Glitch

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  1. Roy: Of course there "is much more to speaker design". Perhaps, my statement would have been better stated as the woofer/cabinet matching as the hardest part of "speaker building" instead of "speaker design". For many people, soldering together crossover components is much easier than building a suitable cabinet from scratch. Starting with a well-designed and matched woofer combination goes a long way. Combining this with a properly sealed cabinet and the right amount of fiberglass stuffing, and one would be pretty much guaranteed good bass response. The mid/highs are trickier. There are many ways to tackle this problem. There are many modern, solid 3-way DIY designs that could be used as a starting point. One could use the high/mid crossover design from DIY setup. The low/mid crossover design from the AR could be used as a starting point. This crossover frequency is designed for the woofers in question and has the added benefit to be at a low enough frequency where the crossover design is relatively forgiving. It would be fairly easy to pick mids/tweeters that are more efficient that the original/missing AR parts. The final speaker voicing for the mid/high could be dialed back using L-pads or adding resistors. JKent: You make a excellent point about verifying that the woofers are good. It would be prudent to take this step regardless of whether the goal is a full restoration or a resto-mod. Juan: If you decide to go the resto-mod route, be sure to buy a sealed back midrange. It might also be worth sending an email to the fine folks at Parts Express to see if they could make specific driver recommendations. It sounds like you have reasonable expectations about what you will end up if you pursue the project. I'm quite confident that whatever you do, you will end up with a set of speakers that sound much better than what you currently have. Anyone: Can you comment on the chances for success of sourcing used, 50 year old AR drivers? My experience with vintage parts is that it can be difficult to find two drivers that match. It is ever harder to find two drivers that match AND are close to the original performance specifications. From what I've read, some AR mids/tweeters are experiencing the ravages of time. How much consideration should be given to this when planning a restoration? As a side comment: I think that it is a great accomplishment to restore a pair of vintage speakers to their original aesthetics and performance. This is not an easy thing to do.
  2. Juan, A full restoration might very well be expensive, but unless you have your heart set on originality, you have other options. You already have the most expensive parts of a speaker with the woofers and cabinets. You also already have the most expensive part of the crossovers, the inductors. I don't know your budget, but there are many "modern" components that you could substitute for the missing pieces and have a nice set of speakers. It might be worth asking the same questions in a DIY speaker building forum before you take a saw to the cabinets. I've built several pairs of speakers based on old woofers and cabinets with Chinese made tweeters. You can get very good value for your money with careful shopping. For instance, digging around a "popular auction site" can yield you a set of dirt cheap foam surrounds from China. The only drawbacks are that the shipping time is long and the woofers aren't original (but more original than the woofers being in a trash can). Your could order the other parts you need from a discount speaker parts website. Stick with non-polar electrolytic capacitors and low cost, highly rated (based on customer feedback) drivers. You may be pleasantly surprised about how good a $15 tweeter can sound. For the cabinets, some wood filler and black paint can make most anything look presentable. Pick a grill cloth that is in line with your taste, install this neatly, and nobody will ever know about the other choices you made or how expertly you did the other work. The hardest part of the speaker design, properly matching the cabinet size to the woofer characteristics, is already done for you. Set the mid/woofer crossover value to something close to the original. Set the mid/tweeter crossover value to something close to whatever the driver manufacturers recommends. This project could be a lot of fun (if you like doing this kind of stuff). Glitch
  3. I forgot to add a few more things... It would make sense that you would have no bass if the PA-1's were installed with the speaker switch in the full range position, The low frequencies from the amp would be routed to the woofer terminals that are disconnected in that switch position. The higher frequencies from the amp would be routed to the all of the drivers from the full-range terminals. Between the active crossovers in the amps and the passive crossovers in the speakers, no low frequency sound would make it to the woofers. I would get your setup working and let it run for a while before trying the resistor modifications. This way, in the unlikely event that something dies early on, you won't be wondering if it was something that you did while making the mods. Glitch
  4. Mark, You can "test" your amps by hooking the outputs to a known working set of speakers. Hook up one speaker to the mid/tweeter output of the amp and the the other speaker to the low output (i.e. one amp, two speakers). You should get full range, mono sound out of this unconventional setup. You could also test your speakers with a known good amp. Set the switch to the bi-amp mode and hook the left channel to the lows and right channel to the mid/high input. In the bi-amp mode, the low inputs are connected directly to the woofers. The mid/tweeters are still protected by the crossovers from low frequencies. Regardless of this, I would keep the amplifier volumes low to reduce the risk of burning out a driver. The attached picture shows the location of the "second" piggyback resistor (upper right of photo). I would recommend that you configure the resistors to match the speakers if you are comfortable with soldering. This is a fairly easy modification to make since resistors are relatively tolerant of too much heat being applied. I've run all four combinations of matched and mismatched setups. None of them sound awful (but why have a suboptimal setup?). Glitch
  5. For reference, here is a picture of the "piggybacked" resistor on the input board with one lead disconnected...
  6. I have a couple of pairs of PA-1's as well as L1290's and L1590's. Hopefully I can help you get your system working. 1) Did you change the "biamp" switch in the back of the L1590s to the "biamp" position? This is the lower switch in the back of the speaker behind the cover (and below the fuses if you have fuses). The switch needs to be set to the left with the PA-1's. You should get a full range of sound regardless of how the L1290/L1590 resistors are set internally to the amp. FYI, the upper switch sets the tweeter level to -0dB (right) or -1.5dB (left). 2) There are at least two versions of the PA-1's. One version needs to needs to change one resistor to configure for L1290/L1590 and the other need to change two resistors. There should be a diagram on the back of the PA-1 cover that indicates which one you have. The common resistor location is on the input board. This in in the bottom of the amp. The resistor is on the lower right-hand side of the board. There will be two resistors soldered in a piggyback fashion (one lead may or may not be connected). The second resistor (if you have that model) is on the main amp board. This is also easy to find since it also has the piggybacked resistor. 3) I believe that the resistors just change the amps crossover frequency to match passive crossover in the speaker. Depending on the mismatch, it either won't make any difference (the crossovers overlap) or you will have a small "hole" near the mid-woofer crossover frequency. A schematic for the PA-1 can be downloaded for free here. http://www.vintageshifi.com/repertoire-pdf/Braun.php The caveat is the manual is in German. There is also a on-line website that the sells an English version of the manual. I don't recall the name of the place but can look it up later if you would like. Glitch
  7. stupidhead, Personally, I wouldn't get too hung up on trying to save the existing veneer, especially if the primary reason is to save the interesting grain. There are many sources for buying beautiful and highly unusual walnut veneer. The sky (and your checkbook) is the limit. A complete re-veneer also opens up the possibility of changing wood species. If you like unusual and breathtaking, there are many, many options. I would be concerned that the marks from where panels were glued on will show through the finial finish. There will likely be marks/flaws from where you patched the veneer and to a lesser extent the nail holes. I don't know what your goals are. If your primary goal is originality, then you are heading down the right track. Of course, you could always complete the speakers the per your current plan and see if you are happy with the results. Re-veneering is always an option. Glitch
  8. Tom, Yes, I did spend some time comparing the L1590s and L1290s. I found the speakers to be very similar in the overlapping frequency bands. For this comparison, I used a Crown pro amp and used the built-in DSP to filter off the lower frequencies (where the L1590s have a clear advantage). This allowed me to more easily evaluate the mid, tweeter and crossover performance. I found overall tonality/voicing of the speakers to be remarkably consistent. I think the biggest difference between the two models is in the "attack" of sharp sounds like a hard snare hit. For these kinds of sounds, the L1590s seem not only faster, but also better damped. Both models exhibit the celebrated ADS sparkle. Both speakers reached highs that are beyond my hearing range. I didn’t notice any difference in the lower mid-range at the mid-woofer crossover frequency. I replaced the L1290s in my main system with the L1590s. I put them in the same location. The overall imaging was slightly better with the L1590s. I found the need to use an acoustic panel with the L1290s to tame some upper mid-range harshness. The L1590s also benefited similarly from the panel at the same location. I believe this confirms my theory that the problem lies in the room geometry and speaker placement. Unfortunately, my speaker placement is more governed by WAF than acoustic optimization. The most dramatic difference between the speakers is in the lower frequencies. The L1290s simply don’t go as low. I used a pair of subwoofers with the L1290s to extend the ultra-low frequencies. I was very happy with how well this worked. I am using the same subs with the L1590s. I had a much harder time integrating the subs with the L1590s. The subs ended up in a very different configuration than with the L1290s. I could live without the subs with the L1590s. I moved the L1290s into my basement workshop and added them to what we affectionately call “The Pile”. The Pile contains many of the speakers that I’m working on. They are all connected to a speaker switch where I can run A-B comparisons as I’m tweaking things. I decided to rework the mids and tweeters in the L1290s. I recently did the same to a pair of L880s and a set of spare mids and tweeters that I had on hand. I replaced the ferrofluid and realigned the voice coils. I performed measurements on all of these drivers and used the data to create matched pairs. Matching the drivers greatly improved the imaging of both the L1290s and L880s. Both of these speakers are Series 2 and use the same mids and tweeters. I’m still doing experiments on these where I’m varying the ferrofluid viscosity. The jury is still out on which combination I prefer the most. The experiments are a slow process. I hope to have this nailed down by summertime. I think that I have been able to improve the “attack” of the L1290s to be more like the L1590s with the tweaks. I suspect that the L1290s may now outperform the L1590s in imaging performance. I won’t really know how successful the changes were until I move the L1290s back upstairs and do direct A-B comparisons. I recently picked up a pair of PA1 amps. One of the amps was dead when I bought it. I was able to repair the broken one and went through both amps to ensure that everything is working well. I have the PA1s installed in the L1290s now. Glitch
  9. It is hard to say if rebuilding is necessary. I can say that the drivers (mids/tweets) that I rebuilt are measurably different. However, almost all of the differences are in the lower frequency of the driver, well below the crossover cutoff frequency. Aside from the quantitative measurements, I also did some qualitative A-B testing using a speaker switch. In general, the tonality of the speakers didn't change. The measurements appear to correlate to the listening tests. I used the Ferrotech ferrofluid from PE. This fluid is noticeably thinner that the ferrofluid that I removed. What I don't know is if the ADS ferrofluid is supposed to be more viscous than the Ferrotech ferrofluid. One could make the argument that the original fluid was thicker because it "evaporated" over the years. An equally plausible argument is that the fluid start off thicker and hasn't changed. I'd love to be able to pick the brain of some of the engineers that designed the drivers. Does anyone know what ferrofluid Richard So uses when he rebuilds the drivers? Does he use Ferrotech or does he have a supply of the original fluid? I'm still on the fence on whether it could "hurt" or not. If the drivers "need" the original ferrofluid (and the original ferrofluid is not available), yes, it could hurt. The place that it is most likely to "hurt" is marking up the cabinets trying to remove the drivers. There is also the possibility of not getting the voice coils properly centered. The ADS drivers do not have a positive indexing system between the cone/coil and the magnet. I found the alignment to be extremely sensitive (i.e. time consuming to get right). If this part of the job is done carelessly, the driver performance will be diminished.
  10. The Braun service manual has the most comprehensive information that I've seen yet about the PA1's. My German is pretty weak, but with the help online translators I've been able to figure out most of what I need to know about the amps. I did notice the the Braun version of the amp has a +-3dB range of the bass equalization, where the ADS version has a 0 to +6dB range. I was hoping to be able to figure out what frequency the bass filter is centered around. One could calculate it from the values given in the schematic, but since the design of the bass filter appears to be different, whatever frequency is found might be different anyway. What ADS subwoofer did you see on CL? What city?
  11. Tom, Have you had any luck locating manuals for the PA-1's? I found a service manual for the Braun PA-1 on this website. http://www.vintageshifi.com/repertoire-pdf/Braun.php It is most likely identical to the ADS version except for the logo. I'm still trying to locate a user manual. Glitch
  12. The components that ADS used in the crossovers were very good. Most of the capacitors in your crossover are of a type that does not degrade over time. Your crossovers do have one large electrolytic capacitor. Some brands of electrolytic capacitors will drift from their specified values over time. That particular electrolytic is not on the main signal path and is part of the low pass circuit for the woofer. As such, any drift in its value would have a secondary effect on the sound quality. I've measured a handful of these capacitors from similar ADS models and have not found any to be out of specification. The remainder of the components on the board (i.e. inductors, resistors, etc.) rarely go bad. It is unlikely that your crossovers are bad, or even could be improved significantly. I've run experiments of original ADS crossovers versus ones that I've modified with expensive capacitors (>$100 per crossover). I had to run carefully set up A to B tests and find specific snippets of songs to hear any difference. Even then, I'm not really sure that there really was a difference or that any difference I thought I heard was an improvement. I think that is worth the effort to pull out the crossovers, remove the components and measure them to verify that they are in specification. Almost always, I end up reassembling the crossover exactly as it was originally. It is kind of a waste of time, but I do get the peace of mind that i "know" the crossover is working per the original design. I believe that the tweeter and midrange on the L730's are before ADS started using ferrofluid. As such, you don't have to worry about the ferrofluid be degraded. About the most you could do is carefully pick off any dust or pet hair with a pair of tweezers. I'd only go after anything that is loosely stuck in the sticky coating. Leave anything that is deeply embedded alone. You will do more harm than good trying to remove it. This exercise won't make the speakers sound any better, but will improve the way they look. There is not much you can do with the woofer other than rotate it 180 degrees to address the possibility of spider sag. I don't do this unless I have the woofers out for some other reason. Unless you are are very careful, and a bit lucky, you may damage the cabinet. I don't think that the risk is worth the reward. The one place that you may be able to make some "changes in sound" is by adding damping and internal bracing to the cabinets. This will make the speakers sound more "point source". I wouldn't do this If you like a more "ambient" sound. When I've experimented with this kind of modification, I do it in such a way that the mod is reversible in case I don't like the results. I've had a few pairs that I kept the cabinet mods. I won't go so far to say that they are better. They do better match my sonic preferences. I've also experimented with changing the stuffing. Most of the time, after days of experimenting, I end up putting the original stuffing back in the speaker. ADS, especially in the era of your L730's, did a nice job of voicing their speakers. If you like the sound, do what you can to ensure that they are in specification, then just enjoy them. If you mess with them too much, you may loose a bit of the ADS magic. Glitch
  13. Has any measured the tweeter/midrange characteristics before and after having Richard So rebuild them? I'm interested in things like SPL vs. frequency, impedance vs. frequency, and T/S parameters. I have replaced the ferrofluid in several pairs of my ADS speakers. I am curious if my results match those of others. Thanks.
  14. What are you trying to accomplish with the modification? A properly working L730 should be a very nice sounding speaker. Some of the newer ADS drivers will be more linear (and bolt right in), but would likely require crossover modifications. Of course, you could install some brand new drivers and make it work. I don't know of any modern mid/tweeters that have the same mounting method (i.e. rectangular plate). The modified speaker would likely have a Frankenspeaker look to it.
  15. lakecat, The "super tape" is a double sided tape. The tape will be covered by the fabric when you are done. I used a stretchy material on the last set of grills that I recovered. IMHO, the tape made the job much easier than glue. For the first pass I lightly pressed the material into the tape. I could then reposition the material to get the right amount of tension and adjust the pattern. Once I was happy with the results, I pressed the material hard into the tape to make it permanent. I wouldn't use the tape if I was attempting a "restoration". Also, I don't think it would work well for folded corners. Hot melt or other glue may be helpful here if you are trying not to use staples. I can't comment about the longevity of the product. I'm guessing that it will hold up pretty well. I tried to readjust the fabric on one of the grills a week after I originally recovered them. I ended up ripping the fabric instead of lifting it from the tape (i.e the tape bonds well). I haven't tried this with a heavier linen type material. The tape definitely won't "bleed through." However, it might not "grab" deep enough into the (thick) fabric to really hold the fibers. I was skeptical about the tape the first time I heard about it. I bought a roll to experiment with and was pleasantly surprised. I figured if the tape didn't work for the grills, I could use it for something else. You can never have too many different kinds of tape on hand. Glitch