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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.
folkfreak
rauliruegas
9,123 posts
 
Dear @folkfreak : What defines the maximum is the phono or line stage overload figure.

Now, the whole subject it's not if your SUT is outstanding ( because it's not. ), it's a good SUT. A SUT is not a rocket science design. I'm not trying to diminish your SUT only to put our foots in the floor. I'm sure your SUT is a good design. I think I tested over 30 different SUT's over my audio life and many of them really good as the Denon 1000  or the top Technics where both has the wider frequency range I seen in any SUT but even that can't even a SS active design in this regards. The Denon is something to listen and to caryy because it weigths 10 fully kilos.

Anyway, What you are experienced tells me that the ARC designs are not up to the task against your new items. I posted " every thing the same " a fullfunction high gain unit beats its counterpart with passive unit as the SUT. EVERY THING THE SAME.

Problem is that you had not a really good design. It's not easy to design it.

Checking levels of quality performance alone needs better electronics designs.

Now, the very important subject is that you are satisfied as never before, good ! !


Regards and enjoy the MUSIC NOT DISTORTIONS,
R.
almarg's avatar
almarg
8,673 posts
 
Assuming I’m getting the same voltage level output from the preamp with or without the step up why would the performance with the step up be so different? Is it inherent to the step up or is it also a problem of trying to amplify too small a signal at the pre amp (or for that matter at the phono stage).
I wouldn’t want to speculate as to the specific technical factors that may be involved, at least without being intimately familiar with the design of the phono stage. I would just note, again, that the two gain choices provided by the phono stage are very atypical, while the output level of your cartridge is well within the bounds of being typical for an LOMC.

I’ll add, also, that the gain of your VTL monoblocks is several db greater than the gain of most power amps, to a greater or lesser extent depending on the mode and feedback settings you are using. So with many other amps the low upstream gain you had prior to the addition of the SUT would probably have resulted in your 70% to 80% settings of the volume control being in the vicinity of 100%.

Best regards,
-- Al


terry9
931 posts
 
Hello Folkfreak.

I use a pair of Lundahl 1931Ag SUT's. These are bare transformers, and require a box, connectors, etc. About $2000 in parts. The whole is quite simple to fabricate and the sound is quite stellar.

My new DIY phono/pre will have sufficient gain to work without, and I am looking forward to the comparison.
roberjerman
2,086 posts
 
Moving coil cartridges have low voltage but high current. Therefore the best way to achieve higher voltage from a mc cartridge is to use a transformer. This neatly accomplishes the task WITHOUT adding ANY noise to the tiny signal from the mc cartridge! ALL active devices (tubes and transistors) ADD noise to the signal. What you will hear is a CLEARER  musical signal with more of the subtle micro details already present in those vinyl grooves - that were masked by the NOISE of active devices! 
roberjerman
2,086 posts
 
I have been using various transformers with different mc cartridges for 40 years and have always found them preferable to any active device - even the esteemed Levinson JC-1.
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