4x woofers - need advice on repairing cone AND surround

[stupidhead]

Kip, on the pots there is a lengthy guide here pot refurb guide which will give you step by step instructions if you need them. Basically a salt/vinegar bath followed by thorough rinse and then a polishing. There are times when the components of the pot have degraded to the point of being fubar, some pics once you crack them open will help.

 

[Kip]

Vinegar and salt? Sounds corrosive   ...wait a minute, I eat that stuff!

Thanks for the reference.  I didn't get the wire nuts part, though.  At first I thought the wire nuts were used to make it easier to disconnect everything the next time.  But the text said they were used to avoid having to solder inside the cabinet "...where there's too many things to ruin with the heat..."  Huh?  There's just air in there at this point, right?  What am I missing?  We used to solder inside speaker cabinets all the time, never did any damage that I know of.

I get what you're saying about the overall corrosion.  I'll post pics when I get it apart.

I'm starting to feel guilty - you guys are giving me more free guidance than I deserve.  Thanks.

[Kip]

Given that the crossover inside the speaker I am working on seems unmodified, I think I am going to try to get an original 4X tweeter, then compare the result with the other 4x, which is still running the Genesis tweeter.

Which brings me to another question (do I need to make some sort of donation here for all this help I'm getting?): I've found info that suggests that the (midrange?  tweeter?) of the AR-2(a)x is the same as the OEM tweeter for the 4x.  Is that true?  That'll obviously increase my chances of finding one.

Thanks!

[ra.ra]

Kip, on your last point, it can be a bit confusing but you are not correct. The midrange from the 2ax model was the same driver used as a tweeter in the original AR-4, not the 4x. In the pic attached, the driver on the left with the diamond mesh and larger magnet is the 2ax mid or 4 tweeter, and the driver on the right is the correct tweeter for all versions of the AR-4x. What makes your speakers somewhat unique is that they were set up to pair the AR-4x tweeter with remaining woofers from the original AR-4 model.

[Kip]

Whew.  Ok thank you for straightening me out on that one.

I'll be actually working on this speaker this weekend (rather than just talking about working on it), so thank you all for your generous help and guidance.

 

[owlsplace]

Okay, looks like Robert (ra.ra) posted the correct early-version schematic diagram for the CTS woofer.

Here is a link to the later schematic -- notice the tweeter polarity is reversed: http://www.classicspeakerpages.net/library/acoustic_research/original_models_1954-1974/original_models_schematicss/ar-4x_schematic.html

Then there is Dave's modded version ...

Forget the Zobel I mentioned as I had my synapses crossed to the AR-6.

Here is the schematic using an L-pad from a previous thread which also reminded me there is a phenolic replacement tweet available from Parts Express if you are interested in a new replacement tweeter. If so, perhaps RoyC will point you in the right direction:

Enjoy your weekend,

Roger

[Kip]

Thank you Roger.  I think I'm going to try to find an original tweeter first - I think I want to do a comparison with the Genesis one.  If I can't find an OEM I'll look at the PE one.  Appreciate all the help.

24 minutes ago, owlsplace said:

Enjoy your weekend,

You as well!

[stupidhead]

'mornin Kip et al,

as to this

16 hours ago, Kip said:

Given that the crossover inside the speaker I am working on seems unmodified, I think I am going to try to get an original 4X tweeter, then compare the result with the other 4x, which is still running the Genesis tweeter.

Which brings me to another question (do I need to make some sort of donation here for all this help I'm getting?): I've found info that suggests that for this but the (midrange?  tweeter?) of the AR-2(a)x is the same as the OEM tweeter for the 4x.  Is that true?  That'll obviously increase my chances of finding one.

Thanks!

which Robert has clarified the tweeter question, I would like to respond to the "donation" part. I will speak for myself but I suspect many will have a similar feeling about this. CSP has proven to be a forum for like minded folks who have a love and appreciation for vintage speakers, a passion for most who participate. For me vintage speakers are a hobby, for others a buck can be made. Sure I have sold some of my projects, but generally to fund the next bigger better purchase of vintage speakers (or other vintage audio gear). In all cases the selfless sharing of info, experiences and guidance is done to help others with a similar passion. There is no gratuity due or expected. I liken it to another community that I have a good deal of experience with and that is the old "tapers" community for live music sharing. The Grateful Dead for example allowed folks to record their shows without having to be stealthy about it, and the resulting "tapes" are (or were) shared freely, and generally speaking never sold. The belief being that karma was positive if you followed the golden rule and didn't try to monetarily gain from these. The same general attitude is here which is a major reason I am an active member. I have often seen folks send people (usually newbies) pieces/parts for a given project at no cost just to strengthen their "karma" and again the golden rule is in the background.

This community is niche for sure, but just seems to attract nice folks who are more than happy to share freely without thought of gain. There may be a little bit of bravado every now and again, but we are humans after all.

Other communities like this may have a minimal subscription fee to help defray the cost of maintaining the site and the associated costs, I have not seen that here. Personally, I would gladly make a contribution to the admin of this site for this if needed but don't know if there is even a way to do it. Possibly Carl can speak to this question which I have quietly pondered in the past.

In closing, I feel that continued participation is how I show appreciation and "donate" to this fabulous forum. Many swoop in to get insights and then vanish, and that is fine, but sharing my experiences and attained knowledge with others is what I choose to do.

prosit

[JKent]

Kip,

I (and most of us here) completely agree with Geoff.

Regarding donations: A previous version of the software used to host this site had a "contribute" button and I sent some money but it wouldn't go through! I contacted the site administrator, Mark, who said he maintains this site at his own expense out of love of the hobby. He wouldn't accept any donations! What a great patron!

Mark has now removed himself from operating the forum and has volunteer moderators Gene and Carl to make things run smoothly. I have noticed, rarely, a small ad for Arsenal among the posts. I believe that's Mark's company and that small bit of advertising is his only "profit" from the site.

Thank you Mark!

-Kent

[owlsplace]

Yes, many thanks to Mark as the classic period AR's are about my only interest these days besides classic Rollei tlr cameras and most of the guys here are pretty classic also...

Here is another wrinkle in your rebuild from 162017375346 currently on the auction site:

This iteration of the tweeter will be hard to find and not necessary as I believe it is the same tweeter with a fiberglass ring to reduce edge artifacts?

The wrinkle at 7-8 o'clock on the woofer surround is caused by the grain of the cloth fabric. The fabric tears easier in the long grain along the crease. IIRC TomT mentioned the purpose of the cross-hatch pattern on the woofer was to decrease high-frequency artifacts not strengthen the cone material.

Will be interesting to see how high the price goes on these. The shipping seems a bit exorbitant to me. I've seen 4's go for $600 in the past in excellent condition.

Roger

[Kip]

Question for Robert (ra.ra)...or perhaps anyone.  Just to make sure, on the freehand crossover schematic you posted earlier (thanks again BTW)...the "+" terminal on the woofer is the terminal marked with a red dot on the frame?

Also, just in case anyone's interested, here's what I measured on the crossover cap block:

• Blue - Green (nominal 20 µF)
  • capacitance: 43 µF
  • ESR: .73 Ω
• Blue - Black (nominal 24 µF)
  • capacitance: 47 µF
  • ESR: .55 Ω

I'm replacing them anyway, just thought this might be of interest to someone.  A thought occurs: I wonder if the designer of the original crossover thought: "...I want 50 µF caps in this circuit, but I know they run high, so I'll spec them around 25..."  If that were true, I probably should use the measured values for the replacements.  A little food for thought, anyway.

Cheers.

[RoyC]

2 hours ago, Kip said:

Question for Robert (ra.ra)...or perhaps anyone.  Just to make sure, on the freehand crossover schematic you posted earlier (thanks again BTW)...the "+" terminal on the woofer is the terminal marked with a red dot on the frame?

Also, just in case anyone's interested, here's what I measured on the crossover cap block:

• Blue - Green (nominal 20 µF)
  • capacitance: 43 µF
  • ESR: .73 Ω
• Blue - Black (nominal 24 µF)
  • capacitance: 47 µF
  • ESR: .55 Ω

I'm replacing them anyway, just thought this might be of interest to someone.  A thought occurs: I wonder if the designer of the original crossover thought: "...I want 50 µF caps in this circuit, but I know they run high, so I'll spec them around 25..."  If that were true, I probably should use the measured values for the replacements.  A little food for thought, anyway.

Cheers.

Kip,

The red dots are +.

You do not want 50uf caps. I believe you are misinterpreting your measurements by combining the total capacitance of the parallel and series capacitors. Each capacitor serves a different part of the crossover. The parallel cap is 24uf and the series cap is 20uf, so you would to need to purchase 2 capacitors per cabinet to replicate the old crossover. The block cap you are measuring contains two capacitors with a common input wire, which often causes confusion.

Roy

[ra.ra]

Good words from Geoff and Kent, thanks.

Kip, I made that sketch after RoyC and JKent helped me figure out my s/n 38XXX AR-4x speakers with same drivers as yours. I was a bit surprised to see yours in the 31XXX range, but then I remembered this link about similar speakers in the 44XXX range. You are correct about the woofer terminals, and you can see in attached pic of AR-4 woofers, I like to use red wire for the "hot"  or "positive" or "+" woofer terminal connection. Also, I have taken to very often using wire nuts for woofer installations - - I solder wire leads to woofer terminals, and then attach these with wire nuts to crossover wires poking thru the stuffing and kempac (tissue). For me, it facilitates easy access in the future.

Roger's posting of the more common 4x schematic again provides an interesting distinction: the typical 4x has drivers out-of-phase, while yours (and mine) have woofer and tweeter in-phase. Glad to see RoyC just chimed in, 'cuz those measurements looked wacky at first, and of course, when you add the two cap values (20+24=44uF), you are pretty close to values (43 and 47) your meter reported.   

And here is the thread on my similar pair.

[owlsplace]

I think those old wax caps are capable of doubling their original values with age. Not sure how that happens unless the dielectric thickness changes.

Roger

[Kip]

Thanks.  I'm pretty sure I measured them correctly.  I'm aware of the impact of the wiring.  I did not disassemble the wax block; I only measured at its three outgoing wires, so I'm not sure how I could have measured the two in parallel unless I went out of my way to do so (tying together the green and black wires then measuring to the blue).  FWIW, as a sanity check I did measure from green to black (the two caps in series) and saw the expected value, around 20.

In my own experience, electrolytic tolerances can be wide, especially at the high end.  For instance, the spec'd upper tolerance of this 20 µF electrolytic is +100%, so it's measured capacitance could be up to 40, even brand new.  Usually not an issue when used to filter ripple out of a power supply, but in a crossover...?

Then again, you would think in a crossover they would use caps with much better tolerances (I'm guessing double values would degrade the sound, probably due to multiple, additive effects [i.e too much lower frequency being shunted across the woofer, too much of the same being delivered to the tweeter.])  Maybe better tolerance caps weren't available back then.  Or maybe my cockamamie theory might just have some merit.

I am planning on getting good tolerance caps at the nominal values, I was just brain-dumping.

Thanks again.

[owlsplace]

The wax cap is a foil cap and in all fairness it was probably well within spec during the 5-year warranty period

Roger

[RoyC]

7 hours ago, Kip said:

In my own experience, electrolytic tolerances can be wide, especially at the high end.  For instance, the spec'd upper tolerance of this 20 µF electrolytic is +100%, so it's measured capacitance could be up to 40, even brand new.  Usually not an issue when used to filter ripple out of a power supply, but in a crossover...?.

 

Kip,

However you measured the caps, you do not want 50uf caps for this crossover! Did you measure the caps in or out of circuit? The values you posted are very high even for worn 20uf+/- npe caps. If you did not disconnect them before measuring, you are not getting an accurate reading. I believe you are reading a summed value because they were not disconnected from the circuit

There is no way the AR-4x or any other crossover cap would be spec'd with a 100% tolerance! AR caps were typically 10%. The least expensive speaker crossovers will sometimes include 20% tolerance cheapo caps...but that's it.

Roy

[Kip]

Hello Roy,

Yep, I got it.  I'm going with the 20 and 24 as shown in the schematic Robert posted.  I was just speculating, sorry if I gave the impression I was going to use 50's.

To answer your specific questions: Definitely I measured out of circuit, for sure!  I do have some electronics experience (used to repair stereo equipment years ago) and I understand measuring something in-circuit isn't valid.  All three wires of the wax cap block were disconnected when I did my measurements.  And I have faith in my meter.  So, I believe that for whatever reason (age, tolerance, etc.) that both of the caps in this wax block do have the capacitance that I measured.  Given that they were +/- 10% tolerance, I'd say that over the years they've drifted quite a bit! (But then so have I).

Forgetting all that, I definitely will be using 20 and 24 exactly as shown in the crossover schematic.

Thank you so much for your advice and guidance, and generous sharing of your expertise.

 

[Kip]

6 hours ago, owlsplace said:

The wax cap is a foil cap and in all fairness it was probably well within spec during the 5-year warranty period

Roger

Hey Roger,

When you say "foil" cap, is that something different than an aluminum electrolytic?  I've actually opened up an electrolytic in the past (call it morbid curiosity) and I remember it being a long strip of dielectric sandwiched between two long strips of foil, all rolled up into a cylinder and stuffed into a can.  Are you talking about something different?

-Kip

[Kip]

On 3/24/2016 at 10:04 AM, stupidhead said:

Kip, on the pots there is a lengthy guide here pot refurb guide which will give you step by step instructions if you need them. Basically a salt/vinegar bath followed by thorough rinse and then a polishing. There are times when the components of the pot have degraded to the point of being fubar, some pics once you crack them open will help.

 

OK another surprise: opening up the first pot, looked cleaner than I expected.  I do see a little corrosion, but check out the windings near the CW end.  They seem to be crushed/deformed.  I don't have a clue what may have done that!

[stupidhead]

Kip, did you take pics of the wiring of that pot before extraction? Please post if you did. I have a sneaky suspicion that it (or they from the set) was bypassed. Not sure what happened to that obviously bent coil, but not likely usable.

On the acquisition of OEM tweeters, it would be prudent to find a pair as opposed to singles. I have evaluated probably 10 sets of these and there is often a notable difference in response from set to set, likely from age and usage over their life.

On 3/24/2016 at 1:50 PM, Kip said:

Vinegar and salt? Sounds corrosive   ...wait a minute, I eat that stuff!

Thanks for the reference.  I didn't get the wire nuts part, though.  At first I thought the wire nuts were used to make it easier to disconnect everything the next time.  But the text said they were used to avoid having to solder inside the cabinet "...where there's too many things to ruin with the heat..."  Huh?  There's just air in there at this point, right?  What am I missing?  We used to solder inside speaker cabinets all the time, never did any damage that I know of.

I get what you're saying about the overall corrosion.  I'll post pics when I get it apart.

I'm starting to feel guilty - you guys are giving me more free guidance than I deserve.  Thanks.

On tmad's guide, I suspect the wire nut reference is not worth getting too wrapped up in. There are many considerations in a given project (speaker rehab) such as the openings available to reach in and do your soldering/reconnecting of wiring. Is the xover board mounted in a way it can be extracted and worked on in open space? In the 4's case, the board is typically epoxied down and stapled, often excessive stapling. Re-soldering through the 8" baffle hole is tricky for some, especially when you have ham hands like mine! Wire nut connections are fine just make sure you use the proper nut for the given connection.

Very anxious to see your progress on the woofer repair. Take your time and above all enjoy.

This thread has evolved into a nice one with many tidbits of info for you, and for others in the future.

[owlsplace]

12 hours ago, Kip said:

OK another surprise: opening up the first pot, looked cleaner than I expected.  I do see a little corrosion, but check out the windings near the CW end.  They seem to be crushed/deformed.  I don't have a clue what may have done that!

 

12 hours ago, Kip said:

Hey Roger,

When you say "foil" cap, is that something different than an aluminum electrolytic?  I've actually opened up an electrolytic in the past (call it morbid curiosity) and I remember it being a long strip of dielectric sandwiched between two long strips of foil, all rolled up into a cylinder and stuffed into a can.  Are you talking about something different?

-Kip

Can't say I ever dissected an electrolytic cap but yes the wax caps are foil in a paper dielectric(?) sandwich.

The pot you are showing is one of the better types with the extra tension follower behind the wiper. The deformed coil could have been caused by impact to the wiper shaft. Clean it an put it back together and measure the resistance change while moving the wiper and see how it responds. It may still work properly even with the deformed coil.

Getting matching tweeters may be a challenge as Geoff suggests but at my age I find it hard to tell the difference. I think the only easy way to get matched tweeters would be to buy new replacements and you have indicated a preference for the stock tweeters. The 4x's have a reputation for sounding way better than they should, even in their old age.

Roger

[Kip]

Hi, back again.  I've received so much help here that I feel obligated to post updates.

Woofer repair

I finished the woofer repair - I ended up using coffee filter material and Elmer's white glue.  I tore (rather than cut) out the paper pieces I needed to help taper the edges of the repair, trying to keep the pieces as small as possible.  The repair seems sturdy enough, although I was a bit disappointed with how much stiffer the repair area feels when compared to other, undamaged areas of the cone.  Hopefully I did not alter the physics of the woofer appreciably.  I used a thin smear of ordinary silicone caulk on the torn part of the surround.  That seems quite adequate.

I saw a blurb of a YouTube video of a fellow doing a similar repair, and as his last step he sprayed some flat black paint over the patch "...to restore the look of the woofer...".  I would guess that would've been an oil-based paint like Krylon or Rustoleum.  I opted not to do the same, given that the woofer is ultimately going to have a grill over it and I'm not sure if I care enough about how it looks to risk adding even more "foreign" material to it.

Crossover

Replacing both caps with 5% Poly caps from Parts Express.  Using specified values (20 and 25)

Tweeters

I decided to try a couple of the Parts Express AR-4x "replacement" tweeters and see what they sound like with the original crossover circuit.  Boxing up the Genesis tweeters for now.

Tweeter control

I plan to remove the existing corrosion.  I may be nuts, but after that, I'm going to try to re-form the windings that have been damaged.  Worst case outcome is I might have to replace the control.

A Question

I believe there is supposed to be a sheet of thin fabric just behind the woofer, to prevent dust from the rock wool stuffing from getting into it.  Mine is missing.  I was thinking of using a sheet of cheesecloth...welcoming any opinions on that.

As always, my thanks to all of you who have guided me through this adventure.

 

[JKent]

Quote

I believe there is supposed to be a sheet of thin fabric just behind the woofer, to prevent dust from the rock wool stuffing from getting into it.  Mine is missing.  I was thinking of using a sheet of cheesecloth...welcoming any opinions on that.

That should work. Originally the sheet was Kimpac (paper). KLH used crinoline. Allison used fine fiberglass window screen. Any material that is porous enough to let some air through but not porous enough to let fiberglass bits through should work.

-Kent

[owlsplace]

3 hours ago, Kip said:

....Tweeters

I decided to try a couple of the Parts Express AR-4x "replacement" tweeters and see what they sound like with the original crossover circuit.  Boxing up the Genesis tweeters for now.

Tweeter control

I plan to remove the existing corrosion.  I may be nuts, but after that, I'm going to try to re-form the windings that have been damaged.  Worst case outcome is I might have to replace the control.

A Question

I believe there is supposed to be a sheet of thin fabric just behind the woofer, to prevent dust from the rock wool stuffing from getting into it.  Mine is missing.  I was thinking of using a sheet of cheesecloth...welcoming any opinions on that.

As always, my thanks to all of you who have guided me through this adventure.

Thanks for keeping us entertained

I've used sheer window drape material in place of the Kimpac ... almost free at the thrift.

Reworking the pot sounds feasible. If it doesn't work out for some reason save the wiper parts.

A lot of people are not fond of using the rock wool and opt to replace it with OCF or the Dow(?) small pack fiberglass from Lowe's. Also the synthetic fiber from Parts Express which is non-toxic but quite a bit pricier.

Not sure if Carl finished working up tweeks for the Parts Express tweeters or not. Might be worth the time to PM him.

Roger