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

Quote:

Originally Posted by tim3320070 

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

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.

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.

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?

Quote:

Originally Posted by pategen 
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).

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

Quote:

Originally Posted by FauDrei 

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.
 

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.

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:

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.)

Quote:

Originally Posted by Newk Yuler 

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.
 

Quote:

Originally Posted by noinimod 

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?

Quote:

Originally Posted by Newk Yuler Is 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.
 

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.