iBasso PB-2 Pelican fully balanced portable, DB-2 Dac . . HiFlight recommended op amps page 16. . - Page 42

Well, in all the time I have had the PB-2 I never even considered using dummy adapters in buffer position . Until now obviously.....

 

I use my DB-2/PB-2 mainly as my high quality portable/transportable rig with my ES5's balanced. I have used balanced D7000's and LCD2's at home but prefer the fuller more powerful HifiMan EF-5 for my full sized cans. With the ES5's this sounds considerably more transparent/coherent. More testing is required but my initial thoughts are to leave the dummy adapters in buffer positions and just take some stacked (8 off) BUF634AU's with me when on vacation to use with full sized cans on the evenings.

 

The other thing which has pleased me no end is without buffers the ADA4610-2BRZ doesn't make that scarey thud/screech when turning of the PB-2. This used to worry me a lot.

 

Thanks for the heads up Mike, I'm enjoying the PB-2 more than ever!

Hey Nigel!

 

 

That's funny!  

 

We'd rather add something to our amps, anything at all, than consider leaving any sockets empty.  

 

You probably saw my post on the opamp thread:

 

 

 

 

This is still haunting me.  I haven't found anyone yet who can even support Headphonia Mike's statement, much less tell me how much current is lost by removing the buffers.  I don't have a hard time understanding that fewer components could yield a cleaner SQ, but at what cost (to power, for example)?  Personally, I value transparency/detail over dynamics/slam/bass control, so my leaning is to yank the buffers and not worry about a drop in current output, but I don't want to cripple the whole reason I upgraded to a PB2 from a Stepdance - for more power...

 

I've tried looking for an article or a book that would shed some light on just what a buffer is supposed to be accomplishing and I haven't found anything yet. I don't want to just do the plug and play game, rolling this and rolling that, then listening to various combinations to see what sounds "good," without at least a little understanding of what I'm doing.  

 

Is it true that buffers increase output current?  If so, how much?

 

Is it true that removing them improves transparency?  If so, how much current is lost?

 

Are there any other downsides to removing them?

 

Is it even "safe" for the amp to run it without buffers when certain opamps are in use?

 

And while I'm at it...

 

Is Class A biasing OK when only using resistors to force the op-amp into Class A?  (From what I've read, selecting the right ohm ratings for the opamp in use and other factors is crucial. Too much resistance is just as bad as too little.)

 

What is meant by using a "bypass" for Class A biasing?

 

What's with using caps instead of resistors for Class A biasing?

 

Aren't the risks to SQ of doing Class A poorly far greater than any hoped-for benefits - at least for some opamps that are already great performers when not in Class A?  

 

What about the heat caused when running opamps in Class A - does this shorten their life - or even cause them to run out-of-spec in terms of SQ?

 

More questions than answers.  I guess I'd have to learn how to design amps to really understand this stuff, so meanwhile, I suppose I should just put on a dunce cap and start rolling. 

 

I'm anxious to be something other than clueless, but try searching Google for the word "buffer."  Now try adding some other keywords.

 

Mike

Edited by zilch0md - 5/1/12 at 4:32pm

Here's some recommended reading for those like me who are clueless, but curious, about op-amps:  http://www.bcae1.com/opamp.htm

 

I still don't know what a buffer is good for (except that he says something about how they can help with sources that supply too little current.)

 

Read the whole thing, but don't miss the section at the bottom of the page on how to interpret Data Sheets.

 

Mike

Interesting page. Way over my head but interesting.

Luckily I can rely on HiFlight to sieve through all of the guff and come up with some awesome kits.

I do need to learn more about opamps and buffers though so that I can become more confident in rolling through the choices. The normal process for my D12 and now Pb2 is that I roll through all of the combos that I buy, plug in the best and then stick the rest in the box for a couple of months and forget what their strengths and weakness were and hence not roll any further.

I have three of Ron's combos that I haven't even tried in balanced mode as I didn't have the right cables in the early days.

I really appreciate your input Kremer930.  I can see myself doing the same thing (not bothering to test combinations that are in my possession.)

 

In fact, I'm so "biased" toward the OPA1612s (because of my experience with the Meier Stepdance use of OPA1611s and how great that sounds to me with my LCD-2), that I'm really having to fight the urge to just drop Ron's Topkit 1612 duals into the PB2 along with his HA5002 buffers, then close it up and forget about rolling anything else!     I can tell you that this is what I plan to do about a week after listening to the stock configuration with the balanced cables for which I'm still waiting. I may not leave the 1612s in there for more than a couple of weeks without rolling something, but just as I'm trying to get really familiar with the sound of the stock PB2, single-ended into my LCD-2 with stock Audez'e cables, I want to change only the cables when I get my balanced Silver Poisons from Toxic Cables (they were shipped from the UK, yesterday).  That way, I'll have had about two weeks with the stock PB2, single-ended before going to the stock PB2, balanced.  

 

Meanwhile, I'm trying to take a scholarly approach (yeah, right!) by at least getting to the bottom of what the datasheets say for all the op-amps in my tiny collection.  I trust specs.  And if the specs say that THD is such and such at 1Khz (and other criteria), but something significantly worse for a different op-amp, I want to know about it.  (But that article I linked is over my head, too!  So much for the "scholarly approach! )

 

Maybe I should just trust my ears more than I'm willing. 

 

Mike

I'm really not trying to turn this thread into my personal blog...  but now...  some pictures...

 

 

 

 

Super-Size me!

 

 

Edited by zilch0md - 5/2/12 at 10:04pm

I didn't listen much to the stock opamps/buffers when I got the PB-2, don't know why?? Probably because I knew I had all these great chips to try and never had much time for OPA604's in the past. I dropped the stock set up back it this evening for fun and it is apparent that ibasso did a great job of selecting the default/stock chipset. Really well suited to my balanced ES5's and I'm going to leave as is for a while, man this is a great amp!

Nigel,

 

I'm glad to hear you like the "stock" sound. I'm increasingly disappointed in my PB2, using the stock op-amps and buffers, but I know it's likely due to the fact that I'm still using it single-ended AND/OR that it hasn't had but a week of burn-in.

 

Still, for the record, with insufficient burn-in and singled-ended, having done a lot of A-Bing with the Stepdance, even running both amps with the same 15V supply voltage, same source (Sony PCM-10 Line-Out), and the LCD-2 with stock Audez'e cables... 

 

...  I'm hearing a significant glare with the PB2 - a harshness that's really quite fatiguing.  When I go back to the Stepdance, it's so sweet in comparison that I feel like I can actually enjoy the music instead of fighting to hear it.  

 

But, I know these impressions are very premature.  More burn-in, balanced cables, etc. and I might yet find the stock op-amps and buffers to be very pleasing - just as you do.

 

Mike

I rolled through just about all of the opamp and buffer combinations that I have last night and arrived right back at where I started. I didn't take notes but there is at least one combination of non stock opamps that is very bright but has a very wide soundstage. In the end Ron's recommended combo wins out as it has bass texture and fullness that just about makes me want to go and play a bass guitar or drums.

One thing that I am findin though is that on some tracks that I may be experiencing some breakup of sound. I don't know if it is the iPod, class or pb2. I don't think that it should be the DT1350 as they are meant to be able to go very loud and whilst I am playing at near live volumes I am not totally negligent to the potential damage to hearing.

I should try the am plugged in or fully charged and see if this makes a difference.

If all goes well a friend may be bringing over his Dx100 and sennheiser HD25's tonight so that we can compar rigs. I will also dig out my Vmoda M80 for a play too.

 

You're having too much fun!  OK...  maybe just enough fun!  

 

Do tell:  What is "Ron's recommended combo" (that's working so nicely with your DT1350)?

 

Thanks,

 

Mike

I think the last topkit Ron came up with was OPA1612 (Class A Adapter) + HA5002 Buffers closely followed by LT1678 in L/R.

 

I listened to stock opamps last night with balanced D7000's but ended up stacking buffers which gave the sound a fuller presence. Still OPA604 is a nice chip that I really haven't given much time to. I agree though there is a certain annoying glare after a while. 

I thInk that sounds familiar. They are a great combo.

With this combination of chips the amp takes on a real fun and energetic sound quality. Even lower quality music takes on a whole new appeal. Sound stage is also right up there. It almost sounds like a three speaker setup.

Nigel,

 

 

That's the setup I'm dying to try with balanced cables (when they arrive) - OPA1612 with HA5002 buffers, but I'm especially curious to A-B the difference in SQ with and without the Class A adapters.  

 

Also:  Given that I don't entirely trust my ability to describe what I hear, I'm pleased to see that you, too, can hear an "annoying glare" with the PB2's stock OPA604 setup.  I'm leaving those in however, until I get the balanced cables, because I want to see the difference that the cables alone make vs. single-ended.

 

Soon...

 

Mike

 

Joy!!

 

I can't wait!  (But I must...)

 

But waiting for my Silver Poison balanced cables doesn't stop me from taking more pictures.  

 

I got the XPAL Willy Cable WI16 in the mail today!  Joy!

 

I hooked it up to the Energizer XP8000 and measured its output (a steady 16.08 VDC) and then used it to successfully recharge the PB2's internal battery (without the AC adatper)! 

 

I then used it to operate the PB2 - inky black!  No power supply noise - just like my experience with the WI15 cable (15V) when using the XP8000 with my Meier Stepdance.

 

This rig allows me to operate the PB2 at its maximum permissible input voltage (16.0V), regulated, while portable (transportable.)  And the 16.0V is constant - it doesn't decay during use the way the PB2's internal battery does when it starts out at 12.6V, fully charged, but falls to 9.0V during use, at which point it has to be recharged.  

 

When using the PB2's internal 12.6V battery, the output voltage swing p-p can't possibly be any better than 12.6V (single-ended) or 25.2V (balanced), and can actually fall to something no better than 9.0V (single-ended) or 18.0V (balanced) by the time the internal battery is ready for recharging.  

 

The XP8000 + Willy Cable WI16 keeps the PB2 running at 16.0V constantly, as the 5-cell lithium ion pack in the XP8000 discharges from 21.0V (fully charged) to 16.0V, through use, at which point the XP8000 will have to be recharged.  Depending on the op-amps in use within the PB2 and whether they are a rail-to-rail design (where output voltage equals or nearly equals supply voltage), the output swing p-p can be as high as 32V, balanced (per the iBasso spec), while operating portable with the XP8000, and again, it maintains a constant 32V swing p-p even while the XP8000 battery is discharging from its fully charged 21.0 Volts down to 16.0 Volts, thanks to the constant 16V supply coming from the WI16 inline voltage regulator cable.   Joy!

 

 

My PB2's AC adapter is supposed to be outputting 16.0V, not 16.38V.  

 

 

The XPAL WI16 measures 16.08, but it's regulated and steady.

 

 

Keep the switch set to 16V for the PB2!   The switch is fairly stiff, but I wrapped clear packing tape around that end of the barrel to make sure the switch doesn't get changed. 

 

 

The Energizer XP8000 can deliver 2000 milliamps from its 21V port, so it can easily deliver more than twice the current available from the PB2 AC adapter.  It recharged the internal battery, no problem.

 

 

Best of all, unlike the folks who have struggled to come up with the adapters needed to connect an XP8000 to the Meier Stepdance, for PB2 users it's a piece of cake!   The connector on the end of either the WI15 or the WI16 is the perfect size to plug right into the back of a PB2.   No adapters or soldering required!

 

More Joy!  

 

Mike

 

 

UPDATE:  Several people have PM'd me asking how to obtain the WI16 cable.

 

You have to go the XPAL Tip Finder site and pretend you are searching for a tip to use with a Panasonic Toughbook CF-270, for example (which is only one of several laptops that require the WI16 cable for use with either the XP8000 or the XP18000).

 

http://tipfinder.xpalpower.com/02tip.php?rp=&cno=&did=3&device=Laptop&bid=50&brand=Panasonic&mid=5837&model=Toughbook+CF-270&pid=2&power=XP18000

 

Then place an order from that page - for just the WI15 Cable, not the adapter shown there.  You won't need the adapter, as the WI16 cable can be plugged directly into the power jack at the rear of the iBasso PB2.

Make sure you select the 16V power setting onthe WI16 (because it is also capable of selecting 19V, which is too high a voltage for the iBasso PB2.

Edited by zilch0md - 3/10/13 at 11:57am