Optimus 1b

[Mongojustpawn]

saw a pair of Optimus 1b speakers in a second hand store today, look pretty nice, asking $30/pr, read a bunch of posts on AK, as expected, all over the place. Everybody around here must have gone to RS.

[Sir Thrift-a-Lot]

I worked at Rat Shack twice, but the 1b was before my time.   Looks similar to the Nova 7s, which I have a pair of and were a most pleasant surprise.   Some will call this a heresy, but I like them better than my KLH sixes.   In good shape, well worth $30 IMHO.

[SunnyDaze]

If they haven't been already, they'd need recapped.

You may want to replace the non-polar electrolytic caps that are currently in there and have most likely drifted far from spec with metalized polypropylene caps.

Watch for real fiberglass insulation in those boxes. Wear gloves if you open them up.

[Mongojustpawn]

Are they grill covers glued, tried to remove in store, didn't want to force to hard.

[SunnyDaze]

Most of those RS / Optimus speakers had one Phillips screw in each corner of the grilles.

[Dicky]

The similar KLH I remember using a credit card to pry them off, not that that means much for the optimus

[Sir Thrift-a-Lot]

Most of those RS / Optimus speakers had one Phillips screw in each corner of the grilles.

This is how the Nova 7 grills are held on.

[Mongojustpawn]

I got them and I'm pleased so far, don't appear to have been altered, used a dentist tool get behind the grills, they're velcroed. Tried some outlaws, pink Floyd, Coltrane, oldies, LP and cd, didn't push too much, I'll need more advice regarding cap replacement.

[SunnyDaze]

There's 1 capacitor in each speaker. The capacitors that are in there now, assuming they are original, are 15 uF non-polarized electrolytic (NPE) capacitors.

If you are going to take the time to replace them, you might as well upgrade from those NPE caps. Whichever brand and type of capacitor you decide to go with, make sure they are the same value of 15 uF.

There are several brands and types of capacitors. Here's a very good non-technical read on several different caps:

http://www.humblehomemadehifi.com/Cap.html

I usually get metalized film capacitors from Parts Express. These will work for your speakers:

Parts Express 15 uF 5% Metalized Film Caps

The 1% tolerance capacitors are about twice the price. The differences between 1% and 5% capacitors in your case will most likely be negligible. There's a plethora of info on the interwebs regarding crossover capacitor tolerance (and everything else crossover cap related). I won't bore you with that.

[Sir Thrift-a-Lot]

Or, more in keeping with your starting budget...

http://www.mouser.com/ProductDetail/Nichicon/UDB1H150MHM/?qs=sGAEpiMZZMtZ1n0r9vR22e0BBN1kF1oi4BtcgPdTEwk%3d

[Mongojustpawn]

been thinking that I'd like to try replacing the caps in these, remember please, I don't have any experience here, tonight I pulled the grill off of one, removed the woofer, didn't remove the wires, they appear to be a bayonet style, tried gently, but they kind of fought back, moved the insulation so I could see the cx, looks kind of straightforward, but what do i know. Put back together, till I get some tips, what pitfalls to beware of. 

[SunnyDaze]

Well, the first thing you need to do is determine the components used in the crossover network. Then determine what you want to replace.

Any capacitors will need replaced. The originals are most likely polar electrolytic. You'll probably want to replace them with either metalized film or film and foil capacitors. There are several other types of capacitor out there, but, I'll let you do your own homework on that.

I believe (but double check) the 1B uses a single 15 uF capacitor in each crossover. You don't have to replace any inductors. If there are any resistors, you may want to replace them with Mills 1% non-inductive resistors or a similar high quality resistor.

Wear rubber gloves, a long sleeve shirt, eye protection, and a respiratory protection while working with that insulation. That old school RS fiberglass is serious stuff.

Replacing resistors and capacitors in those old crossovers are as easy as it gets. You can just snip the old ones out, scrape the remaining leads clean, and proceed to install your new stuff. There are more aesthetically pleasing methods of recapping these vintage RS speakers, but, it's usually not worth the time.

Let us know what you've currently got in there. Then we'll help you select capacitors and resistors.

[rgpit]

When should you use non polarized electrolytics (NPE) in a crossover? NEVER!
*(except for low cost subwoofer circuits)

[Sir Thrift-a-Lot]

When should you use non polarized electrolytics (NPE) in a crossover? NEVER!
*(except for low cost subwoofer circuits)

Why (Not arguing a point, but rather trying to educate myself)?   Weren't the original caps in most of the old Pioneers and Sansuis NPEs?

[rgpit]

1.  Electrolytics are meant for use in DC circuits in which they work fine
2.  They have very high electrical leakage and poor transient response when compared to film caps
             (translation=they sound bad)
3.  If you look at the waveform through one on a scope you'll see how bad they perform for AC.
4.  Electrolytics don't last as long as films and is why tube amps need to be re-capped after a number of years.
5.  Tolerance for electrolytics is horrible, in the 20-40% range
6. A non polarized electrolytic is nothing more than two polarized electrolytics wired back to back in a single package.

Only reasons to use them is that they are cheap and when sound quality is not important.