KLH 17, variance in impedance, pair of tweeters

[Nordfinn]

All--

New here. What prompted joining was the recent acquisition of what appeared to be an absolutely pristine pair of KLH Model Seventeens, in their original shipping boxes.  The cabinets and everything appear so untouched that I might have thought they were never used.  Alas, getting nothing from the tweeters.  So I will be rebuilding the crossovers, according to a couple very helpful threads here.  My question: I do get an impedance reading from the tweeters (which, I take it, indicates that they are not completely blown); however, one measures 3.7 to 3.8 ohms, and the other 4.4 to 4.5 ohms.  Is the difference significant, something to be concerned about?  Indicate damage?

Serial numbers are 032803 and 032816.  There are no date indications (or any script) on the tweeters.  One surprise: the tweeter leads were not soldered to the leads from the crossover, but only (well) mechanically connected with the screwcaps.  Would this indicated that they are replacements?  I am certain, in any case, from comparison with various photos on this forum, that they are the correct KLH period-specific tweeters.

Thanks much,

Nordfinn

[JKent]

Hi Nordfinn and welcome to the CSP!

Pristine Seventeens! Cool! Show us pictures!

The tweeter problem may be bad/leaky capacitors. Could also be corrosion on the toggle switches. You can test the tweeters by wiring them, one at a time directly to the source and playing at very low volume. You should hear the music, albeit only the high frequencies.

When you put the crossovers back together be sure to use the rubber insulating washers on the speaker terminals and check that the crossover is not grounded to that metal plate at any point (stupid design flaw on otherwise outstanding speakers).

KLH used wire nuts (screw caps). This connection method is original and works very well.

Keep us posted.

-Kent

[jessiAV]

 Welcome, and congratulations in finding such a nice pair of classic speakers.

 

       KLH did use (red/orange?) wire nuts in wiring their drivers.  My  untouched KLH model Six's have them. So n worries there.

       The tweeter capacitors KLH used are well known to fail over time. It does not indicate abuse. 

       The difference in resistance you've found in your tweeters may indicate a problem, but a way to tell is to run audio through them. Hopefully they are okay

[ra.ra]

Yep, welcome aboard.

The deep, mysterious realm of KLH is not my particular forté, but I've had my own newcomer experiences this week with a different KLH model. You are getting great advice, but one other thought about your mute tweeters came to mind. In the simple two-way KLH speakers I've encountered, I noticed that the woofer wires were soldered, whereas the tweeter wires had friction-fit crimp connectors. Could it be possible that these connectors have waggled loose?   

Ditto on the original KLH caps - - they should be replaced pronto.

[jessiAV]

  If it will help, here is a schematic of the crossover. I'm afraid I can not remember where this was posted.

[Nordfinn]

Thanks very much everyone.  Somehow I hadn't thought of connecting the tweeters to a source directly.  Just did, and they are both functioning.  My question about differing impedances was more a matter of whether it meant that they would have markedly different responses.

I'll post photos soon.  Don't know where these have been for fifty years.  By all appearances they've been in their original shipping boxes.

Thanks much for the schematic.  I was gonna replace caps according to the below thread.  Already ordered parts from PE.  This is all pretty new to me (not much experience soldering), but it looks pretty doable.

One more detail that might be of interest, to someone, sometime: The hot leads on the tweeters were distinguished, apparently, by putting a knot in the lead.  (The wires are the same color, and there aren't any markings on the tweeter itself, that I can find.)  Oh, and: No, not red and black wire nuts, on the tweeter leads; all black.

http://audiokarma.org/forums/index.php?threads/renovation-of-my-klh-17s-is-complete-long.102176/

 

[ra.ra]

That thread seems like a pretty good step-by-step tutorial, but just one caution: You do not want to use latex caulk to re-dope the woofer surrounds. If your cloth surrounds require treatment, get yourself a small bottle of the stuff cooked up by CSP member RoyC. 

[Nordfinn]

Thanks much.  I caught that, and have already ordered the RoyC elixir.

[Nordfinn]

Photos, as requested.  All the veneered surfaces are as nice as those pictured, even the bottoms.

The finish is a little dull, though, after all these years.  Anyone know: Am I right in assuming the the original finish was linseed oil? 

[ra.ra]

Those Seventeens look really, really nice. Looks like your tweeters have soldered wires, unlike the ones I mentioned. Your grille cloths have only minor discoloration, but they should clean up to become like new. Even the box graphics are wonderful, and that parquet floor is gorgeous.

The tweeter readings you report are DCR (direct current resistance) measurements, and unless you detect an audible difference in output, I don't think these different readings should pose much of a problem.

[Nordfinn]

Yes, I'm pleased with them.  A Craigslist score, and reasonably priced, although I was of course disappointed to get them home and find that they weren't fully functional.  No, those leads from the tweeters were attached with wire nuts.  Note the knot in the lead on the positive side (is this common?).  The RoyC dope arrived today.  I will apply as directed, although I confess I don't fully understanding the physics.  If properly sealed, the cone should slowly return to rest if pushed in?  I would think that, as the whole system gets more airtight, and so behind the cone the volume is being compressed, the cone would spring back that much faster.  Also, seems strange--that slowing down, inhibiting, the cone would be a desirable thing.  But I trust the collective knowledge here, and I'm very appreciative of all the help I got even before I asked a question.

To freshen up the finish on the veneer: What would be closest to what was originally used?  Linseed oil?

I'll probably have them functional in a week or so.  Will report back.

Thanks,

N.

[ra.ra]

3 hours ago, Nordfinn said:

No, those leads from the tweeters were attached with wire nuts.

Yes, I know about the wire nuts, and I generally think they're fine, but perhaps this was the source of your silent tweeters - - this would not be the first time one of these rascals has shaken loose. My comment about the solder connection was referring to the backside of the tweeter, where I have push-on friction connectors. I don't know about that little knot, but when the same color wire is being used, it's a clever way to differentiate.

About the cabinet finish, I would suppose KLH oiled speakers are very similar to AR's, so this discussion may be helpful.

http://www.classicspeakerpages.net/IP.Board/index.php?/topic/8445-oil-for-speaker-cabinets/

 

[Nordfinn]

The wire nut connections were quite tight (not easy to disassemble), so I don't think it was that. I didn't think to check the back switch, however, as someone suggested, before taking out the tweeters  Since I've already partly disassembled and the parts are on order, I'll go ahead and replace the capacitors anyway. 

Thanks much.  Lots of info  and back-and-forth on finishes!  I'm not eager to work with BLO in my little Brooklyn joint, but probably I will, since the speakers are about as near to original as one could hope.

[ra.ra]

2 hours ago, Nordfinn said:

I'll go ahead and replace the capacitors anyway. 

Even though we have not seen your original caps, this is probably the best single decision regarding restoration of these vintage KLH speakers. If your wire nuts were tightly connected, it's a mystery what was the cause of your mute tweeters. 

[Nordfinn]

Proceeding slowly with these: gathering the crossover parts, doping the woofers, refurbishing the cabinets.  Since the finish was in such fine shape, I used Watco Rejuvenating Oil, followed by some paste wax, which worked very well.

 

I'll probably finish up this weekend.  One question: I got two 8.2 uF (with 1% tolerances) caps for the crossovers, in place of the four 4.0 uF caps specified in the thread mentioned above, just because I thought they would be easier replacement for the two 2 x 4 (into a common lead) originals, and also would fit well into the original plastic harnesses.  So I'm just a little off spec, which I assumed was not a problem.  But then I just saw the below (italics), from the extensive guide to AR restoration on the AR forum.  Is this something to be concerned about?  Have y'all been compensating this way?

Thanks,

N.

If you install PP capacitors, you may wish to add a small amount of series resistance to compensate for their reduced ESR and maintain the authenticity of the AR crossover. A 0.27-to-0.33-Ω, 10-W non-inductive resistor is best added in series with the 6-μF hi-range capacitor. One-hundred-fifty- and 50-μF capacitors should each have ~0.27-Ω, 20-W resistors added in series. Solder each series [C+ R] in the same location as the original C.

[ra.ra]

This is a great question, N, but one that I am unable to offer much assistance with, even as I struggle with this same question on my own recent KLH restoration project (link attached). My confusion is compounded by at least two factors. First, I am unsure how (and possibly unable) to measure a new PP cap's ESR, and there is no available data on the original cap's ESR from which to compare. Second, these tweeters are 40+ years old and have possibly diminished in output over the years, so we are no longer working with laboratory-level originals that can be expected to be performing like they did on Day 1 after factory inspection. In these instances, it's sometimes agreed that it's best to eke out every bit of HF you can from these aged drivers. 

Others with more electronics experience should be able to offer more explicit advice, but your question is a very good one. In my case, I've been enjoying the tweeter output produced with a new generic film cap, but I am still experimenting with the external damping regarding dispersion. Your speakers look great, best of luck. 

http://www.classicspeakerpages.net/IP.Board/index.php?/topic/10078-klh-model-thirty-two-loudspeaker/

 

[Nordfinn]

Thanks much, Ra.  I'm just gonna go ahead, then.  Will report back next when done, unless I run into problems.  This site is great.

N.

[Nordfinn]

Got the xo's finished and everything hooked up over weekend.  First impressions: They sound unbelievably good, fantastic, hooked up to my restored Scott 299b amp.  I think I'm gonna be selling my modern speakers.  I had certain preconceptions about acoustic suspension designs: that the bass could be muddy, that the design was inherently inefficient.  These are obviously very efficient, very dynamic, and the bass is very articulate, as well as very much there.  The sound is so open that it's taking a little getting used to.  Perhaps it's the simple xo's, combined with the decent new capacitors, but everything must be accurately in phase, because I'm getting very vivid stereo imaging, which I also did not expect.  The tweeter control differences are quite noticeable, especially with certain material (e.g., ride cymbal).

I'm very inexperienced soldering, but managed it ok.  The two circuits are were put together just a little bit differently, mechanically (pics below), but I expect it makes no difference.  I only soldered in the new caps, used the wire nuts where they had been originally (unlike the thread above).  I had a sheet sorbothane lying around, so put that under all the new caps, and used the original harness for the large cap.  One small mistake was not tightening enough the machine screw binding post on the inside against the nut on the outside, so that everything was rotating when I hooked them up to a source.  There isn't much insulating material there, and it's of course old, so you hesitate to put a lot of pressure.  But I had to open them back up and tighten up the binding posts.

I mounted the woofers 180 degrees from the original orientation, on the theory that the next 50 years of gravity will counteract the effects of the first 50+, on these stamped-metal frames.  Who knows.   I used Mortite for the woofer gaskets; it's just a little more expensive than the duct sealer stuff some here recommend, and it comes already in ropes of about the right thickness.  Very easy.

I used three coats of the Roy C dope for the woofer surrounds, more than one jar.  Seems like enough (see pic), but I get nothing like the delay with the three-finger test that some here say is optimal.  Used the original foam gaskets with the tweeters.

When I opened them back up to tighten the binding posts, I was dismayed to see quite a bit of sawdust and detritus inside the shroud, from remounting the woofers  Took the opportunity to use some wood filler on a couple of holes that weren't holding a screw well.  Not sure what to do about the sawdust.  It's hard to know how to fit the shroud.  I guess it just lays in there.  You can't tuck it into the lip of the mounting hole, so that nothing could get at the driver, so far as I can tell.  Also, I was a little afraid of it getting too close to the tacky underside of the surround.

Long time ago, the guy at the Speaker Shop  in Ohio (he was restoring some old Electro-Voice triaxials for me) warned me of the hazards, for drivers, of pink fiberglass.  Seems like these tweeters could use a shroud also.  Anyone done that?

The grille cloth cleaned up nicely with Scotchgard foam fabric cleaner.  It's very hard to get the grilles on and off without a very slight dent to the veneer.  Keep them off until you're sure you're done. 

Watco Rejuvenating Oil and then Butcher's Wax for the cabinets--they look great.  I'll post some beauty shots everything is properly set up.  A few process shots below.

Alas, the tube amp has to go into the shop, and now the speakers are hooked up to a little desktop T-amp, which drives them just fine, but they don't sound as good.  I hope, and expect, it's just that, and not something having gone awry, with the drivers getting a signal for the first time in who knows how many decades.  The first day of listening with the tube amp was a revelation.

Thanks for all the info on this site.

N.

 

 

 

 

 

 

 

[Nordfinn]

Have a problem, noticed today after further listening.  I think it's new, but it's possible something I hadn't noticed previously.  Speakers still sound overall very good and open, but I have a buzz at certain frequencies. Especially noticable with piano, upper middle register.  Sounds sometimes congested, other times outright distorted or buzzing (for signals that through headphones sound clean).  It's defenitely in the tweeter range, but it's hard to tell if it's the tweeters themselves or something mechanical, something resonating.  Opened them up to makes sure everything was tight and solid.  The sides of the cabinet do vibrate considerably--the tops especially.  There would seem be a lot of variability as to how the fiberglass is distributed when you restuff them.  I tried to get it all in evenly.  Any thoughts?  It's frustrating, because they were sounding so fantastic.  The problem is not ignorable, once you hear it.  I've been checking it out all day, and starting to think it's the tweeters themselves.  And they are not so easy to come by, I guess.

If anyone is curious, the piece of music that I've been using to test this (and on which the buzz becomes unlistenable), is George Cables Trio, "Farewell Mulgrew," from "Icons and Influences."

[JKent]

Hi Nordfimm

I've been following your progress and the good advice you're getting from ra.ra. One thought about the buzzing: It's hard to tell from the photos but do your tweeters have gaskets? The originals were white foam which often got over-compressed and did not seal well but if they are missing that could cause buzzing and air leaks.

A side note: You mentioned your Scott 299b needs service. I have a restored 299a and can HIGHLY recommend Tim at Bristol Electronics in Ho-Ho-Kus, NJ. That's in Bergen County, near Paramus and not a bad drive from Brooklyn.

This is OT but I want to show off  I did the cosmetics and re-cap/re-tube but Tim did all the hard work. He's worked on a lot of vintage amps and receivers for me and he's the best!

-Kent

 

[Nordfinn]

Thanks, Kent.  I had the original foam gaskets in.  Yesterday I replaced them with Mortite.  Maybe it made a small difference, but the ringing is still there.  If I can't tame it, it will be a deal-breaker for these speakers.  I suppose I could try original replacement tweeters, if I can find. (the only source is the auction site, I assume)  I'll try redistributing the damping material, but  otherwise I'm stumped.  The cabinets are very tight and solid.  Seems like the back panel, the metal binding post panel, could resonate?

That's a beautiful amp.  I talked to Bristol electronics some time ago, about a 350 tuner.  I trust that he is indeed good, but the turnaround time!  I'm the second owner of a 299b amp restored by Craig Otsby, in Michigan, so it's going back to him.

N.

[JKent]

That metal back plate is just plain stupid. And a lot of KLH speakers have them. It's a short hazard, but could it resonate? I dunno.

I hope someone will be able to chime in on the buzzing issue.

About Bristol. Yes--It's a 1-man shop. Factory authorized for McIntosh and several other top brands but turnaround time can be an issue. I think typically a month. And there are no rush jobs. I'm fortunate because I'm not in a hurry but if it were my only amp.....

And thanks for the compliment.

-Kent

[Nordfinn]

I just talked to someone at the Speaker Shop in Ohio (lucky to get him, because he's basically retired, and the shop is just taking on occasional jobs at his discretion, it appears).  He worked on some old EV 12-in Wolverines for me a decade ago.  Very knowledgeable.  I didn't completely understand, but the first thing he recommended was to bring to a shop with a frequesncy generator to isolate the frequency of the ringing (I think, though, that I can do myself, with a desktop frequency generator).  He said that if these were much overdriven (which might be indicated by the (apparently) blown original capacitors, they can have a partial unwinding of the voice coil that could account for what I am hearing.  In other words, a problem short of outright failure.  Possibly addressable by adjusting the crossover, but otherwise not repairable, even by him (which I would think means neither by anyone else).  Anyone here have a couple of good tweeters to sell?  I'm seeing a little bit of conflicting info, but it looks like models six, twenty, twenty-two, and thirty all used the same tweeter.  That sound right?  I'll be looking to find on auction.  I assume there's no good modern replacement, or I would have heard of such here.  Worth waiting for, I suppose, because these otherwise sound so wonderful, and they are in such unusually fine shape physically.

N

[Nordfinn]

Below link is very helpful regarding equivalent drivers.  According to it, same tweeter is used in models six (later version), seventeen, twenty, thirty, and thirty-three.

http://centerforawareness.com/misc/electronics/speakers/klh/all_klh.htm

[ra.ra]

Not much further to add here, but it sounds like you guys are chasing the obvious suspects - - if the problem is "ringing" or "buzzing", I'd be checking metal components and mechanical connections. Usually these KLH woofers are very well constructed, and it's rare for a surround or spider glue joint give way which might create some unwanted "flapping" noise, which could be characterized as "buzzing". And these cabinets are usually so stuffed with FG that I can't really imagine those unglued caps rattling about. Have you been able to isolate each tweeter to confirm that each of them seems to be performing properly? 

Good-looking pair of KLH speakers, I hope you can get to the bottom of this nuisance. And that Scott amp is a real beauty, too - - was it the 299's from this era that had the most horsepower?