onplane Posted March 7, 2009 Report Share Posted March 7, 2009 Roy's elegant solution for replacing the old corroded pots with a modern L-pad with a 25 ohm resistor in parallel has once again been verified. See Zilch's work:Zilch's recent measurementsI for one like low cost solutions and applaud Roy's work here. Nice going Roy!!!Regards,Jerry Link to comment Share on other sites More sharing options...
Mexicomike Posted March 8, 2009 Report Share Posted March 8, 2009 Roy's elegant solution for replacing the old corroded pots with a modern L-pad with a 25 ohm resistor in parallel has once again been verified. See Zilch's work:Zilch's recent measurementsI for one like low cost solutions and applaud Roy's work here. Nice going Roy!!!Regards,JerryNeato! Sounds like a perfect replacement to ensure original operating specs if cleaning and di-electric greasing the original pots is not feasible! Link to comment Share on other sites More sharing options...
johnieo Posted March 8, 2009 Report Share Posted March 8, 2009 Roy's elegant solution for replacing the old corroded pots with a modern L-pad with a 25 ohm resistor in parallel has once again been verified. See Zilch's work:Zilch's recent measurementsI for one like low cost solutions and applaud Roy's work here. Nice going Roy!!!Regards,JerryThat calculation was done some years ago; the post and figures were probably not retained when the board migrated to the newer IP software. Link to comment Share on other sites More sharing options...
RoyC Posted March 8, 2009 Report Share Posted March 8, 2009 Roy's elegant solution for replacing the old corroded pots with a modern L-pad with a 25 ohm resistor in parallel has once again been verified. See Zilch's work:Zilch's recent measurementsI for one like low cost solutions and applaud Roy's work here. Nice going Roy!!!Regards,JerryThanks Jerry......and thanks to Zilch for the measurements he is performing on the 3a. He is conducting much more than level control testing, and has a very interesting thread going over at AK. Time do fly! It has been a few years since I ran the idea past John O'Hanlon, who performed the calculations referred to in his post above. (Jerry later posted supportive calculations and comments of his own here and on AK as well.) John included the scheme in the AR-3a restoration guide even though, at the time, I thought it may be a bit too radical and/or confusing for our fellow restoration purists . (John had to field much, sometimes overwhelming, input from the rest of us, and is the one who really made that document happen).Actually I am quite relieved that Zilch's measurements did not reveal anything detrimental (vs the pots) regarding the "8 ohm l-pad/25ohm resistor" arrangement, and pleasantly surprised that it measures as close to the pots as it does. We should keep in mind that the AR pots vary from under 15 ohms to over 16 ohms, and that the very same pots were used for AR's 4 ohm and 8 ohm systems...so "precision" was never anticipated as I experimented with l-pads. The goal was to modify the circuit in a way that would make the l-pad act similarly to the pot around the "white dot" settings (using approximately the same amount of rotation from maximum). I agree with Zilch's assertion that we are simply modifying the crossover with parallel resistors across the drivers, resulting in a circuit in which 8 ohm l-pads produce similar attenuation effects as the original 16 ohm pots. However we define it, it works well enough for those who want pot-like action and performance without the corrosion. I'm thinking of coaxing or bribing Zilch into evaluating some of our replacement tweeter ideas before he starts cutting those big horn tweeter holes in his 3a cabinets...Probably shouldn't push my luck .Roy Link to comment Share on other sites More sharing options...
Zilch Posted March 9, 2009 Report Share Posted March 9, 2009 I'm thinking of coaxing or bribing Zilch into evaluating some of our replacement tweeter ideas before he starts cutting those big horn tweeter holes in his 3a cabinets...Probably shouldn't push my luck .The HF results are now posted here:http://www.audiokarma.org/forums/showthrea...107#post2568107I'm not averse to measuring alternative drivers, but it would be good if others did this as well and posted their results. If they conflict with mine, that's not a problem, rather, it merely raises an issue in need of resolution. If they are consistent with mine, then we all accrue greater confidence in our respective findings.Someone did enough work to determine that the Hi-Vi tweeter requires an inductor across the driver to improve its compatibility with the original. Is that better added before the attenuator, perhaps? I've also seen various values suggested for that inductor; what is optimum? Where are these measurements posted?One factor that is clear in my results is, as you earlier observed in another thread here, the stock AR pot does not normalize impedance with attenuation. The L-pad and augmented L-pad are somewhat better at this, but there remains a 2X impedance variation within the typical operating range when used with the original AR drivers, in the wrong direction, in my view, as the filter frequency goes down when the output drive increases. A 4-Ohm L-pad might do a better job, or an 8-Ohm driver.As it turns out, that's of little consequence in either the AR4x or AR3a, as the natural rolloff of the stock drivers basically establishes the acoustic crossover, not the electrical filters' voltage drives. However, with substitute and upgrade drivers as are by desire or necessity frequently under consideration, whether the same criterion is satisfied should be confirmed by measurement before any such recommendation is deemed acceptable. "I installed Acme tweeters in my AR2axs, and they sound WONDERFUL" doesn't cut it here, certainly not for those desiring to maintain or restore the original sonic character of these vintage designs.We've also learned a bit more about this, as well, that max dispersion and uniform power response were the prime objectives here, and Carl has demonstrated through his investigations of the Hi-Vi tweeter, for example, that it is not as good a match in this respect as I suspect might be found among other modern alternatives. I'm sorry, folks, but the apparently universal desire to find a substitute that looks the same, fits perfectly in the original cutout, requires no changes to the crossover, and costs less than $25 must be traded off against a more fundamental purpose here, and that cannot be accomplished by fiat alone.There are substantial and certainly sufficient resources among the membership to produce a worthy outcome in this endeavor; all that is required is a commitment to get it done.... Link to comment Share on other sites More sharing options...
Shacky Posted March 10, 2009 Report Share Posted March 10, 2009 We've also learned a bit more about this, as well, that max dispersion and uniform power response were the prime objectives here, and Carl has demonstrated through his investigations of the Hi-Vi tweeter, for example, that it is not as good a match in this respect as I suspect might be found among other modern alternatives. I'm sorry, folks, but the apparently universal desire to find a substitute that looks the same, fits perfectly in the original cutout, requires no changes to the crossover, and costs less than $25 must be traded off against a more fundamental purpose here, and that cannot be accomplished by fiat alone.There are substantial and certainly sufficient resources among the membership to produce a worthy outcome in this endeavor; all that is required is a commitment to get it done.... I am not a measurement expert - I'll leave that to those who know much more than me. But I do know music and what I like in sound. I like to listen to my speakers - for long periods. I know what sounds right to me - or should I say pleasing. I tried the HiVi on my AR 5's as recommended by Roy. I don't think there's another tweeter made that will match the original AR's dispersion. So that boat has likely sailed. So then what sounds "good"? I like the HiVi and am sad to see that availablility is in question. I don't want to butcher my cabs - I may want to install original at some point. So the HiVi's are a great solution for me. Though I have them turned down quite a bit in my listening are. My point is - fitting the existing hole is an important factor for those of us who desire originality - or at least something that is easily returned to original. Link to comment Share on other sites More sharing options...
Zilch Posted March 10, 2009 Report Share Posted March 10, 2009 My point is - fitting the existing hole is an important factor for those of us who desire originality - or at least something that is easily returned to original.Uhmm, not ALL solutions require intervention with a SawZall. Full range response measurements are now posted in my AK thread.... Link to comment Share on other sites More sharing options...
RoyC Posted March 10, 2009 Report Share Posted March 10, 2009 There are substantial and certainly sufficient resources among the membership to produce a worthy outcome in this endeavor; all that is required is a commitment to get it done.... This has been a subject of considerable interest here in the past. The actual goal is probably someplace between "good enough" and "just like the original"...while keeping it simple to implement. Few folks here are looking to "improve" upon the original feel or character of these old systems, so major modifications are usually discussed in the mods and tweaks section of the forum. The primary reason a replacement tweeter has been discussed at all, is that the unique original tweeter appears to be degrading (decomposition of the foam suspension and damping material), and used ones are becoming very scarce. A number of us sent tweeters to Ken Kantor for testing awhile back, primarily to evaluate the only true "replacement tweeter" offering from AB Tech. Original tweeters (including new old stock 3a tweeters provided by Tom Tyson) and AR303 tweeters were tested as well. It became immediately apparent that, above and beyond the dispersion issue, the ABT tweeter, like all modern tweeters, does not possess the unique construction and natural roll off characteristics of the old tweeter. A crossover modification was needed regardless of the chosen "modern" tweeter. The ABT tweeter is a 3/4" dome with a perfectly fitting faceplate. Those attributes alone are why most folks were/are choosing it as a replacement without any crossover changes...yet it does not sound remotely like the original, without a crossover modification. It also costs $70, even though its construction is no better than a $20 tweeter. Although a higher order crossover was more appropriate, Ken suggested that a small .07mh coil across the back of the ABT Tweeter would bring it much closer to the original. The reason for this approach is that most folks visiting this forum are looking to "fix" their old speakers as simply and as easily as possible. They just want to make their old speakers work again. Even if a "better" tweeter became available, it is unlikely it would be of much use to most visitors here unless it was easy to install...So, screwing in ABT tweeters, replacing old capacitors, cleaning pots, and re-foaming woofer surrounds are at one end of the spectrum, and Carl's re-designed ("Super Mod") 3a, using only the original woofer and cabinet, is at the other.With the above serving as a quick summary, some of us have continued to passively look for alternatives to the AB Tech tweeter. Carl has provided some great data along the way, and subjective comments have been posted. I recently started experimenting with the HiVi tweeters for only one reason. They fit the hole. It turned out that, imo, they sounded quite nice and more appropriate than the ABT tweeter, while using a similarly sized, .05mh to .1mh parallel inductor ABT mod, for less than 1/3 of the ABT's price. (They are also better constructed for that price.) I purchased a fair number of them, and distributed them to various forum members for some feedback and some fun. Ebay's "Vintage AR" liked them, and began offering them as kits last month. The (subjective) feedback has been positive so far.......you are up to date. There is still much to be explored, and I am sure any input on your part will be welcome and of interest. The nice thing about this is that, as interesting as the AR-3a's "1.8khz suckout" discussed in the AK thread is, as well as the other painstaking measurements you have conducted are, it will not affect the appeal of these speakers one way or the other. There is room for much participation on the part of all who simply enjoy listening to these speakers. To quote a recent CSP post, "If it sounds good, it is good".Thanks once again for your AK thread update.Roy Link to comment Share on other sites More sharing options...
Zilch Posted March 10, 2009 Report Share Posted March 10, 2009 There is still much to be explored, and I am sure any input on your part will be welcome and of interest. The nice thing about this is that, as interesting as the AR-3a's "1.8khz suckout" discussed in the AK thread is, as well as the other painstaking measurements you have conducted are, it will not affect the appeal of these speakers one way or the other.Geddes has a similar issue with the on-axis response of his waveguides. His answer? "Don't listen there!"That might be apropos here, as well, but that AR3a does not appear to exhibit any suitable angle for quality listening.From my findings thus far, CSP member Soundminded has sussed the issues out well:http://www.classicspeakerpages.net/IP.Boar...ost&p=77191If we aspire to the higher purpose of maintaining or restoring the vintage sonic character of these speakers, there is clearly more to be done to accomplish that, and the constraints imposed by "saleability" substantively conflict with the endeavor, both in conceptual and practical terms.... Link to comment Share on other sites More sharing options...
genek Posted March 10, 2009 Report Share Posted March 10, 2009 That might be apropos here, as well, but that AR3a does not appear to exhibit any suitable angle for quality listening.Is that a conclusion drawn solely from your measurements, or have you conducted any subjective tests on these speakers. IOW, if you disconnect the tone generators and run some music through them, how do they sound? Link to comment Share on other sites More sharing options...
RoyC Posted March 10, 2009 Report Share Posted March 10, 2009 That might be apropos here, as well, but that AR3a does not appear to exhibit any suitable angle for quality listening....I suppose that depends on one's definition of "quality listening". Hmmm, on second thought you are absolutely correct, measurements do not lie...the AR-3a sucks. If you promise not to drill or saw any holes in them, I will be happy to take those old boat anchors off your hands for free! Where do you live? Roy Link to comment Share on other sites More sharing options...
Zilch Posted March 10, 2009 Report Share Posted March 10, 2009 Is that a conclusion drawn solely from your measurements, or have you conducted any subjective tests on these speakers. IOW, if you disconnect the tone generators and run some music through them, how do they sound?Just one running right now, I've got to do Roy's L-pad mod to the second, which has corroded pots, bypassed, and does not balance; the parts are on order.The single sounds, well, "Vintage correct." Link to comment Share on other sites More sharing options...
genek Posted March 11, 2009 Report Share Posted March 11, 2009 The single sounds, well, "Vintage correct." I think it's safe to say that that's a plus around here. Link to comment Share on other sites More sharing options...
Shacky Posted March 12, 2009 Report Share Posted March 12, 2009 IOW, if you disconnect the tone generators and run some music through them, how do they sound? Link to comment Share on other sites More sharing options...
Zilch Posted March 12, 2009 Report Share Posted March 12, 2009 It's a personal question, really, about the listener, not the speaker.... Read up here, maybe:http://www.aes.org/tmpFiles/elib/20090312/13686.pdf Link to comment Share on other sites More sharing options...
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