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Review of the Audio-gd DAC-19 DSP & C2 amp - The ACSS connection - Page 9

post #121 of 981
Quote:
Originally Posted by tim3320070 View Post

The stepped pot (if it was the same that used to be in the Roc) is not bad as some had posted here. I never noticed anything using it and there was zero imbalance. Ask Kingwa to make it with that pot.


The stepped attenuator probably doesn't have any channel imbalance at all. If any, it's very slight. Only issue would be the popping/clicking noises as some people have mentioned

post #122 of 981
Thread Starter 
Quote:
Originally Posted by kunalraiker View Post

you are absolutely right I find the OPA604, grainy in the high end,i was afriad to say that because other members wouldn't be happy consideirng such high reputation of Kingwa.

I don't understand why he uses it, if its that bad.

 

I'am not looking for a smoother top end i'am looking for a very neutral opamp, witheout the high end harshness which now I feel must be caused by the OPA itself.

 

I use my iBasso D4 as my DAC and a 3.5mm to RCA  monster cable,would it be the cable,I don't feel it would cvause much of a difference, as I don't want to spend much on it considering I will be getting the DAC19 soon and going ACSS.


Concerning the OPA604, I think that Kingwa just put it there to get the job done. He could have probably put the Earth as a stock opamp but it would have increased the price unneccesarily for those who are going to use the c-2 exclusevily in ACSS mode or those who already have opamps.

 

OPA604/OPA2604 is still a relatively good opamp and you will be surprised to find that many "high end" companies are using the much cheaper NE5532.

 

By the way, opamps are like cables, you won't find any measurable difference in the frequency domain (frequency response, THD...), especially in the 20-20KHz range, which might imply at first sight that they should all sound the same. However, the main reason they sound different is their performance in the time domain which makes it impossible to measure with regular equipment.
If you are curious, you can look at the graph below that I copied from Audio-gd's website (http://www.audio-gd.com/enweb/pro/diy/OPA.htm):

 

OPA Earth vs OPA 2604.JPG

While the Opa Earth follows closely the wave generator, the OPA2604 shows some ringing at the high frequency square wave. While that square wave is beyond the human range hearing, it indicates however that we might hear a difference in fast transients in the 20-20Khz range.

 

Anyway, if you plan going ACSS later, there is no reason (except for curiosity) to try different opamps and RCA cables as the ACSS connection will bypass the opamp/buffer section on the C2. Though if you have to buy only one opamp, the Opa Earth might be a good choice as it is a relatively neutral sounding one.

 

Quote:
Originally Posted by Pacha View Post




Can you post your impressions on AD797 when you receive it?

 

By the way, did you find any ACSS replacement cable for the sharkwire ACSS?
 


I should receive the AD797 this week, I will post my impressions as soon as I get familiar with their sound.

Concerning the ACSS cables, Black_Stuart from head-fi agreed to make me a set of ACSS cables. However, he didn't like much working with the 4 pin ACSS connectors that Audio-gd is using and I am not sure he will readily accept making other cables.
Anyway, I am still waiting to receive them and I will report back my findings if I notice any differences with the stock sharkwire ACSS.
 

Quote:
Originally Posted by haloxt View Post

If you are afraid of channel imbalance with high sensitivity headphones, just ask audio-gd for a very low gain setting :). I think audio-gd should state on their amp descriptions that you'll probably want to do this if you have headphones with <25 ohm >100dB/mW, and probably mandatory for super high sensitivty phones like the 118dB jh-13.


I couldn't agree more. I already suggested to Kingwa a little while ago to mention the same thing in the amp description. Some people might not know that there is this possibility and might order the wrong gain setting.

 

Quote:
Originally Posted by tim3320070 View Post

The stepped pot (if it was the same that used to be in the Roc) is not bad as some had posted here. I never noticed anything using it and there was zero imbalance. Ask Kingwa to make it with that pot.


While I have found that the stepped pot was excellent with the hd-650 and K-702, I noticed a loud popping noise with some IEMs. Personally, it wasn't an issue for me as I don't change the volume much when listening to the same disc (and I don't usually listen to high efficiency IEMs). However, it is worth mentioning it for people who use high sensitivity phones like 118dB jh-13.

Personally, I find the c-2 an excellent value at the current price, and I wouldn't have minded if Kingwa offered the $150 Goldpoint attenuator as an option.

post #123 of 981

slim.a: One could switch the ACSS sockets to mini-XLR instead.  That's what I've (half) done in my rig. The other alternative is ~$200 for the Lemo plugs and sockets that Krell use for CAST.

post #124 of 981
Thread Starter 
Quote:
Originally Posted by Currawong View Post

slim.a: One could switch the ACSS sockets to mini-XLR instead.  That's what I've (half) done in my rig. The other alternative is ~$200 for the Lemo plugs and sockets that Krell use for CAST.


Converting the ACSS sockets to mini-XLRs is exactly what Black_Stuart suggested to me. I might try that in the future as it would allow to try "regular" XLR cables more easily.

 

As for the Lemo connectors Krell is using, I think they are too expensive (and I understand why Kingwa is not using them). Since the whole ACSS/CAST think is supposed to reduce the effect of cables, I feel that there are better places to spend $200 rather than on connectors for the DAC19/C2. It would make more sense however if it were for a Ref-7/Phoenix though.

 

By the way, Currawong, did you upgrade your ACSS cables on your ref-1/Phoenix combo?

post #125 of 981

slim.a,

 

I don't mean to hijack the thread, but just one more thought about the volume control. The C-2 uses the pot as a reference value for setting the gain. Why does it need two of these reference values, as it does using a stereo pot? By using a mono pot and setting the gain with the same reference for both channels, there would be no channel imbalance and the pot would be even cheaper. Is the pot in the C-2 set up in a way that would prevent the use of a mono pot, causing for example channel cross-talk? The thought came to my mind when reading about the Corda Concerto, which uses a mono potentiometer, but the way it uses the pot as a reference is of course way different than that of the C-2.


Edited by pategen - 5/11/10 at 3:17pm
post #126 of 981

Am I the only one to use high gain (+13dB) setting (same on the FUN and C2) and volume knob at 3pm with 600 ohms cans? Do you think it should be better to have a higher gain for me? I guess if there's no more distorsion at high volume setting on the pot, and as there's a little headroom (3 to half past five pm is loud to ear painful), it's ok as it is. What do you guys think?

post #127 of 981
Quote:
Originally Posted by pategen View Post
The C-2 uses the pot as a reference value for setting the gain. Why does it need two of these reference values, as it does using a stereo pot? By using a mono pot and setting the gain with the same reference for both channels, there would be no channel imbalance and the pot would be even cheaper. Is the pot in the C-2 set up in a way that would prevent the use of a mono pot, causing for example channel cross-talk?

Because C2's ACSS gain stage works in current mode and at the resistance (volume pot or stepped attenuator) at the gain output, beside setting gain, performs also I/V (current to voltage) change? Because using one resistance (mono pot or one channel stepped attenuator) would mix channels into one mono channel and we, except for Beatles mono remasters, prefer stereo?

 

In fact, I think that the quality of this ACSS output resistance is quite important, not because it could affect unamplified signal like conventional volume pot does on input of conventional gain stages - but because any mismatch in ACSS output resistance between channels would affect the difference in gain and in I/V change of already (differently) amplified current signals between those channels. It is rather sad that (ignorant?!?) users that complained about clicking persuaded KingWa to set Alps pot as a standard volume control instead of immeasurably more appropriate but "annoying when turned up or down" stepped attenuator.

 

Advice to SQ oriented potential C2/Roc customers: ask for that "annoying" stepped attenuator (or send him attenuator of your preference).

post #128 of 981

Agreed Faudrei,

 

The conundrum Kingwa finds himself in is a classic catch 22  " should I satisfy the majority of customers with an inferior part to kill one complaint but at the same time diminish performance and create, in effect, another known issue with the current part (carbon or plastic wiper channel imbalance) ?

 

Sure the stepped pot has it's annoying features but for the price of it I won't complain ( 30USD vs 160-200USD+ for a DACT or GP) because it gives me a better technical solution and in turn better performance where it counts, at the head amp output.......maybe I'm crazy but I don't fiddle with the volume constantly when listening. I set the volume and leave it alone. Then again I usually listen to entire albums at a time rather than various artist play-list's but on occasion I do mix it up with some variety (I'm not a complete dinosaur ...yet ), the point is... the stepped pot once set at a decent level works very well for my setup. I'll put up with it's quirks in order to advance the performance of the unit, it's a trade off...there are trade offs in all units WRT to topology, parts choice etc etc etc.....

 

There are no perfect solutions (but the relay based system Kingwa has developed for his TOTL stuff is as close to that ideal as you can get IMO).

 

2 cents FWIW.

 

Peete

post #129 of 981
Quote:
Originally Posted by FauDrei View Post



Because C2's ACSS gain stage works in current mode and at the resistance (volume pot or stepped attenuator) at the gain output, beside setting gain, performs also I/V (current to voltage) change? Because using one resistance (mono pot or one channel stepped attenuator) would mix channels into one mono channel and we, except for Beatles mono remasters, prefer stereo?

 

What you're saying seems to imply that the pot is actually not used as a reference, but that the signal does go through it. To me, that seems contradictory to what slim.a wrote in the review. But now, when I read through what Kingwa tells about the C-2 volume control on the Audio-gd site, it is in line with what you just said. Plus, it kind of makes more sense! Thanks for the clarification.
 

post #130 of 981

hi,

i am a proud new owner of the dac-19 dsp / c-2 combo.

i came to head-fi because i was looking for some solid audio gear, so I was cruising around the forums here for a few weeks and finally decided to go with audio-gd.

i do not regret.

sound through acss is ... i do not know how to say ...  a revelation? i did not expect that. wonderful.

this combo will stay with me for many years to come (i hope).

thank you head-fiers for opening a new world to me.

post #131 of 981

After we tossed around the idea of replacing the ALPS with a stepped attenuator and mentioning the expensive Goldpoint, it occurred to me that my best option would be to try to get Kingwa to replace the pot before he shipped it.  (Ordered it over last weekend.)

 

But first, just for a bit of comedy in the thread...

 

Me:

 

Kingwa,
How hard for you to change the C-2 volume pot for a stepped attenuator before shipping?
Thanks

 

Edwin:

 

Dear Sir

Do you mean you want to change C-2 volume knob? If yes, what kind of knob do you want?

Edwin

 

I get the impression Edwin is family.  He took both of my orders okay but he's not too good with technical questions and probably not one of the audiophile techs.  I'm sure the language barrier makes it worse.  You have to go a round or two with him before the message is given to Kingwa.

 

After another exchange explaining my concern in better detail, Kingwa just wrote me:

 

The steps volume can avoid channels imbalance, and sound slight detail than ALPS. But only problems is the noise whilt owners turn the volume pot. If owners don't turn the pot, no noise anymore. I ever try a steps volume pot which is a customer shipping to me for custom order, it is no click noise. It sale in web but my computer had lost the link. Do you sure you want to change the pot? Its noise depend on the headphone, if for low sensitive , the noise is slight, but for a high sensitive headphone, it will be a bit.

Kingwa

 

We understand the noise issue but what do you suppose he means by "and sound slight detail than ALPS"?  I'm thinking he meant "slight better detail".  He also seems to be talking about a quiet stepped attenuator someone is mailing to him for a custom job and he's lost the web link.  Is that person one of you guys?

 

If he meant the stepped attenuator he has on hand gives better detail but makes noise, I'll give the go ahead with that.  If the noise is horrendous in my system I'll drop $150 on the Goldpoint and swap them myself.  Does that sound like a good plan?

 

I asked him to hold my order until I discussed this with all of you.  Your input is greatly appreciated!  (Plus, this will make a good reference for other prospective C-2 owners referencing this thread down the road.)


Edited by Newk Yuler - 5/12/10 at 4:09am
post #132 of 981
Quote:
Originally Posted by Newk Yuler View Post

After we tossed around the idea of replacing the ALPS with a stepped attenuator and mentioning the expensive Goldpoint, it occurred to me that my best option would be to try to get Kingua to replace the pot before he shipped it.  (Ordered it over last weekend.)

 

We understand the noise issue but what do you suppose he means by "and sound slight detail than ALPS"?  I'm thinking he meant "slight better detail".  He also seems to be talking about a quiet stepped attenuator someone is mailing to him for a custom job and he's lost the web link.  Is that person one of you guys?

 

If he meant the stepped attenuator he has on hand gives better detail but makes noise, I'll give the go ahead with that.  If the noise is horrendous in my system I'll drop $150 on the Goldpoint and swap them myself.  Does that sound like a good plan?

 

I asked him to hold my order until I discussed this with all of you.  Your input is greatly appreciated!  (Plus, this will make a good reference for other prospective C-2 owners referencing this thread down the road.)

The best thing for you to do would be to send him a Goldpoint/TKD/etc and let him swap the attenuator in if you're not familiar with soldering/diy. Alternatively, you could check these out

http://cgi.ebay.co.uk/Valab-23-Step-Attenuator-50K-Stereo-stainless-knob-/290427903156?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item439eda1cb4

These don't have any clicking/popping noises and are apparently, a good cost-effective alternative. If you do a search around headfi or other diy forums, you'll find that quite a few people have used them with good reports

 

I won't be surprised if the stepped attenuator will give better sonic results than a typical potentiometer since the signal is typically less degraded.
 

post #133 of 981

Quote:

Originally Posted by noinimod View Post

The best thing for you to do would be to send him a Goldpoint/TKD/etc and let him swap the attenuator in if you're not familiar with soldering/diy. Alternatively, you could check these out

http://cgi.ebay.co.uk/Valab-23-Step-Attenuator-50K-Stereo-stainless-knob-/290427903156?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item439eda1cb4

These don't have any clicking/popping noises and are apparently, a good cost-effective alternative. If you do a search around headfi or other diy forums, you'll find that quite a few people have used them with good reports

 

I won't be surprised if the stepped attenuator will give better sonic results than a typical potentiometer since the signal is typically less degraded.


Heh... Valab.  I have a heavily modded Valab DAC that the DAC 19 DSP replaced and stomped the living crap out of...

 

I'm good with a soldering iron and the Valab attenuator may be a great next step.  Thanks very much for suggesting it.  Is 50k the correct value for the C-2?


Edited by Newk Yuler - 5/12/10 at 3:57am
post #134 of 981
Quote:
Originally Posted by Newk Yuler View PostIs 50k the correct value for the C-2?

That's the bit i'm not so sure. You might want to check with Kingwa since he knows his gear best.
 

post #135 of 981

Another update from Kingwa.

 

He says the stepped attenuator that he's getting for the custom job is a Goldpoint, the one he lost the link for.

 

Kingwa's spec on a stepped attenuator referring to a replacement Goldpoint:

 

C2 need a two floors , 20K, type A characteristic.

 

That would be 20K audio taper but what does "need a two floors" mean?  2 grounds?  The pot gets 2 wires from each channel.

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