Altec Model 15 crossover rebuild questions

[mjcmt]

I have a nice pair of Model 15s. Everything works as it should.

The 12" drivers were re-coned in '91 by GPA.
Cabinets are nice but not perfect with a water stain from a plant and discoloration in a few areas. I will gingerly refinish them to keep that aged patina look. Nothing worse than making them look new in my minds eye.

Now the crossover question!
I'm wondering if rebuilding the x-over will improve the sound, or just leave it alone?
It has a simple x-over w/ 2 inductors, 2 caps, 2 resistors, and 2 pots. Should I just replace the caps, or the inductor coils as well, plus the wire wound ceramic resistors while I'm at it?

What would the value of the unmarked inductors in the x-over be?

Thanks all.

[voice of theatr]

I have a nice pair of Model 15s. Everything works as it should.

The 12" drivers were re-coned in '91 by GPA.
Cabinets are nice but not perfect with a water stain from a plant and discoloration in a few areas. I will gingerly refinish them to keep that aged patina look. Nothing worse than making them look new in my minds eye.

Now the crossover question!
I'm wondering if rebuilding the x-over will improve the sound, or just leave it alone?
It has a simple x-over w/ 2 inductors, 2 caps, 2 resistors, and 2 pots. Should I just replace the caps, or the inductor coils as well, plus the wire wound ceramic resistors while I'm at it?

What would the value of the unmarked inductors in the x-over be?

Thanks all.

Definitely replace those 35 year old capacitors. I recapped the crossovers on my Model 19's and my Model 14's (only a few years newer than your speakers) and the improvement in sound quality was impressive. They are now among the best sounding speakers I've ever heard.

You can also replace the resistors if you wish, but it's not as important as replacing the caps (and I doubt if replacing the resistors will result in any improvement in sound quality). Capacitors values are much more likely to change in 35 years time and can really have a negative impact on overall sound quality. Most likely your resistors are still at their original values, but replacing them while you're in there won't hurt. DO NOT replace the original solid core inductors with newer air core inductors. Those original inductors should be fine and air core inductors will have a totally different sound to them--I know of Model 19 owners who replaced their original solid core inductors with new air core inductors and HATED the sound. They then put the solid core inductors back into the crossovers and the "magic was back"! Just my 2 cents......

[Earl K]

Here's the M15 network , laid-out & simmed, courtesy of Richard C .



- FWIW, I would buy, install & listen to new inductors in the circuit, since both occur on the horn driver circuit ( & these values are inexpensive if you don't like the change ) .

- There is no inductor on the woofer side of the network ( what's seen in this workup are simply approximations of the inductances for the voice-coil of the woofer and the horn-driver ) .

- The woofer in the stock network runs full range .

- FYI, Richard was keen on modifying his M14 networks ( by adding in an inductor, cap, & zobel to the woofer leg of the network ) . This was done to remove excessive "shout" ( as I think he called it ) .
- I believe I would also try this approach with the M15 ( if I had some of these speakers & if I thought they were too aggresive in the midrange ) .

- Here's what Richard ended up with after trying a few things on his M14s ;



<> EarlK

[rgwalker]

DO NOT replace the original solid core inductors with newer air core inductors. Those original inductors should be fine and air core inductors will have a totally different sound to them--I know of Model 19 owners who replaced their original solid core inductors with new air core inductors and HATED the sound. They then put the solid core inductors back into the crossovers and the "magic was back"! Just my 2 cents......

I've used large air core inductors on three Model 19s and one 604E system with excellent results and would like to credit them with the vast improvement in the sound.

[voice of theatr]

I've used large air core inductors on three Model 19s and one 604E system with excellent results and would like to credit them with the vast improvement in the sound.

Everyone has their own preferences--you're the first person I've heard from that switched to air core inductors in their Model 19 crossovers and actually liked the way they sounded. Of course, that doesn't mean you're wrong! BTW, did you do any measurements after switching to the air core inductors to see how it affected the frequency response?

[rgwalker]

Everyone has their own preferences--you're the first person I've heard from that switched to air core inductors in their Model 19 crossovers and actually liked the way they sounded. Of course, that doesn't mean you're wrong! BTW, did you do any measurements after switching to the air core inductors to see how it affected the frequency response?

It's all subjective and the original designers were very smart people. However, IMHO Model 19s are quite harsh and well suited to loud rock & roll with big amps in large rooms. I called them my Led Zeppelin speakers and it scared the cats who otherwise aren't afraid of loud music. The guy that I bought them from was going to put handles and wheels on them and use them as PA speakers for his band. I wanted to keep them and I tried to like them as an all purpose speaker and even used McIntosh tube amps and preamps but my stock Altec 620As with 604-8Gs and 846A Valencias walked all over them for any near field listening and especially playing music at 2:00 AM volume.

I was given the idea by someone here who saw that I wasn't completely happy and he offered the crossover upgrade as a suggestion that he had found successful. He has done a lot of testing with different products and was sold on North Creek air coils.

Perhaps I should point out that mine isn't an apples to apples M19 conversion. It started out with the M19 but by the time that I got around to it I sold them and built a hybrid using the M19 as a model with 620A cabinets. It's a 3 way with Heil ES tweeters, Altec 311-60 horns and Altec 288 drivers sitting on top and only uses the 416-8Bs and the crossovers from the M19s. However, I did run them with the stock M19 crossovers as a two way before changing out the caps and coils (using stock values) and adding the tweeter. It wasn't a subtle difference and the soundstage became much more apparent (for lack of better words) and almost 3D like and it made listening to all music much more enjoyable with absolutley no fatigue regardless of high volume. Every so often I hear things and I'll get doubts but I'll put on a few recordings that I use as benchmarks and all of my original opinions and feelings are affirmed.

I'm good with a soldering iron and can follow a chart to make things but I'm not technically well versed so I can't give you specs or comment on response and frequency etc and my room is difficult but after 3 years I still really enjoy the system. My opinion is purely subjective and I won't claim that using the big coils is technically better but it certainly isn't a failure and I'll never consider switching back to stock.

I've also used the North Creek coils on a pair of Jeff Markwart 604E crossovers and I love the result.

[voice of theatr]

It's all subjective and the original designers were very smart people. However, IMHO Model 19s are quite harsh and well suited to loud rock & roll with big amps in large rooms. I called them my Led Zeppelin speakers......

I'm wondering if there was something wrong with the drivers and/or h.f. diaphragms in your Model 19's. I own two mint pair and both pair sound considerably better to me than my 846 A Valencias ever did or my Heathkit AS 101's (same drivers as 846B). They put out 100 db with one watt of input power so I couldn't disagree more with your statement that they're suited to big amps and large rooms. In fact, a big amp can be very bad for them/very dangerous for them. Yes, they can fill a large room, but I have one pair in a relatively small room and don't usually put more than a watt through them and they sound great--even at very low volumes. They sound great with all styles of music, not just Led Zappelin--strings, piano, classical guitar recordings, brass, full orchestra recordings sound amazing on mine. There is a ground modification that needs to be done on all Model 19 crossovers now that they're 30 + years old for optimum sound performance--the ground lugs in the crossovers aren't connected to each other/grounded via solder connection--they are connected by a mechanical (rivet) connection which with age is not a good connection. After I recapped my Model 19's with the Solens, cleaned the pots/L Pads, corrected the inadequate ground connections, they had clearer highs, mids, and more bass than ever (the Solens did not make them more harsh or give them less bass). If I had to make a guess, I'd say from your description you either had the later version of the Model 19's that didn't come with the light diaphragms that the early ones did, or someone replaced your hf diaphragms with replacement Altec (or non Altec) diaphragms. The light diaphragms that the early Model 19's came with had a really different character to them than the Altec diaphragms that replaced them--they had a very open and airy sound which from your description your 19's didn't have.......

Another possible explanation comes from this quote

The guy that I bought them from was going to put handles and wheels on them and use them as PA speakers for his band.

He may have blasted those things so loud (if he wanted to use 19's for PA he didn't understand how they should be treated) that the drivers weren't in optimal condition and didn't sound good at low volumes any more (or at any volume)....

Perhaps I should point out that mine isn't an apples to apples M19 conversion. It started out with the M19 but by the time that I got around to it I sold them and built a hybrid using the M19 as a model with 620A cabinets. It's a 3 way with Heil ES tweeters, Altec 311-60 horns and Altec 288 drivers sitting on top and only uses the 416-8Bs and the crossovers from the M19s. However, I did run them with the stock M19 crossovers as a two way before changing out the caps and coils (using stock values) and adding the tweeter. It wasn't a subtle difference and the soundstage became much more apparent (for lack of better words) and almost 3D like and it made listening to all music much more enjoyable with absolutley no fatigue regardless of high volume. Every so often I hear things and I'll get doubts but I'll put on a few recordings that I use as benchmarks and all of my original opinions and feelings are affirmed.

I'm glad you mentioned this--it explains a lot. The Model 19 crossover is different than the older Altec crossovers (even ones from a year or two before the 19 was introduced). For one, it has very specific EQ compensation specifially designed for use with the 802-8G/811B horn combo. If you used them with 288 drivers and 311-60 horns you had the wrong drivers and horns for that crossover design. It's no wonder you needed to do crossover mods and add a tweeter etc.--the 288 doesn't have anywhere near the upper frequency extension that the 802-8G (tangerine phase plug) has......

Bottom line, I'm glad the new inductors allowed your crossovers to sound good with your system--288's, 311-60's, tweeter, etc.--that's all that really matters--your system now sounds great! As you mentioned, it's an apples and oranges comparison because your modified crossovers will sound really different used in Model 19's than they will with your (totally different) h.f. driver, horn, and tweeter combination.

By the way, I agree--always save the old caps. If they are still at their original values, they will have a different character than other types of caps and you may prefer them--it's always possible. Also, if you sell your Model 15's some day, it's nice to let the buyer know that even though you upgraded the caps, you'll be including the originals as well so he'll have all the original stock parts--even the original caps......

[mjcmt]

I'm curious as to what compression driver my M-15's have. I've read it is an 802. The driver is stamped 391727 and the paper label says 27-03-033952. I also read someone selling A7-500-II with the same driver stamping and he said it is a 802D. What do I have?

Thanks

[mjcmt]

Thanks for the reply.

voice of theatr,
OK the caps must go. Is a basic Solen Fast Cap adequate?
I see that Mundorf has metal oxide film resistors as well as M-Resist Supreme resistors. What do you think?
The Model 15s use air core inductors, the style that has the solid core wire rapped on a white plastic bobbin. Should I keep these?

Earl K,
I'm not quite sure I understand the x-over w/ the woofer and horn labeling? Are these the original x-over parts?

[Earl K]

Lots of people are really happy with Solens' Fast Caps ( I use them with Altec 288-8Ks ).

Since you've pointed out that the stock coils are already air-core / I'd leave them as is .

<> EarlK


EDIT :

I'm not quite sure I understand the x-over w/ the woofer and horn labeling? Are these the original x-over parts?

- Ignore all the values within the hand-drawn circles that say "WOOFER" & "HORN" ( they are standin values , necessary so that Richards' sim software "works" > it needs a virtual load , comparable to the real transducers to run the simulated voltage drives ) .

- The other 2 smaller circles ( are simple potentiometers ). The values noted represent the measured resistance from those "pots" ( after Richard dialed in the "mids" & "highs" to be "optimal" for his tastes) .

- The rest of the values represent the network according to Richard C ( he bought a pair from eBay about 10 years back & reverse-engineered one to arrive at what you see here ) .

[voice of theatr]

Thanks for the reply.

voice of theatr,
OK the caps must go. Is a basic Solen Fast Cap adequate?
I see that Mundorf has metal oxide film resistors as well as M-Resist Supreme resistors. What do you think?
The Model 15s use air core inductors, the style that has the solid core wire rapped on a white plastic bobbin. Should I keep these?

Earl K,
I'm not quite sure I understand the x-over w/ the woofer and horn labeling? Are these the original x-over parts?

I used the Solen Fast Caps for my Model 14 and Model 19 crossovers and was amazed by the improvement in sound quality. They were originally recommended to me by Bill at Great Plains Audio--he really knows his stuff! I know some people swear by expensive boutique caps or paper in oil--I've never used those in recapping projects so I can't comment on how they compare to the Solens. To be more specific about the Solens, there was noticeable increased overall clarity after installing them, and the h.f. seemed to roll off at a higher frequency as well--no more need on either pair of speakers to add EQ at (or above) 16k (both the 14's and 19's have the tangerine phase plugs like your 15's do/usable frequency response to 20 khz).

BTW, I've never owned a pair of Model 15's--thanks for all the great info Earl! I would agree with Earl--leave the inductors alone......

[Altec Best]

OK the caps must go. Is a basic Solen Fast Cap adequate?
I see that Mundorf has metal oxide film resistors as well as M-Resist Supreme resistors. What do you think?

More than adequate and inexpensive ! Don't waste your money on Boutique caps that are very expensive for very little difference ! Solens,Daytons,Sonicaps all good enough ! I use Solen myself they sounded best to me.Though YMMV

[mjcmt]

Looks like this thread has been hijacked from my Model 15 x-over rebuild to Model 19, Altec drivers and the like. Though somewhat interesting, I keep looking for replies to my post only to have to read through other replies to find appropriate answers.

[voice of theatr]

Looks like this thread has been hijacked from my Model 15 x-over rebuild to Model 19, Altec drivers and the like. Though somewhat interesting, I keep looking for replies to my post only to have to read through other replies to find appropriate answers.

Guilty as charged! Sorry about that. Your thread did get sidetracked--went off on a tangent that began with your Model 15 inductors and then went into inductor/Model 19 discussion. When someone says Model 19's are suited for big powerful amplifiers etc., I can't reach for my keyboard quick enough...... A thousand pardons, please!

I planned on keeping them, mostly to have available if I ever sell these speakers.
I do have one question, are the new Solen caps I've ordered directional? If so what must I be aware of?

OK, back to your thread! The Solen fast caps are NOT directional. No need to worry about orientation/which end of the capacitor to hook up where......

Voice of Theater's post #19 made a good point about the eq circuitry in the 19. The M15 also has some high freq eq to compensate for the rolloff of the 802-8G and (perhaps) in the 32B horn. When I tried a pair of M15 xovers, I found the eq to be helpful but not entirely satisfactory. I later got a pair of 9849 xovers which were also designed for the 802-8G and 32B horn, and the eq circuit in that xover is really good. My 802s no longer sound rolled off on the very top; they are fully extended to my ears. If you're interested in trying the 9849 circuit, send me an email and I'll send a schematic.

Thanks, Yes I make a good point once in a while! That time frame (introduction of the MODEL 15 and 19) was a turning point with the Altec crossovers. The high freq eq compensation was excellent in those and many Altec crossovers that followed (like the Model 14 crossover--I own a pair of those as well) and really did help the h.f. extension of the h.f. driver/horn combination.

[DavidF]

Looks like this thread has been hijacked from my Model 15 x-over rebuild to Model 19, Altec drivers and the like. Though somewhat interesting, I keep looking for replies to my post only to have to read through other replies to find appropriate answers.

A lesson perhaps. Sometimes it all starts with "maybe I'll just upgrade the caps".

I would recommend some contact cleaner treatment on the L Pads for the mid and highs. Those are good source of grunge collection over time. Squirt some cleaner in cases and give them several lock-to-lock spins. Easier to get to them with them on the bench.