M14s: I may have a pair

[Alien_Shore]

Thanks for the pics, VOTT.
I spent a bit of time looking around on the web today, and I think you probably have original cones. I suspect mine are replacements, and probably not GPA. As far as the DCR on the one woofer being low, I agree it is concerning. I may give Bill H a call and see what he wants to just recone them, since the wierd DCR probably indicates a problem with the VC.

I did some further inspection tonight, looking at the HF drivers, and the crossovers. Here are some more pics:

I think this is the 902 8A?


Here you can see the loading cap is cracked. It had a bad bolt on it, which was overtightened




Phase plug on this one is still glued down tight


But VC and phram look fine...looks like the original lightweight ones


The crossover unit looks like it needs some work. I suspect those caps are not what they used to be after 33 years...


A fun project to fix these up and get them in like-new listening shape!

[voice of the theater]

Thanks for the pics, VOTT.
I spent a bit of time looking around on the web today, and I think you probably have original cones. I suspect mine are replacements, and probably not GPA. As far as the DCR on the one woofer being low, I agree it is concerning. I may give Bill H a call and see what he wants to just recone them, since the wierd DCR probably indicates a problem with the VC.

I agree-mine look like an original Altec cone number (format). Well worth having GPA re-cone yours. They'll be as good as new/up to original Altec spec.

But VC and phram look fine...looks like the original lightweight ones

Those do look like the original diaphragms--same original diaphragms that my 902-8A's came with. They are 34647 diaphragms, not the lightweight ones.

The crossover unit looks like it needs some work. I suspect those caps are not what they used to be after 33 years...

I would definitely re-cap the crossovers. I did mine with Solen "fast caps" (recommended by GPA) and they dramatically improved the sound quality..... Somewhere on this forum there is a thread about my Model 14 crossover recap--with pics, etc.....

[Alien_Shore]

Those do look like the original diaphragms--same original diaphragms that my 902-8A's came with. They are 34647 diaphragms, not the lightweight ones. I would definitely re-cap the crossovers. I did mine with Solen "fast caps" (recommended by GPA) and they dramatically improved the sound quality..... Somewhere on this forum there is a thread about my Model 14 crossover recap--with pics, etc.....

I'm curious, what is the part number for those "lightweight" frams? All the doc that I can find only mentions 34647 as the replacement part for 902s...

Also, has anyone done an A/B compare of the GPA 902 and the 902 with the original lightweight fram?

[voice of the theater]

I'm curious, what is the part number for those "lightweight" frams? All the doc that I can find only mentions 34647 as the replacement part for 902s...

Also, has anyone done an A/B compare of the GPA 902 and the 902 with the original lightweight fram?

The vast majority of 902-8A's were originally equipped with Altec 34647 diaphragms. That was the original "stock" part for those drivers. It's the same 34647 diaphragm that GPA manufactures today. So your drivers do appear to have their original diaphragms still installed (same as mine). From what I've heard, some of the very first 902-8A's may have come with the "light" diaphragm that was the "stock" diaphragm for the 802-8G drivers. That was an Altec 23744 diaphragm.

[Alien_Shore]

I've been busy with a bunch of other stuff, but here's a teaser of my messy desk. My Model-14 refurb project is still alive.

[Alien_Shore]

OK, the first prototype is complete.



This is a modified version of the Richard C Model 14 crossover with zobel on the LF side.

Gonna go upstairs and do an A/B comparison to the stock XO.

[Alien_Shore]

XO test #1

Here we are in the home gym / entertainment place...
A/B comparison:


The XO test rig:


Results:
Epic fail. The fatigued, 33 year old stock crossover sounds better.
The new crossover is very flat. It does have a great crossover point and smoother mids, but lacks the definition and punch at the low end and nice sparkling highs of the stock XO.
So much for outsmarting the smart guys, eh? So it's back to the drawing board. I've never used the copper foil coils before, maybe this has something to do with it.
Next step might be to emulate the stock with all new parts and see how that sounds.

[cradeldorf]

If your bored you could always try what I did, a simple 1st order crossover. I'm so happy with how my speakers sound now I could just...poop.

[voice of the theater]

Results:
Epic fail. The fatigued, 33 year old stock crossover sounds better.
The new crossover is very flat. It does have a great crossover point and smoother mids, but lacks the definition and punch at the low end and nice sparkling highs of the stock XO.
So much for outsmarting the smart guys, eh? So it's back to the drawing board. I've never used the copper foil coils before, maybe this has something to do with it.
Next step might be to emulate the stock with all new parts and see how that sounds.

Personally, I'm not surprised that the original crossovers beat out attempts to "best" them. Once I re-capped my Model 14 Crossovers with Solen "fast caps" I was blown away by the sound of those 14's. There's a thread here somewhere about my recap......

[Altec Best]

That's why I always continue to use the original coils/inductors that came with Altecs crossovers, and just replace the old caps and resistors.Clean the pots/L-pads and move on to the next project... Replacing the old caps that are 25-30+ years old really makes a huge difference IMO & experiences... And is really all that is needed.It's been 30 years since these old classics have been manufactured thereabouts and in that time there has really been no magic bullet of a crossover tweak (Passive) so to speak.And for good reason most of Altecs good crossovers Model 19/604H's were top notch designs.Of course there are exceptions that weren't so good.But for the most part just replacing the caps is all you really need to do IMHO.