Rebuilding XOs with new electronics

[gamalot]

Just wondering what the results are when you take and old style XO such as the 1201-8A or Model 19 XO and rebuild it with new Polypropolene capacitors and air coils instead of the tried and true original caps and coils.
I think the new electronics might be better but will this change the resulting sound considerably or just yield the same sound with better technology?
I am attempting to clone the 19 but the real XO is tuff to find and pricy while newly made ones could be had and probably for less.
Opinions appreciated.

Gary

[Old Guy]

Primary gains are in replacing the caps.

Almost any vintage gear can be improved by recapping. Not as much as caps have improved as caps start going bad the day they are made. Fresh ones are always better.
Of course improved quality AND fresh doesn't hurt.

I've talked to a number of people, a few feel the inductors can be improved, quite a few feel there is no or little improvement. You pays yer money and you takes yer choice...

[bfish]

This is a topic I usually won't touch, due to the fact that so many people have spent outrageous $ on "botique" (BS) components that they are convinced you can't get excellent performance from run-of-the-mill components, and take offense if anyone suggests otherwise. With prices for single film caps ranging from 20 cents to 20 dollars or more, it would pay the frugal DIY'er to do a little homework here. Unfortuneately, much of the info on the topic on many sites is merely mass-repeated drivel. Even more unfortuneately, some manufacturers have capitalized on this trend, and in some cases, in a very big way.

There are two main characteristics I recommend for selection of audio film capacitors, low ESR (effective series resistance, get the lowest you can afford), and close tolerance. If a mfr doesn't publish the ESR specs of its' caps, there's likely a good reason...look elsewhere. Close tolereance is a no-brainer, if you need a 5uf for the application, it needs to be 5uf, not 4.6 or 5.5. I consider +/-5% a minimum, closer is better. 30 years ago, a cap's price usually reflected it's quality, but rip-offs have proliferated, so that's no longer the case. Always, buy fresh, NEW caps, NOT NOS. Time and environment is what changes cap values, not usage.

Though we're not discussing electrolytics here, I posted some suggestions about them awhile back in the last post of this thread if you're interested;

http://www.hostboard.com/cgi-bin/ult.../f/3729/t/1907

For inductors, the trend seems to be towards air core, though I feel that merely reflects the fact that few modern inductor mfrs go to the trouble and expense of using HIGH PERMEANCE iron cores. Hi-perm iron cores can yield higher inductances for a given size without adding unwanted resistance. In general, Altec used high quality inductors in their XOs, so if rebuilding one, I'd leave them alone unless you need to change values. Unlike capacitors, inductors seldom change in value over time.

Now I'm gonna duck before the bullets start flying......

[Old Guy]

Originally posted by bfish:

Now I'm gonna duck before the bullets start flying......

<font size="2" face="Verdana, Helvetica, sans-serif">ROTFL. Coward!

The BS gets pretty deep when it comes to audio.

People pay lots of money to buy "oxygen free" copper for instance. In reality, the El cheapo stuff from Rat Shack is "oxygen free". It has to be. A chunk of copper is drawn thru a die into strands miles long. Impurities cause breaks. Most copper wire is .999 pure, same as the gold traded in London and Zurich.

The there are people who pay for solid silver power cables, and hook them to the 10 miles of copper coming into their house.

There COULD be a case made for silver in speaker wire apps, but not in power cords. Just plain silly.

Cap wise, I personally think any good caps are fine. I would rather have fresh medium grade caps than older high grade ones.

I remember back in engineering school asking the Prof "What are major causes of distortion?"

He mentioned a couple things, then said with a grin- "Capacitors more than 6 months old."

That has stuck with me to this day. No I don't replace my caps every 6 months, but pretty often.

[bfish]

Just one more thought (yeah, right, we've heard THAT before..).

Once you've bought new caps, handle them carefully. They're hermetically sealed in production, and need to remain that way to remain stable. Where the leads enter the body are the crucial areas. If you hold the cap body with one hand and flex the leads with the other, you often can "break the seal", and humidity goes to work inside. Dipped caps are particularly prone to this (remember Orange Drops?). Excellent caps, but not particularly suited to rough handling.

Instead, pick up the cap by the lead with a small (4"-5") hemostat, lightly clipped about 1/4" from the body. Leave the 'stats attached till that lead is soldered in place and cooled, they damp the stresses of bending, cutting, and soldering the lead. Unclip and do the other one the same way. If you want to get fancy, a drop of superglue where the leads vanish into the body once you're done jostling it ain't a bad idea. If you wanna REALLY get fancy and ensure you'll never likely have to go there again, test it then pot the whole assy in a metal can.....I know, nobody's done that since way back when Old Guy was little, but ALL the old potted filters I've had and tested were spot-on (except a couple from a fire and one that didn't like lightning), many were over 50 years old.

Not all the old stuff was good though. Nearly any cap with a paper or cardboard body has gone south long ago (I'm gonna hafta quit sayin' that, I'm IN the South). The paper/wax varieties had exceptionally short lives, and I suspect they're responsible in the most part for our teachers' attitudes towards capacitor shelf life, an attitude that we have continued to propogate even though comparing today's caps (or even those of the '70s) to them is hardly fair. For a period of time through the mid-'50s I know Hammond organ tone generators with paper/wax caps were intentionally under-sized so that the known drift in value would settle down (up) to the correct value (hopefully) by the time the organ was purchased.

I should clarify that throughout my ramblings when I refer to "good" attributes of capacitors, it's in reference to stability and longevity, not to any particular audio quality. A cap of the correct value that remains stable and is of a sufficiently-low ESR is a "good" cap for any audio purpose, the only magic involved is that which you can successfully convince yourself exists while promoting others into the realm of the rich and famous.

OK, just one more thing (I promise). NEVER throw away an old Peerless coil......

[Mike Gibson]

Bfish, I can see why you and Old Guy are hesitant to reply sometimes. It seems that voices of reason become primary targets of the legions of darkness

[bfish]

LMAO!!!

That's what I used to tell my ex!

Good to hear from you, Mike!

[Old Guy]

Bfish-if I crossed any line, sorry it was meant in fun.

I agree that caps have improved. Still I'd be suspect if more than ten years old.

As far as passive xovers, they are seriously obsolete. Going active gets rid of all the phase issues and you can solve a host of other problems.

The best cap is one eliminated.

The story of potting reminds me of one you guys might find amusing.

In my early audio days you had to build stuff if you wanted it. Lots of things were not available.

I recall building a nice filter, testing it, it worked great. I potted it in epoxy.

Afterwards it wouldn't work. Looking down thru the clear epoxy I could see two wires touching....

[bfish]

OG, you've no reason to apologize for anything. I meant what I said as a compliment (except the jab about being as old as potted filters, but that was in fun. You've gotta expect that with a handle like Old Guy!)

[GM]

Greets!

Cap comparison: http://members.aol.com/sbench102/caps.html

WRT inductors, until you step up to $$ ribbon wound air core, buying rolls of magnet wire of whatever gauge you want to get the ~desired series resistance that has a bit more inductance than you need and either tapping it or snipping off the excess to use as XO and/or driver connection is the best performance Vs cost IMO. The downsides are you need a portable meter to measure its inductance and a local supplier that stocks a selection of bulk wire, so probably not cost effective for a one time app or if you live well away from a decent size city now that Radio Shack no longer carries them.

Regardless, as BFISH notes, when it comes to Altec inductors, 'if it ain't broke, don't fix it', though again, you'll need a means to measure them to be absolutely sure.

As always though, YMMV.

GM