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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.
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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?
almarg's avatar
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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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rauliruegas
13,084 posts
 
Dear @scottwsmith : """   I know the SUT's historically have been used when you have a phono preamp which is designed for MM cartridges only. """

With all respect that statement is a misunderstood. In the old times active high gain phono stages designs were almost non-existent and almost all the phonolinepreamps were designed for LOMC cartridges using SUTs internally and the external SUT option were used with Phonolinepreamps or phono stages with no internal SUT.

A well designed today SS active high gain phono stage or phonolinepreamp performs with a higher quality that a phono stage with external SUT.

Normally all SUTs has " problems " at both frequencies range extremes. Has inherent limitations at low bass and high frequency against a well designed SS active high gain phono stage. 

Regards and enjoy the music,
R.








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scottwsmith OP
60 posts
 
It seems to me that the ARC PH-5 is less flexible than some other phono stages, because it has fixed gain.  This might be more of an issue if the cartridge is MM has high output.  For example, if the cartridge's output is 4 mv, almarg's math gives me:

4 mv x 750 = 3 volts.

Only a 3X factor for headroom during loud passages, seems likely the 10 volt limit of the REF 3 would be reached often, and hello clipping!  Is my logic faulty, or this combination of components just a bad idea for MM cartridges with higher output?

So a PH-5 and REF 3 are really only good for LOMC?  Yipes. 
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