"Too much gain"? (Cary SLP05 question)

I haven’t tried the Rothwells, so I cannot comment on those directly.

In regards to attenuators, there are some things that should definitely be pointed out.  First off, any attenuator that isn’t matched to output and impedance runs the risk of increasing roll off in the upper or lower frequencies.  Because attenuation works by dumping voltage to ground, and allowing the remaining voltage to pass to the input circuitry, current is also passing to ground.  I tried some basic 600ohm T style first because the case was reusable and I could always try different topologies, buy as many resistors as I wanted to find the sweet spot.  The 600 ohms dumped so much current the tubes were unable to drive any low frequencies.  Keep in mind that the 400 ohm output impedance of the Cary rises to 4000+ as the signal drops to ~20 Hz, as measured by JA in the Stereophile review.  This unit runs out of juice quickly unless you have a high input impedance amp.  50k+ would be my recommendation.   Note that OTHER highly regarded tube preamp makers state they can increase the cost with beefier output capacitors to match equipment.

I was able to find a resistor match that did measure tonally the same. However, and these are my listening impressions only and should not be regarded as a claim to anything but, I found after considerable testing that the XLR inputs and outputs of the Cary sound different (edit: compared to RCA).  With 6 identical tubes, the XLR pathway loses warmth, bloom, depth, microdynamics and more.  Some say adjust with the input trim.  That is BS, they are directly wired to the Alps pot.  Putting 2 cheap plastic trim pots in series serves no purpose except to allow balancing for mismatched tubes in the headphone stage where it will be most noticeable.   Regardless, both the input and output XLR circuitry both have the same character (edit, compared to RCA).

I did ask Cary about this issue and if they would recommend a local service place to diagnose the issue, and they didn’t reply.  Commonly held belief is that properly made RCA and XLR circuits should sound identical.  Indeed, in my other gear they do.  

Having said all that, running RCA with only 4 tubes (leaving 4 empty), replacing the Alps pot with Kozmo, Goldpoint, or other high quality attentuators and removing the input trim pots will leave you with the potential for glorious sound, as long as you buy exceptional tubes.  I did the work myself, but it will cost you around $1k if you get a tech to do it.  

The gain issue should not be ignored.  Running my XLR 4V outputs through the Cary into a Pass amp (+26 db) required the attenuators to dump 99% of the voltage to ground after the input tubes going by resistance level and L circuit configuration. Many users note minimal volume control issues.    Note also the alps is also the most susceptible to internal RMF signal interference at the bottom and top 1/4 of its range.  Note that with output relays turned off you can clearly hear an input signal at low and high volume, but not at 12o’clock.  So you have to be able to run the unit at 11-2 ish to get best sound.  Gain matching and impedance matching are critical to getting great sound with this unit.  YMMV, and others have reported great satisfaction.  

Cheers

Edited to remove ambiguity, and noted as edits

I found after considerable testing that the XLR inputs and outputs of the Cary sound different (edit: compared to RCA).

@khloebo , my impression is the complete opposite.  I have found that when comparing SQ of the balanced circuit vs the RCA circuit, that after listening to my system using the XLRs the sound stage seems  folded in or collapsed when I use the RCAs.  

Out of curiosity, and not that it would have anything to do with perceptions of balanced vs single ended ins and outs, does your SLP-05 have the Cary Upgrade package?  

@immatthewj   Hi there!  Good point for the discussion, no mine does not.  I bought it 2014 as well, it probably has around 7000 hours on it.  

The upgrade package reportedly has a complete capacitor overhaul, which could affect the SQ in a number of ways (especially driving 20k input impedance).  However, I have not read anyone doing a direct comparison between the two, which is not surprising.

Also, and this is just a giant guess as I haven't created a circuit design and asked an EE about it, but if the ultimate upgrade improves the capacitors, AND the circuitry that converts the balanced signals to unbalanced (and vice versa for output) then it absolutely should be better in technical performance and adding input tubes should add tube character. 

One of the reasons why I replaced the input trim pots with Goldpoint attenuators is so that I could figure out some issues I discovered with tonal shifts during digital vs analog attenuation.  Long story short, both the cheap honeywell pots and the Alps act as low pass filters when attenuation is nearing the max.  IE, they remove high frequencies.  Thus sound is perceived to be rich in mids with fat bass.  Using XLR and low volume controls increases this effect.  It can be very pleasing and rich!  However, it comes at the expense of clarity and dynamics.  Listening to a bunch of systems over the last couple years with tubes left me unsatisfied with mine, so I tinkered.  The Goldpoints allow tons of clarity, richness, detail, space and everything else through.  I keep the Alps at max so it is out of the circuit for music, it only gets used now for TV volume.

Having said all that, nothing needs to be done when you love the sound, XLR or RCA.  New purchasers should definitely try the unit before buying or with a full return option.   It is an interesting box that needs the right situation to sound at its best.  

@khloebo , from reading your posts I have no doubt that you are way more tech savvy than I am (and in case that sounds like it might be snark, I am totally sincere) and I didn’t put as much science and knowledge into the comparisons that formed my perceptions as you have.

I acquired mine in ’21 from Cary’s preowned page, and from my memories of the emails I exchanged before I pulled the trigger, it was 8 years old at the time (it is one of the ones with the indentations on the power supply for the preamp feet to sit on, although I don’t have mine set up that way).  When I called Cary on the phone (they will talk to you on the phone if you want to buy something) to close the deal, I decided that I may as well do The Ultimate Upgrade at the same time, and an added "bonus" would be free shipping (no free shipping on preowned, but if one was to send a preamp to cary for the upgrade, Cary would send it back after the work for "free") even though that meant that once the upgrade was done I owned it even if I didn’t like it.

But to understand where I am coming from with my perceptions of the SQ, up until that point I had been listening to a SLP-90 which I had owned since ’99.  And the SLP-90 replaced a B&K digital HT preamp, so as you can see, my experience playing with high quality preamps is, to say the least, limited).

The SLP-90 was a huge upgrade in SQ from the HT preamp, but it was starting to sound as if it was getting tired.  So the fact that I was listening to a 30 year old preamp probably has a lot to with why I like the SLP-05 as much as I do, although I will say that the SLP-05 sounds a bit (or maybe more than a bit) cool and clinical in comparison with my SLP-90.

As far as my balanced input tubes, that’s something else I am doing different that makes RCA vs XLR not a fair comparison.  A friend from another site turned me on to a literal plethora of PAIRS of vintage 6SN7s (note that I emphasized ’pairs’) so after playing around with those in the balanced slots, I did note that some of them really really shined.  At the moment I have a pair of National Union 6F8Gs (obviously with adapters) in those slots, and they really do it for me some nights.  And prior to putting those in, I was giving a pair of Sylvania ’52 Bad Boys an extended spin, and they were making me happy, but for different reasons.  I also found two different pairs of VT231s  in that plethora that I thought were audibly better than the rest, with my favorite being a pair of black glass RCAs which made detail and separation stand out much more clearly and cleanly. (There were also pairs out of that fore mentioned plethora that I was not sure if I heard any discernible difference or not, and there are actually pairs of both 6sn7s and 6F8Gs that I have yet to even try.)  

So with that all typed, I realize that you were making your observations re XLR vs RCA with all tubes being equal.  

Back to the pots:  what you typed about using the input level pots in conjunction with the main Alps pot was quite interesting, because in my near field environment I am usually at 9 o-clock + or - a bit, and that, of course, is with the input level pots turned all the way up.

My vision is not very good anymore and also I am a bit dense when it comes to understanding  this stuff, but it sounds as if what you have been saying is that to get the best SQ given some of my other limitations also means lowering the gain and if I am stubborn about XLRs the next best would be to upgrade the two input level pots and use them for volume control with the main pot turned all the way up?  Or at least set the upgraded inputs low enough so I can run the main Alps at 12 o-c-clock or close to it?

Forgive me  if that is not what you have been saying. 

(Okay, so now I note that you said that basically the Alps is not at its best at the bottom OR TOP quarter . . . meaning that I would not want to run it all the way up if I was combining it  with the input level pots for volume adjustment.)

Regardless, unless I am totally misreading, upgrading the input level pots is definitely recommended.  Even though I make no claims to be a tech, I do have experience soldering and de-soldering . . . how tricky a job is replacing the pots on this unit?    

Having said all that, nothing needs to be done when you love the sound, XLR or RCA. 

Well, there are nights that I am in love.  But who doesn’t want more and more love?

Hey, thanks for your contribution to this thread!

@khloebo 

very nice description of the workings of the SLP 05.  

right now my system sounds so good with the stock SLP non modded or upgraded.   For anyone interested I do have 3 matched pairs of a specific variety of Sylvania 6SN7s running every slot except the headphone amp.  The rectifier is a NOS made by mullard GZ34.   fyi the RCA smoked glass did not work out and neither did several other NOS notables.  

the tubes and rectifier made such an upgrade I recommend them to anyone with or thinking of an SLP05