i guess this would be phono only as the line stage only comes into the equation when volumne is at 100%?
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?
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?
- 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
- 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
- So given 1 and 2 try a step up -- you may be surprised as I was!
- ...
- 49 posts total
@robd2 to your question I've no idea other than to suggest that perhaps they start from a flexible multi-tap arrangement like MFA offer (offering a choice of 1:5, 1:10 or 1:20 and 10K-80K loading)? I'd rather have the step up designed for the specific cartridge however One other benefit of a step up is the ability to optimize grounding for the cartridge/turntable separate from the phono stage. As I observed here (https://forum.audiogon.com/discussions/a-new-ground-benefits-of-introducing-the-synergistic-research...) I found that grounding my phono stage when it was directly connected to the cartridge made the sound worse. Now I go via a step up I recently added the SR Ground block back to the phono stage and found a noticeable positive improvement in removing a level of hash I was not aware of. Maybe the next step is to try something like this (http://www.monoandstereo.com/2017/11/new-akiko-audio-phono-booster.html#more) on the step up itself? |
Robd2, the KAB gain calculator addresses only the gain provided by the phono stage. Also, it can be very important to note the following statement that is provided in its introductory text: The optimum gain is based on acheiving [sic] 325mV rms output at 5 cm/s. For the current crop of CD recorders, 300mV is required for 0dB recording level with the recorder’s level control set at max. Aiming for 325mV gives a little margin.So the calculator will not necessarily provide valid results in a situation where the phono stage is driving a line stage preamp which in turn is driving a power amp. For example, a reasonable line stage gain of say 10 db would boost that 325 mv to about 1 volt if the volume control is set at max. More often than not, 1 volt will not be enough to drive a power amp to full power. And that's with the volume control at max! And of course there are many line stages which provide less than 10 db of gain. So take the results provided by this calculator with several grains of salt, and throw in some additional db as well :-) Regards, -- Al |
Swampwalker, Among commercial phono stages that do have built-in SUTs, the Allnic H3000 does provide a choice as regards gain, probably by internally selecting primaries or secondaries that afford different turns ratios. Of course, the H3000 is not a "budget" product. For manufacturers of MM phono stages that do not incorporate SUTs to facilitate the use of MC phono cartridges, there really is not much more they could do, except possibly allow for a choice of load resistances so as to accommodate a wide range of turns ratios in whatever SUT is chosen by the end user. |
Great thread guys and thank you so much for the info. Let me lob one more question into the mix to keep the conversation going. Looks like we also need to watch out for too much gain (overload margin). Is it true that during loud passages the cart output can increase 10x and run into a ceiling in the phono which also causes distortion? |
- 49 posts total