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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
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rauliruegas
9,123 posts
 
Dear @folkfreak : Yes, I agree with you that the SUT is a valid option but not necessary thwe best one for the cartridge signal. As you said it needs additional IC cables with additional connectors where the signal must pass.

I'm not against SUTs per sé, as you said is a valid option but there are better options. 

Problem with active high gain stages resides in its design where the designer has to have a real deep knowledge levels and skills to that kind of " problematic " design and that's why exist not many active good designs and when the design comes of tubes the " solution " is a SUT inside that tube design because tubes levels of noise preclude to design an all tube active high gain phono stage. Other designers of tube electronics decided that the first gain stage be handled by SS devices.

The use of external SUTs can produce in the audiophiles several questions and normally came by the cartridge needs of load impedance when the LOMC cartridge is no sensitive to changes in load impedance as I staed here and where @almarg gaves a wider explanation about and where other gentlemans in other threads repeated the same several times.

Of course that always exist people that read but understand nothing, just never learn. Are ignorants for say the least.

Anywa, again SUT is a valid option.



Regards and enjoy the MUSIC NOT DISTORTIONS,
R.


robd2
44 posts
 
Question for the group. I think we all agree that it's important to choose wisely when matching a SUT to a specific cart (1:10, 1:20, 1:5, all that good stuff). How do the phono stage manufactures handle this with such a one size fits all approach when they build in a SUT to the phono stage?
lewm
6,770 posts
 
A very recent experience:  Last week my neighbor emailed me, as he usually does when he has a question about his very expensive audio system.  He recently purchased a new $30K phono stage (39db gain according to mfg spec) which is fed by a SUT suited to his previous phono stage (which had 42db gain, minimum).  Between the phono stage and his amplifiers, he was using a very high quality passive attenuator.  With his new phono, he was noticing that the sonics were occasionally anemic during orchestral crescendos and on similar demanding passages, and he wanted me to help him decide which of two more powerful power amplifiers he should now buy, in order to fix his problem.  

I noted that he currently owns an 8W SET powering a pair of speakers rated at 105db(!), and I told him his problem should hardly be an indication of a need for more amplifier power.  (8W should produce 107db spl at 10 feet from a 105db speaker, based on my calculations.) Instead, I advised him to save his $$$; I guessed that his upstream components were not driving his amps to their full output.  Indeed, if I assumed that his SUT was providing about 5.0mV at its outputs (i.e., the voltage output of a typical HO MM), I calculated that the signal voltage delivered to the amplifiers via the passive attenuators was less than 0.5V, not enough to drive most amplifiers to full output.  To prove the point, I lent him my vintage Quicksilver preamplifier which can provide quite a bit of gain via its active linestage section, although I don't know precisely how much gain in db.  Once we inserted the Q into his signal path in lieu of the passive attenuator, all was well, and I left it with him for a couple of days.  I have no intention of parting with my Q, so he bought an (expensive) active linestage of his own.  Now he's "cooking with gas".  What was striking to both of us is that the active stage made his system sound better in all respects, not just on musical peaks.  And strangely, this applies also to digital, where gain should not have been a problem.
The story has no moral, because he has now also made a deposit on a more powerful amplifier even though I proved to him he did not need it.  I am happy to help him, because, besides the fact that he is a nice guy, listening to his system after each "upgrade" allows me to educate myself on the price/performance ratio prevalent in high end audio, at no cost to me.
robd2
44 posts
 
I thought I saw an excel based calculator out here somewhere that would answer a lot of these questions for a given cart. Punch in output of cart, SUT, Phono, Pre, ect and it would tell you what you needed to stay in "ideal" ranges.

Anyone have the link?
swampwalker's avatar
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swampwalker
5,132 posts
 
@robd2- Here is the gain calculator and a good explanation of how the parameters interact: https://www.kabusa.com/pregain.htm.

As far as how phono stage manufacturers handle the issue of SUT:cart matching, they basically don't.  Some have a choice of loading, but I don't if there are any that have a choice of step-up ratio.
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