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Dynaco A25 Musings

Speaking of opinion- I have to defend the 27TFFC tweeter here, that's listed as the "recommended replacement".

I've heard the metal dome and fabric dome SEAS tweeters... and the 27TFFC, IMHO, BY FAR is the winner. Much less artifacts (resonant peaks), and a better blend with woofers in a 2-way situation with a low crossover point than any SEAS short of the mighty Excel tweeter.

Don't let the plots fool you... that tweeter does FAR more than it looks like...

Regards,
Gordon.
 
I've recapped a set of A25s and my A25XLs both with solid results. One thing folks might not realize is that the old electrolytic caps develop resistance and choke off the signal to the tweeter, and prevents it from doing its proper job. Like Glenn alluded to earlier, if you don't have bad tweeters, go ahead and recap them first; it's like a $10 or less tweak.

The other issue is that the caps were different in my speakers. It's kinda funny about how many folks say the XL: is basically the A25 with a different tweeter in a tweaked box that's 3 dB more efficient, but when I opened mine I found a different woofer, different tweeter, an 8 uf cap, not a 5 uf cap, so a different crossover, in a different box with a different level control.

They both sound nice and very similar, but so much for the "same" speaker.
I'm keeping mine though. Well at least for now :D
 
Ken/Urizen brought a pair of A25's to the fest that had a natural, inviting SQ. As memory serves, he replaced the stock tweeter with (now discontinued) Morel models and upgraded the crossover caps, which included adding bypass caps.
 
"they haven't come close to changing my opinion that modern speakers kick the snot out of 98% of the stuff built before 1980"

Would you include the AR-3a, AR-5, and AR LST in that statement? Because in terms of my own personal preference with the treble bumped up a notch the ARs beat any modern speaker I have heard in terms of natural reproduction of the frequency spectrum. And I suspect the same would be true of high end Klipsche, JBL or Altecs as well though I haven't heard any of those yet.
 
Celt said:
Ken/Urizen brought a pair of A25's to the fest that had a natural, inviting SQ. As memory serves, he replaced the stock tweeter with (now discontinued) Morel models and upgraded the crossover caps, which included adding bypass caps.
Click to expand...

Dan, with those speakers, now owned by jaymanaa, I installed Morel MDT-20 (the same tweeter used in RayW's infamous "Bobs") and Dayton 5.1uF metalized 1% polypropylene caps without bypass caps. They did sound mighty smooth on Mr. Manaa's ST-35 super-clone amp.:yes:

AK Fest 2009:

IMG_0650_edited.jpg
 
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I own a pair of dusty pair of A-25’s waiting an upgrade and a chance to show their stuff.

A couple of weeks ago I read a thread with the xcross topology posted, showing the resister values. Personally once mine are opened up, along with the cap I thinking better resisters. After some extended listening, and the favourite tweeter setting is known, I may remove the pot all together.

With the pot out of the way, an upgrade in terminals is possible.

I would love to replace the grill cloth, but have not been able to locate a duplicate. Other then a fabric shop clone, do you fellows have any ideas?
 
jn229 said:
After some extended listening, and the favourite tweeter setting is known, I may remove the pot all together.

Other then a fabric shop clone, do you fellows have any ideas?
Click to expand...

I'm sure better resistor would be of benefit, however, I found the adjustable tweeter settings useful with different amps and recordings. Although not of the highest quality or gold-plated, the Dynaco's 5-way binding posts are more than adequate, and a surprising feature given their low cost "back in the day".

The fabric I used, an open weave off-white "burlap", came from Joann Fabrics, and I could hear no difference with the grills on or off.
 
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Urizen said:
The fabric I used, an open weave off-white "burlap", came from Joann Fabrics, and I could hear no difference with the grills on or off.
Click to expand...

Thanks for the fabric info.

As for the pots and terminals: I was thinking out loud with the idea of pushing these diamonds from the past to the max, without modifying them to the point where they are not a reflection of themselves.
 
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Crossover bypass cap question

I thought I would add this here rather than starting another thread.....

I was curious about this when I did these. Does the C2 bypass cap need to be connected between C1 and the + speaker wire or can it also be connected where the red X is in parallel with C1?

thanks,
mark

schematic-1.jpg
 
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Those "tiny" magnets on the original Seas woofer are alnico.
Alnico magnets are almost always correspondingly smaller than the (now) much more common ferrite magnets.


Steve
 
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