Some AR-9 Capacitor Measurements

[johnfalc]

I finally got around to changing out most of the capacitors in the AR-9s I picked up about a year ago.  I had always felt, that in spite of their fabulous bass, the mid and upper ranges suffered by comparison to my AR-90s (which I had recapped seven years ago when I got them).  Anyway, for anyone who's on the fence about doing this job ... please take a look at the values I measured for the old caps - quite illuminating, especially the measurements for the 6 uF caps.

The sound is now just as it should be, to my ears.  Imaging, especially of solo instruments and voices is now rock steady and frequency response (no I haven't measured it yet) feels terrific.  We've been in "concert mode" here since I made the changes yesterday.  BTW - I used Erse metalized polypropylene film caps, just as I did (and was pleased with) in the AR-90s.  I replaced all the caps in the LMR, UMR, and HF circuits.  The new caps measured spot on their nominal values.

[johnfalc]

BTW - measurements were taken at 1KHz.

[Stimpy]

Hi John,

You've documented some alarming results!  I guess it's a good thing that the tweeters used a 3rd order crossover circuit.  Otherwise, I believe both of your tweeters would have been blown, with the readings you've reported for the 6.0uF capacitors.  Something to think about, for owners of the Vertical Series speakers.

Also, the defective 6.0uF caps; were they the black/red Callins capacitors?  Just curious, and I'm not surprised if they were.

Good work,

Stimpy

[AR surround]

It's interesting that you got a huge variance from spec with those 6uf caps.  I also got similar measurements with the 6uf caps taken out of my AR9's back in 2017.  (See chart.) I'm suspecting that those particular caps had a serial defect.

Are you satisfied with the performance of the UMR given that you used an Erse poly film cap in the 24uf spot?   I initially tried a Solens poly film cap, and then later added a F&F bypass cap, both which yielded horrid results.  Then I went to a Jantzen poly with F&F bypass which was slightly better.  Finally I gave up on using a poly cap in that 24uf spot and went to a NPE Mundorf E-Cap with F&F bypass.  I'm extremely happy with the Mundorf E-Cap.

 

 

[johnfalc]

1 hour ago, Stimpy said:

Hi John,

You've documented some alarming results!  I guess it's a good thing that the tweeters used a 3rd order crossover circuit.  Otherwise, I believe both of your tweeters would have been blown, with the readings you've reported for the 6.0uF capacitors.  Something to think about, for owners of the Vertical Series speakers.

Also, the defective 6.0uF caps; were they the black/red Callins capacitors?  Just curious, and I'm not surprised if they were.

Good work,

Stimpy

Yes, they are the red Callins caps.  I measured the first one multiple times ... then was amazed when the second one was even further from nominal.  I agree there must have been a serial defect ... I wonder how many are still out there in 9's.  And yes, thanks to the 4uF and associated inductor, the tweeters are fine.

[johnfalc]

9 hours ago, AR surround said:

It's interesting that you got a huge variance from spec with those 6uf caps.  I also got similar measurements with the 6uf caps taken out of my AR9's back in 2017.  (See chart.) I'm suspecting that those particular caps had a serial defect.

Are you satisfied with the performance of the UMR given that you used an Erse poly film cap in the 24uf spot?   I initially tried a Solens poly film cap, and then later added a F&F bypass cap, both which yielded horrid results.  Then I went to a Jantzen poly with F&F bypass which was slightly better.  Finally I gave up on using a poly cap in that 24uf spot and went to a NPE Mundorf E-Cap with F&F bypass.  I'm extremely happy with the Mundorf E-Cap.

 

 

Quite interesting that both your and my 4 and 8uF caps were very close and that it was the 6uF in both our cases that were so far from nominal.  Looks like anyone with AR-9s or AR-90s (maybe others) should take the time to, at least, check those.  Of course, your and my measurements suggest that anyone who wants something close to the original sound should get in there and do a replacement of all those caps involved in the upper drivers.  I'm quite happy with the Erse caps and am still running my 9's and 90's with the switches set to maximum output to the drivers.  I may take some measurements later this week and may also do some listening sessions with the Tweeter and UMR attenuated to see what I think of the sound then.

[lance G]

Gentlemen, watching this with great interest, top work.

Not intending to drift off the core subject but, Stimpy (and others), thanks for your earlier help with my AR9's. Hope you (and all contributors) are keeping well. All will be well after the election !🤢

[DavidR]

I'm currently working on one pair of 9s. Still doing cabinet work and haven't gotten to the caps yet. However, I did my AR90s and the results are below. For some reason it will not format correctly so hope you can follow. Even though many of the caps were within spec the speakers were VERY dull. I thought my tweeters were suffering from dried ferro-fluid - Nope, they were fine. Old caps can act like resistors. My point is to change them when they are old no matter what they read. Caps tested with an Agilent U1733C at 1 kHz   AR90 caps Old caps (L) New caps (L)   Old caps (R) New caps (R) Brand Tweet 'S' 4 uF - 100V 4.14 4.04   3.93 4.02 Mundord E-Cap 70 Tweet 'S' 6 uF - 50V 5.49 6.04   5.98 6.09 Mundord E-Cap 70   2.4   2.41     2.41   UMR 'P' 8uF - 100V 8.00 7.85   8.38 7.84 Parts Express UMR 'S' 24uF - 100V 26.77 24.19   29.82 24.15 Mundord E-Cap 70 UMR  'P' 40uF - 50V 44.49 40.79   52.50 41.12 MDL LMR  'P' 30uF - 50V 37.81 30.60   29.73 30.30 Bennic LMR  'S' 80uF - 100V 91.93 80.10   92.75 80.10 Parts Express Woofer  'P' 350 uF - 50V   349.7     350.1 Parts Express   150uF           PE   200uF           PE                   6 ohm resist 6.3 6.007   6.35 5.999     1 ohm resist 1.2 1.016   1.3 1.015