Review of the Audio-gd DAC-19 DSP & C2 amp - The ACSS connection - Page 7

Quote:

Originally Posted by slim.a 

I think that the channel imbalance will be the most noticeable with high sensitivity cans and the ACSS connection.

I remember than when opening up the C2, I noticed it was an ALPS blue. It is not the worst but not the best neither.

I might upgrade (in the future) the ALPS pot to the Goldpoint stepped attenuator to get perfect balance at the lowest values. However, since I am only using the hd-650 with it, it is not on the top of my upgrade priorities.
 

 

Thanks for that. I guess it will be ok with K601's, but for me that stepped attenuator upgrade might be imminent... If only I could get my hands on the gear. The anxiety is killing me!

Quote:

Originally Posted by slim.a 

 

BTW Newk Yuler, did you get a chance to listen to the DSP bypassed with your Off-Ramp 3? What do you think of it?

Not yet.  I'm going to let the DAC19 burn in for a couple of weeks to be sure how it's sounds post burn-in with the default settings.

I asked Kingwa for detailed instructions on the DIP switches and he just forwarded the same image that Currawong got for the Ref One some time back. It's just a vague reference and I still have questions concerning the actual functions of most of the switches and how they interact with each other.  I asked Kingwa if the "filter - NOS bypass" switch was an actual DSP bypass to feed the BB chips, just to be certain there's no confusion, and he said 'yes'.  Getting the simple image after asking for detailed instructions makes me think I probably shouldn't try to get more out of him, like the language barrier is going to cause problems.  So how do we get detailed instructions about the DSP-1 DIP functions?  Seems like that should be easily available for owners.

I noticed one of the switches refers to TDA1541 DAC chips.  Is that what Kingwa use to use in his equipment?  I'd like to know the story behind the evolution to the PCM1704UK.  (I'd like to know the difference in settings in that particular switch...)

This new message composition feature is not better than the old one.

slim do you get the same volume output on the C2 than on the FUN when turning the knob at the same level?

I forgot that you (slim.a) used Jkeny’s modified Hiface in your review.  That should have proved something with your DAC19 in bypass/NOS, although there's one difference with the Off Ramp that may make a difference with the way the DAC19 responds with high quality SPDIF sources.  The Off Ramp provides galvanic isolation in its SPDIF connection.

I'm not certain Kingwa doesn't have the SPDIF input similarly isolated in the DAC19 or other A-gd equipment.  I've participated in the HeadFi Teradak NOS TDA1543 DACs (Valab and Chameleon) modders threads that proved the benefit of galvanic isolation by a 1:1 pulse transformer (example).  It was subjectively proved in the Valab (using a DIR9001) and included in production with the Chameleon.  If we find the DAC19 does not have galvanic isolation on the coax SPDIF input, a simple pulse transformer mod behind the coax jack may make a noticeable difference in SQ when used with a Hiface or similar high quality, very low jitter source.  It's a simple mod for someone with half decent soldering skills and just as easy to undo.  I can point to the examples in the HF Valab thread if anyone is interested.

I ordered that pulse transformer to add to the DAC19 when I ordered the DAC in spite of the fact the Off Ramp is already isolated because it made a SQ difference in my modded Valab.  Not sure why.  May have something to do with the way the Off Ramp is isolated.

Quote:

Originally Posted by slim.a 

If I remember correctly, it is about the same. I will try it again tomorrow and update this post.

However, the main difference is that you can play a lot louder with the C2 without hitting "compression". In very loud and complex orchestral passages, the FUN sounds a little bit "stressed" and "compressed". The C2 sounds "effortless" in comparison.

Also the perceived resolution at the lower volume settings was better with the C2 in comparison with the FUN.

Thank you, waiting for your reply.

Anyway, what you said here (and already detailed in the review) makes me more and more impatient to get the DAC19DSP/C2 combo.

Quote:

Originally Posted by slim.a 

The stock hiface already uses a pulse transformer in its output stage. I don't know if there will be a lot of benefit in adding another pulse transformer on the DAC19DSP. But the effect of those pulse transformers might be cumulative or maybe the one you ordered might do a better job at isolating the transport from the dac... but that is only speculation from my end.

 

BTW, the modified Hiface I used for the review was using battery power for the 3.3v which means that it bypassed the usb power for the following: USB receiver chip, FPGA chip & clocks. I could have totally isolated the modified hiface from the computer by using the special usb cable jkeny sent me but the sound was so good I didn't bother trying another tweak at the time of the review...

And as I indicated previously, I already sent my stock hiface to jkeny for modding and I should receive it shortly (he mailed it to me yesterday) :)

 

Anyway, I will be curious to have your findings with the pulse transformer on the dac19. If you notice improvement with the Off Ramp, there is a good chance that people using other transports will notice a difference/improvement as well.

 

ps: I will send Kingwa an email to check if the dac19 has any galvanic isolation on the coaxial input.

I'm going to wait a couple of weeks before I change anything from the default.  Past burn in, I want to be well acquainted with the SQ before I make changes.

I've been using a stock Kingrex Pre-Amp in my little high res system.  It's a well thought out opamp design with buffer and DC servo chips, and a diamond buffer that makes it shine.  It's a great little pre but it's outclassed by the DAC19.  I thought a lot about opamp rolling but after a lot of reading and thinking I've decided to get either the C2 or P2, probably the C2 for the versatility and benefits of ACSS or the opamp/RCA route.  I would rather be using a C2 on ACSS before I add a pulse transformer to the DAC19's SPDIF.  Anxious to know what Kingwa tells you about SPDIF isolation.

I'm a bit familiar with the modded Hiface as Jkeny is currently working a lot with the Teradak Chameleon modders with his version of the Hiface.  He just modded one for I2S into a Chameleon's 16x TDA1543 chips for one of the guys in that thread.  He's also developing a proper SPDIF input board for the DAC.  Guy knows his stuff well and we're very lucky to have him.

Quote:

Originally Posted by slim.a 

 

So my interpretation is that adding a transformer to the DAC19 DSP will probably be more beneficial to lower end sources (that don't use transformers) and probably degrade slightly the performance of higher end sources (that already use transformers and have 75 ohms impedance).

This design choice might explain partly why I have found that the older dac19mk3 and the newer dac19dsp are very sensitive to the quality of the source and scale up very well with good transports and digital cables.

Certainly makes sense.  Steve Nugent well understands and has talked about SPDIF inadequacies and has upgraded poor SPDIF inputs as mods for customers.  I expect the SPDIF ports in his hardware to be top notch and no worry as to how they measure as links in the chain.

Much of the Empirical Audio hardware is currently being revised to use newly designed async USB modules with M2Tech's async driver.

FWIW, I'm using an Audioquest VDM-5 silver conductor coax digital cable, what I used with previous setups fed by the Off Ramp.  The Audioquest stuff has a lot of hype and relatively high prices but they have an earned reputation for excellent cables.  One thing that attracted me to them above others is their use of silver plated RCA jacks.  If I needed a BNC digital cable I'd likely get the BNC version of this cable.  My analog interconnects are Audioquest Diamondbacks.

All that said, I still intend to install the pulse transformer behind the DAC19's coax input after I've spent a bit of time getting use to the DAC19DSP with a C2 preamp that I'm going to order in the next few days.

Quote:

Originally Posted by Zhirc 

Could someone else check too the point when the channel imbalance disappears on C2? I've played normalized pink noise quite a bit and on my unit the levels sound to be equal around/after 8:30 - 8:40 - just a bit too 'far' for many louder albums (or pretty much for the most music that isn't ambient or classical) that I have.

Anyone?

Would be really interested to hear if it's just my crappy unit or if the others have channel imbalance to as high scale too. Kinda annoying with ACSS-cables and high gain, currently using just RCA and low gain when watching TV as the very slight quality difference isn't that big (for my wooden ears at least) than the channel imbalance, as the left channel is somewhat dominating during the whole lower-level stages.

Quote:

Originally Posted by Zhirc 

Anyone?

 

Would be really interested to hear if it's just my crappy unit or if the others have channel imbalance to as high scale too. Kinda annoying with ACSS-cables and high gain, currently using just RCA and low gain when watching TV as the very slight quality difference isn't that big (for my wooden ears at least) than the channel imbalance, as the left channel is somewhat dominating during the whole lower-level stages.

Did you email Kingwa about it?  I imagine he would be able to say right off if it was the pot.

I don't have a C2 yet but it's on the way.  If you think it's the volume pot why not replace it?  As I understand it, the pot is dialing resistance for gain reduction to follow instead of acting as a typical signal-through-the-pot volume control.  It may be something else is out of whack, but if it is the pot, that's not so big a deal to fix yourself if you have half decent soldering skill.  If you don't you may know someone that does.  If you can't see numbers on the pot, remove the knob and remove the pot from the panel but don't cut wires, look at the numbers, find it on the net at Newark or Digikey, or wherever.  If Kingwa says it could be the pot it's well worth the effort.  He could tell you the make and model of the pot.  Maybe he'll send you another pot.  It would sure beat mailing the C2 back to China.

Nope, the volume pot itself probably has issues. And you can't fix it - the only way would be to replace it. Strangely enough, kingwa used to offer a stepped attenuator with almost perfect channel balance at all volume levels with the c2c i think, but because of the popping noises when changing volume, people complained and so he reverted back to using the normal pots. He does, however, still keep stepped attenuators in stock so you might want to check that out with him.