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In Reply to: RE: ARC LS27 - mistake to buy for my application? posted by Tre' on January 28, 2017 at 12:31:03
I did try running from the Mac Mini to the Bifrost DAC directly to the Amp. The sound quality just was not there compared to having the ARC Preamp in place. So I guess there is a general reason why you have a preamp. Your question seemed like a logical thing to do. I tried it. But it didn't work out well. Wish it had.
Follow Ups:
I tried that as well. Those older tube amps seem to really need or want a preamp in front of them. All the preamp is doing is buffering. At $6k or so that is a hell of a buffer?
Heck, throw out the offer to the seller. If he doesn't bite then nothing lost because you still have your amp. Then start looking into tweaking up your digital sources.
"All the preamp is doing is buffering"
Not true. That preamp has 24dB, 18dB, or 12dB of gain and a higher output impedance (350 ohms vs. less than 30 ohms) than his source.
So I would call it an "antibuffer with gain". :-)
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
The output impedance of the buffer (AD8512) of your DAC is less than 30 ohms.
There is no reason for it not to drive the cables and the input of the Cit2 just fine (probably better than your preamp).
So that leaves us with the volume control. If the DAC's volume control (or whatever volume you used when listening without the preamp) is digital then that could be a sonic problem. (lower the volume, lose bits, not good)
On the other hand, if the DAC's volume control is analog then what you are hearing (and liking) is the distortion of the preamp.
Harsh words but in the absents of some other reason for the sound to be compromised coming straight off the DAC vs. through the preamp, what other conclusion can we come to?
Do you hear a loss of sound quality turning the volume down using the DAC's volume control when playing through the preamp?
This can be tricky. Less volume always sounds poorer than more volume. Using the volume control on the preamp, keep the sound pressure level as you turn the DAC down while turning the preamp up.
If you decide that that doesn't hurt the overall sound then we're back to you liking the "color" that the preamp is adding.
"The best line stage preamp is no line stage preamp at all" (as long as the drive requirements present are meet by the signal source and you have a way of controlling the volume)
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Tre' you said "then what you are hearing (and liking) is the distortion of the preamp." What I like hearing is accurate reproduction of what professional instruments played by professionals actually sound like. I've had the benefit of playing next to a very large number of Professional Players on professional instruments (Concert Grand Piano's, Cello's, Violins, Drums, Brass Instruments, etc...). And I know what the subtle sounds of instruments are like (piano hammer and mechanical noise, guitar or cello player moving their fingers down the strings, trumpet valve noise). I can not argue with you from a technical approach what should work the best, but the ARC preamp in my system actually takes me closer to a professional instruments sound. And if moving from the LS17 to LS17SE moved me closer to that end, than will moving up to the LS27 take me even closer?
I have no idea. It's all subjective personal preference.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Harsh words but in the absence of some other reason for the sound to be compromised coming straight off the DAC vs. through the preamp, what other conclusion can we come to?
Rather firmly, too. And once participated in a thread with Charles Hanson on this topic.
That was until I heard really nice actives in my system and others. Why? Dunno. Now I find improved dynamics, both at the micro and macro level.
And sit corrected, Charlie. :)
How do you define "really nice"?
I look at all of this from a strictly technical point of view.
A circuit, any circuit, will add noise and distortion.
A line stage preamp will not, can not, make things technically better unless needed to satisfy impedance and drive requirements.
If the source meets those requirements on it's own then no line stage preamp will make things technically better.
Adding technically un-needed circuitry to a system can only make things worse.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
and you do need that IMO with that DAC. Id still upgrade to a better DAC. Do you think a $6K pre when new should be mated with a $399.00 DAC? Come on. Get a nice 4V out DAC and see what happens. Just get a loaner and see. Stop speculating. Its not all about input Z on the amp. Sensitivity is important too. 1.5V for full out......your are mistaken if you think your DAC magically takes whatever source material you play and puts out 2V. NO WAY>
ET
"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936
Edits: 01/31/17
So as I look at Schiits DAC line, I have to get into a unit that has Balanced outputs to get 4v outputs. So this is going to put me at $1,250 or $2,300 (Gungnir with Multibit or YGGORASIL). So the ARC has Balanced inputs and outputs, but my amp doesn't have Balanced inputs. My understand was unless you are doing Balanced all the way through, don't bother. So is there another good DAC that has 4v out on the RCA's? Or is it OK just to run balanced into the preamp to get 4v? Side note, I just passed on the LS27.
How do you define "really nice"?
Hate to put a price tag on it, but the four I heard were around the $10k (or beyond) ballpark Charlie mentioned in the linked post. My SP20 meets that criteria. I used DACT stepped attenuators using JPS Labs wire and Cardas connectors for many years. Still have them if anyone is interested. They're in a really nice Par-Metal case.
A circuit, any circuit, will add noise and distortion.
And you can find multiple posts here where I stated exactly the same thing. :)
"Hate to put a price tag on it,..."
No no.
Tell me about the circuit, not the price tag.
"My SP20 meets that criteria"
I'm looking for a schematic but can't find one. I do see pictures on the inside. There's a lot going on in there.
I'm much more a "straight wire with gain" sort of guy.
"I used DACT stepped attenuators using JPS Labs wire and Cardas connectors for many years."
What is the value of those attenuators?
With resistive attenuators, too low a value can make it hard for some sources to drive. Too high a value and the output impedance can be too high to properly drive cable and input capacitances.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Tell me about the circuit, not the price tag.
The price tag mentioned by Charles does imply a number of factors: hand assembly, careful matching of active devices, use of highest quality wiring, passive devices (including solder) and multiple, ultra stiff power supplies.
I'm looking for a schematic but can't find one.
The line stage (as the SP20 also has a phono preamplifier) is similar to the LS27 which in turn is a refined version of the LS25 MKII found here . It is a zero feedback, Class A hybrid design.
There's a lot going on in there.
Ok. Aside from being a full function preamplifier, there are few bell and whistles. It does, however, offer remote operation, switchable phono loading and the line stage is switchable for headphone output.
What is the value of those attenuators?
10k as recommended by DACT.
While I run my DAC directly into the power amp with my garage system, I prefer using a high quality preamp in the main system for optimum sound quality. BTW, John Atkinson also mentioned the quandary he also experiences with the notion of improved sound quality using an active stage with Hanson's KX-R:
" To my astonishment, the sound of my system with a Transporter D/A processor feeding the preamplifier was better than when the DAC fed the power amplifier directly. Through the KX-R, images sounded more tangible, and the sound was better focused, despite the signal's having been passed through not just another set of interconnects but also through the preamp's input and output socketry, switches, a volume control, printed circuit-board traces, and active and passive parts. Logically, you'd think that having nothing in the signal path would have less of a degrading effect than so many somethings. But no, that was not what I heard, much as I would have preferred otherwise."
Well said John!
if we assume Mikey left it stock the input impedance on the duece is a meg but it needs 1.5 volts for full out. The Bifrost is listed as a max out of 2V @75 ohms. So it is likely that on most CDs he often cant even drive the amp to full out. Not good. You want to be able to always drive the amp to full out plus 6dB in my opinion active or passive. If he listens to classical, jazz or other less or non compressed recordings then I see a problem.
I'm a passive user and have a DAC that does 2.35VRMS @50 ohms. My amps need only a volt for full out and I have many CDs that cannot drive the amps to full out with my Placette all the way up. Luckily my speakers are 91dB efficient and in my biamp I can do 250/ch LF, 100/ch HF.
ET
"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936
CD's and digital files are normalized. The loudest moments will be at full digital level regardless of the dynamics of the music.2 volts will drive his deuce to beyond full power.
"You want to be able to always drive the amp to full out plus 6dB in my opinion active or passive"
Why? I do my best to never over drive any stage of my system.
Bad things happen when a tube is over driven.
I know some amps are rated for so called "headroom" but 6db would be 4 times the rated power. 240 watts per channel? I can't imagine how distorted that would be for the deuce.
I'm I missing something?
Edit; I reread your post.
"..if we assume Mikey left it stock the input impedance on the duece is a meg but it needs 1.5 volts for full out. The Bifrost is listed as a max out of 2V @75 ohms."
Do you think the Bifrost will not output 2 volts into 1 meg ohm?
It will. The higher the impedance it has to drive, the easier for it.
It's own source impedance dominates but technically the higher the input impedance, the higher the output voltage will be. Not lower.
In practice, because it's own output impedance dominates the equation, the output voltage will be virtually the same.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 01/28/17
You are assuming every CD you play outputs 2V. My post says they dont because they dont. You should measure that and see how seldom even a volt comes out of your DAC. When you had a cassette deck were the VU meters always at zero? No seldom or never. When they were at -6db if zero db is full out (2V) then -6 is a volt.
Also in my post I told you my higher out, lower Z DAC than yours very seldom (meaning almost never) drive my amps that need only a volt for full power to put out their full power.
ET
"If at first you don't succeed, keep on sucking till you do suck seed" - Curly Howard 1936
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