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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.
scottwsmith

Showing 12 responses by scottwsmith

scottwsmith OP
60 posts
 
So, it would seem there is something wrong with the PH5, in your opinion?
scottwsmith OP
60 posts
 
Thanks for the responses.  Perhaps my logic is faulty, but I suspect it is the PH-5 simply because the clipping disappears when I remove the SUT.  Without it, and with the REF 3 cranked up to a fairly high volume (about 2/3rds of maximum) there is sweet sound with no clipping.  Now, perhaps I am being paranoid, but I don't particularly like running the REF3 at that high a volume.  So I prefer to use the SUT. 
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?
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?
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. 
scottwsmith OP
60 posts
 
I am learning some good stuff here.  Switching gears a little, I also have an ARC DAC7 (which I use in balanced mode) with these analog specs:

OUTPUTS, ANALOG: (Stereo)1. Balanced XLR 5.2V RMS (+14.3dBv) max.2. Single-Ended RCA 2.6V RMS (+8.3dBv) max

And yes, I do operate the REF3 at rather low volumes (maybe 20%) when using the DAC.  Is there any possible benefit in using an attenuator?
scottwsmith OP
60 posts
 
almarg, I'd be interested in knowing if you have any favorites in the phono preamp category, care to comment?
scottwsmith OP
60 posts
 
Yes I have noticed that one is recommended a lot.  Looks like a move from PH-5 to Herron could cost about $ 2K.  Will have to consider whether that is "reasonable" or not.  But for me, swapping gear and upgrading is part of the fun.  It seems that used versions of the Herron are hard to find.  I guess those who have them, keep them.  Did you purchase yours new?
scottwsmith OP
60 posts
 
In the ARC world, you can move to the Reference product line, which does offer different gain levels, but they are pricey, I don't think I am too interested in that solution.   For those phono preamps that really do have an MM/MC switch -- I think you are saying using the MM setting with an SUT, instead of the MC setting might yield better results for a MC cartridge with output in the .25 range, such as mine.

For example, on the Manley Chinook, there is an internal setting to set the gain at around 45 dB, " for MM cartridges".  With my SUT's of 1:13 and 1:7 and that gain setting, what would be the input levels to the REF3, and given your suggestion of possible lower noise and distortion, is this a good upgrade?  Same set of questions for the Herron, if you would indulge me?? 
scottwsmith OP
60 posts
 
And to follow up, my thinking now is NOT to use an external SUT.  I am getting good results with the PH-5, without it.  
scottwsmith OP
60 posts
 
Not particularly motivated to swap cartridges.  The A-90 is the best I have heard.  Was considering an upgrade in the ARC line to a reference series phone preamp.  any thoughts on that?  
scottwsmith OP
60 posts
 
Anybody have an opinion on the ARC Phono Reference Mark 1 that has just shown up on Audiogon?  Those gain numbers appear to be in the sweet spot for my A90 cartridge.
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