Audio Blast: PureAudioProject PAP-C1 Custom Active Analog Crossover

Setup and listening

I did two variants of the following system, one without a dedicated preamp and the other with preamp inserted. A couple thoughts about the following system. I am bereft of a multi-channel amp at the moment, so I am having to pair stereo amps for this review. That is not a problem with the PAP-C1, and in fact use of different amps, even of different genres, such as a solid-state amp and a tube amp, are welcomed. Because an active crossover allows level controls for each amp, the expected different output of unmatched amps is no trouble. In my system, using quite different amps demonstrate the potential for exciting results.

I used the Small Green Computer I7 with SGC Linear Power Supply; SONORE Signature Rendu SE with systemOptique; Clarity Cable Supernatural USB 1M; Eastern Electric Minimax Tube DAC Supreme; Clarity Cable Organic RCA; PAP-C1 Active Analog Crossover; Schroeder Method Audio Sensibility RCA interconnects (2 pair); Kinki Studio EX-M1+ Integrated Amplifier – in HT Input mode (amplifier use only); Tri-Art audio Series B amplifier with tube buffer power supply; Clarity Cable Organic Speaker Cables (2 pair); PureAudioProject Trio15 Horn1 Speakers with Bi-Amp Distribution Boards (pass through, unpopulated crossover boards). NOTE: In this setup I was using the Roon software’s volume control. Never set up an unattenuated source direct to amplifier.

At the moment I also have the Pass Labs XA200.8 Monoblock Amplifiers, but I’ll refrain from discussing them here because I intend on giving encouragement to more budget-oriented audiophiles. As that review is also underway, I can state confidently that those monos would elevate the results I share, and while discussing them would add color, it would be a moot point to talk about amps that cost seven times the speaker’s value. At some point, if I can grab the time, I will press them into service with these speakers and crossover, but already the performance attained with the system described above was at such a level that I am confident in the conclusions about the speaker and the recommendations I will make.

Pure audio mess

I had not analyzed the images on the PureAudioProject website closely enough prior to the arrival of the perfectly shipped, just-about-half-chassis-sizedPAP-C1 crossover. It is disarmingly simple, with classic Pass Labs inspired understatement, involving a single blue LED and twin Bass output knobs on its face. The PAP C-1 repurposes the First Watt B5 active crossover, notable among open baffle fans in the DIY community. I have a saying, “Don’t jump to contusions!” I did by presuming that the B5 had been simply rebadged for PureAudioProject. My second mistake was to not open up the unit to look at the circuit layout. I don’t typically rip the cover off components as quickly as possible; most of the time I see no need to open them up, as images are usually readily available.

As there was no Owner’s Manual, I retrieved and printed the one for the B5. In my presumption I studied the First Watt B5’s Manual and struggled to see how the circuit design would integrate with the Trio15 Horn1. No wonder I struggled, as the PAP-C1 is fundamentally different than the B5, eschewing several of the dip switch controls that are in the B5! I had mounting fear that this was going to be a serious issue if I didn’t understand the interface, especially since the B5 Manual proclaimed that more than 1,000 possible settings were available! It’s tough to review a product if you don’t understand how it works.

To further induce fear, when I hooked the PAP-C1 up, it didn’t yield beautiful sound, but in fact produced something normally associated with a broken speaker. I had the system set up correctly, yet there was no bass. I’m not talking minimal or weak bass, but no bass. The speakers sounded like oversized hand-held transistor radios. I thought, “This is not good!” I reached out to Ze’ev Schlik, Thomas Sulentic and Nelson Pass with a “Help me” email. Ze’ev responded with a casual, “No problem” attitude —and he was correct. The settings were way off, I surmise due the unit being used previously with a different, far less efficient primary driver. I needed to use a tiny, flat screwdriver to adjust the controls inside the unit. I learned that in adopting the B5 for the Trio15 Horn1 some functionality of the B5 had been jettisoned. My task would not involve studying a manual, but deciphering an image of the PAP-C1’s internals and some graphs posted on the PureAudioProject website. Some close-up images of the internal adjustable controls sent by Ze’ev also inspired confidence that the adjustments would be well within reach of my abilities.

Looking at those images allowed me to calibrate the unit, which did nothing to resolve the issue. Thankfully, having enough background to know that a High Pass Level control would dictate the volume of the horn, I played music and began to dial the diminutive control down (controls in this unit are in pairs, in mirror image for L/R operation), so as to lower the output of the horn. I surmised that the horn was so efficient relative to the bass drivers, and had its output set so high, that at the level the bass was set, it was missing in action. As I did so some warmth from lower frequencies emerged and I continued to bring the control down—perhaps 90% from the starting point—to get balance between the bass drivers and the horn. Was it a Heil driver being used previously? Wow, what a disparity between the initial Level output setting of the horn and what I needed! This is instructive for anyone who is unnerved upon hearing the unit not sounding right at all initially, and reassuring that with proper adjustments the speaker’s expected performance can be resurrected. As I said previously, the controls allow monumental changes, so the spectrum of performance based simply on the user-adjustable settings in the PAP-C1 can range from improperly set up “it sounds broken,” to properly set up “it sounds glorious!” Trust me, it does get glorious.

Stunning soundstage, glorious openness, golden warmth

Panel fans will hate this next assessment. The PureAudioProject Trio 15 Horn1 with the PAP-C1 can be more revelatory in terms of expansiveness of the soundstage than even big panel speakers. Frankly, I would not have believed this if I were not experiencing it here. I did not anticipate that the active crossover would explode the scale and deepen the sound field so expansively.

In addition, the degree to which one can alter tonal warmth is exciting; with the passive crossovers, achieving a strong midrange bloom was more difficult and limited. But now, with the PAP-C1, a reorganization has occurred such that the horn is much warmer sounding, with suppleness that was lacking previously. The former was not displeasing, but now it is eminently pleasing.

The performance of the Trio15 is overhauled by the presence of the PAP-C1 to a degree that one feels they are not listening to the same speaker as with the passive crossovers. The horn especially benefits from this change and becomes a masterpiece of the design. Ze’ev had told me when I wrote my first review that the anonymous designer of the horn knew his stuff and the horn used in the Trio15 was special. Now, I think, “OHMYGOODNESS! This is an insanely good driver!” Can a change from passive to active crossover do that for the speaker? Don’t you doubt it!

Hitting the setting adjustments hard       

It took me a couple hours to go from initial disaster state of complete imbalance of the crossover to a state of pleasure. I had to make perhaps 15 running adjustments (the PAP-C1 allows real time adjustments while music is playing, a big advantage in tuning) to the crossover; initial adjustments were huge, and quickly became minute with the acquisition of my baseline.

One gripe about the PAP-C1 is that it uses a “good enough” power supply with a horrific wire. I entreat the powers that be to get a serious regulated power supply and power cord on this unit! It irritates me to see a pissy power supply, and I am reminded of the substantial gains experienced when I removed the stock power supply for the Kingsound King electrostatic speakers and replaced them with the Kevin Hayes-designed Royal Power Supply. I still use the Royal Power Supply with my King III speakers, and the ability to swap out power cords for them is foundational to good results. So much more could be gained from this unit if the power supply and cabling were improved.(Note to PureAudioProject; I certainly want a replacement, and opportunity for follow up, should you heed my advice.)

I add, dear reader, please do not write me nasty things about the fact that I am chastising Nelson Pass for this power supply. I know Nelson as an acquaintance enough that this will not cause a rift, nor ruin his or my reputation. Frankly, if the power wire was not captured at the back of the unit, I would have already on my own initiative secured an upgrade PSU for the PAP-C1 and would discuss it here. If you wish to excoriate me, I will likely ignore you.

Does the power supply caveat negate the accolades for this crossover? Not in the least! I would be a fool to stop using the PAP-C1 simply because it has potential to be improved in the power delivery area. Guessing that a model with IEC input and superior power supply would become available at a reasonable price, I would not have a nanosecond’s hesitation to acquire it.

To establish my progress while tuning the crossover I took a close-up picture of the board with my current settings, then I experimented. I shifted the crossover point at which the drivers mesh to see if there was an even better result to be found. As far as long term use is concerned, I was just getting rolling with this device, and I suspected there was more improvement to be had. But, already, on the first day of use, it was resoundingly confirmed as a superior method of setting up the Trio15 speaker system.

Another potential source of consternation for objectivist readers is that I did not spend time in tuning with a microphone and suite of measurement software. The tuning was done by ear. Feel free to condemn me for my atrocious lack of “measurementalism,” but I adjure that you do not have to tune this crossover with software. It would make sense, then, that if you spend time tuning it by ear, you will enjoy the sound.

When Bill Dudleston brought the first huge speaker I reviewed, the Legacy Audio Helix, he spent a lot of time with a real time analyzer to tune the speakers. He taught me how to go into the software settings and adjust the drivers to suit. I did so, and the end result was significantly different than his settings. Is it any wonder I preferred my settings? That’s how it goes with the PAP-C1; if you want to measure the shit out of it, feel free. But it is not necessary. If you must, do your “perfect” adjustments, then struggle with the realization that you prefer some variance. So much for “perfect.”

As I began to focus on the desired balance of bass and horn output, there were glimmerings of the strong bass that the tri-art Series B 5 open speaker can generate with a twist of its attenuator. The potential to rework the low end completely, as well as the high end, gives owners of the Trio15 Horn1 far more flexibility in personalization. But I was still not hearing the overwhelming LF that the 5 open has. I concluded the solution was to ever so gently adjust the High Pass Level control downward again. I do mean ever-so-gently, as too aggressive a movement turns off the driver entirely! It is conceivable that the owner may need to adjust and counter-adjust the Left and Right Level controls for the primary driver (such as the Horn, Voxativ or Tang Band drivers) 10-20 times to find the perfect setting. It will be worth it, as the speaker will be even more pleasing. With an adjustable active crossover such as this, a solution is waiting. One of my friends in the industry has literally been tuning his speaker system for years. That is his thing; he always intones, “I have a bit more adjusting to do…” He and I make an interesting pair, because when I review I am ripping out and replacing components and speakers continuously, so I tune by ear. As his setup is much more stable, and he makes a living off of the minutia of performance parameters, he is always watching the numbers. I do not want the futzing to never end, but I need certainty beyond a day or two of fiddling that I am getting the most out of the setup.

If I were the impatient type, if the bass was too light, I would just plop the Legacy Audio XTREME XD Subwoofers down beside the Trio15 Horn1. I have done so in the past with speakers having passive crossovers to bolster a perceived insipid low end, and most assuredly will do so again.Regardless of how much bass output I get from this setup, at some point I will try the subs with it because it is fun to see just how much bass a system can create. It’s a matter of doing so because I can! Perhaps a guide to bass output would be helpful in terms of assessing this setup. If you go nuts over HT-level bass, then you would want to integrate subs with the Trio15 and PAP-C1. However, if you feel that such things are overkill, then you likely will be happy without them.

“One hand behind the back”

All experienced DIYers and system builders will be haranguing at this point, “Well, of course you can’t get sufficient bass! You aren’t using a preamplifier!” The first setup was using the Eastern Electric Minimax Tube DAC Supreme’s output directly into the PAP-C1, and from there to the amplifier only of the Kinki Studio EX-M1+ (reviewed) to drive the bass, and the Tri-Art Series B preamplifier with tube buffer to drive the horn.

After a run with that setup I converted it to one that from past experience I expected would be superior; I changed out the DAC for the Exogal Comet with PLUS Power Supply. As has been the case consistently, the Comet brings more refinement, suppleness, impact and richness over the Minimax. In that I was not disappointed; vocals were even warmer, fuller, and an increase in refinement was evidenced.

In not yet using a dedicated preamp I suspected that the system was still wrangling with the signal with one arm behind its back. Adding a preamp would be transformative once again. Then I would be subjected to the full glory of the PAP-C1, just as Moses was immersed in the glory of the Lord on Mt. Sinai. I could sense the awe gathering!