604 crossovers - polypropylene vs PIO

[rogerh113]

Hello,

Starting to look for parts for my crossover build, and have run into some interesting endorsements of Russian PIO caps. Has anyone specific experience with the PIO caps in a crossover? It would be great if you had an opportunity to compare with polypropylene (before or after the PIOs). I do realize that much of this is personal taste, but I would be interested in personal opinion (if it is based on first hand experience).

regards -- Roger

[Altec Best]

What model 604 do you have ?

[GM]

Greets!

Quite a bit since they were the reference standard until PCBs were outlawed. The only audio comparisons I've done were with whole XOs [and even then not completely identical otherwise] and in simple 1st order XOs of horns, 'full-range' [FR] single drivers. Also, these were physically large capacitors like motor runs, both with PCBs and the later mineral and a few synthetic oils.

Other than the cheap caps Altec and others were forced to downgrade to and whatever popular caps the cone/dome 'monkey coffin' folks tout as 'best' or at least best 'bang/buck', I can't say for certain if I've ever auditioned good sounding PPs or not, only some claimed 'excellent' mylars.

Even though some either dismiss it out of hand or at least downplay it, PIO isn't just a personal preference [mine], but technically superior and why the pioneers spec'd/modified them even though with their basically 'cost no object' budget for developing a high performance sound system for 'talkie' movies that allowed them to make whatever they wanted: http://diyaudioprojects.com/mirror/members.aol.com/sbench102/caps.html

All that said, any perceived superiority I've heard is pretty much limited to 'FR' or at least 'wide-range' drivers and horn systems where the superior self damping of PIO can 'shine'. The majority of speakers, especially lower efficiency ones become so distorted even at fairly low power that it 'swamps' any subtle gains in performance made elsewhere in the signal chain.

GM

[rogerh113]

They are 604-8G. I have not even fired them up yet - waiting for some replacement diaphragms from GPA (and associated wire kits). Really looking forward to the project. I currently have 1 (supposedly working) Altec crossover (8G) so I can at least use that to make sure the drivers are functional once the diaphragms arrive. I am usually pretty methodical in selecting components - better to take a bit of time and do the research, rather than being disappointed after the fact....

regards -- Roger

[SD-50]

I replaced all the caps in A7s with PIO main caps, bypass with Russian military surplus Teflon caps.. The Solen caps could not match the PIO/Teflon caps for transparency, delicacy, realism and musicality. Mega-buck audiophile caps may be superior performers but to find out will cost you.
I have a pair of 604-8Ks, XOs will be getting the whole PIO/Teflon treatment once I get off my lazy butt.

[rogerh113]

Thanks very much for the info and insight into the performance of the PIO in your systems. I am in the process of ordering PIO and teflon for my crossover. Still have to get the inductors and resistors, but this will be a big chunk finished..... Really looking forward to getting started on the crossovers.

New diaphragms come in on Friday, and I finally will get to hear the 604s at home for the first time!!!!!

regards -- Roger

[LowOhms]

Paper In Oil caps are not a panacea. They are generally narrow band caps, very smooth and easy to listen to, but not extended in response.

The truth, to my way of thinking, is NO cap is very good, and no ONE cap will be optimal for a crossover. Different types, and values of caps play different parts of the audio spectrum.

The jury is "out" on what caps to use.

There IS one cap "I" use in every position on my two way ALTEC crossover however, without reservation.

In 2016, I find the DynnamiCap 4.0 uF E ( not the speaker 4.0 uF ) to be indispensable in my custom crossovers.

I eliminate the DynamiCap's cap's stock leads, and use a pair of Mil Spec heavier lead outs on each side, soldered QUICKLY right against the body of the cap, with ZERO lead length - attaching to the original 1/2 inch stub of a lead out. I will only use Wonder Solder Signature ( Percy ) there. The Mil Spec lead wire is M22759/11 and I find a paired run of 12 AWG and a run of 14 AWG, in parallel, gives me the best sonic results. This 4.0 uF "E" is a GREAT sounding cap !!

Another cap I use, in my amp's power supply Final's filter, and in EVERY position on my A7-800 crossover, is the commercial equivalent of a Clarity Cap DTAC, which, if wired with double 14 AWG leads, gives a TREMENDOUS sense of dynamic thrust, punch, instant dynamic contrasting, that I do not find with any other cap type I have tried.

So, my two way crossover will have pairs of these caps, for each channel. What you do on the high pass section, NEEDS to be precisely duplicated on the low pass section, I find !!

I also use additional smaller value caps, to get proper voicing on high. I use 0.68 Russian K-75s, with Lavsan Oil, designed to ignite Hydrogen Bombs I was told. Also use some Russian Teflon K72-P6s, 0.033 uF at 1600 VDC, as the smallest uF value bypass cap. I ALWAYS try to use the highest voltage rating I can find. They usually will sound superior, to the lower voltage ones. Dielectric difference I suppose.

A non polarized film cap's polarity is audible, and if you are a perfectionist and fussy, you may orientate the caps polarity by ear, for optimal result.

I find that wiring in my crossover is critical, an inch of bad wire can ruin the musical experience. So, on all the systems four inductors, I cut off their lead outs, 1/2 inch from the winding, and wire to the inductor with parallel runs of M22759/11 14 mil Spec wire. Lead outs, from the crossover to the drivers are always 57 1/8th inches long, a Bob Fulton lab-derived length from several decades ago.

I also find that soldering the lead out wires to the speakers, DIRECTLY to the solder tabs holding the voice coil wire ( by-passing the poor "mechanical interface" that is stock ) is a BIG improvement. Lowers distortion on music's peaks. I run TWO runs of 12 AWG M22759/11 ( equals 9 AWG ) to each polarity of my 515B A7 woofer, and one run of M22759/11 14 AWG, to the voice coil of my 802, each polarity, soldered quickly and carefully, with some risk.

It is all sounding fairly good to me, don't know what else to try.

Reworking my DIY DC SET amp, this month, is next !!

Jeff Medwin Dr Low Ohms.