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

[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]

OK, Solen it will be great. I think before a complete x-over redesign I will replace caps and rewire. I have Carol Cable 14 awg 2C architectural in-wall speaker cable I am using for speaker wire (mostly because it fit in the Altecs binding post w/ out using pins on better cable). Should I rewire the inside with this too, or get something more audiophile?

[mjcmt]

I pulled the Model 15 x-over. It uses one 3uf - 75v and one 8uf - 75v cap.

Can I replace the 3uf - 75v with a Solen PP cap 3.0uf - 400v?

Should I replace the 8uf exactly? I will have to use a 3.3uf & 4.7uf in parallel (I'm guessing?) to equal 8uf. Both are 400v Solen PP caps.
Or can come close and use a 8.2uf or 7.5uf that are available.

Caps are from Parts Express.
Thanks

[Earl K]

Can I replace the 3uf - 75v with a Solen PP cap 3.0uf - 400v?

Should I replace the 8uf exactly? I will have to use a 3.3uf & 4.7uf in parallel (I'm guessing?) to equal 8uf. Both are 400v Solen PP caps.
Or can come close and use a 8.2uf or 7.5uf that are available.

> Using the higher voltage rating ( 400v ) is not a problem .

> 8.2uF is your better choice ( plus you save a couple of bucks compared to the combo choice ) .

<> EarlK

[mjcmt]

I see that Madisound has the Solen PP 3.0uf and 8.0uf with cheaper shipping. I think I will buy from them.

[voice of theatr]

I see that Madisound has the Solen PP 3.0uf and 8.0uf with cheaper shipping. I think I will buy from them.

When I recapped my Model 14's and Model 19's I used all exact values (Solens). I noticed at the time that Madisound carried some values (of Solens) that Parts Express didn't carry, and Parts Express had some values (of Solens) that Madisound didn't carry. I actually called Solen (found their number online) and they said they make custom values for companies like Parts Express and Madisound since they order 1,000's of capacitors at a time. Anyways, to get all the exact values I needed I had to order from both companies (and pay two shipping charges) but it was well worth it for the end result. It was the least amount of money I've ever paid for a significant upgrade in sound (and it upgraded TWO pair of speakers)......

P.S. To replace the highest value capacitor needed for the Model 19's I did have to combine two lower value capacitors (to get the exact value).....

[mjcmt]

I actually called Solen (found their number online) and they said they make custom values for companies like Parts Express and Madisound since they order 1,000's of capacitors at a time. Anyways, to get all the exact values I needed I had to order from both companies (and pay two shipping charges) but it was well worth it for the end result.

The Solen website shows 3 uf and 8.2 uf, but no 8 uf. I therefore deduced that the 8 uf that Madisound carried was custom made by Solen for them because it is a common x-over value.

I was pleased that I only had to shop Madisound. I have bought speaker drivers and components from them to build 4 DIY speakers in the past 15 years, and was glad to give them my business again.

I'm excited at the improvement in sound I will achieve and want to thank you all. I will keep you posted.

[voice of theatr]

.....I'm excited at the improvement in sound I will achieve and want to thank you all. I will keep you posted.

Depending on how bad your old caps are (and they're likely not at their best after 35 years) there will most likely be a noticeable improvement in sound. Please let us know. Before and after photos of the crossovers are always nice to see as well! BTW, while you're in there, I recommend a thorough cleaning of the pots/L Pads with Deoxit and also check all the solder connections including ground connections......

[Salectric]

When you replace the caps in your M15 crossover, be careful not to damage the old caps when you remove them and do not throw them away. In my experience, those old non-polar caps sound very good, and you may just find that the speakers don't sound as good with the new and "improved" caps as they did before. Modern caps like the Solens will sound faster and more extended in the highs, but they also can sound thin and lean in the midrange and midbass.