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Infinity Quantum 2 - High Impedance Readings

Discussion in 'Infinity Loudspeakers' started by MoreBeer, Nov 22, 2017.

  1. MoreBeer

    MoreBeer Money + Money =More Money

    Messages:
    611
    Location:
    New Jersey - It Sucks Here
    I haven't used my Q2's in a while as they no longer sound that great and have haven't had the time to look at them internally. Anyhow, the other day I hooked them up again just to see if they still work. All the drivers function although the sound is very poor. Just no life to these things any longer. Mids and highs are weak, bass is muddy and overall not that pleasing.

    Only thing that helps somewhat is to play them loud and even at that, not exactly a great experience. Tried on two different amps, Yahama MX-1000 and a Yamaha MX-600 that I know are and sounding good with other speakers.

    No time to take them apart yet but I did disconnect from the amp and checked the resistance across the terminals. One speaker is reading 24 ohms and the other I can't even get a resistance measurement which I find odd as the speaker (all drivers) do work. Using a very good multimeter so I know that's not the problem. Plus I tested some other speakers with it and got accurate readings.

    So I would imagine the crossovers are shot. When I open these things up, is there a particular part(s) in the crossover I should focus on? Or could just about anything (and everything) be bad?
     

     

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  2. swechsler

    swechsler Frog Whisperer

    Messages:
    5,004
    Location:
    7th row center
    Wow, those are nice speakers. I'd definitely put a little effort into them.

    I'd say there are three areas that likely need work.

    1. Woofer surround foam is probably deteriorated if it hasn't already been replaced. Contact Rick Cobb (rcobb at tampabay.rr.com) for replacements
    2. Capacitors in crossover probably need to be replaced
    3. Pots on crossover probably have some corrosion. A shot of Deoxit and working them back and forth a few times should clean them up.
     
  3. chef free

    chef free AK Subscriber Subscriber

    Messages:
    2,233
    Location:
    Hayward, Ca
    I have a pair of QLS-1 I restored so I know a few common problems and their solutions.

    1. The EMITs become high impedance and therefore quieter. You must re-melt the "soldier buttons" on the diaphragms. You'll need a pair of 6/32 1 1/2" machine screws to safely disassemble the tweeters. Take out two of the pan head machine screws at diagonal corners from each other, and thread in the 1 1/2" screws in their place. Now remove the four remaining pan head screws and the hex head wood screws that mount the tweeter to the cabinet. CAREFULLY separate the two halves of the tweeter to expose the plastic diaphragm with the little metal "racetrack" on it. Find the two little "soldier buttons" on the back of the diaphragm where the race track connects to the speaker wire. Test them for resistance, they should be about 4.7 - 5.2 ohms, if they are higher they need their soldier buttons reflowed (if they are "open" the racetrack might be broken, which might be fixed with an automotive window defroster repair kit.) Using a very well tinned, low power (15-23 watts), iron with a fresh tip, Just touch the buttons until they give, then IMMEDIATELY remove the iron. Check for resistance and repeat if necessary. When an acceptable resistance is achieved, use the 1 1/2" screws to reassemble the the tweeters, be sure to get all the spacers and other parts back in the right way, and be careful of those super powerful magnets! The long screws hold the parts in place while you close the two halves and re assemble the tweeters. This really helped my speakers to image.

    2. The pots in the crossover are known to get very corroded, this can make to drivers sound muffled or cut out completely. They are pretty easy to clean however. Take out the Watkins Woofers, this is a good time to test the woofers too, should be about 4-5 ohms on voice coil 1 (red wire) and 2-3 ohms on vc2 (black). Then draw or photograph the crossover for easy reassembly. Unsoldier (desoldier?) the wires from the pots and remove the control knob and mounting nut. The pot will come right out, it is held together with a bale, by flipping the bale wires to the side, you can open the pot. Clean it out with some DeOxit D5 or the like and a soft toothbrush. Don't use rough sandpaper of anything that might scratch the wires, this will just promote more corrosion, if it's really crusty, try a small brass wire brush. Reverse the procedure to reassemble.

    3. Electrolytic caps have a finite life span because the electrolyte drys out. Replace any black and red caps you find in there, they are DONE, every single one in my speakers was leaking crust!. Big caps, like soda/juice can size, last a long time, the yellow oval caps are film caps which have a very long life, they are part of the "Infinity Sound"; leave them alone.

    4. Check for air leaks. I had a bad one around one of the mid-bass couplers. It would make a weird noise when the speaker played a certain frequency.

    I hope this is clear enough to follow, if not please reply with questions or comments. These are such nice speakers and everyone here at the Infinity forum wants to see you bring them back to their former glory!

    RIP Arnie Nudell
     
    Last edited: Aug 10, 2018
    Bobbyd38, Harvestor and Spitfirejoe like this.
  4. MoreBeer

    MoreBeer Money + Money =More Money

    Messages:
    611
    Location:
    New Jersey - It Sucks Here
    Thanks for the replies. Once I get my son in law here on Friday to assist with lifting these up onto work tables, I'll open them up this weekend. First thing I'll do is check each driver then clean the pots as suggested. In fact, if not a major project, maybe I'll bypass them completely and see what kind of difference this makes when taking the old pots completely out of the equation.

    I repaired the woofers a while back but don't remember checking the crossovers at the time, although this was a very long time ago when the speakers sounded great. Just looked at a few pics of the crossovers and their appearance is extremely crude. Almost like something out of a 1940's console radio.
     
  5. swechsler

    swechsler Frog Whisperer

    Messages:
    5,004
    Location:
    7th row center
    If they're anything like the crossovers in the Qa/Qb, that's typical of the time, and even of more contemporary speakers. But they're pretty easy to work on. Contrast with the crossovers from the Kappa series and consider yourself lucky.
     
  6. MoreBeer

    MoreBeer Money + Money =More Money

    Messages:
    611
    Location:
    New Jersey - It Sucks Here
    The crude appearance of the crossovers isn't actually a bad thing. Everything looks very simple and right there. Sometimes I wonder how these might sound if just ripping out all the old electronics and building new crossovers from scratch, even if not identical. I just might have a chance to do this as I have another pair of Q2's waiting for me a friend has with no woofers.

    The pair I have now I'm the original owner of. Bought these new at the old Sam Goody. Must have been 1978 for something like $1600 which was crazy back then. Especially for an 18 year old kid with no money.
     

     

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  7. swechsler

    swechsler Frog Whisperer

    Messages:
    5,004
    Location:
    7th row center
    I remember Sam Goody, that's where I saw my first set of high end Infinitys. I think they were RS 2.5s. Their prices were high, even for the time.
     
  8. MoreBeer

    MoreBeer Money + Money =More Money

    Messages:
    611
    Location:
    New Jersey - It Sucks Here
    Well, I took one speaker apart tonight, managed to slide it onto the bench myself. The pots are the main issue. Massive corrosion. Took them out and luckily these can be snapped apart and cleaned. Took almost an hour to clean just one and get it back to spec at 5 ohms closed and just about no resistance wide open. All readings as the pot is adjusted work as they should. I was amazed these could be cleaned considering how bad they were. I'll post a few pics this weekend.

    Another issue was one of the wirewound resistors as that just snapped off when removing one of the pots. So I'm just going to replace the three resistors in each of the crossovers. Madisound has these 25 watt resistors in the specs needed. Parts Express didn't.

    There's only one black cap. It looks okay but might replace that as well. Tough to tell what size it is so I'll try and get a better look. Says made in Mexico so that's some high quality capacitor we have here!

    One big...big...big problem with the crossovers is they glued the particle board all this garbage is mounted on to the cabinet so removing the 4 screws through the back releases nothing. This has to be removed somehow to work on the crossovers. Hopefully they only used silicone and getting a chisel under there releases it.

    On yeah...tested the drivers and they were okay. At least in the first speaker.
     
    tubed likes this.
  9. tubed

    tubed Lunatic Member

    Messages:
    15,221
    Location:
    Aztlan
    It'd be nice if you were to provide us pics of your progress.
    Many Infinity crossovers showed different parts and arraigned in varying ways and condition.
    Those black caps are bad.
     
  10. tubed

    tubed Lunatic Member

    Messages:
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    Location:
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    Silicone and staples.
     
    MoreBeer likes this.
  11. tubed

    tubed Lunatic Member

    Messages:
    15,221
    Location:
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    For emphasis.
    :needpics:
     

     

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  12. tubed

    tubed Lunatic Member

    Messages:
    15,221
    Location:
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    Picture 821.jpg
     
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  13. MoreBeer

    MoreBeer Money + Money =More Money

    Messages:
    611
    Location:
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    Here's a pic of the pots prior to taking them out. Check out the corrosion on these things. Almost looks like battery acid. It was definitely just from the pots themselves and not from another component leaking. I've never seen anything like this. The one I did clean up last night seems to be okay. I would have preferred to replace them with new however if available.

    Took a reading on the black cap and its at 47µF. I believe the printed rating on the cap says 40 µF. So I'll replace these too in addition to the resistors. Any recommendations on the cap to buy is appreciated.

    pots-corrosion.jpg
     
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  14. MoreBeer

    MoreBeer Money + Money =More Money

    Messages:
    611
    Location:
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    Here's a pic with crossover still glued in the cabinet and the pots out. One resistor is also out. The white crystal dust you see next to the big yellow cap was from the pot next to it. Nothing was from the caps. I've read to not replace the yellow caps? Is this correct?

    Going to yank the crossover out of cabinet tomorrow.

    crossover-no-pots.jpg
     
  15. slimpikkins

    slimpikkins Super Member

    Messages:
    1,783
    Location:
    South East PA
    I'd replace that 40uf as cheffree said (pretty much do all he said) One on my q2 was split. While your in there maybe check the resistance of the tweeter array. If it's high you know you have a tweeter or two that needs work. Post 3 covers that well. The yellow caps can be left the big cans too but that's just my opinion.

    Good work on the pots. Dissimilar metals causes this I presume.

    Mine are non recapped except for the 40ufs and sound very zippy, not lifeless at all.
    Jim
     
  16. Spitfirejoe

    Spitfirejoe Cheap Audio Aficionado Subscriber

    Messages:
    785
    Location:
    Fremont, Nebraska
    Some day, I'll get lucky enough to find a set of these to restore. And you have two pair?:rockon:
     

     

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  17. idadude

    idadude Well-Known Member

    Messages:
    912
    Location:
    Meridian, Idaho USA
    Check all your mid domes with an ohm meter. I re-tinseled three of the mids with a flexible braided tinsel and they all sounded louder than the one I did not do yet. You may have a tinsel wire that has a higher resistance due to years of flexing. It sounds like you have found your problem with the pots, but it is something else to check to be sure you got it all. I also read that the tweeters should have their solder joints re-flowed. You might have to look up some old posts to see exactly what to do with the solder joints.

    Larry D.
     
  18. Northwinds

    Northwinds Huh? Turn what down? Subscriber

    Messages:
    7,476
    Location:
    Connecticut
    I have a set of Xovers from Quantum 5's sitting in the garage. I hated those pots though, lots of problems so I did not save them
     
  19. MoreBeer

    MoreBeer Money + Money =More Money

    Messages:
    611
    Location:
    New Jersey - It Sucks Here
    I'd like to just replace the 5 ohm pots. Although the pots taken out of the speakers can be repaired, they're really bad. Plus cleaning these is getting a little insane. Only problem is most all the pots easily available from the usual distributors are really small low wattage pots, such as the type found in guitars. Guess this type of part isn't of much use with modern electronics.

    After searching around I found some wirewound 5 ohm pots with the ceramic insulator. It appears these are all from the same manufacturer in China. The 25 watt looks to be about the right size. Anything bigger and they won't fit as they're too wide.

    01-pot1.jpg
    02-pot1.jpg
     
    Last edited: Nov 24, 2017
  20. idadude

    idadude Well-Known Member

    Messages:
    912
    Location:
    Meridian, Idaho USA
    I replaced the midrange pot in my RS 2.5 with a 3.0 ohm resistor and couldn't be happier. They sound perfect.

    Larry D.
     

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