Pure Audio Project upgrades and tweaks

Starting this thread to discuss Pure Audio Project open baffle speakers, upgrades and tweaks. @Kingrex - if you have had both the horns and Coax10, I would be interested in hearing how they compare. And I copied your earlier post below.

What cables upgrades did you use? And can you share a picture of where you located the crossover? Is it attached to something else, or sitting on the floor? I was wondering about the height of the midrange/tweeter and if I should rake the front up. My system will be the Trio15 Coax10, Playback Designs MPS-8 source and Pass Int-25 amp. I'm still waiting for my walnut baffles to ship from RJ Millworkers.

You have to get the updated speaker cables. Its critical.

And , you have to separate the crossover from the frame. Again critical.

If the crossover is touching the frame, the music is very smeared from the intense physical vibration.

If you use stock, instead of upgraded cables, you loose life, air and bass. Less coherent.

The speaker is very good with these tweeks. You don't need to futz with any caps or reaistors with the Coax crossover.

You need to be patient. They take 500 hours like any speaker to break in. 2000 or a year to really be there. I actually put my coax in the basement connected to a class D amp and laptop for week and let it rip sitting on the floor. I would go dowm 3 or 4 times a day to switxh the album and volume.

Also, mine sit on a 9 inch tall very heavy block of wood that sits on fiberglass insulation. A rug would also work. Massive improvement in bass. Just shocking. And, it raises the center of the coax much closer to ear height. Otherwise its too low and like sitting in a balcony.

The fabric over the top keeps the sun from striking the driver. That is all its for.

 

Interesting, thank you. How do you know the precise layout of the crossover without de-engineering it?

I was advised the 82uF is draining the bass out of band to earth, and affects the sound of the mid driver as well which has no limit to its lower bass.

Thank you for the recommendation of the coil, which is rated at 0.39 ohms. I am nervous changing that spec as it may affect the design of the crossover too much? That may affect tubes amps negatively, more than an SS amp, i.e. expecting the amp to control the drivers more (damping factor?).

Your thoughts?

Well, I know your speakers i have something similar here, but it's completely DIY.
Yes, a tube amplifier reacts more to changing the bass coil because the ratio of amplifier output impedance to speaker impedance is lower than with a transistor amp.
With a tube amplifier, it always helps to keep the resistance between the amp and speaker low in the bass range, e.g. cable cross-section and coil in the xover.
The only negative thing that can happen is that the bass sounds too thin.
But it's usually just an adjustment period when listening.
The advantages of dynamics and precision outweigh the disadvantages very quickly.
I use my bass active, the advantage is unmistakable, and I would never switch back to passive in my open baffle.

 

Interesting. But without seeing the actual PCB, or a schematic, you can't know how the circuit is configured. The crossover is a custom 4th order, so quite complex. I prefer to stay on the stock values to avoid sonic degradation. I also not keen to risk bass sounding thin.

Your DIY OBs look nice. Where is the mid/ treble drivers? Or are they full range drivers? If yes, your crossover will be really simple (ideal).

Crossovers IMO can be the most complex part of a speaker, and without lengthy testing and measurements it is possible to really screw up the sonic performance.

 

Interesting. But without seeing the actual PCB, or a schematic, you can't know how the circuit is configured. The crossover is a custom 4th order, so quite complex. I prefer to stay on the stock values to avoid sonic degradation. I also not keen to risk bass sounding thin.

Your DIY OBs look nice. Where is the mid/ treble drivers? Or are they full range drivers? If yes, your crossover will be really simple (ideal).

Crossovers IMO can be the most complex part of a speaker, and without lengthy testing and measurements it is possible to really screw up the sonic performance.

It's ok your decison have fun with your speaker.
My openbaffle is 15"coax only xover for compression driver fullrange with a tube amp.
the 15" woofer underneath is driven actively by a studio amp with internal xover to realize 30hz in my room.
P.S
Your bass xover 12db scroll the homepage to the part xover trust me 12mH+ 82uf the rest for mid+high 24db

 

Ok so you were guessing. Understood.
The problem with DIY and tweaking ourselves is the rewards can be great, but mistakes can end up being costly in parts that don't work as expected in the circuit we are using. I know the Coax crossover that PAP uses took many hours of testing, and was the hardest one they have done so far to realise. We just don't have the resources to do that.

So in your case, I suspect your crossover is quite simple, and easier to achieve, having only the comp drivers in the Coax to control, roll off the driver, and bring in the CD at maybe 3-4K?

 

Well, I know your speakers i have something similar here, but it's completely DIY.
Yes, a tube amplifier reacts more to changing the bass coil because the ratio of amplifier output impedance to speaker impedance is lower than with a transistor amp.
With a tube amplifier, it always helps to keep the resistance between the amp and speaker low in the bass range, e.g. cable cross-section and coil in the xover.
The only negative thing that can happen is that the bass sounds too thin.
But it's usually just an adjustment period when listening.
The advantages of dynamics and precision outweigh the disadvantages very quickly.
I use my bass active, the advantage is unmistakable, and I would never switch back to passive in my open baffle.View attachment 137129

What do you use for a bass amp? and crossover? Did you start with active DSP. Then get a active analog unit? That is what I was considering.

 

What do you use for a bass amp? and crossover? Did you start with active DSP. Then get a active analog unit? That is what I was considering.

No dsp i don't like it.
Yamaha p 3500s amp int xover 12db from 25hz-150hz adjustable.
The yamaha have no high damping factor the bass sounds not dry more full tone i love that cheap thing.
Backside amp

 

It's ok your decison have fun with your speaker.
My openbaffle is 15"coax only xover for compression driver fullrange with a tube amp.
the 15" woofer underneath is driven actively by a studio amp with internal xover to realize 30hz in my room.
P.S
Your bass xover 12db scroll the homepage to the part xover trust me 12mH+ 82uf the rest for mid+high 24db

I think ALL caps and resistors in a passive crossover are in the signal path, and do / will affect the sound. After all, everything in the crossover is the signal from the amp going through it. In an amplifier you have power supplies and other aspects, then a final gain stage, where caps will be in the signal path.

In your bi-amping, the amp you use for the bass needs to be excellent quality, to compete (IMO) with a good power amp driving both bass and mids and highs. But you do have more control over the setting I admit, at least rapid changes. I am tweaking parts and it is a slower process.

I can imagine SS on the bass drivers, and tube on the Coax would be a very nice solution, pending phase shift, time delay and levels matching.

 

Ok so you were guessing. Understood.
The problem with DIY and tweaking ourselves is the rewards can be great, but mistakes can end up being costly in parts that don't work as expected in the circuit we are using. I know the Coax crossover that PAP uses took many hours of testing, and was the hardest one they have done so far to realise. We just don't have the resources to do that.

So in your case, I suspect your crossover is quite simple, and easier to achieve, having only the comp drivers in the Coax to control, roll off the driver, and bring in the CD at maybe 3-4K?

I don't need to guess, I have been building speakers myself for over 20 years, from horns, full-range speakers, 2-3 way loudspeakers and open baffle.
It's OK if you don't trust me.
My speaker is a full dipole, the horn driver is open at the back (lower distortion, flatter frequency response) more 3D sound. The bass drivers are magnetically weakened to achieve a higher QTS value and play deeper in the bass range. Horn driver is 12db at 2.5khz. The active bass run 30- 80hz 12db.

 

Respect for your DIY work. But I defer to this subject:

So IMO all parts can have an effect on the final sound in a crossover.
I would point out a crossover can be (IMO) one the weakest parts in a loudspeaker, based on budget constraints, and the fact it is hidden from view. I respect the brands that show the crossover in their websites (example Sonus Faber). I have over the years always upgraded or tweaked the crossovers in speakers I bought.

 

So IMO a high end system can be a mix of different brands that are then merged together to create what the owner hopes is an ideal solution, not unlike cooking lets say. The ingredients invariably need to be tweaked to play as the owner wants / expected.

Cables and tube rolling are common things to tweak, and recognised as such. Less recognised is the crossover in a speaker. The speaker has been voiced by the designer with other sources and amplifies, in a different room acoustic and to that brands ideal sound signature. So it can be spot on or not in any system I would suggest.

Added to the fact many speakers use low quality parts in a crossover, but not all. Some speakers I owned in the past, circa 20K had shocking low quality caps and inductors, even used cement resistors. Zingali for example. These were easy to upgrade and cost little v the performance gains after the upgrade. I upgraded mine for under 800 euros and the difference was dramatic.

In the Pure Audio Project Quintet15 Coax, the crossovers are very high quality, the best I have seen in speakers I have owned. But little tweaks to the crossover can tilt the sound in a direction that shuts my room acoustic, source and amp combination. Not better quality, rather edit the sound signature.

 

I have fitted the Clarity Cap combo. I used 3 x 27uF cpas to replace the single 82uF cap. I also added a tiny Mundorf Bypass 0.01uF.

Fired up the Quintet15s, and immediately noticed a change. The bass is the same volume, but has more details, less boom. Interestingly the lower mids and lower treble is more detailed and delicate as well. I think the old bass cap was muddying the sound a bit, and masking what the mid and compression driver were doing. The mid driver has no restriction on the low end response, so I think tails off at 80hz approx. So there is overlap with the big 15inch drivers and the 10inch mid driver, probably why I am hearing the mids clearer?




So, so far a nice upgrade. I will let in burn in for 6 weeks, then look to add the Jensen Copper Foil caps on the compression driver, see how they sound. I have Path Audio resistors in 3 places so I can adjust those at the end of the updates, bring the treble down if required.

IMO the exact treble detail / level and timbre, how cold or warm, this is the final piece to the puzzle - and what makes a good system great of average. Tiny adjustments. It is good the PAP has this ability, though the Coax crossover is 4th Order so much more complex and risky to tweak.

 

This looks like great work! Congratulations!

 

So a week in and the sound is getting really nice indeed. The bass is defiantly more defined and has more texture and details. It also sounds much more separated from the mids, and the soundstage has opened up more. It is defiantly a mods I am happy with.

I will fit the Jupiter copper in oil caps to the compression driver circuit in another week, see how that affects the treble. These caps are very like the Duelunds and are smoother and warmer than the Mundorfs. If that happens, and I don't loose any tribe detail, it will be a win.

 

So I fitted the Jupiter copper in oil 2.2uf cap on the Coax circuit (compression driver). Plus 2 Mundorf 0.01 bypass caps and 2 Duelund 0.01uf. So all the caps are now bypassed, inc the woofer. Note I glued the caps down to reduce vibrations, as you often see in a sub crossover/amp.

I will report back how it sounds.

 

I'm very glad this is working out for you so far, Julian! Great work!

Upgrading parts on components we buy seems like a very smart way to improve sound quality at comparatively modest cost. You are smart about it, because you don't just assume they will sound better; you wait for the components to prove to you that they sound better.

 

I'm very glad this is working out for you so far, Julian! Great work!

Upgrading parts on components we buy seems like a very smart way to improve sound quality at comparatively modest cost. You are smart about it, because you don't just assume they will sound better; you wait for the components to prove to you that they sound better.

Thank you Ron. I am trying to build a good system on very tight budgets, hence the DIY subjects.

 

I'm confused why your house is 12mH. I thought they were 6.6mH.

I wish you would have gone step by step with the cap change and bypass cap adds. You have no idea where the issue resides if its not right.

 

Hi Rex
On the Quintet15s Coax, the inductor is 12mH as stock, I haven't touched that.

On the caps, I fitted the bypass 2 weeks ago. The big Jupiter is this stage now, so I am testing as I go.

One thing I am not so happy about, is the odd resistor seems to work loose, mainly the Mundoft M Resist ones which poke upright. I may look at soldering them at some point.

 

A lot of music comes comes from the coax. Did you do anyrhing to do that. I would like to hear the Jupiter Copper Foil on the Coax.

 

The Jupiter is on the Coax comp driver. I got a tip off from a member on here to use that in that position. He has the Coax as well.

I am thinking it may smooth the compression driver a bit, hopefully not effect the treble volume level. We shall see. If required, I could adjust a resistor on the board to bring it up a bit if required.

Rex, I found the angle of toe in massively affects the bass output? I guess you already know that. I am taking tiny amounts of angle changes. I set mine to get the balance just right. About 15°. So no toe in is big bass, but is to much in my setting, and the treble / mids need a bit of toe in tio max out the imaging.