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dynaco_dan

Tweet, tweet, tweeter

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Hi there

I dissected this tweeter about 8 years ago, I just came across it recently.

This is the magnet assembly only of the typical 8 ohm Seas 1 1/2" dome tweeter, as used only in the classic A-10, A-25, A-35 and A-50 speaker systems.

The firm fibrous cream coloured dome is slightly off center but appears not to have touched the voice coil form.

This absorbent material was used to cancel any rear sound reflection, thank goodness it was not, polyurethane foam, aka foam rot.

I will be taking gap and voice coil measurements, when I find my digital calipers.

I want to present the gap clearances for those interested in this aspect.

The dome voice coil and screen are still hidden somewhere, hopefully not junked, so no photos of them here yet.

Usually the paper labels are printed with a very faint blue Seas watermark, such as this label has.

Some tweeters, such as this one example, have Seas and Made in Scandanavia stamped onto the rear round backplate.

The label here uses the rarer red ink, rather that the usual blue or black ink.

This label has 4/8 ohms rather than the usual 8 ohms or 4 - 8 ohms printed.

There will be other photos posted here of different Seas tweeters that I have in the near future.

The rightmost lower numbers are usually week followed by year of manufacture.

I have found this to also to be different on some labels.

I do not know the power rating of this tweeter, under warantee I replaced at least 100 woofers in A-25's to every tweeter.

Most of those A-25 woofer voice coils were absolutely toast, as in burnt to a crisp.

Considerable tweeter power handling capabilities to say the least, considering it's low crossover point.

It was crossed over with just a simple, single capacitor to filter out the lower frequencies.

It has a relatively smooth output, with a consistently magazine reviewed high level peak in the 10,000+/- Hz region.

It begins it's gradual roll-off at that point with some output still usable at 14,000 Hz.

Their off axis dispersion was not great, but adequate, especially when the price of the entire speaker system is taken into full consideration.

I experimented, unsuccessfully, trying to make a Microstatic tweeter array clone.

I do not have anything left but the tweeters, pot, switch and capacitors.

I had a switch between the 5 and 8uf capacitor to resemble the A-25 and A-35 crossover points.

The cabinet that I had made out of particle board, was not, as you would say, very good looking.

I was not impressed or something with the increased sound output and dispersion and destroyed those cabinets.

In all fairness I probably did not very likely give them a suitable setup or longer listening evaluation than I feel that they justifiably deserved.

I have not read anywhere, yet, as to this tweeter being used as a retrofit for AR, KLH, Allison, Advent, EPI or any other brand speaker.

The Allison tweeter, as I understand it, was outstanding and may have been experimented with more.

More to follow soon.

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Thanks for all the info, but on my end at least, there's no photos visible or links to photos. :(

Hi there

Sorry, I've been busy and the photos are still in my camera.

I will upload them Tuesday.

Nice to see someone interested in something I wrote at least.

I usually just ramble to myself. LOL

UPDATED 20110906 8:30 AM

Here is the photos.

I cannot see the large Seas watermark here on the label, I think I would need a better lens.

The 788 may be a part number or batch series maybe.

UPDATE 20110909 5:45 PM I added another 2 photos, different tweeters, you can see the much more visible SEAS watermark on the one label.

I now believe that I need to use the camera stand more often and remote shutter switch as well.

UPDATED 20110913 9:15 AM

Last night I did a very scientific test on the magnet assembly.

I stacked together 10 - 1" wide strips of laser printer paper and slid them into the gap.

I could just slide the pieces around in the gap.

I don't have my .0001 digital calipers or micrometer to measure the thickness of each sheet or all 10 sheets, yet.

Interestingly a small amount of rust, or at least rust colour, was smeared on the outer side of the paper, opposite to the magnet side.

There is no visible signs of rust anywhere on the metal surfaces.

Some science, heh?

I may drift out the magnet at some future date and take more photos of the pieces.

The rear of the backplate is automatically centered.

I don't see how the magnet is attached to it, yet.

I also used the science of a small steel safety pin.

I could just lift it with the rear of the magnet, very little magnetism.

No pin pickup anywhere else behind the front flange.

In front where the white magnet top is, is another story.

At about 1" distance, the pin would pick it up and hold tight.

I tested also with a standard steel sheet metal screw and had a dickons of a time trying to remove the screw.

Like trying to pull teeth from a chicken.

When I had used my AR-LST's as my home theater system, I had them placed too close to my CRT TV and the tweeter/mid magnet radiation affected the colour.

I am not sure if we can say the Dynaco tweeter is shielded or not, but certainly not in front, same as the LST drivers.

If and when I do find the Dynaco tweeter voice coil that I had removed, I will digitally mike it and report back here.

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Great pics!

I assume the larger-than-normal dome was to allow for a relatively low crossover point and/or possibly so a 6dB/octave slope (one capacitor is used with this tweeter, correct?) could be safely employed.

FYI: one of KEF's best speakers in the late 70s, the Reference 105, used a TWO inch dome tweeter. IIRC they did this to increase the quality of the stereo image since such a large radiating surface had a relatively narrow dispersion angle and in turn that would reduce floor/ceiling/wall reflections which can interfere with the sound that arrives at the ears directly from the tweeter.

I wonder how well a modern version of the A25 would sell nowadays - more specifically, in this money-conscious economy - where anything larger than something that fits in your hand is "uncool" - I bet if the correct marketing was used it might sell quite well (hey Apple has sold millions of iPods to millions of people I bet would never have considered using headphones on a regular basis, even though they never even said anything disrespectful about loudspeakers). "Retro" seems to be a big selling point for many 20-somethings and these speakers are pretty attractive IMO (unlike much old stuff an old guy like myself thought looked nasty when it was new!), so you never know..........

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Great pics!

I assume the larger-than-normal dome was to allow for a relatively low crossover point and/or possibly so a 6dB/octave slope (one capacitor is used with this tweeter, correct?) could be safely employed.

FYI: one of KEF's best speakers in the late 70s, the Reference 105, used a TWO inch dome tweeter. IIRC they did this to increase the quality of the stereo image since such a large radiating surface had a relatively narrow dispersion angle and in turn that would reduce floor/ceiling/wall reflections which can interfere with the sound that arrives at the ears directly from the tweeter.

I wonder how well a modern version of the A25 would sell nowadays - more specifically, in this money-conscious economy - where anything larger than something that fits in your hand is "uncool" - I bet if the correct marketing was used it might sell quite well (hey Apple has sold millions of iPods to millions of people I bet would never have considered using headphones on a regular basis, even though they never even said anything disrespectful about loudspeakers). "Retro" seems to be a big selling point for many 20-somethings and these speakers are pretty attractive IMO (unlike much old stuff an old guy like myself thought looked nasty when it was new!), so you never know..........

Hi there

The A-25 used a 5uf cap and the A-35 used a 8uf cap only in their simple crossover, no coils were used.

It speaks well of the woofers bass performance and it's mid range using it's natural roll-off.

I never read of any issues at the crossover point, such as with the original Large Advent.

The 1 1/2" Dome tweeter was a very unusual device as it could handle from 1,000 Hz up to at least 14,000 Hz.

It was not perfect by any means, but very versatile.

In my experience it could handle one load of wattage.

I never heard or read of it's power handling capabilities or any other specification of interest.

The dispersion was adequately good and slowly dwindled as the frequencies climbed, still usable slightly off axis.

Considering the low street pricing of the Dynaco speakers, the A-25 in particular at a low of $52.00 CDN each here in Vancouver, it offered a lot of bang for the buck.

There was a fairly consistent peak, reported by reviewers, around the 10,000 Hz point and still usable low output past 14,000 Hz.

I've never heard or read of any particular driver testing other than the few old reviews in magazines, including the original, J Gordon Holt's, Stereophile magazine.

He raved about the A-25 and compared it to the AR-3A's, KLH Nines, Janszen Z-600, AR-4X, KLH Seventeen and others.

He stated that the A-25 ran circles around all of them.

Clarity of the electrostatic speakers beat the Dynaco and probably every other brand and model as well.

The Dynaco tweeter was reviewed as comparable to the AR-4X's, KLH Seventeens and others.

The version that was used in almost every review was not known or stated whether it was the Scan, or the more common Seas driver system.

I will guess here that Dynaco would not have allowed an appreciable sound difference between them without changing their identity.

Other companies made unannounced driver and crossover changes, without changing identities, so who knows.

A dynamic and not an electrostatic tweeter but I've enjoyed listening to them in several Dynaco speaker versions.

My older reference speaker was the AR-3A and I did not do any kind of A - B comparison between them.

No point when you have both.

I found that when you own one speaker system and continue to listen to other systems or higher priced speakers a fever begins.

You then begin craving the better one, which is always the one you don't own of course, and then you want them.

On and on the cycle goes.

Each speaker system in my home sounded fine to me as factory stock.

I did adjust the tweeter level control more than once but eventually left it in the highest position.

I did notice a slight sound change, whether it was an improvement or not remains to be seen.

Normally I do not change bass, treble or add tweeking to my sound system, I accept standard room acoustics as the norm as well.

Need to sit down a connect up my Scan and Seas A-25 models to see if even with my poor hearing, I can hear a difference between them, a battle of the speakers, so to speak.

With the old day's fever in the stereo store one could ( did ) always want another setup, always more money of course, it kept the finance companies in business at least.

Just to add a little bit to the tweeter analysis, the white tweeter material is sort of like, heavily compressed cotton or such.

Thank goodness it wasn't polyurethane, foam rot.

The tweeter, if sold new today, would likely be well over $200.00 U$, they sell used on ebuy for around $50.00+/- U$ today each.

If I was an experimenter today, I would likely take one of my Allison tweeters and try it out in one of my A-10, A-25, A-35 or A-50 enclosures.

UPDATE 20111004 10:45 PM

Just a missed comment about the tweeter magnet used by this sample photographed Seas tweeter.

The more common horned Seas woofer used the exact same magnet assembly as this tweeter.

At the moment I do not have a Seas smaller, the more common, disected woofer.

I only difference that I anticipate is in the pole piece not having the cream coloured top padding.

I already posted photos of the larger magnet Seas round woofer in the, "woof, woof, woofers", write-up.

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Thanks for your informative posts. FYI, I replaced my AR4X tweeters with a spare pair of SEAS from A25s; I made no other changes. The improvement in smoothness & range was so great, I left the SEAS in permanently. The AR4X tweeter pots seem to do much more with the SEAS than with the originals.

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I thought the crossover frequency was the same for A-25s and A-35s. Now I'm going to have to poke around inside next time I score a pair of A-35s and see what I find.

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I thought the crossover frequency was the same for A-25s and A-35s. Now I'm going to have to poke around inside next time I score a pair of A-35s and see what I find.

Hi there

I've enjoyed reading several of your Epinion reviews.

I have taken a few photos of my spare A-25, A-25XL and A-35 crossovers.

When I return i will post them here under the appropriate speaker model crossover heading.

ps I miked the 10 layers of paper I used to test the gap.

I measured 0,011 inches and also when I pulled it out last time a whack of rust particles came out as well.

More when I return.

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Hope you elaborate on the gap testing. Do your falling rust particles imply that sometimes a woofer will "loosen up" with some use, and that some that are rubbing slightly will "un-rub" with use?

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Hope you elaborate on the gap testing. Do your falling rust particles imply that sometimes a woofer will "loosen up" with some use, and that some that are rubbing slightly will "un-rub" with use?

Hi there

This topic is just for the classic Seas 1 1/2" tweeter at this time.

Previously I tore up 1/2" strips of general printer paper to see what the gap opening was.

I do not have the dome/voice coil, yet, to measure the thickness of the voice coil and form combined to have an idea of that knowledge and the gap

opening to see how much gap was allowed in assembly at the factory.

This of course will very likely be different than the Seas woofer voice coil/ form thickness/clearance.

I do not have a lot of experience dissecting raw drivers and I am guessing that the tweeter will have a tighter clearance than the woofer.

I used 10 layers and with my micrometer and I measured 0.011" thickness of paper.

The massive amount of rust chunks came up from inside the gap.

Earlier when I took the photos there was slight discolouration on the paper when I ran it around the perimiter and removed them.

That was done several times without any pieces. just a slight rusty/oranage shade.

I would need to destroy the magnet assembly to see what happened inside the cavity.

You all may already know that the 1 1/2" magnet assembly is used in the A-10 wooferand tweeter, A-25, A-35 and A-50 woofers and tweeters in the classic line.

This kept production and inventory to a minimum.

Because this sample I have is very old and incomplete I do not know where it came from.

There is no signs that it was immersed in water and there is no signs of rust in general.

The pieces that came out with the paper are black chunks and are not dirt but metal.

At this point the magnet assembly is a writeoff and perhaps I will slam dunk it with a hammer to investigate further.

From my experience at the warantee depot the woofers had 200 to 1 replacement compared to the much sturdier tweeter.

There was a batch of woofers with defective glue bonding the voice coil to the form and when it slipped in use it was causing a buzz..

Also some batches when over heated caused bubbles to form on the outer surface of the voice coil, causing a buzzing, rubbing sound.

We would, as directed by Dynaco, replace those under warantee even if they were toast.

Maybe a handful of the 200+ woofers were not covered under warantee.

If you hear a scratching sound it is my opinion that the voice coil is damaged and it will not heal itself.

An extreme example of damage to a voice coil is where the voice coil and it's form are little more than charcoal.

This is the case with woofers only as I never saw a scorched tweeter voice coil, yet, that is.

Speaker damage is cumulative and cannot be reversed.

It can be protected as near as possible by fusing with the appropriate fast blow fuse in an open fuseholder from most all damage except

plugging the speaker into an electrical outlet (too large a serge and too fast).

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