Time to upgrade the pre-amp.

40year old electronics are problematic as they likely are in need of repair. I’d check w/ ARC on the cost to ‘refurbish’ and if they even have the parts available. 
You should be able to get a good deal on a used Ref 5SE and trade that up later if you so desire.

 Also, if you’d prefer new, the Ref 6SE has been out for a few years now. My own experience is limited to the LS 28 SE which I think is very nice.

ref series all day long... a ref 3 is quite reasonably priced, superb

my 2 cents

@saulh I agree that the older ARC preamps are more prone to electronic problems down the road given their age, and newer ARC preamps deliver a more whitish / neutral sound, which is less reminiscent of the classic tube preamp sonic signature that you are searching for. One ARC preamp I found that delivers warmth and bloom is the LS28, which exhibited well more of this over the Ref 6, which is much more neutral. 

That said, for thousands less, I would encourage you to consider Modwright preamps, either the LS-100 or LS-36.5, or preamps from Rogue audio. You can get much further for the money, both are made in the USA, and their service is impeccable. 

Some great advice here. Much appreciated! I'll check out Modwright, 

Good points about the repairs and especially the potential that parts may not be available for the older amps.

@blisshifi the LS28 is a hybrid I thought vs the Ref 6 all tubes. I may need to listen in person, as we got 2 votes here. 

I didn’t mention earlier but I had the LS28 and Ref 6 in possession at the same time and demoed them against each other in the two systems I had at the time , which I’d how I landed the comment above. Despite my preference for the tone, warmth and bloom of the LS28, the Ref 6 did resolve and sounded more “hifi”. 

You might consider the BHK preamp from PS Audio. 
 

All the best.

Buy a nice older Counterpoint nd send it to me for upgrades.  You won't look back at anything else and it will be below your budget or you can buy one of my products that are customer built, point-to-point wired.

Happy Listening.

Van Alstine Transcendence RB 10.

@curiousjim Great call on the BHK. It is a hybrid tube preamp but it is spectacular for its price point and really hard to beat if you can get it on the used market for $3500 or less. I actually preferred it to more euphoric preamps like the $18K Viva Linea. Aftermarket tubes bring the unit to an even better level than the already decent stock Psvane. 

If you decide to go the vintage route, I had my SP11 Mk II refurbished by ARC just last year. Cost about $1k all in, including new tubes and shipping. It sounds fantastic, and was well worth the cost, in my opinion. Though, I haven’t heard the others on your shortlist to compare. I have it paired with a VS115, into Proac D48’s. 
 

You may want to check timing with ARC on service before going that route, they were/are quite backed up last I’d heard. Mine took about five months total. 

@blisshifi 

“@curiousjim Great call on the BHK. It is a hybrid tube preamp“

I was totally tube or hybrid separates until last year, when I bought my first SS integrated amp.  But before I bought the Hegel, I was looking seriously at the BHK and a few others .  I’ve has ARC forever, in fact I still have a SP9mkll  with some Acoustat Model. X’ and both of them are hybrid.

JD

@curiousjim I’m the same way. I used to have between 15-45 tubes in my system at any given time (the higher end of that number due to Atma-Sphere monoblocks at one point), but now I am fully solid state as well, no more tubes in any components. T+A and Audionet changed the way I perceived solid state, and I have recently since become a dealer for both. 

though I am definitely looking for that full mid-range and "musicality" typically associated with all tube architectures.

Not sure ARC would be my choice for this type of sound.  You’ve got other better recommendations for that above, and I’ll add VAC.  Best of luck. 

I owned a BHK preamp for four years and as the OP's amp is SE I would disagree that the BHK is a good choice.  The BHK is best matched with a fully balanced amp unless the increased clicking noise from the "unique" volume control with a SE amp doesn't bother you.  As I tried it with five different SE amps the problem is not with the connected amps.  Also very fussy about needing almost perfectly triode balanced tube sections.  The LS-100 from Modwright which I owned before the BHK is a better choice in my opinion for the OP's amp.

SP10 is a classic.  I have had one for 40 years. It has given great pleasure.  It was state of the art when introduced.  Although very accurate and detailed, it is a but soft for some relative to today's high-end amps. You could call it a 'classic' sound and it is very good it that is your bag.  SP10 is all valve.  SP11 is hybrid.  On introduction, many reviewers mourned the demise of the SP10 as the transistors did change the sound.

Yes, capacitors and valves have been replaced in my SP10, but it is not my main pre-amp now;   I have a Ref 6.  Removing the rose coloured specs, Ref 6 is clearly a much better pre-amp than SP10.  But when I listen to the SP10 in my second system (all iconic old pieces) there is unmistakenly a warm pride of ownership and reminiscence.

So there you go OP.  Unless you are a fan of an older warmer sound or, like me, are a bit of an anachrophile, go for the modern amp.

Best performance with that PX25 is going to have very little gain due to the high sensitivity of that amp.  The Art Audio Conductor or Conductor Simply MKii has an active tube stage with no gain (changes impedance) for optimal performance.  Whatever you choose, do your best to keep the gain in the preamp low.  Avoid CJ, KR, etc... 

0bigkidz did a upgrade and rebuild on my Counterpoint SA-2000 using top end parts. I really liked the stock unit, but he took it to an entirely new level in all areas!

With the input sensitivity and gain of the Art amp, why do you think you need something with so much gain? You are only throwing it away.

Edit, I just saw @verdantaudio addressed this issue already.

I've been very interested in the AR preamps as well.

I'm curious, what parts in the older reference models are of concern as far as potentially not  being available?

OP,

generally, what volume level is your ARC preamp set at for normal listening?

What about the amp's GAIN? OP's Speakers sensitivity are 94 db/w/m

found this pecking about:

https://www.audiocircle.com/index.php?topic=176890.0

"It might be useful in the specifications section to inform the buyer of what the overall gain of the amplifier is since you are stating that it has too much gain for your 108dB horn system.

The specs state a power output of 6 watts. I am going to assume that this is RMS and also that it is at an impedance of 8 ohms. The specs also state a 400mV input sensitivity. I am going to assume that this input sensitivity is what is needed to pump out 6 watts RMS (clipping).

So let's do the math.

Using P=V (squared)/R; where P is wattage and R is impedance. V then works out to 6.93 Vrms.

If the maximum output power is 6.93 Vrms and to reach that maximum power you need to input 400mV rms (or 0.4V rms), then gain is calculated by:

gain = 20 *dB log (X) where log X is equal to log (6.92/0.4) or 1.24.

gain = 20*1.24 = 24 to 25 dB.

So gain works out to be 25 dB, which indeed might be too much for a 108dB horn system (power being a separate issue of course). I would aim for 12 to 16dB of overall gain in a system that is that sensitive.  This is of course relative to what your source (dac, vinyl, others) is producing and if you have a preamp in the system as well. It requires a careful balance.

Pretty amps though! GLWS!

Best,
Anand."

.........................................................

I've visited OP's home, heard his wonderful system.

One of the issues with the ARC SP16L Preamp is each 'step' in the volume is too much of a jump, not smooth like normal remote volumes. We thought it was inherent to that model, a motivation to change. Are the steps 'heightened' by the amp's gain? Avoid any 'stepped' volume control in an alternate unit?

Anyone have experience with this one?: https://www.decware.com/newsite/ZTPRE.html

I am of the mind that if a system is passive friendly, and I think that the OPs, like mine is, then a very good passive linestage is hard to beat. I have plenty of gain from both digital and analog sources. I understand that an analog front end can be challenging, but with my SS Carmen II (2.2 mV) into an SPL Phonos using the 50db of MM gain, I have plenty of volume.

I know some think only active preamps can give the body and slam to the music they prefer. But I contend that in the right system, this is not so. I suggest anyone interested in a good passive give Hattor Audio a look.

http://www.hattor.com/dualmono_preamp_the_big.html

I’ve had an ARC SP6B since 1981, and most of the repairs needed on it were for cold or cracked solder joints. Nothing serious. I imagine the same would be true for an SP10 or 11. But my preamp has needed repairs once every 5 years or so since 2000.

This is the first time I am thinking about the gain from the preamp. So e.g. I see the Ref 6SE as having 6DB gain from its single-ended outputs vs 75db for the SP-11. @verdantaudio @ozzy62 is that more in line with what I should be looking for?

Specs for the PX25 are:

Power Output: 6 wpc
THD: less than 1%
S/N Ratio: >85 dB
Output Impedance taps: 4 and 8 Ohm
Input Sensitivity : 400mV
Input Impedance: 180 kOhm
Frequency Response: 10 Hz to 20 kHz +/- 0.5 dB

What am I trying to match in a pre-amp?

Lower the better. 6dB is good.  You aren’t going to find many preamps in the market that are going to be active and have lower gain.  

My take is that you need zero gain, and will be the better for it. YMMV...

There is no way SP-11 main preamp stage has 75dB of gain.  Not sure what its main preamp stage has.  I don't have a PX25 here but have a diavolo which is a very similar amp.  Just 300B instead of PX25.  

I have tried it with a myriad of preamps and it sounds best with no gain but is fine so long as gain levels are in single digits.  You are okay with 6dB.  0dB is better but the matching preamp is uncommon used and new is $8500.  I think above where you are looking in the used market. 

I have one arriving later this week or early next week and am in central jersey if you want to arrange a demo.  

Seems to me you're a pretty experienced audiophile and already have a pretty solid sense of direction. You might just want to go with the options you're already considering.

I think you've got some good recommendations. And I'll add another, below. One thing I think you should consider is whether the equipment you buy is hard wired or employs the use of circuit boards. For myself I prefer point-to-point wiring and tend towards small, boutique or semi-boutique specialists. 

Consider that probably much of the advice you'll receive (including that which I am about to give you) will be heavily biased in favor of the equipment that the person giving you the advice owns. Let's not "call anybody out" for this, like there is an intention to deceive. I think it's reasonable to simply recognize it. In a way, it should provide some confidence that those who are chiming in here at least have some familiarity with the equipment they're talking about. Consider, though, that probably nobody has been able to compare all the options being discussed. And even if they had, their listening preferences might not be the same as yours. And, of course, the context of your system is what really matters.

Having said all that, I recommend a Supratek. If you do a search for "all time most popular threads" you'll find the "preamp deal of the century" thread, which is now approaching maturity, as it is almost 20 years old. One of the things that attracted me to Supratek was the fact that many who posted on that thread had previously owned many of the well-respected brands we are talking about and felt that Supratek was sonically an improvement over what they owned before.

But whatever you go with I expect you're in for a fun change.

First of all, I misread the SP-11 gain. looks like 29db if I am reading this right: https://www.arcdb.ws/model/SP11.

@markusthenaimnut thanks for the comment re "experienced audiophile" but I am afraid you are mistaken. Perhaps "old audiophile"... that said I am attracted to P2P vs printed boards. Instinctively I think the former is better. My Icon Audio phono stage also fits that them. With ARC, i must admit that I appreciate the polished presentation, the copious documentation and the ready resale market.  That said I will be taking a detailed look at Supratek. @verdantaudio, is the matching pre-amp for the PX-25 the Conductor Simply? I think I saw it had no remote and stopped looking, but I will take a deeper dive.

Conductor Simply 2 and it comes with a remote.  I don’t offer the non-remote version as no one really wants it.  Mine is literally in-transit from UK.  

With ARC, i must admit that I appreciate the polished presentation, the copious documentation and the ready resale market.

Yeah, but does it offer the sound qualities you’re looking for?  You already have an ARC pre and yet are searching for a fuller midrange and more musicality, so you’re going to replace your ARC with, uh, another ARC???  For these reasons I recommended VAC above and many others have also recommended preamps that will bring you in the direction you’re looking to go.  Or just keep doing the same thing and hope for a different result — know what that is?

Having just gone through the "preamp shuffle," Get an ARC REF6. They can be had on the used market of about $7K and it is a fabulous pre, IMHO, a significant step better than the new LS28SE, both of which I had in my system. In fact, I thought that the LS28SE was just barely better than going direct from my MSB DAC to my Pass Labs 250.8 amp. I also experimented with a VAC Renaissance Mk V, primarily because it had a built in phon stage, and the VAC was also good, and slightly better than going DAC direct, but not in the same league as the ARC REF6, again, in my system. Owners of the Allnic 7000 rave about those as well, and you can get one for around the price of the ARC REF6. I have no experience with that pre but talking to owners, and someone from The Music Room who had listened to one, that was on my short list, but resale on them is very slow if I ever wanted to sell AND there is no volume display. For me, I like a visual volume display too, so I am very pleased with my REF6 over everything else.  Note that I replaced the stock ARC PC which has a 20 amp termination, with a Shunyata Research Alpha NR V1 PC and the difference was so startling that I went all Shunyata!

@soix a lot of logic in that post! Not sure I can afford VAC... But they look awesome. 

Just purchased a PATHOS SYNAPSE Preamp. Now Kevin Deal and I have something else in common!!! ;)

It proved to be the biggest upgrade I have ever experienced...and after much thought conclude that the fact it is a Dual Mono design has to be a major contributing factor.

I know this...never has it ever occurred to me to ask: "Hmmm...I’m not getting the BASS I think I should be...I wonder if it is the Preamp???" Well...guess what...IT IS THE PREAMP!!!

The LS28 was transformed by changing the tubes to 6N6 (also known as 6H6).  I compared my friends system (YG Sonja 2.3s) with my pre-amp (custom) and they sounded 90% similar with the new tubes.  With the 6H30s, yuk!   After hearing the slightly modified LS28 (tubes), and having extensively heard the SP10 and 11s over the years, I would choose the LS28.  The SP10 is very big sounding, lovely, but so many tubes and not as clean sounding line stage as an LS28.   The SP11 is different sounding and I missed the big open sound of the SP10 when I heard it although it is very clean (I owned an SP14 back 40 years ago-nice preamp).  

Check this out.

https://www.zestoaudio.com/leto-ultra-ii-preamplifier/

I have a Zesto Allesso SUT.  I was using it with a Benz Ruby 3 until it wore out.  Now, I am very happy with a Dynavector 20X2 L dialed in perfectly with the SUT.   Zesto has an interesting presence feature.  I would note that their BIA 200 amp is a dead ringer for the EAR 890 amp.  

A couple of observations/suggestions based on my experience with older ARC gear. ARC can rebuild every piece of equipment they have manufactured, EVER! That is unparalleled product support. I have owned 2 ARC preamps, SP9 mk2 and LS-25 mk2. The SP-9 mk 2 has an integrated phono stage, whereas the LS 25 mk2 is used with an all-tube ARC Reference Phono. The Reference Phono has 14 tubes, 11-6922s in the gain stage and 3 tubes in the all-tube power supply. The resulting combination has the best of both worlds IMO. The "newer" ARC hybrid line stages are much more neutral than the older all tube models with better extension at the frequency extremes. With the all tube Ref Phono, you can "roll tubes" to get a warmer, more full sound, or use the Sovtek tubes to get a slightly leaner, but more "accurate" sound. I recommend trying out some 6922 JJ tubes if you haven’t already in the LS-16, and I while prefer them to Sovtek in the Reference Phono, your mileage may vary. I have found that they excel in the areas you find lacking in your current setup. Tube Depot or The Tube Store have them in stock routinely and will match them for gain and low noise, which I highly recommend for preamp use. Best of luck with your endeavor.

Question:

IF wanting to bi-amp those speakers,

https://www.blumenhofer-acoustics.com/Products/SerieGenuin/GenuinFS2-2/GenuinFS2-2.php

use the 6 wpc PX25 tubes for the upper driver, and something stronger for the bass driver:

IF preamp want's little or no gain for the PX25, how does that low gain leave you for the amp(s) driving the bass?