Polyswitch replacement options

littlewoodboats

I am ordering parts to rebuild the crossovers in my SDA-2a's. Thank you to all who offered advice

Replacing the aged polyswitches being on the list of things to do. I have been told to replace the switch with a resistor whose value impacts the level of the tweeters.

Has anyone done a L-Pad or stepped attenuator in place of the resistor? I am in the final stages of selling my house and am looking at two moves to get into my new place. As rooms and structures differ it would seem that some adjust ability would be a good idea.

I would think that once in my new house that the adjustment would be a one time thing during voicing. It would be nice to be able to get the correct level without going back inside the cabinets.

Any thoughts?

Joe08867

I don't know anyone that has triad an L-pad or attenuator. I prefer not to add more stuff in line myself so I just added a small resistor.

gdb

It is my plan to replace the polyswitch with a fuse so as to continue protecting the tweeters with something that doesn't degrade over time like the polyswitches did/do. I'll have to consult with a solder geek as to whether a resistor will also be required though.

littlewoodboats

Gimpod was kind enough to give me a parts list. Included were two resistors to replace the polyswitches. 0.1 to 0.5 ohm depending on tastes. Lower the value the brighter the high range with 0.22 being a good starting point.

I understand about adding as little as possible and I know good attenuators will add to the cost. It looked like an attractive idea as I would only have to go into the cabinets one more time.

pitdogg2

.5 ohm mills resistor call it a day weather using SL2000 or Rdo-194. Just keep watch on the eviction knob...

westmassguy

My older Monitor 5 has an external 2.5 amp, fast blow fuse. It's measured resistance is .5 ohms. This coincidentally, is one of two recommended values for replacement resistors, when removing the Polyswitch. .2 ohms or .5 ohms are what most recommend here, and all my Polyswitches were replaced with .5 ohm Mills resistors.
I wouldn't recommend an L-Pad or any type of variable resistor for several reasons. 1st, L-Pads are notorious for corrosion. Any moisture that finds its way inside the cabinet will attack it, due to the dissimilar metals inside, so your set value will drift over time. 2nd, L-Pads are essentially the same as the ceramic resistors that we all replace, that being a wound coil. You could do it temporarily, find the value you like, and then solder in the correct Mills resistor.

pitdogg2

westmassguy wrote: »

My older Monitor 5 has an external 2.5 amp, fast blow fuse.

That is the wrong fuse in your 5's it should .75 or 1.0amp fast blow. Depending on the model they came with either .75 earlier models and 1.0 later models

westmassguy

pitdogg2 wrote: »

That is the wrong fuse in your 5's it should .75 or 1.0amp fast blow. Depending on the model they came with either .75 earlier models and 1.0 later models

Thanks for that. I just pulled the other fuse, and it's a 1 amp fast blow. I'm not the original owner, so someone threw it in there at some point.

Schurkey

littlewoodboats wrote: »

I am ordering parts to rebuild the crossovers in my SDA-2a's. Thank you to all who offered advice

Replacing the aged polyswitches being on the list of things to do. I have been told to replace the switch with a resistor whose value impacts the level of the tweeters.

Another possibility is to use a "zero resistance" jumper where the polyswitch was, and order a replacement main resistor with a touch of added resistance.

The 2A uses a polyswitch followed by a 2.7 ohm resistor. Use a zero-ohm jumper, and order a 3.2 ohm resistor instead of that 2.7. Saves the cost of one resistor per speaker. In my case, the zero-ohm jumper was free--I used the lead from the resistor soldered across the polyswitch connections on the circuit board.

littlewoodboats wrote: »

Has anyone done a L-Pad or stepped attenuator in place of the resistor? I am in the final stages of selling my house and am looking at two moves to get into my new place. As rooms and structures differ it would seem that some adjust ability would be a good idea.

I would think that once in my new house that the adjustment would be a one time thing during voicing. It would be nice to be able to get the correct level without going back inside the cabinets.

Any thoughts?

When it was me, on 1Bs, I just ignored the resistance of the polyswitch. In retrospect, I wish I'd LESSENED the value of the main tweeter resistor, I don't have ENOUGH treble for my taste.

Going back into the crossovers and increasing/decreasing the value of that main resistor (if needed) is probably the best way to achieve a pleasing treble balance; I'm not sure I'd want additional components in that signal path.

littlewoodboats

Thank you for the input. I agree with the keep it simple format and would prefer to have as few components in the signal chain as possible. That being said it seemed to be the simple option to not have to go back into the cabinets once buttoned up after the crossover rebuilds. Most likely making a mountain out of a mole hill.

Schurkey. I was given .22 ohms as a good place to start when removing the polyswitch. .1 to .5 ohm was the range given for replacement value so your jump to 3.2 would put you at the top of the scale. Going the route you chose it seems 2.92 (if available) would be the target. I am guessing on that as I have no idea what additional variables might exist when replacing two resistors with one higher value resistor and a jumper.

Has anyone rewired their cabinets and if so does that effect any change?

cristo

westmassguy wrote: »

My older Monitor 5 has an external 2.5 amp, fast blow fuse. It's measured resistance is .5 ohms. This coincidentally, is one of two recommended values for replacement resistors, when removing the Polyswitch. .2 ohms or .5 ohms are what most recommend here, and all my Polyswitches were replaced with .5 ohm Mills resistors.
I wouldn't recommend an L-Pad or any type of variable resistor for several reasons. 1st, L-Pads are notorious for corrosion. Any moisture that finds its way inside the cabinet will attack it, due to the dissimilar metals inside, so your set value will drift over time. 2nd, L-Pads are essentially the same as the ceramic resistors that we all replace, that being a wound coil. You could do it temporarily, find the value you like, and then solder in the correct Mills resistor.

I'll bet that 2.5 amp fuse has a resistance well below 0.5 ohms. You're probably measuring the resistance
of the leads of your meter along with the amp's resistance. Try measuring ohms with the two lead ends
of your meter held together and you can subtract that from the 0.5 ohms measured.

Schurkey

littlewoodboats wrote: »

I was given .22 ohms as a good place to start when removing the polyswitch. .1 to .5 ohm was the range given for replacement value so your jump to 3.2 would put you at the top of the scale. Going the route you chose it seems 2.92 (if available) would be the target.

Yes, 2.9 or 3 ohm would be fine. I would order those and several pairs of resistors near that value--perhaps + .25 ohm, and -.25, .5 ohm. Then you have some choices when you tune the treble balance in your new listening room later without having to pay another round of shipping/handling charges. As I said...on my 1Bs, I wish I'd installed 1.5 or 1.75 ohm resistors instead of eliminating the polyswitch and then using the stock-value 2 ohm units. Getting rid of the polyswitch resistance wasn't enough, the speakers were/are still treble-shy!

littlewoodboats wrote: »

I am guessing on that as I have no idea what additional variables might exist when replacing two resistors with one higher value resistor and a jumper.

If you use the lead from the resistor as your jumper, you're also eliminated two solder joints and a short bit of copper trace on the circuit board. I suppose all that has some resistance; whether it's a meaningful amount is debatable. Bypassing it can't hurt sound quality, though.

littlewoodboats

I think I get it now. You went from the input side of the polyswitch to the output side of the 2.7 ohm resistor? Poor choice of terms I am sure.

Schurkey

littlewoodboats wrote: »

I think I get it now. You went from the input side of the polyswitch to the output side of the 2.7 ohm resistor?

Exactly right, except in my case (SDA 1B) it's a 2-ohm resistor.

westmassguy

cristo wrote: »

I'll bet that 2.5 amp fuse has a resistance well below 0.5 ohms. You're probably measuring the resistance
of the leads of your meter along with the amp's resistance. Try measuring ohms with the two lead ends
of your meter held together and you can subtract that from the 0.5 ohms measured.

Meter reads 0.00 lead to lead

cristo

westmassguy wrote: »

Meter reads 0.00 lead to lead

I stand corrected, or maybe I should say your meter is well corrected.
Not all of them read 0 lead to lead.
Still, .5 ohms sounds on the high side for resistance of a 2.5A fuse.

westmassguy

cristo wrote: »

I stand corrected, or maybe I should say your meter is well corrected.
Not all of them read 0 lead to lead.
Still, .5 ohms sounds on the high side for resistance of a 2.5A fuse.

It's a quality ExTech Meter, which I believe is pre-compensated at the factory.