81 of 1424
Originally Posted by jamato8 View Post

Originally Posted by GeorgeGoodman View Post

I will have to try my balanced PortaPros when I get the PB2. 

Thanks. Just curious, how did you terminate them?

With a HiRose. I would like to use Twag on them, I think the PortaPros are that good but I have limits. :^)

Thanks, Jamato. I will probably do what Ron says below, are send it to somebody to do it.



Originally Posted by HiFlight View Post

I don't have my KSC75's balanced, but I do have a set of balanced KSC35's with TWag cable and they sound superb, more like multi-hundred dollar phones. The PB2 drives my K1000s much better than the PB1 did. Bass is now very satisfactory. Not much different than my desktop. I must say, though, that I have changed opamps MANY times today searching for what will ultimately become the PB2 Topkit. I am also using the stacked BUF634's in Hi-C mode.


Most of the improvements that I noticed as a result of balancing my KSC35's were related to imaging and stability of soundstage. Tonally, I don't notice a great deal of difference.


I have been too lazy to keep changing gains, as this is accomplished by internal jumpers. Even at high gain which is what the PB2 comes with as default, the channel balance is perfect even at the very low settings necessary with the high gain and KSC35s. I can also turn down the input from my source if I need to as that is easier than changing jumpers. .  BTW, all of my IEMs and smaller phones I terminated with mini-XLR connectors, then made up a Hi-Rose to Mini XLR pigtail that I can use with all of my smaller phones.  For the larger cans, I made up a Hi-Rose to standard XLR 4-pin pigtail.  

Originally Posted by GeorgeGoodman View Post

Sounds awesome! What about the K1000? I know you posted your rig of the Boomslang and PB1 with the K1000s a while back, and mentioned it lacked some authority in the bass but you loved it because you could take it around. I think I am going to get this amp sometime, it is just a matter of when.


BTW, how do balanced KSC75s sound out of this? If you no longer have a pair, can you mention the improvements to balancing them? I just got a pair and really love them, and am going to really mod them in the future.


Thanks for the reply. Sounds really amazing. I am still getting my mind around how much the various adapters cost. Do you think it would be economical to just get the 4 pin to Hirose adapter and then have all the phones I want balanced balanced in a four pin? It would make them easy to run out of a receiver and one connector instead of two would be less cumbersome. Of course, none of this is going to happen until I get the PB-2, which might be a while. I am actually going to run an equalizer in the middle of my balanced setup, as I have always wanted one and it has level control for both channels, useful for my unbalanced phones and any others I get. I find myself adjusting the bass between songs on my H120, as well as the pan balance, so this would make it easy. This or a JH3A or SR71B, both of which are out of my reachbiggrin.gif!

post #82 of 1424
Thread Starter 

The balanced voltage swing of the PB2 with the adapter is 32  volts or 16 pos and 16 negative. With the battery, it is 25.2  as the battery is 12.6 not 16 volts. With  a 16 volt charger, unless you stepped it up, you couldn't have a 16 volt battery, the adapter would have to be of higher voltage. iBasso confirms that the battery is 12.6 and the same battery as the other 12.6 amps they have. So to maximize everything on the desk top, it would be run from the adapter, giving it 32 volts of swing. 

post #83 of 1424

I see. However, there is still more power than the PB1 obviously, even without the adapter.


How much of a difference do the people who have it hear with adapter and with the batteries?

post #84 of 1424

Hi qusp, 



For prototyping the possibility of your mod

I could not find 4 unused LME49600 instead I used 4 TO220 with an possible (Still need to cut the bottom) heatsink that may fit into the PB-2. 

One thing I notice on the PB-2 is that the position of the buffers are between the OPA and the vol pot 3.5mm connectors 


That leaves a few option.

1) Leave the cover open all the time.


2) Take the battery outside the box and leave the heatsink with LME49600 at the space occupied by the battery

(This will open up the options of having a bigger battery and maybe a higher voltage)


3) Reverse mount the 4* LME49600 on the cover of the PB2 using the cover as a heatsink maybe with the LME49600 pin wired into a 8 pin socket. 

Either that or some precision positioning so that when the cover is close the leads will slot into the 8pin sockets nicely. 


Option 2 and 3 require some wire which might not be a very good idea if you are concern of high freq osc. 


But anyway it certainly sound like a very interesting and fun mod, just for the hack of it.  



4X To220.jpg


post #85 of 1424

I'm planning to buy a balanced portable amp for use at home and work with balanced HD650s and balanced DT770/600s - can anyone tell me how the PB1 and PB2 compare in terms of SQ when used with either of these headphones? Also, if there is an audible difference do you think it's worth the extra $96? I won't be rolling the opamps.

post #86 of 1424

haha madwolf yeah thats the ticket cool.gif . option 3 sounds best to me, but add some small damping resistors to help with the lead inductance in case of oscillation; with such a wideband device could be a problem. this trick seem to work with offboard mounting of wideband power transistors in power amps, though not ideal. I had in mind a PCB with 2oz or 4oz copper with the national LME46900/10 and use some silver epoxy to glue some little CPU heatsinks either directly to the package, or to the underside of the PCB with a heap of thermal vias to suck the heat through. the PCB will have a fair bit of copper and surface area on its own if you use 2 or even 4oz FR4 double side, leave one side solid copper with only connections for the dip pins or whatever surrounded by copper pour and the other with just some local SMD bypass caps on the power pins and the rest coper with vias to connect to the other side. you could even use the 2 or 4oz without the sink and just tin it with a crapload of solder to add mass. the sink would be ideal though of course, PC tweaking extremist sites should have something suitable


haha even a little waterhblock lol now i'm just being silly



i'll do up a rough so you see what I mean. 


indeed looks/sounds like fun!! good luck!! beerchug.gif

post #87 of 1424

Warning !!!!! qusp


The Tab or what you call it on the LME49600 is connected to Vee, might need to check if there is anything connected to the case before using silver epoxy. 

Otherwise I assume all 4 chip should be connect to the same Vee and Vcc but not sure if there would be any ground loop problem later on. 


Unlike the To220 the T263 case does not come with a screw mount. so I am a bit worried of the mounting. maybe silver epoxy with individual islands of heat sink


Notice the Mica sheet on the photo. 

post #88 of 1424

sorry I assumed you knew the tab would be live, it usually is, need to use an isolation pad. keratherm red is my fave, but a silpad will do. I dont have this amp mate, I just dropped in to have a look and saw you here so thought I would throw some suggestions around and egg you on as I kniow you are usually up for some extreme mods ;)


thats why i've been talking about a PCB for the heatsink primarily, so it could be easily thermally coupled but not electrically, but even with the LME49600 you could do it no problem with one heatsink with silver epoxy sticking it to the isolation pad and silver epoxy to bond it there from the other side. separate sinks would work too, but my favorite is TO263 with a heavy copper PCB, have you made PCBs before?


it would be extremely unlikely to get a ground loop with such a small build with elements that all draw their power supply 'ground' from the same reference, but for power I would check VCC to see if there is continuity already. I wouldnt personally as this amp probably has 4 regulators and 4 discrete power supplies, I wouldnt waste that by connecting them all together. thermally coupling them is ideal because they will all track thermally and CMRR will be better that way as the performance changes with temperature, but probably best to keep them all electrically isolated

post #89 of 1424

you can also leave out the epoxy and use a hole drilled on either side of the tab/body and screw down a small bar or piece of copper over the plastic molded body part to pinch them against the sink with an isolation pad underneath. ive used this method before with the fiddly little LU1014D TO251 (IPAK) power jfet package

post #90 of 1424
Originally Posted by saggett View Post

I'm planning to buy a balanced portable amp for use at home and work with balanced HD650s and balanced DT770/600s - can anyone tell me how the PB1 and PB2 compare in terms of SQ when used with either of these headphones? Also, if there is an audible difference do you think it's worth the extra $96? I won't be rolling the opamps.


I think the difference is worth it. The PB2 sounds better, and is more powerful. Besides, you may decide want to roll opamps later. Hiflight usually makes up a topkit that includes everything you need to make the amps sound better, so it is not hard. Also, if you decide to get another headphone or get a deal that you can't resist, especially on one that is hard to drive, the PB2 can probably drive it. 

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Head-Fi.org › Forums › Equipment Forums › Portable Headphone Amps › iBasso PB-2 Pelican fully balanced portable, DB-2 Dac . . HiFlight recommended op amps page 16. .