2. analog
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On Step Ups and the Importance of Managing Gain

The past several weeks have been some of the most eye opening in my entire audio journey. Despite over 30 years listening to LPs across a range of setups it seems I've only just stumbled across one of the secrets of analog reproduction -- the step up transformer AKA the importance of managing gain across the analog reproduction chain.

To understand what I mean you need to start with an understanding of my gain cascade prior to my most recent changes. My cartridge is an Acoustical Systems Palladian which is a relatively low output MC at 0.33mV. I've been running it into an ARC Ref 2SE Phono and then an ARC 40th pre. Both are connected balanced so the gain is 51dB (for the phono stage) plus 12dB (for the pre) = 63dB at the LO gain setting -- I tried listening to the HI gain (74dB) setting on the phono but found the added FET amplification added an edge to the sound, amplified hum and restricted dynamics. I'd therefore learned to live with having the Ref 40 volume control on the high side (about 70-80% of range) and "thought" I was getting good sound - great clarity, sound-staging and frequency delineation.

However with a pending upgrade in my phono stage to the VOSS phono, a pure 40dB only single ended affair, I was forced to add a step up to my setup. I've always sworn off the added complication and additional switching and cables so had assumed it would not do anything to improve things. How wrong I was. The model I have is the Music First Audio Classic V2 in a custom configuration built for me with two inputs (one for my mono arm and cartridge) and fixed 20dB gain (1:10 ratio). It also has a three way ground lift switch so any hum issues can be addressed at source (which works btw). At about $3K it's not cheap (and MFA have cheaper options) but in the scheme of things actually much less than the list price of the interconnect I needed to add to connect it to my phono stage (so in the context of my system a stone cold bargain). 

My gain cascade is now 20dB (step up) plus 45dB (phono, now single ended) plus 12dB = 77dB and the volume control is at 40-50% of range. Once I'd realized that running a step up into 200 ohms is not going to work at all and switched the ARC Ref2SE to 47K I was off -- and was I surprised! All of the sudden the soundstage opened up by 50% side to side, front to back and up and down. Dynamics on individual instruments suddenly snapped into focus and the overall presentation was transformed in a way I would not believe possible. One instance can serve as a sense of what I mean -- the two opening cuts on Joni's Hejira, "Coyote" and "Amelia", are mostly similar sounds layered over one another and can be pretty hard to sort out. With the new step up in place it's as if everything now makes sense and each instrument is positioned in space perfectly in location and scale with all the others.

So what's my take away and potential advice to any reading this?
  1. High gain (i.e. 60dB plus) phono stages are, as we all know, problematic so if you can avoid going that way consider looking into it, BUT
  2. Don't "push your gain" i.e. try to under drive a stage, you may not know it (as I didn't) but trying to amplify .33mV with "only" 51dB is probably losing a lot of detail into the noise floor of your amplification stage and/or giving you problems down stream if gain is set too high
  3. So given 1 and 2 try a step up -- you may be surprised as I was!
Not sure if this experience matches with others and would love some perspective from amplifier designers as to why I may have had such a bad (in retrospect) experience with my prior gain cascade.
128x128folkfreak

Showing 1 response by willemj

willemj
1,036 posts
 
In the old days amplifiers like my old Quad 33 had interchangeable input boards with gain and other characteristics that could be matched precisely to the cartridge for optimum S/N, frequency response and distortion. Quad supplied them ready made for the most common high end cartridges of the day, and others could easily be made from blank boards.That same amplifier had similar adjustment options for the tape input and output. As you are discovering, this is indeed very important.
The same issue also exists with the analogue output of CD players or DACs. CD Red Book specifies a 2V output, but many amplifiers have much more sensitive line inputs. The result is that the input stage may be driven into clipping, with increased distortion and compression of peak signals as a result. The solution is simple: just fit inline attenuators or an attenuating cable. The result is often a far smoother sound. The giveaway sign that this is indeed a problem is when you only have to turn up the volume control a little bit to have a loud signal.
The commercial reason behind this strange situation is that the human brain interprets louder as better. So if a CD player or DAC is slightly louder than another, this gives an unfair advantage in de demo room because the innocent listener will interpret this difference in level as a quality difference (as that is how the brain works). The same applies to amplifier input sensitivity. The more sensitive amplifier will be louder and hence seem to be better. Proper comparison should be level matched within 0.2 dB, but that requires the serious Volt meter that I at least have never seen in a demo room.
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