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It is about Schiit 'SYS' or any passive preamplifier

srisaikat

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#1
I am going to tell the story in the fashion it was encountered. I had never had that interest about passive preamp. Usually because of impedance mismatch related problem and due to warning from some users who found their music become dull, lifeless after using the passive preamp. Few months ago I gained some interest about pass B1, but that did not last long due to discourage from some fellow members who found it little over rated based upon their own experiences.

Whatever it is, after buying the Audio-gd NFB-3(2014) DAC last year, I found the output was louder, so felt little uncomfortable for long listening sessions than my previous Audio-Gd DAC FUN (which I found very effortless and comfortable sounding), but NFB-3 offered more details with delicacy (when I tested it playing some soft files with lowered gain) and sounds quite transient compared to FUN. Only problem, it was more louder at 9'O clock of volume setting than FUN at near 10'O clock. Later, after reading the specs carefully I found the NFB-3 have output voltage of 2.5V where as FUN had 2V output. I know I should had taken more care to read specs before buy.

My amp is music hall A70.2, the manufacturer had not published that much specs that I could make an easy decision. But it is the bitter experiences that make one more wise:rolleyes:. I should have studied other Music Hall components like their CD player or stand alone DAC to know what output voltage was better match for my Amp. Guess what! All the Music Hall DAC and CDP have 2V output. That's why FUN as a DAC sounding so easy and effortless as it also have same output voltage like those of Music Hall components.

Luckily the NFB-3 has 2 gain settings, 2.5V and 1.25V, for some albums I used to set it low. But I never liked the toggling option. I had even emailed Mr. Kingwa of Audio-gd about my dissatisfaction over making such high voltage output of NFB-3. As expected he replied that it was the reason he is offering 2 gain settings. Simple fact is, it was little gain mismatch problem between my DAC and Amp where 1.25V is little low and 2.5V is little high for my comfort.

So for last few weeks I was googling around for a correct solution, found many people suffering from same (loud output) problem either from DAC or CDP, some suggested to take the DIY route to customizing the gain stage replacing some resistors, some suggested to use inline RCA attenuator, some suggested to use passive preamp as a voltage divider. A few advised to use a passive preamp when the output voltage of DAC or CDP is strong enough to drive a Power amp.

DIY is not my comfortable zone, I am also always against any modification on a well designed and implemented circuit without knowing the side effects of the mod for sure. For inline RCA attenuator I do not know how much attenuation I need. So make my decision to use a passive preamp to dissipate some unwanted voltage to get the proper one. That decision also was not easy as the signal will travel extra length of conductor and stage which surely degrade** (may be very little but sure) the signal. But I had to take a chance to find if it can comfort my ear.

So it was about taking a chance with minimum possible damage on pocket with reliable quality. Found schiit has introduced 'SYS' (link- Schiit Audio, Headphone amps and DACs made in USA.) a passive preamp at $49. No other passive preamp I found except EMOTIVA (Control Freak- https://emotiva.com/products/electronics/control-freak) at that price range from any reliable or well known brand (greater chance is, maybe I am not so knowledgeable).



There was an another logic behind purchase of 'SYS'. In the distance corner of my mind there was a 2nd thought scratching my head, why should not I use it simply as preamp as my Music Hall has direct power-amp input (preamp bypass) option. Many of us may well aware of the fact that all Audio-Gd products generally have quite beefier power section and it's (NFB-3) output impedance is only 10 ohms, which is pretty low. Music Hall A70.2 have input impedance of 47k ohms. 'SYS' have 10k ohms input impedance and output impedance is up to 5k (maximum) means it has 5k pot, but Emotiva passive (Control Freak) had 10k pot. So I felt, between 10 ohms (output impd.) of NFB-3 and 47k ohms (input impd.) of Music hall amp, SYS will seat more comfortably than Emotiva Control Freak for the sake of maintaining the minimum standard of 1:100 ratio between output and input impedance (for example 1:1000 is always better than 1:500).

So ordered the 'SYS' and it landed my address at little more than double cost (with shipping and duties total cost was $110). Instead of settle it as a voltage cutter first I used it as passive preamp. My god! It was a bingo! Mind blowing! It was like a replacement of a shady glass with very transparent one. No RCA cable replacement yet has uplifted the sound quality so much so far. Vocals are like the singer are singing at their own wish with great comfort, pleasure and freedom at real world without mic, lows and high are so effortless with detail, type of three dimensional reality that I cannot describe. Every instruments and vocal got their own room to play and breath. First night had to spend sleepless hearing one after another tracks. Even some known tracks I found to be unknown at the beginning. It really made difference.



From my previous experience of switching different gears and cables (except 6 feet COAX from Blue jeans) I found they usually lift up the quality of few genres of music, but do not good or even do worse to other genres. This time the passive preamp lifted up the quality of all the genres of music with its grace (just like 6 feet COAX from Blue jeans). Few years ago I also tested NAD preamp which worked well with NAD amplifier only but failed to impress me with other amps. So at this moment my conclusion is, an active preamp especially cheaper or mid budget one generally corrupt the incoming signal to various way and extent.



So after initial 3 days of trying I went back to my old setup that is DAC to integrated amp, it took me less than a hour to know that I took an one way route, no move back. Later I tried to use the 'SYS' as voltage cutter or divider (the original intention for which SYS was imported) I mean the connection is from DAC to SYS to preamp of Music hall, volume pot of 'SYS' was set at 3'O clock to match my required gain. But it was the worst sounding combination out of three as I reckoned before**, gain was settled down at right spot successfully at the price of details and air. The score of three types of combination is like below,

1) SYS as Voltage cutter - 'NFB-3 DAC' to 'SYS' (set at 3'O clock) to preamp input of 'Music hall' - Score is 7

2) My old (without SYS) combo- 'NFB-3 DAC' to preamp input of 'Music hall' - score is 8

3) SYS as passive preamp- 'NFB-3 DAC' to 'SYS' to direct power amp input of 'Music hall'- Score is 9

An extra combination I tested was, 'Pioneer BDP-170' to 'SYS' (as Passive) to direct Power amp input of 'Music hall' - Score is 7.75 that is very close to my old combo (2).

where as if I connect the 'Pioneer BDP-170' to preamp input of 'Music hall' (without any external DAC and SYS) - Score is 7.25

It was a clear margin to repeat the old statement "when passive preamp match with a system, it have an upper hand compared to many times more valuable active preamp." But on my part it was calculative chance I had taken where power and impedance matched well beyond my expectation. It also proved the genius and quality of Audio-gd DAC which are quite reasonably priced compared to many others. After all, if the source DAC had not offered such high quality output then the broad highway made by the passive amp (to introduction the signal with power amp without any hindrance) would have gone mostly in vain. Now I am thinking, there are so many components we use to ditch without knowing so many factors can go wrong or so many tweaks out there to make it work.

I am undecided about one last thing whether to use the 1.25V or 2.5V from NFB-3 to use with the 'SYS'. It will take little longer time I think. Till now I never felt any channel imbalance with 'SYS'.

Please note, I am not aware about your system impedance and gain stage to tell that you will surely have the same experience. Also it may be 'SYS' or any other passive preamp would do the trick. I think, our expert DIY friends will be more capable to advice before one set into such venture. But little calculation and risk might help you to achieve greater award. One more important thing, for better result you have to keep the interconnect length as short as possible to use with a passive preamplifier due to maintaining minimum interconnect capacitance to prevent high frequency roll off. I have used 6 inches cable from DAC to SYS and 12 inches cable from SYS to Power amplifier.

Sorry for the poor pictures.
 
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omishra

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#2
Congratulations ! Nice review.

I don't know how people discouraged you for buffered preamplifier, pass B1. But that's solely user's choice. SYS is nice box but basically simple toggle switch and volume pot. Nothing more than it. Still when you drive amplifier it needs buffer, and that colors sound. As you are using no-gain in SYS and volume position at 3'0, it does not make difference for power amplifier. Basic use is attenuation.
How sources react to that volume pot is main problem. Here your sources are tolerant to SYS. and that makes you happy.
Believe me, buffer makes difference and neutral silent buffer is must must! But only if you have to listen at 7-9'o clock position in night silence. mostly 1/5 position and below for 50K pot.
 
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srisaikat

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#3
I have made little clerical correction to my original post, I will be obliged if any moderator kindly replace the original post with this one.

Done
 
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spirovious

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#4
Thanks for review.I also felt many times that adding a bad pre in between source(DAC) and poweramp,kills sound quality.I felt its a compromise.Since its passive pre and impedance is matched,no doubt you are listening to exactly what your DAC is outputting.
Congrats.
 

srisaikat

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#5
Recently I was reading various articles on preamp and other tweaks to improve the listening experience. Now I am a firm believer that one need to be very serious about preamp stage to enjoy music at it's best. I also bought some Harrison Labs inline attenuator (various value) to try at different position. Found that, some options did worse and some did better to the Signal. I will discuss it later.

But here is a handy link how attenuators work to understand the journey of signal path in general, from source to preamp to power amp, limitation of specs provided by Audio Manufacturers. Reading the article carefully one will gain fair bit of idea where should attention required without spend much.
 
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soundbuff

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#6
Hi,
It's over a year now since your discovery, are you still finding it satisfying. I have a direct power in socket in my integrated. Just wondering ....
 
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