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Audio Blast: PureAudioProject PAP-C1 Custom Active Analog Crossover

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Hold off on the preamp for a moment

I tend to be a perfectionist sonically and I usually cannot walk away from a system indefinitely if it has not been optimized to my satisfaction. I had made great progress and now had a better DAC in the system, but there were still idiosyncrasies that needed to be cleaned up, primarily the still insufficient bass output. I had not put in an all-out effort at finding the perfect setting for the horn’s output relative to the bass, so I made that my focus of an evening’s work.

I wasn’t quite ready to relinquish the DAC to amp setup, suspecting that I had not followed through with enough attempts at fine tuning the High Pass Level adjustments. The output of the horn relative to the bass drivers is the foundational and pervasively influential setting. It had to be optimized before I could tune the speaker further. Also, there was more work that could be done with the Notch filter (for “high-mid shaving”) as described on the website. Basically, this adjustment lets you move the filter for the high pass lower or higher on the frequency spectrum. It is a valuable tool to tune the interface of the bass drivers and horn driver to one’s taste.

I spent a couple hours rifling through demo tracks and revisiting continually the L-R-C test track to get the balance, center image and tonality as perfect as possible. It is surprising how informative spoken voice is to assess each channel’s tonality! It was obvious when one was warmer than the other. I made perhaps 15 separate adjustments to the PAP-C1 in the span of two hours. I do not wait for burn in, “settling,” or any other nebulous, longer-term mystical improvements. I make changes happen until I’m satisfied.

The turns with the small screwdriver on the tiny white vinyl set screws of the High Pass Level adjustments were painstakingly small. I had to use so little pressure on the screwdriver to turn it that several times I wondered if I had actually moved it, and at other times went back to the listening seat only to hear that it had moved far enough that the output was either far too high or far too low. I suspect I did approximately 15 attempts to get the ideal relationship between the horn output and bass driver output.

This is tedious and not so much fun. It is, however, instructive as to hearing how little it takes to throw off a perfect symmetry, and how the output of the horn can dramatically cause a very powerful shift in the speaker’s sound.

The infinite controls for continuous bass output per channel were critically important, as it was fiendishly difficult with such miniscule movements of the adjustment to precisely match the two channels. By judicious and slow adjustment of each channel’s bass output the two channels could be made to match. I had gone too far when the bass output was overshadowing the horn. Consequently, whereas previously I had the front panel bass output dials at 3 o’clock, I turned them down to about 12 o’clock. There was an ever so slight difference in the setting of the dials between the Left and Right channels, which did not concern me; the center image to my ears was dead on.

I have come to accept that in complex systems a slight variance in one channel is not an ordeal. The settings of the 5 open’s crossover’s full range attenuator also needed to slightly diverge. I suspect the primary reason for this is that the outer walls (exterior of the home) of the listening room were built with 2×4 construction, while the inner walls, even though built with 2×6 construction, seem to get less bass reinforcement. When the adjusting was over, the Trio15 Horn1 played voluminously, its low end surprisingly close to the Kingsound King III electrostatic speakers. The midrange and treble were capturing the beauty of a small tower with a premium midrange driver, such as the Van L Speakerworks Silhouette (reviewed). But the bass was still not as prodigious as I had experienced with the Tri-Art 5 open, and I was not going to accept it.


Insertion of a dedicated preamp

One continuing aspect of difficulty in playback related not to the crossover itself but to the system setup. There were some pieces of music that were recorded at low enough levels that the gain from either the Eastern Electric or the Exogal DAC was not enough to bring playback to a sufficiently high levels. For example, choral pieces by John Rutter or Al Jarreau’s “After All” won’t fare as well with the DAC direct method of system setup.

Also, typically in the past, insertion of a preamp has also benefitted the system in terms of headroom, impact, and immediacy. I had actually put the preamp into the mix in my very first system setup, when the sound was so skewed, before balance between the drivers was achieved. Initially I thought that the preamp was not driving both of the amps well, but upon removal of the preamp I discovered that the issue, ultimately resolved as discussed above, was due to the crossover settings. Now I was eager to revisit the original setup with the preamp! I expected an even more lively presentation.

Here comes the unusual, value added proposition of this review, dependent upon an unusual, but affordable component, the Tri-Art Series B preamplifier and tube buffer power supply. I had worked with this preamp quite a bit in the preceding several weeks to the point that I felt comfortable with the plentitude of adjustments on it and the power supply. The preamp itself has a built-in gain setting switch with 5 settings and the tube power supply sports another switch with 3 additional settings. Recall also that I already had in the rig the Tri-Art Series B amplifier (class D) with its own matched tube buffer power supply —yes, add another set of 3 gain settings! The permutations of the settings run into the dozens.

An unpredictably powerful ballet of “gain” ensues when one makes adjustments to all of these switches. It reminds me of the past days of receivers with powerful listening modes, such as “Hall” or “Concert,” when an EQ curve was applied. Now, this is a passive preamplifier, so the term “gain” is a bit misleading. The switch influences the tube in the circuit, but no actual gain is seen. It manipulates the tube output such that the tonality of the system is altered across the board. Further, one can turn On or Off the tube in the power supply, and then the 3-position switch has negligible effect. The preamp Gain control still operates, however.

Make no mistake about it, however; there is a large influence upon output at certain frequencies. One can build up the treble, midrange or bass in a mix of proportions. This was the golden ticket in terms of getting big slam out of the Trio15 Horn1 with the PAP-C1, because the bass output was already maxed, but if I turned down the horn driver further, it would become reticent sounding, bordering on muted. The bass was at the best it would get. I suspect most OB fans would conclude it was adequate and not much more could be done. I refused to accept that; I had heard what the 5 open could do!

Not only did these settings on the Tri-Art components alter the tonality, they also altered the definition. If the treble was recessed it became more diffuse, which some may love, as it mimicked a ribbon driver. If the midrange was recessed, it caused voices to pull in from the listening position. The complexity of the contouring of the sound grew greatly, so I determined to not continue to adjust the PAP-C1 buttofocus on the adjustments of the Tri-Art preamp.

The change that locked everything I wanted to hear hit like a punch press, with huge force. I was looking for subwoofer-like impact, and when it happened it could be easily felt. At the same time, the other parameters aligned; treble floated with the most delicate shimmering aspect, vocals fattened and lost the in-the-throat character, spatially the instrumentation was properly positioned and not stepping over each other, and the bass, oh the bass! It was pounding, with fullness.

There is a very powerful compounding effect of partnering both of these control units, the Tri-Art preamp/power supply and the PAP-C1. I noticed no offensive growth in noise as a result, or else I would not make the recommendation. Secondly, to address the objection of those who think that an active crossover will negate the benefit of any external controls, you are simply wrong. Time after time with the Legacy Audio Helix, Whisper, V, and Valor speaker systems, all of which use active crossovers, not a one was impervious to power cables and other system adjustments. Tube rolling, interconnects and discrete opamps all influenced the active crossovers. It was no surprise, then, that the settings of the Tri-Art preamplifier did the same.

Shockingly, the outcome of tumbling the adjustments seemed magnified by the PAP-C1, in most pleasurable ways! I had been searching for days for the big, bombastic, powerful, ripe bass that the Tri-Art 5 open speaker had, and when I found the magic settings,I was rewarded with not just big bass but with a reworking of the entire speaker.

Am I overstating the case? Is the real result a fraction of what I have described? Can an affordable passive pre with tube power supply even do such things? It certainly can when used with the PAP-C1! I am not overstating the outcome. I do not wish to convey that these two speaker systems are interchangeable, but when I worked with the Legacy Audio Valor with its Wavelet that allowed sweeping changes, for example, I get much the same user control and authority, albeit on a smaller scale, with the combo of the Tri-Art preamp/power supply and PAP-C1.

My apologies to owners of other speakers, because this is exclusive, at least when it comes to use of an active crossover for an Open Baffle speaker. I suspect that those who are motivated could obtain very similar results with any OB design using an active crossover. Passive speakers will not react in such a commanding fashion, but as I will discuss in the Tri-Art review, more satisfying results can be obtained from Tri-Art’s methods than typical passive speakers. Will owners of the Tang Band and Voxativ versions of the Trio15 benefit as well? I don’t see why not. Would it also work with the Quintet? Probably. I think there is a lot of room to roam with this method and setup. Recall that I haven’t even worked into the mix the prodigious Pass Labs amps, and I’m already smitten.

Do you have to buy the Tri-Art preamp and power supply to get this kind of result? As far as I know, yes. Would there conceivably be other great combos? Sure, but unless the component has dozens of configurations available, it won’t have nearly the flexibility to help you get to astounding sound quality. You may get one or two shots at perfection; here, I have many to choose from, and if I ever lose the love, I can find another variant in a day. There are not many more perfect, affordable speaker options than that.

I’m obviously sold on this configuration! I don’t have to pump any product, or overstate anything; I’m building sensational systems and sound with both the Tri-Art pre and the PAP-C1. I have already decided I’m staying with the active crossover on its own merits. Regardless of the review of the 5 open speakers, the tri-art preamp and power supply are a home run addition to the PAP-C1. It is a “must be heard to be believed” product. It is a passive preamp with the capacity to slap a speaker system around, and I don’t know that I have encountered that prior.


So many options, all good!

Variety with quality is exceptionally important to me because with it I always can make an arresting system, one that I loathe taking down to continue with other reviews. Consider that all this was achieved with affordable amps, and the feat becomes even more impressive.

Last night I sat for three hours transfixed as I worked my way through several selections from the Voices Forte series of recordings. If you want a thrill, hear a system that renders both lyrics and vocal effects as clearly produced by the human voice, yet done so cleanly that the sound fascinates and begs the questions, “How is a voice making that sound?” Now, with my latest settings between the PAP-C1 and the Tri-Art preamp/PSU, I’m dialed in, I’m rocking even acapella recordings.

I am going to bring to a conclusion this brief article, because I have achieved my goal, showing that the PAP-C1 active crossover is a powerful upgrade for the PAP-Horn1 Speaker, and together they are a compelling choice for someone who wishes to delve into active crossovers.

I close with a listening experience that moved me to admiration of the capabilities of the Trio15 Horn1/PAP-C1 experience. In recent years I have been using select pieces from soundtracks of movies as demo material. Symphonic scores have become quite interesting now that equipment formerly associated with rock bands is employed, including electric guitar and synthesizers. One of the least urbane but most fitting for assessment of a system is “End Credit Suite” from Holmes and Watson, music by Mark Mothersbaugh. Yes, it’s an atrocity, a mishmash of musical styles and instrumentation, but look past that to focus on the recording itself. The dynamic swings between quiet passages are huge, the particular, deeply recessed solo instrumentation is great for assessment of how deeply a speaker system can recreate a huge acoustic space. The recording is excellent for listening in to the symphony’s string and horn sections. I especially enjoy the attempt by the harpsicord to get aggressive. When least expected a bit of synth pop pops out. It is corny, but the Trio15 Horn1 and PAP-C1 open up the piece gloriously, especially in the closing measures of the piece, at the crescendo of the finale. There is no hint of compression or straining in this system.

Over time I plan on elevating the PAP-C1 and Trio15 Horn1 with even better electronics, but this all takes time. This is supposed to be an Audio Blast article, short and punchy. It’s a tribute to the PAP-C1 (and, yes, the Tri-Art preamp paired with it) that I couldn’t stop writing about it! Already in a few weeks of listening to the PAP-C1 and Trio15 Horn1 it is unquestionably the superior route in terms of performance for this speaker. I presume it would also be superior in use with the Voxativ or Tang Band drivers, but I will refrain from making a declaration as I have not tested them. For those with the inclination to delve into tuning the speaker more heavily, and a thirst for higher performance from PureAudioProject, this crossover is a must.


Copy editor: Dan Rubin


4 Responses to Audio Blast: PureAudioProject PAP-C1 Custom Active Analog Crossover

  1. What a great review. A good active preamp could improve the system still more.

  2. Vladimir,
    God’s Peace,

    Thank you for the complement. No doubt the addition of an active preamp could add another level of excitement to the experience. I will not argue about that. Much would depend upon the selection of amplifier and preamp. One thing I love about the Tri-Art Preamplifier is that it is configurable in terms of the “Gain” switches on the Preamp and the Linear Power Supply used with it. The multiple settings on both allow a wide variety of voices for the system, a compelling feature of the passive Tri-Art Preamplifier that would not typically be found with most active preamps. Something to consider. It is possible that an active preamp could improve the system; one simply has to compare to find out.

    Douglas Schroeder

  3. ric escalante says:

    I recently upgraded my Spatial Audio OB speakers crossovers to some Jupiter caps and can say that it seems that cheaper crossover parts while keeping costs down, don’t reveal what a speaker or system can really do. I’m surprised there aren’t more outboard crossovers (with upgradable price options) available. Sounds like the PAP is a great device for those interested in maximizing sound quality. Of course I use the Schroeder Method to great success and recommend such, thank you!

  4. ric,
    God’s Peace,

    One of the great things about the PAP speakers is the upgrade path, which can be done simply with one screwdriver! I found that changing the resistors and capacitors were both efficacious, as discussed in my previous articles. I am not surprised at all at your success.

    As you speculate, the PAP C-1 is great for those wishing to push the boundaries further than a passive crossover, albeit with more mild effort.

    Thank you for the plug for the Schroeder Method of Interconnect Placement. It’s a wonderful means of elevating an audio system! I use it without exception in my personal systems.

    Douglas Schroeder

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