"Too much gain"? (Cary SLP05 question)

@immatthewj, sure. If gain issues exist in the system (in my case, due to relatively high voltage output of the upstream DAC), this results in my using the downstream volume pot (of the headphone amplifier/preamplifier being fed signal from the DAC) rotated nearly all the way counterclockwise. That means if I rotate that pot very far at all in the clockwise direction--to increase volume--the already borderline-excessive volume increases quickly and to an intolerable level.

Traditional wiper-type volume pots often exhibit sonic nonlinearity at this extreme counterclockwise rotation. Typically this is experienced as poor channel tracking, with one channel sounding louder than the other. Depending on the specific volume pot, there also might be higher than usual audio distortion at extreme counterclockwise settings.

One goal of reducing system gain via devices such as the Rothwell attenuators (installed in the RCA inputs of the amp/preamp) is to reclaim some of the lower roatitonal range of the amp/preamp’s volume pot, so I can adjusting the desired volume a little further up from the farthest counterclockwise position, thus avoiding any non-linearity at that position.

Note: with certain other types of volume pots (ie, stepped, reed-relay, or digital domain designs) there is no apparent non-linearity at the pot’s rotational extremes. Thus these pots exhibit little or no nonlinearity with in systems with excessive gain, Howeverr, there may still remain the issue of having "too few steps" for effective volume adjustment.

@desktopguy

thanks for the explanation.

I am actually the OP on this thread, & one of my questions/concerns was "am I losing anything, sonically, by having to keep my volume pot backed off to a low setting?" It sounds as if I may be.

6 oclock is my volume pot backed all the way off. Normal listening volume for me depends upon the CD (how loud, or I guess how much gain(?) of the CD itself) but it is usually at or about 9 oclock & sometimes, but not often, as high as 10:30 or 11 oclock. I would think it would be screaming at me if I ever put it at 12 oclock. (Part of this is probably due to the small listening room I am presently in.)

As far as what you said about nonlinearity at volume pot extremes, a little while back ago I was messing around with a Sheffeiel Labs test CD that I bought a long time ago & I came upon a test I had never done, & that involved a test tone & the instructions were to put the leads of a voltmeter on the speker wire terminals & compare the readings of both speakers. I did note that one was a bit higher than the other, so I used one of the balance pots of the preamp to make them even. This was a while ago, but I think I remember doing tube swapping on the preamp to see if the discrepancy followed the tubes, & I was thinking, at the time (if I hadn’t confused myself) that it was following the position of 2 tubes (L & R) for the balanced inputs of the preamp.

After reading your replay, I guess I should repeat that test & see if I was correct about it following those tubes.

Anywy, thanks again for the explanation.

@immatthewj Definitely think you will be happy with your decision. I went through the same litany of issues running SLP-05 into Pass X250.8. The Rothwell’s have worked out great. I usually run main volume pot between 10 and 1 with small. Balancing L/R pots at 100% and system is dead silent and very dynamic.

@harpo75 Thanks for the clear explanation on balanced gain, pot issues etc. i run balanced from the Cary to the Pass and my analogue from the phono preamp to the Cary. I actually loved the extra balanced dB bump on the mc cartridge. I am currently running rca from my 2.0 v digital source as I have not been able to hear a difference and I like the reduced gain even at the 2.0 volts( still run main volume between 10-12 for digital) I will revisit this again but since cables are different that clouds the comparison and I want to stay away from lowering main volume below 9 o’clock. Enjoy, looks like you got some great experienced advice here.

@immathewj

I have learned your issue the hard way having bought a power amp with 26db gain for my Cary SLP-05 (Pass Labs XA30.8).  Even when the Cary's gain is backed off to half (going any lower affects dynamics) there is too much gain in the system. 

I tried the 10db rothwell attenuators and did not care for the results.  

I also tried using the RCA outputs which drops the Cary gain from 24 db to 17db.  This definitely helped but I lost a lot of the 3-D huge soundstage when not using the XLR outs on the Cary, the balanced outs run through another set of tubes and the sound stage is much larger and the sound is ore dynamic.  

Ultimately an amplifier with 23 to 20 db gain works best- or an amp with adjustable gain like Parasound a21+ or JC5 which I run at about half gain.  

Hello all,

I thought it would be worthwhile to add to this thread as the unit does have a ton of gain that will severely limit use of the main volume pot. After reading through this thread and others, there has been some good information and some incorrect conclusions. I thought I would relay my experiences here to help future owners resolve the question of what to do with the excessive gain in a pre that they love.

First, let’s be clear what the circuitry is. ALL inputs, xlr (via input tube buffer) or rca get routed to the right and left input trim pots. The pots are a cheap Honeywell plastic potentiometer, 100kOhms. Recommended use for this pot from the Honeywell sheet is in ATVs, joystick controls, and more. Ruggedized for military standards. These Honeywell pots are directly wired to the two plastic potentiometer layers of the Alps 100 kOhm pots, which has a motor control. So you can use either the trim pots or the volume knob to control volume, or both. It doesn’t matter electrically, you just have 2 pots in series.

I have played around with the pots on the Cary, as well as digital attenuation. Re digital, some software driven attenuators are definitely better than others, but it seems like -10- to -15db is the limit where I don’t hear issues in volume matched back to back comparisons. Yeah, I know it shouldn’t be the case mathematically, but something is off. Besides, even -30 or -40 db digital attenuation isn’t enough to give you full use of the volume knob. So that isn’t the answer.

Playing with the pots is interesting, because you will quickly notice with volume matched testing that the balance trim pots are clearly filtering the signals. This shows up with low level information at all frequencies, but it is most easy to see with higher frequencies. Maybe a system runs a bit bright? Well ok, but the full spectrum loss of clarity and detail is not a favorable trade. Buy tubes that are rolled off on top, *cough* I meant warm sounding.

Playing with the Alps volume pot gives similar results, but with less severity. The channel imbalance near max attenuation is a problem though, as is the high frequency filtering which makes the bass seem exaggerated.

So what are the solutions? I guess you have to decide what you want out of this pre. Do you use the headphones a lot? The input trim will likely be important unless your tubes are perfectly balanced. Input trims are useful for troubleshooting, but that is limited case scenario when it is also easy to just pull a cable. Only use the volume knob and you just want it to work better?

If you want it all I would look at replacing the volume and the trim pots with high quality stepped attenuators. Goldpoint,Khozmo, or others are good examples. Yes they are expensive. But your $6-8k amp deserves better than 3$ and 12$ pots. I put in a 24 step mono 100k pots in place of the trim as I don’t use headphones. If you do, maybe see if 47 step will fit.. First off, night and day improvement in clarity at all frequencies, you will sit up in your chair. Second, with high quality pots you will notice that the Alps isn’t exactly bad. If you do most of the attenuation with your stepped pots, then you can run the Alps from 12o’clock to full on with good results. In messing with this configuration over the last month, I would say that the less the Alps is in the chain, the clarity improves but with diminishing returns. My next step will be to replace the Alps with a 47 step attenuator and call it good. The upper range of the 24 stepped input trim is just a teensy bit limiting in my system.

Motorized volume knob mandatory? Well there are solutions depending on the attenuator you choose, but they are expensive. I would go this route if you plan to keep the pre for as long as you can. I haven’t decided what to do yet, I might see if I can use the existing RC design and fabricate an adaptor for the new attenuator. We’ll see.

Hope this helps. Yes, get a professional to do the work and the usual disclaimers. I have no knowledge of EE or circuit designs, these conclusions are my own experience and you may get different results. Make modifications at your own risk.