Problem with preamp volume control

As a point of information, the preamp was fairly recently Teflon recapped by Conrad-Johnson. 

The important point of information would be what is the gain of your phono stage and what line stage are you using, if you have a separate line stage. It also would not hurt to say what amplifier and speakers you use. Are you hearing distortion? Audible distortion would be a sign that the cartridge is overloading the phono stage, but in its absence, then you likely have an issue with sorting out the gain of your various components and the sensitivity of your speakers. There is nothing really wrong about using a low setting point on your volume control. So long as you have no distortion related to overloading.

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.

@almarg,

Unless the inline attenuator adds capacitance, the added resistance 'may not' be that bad for a MM cartridge and could be good, https://www.tnt-audio.com/sorgenti/load_the_magnets_e.html.  But I will defer to your experience with these attenuators.

My setup includes a Benchmark AHB 2 amplifier and GoldenEar Triton 1 speakers.
The line stage gain is 27 Db
The phono stage is listed as:
High gain 54 Db
Low gain 40 Db
I don’t know why there is a high and a low gain listing for the phono stage.
Is there a setting for this?
I don’t hear any distortion whatsoever.
I don’t mind the low setting.  I just would like more play in the volume control.
Right now, minuscule turns achieve large changes in volume.
i wouldn’t know how to attach an attenuator. I will call CJ and see if I can get Help

RV,

The Benchmark AHB2 has three different sensitivity (gain) settings - there is a small toggle switch on the back - see your manual pages 8/9 or download https://cdn.shopify.com/s/files/1/0321/7609/files/AHB2_Manual_-_Rev_G.pdf?6581480924542235084. 

The line stage gain is 27 Db
The phono stage is listed as:
High gain 54 Db
Low gain 40 Db

Not sure what to make of that, RV. The description of the PV11 at the CJ website, the manual for the PV11 that I found online, and Stereophile’s measurements all indicate the gains that I cited in my initial post, or very close to them (47 db phono stage gain; 18 db line stage gain).

In any event, though, if your preamp is in fact providing 40 db of gain in its phono stage and 27 db in its line stage (27 db being **very** high for a line stage, but not atypical of many CJ designs), the total of those two numbers and the total of the numbers I cited constitute very similar overall gains. But if perchance your preamp is providing 54 db of gain in its phono stage, that is something that is probably in need of correction, IMO, given that a high output cartridge is being used.

But regarding your amp, as Antinn pointed out it provides three different gain settings, namely 9.2, 17, and 23 db. If you are not doing so already I would suggest trying the 9.2 db setting, even though the website description suggests using one of the other two settings when single-ended inputs are used.

Regarding attaching an attenuator, as you can infer from the photo provided at the Rothwell site you would purchase two of them and simply insert one into each of the RCA-to-XLR adapters you are presumably using at the amp inputs, instead of plugging the interconnect cables into the adapters. You would then plug the interconnect cables into the attenuators. Very simple.

Best regards,
-- Al

I just had a long conversation with a CJ tech. He said that an attenuator is very feasible in the line stage but not in the phono stage.
He was very interested in getting me to buy a new CJ preamp.  So I don’t know if that had any influence on his advice. Basically he said get a new cartridge or a new preamp.
 

Antinn,

I had forgotten about those Benchmark settings.  Thanks, so much, for bringing that up.  It just might be the solution!

Al,

 Thanks, as usual, for your valuable advice.  Hopefully, the amp settings will do the trick.

Richard

P.S. to my previous post: If you are using RCA-to-XLR cables, rather than adapters, and you ultimately find it necessary to purchase Rothwell attenuators, my suggestion would be to replace the cables with RCA-to-RCA cables and use them in conjunction with inexpensive RCA-to-XLR adapters, such as this one.  But hopefully (and I suspect probably) the amp's adjustable gain provisions will do the trick.

Also, regarding ...

He said that an attenuator is very feasible in the line stage but not in the phono stage.

To be sure it’s clear, the attenuators would not be used in either the line stage or the phono stage. They would be used at the inputs of the amp, as I described above.

Best regards,
-- Al

Using the lowest gain setting on the amplifier may also have subtle benefits for SQ overall.  That is without a doubt the first thing to try, IMO.

Well, the amp settings did the trick.
Of course, in the back of my mind is Benchmark’s recommendation, which I’ll have to forget about.
I think the problem is solved.
It still sounds great!

Thanks to all, especially antinn and Al.

Viva Benchmark!

Lewm,

I think you’re right.
 It’s sounding even better.

Great that you have it solved.
To summarize my comments on the various options.
1. Al was spot on. hey. he's two for two in my book this week.
2. messing with cartridge loading (between cart and phono preamp) is dicey unless you redesign the interface as a system, and with full schematics.  Simple answer: if you have to ask, don't.3. You can often modify the line or amp gain - and its far less sensitive to various loads in those places. Sometimes even a setting.
4. You can successfully add an attenuator between a preamp and amp, but again need to know the I/O impedances first. IN fact nearly every amp has a voltage divider of sorts right at the front end.  Simple to just change its ratio.

Comment:  18 dB in a in the stage is a huge amount! I typically have 6!  and at most common knob settings, its fractional. Yikes!
G

ps: rare problem!  Most people don't have enough gain with low output 'coils. Tons of gain without noise or hum (which is a form of noise, ok, ok) is tough.  be happy you have it.

build build an in-line attenuator inside a m-f RCA jack shell. A 47K 1/8 watt 1% metal film resistor worked for me when I had excessive gain on my Parasound preamp  

Antinn,

I have to thank you so much for your reminder that the Benchmark had three gain settings. I have much more control and seemingly more headroom in the sound now.
Without your post I would  probably be caught up in some convoluted solutions, 
This way, all I had to do is flip a switch.
You made a big difference!

RV,

Thank-you for the thank-you :).  It was about a month ago when a similar item came up, but that time it was a Bryston amplifier that like the Benchmark had a selectable sensitivity, and the simple flip of a switch yielded similar success.  Enjoy the music!

I was just reading the Benchmark manual and came across a potential problem.
It says:

“If you are using an unbalanced input, you must use one of the top two switch positions.” (Must underlined.)

 My CJ only has RCA outputs which connect to the Benchmark inputs with RCA plugs.
 I’ve just switched to the bottom switch position (lowest gain.)
 The SQ is just fine.
But am I doing something wrong vis-a-vis the manual?
 

I suspect that statement is predicated on typical combinations of preamp gain, source output level, and speaker sensitivity, while also taking into account that providing the amp with unbalanced signals will result (everything else being equal) in less volume than if the amp is provided with balanced signals.

In this case, however, the gain of your preamp (line stage + phono stage) is **much** higher than is typical for use with a high output cartridge, and so I can’t envision any reason to pay attention to that statement.

Best regards,
-- Al

Al,

I was hoping you would see this post.
Thank you much for the reassurance!

Richard

I phoned Benchmark
They corroborated that, with my preamp, there’s nothing wrong with putting the sensitivity switch in the lowest position if I’m getting enough volume.