Infinity Quantum III "coupling capacitors"

[Looking4help]

Well they were within tolerance.
Out of curiosity I was hoping you had a capacitance meter that also measured ESR buildup to measure the big blues.
Have Fun.

Thanks. I have a basic digital capacitance meter, which I bought only a week ago to complement my basic digital multimeter.

I found a website that explains ESR, hosted by a company that sells a meter that measures it, but according to the disclaimer at the bottom of the page, I am not allowed to "use" the information on the page, https://xtronics.com/wiki/Capacitors_and_ESR.html because I left engineering school after freshman year, and my next door neighbor is a lawyer.

"This information may have errors; It is not permissible to be read by anyone who has ever met a lawyer.
Use is confined to Engineers with more than 370 course hours of electronic engineering for theoretical studies."​

Heck, after doing the math on the course hours, I don't think anybody can use the information on that page.

Is your point that the big blue caps may be out of spec on ESR, even though they seem to be okay on capacitance?

 

[Blue Shadow]

are the replacement caps bipolar?

I find it funny that someone is asking why a Phase Linear amp would blow up. Old habits and stereotypes die hard I guess.

 

[Looking4help]

are the replacement caps bipolar?

I find it funny that someone is asking why a Phase Linear amp would blow up. Old habits and stereotypes die hard I guess.

Yes, the replacement caps are bipolar. I got them from Parts-Express. They were listed as "non-polarized crossover capacitors."

There was an big old 1980-ish receiver that came with the speakers. It was huge. It had six or seven knobs and six or seven big switches and a couple of meters on the front of it. I don't remember the make. It only worked on one side. So I dropped it off at a repair shop. I was a student at the time, so when the shop called with a $950 repair estimate, I decided to abandon it at the shop and let them do whatever they wanted with it. I picked up something functional at Radio Shack at a price a student could pay, and it has served well enough for about 20 years.

When I started looking up information about the Infinity Q3s, I found a post on Audiokarma explaining that these speakers had a reputation as "amp killers." Then I found the service bulletin posted at the top of this thread warning that QLS speakers should have a resistor mounted across the binding posts to drain the "coupling capacitors." Since I still wonder why that old old receiver needed nearly $1000 worth of work it seemed worth investigating.

 

[Looking4help]

I took out the second crossover today and changed all the caps. I also cleaned all the pots.

The pots in this one were dirtier, but they cleaned up very nicely. I was amazed at how well plain white vinegar worked on this.

The 25W 5.4 Ohm resistor for the mid-bass coupler on this crossover had corrosion on it, and when I tested it on the multimeter, it did not even have continuity. It is dead.

That explains why that speaker did not work.



What is the best replacement for this resistor?

 

[Looking4help]

https://www.madisoundspeakerstore.com/wirewound-25-watt/5.6-ohm-25-watt-wirewound-resistor/

I ordered two of these this morning.

 

[Looking4help]

I used hot melt glue to mount the caps on the crossover board.

Is this a good way to mount the resistors on the crossover board?

Thanks and have a good day,

Chris

 

[goodolpg]

Hot melt should work fine.

It appears the resistor you ordered is non variable, ie not adjustable?
The original one was adjustable.

 

[Looking4help]

Thanks, goodolpg.

There seemed to be heat damage on the old crossover components, so I was a little nervous about the hot melt glue.

The crossover schematic shows two resistors on the mid bass coupler.

http://www.infinity-classics.de/technik/manuals/Quantum_3_technical_sheet.pdf

One is adjustable; that is one of the three 25 Watt 5 ohm round pots that I cleaned. Those will be going back on.

The other does not appear to be adjustable. That is the one I am replacing. It is a block of ceramic with a crack running its length on one side and white corrosion leaking out of the crack. In the pictures above, it is located on the upper left part of the board, just above the black panel that holds the pots, the terminal, and the fuse. It looks just like the one I ordered, except that the originals were rated at 25Watts 5.4 Ohms, and the new ones will be 25 Watts 5.6 Ohms. I figure I can make up for the 0.2 Ohm difference between the old and new by adjusting the pot.

Do I have this right?

Thanks again and have a good day,
Chris

 

[goodolpg]

Thanks, goodolpg.

There seemed to be heat damage on the old crossover components, so I was a little nervous about the hot melt glue.

The crossover schematic shows two resistors on the mid bass coupler.

http://www.infinity-classics.de/technik/manuals/Quantum_3_technical_sheet.pdf

One is adjustable; that is one of the three 25 Watt 5 ohm round pots that I cleaned. Those will be going back on.

The other does not appear to be adjustable. That is the one I am replacing. It is a block of ceramic with a crack running its length on one side and white corrosion leaking out of the crack. In the pictures above, it is located on the upper left part of the board, just above the black panel that holds the pots, the terminal, and the fuse. It looks just like the one I ordered, except that the originals were rated at 25Watts 5.4 Ohms, and the new ones will be 25 Watts 5.6 Ohms. I figure I can make up for the 0.2 Ohm difference between the old and new by adjusting the pot.

Do I have this right?

Thanks again and have a good day,
Chris

OK, I had seen a post where you had dirty pots and had taken them apart and cleaned them, I was thinking the resistor you posted in this thread was to replace one of those. That's why I wondered about adjustability.
I think what you ordered should be just fine for the purpose you intend to use it for.
Not sure about the minor .02 ohm difference or if it is even a factor, maybe someone smarter than me can help you with that.

 

[Looking4help]

Thanks, Goodolpg.
I am still just figuring things out, and I appreciate your asking about that.
Have a good day,
Chris

 

[Looking4help]

I finished the crossovers today, reinstalled them, and put on some music.

The 1 1/2 inch soft dome midranges are packed up to send to Millersound, so I wired some other speakers into the midrange wires for the time being.

It sounded very good.

One of the four EMITs is silent. Everything else sound great.

Thanks for your help and guidance. If it were not for Audiokarma, I would still be wondering what to do.

Have a good day,

Chris

 

[Looking4help]

Wow! I sat down this morning and listened to my favorite tracks from Rush, Exit Stage Left. I felt like I had never heard any of it before. What a difference! The detail is unreal. Next up, Bruce Springsteen, Born to Run. My amp is an Optimus STAV-3770 4x100 Watt that I got from Radio Shack twenty years ago, and it is doing a pretty good job.

 

[7.62]

Hi Chris, curious where you found the new pot. I'm dealing with this very issue right now.

 

[Looking4help]

Hi Chris, curious where you found the new pot. I'm dealing with this very issue right now.

I did not have to replace the pots. There is a thread on Audiokarma about cleaning them:

http://www.audiokarma.org/forums/in...storation-guide-very-long-with-photos.306818/

This thread deals with the same kind of wire wound pots that were in my crossovers.

I used only vinegar to clean them, rinsed them thoroughly with water and dried them before reinstalling them. Out of six, only one was seriously corroded on the inner contact ring. When I tested it after initial cleaning, that one had greater resistance in many places as I turned the dial. I took that one apart again, polished it until it was very clean and then sprayed it (and the other two from the second crossover) with silicone lube to keep the metal from corroding again. When I tested it again, it gave consistent readings from 0 to 5 Ohms.

I did replace the wire wound resistors. I got those replacements from Madisound.

Have a good day,
Chris

 

[Looking4help]

I received a shipping notification from Millersound today. The soft dome midrange speakers will be back, fixed, later this week.

 

[Looking4help]

Done. Someday I will do something about the surround on that midbass coupler. Millersound did a great job! The repaired midranges sound very good. the new wires seem likely to attract the cats, so I think I had better keep the grills on.
Thanks again!