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Getting the best out of Allo.com's new Katana DAC...
Getting the best out of Allo.com's new Katana DAC...
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Old Today, 07:21 PM   #121
Greg Stewart is offline Greg Stewart  United States
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Join Date: Jul 2003
Location: Columbus, Mississippi
Getting the best out of Allo.com's new Katana DAC...
Some quick responses...

@terry22, on testing the IsolatorPi on the Katana, I have not. Actually, I was not planning to do that test myself, just find out if the IsolatorPi should work ok under a Katana and post that info here.

Ian did tell me his I2C signals are bi-directional, but I have yet to find out exactly what mods Allo made to the Isolator 1.2 and what lines need to be bi-directional to make it work. Should have that later this week. IF you have one of Ian's IsolatorPi's, give it a try and let us know... as long as you have things powered correctly, it should not hurt anything. EXCEPT I would not have it hooked up to an amplifer and speakers (or expensive headphones) to test. In situations such as this, I plug in a cheap RCA cable at the DAC output and use a cheap cellphone headset across the output contacts to verify if things are working correctly before I risk my amps and speakers.


@alexkosha, I have to correct what I said above... I have a couple of Salas Mini-Reflektor boards almost built for 5V each, that's what I'll try at some point, but again likely not soon. BUT I suspect the latest Salas UltraBiB will be near the top of the performance curve for all of the rails on the Katana and very likely above what I'm using and have tried so far.


@Markw$, I also have some other large (100uF/200V & 1,500uF/700V) polyprops I can try across various lines... sort of like with the Salas above, someday.


@stellarelephant, thanks for the review... I'll send you a check later this week . Actually, Kevin's tests with the modified Jamecos are why I started considering them for things like Katanas. I originally modified several for use replacing the SMPSs on networking gear, with the mods mostly designed to lower noise fed back into the AC line by the Jamecos (adding an AC filter cap, a John Swenson transformer secondary ringing snubber, and good Schottky diodes). I never intended to use them as low-cost alternatives power supplies for DACs and boards like Isolators and Kalis. Darned surprised that they work as well as they do!


Then a general note... I want to be clear I DO NOT intend to try to test ALL available options under consideration or discussion here. I do not have interest, time, money, bench space, bench time, or listening time to do so. I've got a lot of other projects in the works... now including improving my other 'best' digital sources. I'm hopeful that others will continue to chime in with their suggestions, ideas, and results. AND thanks for those who already have!!!!

One area I do want to test further that I haven't mentioned before is output stages. I strongly suspect a LOT of the SQ I'm hearing out of the Katana is due to the Sparkos discrete opamps used in the output stages. I think it's worthwhile to confirm that and how they stack up to some other options. BUT, using a different output stage on the Katana would be tricky, given how that board is sandwiched between the DAC board and Microprocessor board. My thought is to use Ian's ES9028Q2M board as a test bed for those comparisons, as his controller is a seperate unit and his output stage is the top board of the stack. I've given some thought on how to adapt the Katana output board onto Ian's boards (heck, I've given some thought on how to fit one on my ES9028 BIIIPRO setup too!) and think it is do-able. I'll get Markw4's OPA1622 I/V stage info from his ES9038Q2M board thread. I've got Ian's OPA1632 board here (need to populate it) AND am getting info on his OPA861 I/V setup too. Another one that is pretty easy to implement is one based on the AD844 chip, there's a long thread on that in another forum here.

AN interesting aside on this, there's a recent thread on Audio Asylum discussing alternative opamps to replace LM4562s for DACs and other purposes here:

LM4562's - bobwire - Tweakers' Asylum

While it goes off the rails for a bit, it has some interesting discussion of various options including the OPA1622 (and the FET-input OPA1642, which also now goes onto my list) AND several posted experiences with using discrete opamps too, including the Sparkos. Their comments mirror what I've seen in other similar threads, that the discretes generally beat the monolithics, but it will be useful to try I think.


Finally, I did some additional listening tests on alternative supplies last night with some VERY positive results... should make @randytsuch happy... more later today or tomorrow.


Greg in Mississippi
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Old Today, 08:35 PM   #122
Markw4 is online now Markw4  United States
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Quote:
Originally Posted by Greg Stewart View Post
I'll get Markw4's OPA1622 I/V stage info from his ES9038Q2M board thread.
Greg,
It's OPA1612, just to be clear. Post #3003 contains that schematic, although I am not using nor do I recommend the balanced outputs as MrSlim showed them. I replied in a subsequent post about a preferred approach if balanced out were wanted. Output stage assembly instructions I was requested to create can be found here: Dropbox - Output Stage Instructions.zip Also, after writing up the instructions, I went back and put in heavier gauge +-15v wires for each opamp to help keep power supply impedance low back to the bigger filter caps. In addition, Katana locates the AVCC dividers to produce Vref on the output stage boards, whereas the modded dacs do that closer to the AVCC power supply. As a result, the dividers are not shown on the output stage schematic.

Regarding opamps, I tend to go for low distortion types, and try to avoid picking opamps to color the sound. Philosophically, I don't want to color the sound and most low distortion opamps used for audio should sound almost exactly the same unless there is still a problem with the circuitry somewhere. For LME49720/LME49860, RF such as from DECT phones can also cause problems. Also, when discrete opamps are preferred over IC, I always have to wonder if a little low level euphonic distortion is behind the preference. It can sound nice in some ways, but there may be more IMD too for people who notice that. It may be more audible on musically dense recordings.

Last edited by Markw4; Today at 08:52 PM.
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Old Today, 10:50 PM   #123
Greg Stewart is offline Greg Stewart  United States
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Join Date: Jul 2003
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Getting the best out of Allo.com's new Katana DAC...
@markw4,

Thanks for the correction. Yes, it was the OPA1612 that was mentioned in that Audio Asylum thread as a very good monolithic IC opamp for I/V purposes. Apologies for the confusion.

Also thanks for the guideance on where to pickup the details on your OPA1612-based I/V stage. I've downloaded the instructions and will look at those posts.

AND I'm getting the impression that we have somewhat different perspectives on what constitutes good audio design. I tend to align with those who suggest that after a certain level of measured distortion lowering, further improvements are not audible. AND that some of the techniques used to produce extremely low distortion measurement in circuits and filters will produce poorer sounding results.

Of course, given that each of us have different and personal 'hearing mechanisms' (physical and our internal processing systems), different sets of criterial by which we judge how audio systems should be designed, built, and sound, and that the filtering of our former through our latter will always produce somewhat different results person-to-person, I do think it's good we have plenty of space in our hobby for a variety of views. AND I appreciate and respect yours!

Greg in Mississippi
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Old Today, 11:12 PM   #124
Markw4 is online now Markw4  United States
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Quote:
Originally Posted by Greg Stewart View Post
I tend to align with those who suggest that after a certain level of measured distortion lowering, further improvements are not audible. AND that some of the techniques used to produce extremely low distortion measurement in circuits and filters will produce poorer sounding results.
No, that's not it I don't think. I can hear very low distortion levels here, and you probably could too if you were here. For one thing, my power amp is ultra low distortion. Also, I don't know about "techniques that produce low distortion produce poor sound." The only times I see something like that happen is when the low distortion "lowers the water to expose the rocks." In other words, it makes audible that there is still some problem with the circuit. What some designers do is use other low level distortion to mask the remaining distortion they don't know how to get rid of. That is exactly what I was talking about when I said something to you (by PM?) about a particular brand of headphone amp that sounded better at first, until the remaining problems where fixed, then it sounded worse.
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Old Today, 11:49 PM   #125
Markw4 is online now Markw4  United States
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Greg,
You might be surprised to know that Benchmark DAC-3 uses plain old LME49860 IC opamps, and it is on the Stereophile A+ recommended list. Another dac on that same list is Chord Dave, which according to its maker uses composite IC opamps. A composite opamp is two opamps combined together to effectively make one higher performance opamp. They do that so that feedback loop gain can be very high and stay that way up to pretty high frequencies. It makes the distortion so low that they don't have to worry about it.

I agree with the philosophy of Benchmark and Chord that one should strive for low distortion and if it seems to sound worse when one source of distortion is lowered, then find the source of the now audible distortion that you just unmasked and fix it too. Then, if customers want to follow a low distortion dac with tube preamp or something to add a little color back in, fine. Or people who just want clean, elegant, low distortion that sounds great can have that too.

Last edited by Markw4; Today at 11:53 PM.
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