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Audio Research PH5 Phono Preamplifier Input Clipping Problem

I have an ARC PH5 phono preamplifier and most of the time it sounds fine.  But on a few of my favorite LP's with wide dynamic range, it will clip and distort on loud sections, especially those with lots of bass content.  This only happens with use of a step-up transformer, without the SUT in line, there is no clipping. I do prefer to use the SUT, as without it I have to turn the volume setting on my ARC REF 3 preamp to a very high level.   I have to conclude that the PH5 is distorting because of high input signal levels, due to the gain of the SUT.   I have tried two SUT's, one with 13:1 and the other at 7:1, both exhibit the same problem (although the lower gain SUT is much better).  The cartridge is Ortofon A90 with .27 mv output.  Given this, would you expect clipping or do you think there is something wrong with the PH5?  I have talked to ARC about this issue, and they seem to think that there is a chance the PH5's maximum input of 70 mv is being reached on these loud sections.  Would appreciate opinions from those that have experience with a similar setup.  Thanks.
Ag insider logo xs@2xscottwsmith
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scottwsmith OP
60 posts
 
almarg, I see your point.  It could be the mismatch between the PH-5 and the REF 3 output/input.  Is there an easy solution if this is the case?
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almarg
9,670 posts
 
My suspicion is that the REF 3 design includes active circuitry that is "ahead" of the volume control in its internal signal path. If so, the fact that the volume can be cranked up to high levels without clipping when a SUT is not being used would still be consistent with the clipping occurring in the REF 3 rather than in the phono stage.

IMO there is no reason to be concerned about using the volume control at 2/3 max or other relatively high settings within its range. In fact that is considered by some to be generally preferable, as in some designs it might minimize whatever sonic side-effects may be introduced by the volume control mechanism itself.

So I would simply go without the SUTs. Keep in mind, of course, that without the SUTs the resistive load setting in the phono stage that is sonically optimal stands a good chance of being lower than the setting(s) you use with them.

Regards,
-- Al
rsfphil
139 posts
 
Agree with Al 100%. As long as you can get it to play as loud as you want without excessive noise you are fine. It doesn't really matter where the volume control is. 2/3 of max is fine. You are not going to hurt anything. Generally speaking the more wide open the volume control the better it will sound' There is no need to be paranoid about the volume control. Lose the SUT.
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scottwsmith OP
60 posts
 
So i have been happily listening without the SUT for several days, no clipping.  Been through several albums that used to clip, no problems now.  Given that this cartridge at .27 mv. is pretty typical MC output, and the PH5 at 57.5 dB is mid-range gain for a phono preamp (many have gain settings that exceed this), why would anyone use a SUT with modern equipment?  I know the SUT's historically have been used when you have a phono preamp which is designed for MM cartridges only.  But now, with so many phono preamps designed for MC and lower outputs, are they really necessary at all?  Does anyone perceive value in the use of a SUT when the gain of the phone preamps is such that it is really not necessary?  In other words, is the gain provided by the SUT "better gain" than the phono preamp's gain?  Or is gain just gain, regardless of its source?
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almarg
9,670 posts
 
All gains are of course not created equal, even if they are numerically equal. Noise performance and consequently hiss levels can certainly differ among different phono stages that provide similar amounts of gain, with that being likeliest to be an issue if an LOMC cartridge having particularly low output is used. Also, in some cases the sonics provided by the moving coil circuitry in phono stages having both MM and MC capability might not be as good as the sonics that would be provided by the combination of a good SUT and the MM section of the same phono stage.

Enjoy! Regards,
-- Al


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