Pete B
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Posts posted by Pete B
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Next year this thread will be 20 years old, time flies!
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As the title says don't want to ship but will try to figure something out if further.
Anyone? Don't mind doing a few or more repairs.
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I have a pair of LA woofers here that were refoamed by Bill LeGall of Millersound about 6 months
ago and there's no sign of the dust caps being removed.
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If you found an 8 ohm SA woofer I'd say that it was probably worked on with a VC replacement or
they mixed up some LA woofer voice coils in with the SA ones. It is in the "engineering" sales
literature that while they SA maintains the same F3 as the LA they lowered the impedance to 4 ohms
in order to keep the system voltage sensitivity as close to the LA as possible.
However, even the LA is lower than 8 ohms with the DCR usually measuring under 5 ohms.
When I worked on a few SA woofers I was surprised how similar, if not the same the magnet pole
piece, VC were to the LA, probably a parts commonality thing for mass production.
I repair two SA woofers here with some notes:
https://audiokarma.org/forums/index.php?threads/small-advent-woofer-repair-some-measurements.819443/
I measured a DCR of 3.3 ohms for the SA woofer.
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They look like Advent Legacy woofers with very large replacement dust caps.
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I discuss a bit more about the presentation in this thread:
I measured the LA Econowave here and found a few serious issues that are corrected in the PB1 modded
version that I'll be demoing:
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Giving my presentation "Why Waveguide Speakers?" and demo of the Large Advent Econowavesat the 2023 Spring Blue Mt. Audio fest. Peekskill, NY Tomorrow Saturday May 6,Doors open at 10 AM presentation at 1 PM or so, playing it by ear, very informal. $20 fee, also audio gear swap meet.Blue Mountain Park, Welcher Ave. Peekskill NY
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I use a 10 ohm resistor so it is about half the voltage at the speaker.
One thing I should have mentioned is that the rubber edge could have hardened, though mine
looked fine. It depends on the type of rubber and I have many woofers with rubber edges
that have Fs now that is 2X what it should be. Wintergreen oil is talked about a lot on the Web
and Youtube and it works great for a day or 3 let's say. Doesn't take long for them to be back
to 2X. I will probably try brake fluid next time being careful not to get it on the glue.
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5 hours ago, jonwb said:
Once I commited to the sandpaper, I noticed that the dust was brown in color and I may have taken too much of the original finish during that process. The last pic showing the frame face (around the blue tape) kinda shows this.
I was given some very beat up large Advents, did some repairs and did a lot of sanding thinking I'd just
apply a new finish. I found the same thing, that sanding, even the first layer produced a lot of colored
dust. What I found was that the front trim was not even close to the rest of the cabinet. And the cabinet
had large color variations. It seemed to me like there was a tinted clear coat and after doing some research
I found that this was common since the 1940s to even out the color and I'm quite sure that it is what Advent did.
I think that AR's used a better quality wood and perhaps this wasn't needed but it is something to keep in mind.
Certainly, if the owners manual says it is finished with BLO and that's what to use to freshen it up, then that's
what you should do.
Please keep us up to date since It might help with my effort. These were almost ready for the dumpster so I
consider it a learning experience. I'm considering trying a black dye/stain just to get the job done.
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Great that you already rebuilt them!
Yes I'd add the shunt cap but no rush.
Hope you enjoy them very much.
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Your tweeter impedance certainly looks to be 4 ohms.
That is of each series-parallel array?
If they all work, I would just use them and listen for distortion in case any of them have problems.
Perhaps they were already rebuilt with 4 ohm coils?
Both arrays have an impedance peak around 4KHz which is very high and makes them super tweeters.
Most of those tweeters that I've measured, perhaps were worn out, did not show much of a peak at all.
I don't know what the correct impedance peak frequency is for those tweeters.
As far as caps go, I would replace the tweeter and mid caps as soon as possible. I prefer film caps because
I don't like to have to change them every 10-20 years. I'd probably replace the cap across the woofer with an NPE.
The large input cap I'd check for leakage and it might be okay, otherwise you might want to replace them with new.
See how they measure for leakage and how they sound.
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If you decided to build the 16/8/3 then the DCR is lower, you have to tell us what you decided to do.
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The white dot inductor is only used in the decrease position, if you want yes it is better to change it.
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What I'm suggesting that you do is make them both 16/8/3 crossovers, that is why you'd use the value that I gave you.
Did you have another plan?
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Build it as 16/8/3 and use this inductor to replace the one with the red top:
Dayton Audio 0.45mH 20 AWG Air Core Inductor Crossover Coil
Part #257-034
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Do you plan to just make them 16/8/3 with the new inductor?
The other off white inductor is only used in the decrease position, and doesn't need to be replaced
mainly because that position is useless with modern recordings.
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Sorry I used the big inductors in another project.
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I read Don Keele's review of the T1030 when in was published in Audio in 1991 starting on page 81 in the .pdf here:
Audio-1991-01.pdf (worldradiohistory.com)
Took another look at this test report and the T1030 looks to be 6 dB down at 40 Hz which is a
bit much, boosted high pass EQ would make sense to bring it up by 3-6 dB to get a flatter response.
Figure 8 in the test report shows that the system resonance (Fc) is at about 40 Hz and that the
impedance dips to 3.4 ohms around 100Hz indicating that the bass section is 4 ohms even
though the system is rated as 8 ohms.
I liked this design, very nice work and always wondered what the crossover design looked like.
Bought a pair of crossovers on ebay, measured the inductors and here is the schematic:
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I've also seen those schematics Roy but never kept the links to them.
If I understand you, you want the large magnet schematic?
I'm looking for a pair of SA woofers if you come across some.
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I drew the T1030 schematic a long time ago but I wasn't sure on the driver polarity for the mid
and tweeter with regard to the wire colors and that's probably why I didn't post it here.
I assume that the 2 red wires go to woofer + and two black wires to woofer -.
Does anyone know how the mid and tweeter are wired? I'd like to get it right the first time I post.
Tweeter: Brown, and Yellow wires
Midrange: Brown/White, and White wires
Anyone know?
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I've been measuring with Bill Waslow's very old program LAUD for over 20 years and I trust it.
I try to measure tweeters around 1V and 2 to 3V for midranges and woofers.
I wonder if Fs depending on drive level has anything to do with the rubber aging.
I also wonder if REW might have an error in the calculations. There are free programs that
go along with ARTA for measuring T&S parameters, perhaps you could use that as a sanity check.
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Qe and Qm scale linearly with Fs, so part of the error can be accounted for due to the Fs difference.
Consider that a base set of measurements do not require the delta mass or compliance second
measurement. Fs and the Qs are included in that and Fs simply requires an accurate generator
which should be easy with a digital source. You could check for distortion in your gear, do you
have an oscilloscope to have a look. You could try to confirm Fs by the old way of using a high
impedance source and just measuring the voltage peak with a voltmeter. I'd say that this is the
first step.
The Q values can have error due to resistance in your test leads or calibration error. If your system
can measure impedance try an 8 ohm resistor and see if there is error across frequency.
AR4x replacement tweeter recomendations?
in Acoustic Research
Posted
I wonder how this Visaton paper cone tweeter with a smooth response would do as a replacement,
with a parallel resistor to match the impedance:
https://www.mouser.com/ProductDetail/Visaton/TW-70-8-Ohm?qs=VWNNG7jHlrLkQoY0VZlmUA%3D%3D
Mounting would have to be worked out, perhaps 3D printed.