Pete B
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Posts posted by Pete B
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I noticed that one of the two systems here sounded harsher in the midrange than the other, it was subtle and I was not positive that it was a speaker problem. I decided to open the tweeters and take a look.
I have quite a bit of experience with older dome tweeters and midranges that often did not have any sort of alignment pins for centering the voice coil. In this case you play a test tone at resonance and adjust the position until there is no voice coil rub or buzz, then tighten the screws.
The SEAS H-087 has a thin donut shaped ring in the frame, and a matching ring shaped depression in the dome assembly which is used to center the dome.
Removing the four screws in front allows the front face plate to be removed. This is not something to do if you do not have a gentle touch since it is very easy to damage or deform the voice coil in the process. I inspected everything once the dome was off and checked for debris in the gap. One driver did have a small piece of metal lodged in the gap, which I removed. Otherwise, both looked fine, voice coils looked good, and were reasonably centered. I also cleaned the two alignment surfaces to be sure that they would match up without binding.
One tweeter went back together without any buzz issues. The other was sensitive to the order in which the screws were tightened and there was a definite buzz when not reassembled correctly. I found a combination of pressure toward one side and the correct order in tightening the screws eliminated the buzz. Even modern tweeters from top name suppliers have consistency issues and I have often seen misaligned voice coils and other problems.
These tweeters otherwise look to be in very good shape.
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The 1.5" SEAS H-087 (ALNICO magnet) tweeter was the one most commonly
used in the A-25. It can be seen here in this picture, thanks Vern:
http://www.classicspeakerpages.net/dc/user_files/1871.jpg
This large tweeter was probably in an attempt to provide better power
handling. However, this tweeter utilized a paper voice coil former
which does not function as much of a heat sink. Aluminium or
aluminized paper is much better.
The H-087 was a good tweeter for its day, but it was a dated design
even in the early 1970s. The SEAS 27TFFC suggested as a modern day
replacement is a far superior tweeter.
It does employ tinsel lead in wires which helps to avoid wire breaks
with first order crossovers.
It is a simple design with a felt pad under the dome, no pole vents
or chambers to add resonances to its response.
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>On my A25s,the version with Scan-Speak tweeter and SEAS
>woofer,it's around 25 threads per inch -one thread per
>mm-although it could very well be made in India or
>whatever.It's not evenly woven though,about every inch or so
>there's a thicker thread and also some extra thicker threads
>woven in uneven intervals.Sounds a little complicated,I
>guess.I'll see if I can scan the fabric.
Thanks very much for this, I used some thing close to that and it does look very good so it should be fine.
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Vern wrote from:
http://www.classicspeakerpages.net/dc/dcbo...=97&mesg_id=350
>Hi Pete;
>
>Have you continued with your A-25 investigation?
>
>How are you making out?
>
>I kept a printout of your great schematic, 2/24/06 Rev 1.0 and
>started to look from where I copied it from.
>
>Thank goodness the Dynaco forum doesn't have thousands of
>files, it wasn't too difficult to find.
>
>I wrote elsewhere, without seeing your comment, about that
>A-50 schematic not being in my mind, correct as well.
>
>I feel the 10 ohm w-w resistor in series at the lowest
>setting, is incorrect.
>
>This would place the tweeter down at least 10 db +/- for
>starters.
>
>It would be appropriate to have it at the end of the switch to
>common ground, such as with the A-25 crossover.
Hi Vern,
I bought these with the intention of mainly investigating the Aperiodic woofer loading, and they were not in great shape.
I ended up refinishing them, making new grills, they were missing when I got them, and finding a new woofer to replace the newer FEW type.
I spent a lot of time looking for a close match to the grill cloth but I didn't have the original so it was a best guess. Still would like someone to count the threads per inch on an original pair of A-25s and report it here.
I'm going to have a look at the tweeters, take some measurements and then close them up and hopefully be done with them for now.
I'm not in a rush to do some detailed bass experiments, I just saw them for sale near by and picked them up.
It will be nice to have a restored pair as a reference for the original sound.
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Vern wrote from:
http://www.classicspeakerpages.net/dc/dcbo...=97&mesg_id=350
>Hi Pete;
>
>Have you continued with your A-25 investigation?
>
>How are you making out?
>
>I kept a printout of your great schematic, 2/24/06 Rev 1.0 and
>started to look from where I copied it from.
>
>Thank goodness the Dynaco forum doesn't have thousands of
>files, it wasn't too difficult to find.
>
>I wrote elsewhere, without seeing your comment, about that
>A-50 schematic not being in my mind, correct as well.
>
>I feel the 10 ohm w-w resistor in series at the lowest
>setting, is incorrect.
>
>This would place the tweeter down at least 10 db +/- for
>starters.
>
>It would be appropriate to have it at the end of the switch to
>common ground, such as with the A-25 crossover.
Hi Vern,
I bought these with the intention of mainly investigating the Aperiodic woofer loading, and they were not in great shape.
I ended up refinishing them, making new grills, they were missing when I got them, and finding a new woofer to replace the newer FEW type.
I spent a lot of time looking for a close match to the grill cloth but I didn't have the original so it was a best guess. Still would like someone to count the threads per inch on an original pair of A-25s and report it here.
I'm going to have a look at the tweeters, take some measurements and then close them up and hopefully be done with them for now.
I'm not in a rush to do some detailed bass experiments, I just saw them for sale near by and picked them up.
It will be nice to have a restored pair as a reference for the original sound.
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>Thanks Pete.
>
>I just wrote up a rather lengthy post about refoaming that
>will probably bore most readers to tears but there you have
>it.
>
>I have been following your measurments regarding the New
>Advent and variations and this is the type of information that
>should be made a "pinned" thread if any.
>
>That and maybe practical applications such as
>refoaming/rebuilding as you mentioned in another thread.
>
>Regards,
>Doug
Hi Doug,
I did enjoy reading your thread, good to see you get them in perfect working order. I think Mark is probably too busy to worry about pinning threads, perhaps he would make you a moderator with that ability, that would be nice. Certainly, how to refoam, where to get foam, etc. should be pinned, grille cloth discussions, etc. etc.
I'm having trouble finding my own threads, LOL!
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Hi Carl,
My friend is not Andy K., he wishes to remain anonymous.
I'll ask him next time we exchange e-mail.
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Hi Doug,
Yes I'm sure, I'm surprised that they made the mistake of going
to the 16/16 version, but not so surprised that they went back.
My friend is very methodical so I have a lot of confidence in his
schematic, but who knows how many were shipped with that. He said
himself that the later design(s) was the high volume seller, what
we've called Rev1 (16/16) and 2 (later 16/8).
The very thin wire inductors in Rev 0 and 1 were also a mistake, IMO.
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My friend sent me a schematic from his personal files, he says that he drew it since
he owned a pair of the Advents from that time and it is dated 26 August 1970. My
friend wrote: "The date would place it at 377 Putnam Ave., which was the
original location of the company and where I started working for them. Don't know
which value of L1 and L2 they finally settled on." So this indicates that he did start in 1970.
It is earlier than anything we've been talking about here, one member mentioned a
very early version with a 4 ohm resistor and this should be it. It is what I've called
Rev0, and it has a 16 uF main cap, with an 8 uF extended cap. The resistor is listed as 4.14 ohms.
The inductors are listed below:
L1 .149 mH, .208 mH, Q=1.6, R=.56 ohms Decrease inductor
L2 .850 mH, 1.055 mH, Q=2.0, R=2.5 ohms Tweeter shunt inductor
L3 1.42 mH, Q=14 @ 1 kHz, R=.273 ohms Woofer inductor
Note that there are two values for L1 and L2 and he states that he's not sure which value they settled on.
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Hi Doug,
Nice to hear from you!
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My friend also spoke very highly of Andy K. and I don't think there is any disagreement, he did say that Andy K. fine tuned the voicing on most of the early Advents.
I am completely of Greek heritage and people like Andy Kotsatos, I'm sure, make all Greeks feel proud. I don't think I'll return to my family's original name though.
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Hi Vern,
Thanks for your comments.
Thinking about this more, my friend says he arrived
there in the early 70s, which could be 1972-73, when
the revision from the Rev1 to Rev2 crossover was done.
I would agree that something doesn't sound right
especially in the extended position with the Rev1
design, however, I don't recall any changes in the
tweeter from Rev1 to Rev2. There was the tweeter grille
and use of bulb dye from the very early to Rev1 change,
so I think more likely this was it.
Perhaps, I'll send him the email from Andy Kotsatos where
he mentions the bulb dye on the tweeter is mentioned.
My friend also mentioned during our conversation that an
MIT grad student did most of the Small Advent work, again
with Henry's input and oversight. Really, it is just a box
reduction, and new woofer.
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I worked over 10 years ago with an analog engineer who had
previously worked at Advent in the early 1970s. We often had
lunch together where we chatted about what went on behind
the scenes.
I ran into this friend coming out of the Grand Hyatt in NYC
recently when the HE 2007 show was going on. I have to say
that I was surprised to read on this forum that some believe
that Andy Kotsatos designed all the Large Advents. The early
Large Advents have the writing on the back "Designed By Henry
Kloss" and I believe it. I posed this question to my friend
when I ran into him, and this was his response in a later email,
posted with his permission:
=================================================================
"Regarding your Advent query - the way I remember it happening was that Henry Kloss had a noncompete clause when he left KLH that prevented him from peddling loudspeakers for some specified period of time. According to legend, he designed the Advent loudspeaker and filled a couple of trucks with the things. On the day that the noncompete clause expired, the trucks rolled out to the stores! It is entirely possible that these very first loudspeakers were entirely of Henry's design."
"By the time I arrived at Advent R&D in the early 70's, I vaguely remember there being some brouha about the loudspeaker not sounding right. One of my first tasks was learning how to run the General Radio stripchart equipment, and I wound up running lots of loudspeaker and crossover curves. Bruce Gregory, the lead electrical design engineer, wound up redesigning the crossover and Andy did the voicing by tweaking the parameters. There was a lot of back-and-forth (and lots of curves) getting the thing right. They also made a design change to the tweeter, but I don't remember the details. If anyone has an early Advent Utility, most likely it is one of these revised units, since they were the ones that sold in volume."
"Personnel involved with auditioning the Advent loudspeaker product line most likely were Andy, Bruce, Henry, Stan Pressman (head of marketing), and Joe Hull."
=================================================================
Comment: We have only identified 2 early versions of the Large Advent
what I call the Rev1 16/16 uF, and the Rev2 16/8 uF, what I call Rev3 is
the New Advent. The Rev1 that I worked on was from 1972, and I have seen
a very early version without the metal mesh screen over the tweeter. This
earlier version might also have the crossover that was "not sounding right".
There is also the addition of bulb dye to
the tweeters to seal the sometimes porous paper cone. I have never
seen a natural paper color Advent tweeter but they probably exist.
The Rev1 and Rev2 versions are the ones that sold in large volumes.
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I spoke to Roy C. who spends more time here on the AR forum and commented about how excellent his AR-2ax's looked:
http://www.classicspeakerpages.net/dc/dcbo...pe=search#11164
That material, in his first picture, is 18 ct, and it has the most open weave that I've seen so far. The texture is more of an expensive linen and it looks very close to the original Dyna A-25 material. Roy offered his source as:
http://www.123stitch.com/cgi-bin/fabric.pl
It is under linen, 18 ct, "Lambswool" color.
I estimated the count for the Dyna A-25s as closer to 28 but this was based on pictures and memory. I completed these grilles using "Zweigart 100% Linen, 28 Count, Cashel Raw Linen" purchased at a Michael's store. The color is a bit darker than what I remember and I believe that the 18 CT linen mentioned above is a better match.
Moderators can you pin this thread since it is such a common
question?
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Grille Cloth link
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I have finally made new grilles for these speakers.
I estimated the thread count at 28, however I'm wondering now if it might have been 18. It would help if someone with original grilles would please count the threads per inch.
I spoke to Roy C. who spends more time here on the AR forum and commented about how excellent his AR-2ax's looked:
http://www.classicspeakerpages.net/dc/dcbo...pe=search#11164
That material, in his first picture, is 18 ct, and it has the most open weave that I've seen so far. The texture is more of an expensive linen and it looks very close to the original Dyna A-25 material. Roy offered his source as:
http://www.123stitch.com/cgi-bin/fabric.pl
It is under linen, 18 ct, "Lambswool" color.
I estimated the count as closer to 28 but this was based on pictures and memory. I completed these grilles using "Zweigart 100% Linen, 28 Count, Cashel Raw Linen" purchased at a Michael's store. The color is a bit darker than what I remember and I believe that the 18 CT linen mentioned above is a better match.
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Would someone with original Dyna A-25 Grilles please count the thread count per inch? I have A-25s but the grilles were missing. This would help to find a good replacement material.
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Aperiodic Vent link, see previous post.
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Anyone know if Dynaco used a black cloth behind the light grille cloth or did they just paint the grille frame black?
>Has anyone found a close match in replacement grille cloth?
>These did not have grilles and I just need the cloth for a
>replacement pair. I've seen the various discussions of the
>more coarse cloth used on Advents and ARs but I'm looking
>for a close match to the origianal A-25 cloth. Anyone?
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>I found the pic below on AK and it's supposed to be the xover
>of an A-25. I've seen written many times that the A-25 has no
>coil in the woofer xover, yet there clearly is one in this
>pic.
>
>Any guesses as to what's going on here?
>
>Regards,
>Jerry
>
>http://www.classicspeakerpages.net/dc/user_files/1862.jpg
>
It has 5 resistors on the tweeter switch which is correct for an A-50. The woofer section is too simple for an A-50:
http://www.classicspeakerpages.net/dc/dcbo...g_id=&page=#106
It could be a normal A-25 that had the woofer replaced with the newer XL version. One tweeter resistor would be removed. The woofer inductor would help with the newer, more efficient woofer. The extra cap in the tweeter circuit looks to be like the modification that I suggested:
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Has anyone found a close match in replacement grille cloth?
These did not have grilles and I just need the cloth for a
replacement pair. I've seen the various discussions of the
more coarse cloth used on Advents and ARs but I'm looking
for a close match to the origianal A-25 cloth. Anyone?
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Some here ask about the large Advent sounding harsh:
The peaking in the dotted lined response starting at 500 Hz, peaking at 1.2 kHz, continuing to 5 kHz is one reason for harshness in the Advent sound. BSC helps to correct the response below 500 Hz, and combined with tweeter level adjustment makes a significant improvement in improving the FR balance.
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>So here's the scoop, Pete.
>The woofers in my 5102s are like Ed's, with a raised
>backplate.
>Front and back plates are 1/4".
>Magnet is 5/8" thick.
>There's a pair of 5012s on eBay now at $100 + shipping from
>NY.
>
>What's the big deal about a raised/bumped backplate? Allows
>longer cone excursion? Is the second question good enough for
>another laugh?
Hi Russ,
Oh, Interesting, it is different then.
Original:
3/8" plates
3/4" magnet
5012:
1/4" plates
5/8" magnet
I could enter the numbers in the spread sheet that I have,
but we'd need to know the voice coil length. Don't know
if the kept the 5/8" length, another common one is 3/4" for
these old long throw woofers. But we won't know without
looking at one. Anyone have a blown 5012 woofer?
Yes Russ the raised back plate allows the VC to move further
back before making the loud crack sound as it hits the plate.
We should probably start a new thread about the 5012 woofer.
Thanks Russ,
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I think your joking but, your comment did give me a laugh!
Here's a picture of Ed's 5012 raised or bumped back plate:
http://www.classicspeakerpages.net/dc/user_files/1543.jpg
Here's the thread where we discussed it:
http://www.classicspeakerpages.net/dc/dcbo..._id=&page=#1336
I would be very interested to know the back plate, front plate,
and magnet thickness. 1/4" plates are very common, however the
original and New LA woofers had 3/8" plates. I'm curious about
the 5012 woofer if you happen to take a look.
Thanks very much for the offer about the crossover, but I
bought a pair of 5012 XOs on ebay just for curiosity sake.
There's a 7 uF from the + input to the fuse. Other end of fuse
has an inductor to ground (fairly large air core), also a
32uF to a 3 ohm resistor, other end of resistor to tweeter +.
Woofer has a not so large air core inductor in series with
the + lead, wired with positive polarity.
Best Regards!
Pete B.
>Pete—you know enough about me to know that I don't know what
>a backplate is. But if you tell me, I'll take the woofer out
>and try to find it. If it's big enough, I just might have
>lunch on it tomorrow, and even outside, if the sun shines.
>
>I have these 5012s just sitting idle. I don't want to put them
>on eBay because they never bring what they're worth. And
>they're quite good. The cabinets are just a little larger than
>the original Advent Loudspeaker, the x-over is different,
>there's no tweeter level control, and the tweeters haev fuse
>protection (which I have disabled).
>
>While I'm inside, I'll examine the x-over and note the details
>for you, so you'll have something else to think about this
>week ;-)
Dynaco A-25 Restoration - Measurements - Comments
in Dynaco
Posted
I should probably mention that it is easy to see the buzz in an impedance measurement or even better by measuring the distortion at the driver terminals when driven by a high Z source. This allows distortion on the acoustical side to be reflected back into the primary side. I did this and could easily see the distortion with the driver that buzzed. I could have gotten out my mic, but the driver was already wired up for this test and it worked fine.