Problem with preamp volume control

rvpiano,

You have a couple choices depending on what else plugs into the preamp, and what amp you are using.

The easiest is to reduce the gain on the amplifier IF it has this option, Bryston amps have different amp gain setting, check the amp manual.

You can add an inline RCA attenuator such as  Harrison Labs 6 dB RCA Line Level Audio Attenuator, Parts Express sells them, better ones are made by Russ Andrews but these are sourced UK and they do not come in 6dB.  You can search inline RCA attenuators and there are a number of different forum discussions with differing results, but the Harrison are cheap.  You can install the attenuators on the phono input or on the amp input depending on what else plugs into the preamp.  I can't tell you which is better, I have never used them.

If you can use the attenuator on the amp input, you may want to check with CJ to see if they can mod your preamp gain from 18dB to 12dB.  As a bit of a guess, also check with CJ to see IF they know if different phono tube manufacturers provide different gain.

Hi RV,

The root cause of the issue is that like many Conrad Johnson preamps yours has higher gain than most. Although many other CJ models have considerably higher gain than even yours. The PV-11 specs being 47 db for the moving magnet/high output moving coil phono stage and 18 db for the line stage, those numbers closely corresponding to Stereophile’s measurements.

My suggestion is that you insert Rothwell attenuators into the input jacks of your power amp. They come in 10 db, 15 db, and 20 db versions. I suspect that the 10 db version would result in volume control settings roughly in the area of 11:30 on the dial, and the 15 db version would result in settings in the area of 1:00. I would choose one of those two, rather than the 20 db version which I suppose might increase the possibility of unwanted side-effects.

Over the years here some members have reported compromises to dynamics or other unwanted side-effects using Rothwell attenuators, while others have had very positive experiences with them (including me in a past incarnation of my system, using the 10 db version). I suspect that some of the reasons for that discrepancy involve impedance considerations specific to the particular system. I wouldn’t want to speculate as to whether or not that would be an issue in your particular case, but given the cost of these attenuators it seems to me to be a very reasonable gamble.

Finally, I would strongly recommend against any other brand of inline attenuator, as I know that some of the others have impedances that are too low to be suitable for use in many and perhaps most consumer-oriented/non-pro applications.

Best regards,
-- Al

You can install the attenuators on the phono input or on the amp input depending on what else plugs into the preamp.

I would not install any such attenuator on the phono input in a case such as this, where a high output cartridge is being used. The resultant loading of the cartridge will be very non-optimal.

Also, I recall that some time ago a member here measured the impedances (i.e., the series and shunt resistances) of Harrison labs attenuators, and the numbers were vastly lower than those of the Rothwells, and are likely to be problematical in many home (non-pro) audio applications. Especially when driven by many and perhaps most tube preamps.

Regards,
-- Al

rvpiano,

To follow my discussion on vacuum tube gain, for 12AX7 and 5751 tubes see this list, https://www.tubesandmore.com/tech-corner/12ax7-comparison-current-made-tubes.  

Otherwise, the recommendation to use Rothwell attenuators is supported  by many reviews such as TNT Audio, but again these are sourced UK.

What Almarg said.  Or live with it.