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Triumph then Disaster (Mission Argonaut 780MkII)

J

jazzspeakEZ

New Member
I had hoped my first post on the Audiokarma forums after being a long time lurker would be triumphant, but what follows is a tale of Sisyphean disappointment.

I picked up a pair of Mission Argonaut 780MKII tower speakers via the Facebook for sale section for $70. He didn't know the model number or have any idea what he had, but I was able to figure it out based on the pictures--he got them at an estate sale and likely didn't have anything to drive them. I picked them up, brought them home, and they were in excellent shape--no damage to the cabinets a good buffing wouldn't mask, grills were mostly intact, foam, you name it. The tweeters had been replaced when I got them, which from the research I've done is a pretty common issue, but they sounded excellent, if a little light on the high end (which I had read, also--but then my main speakers have a tweeter and a super tweeter). I had gotten home late, so I left them in the living room of my shared apartment.

And the next day, one of my soon-to-be-former roommates struck. (He downs, on average, a fifth of Evan Williams a day, and wasn't allowed to renew his lease by the landlord because he played his awful, awful music on a pair of Bose computer speakers far too loudly, a fact that was far too poetic to leave out.) I can't say for sure what he did, but one tweeter is completely blown--I heard it the second I put a signal through them.

I'd picked up some good deals before--a pair of Ohm Model Ls for $30 at Sally's, a pair of Infinity bookshelf speakers (I've forgotten the model now) that I gifted to my father, which I picked up for $20, but I was really proud of this acquisition. I have the know-how to replace the tweeter myself, but I'm at a complete loss as to how to find a suitable replacement. And so I come to you, netizens of AK, in my time of need. Does such a thing as a suitable replacement for an Argonaut 780mkII (so the later, 1986-87 model) tweeter exist, and where might I find one?

Thanks guys--happy to no longer be nameless.

JSE

Edit: And in the meantime, given that the MKIIs have a passive crossover, is there any compelling reason not to wire the Argonauts' LF in series with the Ohms for a full range?
 
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I found a thread by a fellow who had contacted Mission about replacement tweets and they claimed to have them in stock - for $300. I could not determine from his post whether that was for a pair or for one.

Personally, I'm cheap. I have to be. So, in a situation like yours, I'd be trying to find the specifications on the Mission tweeter and finding a close match on Parts Express. I'd remove the motor from the Mission waveguide and attach a new dome to it. Perfect? Not even. But there is also the chance that you may actually improve the tepid performance you've heard from the stock tweeters.

As to your roommate, check CL for ads titled, "Dirty Deeds Done Dirt Cheap."

By the way, welcome to AK. Fellows with erudite language skills are always welcome. Complete sentences with proper spelling is quite a thrill nowadays.

GeeDeeEmm
 
Welcome to AK. :hug: I think? Your 1st post brings me pain! Reason being, I was given a pair of Argonaut 780MKII tower speakers, that were missing a woofer from each speaker. For whatever reason, someone had stolen a set of the woofers. So, I got them for free, and promptly put them in storage. While in storage, another someone broke into my unit, and stole a bunch of stuff, including my Argonaut speakers! I never even got to hear them. :eek:

As to your tweeter problems, that sucks! It sounds like that room mate needed to go. :rant: In looking around the net, nothing on eBay, as far as tweeters are concerned. But, I seem to remember that the same horn loaded tweeter was used in a smaller 2-way as well. So, maybe something will eventually pop up at auction? Also, when Stereophile reviewed the speakers, they mentioned that the tweeters were built by Vifa. Maybe contact them, to see if they have a modern equivalent? :dunno:

Good luck! :banana:
 
GDM,​

Thanks for the welcome aboard. I'd considered contacting Mission, but expected to run into that very issue. Problem is, I'm not entirely sure what the specs of the stock tweeters are. The replacements aren't originals--the face plate size is different-- and so far I've only been able to find the manual to the earlier 780, not the MKII.

I got into HiFi after playing bass for years--I often have a difficult time adjusting my perspective with things like this. (In fact, I bought my gigging bass cabinet with the goal of no tweeter, and have ripped out tweeters on guitar and bass cabs but never replaced one on a bass cab.)
 
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StimpyWan said:
Welcome to AK. :hug: I think? Your 1st post brings me pain! Reason being, I was given a pair of Argonaut 780MKII tower speakers, that were missing a woofer from each speaker. For whatever reason, someone had stolen a set of the woofers. So, I got them for free, and promptly put them in storage. While in storage, another someone broke into my unit, and stole a bunch of stuff, including my Argonaut speakers! I never even got to hear them. :eek:

As to your tweeter problems, that sucks! It sounds like that room mate needed to go. :rant: In looking around the net, nothing on eBay, as far as tweeters are concerned. But, I seem to remember that the same horn loaded tweeter was used in a smaller 2-way as well. So, maybe something will eventually pop up at auction? Also, when Stereophile reviewed the speakers, they mentioned that the tweeters were built by Vifa. Maybe contact them, to see if they have a modern equivalent? :dunno:

Good luck! :banana:
Click to expand...

You are correct-- I thought I'd seen something about the tweeter manufacturer somewhere, and that was it. They're produced by Tymphany now, it seems, as "Peerless by Tymphany," so perhaps if I send them an email they'll have a reasonable solution.

The goal is ultimately to spend as little as I can while allowing the speakers to at least approach their potential. But then isn't it always.

JSE
 
Assuming the tweeter is blown electrically (in other words, if your roommate didn't put out a cigarette on it) then you might not be completely out of luck. More than one AK member has been able to repair a tweeter by carefully disassembling it, unwinding one revolution of wire from the voice coil, then resoldering (assuming that the coil failed on the outermost winding). Search this forum for "tweeter repair" for much better descriptions, some with pictures.
 
jazzspeakEZ Welcome to AK. Sorry to hear about what happened to the Argonauts. Checked oaktreevintage.com nothing on the Argonauts. Have737Rs. Wonder if the crossovers were damaged? Best way to check is to measure across the tweeter terminals to see if the tweeter is open.
 
Update: as it turns out, the tweeters had been replaced with a set of these piezo tweeters from RadioShack. The copper film that had been adhered (epoxied?) on was visibly split-- but I think it's probably safe to move in the direction of replacing them rather than attempting to repair it (if it's even possible on piezo tweeters).

gdmoore28 said:
I'd take a look at something like the Tympani OC25SC65-04 https://www.parts-express.com/pedocs/specs/264-1018--tymphany-oc25sc65-04-spec-sheet.pdf Replacing your current dome with one of these from the same family might prove to be the bee's knees.

Better yet, call Tympani direct and ask for their recommendation.

GeeDeeEmm
Click to expand...

That's an excellent suggestion. Now the problem is that the tweeter used to replace it included a different sized horn faceplate (the replacement is 2")--any ideas on how I might handle the issue of mounting new tweeters?

JSE

EDIT: I had a terminology mixup--I hadn't given enough consideration to what exactly a "waveguide" is versus the tweeter itself. A faceplate is easy enough to fabricate, but what about this waveguide business? (I'm suitably uninformed to call it "business," I think.)
 
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jazzspeakEZ said:
Update: as it turns out, the tweeters had been replaced with a set of these piezo tweeters from RadioShack.
JSE

EDIT: I had a terminology mixup--I hadn't given enough consideration to what exactly a "waveguide" is versus the tweeter itself. A faceplate is easy enough to fabricate, but what about this waveguide business? (I'm suitably uninformed to call it "business," I think.)
Click to expand...

Piezo tweets? No, no no! You have nowhere to go but up from here.

See my previous post. If the waveguide fits the cabinet fairly well, just remove the piezo element and graft the new dome onto the back of it.

If the current waveguide fits badly, give us a picture with the current dimensions and the available space, and I'll bet we can come up with a good replacement for the entire unit. We'll need the outer dimensions of the old waveguide space, and the cutout for the driver.

Replacement of the waveguide/driver when you have no access to an original is your only option here, and it shouldn't be that difficult. I just wish we had some idea as to the original driver's specifications and the crossover frequency. Sometimes you're forced to wing it.

GeeDeeEmm
 
Here's a good starting point on choosing a new Vifa tweeter. From the stereophile.com article that Stimpy referenced above:

"The crossover point of my pair appeared to be a little higher than spec at 2.2kHz. Acoustic crossover slopes appear to be 18dB/octave for the low- and 12dB/octave for the high-pass....

Mission says in its literature that, as a 4 ohm design, the 780 needs a "modern" amplifier to drive it properly, it should not present a drive problem to amplifiers, particularly in view of its high sensitivity, measuring a genuine 93dB/W/m for the 1kHz 1/3-octave noise band."

GeeDeeEmm
 
We need a picture of the existing tweeter and waveguide, from the front and the rear. With that, we can get into what will be needed to repair or reconstruct the whole assembly. I've been able to retrofit tweeters onto such waveguides before with good results- just is a matter or what direction to take with replacement parts.

Regards,
Gordon.
 
nexus said:
i would go with an entirely different tweeter from the selection at PE. you might be able to get the xover specs and that will help. having atweeter with a wide range makes it able to replace a broader range of OEM tweeters.

this one is my fav for an excellent cheap replacement for any speaker:https://www.parts-express.com/peerless-by-tymphany-bc25tg15-04-1-silk-dome-tweeter--264-1040
Click to expand...

That's a great tweeter. I used a pair in a build I did for a friend a couple of years ago and he is very pleased with it.

My only concerns with using it in this application would be, first, its 89dB sensitivity in a system that specs out at around 93dB. Of course, this is a concern that's going to include a number of replacement tweets with sensitivity hovering around 90dB. Second, the BC25 is a little "soft" on the hf extension. It's shown in the charts and it's noticeable in those I used in my build.

Of course, all of this will depend on the type of hf performance the OP wants. Tastes vary.

I'm thinking that if the OP likes sterling hf performance he might be best served with a horn driver with an L-pad to control it. They will easily handle the 2.2k crossover frequency, easily exceed the 93db ratings of the mid-woofs, are available in 4-16ohm ratings, and are relatively inexpensive.

For instance: https://www.parts-express.com/pedocs/specs/294-600-bc-speakers-de10-8-specifications-44863.pdf

Great bargain at $43 each. Bolt these up to an appropriate WG or horn, and let the sparks fly - figuratively, of course.

GeeDeeEmm
 
I had a good friend like that helped him out Vietnam vet hell of a musician he was taking down around a gallon of Crown every four of five days.
I booted him out, haven't had contact with him since going on five years after a 16 year friendship.
Get the speakers going if they look great the roomy is history.
 
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