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Dynaco A-25 model?

Not a problem it is just a lug. Resolder it or replace with a small lug and wire




As this is my first time to open a set of speakers of course I managed to break something :) ... the flat brass connector to the negative terminal. Is this some kind of fuse? I don't suppose you can solder it together? I hope I haven't screwed things up! Thanks for any help.

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That brass thing is only a physical support for the wires.Can be found in other Dynacos too.
Now,to the interesting part!Your crossover is different from the standard A25.Not only do the resistors have different values,but there are other differences too.We need your help with this to be able to draw the new schematic.
What are the values of all 5 resistors?
There's a extra resistor in series with the 1.2uF cap.What value?
 
Rolf Zetterberg said:
That brass thing is only a physical support for the wires.Can be found in other Dynacos too.
Now,to the interesting part!Your crossover is different from the standard A25.Not only do the resistors have different values,but there are other differences too.We need your help with this to be able to draw the new schematic.
What are the values of all 5 resistors?
There's a extra resistor in series with the 1.2uF cap.What value?
Click to expand...

Hi Rolf, hope this helps... what wattage values are these?

A-25%20Crossover%20Values.jpg
 
This is such a cool find! Thanks for showing off the guts. Of course it's difficult to improve upon the original stock A25. I hope you enjoy what you hear.
 
Thank you,Bruce!
The resistors seem to be 3W types,possibly with the exception of the 10 Ohms resistor lowest in the resistor chain,which sometimes is 10W.
Then we have a schematic(please do correct me if I'm wrong):
 

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Yes,I was wondering about that too.
Are you thinking about output or impedance?
The output will be higher than the standard A25,but since the extra tweeter has a 10 Ohm resistor in series and only a small 1,2uF cap,it's contribution will not be that much and only at higher frequencies(maybe that's the whole idea??)
The impedance won't change much due to the resistor's rather high value.
And the tricky bit- as far as I can see,the switch is in normal position and the lug far left is "common".So they must be paralled(I'm assuming the red thick wire is woofer,the red thin wire is the extra tweeter,and the blue wire is the dome)
Or?
 
no, I thought it may be added turning the swich or be switchable. This is too simple :)
My intention would be having in normal position the normal set of speakers and rising the tweeter control adding the super tweeter in 2 or 3 steps :)

bhamham should add marks to where the wires lead.

They gave the A-25xl the other tweeter because of the H87 lack of high range. Maybe this was something in between...
 
Is this a rational A-25 upgrade today?

Are those supertweets or their equivalents still available?

[I'd sure want to work with mirror-imaged pairs, tho.... :yes: ]
 
Larry,I agree with you that they do look new or replaced,but those screws-actually screw and washer being one unity-are original.I have them in my later pair of Scan Dyna A25s and have seen them in other A25s and also in Seas boxes.
Zilch,probably not,since by replacing the dome tweeter with a more modern,you'll probably get a similar result.On the other hand-why wreck a beautiful old VW by throwing in an automatic gearbox?
No,keep them original as much as possible!
If I'll ever find the time,I would like to build one like this and listen.Easily done,really, since I have a pair of DIY A25s(not by me) that could be converted.
The 5TV-HF tweeters are not available any more(they were in 2005 I believe),but they are quite easily found at least here in Scandinavia.
 
Dynacophil said:
bhamham should add marks to where the wires lead.
Click to expand...

Hi Dynacophil, the small red wire goes to the 5TV-HF and the large red wire to the H336. The shielded blue wire to the 87H dome tweeter (sorry, don't know how to add color to arrows in Irfanview)

A-25%20Crossover%20Values.jpg


Thanks Rolf for the schematic - very good!

Just curious what anyone would do with these? The larger resistors are out of spec 20% - at 8R - the smaller 3.9s are about 10% out but the 4.7s are good. The caps seem OK. Would you replace these out of spec componets? Or, all of them? I thought I would use contact cleaner on the switch being careful with the wafer material. The sound was very nice listening to them for a couple of days. I use a pair of Klipsh KG4.5 and the A-25's mids & highs were more present. Bass wasn't earth moving but more natural, very nice with acoustical pieces - sorry, not very good at sound criticism.
 
Zilch said:
Is this a rational A-25 upgrade today?

Are those supertweets or their equivalents still available?

[I'd sure want to work with mirror-imaged pairs, tho.... :yes: ]
Click to expand...

Yes it's an entirely rational and worthwhile upgrade, and I can report that mirror-imaged baffles and good bracing are large upgrades as well. After being in and out of mine a few times I'd recommend using a decent copper binding post (I used Pomona), good quality capacitors (I used Obbligato), and good quality wire. There are so few caps it doesn't hurt to use high grade ones.

The super tweeter here is the Vifa D25AG, operating above 14kHz or so. After trying out a handful of crossover points and choosing one by ear, Dennis Murphy helped out with a plot and confirmed my choices. Lucky me!

These speakers are the "after" picture obviously. I had to build new cabinets because the existing ones were beyond repair and had no potential for WAF. Calculating for some bracing these cabinets are the same volume but slightly different dimensions than the original, in order to fit the Vifas on the baffle. The aperiodic vents are at the rear. Cherry and veneered MDF. They sound wonderful, replacing a well regarded pair of ACI Sapphire III LE speakers.

Jim
 

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dean man jim said:
These speakers are the "after" picture obviously. I had to build new cabinets because the existing ones were beyond repair and had no potential for WAF. Calculating for some bracing these cabinets are the same volume but slightly different dimensions than the original, in order to fit the Vifas on the baffle. The aperiodic vents are at the rear. Cherry and veneered MDF. They sound wonderful, replacing a well regarded pair of ACI Sapphire III LE speakers.

Jim
Click to expand...

Wow! Those are lovely! Would you have any pics of the insides to share? Crossover? I bet they sound superb! Really nice gear too.
 
bhamham said:
Wow! Those are lovely! Would you have any pics of the insides to share? Crossover? I bet they sound superb! Really nice gear too.
Click to expand...

Thanks very much! I've been using them this way for 18 months now, following a few months of experimentation after digging them out of the trash. I'm sorry that I don't have any pics of the insides, but here is a "before" photo when I was experimenting with crossover values for the supertweeter. I used FM signals in the experiments (hence the restored Marantz receiver that I brought in from another system, and the felt rings), the lowest crossover point that resulted in my not being able to hear the Vifas on FM is the one I chose.

In any event the Obbligato capacitors are the third set I've put in them. The first recap was with inexpensive NPE capacitors, the second was inexpensive Solen film capacitors, currently I have the Obbligatos in there. The Obbligatos are worth it IMHO, you might also consider ClarityCap?

If I were you I'd skip over the NPE and cheap film caps if I were to recap, and get come good ones. Simply replace the existing two capacitors in each speaker with those of the the same values and report what you hear! I think the weakest spot of the stock cabinets is on the baffle between the woofer and tweeter, it would be worth installing a brace of one kind or another there I think.

Hope this helps a little bit.

Jim
 

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Never seen that driver in an A25 before! Must be pretty rare, and it's even better you managed to find a scan of the advert.

I had a pair of Scandinavian made Sonys of a similar vintage with that exact same tweeter in it. These were a 2 way with a Seas AlNiCo 8" woofer.
 
dean man jim said:
Hope this helps a little bit.

Jim
Click to expand...

Is that the original Seas tweeter in the cabinet, and is that a felt ring around it? If so, did the ring make an improvement? It looks like a good cheap mod.

I actually like the original A-25 tweeter. I know a lot of guys upgrade it to a modern tweet, but I don't find my A-25's lacking detail or air. I think the old Seas tweet is one of the best tweeters I have personally owned. It blows away the popular Peerless tweeter used in Polk speakers. To my ears anyway.
 
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