AudioCircle
Audio/Video Gear and Systems => Owner's Circles => Digital Amplifier Company Owners => Topic started by: AmpDesigner333 on 6 Jan 2020, 11:30 pm
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I always lean toward no preamp. Preamps are typically not DC coupled. This is because DC offsets are cumulative and multiplied by the gains of each stage.
Driving Cherry amps (post-2013 models) directly with a Cherry DAC DAC is just about the only way to have an end-to-end DC coupled system. This is simply the way bass was meant to be delivered! Zero phase shift.
Some preamps have four AC couplings between the input and output, then most amps have another one or two. The source usually has one or two as well, so there can be as many as 8 AC couplings total. That's a lot of cumulative phase shift, which exhibits itself as "group delay" in the end. There's significant delay at 20Hz from only one AC coupling at 5Hz. An AC coupling is going through a capacitor, for example.
Check out the simulation circuit (in x100 steps for loading purposes) and note response plot (right vertical axis is group delay) showing group delay approaching 10mS at 20Hz with only 4 stages of AC coupling (5Hz "cutoff")!
(https://www.audiocircle.com/image.php?id=202992)
(https://www.audiocircle.com/image.php?id=202993)
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Looks like I need to post an inverted version of the graph. It’s pretty hard to view on my phone!
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(https://www.audiocircle.com/image.php?id=203006)
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Even better....
(https://www.audiocircle.com/image.php?id=203009)
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A little math.... 20Hz is 1/50mS, so a 7.5mS delay is 15% of the total 20Hz waveform (54° phase shift).
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Cherry Amps is on my list on amps to buy.............one day.
no Pre amp is always bettering my system. 64bit volume control on the computer or 32bit on the DAC (maybe a little bit not as good as the computer) but always better than the pre.
You'll never be able to convince someone that no pre is better when they have spent big bucks on a pre.
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As you read through various forums and reviews, there are plenty of people that prefer no preamp...and maybe just as many that prefer the sound with a preamp (let alone some convenience switching issues)...and each with various descriptions of the sonic advantages...so maybe no clear cut winner here, just personal preference, I'm not sure...I use a preamp, I like the sound?
The issue of DC coupled is maybe more interesting. Pass Labs well respected XS preamp lists specs of:
Frequency Response -3dB @ 2 Hz and 60 kHz
Input Impedance 42k balanced
Output Impedance 120 Ohm bal, 120 Ohm SE
CMRR -65 dB, 1 kHz
Cross-talk -100 dB, 1kHz Ref 1V
Signal to Noise Ratio < -110 dB, Ref 5V
So, not sure if the Pass XS is DC coupled and if not, does it matter given how many people seem to like the sound...again????
Benchmark (pretty much the darling of ASR for their great measurements) shows a phase spec at 20KHZ for their DAC3 HGC:
Inter-channel Differential Phase (Stereo Pair – any sample rate) +/- 0.25 degrees at 20 kHz
Inter-channel Differential Phase (Between DAC3 Units Fs<110 kHz) Any sample rate. +/- 0.25 degrees at 20 kHz
Is this DC coupled...and if not, did it matter to their measured performance numbers?
OK....so what is my point?
If you take the crowd at Audio Science Review....they seem to be pretty focused on numbers implying that the numbers directly relate to the quality of the sound.
If you take the Audiogon crowd, they care about numbers but the numbers don't determine the sound quality...the sound quality is much more a function of the tuning by the designer and the interactions with other equipment (and for speakers, the room)
Personally, I'd like to see more correlation of numbers to sound perception...even though this in itself is imperfect. This might tell us, is DC coupled audible to most people? Or is THD + N = 115db audible to most people : and does it sound "better"?
My sense is that Tommy has it right....you need great numbers but you also need tuning to the final "best sound"....and if you don't happen to prefer the designer's final tuning, well that is a different story.
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As you read through various forums and reviews, there are plenty of people that prefer no preamp...and maybe just as many that prefer the sound with a preamp (let alone some convenience switching issues)...and each with various descriptions of the sonic advantages...so maybe no clear cut winner here, just personal preference, I'm not sure...I use a preamp, I like the sound?
The issue of DC coupled is maybe more interesting. Pass Labs well respected XS preamp lists specs of:
Frequency Response -3dB @ 2 Hz and 60 kHz
Input Impedance 42k balanced
Output Impedance 120 Ohm bal, 120 Ohm SE
CMRR -65 dB, 1 kHz
Cross-talk -100 dB, 1kHz Ref 1V
Signal to Noise Ratio < -110 dB, Ref 5V
So, not sure if the Pass XS is DC coupled and if not, does it matter given how many people seem to like the sound...again????
Benchmark (pretty much the darling of ASR for their great measurements) shows a phase spec at 20KHZ for their DAC3 HGC:
Inter-channel Differential Phase (Stereo Pair – any sample rate) +/- 0.25 degrees at 20 kHz
Inter-channel Differential Phase (Between DAC3 Units Fs<110 kHz) Any sample rate. +/- 0.25 degrees at 20 kHz
Is this DC coupled...and if not, did it matter to their measured performance numbers?
OK....so what is my point?
If you take the crowd at Audio Science Review....they seem to be pretty focused on numbers implying that the numbers directly relate to the quality of the sound.
If you take the Audiogon crowd, they care about numbers but the numbers don't determine the sound quality...the sound quality is much more a function of the tuning by the designer and the interactions with other equipment (and for speakers, the room)
Personally, I'd like to see more correlation of numbers to sound perception...even though this in itself is imperfect. This might tell us, is DC coupled audible to most people? Or is THD + N = 115db audible to most people : and does it sound "better"?
My sense is that Tommy has it right....you need great numbers but you also need tuning to the final "best sound"....and if you don't happen to prefer the designer's final tuning, well that is a different story.
Ron,
Thanks for your comments. The line "Frequency Response -3dB @ 2 Hz and 60 kHz" gives it away that this preamp is not DC coupled. DC coupled is flat to 0Hz.
-Tommy O
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Cherry Amps is on my list on amps to buy.............one day.
no Pre amp is always bettering my system. 64bit volume control on the computer or 32bit on the DAC (maybe a little bit not as good as the computer) but always better than the pre.
You'll never be able to convince someone that no pre is better when they have spent big bucks on a pre.
Good point! It's always a task to break past the status quo (: Volume control in the digital domain is facilitated by 24-bit DACs. Otherwise, resolution suffers. With 24 bits, you still have 16 bit resolution at more than 50dB down from full scale. That assumes a few things, but the point is that there's virtually no downside to digital attenuation with modern, properly designed, high performance audio equipment.
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Cherry Amps is on my list on amps to buy.............one day.
no Pre amp is always bettering my system. 64bit volume control on the computer or 32bit on the DAC (maybe a little bit not as good as the computer) but always better than the pre.
You'll never be able to convince someone that no pre is better when they have spent big bucks on a pre.
This is why I use a TVC line controller. I get to select sources and control volume - no other circuitry necessary (VERY clean sound.)
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This is why I use a TVC line controller. I get to select sources and control volume - no other circuitry necessary (VERY clean sound.)
If you're referring to a Transformer Volume Control type preamp, it's not DC coupled. Transformers also add distortion, but not noise unless they're picking it up from a local AC/RFI field. What model do you use?
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Sonic Euphoria PLC. ALL components add distortion. Depends on what distortion type is more of an audible issue.
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Passive preamps CAN be DC coupled....
There are probably some with caps in the signal path out there. Caps can't DC couple, so if there are caps in the signal path, it's AC coupled.
TVCs (transformer volume controls) are also AC coupled since transformers can't DC couple.
....Otherwise, "passive" preamps are DC coupled.
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You'll never be able to convince someone that no pre is better when they have spent big bucks on a pre.
That's very true but there are exceptions to the rule, that being those who are honest enough to set aside their pride and preconceived ideas. It takes audacious honesty to admit that a very inexpensive passive preamp sounds superior to a very expensive tube preamp!
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That's very true but there are exceptions to the rule, that being those who are honest enough to set aside their pride and preconceived ideas. It takes audacious honesty to admit that a very inexpensive passive preamp sounds superior to a very expensive tube preamp!
I have been doing a lot of research on passive and active pre-amps. Of course there are situations where you "might" need and active pre-amp with some gain but for the most part, what's the point? I am sure something like this is as clean and simple as it gets.
https://sites.google.com/view/pine-tree-audio/devices/sp-1-passive-preamp
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I have been doing a lot of research on passive and active pre-amps. Of course there are situations where you "might" need and active pre-amp with some gain but for the most part, what's the point? I am sure something like this is as clean and simple as it gets.
https://sites.google.com/view/pine-tree-audio/devices/sp-1-passive-preamp
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I have been doing a lot of research on passive and active pre-amps. Of course there are situations where you "might" need and active pre-amp with some gain but for the most part, what's the point? I am sure something like this is as clean and simple as it gets.
https://sites.google.com/view/pine-tree-audio/devices/sp-1-passive-preamp
The Nobsound is 1/3 the price and it has both balanced and single ended inputs and outputs.
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Hey... and while you are on the Pine Tree site... check out their wires. Great looking wires at an affordable price.
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The Nobsound is 1/3 the price and it has both balanced and single ended inputs and outputs.
Has anyone tried mounting the Nobsound passive preamp to something like a slab of marble? I have one, and keeping the wires from pulling it off the table can be an issue since it's so small/light....
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Has anyone tried mounting the Nobsound passive preamp to something like a slab of marble? I have one, and keeping the wires from pulling it off the table can be an issue since it's so small/light....
That is why I like the HK passive if using SE wires. It does not move.
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Ron,
Thanks for your comments. The line "Frequency Response -3dB @ 2 Hz and 60 kHz" gives it away that this preamp is not DC coupled. DC coupled is flat to 0Hz.
-Tommy O
I did not know was any benefit in zero Hertz response capable preamp, I though DC Coupled was battery powered power supply to run out of the public AC electrical network.
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I did not know was any benefit in zero Hertz response capable preamp, I thought DC Coupled was battery powered power supply to run out of the public AC electrical network.
With a Cherry Amp, listeners can remove a few stages of AC coupling in the system, but only with a DC coupled source (like the Cherry 130dB+ DAC DAC 2) can you have end-to-end DC coupling. Some DACs and DAC chips also have a option to apply a "software" AC couple (auto-zero or "offset cancellation"), which adds one or two poles of High Pass filtering, so in DAC designs, this must not be used to have true DC coupling from the digital domain all the way to the speaker.
Care must be taken to design the lowest offset possible at the source since it will be amplified by the amplifier's gain. Thanks for your comment.