Audio Research PH5 Phono Preamplifier Input Clipping Problem

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. 

Yes, under most circumstances 57.5 db is considerably too much phono stage gain for use with a MM or other high output cartridge. Typically MM phono stages provide gain that is in the area of 40 db or so.

In addition to the possibility of clipping, another downside that can occur in many applications would be having to operate the volume control undesirably close to the bottom of its range. As you may have seen in other threads it is not uncommon for that problem to occur with digital sources having **maximum** outputs in the area of 2 volts.

That much gain would often be suitable, though, for use with MM cartridges in systems employing passive preamps, to cite one example.

In your particular case, given the very high overload margin of the phono stage itself a means of utilizing a high output cartridge without overloading the preamp would be to insert a Rothwell in-line attenuator, or something similar, between the two components. Although reports I have seen over the years on the sonic effects of those devices have been mixed, with some (including me) having found them to be quite transparent, and others reporting significant adverse effects on dynamics or other sonic characteristics.

Rothwell attenuators are available in both balanced and unbalanced configurations, and in 10 db, 15 db, and 20 db versions. I believe that most and probably all of those versions would be suitable with respect to ARC’s loading recommendations for the outputs of your phono stage (quoted below from www.arcdb.ws), and certainly with respect to the 10K minimum requirement. But I know that some similar devices from other manufacturers would not meet that requirement.

ARC PH5: Recommended load 50K-100K ohms and 100pF. (10K ohms minimum and 2000pF maximum.)

Regards,
-- Al

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?

In many designs low settings of the volume control may result in an inability to adjust volume in fine enough increments. I see that your REF3, however, provides 104 steps of volume adjustment, so I suspect that is not an issue in your case.

Also, in some designs channel imbalances can occur at low settings of the volume control. But again I would suspect that is not an issue with the REF3.

Finally, it is conceivable that in some designs having to operate the volume control at low settings may result in whatever sonic side-effects may be introduced by the volume control mechanism itself being worse than at higher settings. I have no knowledge, though, as to whether or not that possibility may have any applicability to the REF3. And even if it does, it would be anyone’s guess as to whether or not the possible sonic side-effects of an in-line attenuator, used with these particular components, would outweigh the possible benefit.

Best regards,
-- Al

almarg, I'd be interested in knowing if you have any favorites in the phono preamp category, care to comment?