[Villy]

Yes, didn't mention it but I made the K7XX balanced too, change the 3-pin mini XLR plug inside the cup with a 4-pin one so it looks 100% stock. They sound great, no question about it, but the amp upgrade really expose their limit...sigh...I definitely need better cans...sigh again...I'm getting TH-0XX in 6 weeks or so which by all accounts gotta be noticeably better, still I'm afraid I will have to get mentally prepared to shell out much more than that. Would love to hook something in the caliber range of LCD-3...another sigh...may borrow from the local shop to check that (and my wife ain't really liking any of it)

Anyhow, had it running continuously since yesterday, notice it is running a bit hotter, just an observation, not so hot to concern me. And let me expand on my comments regarding the sound.

The stage is certainly wider by a lot. So much so that Dr Chesky's right/left ear test doesn't feel like he's whispering right in my ears. It is close but no longer possess that spookiness of a real person whispering, down to feeling his breath. Now it feels as if he's whispering from about foot away. And the imaging, the spacial orientation of the instruments is much more accurate. Again from Dr Chesky's test tracks, there's one where he walks around with a shaker announcing his position. Before, when he announces his position right behind the microphone it felt quite distant, like few feet away at last, not right behind the microphone. Now it is indeed right behind the microphone, it feels as if he's talking right behind my neck, literally, which is how it is supposed to be.

I don't plan to do more mods though, I love what you've done but I'm afraid won't have time for it. I can imagine the sound on your must be really something, that...im afraid requires exquisite cans to appreciate it. I'm grateful that you posted your project for it inspired me to whip the solding gun and dare my ability in that regard. It was 100% worth it, for it not only transformed a great amp into an exceptional one, but also came with the sense of pride for doing it myself.

Will let it burn for a couple of more days and go for another evaluation session.

 

[Exophaze]

Yes, didn't mention it but I made the K7XX balanced too, change the 3-pin mini XLR plug inside the cup with a 4-pin one so it looks 100% stock. They sound great, no question about it, but the amp upgrade really expose their limit...sigh...I definitely need better cans...sigh again...I'm getting TH-0XX in 6 weeks or so which by all accounts gotta be noticeably better, still I'm afraid I will have to get mentally prepared to shell out much more than that. Would love to hook something in the caliber range of LCD-3...another sigh...may borrow from the local shop to check that (and my wife ain't really liking any of it)

Anyhow, had it running continuously since yesterday, notice it is running a bit hotter, just an observation, not so hot to concern me. And let me expand on my comments regarding the sound.

The stage is certainly wider by a lot. So much so that Dr Chesky's right/left ear test doesn't feel like he's whispering right in my ears. It is close but no longer possess that spookiness of a real person whispering, down to feeling his breath. Now it feels as if he's whispering from about foot away. And the imaging, the spacial orientation of the instruments is much more accurate. Again from Dr Chesky's test tracks, there's one where he walks around with a shaker announcing his position. Before, when he announces his position right behind the microphone it felt quite distant, like few feet away at last, not right behind the microphone. Now it is indeed right behind the microphone, it feels as if he's talking right behind my neck, literally, which is how it is supposed to be.

I don't plan to do more mods though, I love what you've done but I'm afraid won't have time for it. I can imagine the sound on your must be really something, that...im afraid requires exquisite cans to appreciate it. I'm grateful that you posted your project for it inspired me to whip the solding gun and dare my ability in that regard. It was 100% worth it, for it not only transformed a great amp into an exceptional one, but also came with the sense of pride for doing it myself.

Will let it burn for a couple of more days and go for another evaluation session.

Been following this thread for a while and managed to find a used A28 which is coming in a couple days!
I haven't had much practice with a soldering iron so seeing your post gave me the much needed confidence to go ahead and purchase some of the parts needed

.
 
So far just the sonic op-amps and sparko regulators are on their way. Also already had a pair of sparko op-amps on hand but are in use with my dac. The rest of the parts can wait once I get a bit more practice with soldering

(and the fact I have no idea what to put down in the custom transformer order sheet).
 
Cheers on your build and hope I get a somewhat similar outcome.

 

[Villy]

Hi Exophase, I think you are making the right decision and won't be disappointed, go for it.

I have done only few very minor fixes solding things like plugs and replacing internal battery, so I'd say my solding skills were next to nothing. If you have similar level of experience it may not be enough to get you through replacing the opamps. You'll need to practice a bit before engaging with the A28's board. In particular disoldering the old chips, it doesn't take much to inflict damage with hot solding iron so be careful.

Go to YouTube and check on videos that go over disoldering chips, get disoldering wick and don't hold the iron too long to the board. And practice before that. I did quite a bit of practice recently building my own cables, including interconnects with micro usb endings, these require really tiny solding points so that helped me a lot. It is not difficult, but you need a little practice to make you understand how solder behaves, and be careful and patient. Don't hesitate to ask questions if in doubt or something's not clear or obvious.

I thought about the transformer, but decided to leave it alone as my components are hooked to very good power filter/cleaner via some of the best power cables available. Speaking of cables, cables are very important but that's a whole another topic. And I wish I could go for the rest of the mods b0bb did, but that's only in the realm of wishes at this point.

 

[Exophaze]

Thanks for the advice, I'll definitely try to do some more research first and do some actual practice. I probably have some usb cables lying around the house that I could use as a sacrifice

. Also have a pair of headphones that keep cutting out so that's another source for some more experience.
 
Funny how I actually planned on making interconnects first and came upon this thread after finding an A28 at an enticing price especially since I was in the market for a balanced amp. If I see myself not screwing up too much I might try to re-cable some of my headphones, though preferably I'd like to have them outfitted with detachable cables.

 

[Villy]

Definitely fix your headphones first, it is easier than replacing the opamps and there is far smaller chance to screw by overheating. And yes, replaceable cables is the way I'd go. Here's a pair of Musical fidelity cans which I outfitted with 3.5mm plugs for quick connection in place of the fixed cables.On top of one of my diy set of cables. The way the connectors stick out of the cups is a bit kludgy but I'm not concerned with that at all, functionality and solidity were my goals and it satisfied both. Ideally, if the cup can accommodate a connector either natively (like K7XX, second picture, the original socket was 3-pin and the 4-pin fitted in its bed perfectly) or by expanding the hole then do that, else this is one of the options but you can choose any type of connectors, I see it as a matter of preference.
 
So fix your headphones and finish the interconnects first, then embark on replacing the opamps and regulators.
 


 
Having detachable connections allows you to swap cables in the quest for the best sound, very important. Cables matter, and matter far more than people like to admit (I think because it is difficult for many to justify spending big money on 'just some' cables), and like all else cable are not created equal.

 

[b0bb]

I have no idea what to put down in the custom transformer order sheet

 
The transformer I used was to enable increased power delivery, to drive the LCD3, the A28 in stock form is a touch underpowered.
 
I noticed from Villy's pictures that the standard transformer is bigger that the one originally in my A28 so Yulong may have realized this as well.
 
If you have difficult to drive phones consider the transformer and it will need the Belleson regulators as they handle up to 2A while the Sparkos stop at 1A.
 
Simpler options like the opamp swap should be the first attmpt at mods before changing the transformer.

 

[Villy]

The transformer I used was to enable increased power delivery, to drive the LCD3, the A28 in stock form is a touch underpowered.
 
I noticed from Villy's pictures that the standard transformer is bigger that the one originally in my A28 so Yulong may have realized this as well.

 
Hmm, it just now occurred to me to look at your pics and the transformer in my amp looks just about the size of your upgraded one. As for as power, yes Sparkos have 1A output, but with volume on my amp set at 9 o'clock K7XX are pretty loud, about as loud as I would normally take when listening to music with purpose. As opposite to when I have my headphones on and simply used them as a pleasant background while I am engaged in work or otherwise some other activity that isn't attentive listening to music. And when the latter is the case, the dial will be around 7 or just barely off point zero. And this is at 0db preamp gain from JRiver (my player of preference), equalizer off actually, where with EQ on the preamp signal can be boosted by 12db and that's quite a bit.
 
Now, granted K7XX is only 62ohms, very lightweight compared to 600+ohms beasts, and LCD3 is rated at 110 (though optimal power requirements call for 1-4w). Stock A28 puts out 1.3 at 150ohms and likely 1.5-1.7 at 110, I thought that would be OK. I hope it would be, for when time comes to get my hands on something like LCD3

. And if it isn't, I guess will be replacing components as needed.
 
The amp has been running non-stop since the mods I did yesterday late afternoon, and as I noted is notably warmer than before. Don't have thermometer handy to take exact measurement, my guess is the top is warmer by some 20-30F. I realize this isn't actually hot (temperature overall doesn't feel higher than maybe 130F), but maybe I should help it ventilate, thinking of a tiny PC fan blowing silently thru the side vents just stirring air.

 

[b0bb]

   
Now, granted K7XX is only 62ohms, very lightweight compared to 600+ohms beasts, and LCD3 is rated at 110 (though optimal power requirements call for 1-4w). Stock A28 puts out 1.3 at 150ohms and likely 1.5-1.7 at 110, I thought that would be OK. I hope it would be, for when time comes to get my hands on something like LCD3

. And if it isn't, I guess will be replacing components as needed.

 
The numbers you are using is based on a steady state case, for headphones like the LCD3 it is the peak dynamic current demand that is important.
Impedance is measured at specified frequencies so it is steady state type measurement.
 
The current is needed to accelerate and decelerate the heavy panel, this is one of the things Audeze fixed in the LCD4 with the very light diaphragm.
 
Audeze quotes a sensitivity of 103dB output for 1mW input for the LCD3F
The drive requirements for the amp is 1-4W.
This means 99.975% of the power is used to move the panel back and forth.
This is not real power as the charge is moved from one side of to the power supply to the other. It is referred to a reactive power.
In the example below only 20mW is expended as real actual power.
 
Typical drive voltages for the LCD3F with music is between 500mV and 1.5V.
The peak current requirement is 4/1.5 = 2.67A
 
This is a very short lived spike, the closest analogue is the initial current spike that is observed when a capacitor is charged up, traditional measures like impedance are averaged values over time, it does not adequately capture this initial behavior.
 
The powersupply however must be able to supply the required current in order to bring the LCD3F to its full potential.
 
 
The Belleson tops out at 2A so it just barely makes the grade.
 
My transformer is 57VA@36V, this 1.58A at full load, stock is 30VA@30V, this is 1A at full load.
 
Transformer makers define full load as the maximum current that the transformer can deliver before the voltage output drops below the rated specification.
 
If the amp starts to demand more current beyond full load, the raw voltage from the transformer will fall in order to deliver the current demanded by the LCD3F load
 
DC input at idle is ±25V with my mod  and ±18V stock.
 
Stock has 20% margin, so the stock powersupply is able to supply up to 1.2A
With my mod there is 60% margin (10V margin over the 15V DC output), the powersupply is able to supply up to 2.52A, the Belleson will allow for this for short periods.
 
The downside is the extra 40% margin is burned off as heat when the amp is idle, it actually runs a little cooler when active, the A28 is overbuilt with oversized heatsinks so it makes it possible. This is  also the reason for all the thermal interface material, it transfers the heat onto the case.
 
If the LCD3F's ideal peak drive current is not met, the soundstage collapses and the music starts to lose its transient content, adequately driven with sufficient current, the LCD3F becomes a completely different animal, putting the transient performance within striking distance of the HD800. This is my experience with my LCD3F compared to my HD800.

 

[Villy]

Now I understand why it is not easy to drive properly those planars, and how to approach acquiring one if and when I get around to do it. And the heat dissipation, no wonder my amp is warm - it pretty much idles. Thanks for the breakdown, concise and straight to the point!

 

[Exophaze]

Luckily most of my cans are fairly easy to drive... except for the HD800. b0bb, would you by any chance know if they'll be fine with the sparko regulators and default transformer?

 

[b0bb]

  Luckily most of my cans are fairly easy to drive... except for the HD800. b0bb, would you by any chance know if they'll be fine with the sparko regulators and default transformer?

The stock transformer is good to 1-1.5W output.
 
The only thing in your inventory that might give the A28 trouble is the HiFiMan HE500. If you have not sold yet, hold on to it to stress the A28 before and after the mod.

 

[Exophaze]

Thanks! Getting the A28 tomorrow so I'm looking forward to it

  The stock transformer is good to 1-1.5W output.
 
The only thing in your inventory that might give the A28 trouble is the HiFiMan HE500. If you have not sold yet, hold on to it to stress the A28 before and after the mod.

Thanks, appreciate the input. I've been running the Hifiman and HD800s over speaker taps so I'm just glad I finally decided to get a proper amp for these two (though the Hifiman may be going soon).

 

[solblack]

A28 Push my HD650 with no problem but my Alpha Dogs I believe A28 does not step up to the plate as well.
Change cable and plug into my DA8 and the dogs are rocking.
Strange?

 

[b0bb]

  A28 Push my HD650 with no problem but my Alpha Dogs I believe A28 does not step up to the plate as well.
Change cable and plug into my DA8 and the dogs are rocking.
Strange?

What was the problem?
I was thinking about getting the Alphadog prime before it disappears.

 

[Villy]

I got the Alpha Primes today, used year-old, listened to them for 5-6 hours - in short, WOW! I posted (maybe not so) brief impression summary on the impression thread, please check it out if interested (I rather save my typing for later . And I'll be glad to answer any questions/inquiries.
 
A28 drives them just fine, and I'd say with relative ease thru the high-nonbalanced - at 12 the sound is really loud, at 3 becomes unbearable. With 0 pre-amp gain. Don't have XLR cable yet, will have it in few days and report back on that, but expect the balanced connector to put even moire juice out. not to mention upping audio quality. Apparently they are much more efficient than the Dogs, because of the redesigned drivers, so that I guess that explains it why A28 seems to have no problems with them.