XO Component Check

StantonZ

Before I order parts for my Monitor 10B XO rebuild (going to use Sonicaps+Mills resistors), I need to know what to do about the polyswitch; specifically, I want to remove it. The schematic I'm using (dated 5/17/1989) specifies a 2.0 Ohm resistor in parallel with the 12uF cap. If I eliminate the polyswitch, do I change that resistor back to 2.5 Ohms (like the previous version of the schematic that used a fuse), or leave it at 2.0 Ohm and just replace the polyswitch with piece of solid wire?

zane77

Try it with a jumper, in the SDA's that's supposed to increase the highs slightly but you could try it both ways and see (hear) which way sounds best to you.

westmassguy

StantonZ wrote: »

Before I order parts for my Monitor 10B XO rebuild (going to use Sonicaps+Mills resistors), I need to know what to do about the polyswitch; specifically, I want to remove it. The schematic I'm using (dated 5/17/1989) specifies a 2.0 Ohm resistor in parallel with the 12uF cap. If I eliminate the polyswitch, do I change that resistor back to 2.5 Ohms (like the previous version of the schematic that used a fuse), or leave it at 2.0 Ohm and just replace the polyswitch with piece of solid wire?

A .5 ohm resistor is all you need to replace it.

StantonZ

If I replace the polyswitch with a .5 Ohm resistor, I assume I leave the 2.0 Ohm resistor alone. My question is: if I replace the polyswitch with a wire, do I change the 2.0 Ohm -> 2.5 Ohm to compensate, or will that alter the frequency response?

westmassguy

StantonZ wrote: »

If I replace the polyswitch with a .5 Ohm resistor, I assume I leave the 2.0 Ohm resistor alone. My question is: if I replace the polyswitch with a wire, do I change the 2.0 Ohm -> 2.5 Ohm to compensate, or will that alter the frequency response?

I prefer to keep the 2 ohm separate. You've got a 12uf cap accross it, as a shunt. Changing the value of the 2 ohm resistor, may have an affect on the overal frequency responsee of the tweeter in unexpected ways. You can change out the .5 ohm with a .2 or .3, or even a wire jumper, and experiment, see how hot you want the top end, without affecting the resistor/capacitor arrangement.

StantonZ

Makes sense; that's what I was looking for. Thanks!

westmassguy

StantonZ wrote: »

Makes sense; that's what I was looking for. Thanks!

You're welcome. Play with the values if you want, they're your babies to do with as you see fit.

TennMan

westmassguy wrote: »

I prefer to keep the 2 ohm separate. You've got a 12uf cap accross it, as a shunt. Changing the value of the 2 ohm resistor, may have an affect on the overal frequency responsee of the tweeter in unexpected ways. You can change out the .5 ohm with a .2 or .3, or even a wire jumper, and experiment, see how hot you want the top end, without affecting the resistor/capacitor arrangement.

That's interesting. I once owned a pair of Bozak LS250 speakers that had a three position brightness control on the rear for the tweeters. It was really nice to be able to select how bright you wanted them to sound. If I understand you correctly it would be possible to to the same with with Polks by adding a three position rotary switch like the Bozaks had, with three different resistors attached, connected by to replace polyswitches.

westmassguy

TennMan wrote: »

That's interesting. I once owned a pair of Bozak LS250 speakers that had a three position brightness control on the rear for the tweeters. It was really nice to be able to select how bright you wanted them to sound. If I understand you correctly it would be possible to to the same with with Polks by adding a three position rotary switch like the Bozaks had, with three different resistors attached, connected by to replace polyswitches.

Theoretically, yes, but I've serviced quite a few of those multi-position switches, they get dirty and corroded, and are usually more trouble that they're worth.

TennMan

westmassguy wrote: »

Theoretically, yes, but I've serviced quite a few of those multi-position switches, they get dirty and corroded, and are usually more trouble that they're worth.

I had the Bozaks for about 20 years with no problems from the switches but I can see how it could be a problem. The KISS concept is usually the best way to go to avoid problems down the road.

westmassguy

Kiss?

Jimbo18

westmassguy wrote: »

Kiss?

K.I.S.S. as in Keep it Simple Stupid. Not you, of course.

westmassguy

Jimbo18 wrote: »

K.I.S.S. as in Keep it Simple Stupid. Not you, of course.

Gotcha

TennMan

Yeah, what Jimbo said. Just an expression that usually applies to me. I tend to think a little out of the box sometimes and over-complicate things.

Jimbo18

TennMan wrote: »

Yeah, what Jimbo said. Just an expression that usually applies to me. I tend to think a little out of the box sometimes and over-complicate things.

It does sound like a cool idea though.

westmassguy

TennMan wrote: »

Yeah, what Jimbo said. Just an expression that usually applies to me. I tend to think a little out of the box sometimes and over-complicate things.

You, over-complicate? Nah, say it ain't so

TennMan

westmassguy wrote: »

You, over-complicate? Nah, say it ain't so

haha... Let's just say I like lots of options to play with.

westmassguy

TennMan wrote: »

haha... Let's just say I like lots of options to play with.

Just busting your chops Ronnie

StantonZ

FWIW, I'm going to order the 0.5 Ohm resistor but start with a solid wire (short) and see how it sounds; I just need to look for a nice thick (solid) piece of wire here at work.

Schurkey

Remove polyswitch, measure it with an ohmmeter, see what it's resistance REALLY is. Order resistor in the same value.

(Better still would be to measure a NEW polyswitch, as they burn up in use. Resistance increases as the contacts fry. First Guess: A new polyswitch has nowhere near 1/2 ohm of resistance.)

westmassguy

Schurkey wrote: »

Remove polyswitch, measure it with an ohmmeter, see what it's resistance REALLY is. Order resistor in the same value.

(Better still would be to measure a NEW polyswitch, as they burn up in use. Resistance increases as the contacts fry. First Guess: A new polyswitch has nowhere near 1/2 ohm of resistance.)

Polk eventually removed the polyswitches, and in many cases, the 1st resistor down-stream was bumped up by .5 ohms.
That value wasn't just pulled out of the air. If memory serves, new polyswitches measured between 2 and 3 ohms. After several "trips" is closer to 5 ohm. There was talk of pre-conditioning the polyswitches at the factory for consistency.

Schurkey

westmassguy wrote: »

If memory serves, new polyswitches measured between 2 and 3 ohms. After several "trips" is closer to 5 ohm. There was talk of pre-conditioning the polyswitches at the factory for consistency.

Decimal error? Between .2 and .3 ohms, new, .5 ohms after the contacts burn?

I thought Polk did end up tripping the polyswitches at least once because they were unreliable in terms of amperage needed to trip them the first time.

westmassguy

Schurkey wrote: »

Decimal error? Between .2 and .3 ohms, new, .5 ohms after the contacts burn?

I thought Polk did end up tripping the polyswitches at least once because they were unreliable in terms of amperage needed to trip them the first time.

Thanks for pointing that out, a 5 ohm resister would not be a good thing
From what I've read, they were a constant headache, which is why there was talk of pre-conditioning, and also why they were eventually done away with. Sometomes "Old School" is better. Fuses still work as intended. Problem is, some people don't put the right fuse back.

PolkieMan

Gimpod told me mills 0.22.
Of course you could be a Nutty Professor and get a toggle switch
to switch the Poly switch in or out,
sort of a Safe Mode so when you have a party or
leave the kids Home Alone. :cheesygrin: