May 292016
 

As I have gotten older I’ve found myself becoming more interested in history in general, and our audio history in particular. Over the last ten or fifteen years I’ve become increasingly fascinated with the vintage Altec Lansing Voice of the Theatre loudspeakers that started their storied journey into theaters back in 1945, as World War II was winding to a close.

Altec literature courtesy of Great Plains Audio.

Altec literature courtesy of Great Plains Audio.

I was most interested in the A5 Voice of the Theatre model that was first released in 1945, and which continued to evolve into the 1960’s (above center). The A5 had become legendary for its role in the theaters across America, and had quite literally become The Voice of the Theatre in the hearts and minds of American movie goers.

Then later in 1986, the A5 wowed audio enthusiasts when Jean Hiraga did L´Audiophile demonstrations in Paris with it combined with 300B single ended triode (SET) amplification, and listeners praised the combination for its musical realism, exquisite textures & tone colors, and the dynamic truths that were so easily achieved.

Jeff's A5 VOTTs without grills.

Jeff’s A5 VOTTs as restored by Gary Fischer (without grills).

What would it be like to hear a loudspeaker whose first model introduction was over 70 years ago now? It was this loudspeaker that I really wanted to hear for myself, so I contacted Gary Fischer and commissioned one of his expert restorations of a pair of Altec A5 Voice of the Theatre loudspeakers.

For my restoration, I chose two 825B bass horn cabinets, two 16 Ohm 515B Alnico low-frequency drivers, two N-500-D ‘Dividing Networks’ (crossovers), two 1005B 10-cell horns, and two 16 Ohm 288C Alnico high-frequency compression drivers, which is a classic Altec-Lansing A5 Voice of the Theatre combination of components from that period.

Pricing for one of Gary’s beautiful restorations varies depending on the choice of components and their availability, but mine came to $6525 USD (without shipping) for that particular complement of components, which I though was very fair. You can read a more detailed discussion of Gary’s restoration here: Part 1, Part 2, and Part 3.

Jeff's A5 VOTTs as restored by Gary Fischer.

Jeff’s A5 VOTTs as restored by Gary Fischer.

Gary told me how the A5 Voice of the Theatre loudspeakers were designed to project their high frequency horns out through theater screens into the large space where the audience was sitting in the auditorium, and their bass drivers were designed to couple with and load the theater screen for additional low frequency response into the theater, and their crossovers were designed to provide that sort of equalization.

Nude A5 Voice of the Theatre loudspeakers, with stock Altec crossovers from back in the day, when plopped down in the low volume of a typical listening room are going to sound hideous, as what works well for theater equalization is not going to work in a domestic listening environment.

When Ron and I first listened to the newly arrived pair of A5 Voice of the Theatre restorations from Gary, we listened to them with a vintage pair of  Altec N-500-C crossovers, and it was some of the worst sound I’d ever heard coming from a pair of loudspeakers. Both Ron and I ran from the room with our hands over our ears!

Altec A5 VOTTs with Altec 500C crossovers being installed.

Altec A5 VOTTs with Altec 500C crossovers being installed.

I should point out that this is not at all the fault of the A5 Voice of the Theatre loudspeakers, rather it’s the theater-style equalization of those early crossovers working exactly the way they were designed to in a theater, which is not at all compatible for a home listening environment.

Fortunately the crossover issue has been solved for us by the afore mentioned Hiraga-san, with his artful crossover design optimized for the A5 Voice of the Theater loudspeakers, which adapts them to a home listening environment perfectly well.

Hiraga A5 16 Ohm crossover design courtesy of Sound Practices.

Hiraga A5 16 Ohm crossover design courtesy of Sound Practices.

So save your money, and don’t order Altec crossovers when you order your A5 (or A7) VOTTs from Gary, and with that money instead build yourself a pair of crossovers like I’m about to describe to you based on the design of Jean Hiraga. The cost will be about the same. I think you’ll be amazed at the result, at least I was!

I conferred with Yazaki-san on the Hiraga-san A5 crossovers, and Yazaki-san made suggestions for a couple of modifications.

Unlike the stock Altec crossovers, Jean Hiraga’s A5 crossover design doesn’t include a way to adjust the level of the high-frequency horn so you can more easily match it to a room, a feature which I’ve found to be very handy with the Altec N-500-D crossovers of my ‘Stokowski’ A7 VOTTs.

Yazaki-san proposed a very clever addition to the high-frequency circuit that would allow adjustibility by using vintage Clarostat variable resistors, which he was able to find in Japan, and then sent them to me as part of a ‘crossover kit’ he put together for me (thank you!). In Yazaki-san’s modification the 24Ω R3 resistor is replaced by a 10Ω R3-1 resistor, a 10Ω R3-VR (variable resistor), and a 10Ω R3-2 resistor in series. See the left side of Yazaki-san’s diagram below for details.

Yazaki-san also suggested we modify the low-frequency section of Hiraga-san’s A5 crossover circuit by installing a Zobel network. In this modificationYazaki-san proposed adding a series connected 10uF C4 capacitor and a 20Ω R6 resistor in parallel with the 16Ω 515B Alnico low-frequency drivers, to neutralize the effects of the driver’s voice coil inductance for improved performance. You can see this modification as inset 1 in the upper right-hand side of Yazaki-san’s diagram below.

Hiraga-san inspired 16 Ohm A5 crossover with Yazaki-san mods.

Hiraga-san inspired 16 Ohm A5 crossover with Yazaki-san mods.

After my post announcing the commencement of my Altec-Lansing A5 Voice of the Theatre loudspeakers crossover project after a six-month delay, I now have received all the parts I need to get started, and have done a first iteration of bread boarding a pair of crossovers, albeit with some deviations from Yazaki-san’s schematic due to a bit of intervening serendipity.

That intervening serendipity came in the form of Pete Riggle. As I reported in my last post on vintage tone I had asked Ron, Yazaki-san, and Pete for capacitor recommendations for the capacitors I still needed for the crossover. Very atypically neither Ron or Yazaki-san responded to my request for advice on capacitors, but Pete Riggle did (it turned out Ron’s computer melted down and he lost a bunch of emails in the process, so Ron was out of communication until I called him. I never did hear back from Yazaki-san, so we hope he is ok and happily listening to music somewhere).

Back story: Pete was impressed after hearing my ‘Stokowski’ A7 VOTTs and wanted to try a pair for himself. It turns out that Pete’s friend Harry came by a pair of well loved Altec A7’s that were decommissioned from a church, and are now under Pete’s care.

Pete's A7 VOTTs.

Pete’s A7 VOTTs.

Pete adapted the 8Ω version of Hiraga-san’s A5 crossover to his A7 VOTTs, using some ‘new’ vintage capacitors he discovered. This turned out to be serendipitous for yours truly, who needed to get some advice for the rest of the capacitors needed for my Hiraga-san inspired crossovers.

I told Luke part of the Peter Pan story about this in a comment:

Hi Luke,

I was absolutely blown away by Pete Riggle’s A7 VOTTs last week. Pete built a variation of the Hiraga crossover that he adapted to the A7’s, and he used iron core inductors, so you may be on to something there. Pete’s A7 system is one of the best hi-fi systems I’ve ever heard. It was love at first listen for me.

Pete also has some capacitors that he’s discovered that area really something special, and that is part of his secret for good sound too, I think. It doesn’t hurt that Pete has six decades of experience modifying and designing loudspeakers, and once owned a loudspeaker company.

His A7’s are rich, warm, musical, and utterly captivating to listen to music with. If I can get my A5’s sounding that good I’ll be in heaven!

Best,

Jeff

What I didn’t go into detail about in my response back to Luke was the nature of the capacitors Pete wanted me to hear in his Hiraga-style crossovers for his A7 VOTTs.

If you’ve read the comments here at Jeff’s Place carefully over time, you may remember Pete Riggle confessing his fondness for Ronken P61 style of industrial capacitors. They’re big, clunky looking, rugged industrial capacitors that use ‘wetmet’ film & metalized paper in oil (see the photo of the Ronken catalog page below). They are also relatively inexpensive out at Tedss.

10uF Ronken P61 capacitors.

10uF Ronken P61 capacitors.

Ronken (and other companies) made/make these style of rugged industrial capacitors, and they’re commonly referred to as ‘motor run’ capacitors.

Ronken catalog page

The Ronken P61 ‘wetmet’ oil-filled capacitors have been out of production for a while now, and getting harder to come by, and they have been replaced by current production ‘filmet’ Ronken P91 series capacitors, which I think (not sure) are a metalized polypropylene in-oil capacitor.

Ronken also made ‘all-film’ P64 series industrial commutation capacitors, the ‘all-paper’ in-oil P71 series of industrial capacitors, P81 series of ‘film-paper’ in-oil industrial capacitors, and the P86 ‘film-paper’ in-oil industrial commutation capacitors.

Well it turns out that these early Ronken P61 (and other) industrial motor run capacitors may very well be the Black Beauty, Bumblebee, and Tropical Fish tone capacitors of the industrial capacitor world. From what I have heard so far, these crazy industrial ‘motor run’ capacitors have absolutely gorgeous vintage tone.

Pete suggested I start with the Ronken P61 ‘wetmet’ caps for my A5 VOTT crossover project to get a feel for what they can do, and given what I had just experienced at Pete’s place, I ordered up what I needed from Tedss lickety split. Tedss didn’t have the P61’s in all the values I needed, but they had most of them. For the P61’s values they didn’t have at Tedss, I ordered some similar capacitors with the values I needed. Here’s what I ended up using for capacitors:

  • C1: For C1 I needed two 18uF capacitors, so I ordered six 6uF Ronken P61A23605H02 capacitors, ($13.20 each) with three each connected in parallel to give a C1 of 18uF for each crossover channel. Total cost with shipping was $94.93 USD.
  • C2: For C2 I needed two 10uF capacitors, so I ordered two 10uF Ronken P61A21106H11R capacitors ($22 each). Total cost with shipping was $56.40 USD.
  • C3: For C3 I needed two 0.82uF capacitors, so I ordered two each of 4.5uF CDE KKSF44P455QP1 capacitors ($5.50 each) and 1uF CDE KKNP66U105QPI capacitors ($12 each), that I connected in series to give two C3’s of 0.818uF capacitors. Total cost with shipping was $47.40 USD.
  • C4: The C4’s are for the Zobel networks, so I ordered two 10uF CDE KKSM66U106M3E capacitors ($16.50 each), with a total shipped cost of $33 USD. They haven’t arrived yet, but should be here soon.

I thought it would be fun to try these first, then later I can compare them with the Arizona Capacitors & SPEC Ruby-Mica capacitors combination that Yazaki-san sent to try for C3.

Initial crossover breadboard.

Initial crossover breadboard.

I retrieved the breadboards from the garage that I used for the Duelund-Westminster crossover project, and laid out a crossover. Those Duelund components are huge, so the breadboard was twice the size it needed to be for the A5 VOTT crossovers.

I took a quick trip over to Pete’s so he could cut the breadboards in half for me so they would be a more suitable size to work with, then I got back to work breadboarding the crossovers. Thanks Pete!

Initial crossover breadboard attached to A5 VOTT.

Initial crossover breadboard attached to A5 VOTT.

I wired my A5 VOTTs’16 Ohm 515B Alnico low-frequency drivers internally with Western Electric WE16GA for that desirable vintage tone, and used a run of WE16GA from the 16 Ohm 288C Alnico high-frequency compression drivers to the crossovers. I also wired the breadboarded crossovers with WE16GA, save for where the Zobel network will go after the rest of the parts arrive, which is connected with alligator clip connectors for the moment.

Initial crossover breadboard attached to A5 VOTT with WE16GA.

Left channel: Initial crossover breadboard attached to A5 VOTT with WE16GA.

Right channel: Initial crossover breadboard attached to A5 VOTT with WE16GA

Right channel: Initial crossover breadboard attached to A5 VOTT with WE16GA

After I got everything all wired up on the breadboards, I moved my very hefty Westminster Royal SE loudspeakers to the sides of the room, and then moved the A5 Voice of the Theatre loudspeakers into place and attached the breadboarded crossovers.

A5's room view.

A5’s room view.

After I got everything in place I warmed up the system and began to play music while writing up this blog post for you. Keep in mind that these elderly A5 Voice of the Theatre loudspeakers haven’t played music for a very long time (Gary could probably tell us how long), they have new diaphragms on the compression drivers that need some break-in time, and the crossovers have never seen a music signal go through them until this moment.

Preliminary Listening Impressions

I’ve been listening to music all morning while writing up this blog post, and my A5 Voice of the Theatre loudspeakers are sounding ridiculously good!

A5's room view 2

Like Pete’s A7’s, the A5’s are rich, warm, musical, and utterly captivating to listen to music with. In fact, they’re sounding so good with the Hiraga-san inspired crossovers, from a musical standpoint I’d say they are among a handful of the best sounding loudspeakers I’ve heard, which is sort of remarkable given I haven’t even started to optimize them.

My A5’s sound very good, but they don’t really sound like Pete’s A7’s. The A5’s and A7’s seem to inhabit two delicious parallel universes. I’ll look forward to getting Pete over here to give them a listen and get his take on things, and to hear what sort of advice he might have for me on further optimizing the A5’s. Iron core inductors like Luke recommended? (Hey Luke, what iron core inductors are you using?)

The Hot Spot sound track with John Lee Hooker, Miles Davis, Taj Mahal, Roy Rogers, et al.

The Hot Spot soundtrack with John Lee Hooker, Miles Davis, Taj Mahal, Roy Rogers, et al, Analog Productions 45RPM.

For an example, with The Hot Spot playing on the turntable, John Lee Hooker, the guitars, the bass, Miles Davis’ trumpet, and the drum kit, all sound like they are sitting here in the room with me, it’s so tangibly present. Along with their rich, warmish, and liquid presentation, the A5’s with the Hiraga-san inspired crossovers are remarkably transparent (which surprises me), but in a very naturally detailed sort of way, and throw a big billowing sense of space.

Timbral textures are extremely natural & nuanced, and the tone color is vivid and remarkably lifelike. The A5’s seem very well balanced top-to-bottom in my main room, so perhaps I need not have been worried about adjustibility. The low-end has power & impact on bass & drum hits, the mid-range is utterly seductive & nuanced, and the highs sound silky smooth.

On The Hot Spot the A5’s are positively breathtaking! The Hiraga-san inspired crossovers with the Peter Pan capacitors really excel in their ability to relay the artistry of the musicians on the Hot Spot, and the emotional impact is staggering.

Paul McCartney's Unplugged LP - a favorite of mine!

Paul McCartney’s Unplugged LP – a favorite of mine!

I got out some average recordings of some of my favorite music to see how the A5’s would fare with a challenge, like Paul McCartney’s Unplugged, and Nirvana’s Unplugged In New York.

The McCartney Unplugged LP sounds better than it has any right to with the Hiraga-san inspired crossovers feeding the A5 Voice of the Theatre loudspeakers. There is a very uncanny ‘Real Sound’ aspect to the reproduction, as Yazaki-san would say, and it is almost eerie, yet incredibly beautiful, and emotive, like being there at a concert. Again, in McCartney’s Unplugged, I’m hearing the same sort of truth of timbre, gorgeous textures, and deeply saturated tonal colors from instruments like I did on The Hot Spot, and McCartney’s voice sounds rich and expressive, just as John Lee Hooker’s did. Truly, the A5 Voice of the Theatre loudspeakers are capable of a magic that places them solidly in ‘super speaker’ territory, for the very fair price of around $6500.

If you’re a lost boy and need to come home and enjoy a little music in a way that won’t break the bank, I can heartily recommend a pair of Altec A5 Voice of the Theatre loudspeakers with Hiraga-san inspired crossovers & Peter Pan capacitors (you can probably tell I’m having fun with this, but man, this crossover with the motor run caps is sounding gorgeous!).

Nirvana Unplugged In New York - another favorite!

Nirvana Unplugged In New York – another favorite!

Washington State grunge band Nirvana’s Unplugged In New York was another musical treat through the A5 VOTT’s, with Kurt Cobain’s raw tortured vocals evoking awe in me as I sat and listened. I’d love to see this get the Chad Kassem 45RPM treatment, in fact I wish Chad would do s series of reissues of 45RPM LPs from the Unplugged performances, they were truly wonderful musically.

Ok, that’s a couple snippets from the bunch of albums I listened to this morning, but you get the idea, the A5 Voice of the Theater loudspeakers with Hiraga-san inspired crossovers & motor run capacitors sound fantastic and make music incredibly fun & satisfying to listen to.

Consider this post just a teaser, as I’ve got a lot more I want to do with these speakers and crossovers, but I feel very, very, fortunate that they’re working this well at this early point.

I’ll be adding in the Zobel network Yazaki-san suggested when the capacitors for it arrive next week, and will report back on that. I’m not sure I’ve got the Clarostat working the way it’s supposed to yet, as the adjustment range doesn’t seem to have much affect, so I’ll be investigating that further as well.

I’ll also be comparing the C3 combination of Arizona Capacitors & SPEC Ruby-Mica capacitors that Yazaki-san sent to the motor run capacitors that I put in there for now, so that should be fun, and Pete also wants to run some SPICE modeling on the crossover to see what that reveals.

Once I get everything dialed in the best I can, then I’ll get everything mounted in some respectable looking chassis.

As always, thanks for stopping by, and may the music playing make you happy!

 Posted by at 1:19 pm

  26 Responses to “A Couple of Breadboards for the Altec A5 VOTT Project!”

  1. HI Jeff

    I haven’t as yet built my crossovers. I have ordered some iron core inductors for my crossover. I only know from experience from building previous speaker crossovers the differences I noticed between using the air cored and iron cored inductors. The iron cores had that wonderful ‘classic tone’ and the air cores sounded more tonally leaner and slightly more ‘clinical’ in their sound.

    I will let you know how my crossover gets on but my present 16 ohm driver combination (as per A7) with the Altec 800hz crossover already sound very balanced and coherent, so it will be interesting to see how much further they can be taken. I did mention a slightly shouty horn sound and a slightly at times exaggerated lit up top end which I seem to have now controlled significantly with the addition of damping around the bass horn as per Gary Fischers suggestions.

    All the best Luke

    • Hi Luke,

      I’m glad you told me about the iron core inductors, that’s food for thought, and I want to look into it and give them a try. I’m not quite sure which ones to get, so I’ll have to study up. If you come up with a good recommendation let me know.

      Keep me posted on your Altec A7 adventure!

      Kind regards,

      Jeff

  2. Hi Jeff,

    Nice to see the project is finally moving forward. I have tried a few of the common audiophile caps in my Hiraga crossovers and I also have found motor runs to be my favorite. I have a mix of GE’s and Aerovox. I am using air core ribbon foil inductors because the consensus at the time was they were the best. Now I am excited to possibly experiment with iron cores. Glad to see you liked the sound right off from the start. I was thinking your 1005 would be to shouty being that it is 2db higher level than the 1505 Hiraga used. I have found that balancing the HF horn to be very critical to the overall sound. Also surprised you are getting a good low end with the enclosures out in the room that far. I have found they always needed to be close to the front wall or they sounded thin. Goes to show no room behaves the same. It will be interesting to see how much further you can take your A-5’s.

    Regards,
    Steve

    • Hi Steve,

      I’m really excited to have the A5 project moving forward. I’m with you on the iron core inductors, after Luke brought the topic up I want to give them a try. They may be part of the reason Pete’s A7’s are sounding so nice.

      I’m glad you mentioned the 2dB difference in sensitivity of the 1005 and 1505 horns. It should have dawned on me their sensitivity would be different, but it didn’t occur to me until you mentioned it. I suspect I may have just lucked out with the addition of the Clarostat’s to the HF circuit, although now I’m wondering what the 1005 might sound like damped down a bit more than it is now.

      The big surprise for me was the bass response, I wasn’t expecting it to be that good, but it sure is nice. Tonight the 10uF capacitors arrived for the Zobel network mod to Hiraga-san’s circuit, so I did a quick A-B with the Zobel network in and out of the LF circuit. The experiment with the Zobel network was a bust, as the sound leaned way out and became screechy when it was in the circuit, and bass output dropped off significantly. You just never know how something is going to work until you try it.

      The sound has been all over the place as I’ve put more time in on the A5’s, must be that everything is settling in. I feel lucky that it is working as well as it is right now though, as it gives me a solid place to work from.

      Thanks for your comment, it was illuminating! Keep them coming!

      Kind regards,

      Jeff

  3. Shouldn’t the C3 capacitors be parallel to achieve you target value? And I don’t see the Mica bypass there?

    • Hi Josh,

      With the motor run caps I’m trying at C3 (in the photos) a 4.5uF cap in series with a 1uF cap gives a capacitance value of 0.818uF.

      With the Arizona Capacitors plus the SPEC mica caps as per Yazaki-san’s diagram you are correct, they do have to be in parallel to add up to 0.82uF. I haven’t tried them yet, but hope to this weekend.

      Kind regards,

      Jeff

  4. Also, one more comment regarding your air-core inductors… I don’t know the exact scale on your mock-up crossover, but generally you’ll want to space them out by >10″ or even a foot if possible – they will crosstalk if too close and their effectively values will be off. Alternatively, you can make sure they are all oriented at right angles to each other (x,y,z).

    You can find some helpful measurements and guidelines here:

    http://www.troelsgravesen.dk/coils.htm

    Good luck!

    • Hi Josh,

      I’ll put the inductors at right angles to each other, there isn’t enough room to put them that far apart! I’ll report back on if I can hear a difference.

      Thanks for the comments, and keep them coming! It takes a village (for me) to raise a crossover! 😉

      Kind regards,

      Jeff

      • Even on that monstrosity of a board! hahah!

        Also, I know you are using the Ohmite R’s…and they are consistent with what Altec was using… found in both the N-800-F I dissected sacrificially and in my Altec 100A’s but I’ve also played around with: Duelund, Vishay Z;s, Mills. Currently, I am running your beloved Allen Bradley 2w R’s which are a lot of fun and obviously look cool. Those horns are so efficient that I bet you’ll barely see milliwatts through them but thought I’d throw that out there if ya want to get a little crazy and play around with that sometime. 😉

        • Thanks for reminding me about the inductors, Josh, I just flipped them so they were at right angles to each other, and it was immediately noticeable.

          I think I feel an Allen Bradley order coming on! 😉

          Cheers,

          Jeff

  5. Hi Jeff with regard to the zobel network. I would like to test it on my 8ohm VOTTs. Would 1/2 the values of the zobelnetw. for your 16ohm system do the job ( 5uf and 10ohm vs 10uf and 20ohm )?
    Regards
    Kjartan

    • Hi Kjartan,

      I don’t know the answer to your question, sorry about that. Perhaps Yazaki-san or Pete Riggle can help out here?

      My advice would be to save your money, as when I tried implementing the Zobel network into the LF circuit it seriously degraded the sound quality & tone.

      Kind regards,

      Jeff

  6. Hi Jeff, I follow your A5 project closely as I am on a similar path. Similar, but different drivers and horns: Onken 360 cabinets with Altec 416z 16 ohm and 288g 16 ohm on 311-90 horns. Different enough from your A5 that I’m not sure if the Hiraga crossover would work for me. That’s why I am writing now–I want to build a crossover for my speakers and if either you, Pete, or another of our audio brothers offers help I’d appreciate it!

    I’ve run a number of crossover calculators and I’m more confused than ever. This seems like a time when those who have been down the path before would have the best input. I am hoping that’s you or another reader.

    Best,
    Doug

  7. Hi Josh,

    Thank you for your reply, however, I already own a pair of Werner’s crossovers. I’ve been running them for a year or more and they sound good, but I want to build my own. A friend brought over a pair of his Solen inductor and various caps crossovers and I liked the sound more. So this has me on a quest to build something that works well for my specific driver/horn arrangement. I’m thinking the Solen or Goertz foil inductors and the Jupiter beeswax aluminum foil caps, but in what values? And what about HF compensation a la Hiraga design? My sectorals are not the same as the multi cells, so I don’t know if the compensation circuit is needed or should be changed.

    Anyway, thanks for the suggestion. Any additional input is appreciated!

    Best,
    Doug

    • Hi Doug,

      The Hiraga crossover has proved to be effective with a variety of Altec A5 & A7 variations, and the addition of a pair of L-pads really helps with balancing the low & high-frequencies.

      I think I’d start by building a pair of 16 Ohm Hiraga-style crossovers and adding the L-pads to help dial in the high-frequencies. There’s no secret other than obtaining a balance that you find enjoyable to listen to, which is fairly easy to do with the Hiraga crossovers with the addition of L-pads.

      It would also be worthwhile asking Pete Riggle about adapting the Hiraga crossovers to your speakers, he’s got lots of experience designing crossovers, and his Altec designs have really impressed me.

      One thing I’d suggest is to ask Frederik at Duelund about the possibility of making some CAST tinned-copper capacitors for use in your crossovers. I’ve been using prototype Duelund CAST tinned-copper capacitors in my preamp and Altec A5 crossovers, and they’re just blowing me away with how musical they are.

      Anyways, I hope that helps, and let me know how things work out.

      Kind regards,

      Jeff

  8. Hi Jeff,

    I just stumbled upon this site and am blown away! Thanks for putting it up.

    I’m building a VOTT system based on the “210-split” concept found in Sound Practices (issue #15). It will use a Hiraga-style crossover, so your website is a great resource for me.

    One question I have concerns R3 in the circuit. Its not clear to me why the variable resistor is stuck between two flanking resistors in series. Wouldn’t it be simpler to combine R3-1 and R3-2 into a single 20 Ohm resistor? This would reduce the number of solder joints, lead wires and components (simpler is nearly always better). If you are using expensive resistors (like Lefson), this would lower the price, too (or allow you to use a single Ultra instead of a pair of Premiums).

    One more query, if I may. I see you’ve modified the Yazaki-san drawing by adding an L-pad at the output of the high frequency section. This controls volume to allow matching of the 288C and its horn with the woofer section. What is the function of the variable resistor in R3? Does this affect tone or crossover frequency, or is it now redundant to the L-pad?

    As you can see, I’m looking for ways to simplify R3. I suspect it has a major impact on sound quality.

    Thanks again for all your work on this incredible site and keeping the flame alive! I’m really enjoying the process of catching up.

    Cheers,
    Brian

    • Hi Brian,

      I would recommend going with the stock Hiraga circuit, with the addition of an L-pad.

      Yazaki-san’s circuit mod for the crossover works well (and is similar in concept to using an L-pad), but I really like the performance of the Hiraga circuit with just the addition of an L-pad, which is what I’m going to do with the A7 crossovers I’ll be building in the not too distant future.

      Thanks for the kind words, appreciated!

      Jeff

  9. Jeff,

    Thanks for the advice. Best to get it all working before engaging in tweaks. They might be unneeded.

    I was suspicious of inserting a variable resistor at such a critical point (R3). For what its worth, I think I figured out why Yazaki-san didn’t combine the two fixed resistors into one unit. The brown devils can’t handle the specified watts unless you wire two of them in series. If you try to put Lefsons here, you would need to heat sink them and you would need at least two in series.

    Do you still recommend the Ronken P61 oil, and the Arizona/Jupiter capacitor combinations discussed in past posts? My split A4 cabinet is progressing nicely and its getting close to time for ordering crossover parts. 🙂

    Again, thanks for your support of the VOTT community.

    Cheers,
    Brian

    • Hi Brian,

      I’ve been learning as I go on the parts and circuit choices. The biggest lesson so far is sticking with the Hiraga circuit and using an L-pad to blend the LF & HF. There’s so much variation in sensitivity for a given Altec driver/horn combination that the L-pads are really handy, and why the original Altec crossovers were adjustable – it was a necessity.

      Once the resistance values get figured out with the L-pads, one could always replace them with fixed resistors. So far, the Lefson resistors are at the top of the mountain for the resistors I’ve tried, followed by the Duelund’s, the Path Audio, and then the Brown Devil’s.

      The Ronken’s work nicely. Pete Riggle Audio Engineering has some hand-picked oil caps that sound really nice in his A7 crossovers, and would be worth checking out.

      The Arizona/Jupiter cap combo sounds really good in the HF circuit, but the Duelund tinned-copper caps are much, much, better in the HF circuit. If you can splurge they’re definitely worth the extra $.

      In the near future I’ll be building A7/A5 Hiraga-style crossovers using all Duelund tinned-copper components (the Duelund components are being built now), which I’ll be able to compare with my current A5 crossovers. So if you can wait a month or two for me to report on the results, I should have some additional insights to share.

      The Duelund tinned-copper caps in crossovers and electronics circuitry are astonishingly good. I recently replaced a pair of Arizona Blue Cactus caps in my pal George’s MX110Z preamp with the Duelund tinned-copper caps, and it was an object lesson of how incredibly good those Duelund caps are. I had previously done the same thing in my MX110Z, but I was amazed all over again at the improvement the Duelund’s brought in George’s MX110Z in before and after listening – they’re a revelation.

      Have fun with your project, Brian, and let me know how it turns out!

      Kind regards,

      Jeff

  10. Jeff,

    Before the late 1960s, Western Electric and Altec Lansing labled their 288 drivers and 515 woofers with terminals marked “T-1” and “T-2”. After that date they switched to red and black. This is causing me some confusion regarding how to hook up these older drivers.

    Further complicating matters, I know that the 515 woofers locate the voice coil in front of the magnet, but the 288 drivers position the voice coil behind the magnet. Sending a positive signal to each terminal T-1 causes a forward pulse (compression wave) on the 515 woofer, but produces a backwards pulse (rarefaction wave) from the 288 driver. I have an “Application Note” published by Altec that discusses this topic (AN-9).

    It has been my understanding that a second-order (12db/octave) crossover (like the Hiraga design) always inverts the signal to one driver with respect to the other. I have assumed that this inversion-effect would bring the two drivers back into synchrony so they both produce compression waves when a positive signal from the amp’s red terminal reaches the T-1 terminal on the drivers. Does this sound right to you?

    In other words, if I use the Hiraga diagram and hook the crossover’s (+) woofer-out to the 515 driver’s T-1 terminal, which terminal on the 288 should I hook up to the crossover’s (+) tweeter-out? (T-1 or T-2).

    Thanks in advance for any help you can provide on this querry.

    Cheers,
    Brian

    • Hi Brian,

      The Altec 288 and 515 terminal connections can be confusing.

      For the 515 Altec originally labeled the terminal connections “L1” and “L2” with the idea that when (+) is applied to L1 and (-) to L2 the 515 driver will send a sound wave towards the listener. So for the 515 driver L1 is the positive connection and L2 is the negative connection.

      On 288 compression drivers’ binding posts sometimes there’s a “1” and “2” and other times there’s nothing, so the only way to be sure which binding post is which is to take the back off the compression driver and look at the diaphragm. Just look, don’t touch the diaphragm! One side of the diaphragm will have an “L1” on it, and so the terminal associated with that side is the L1 terminal.

      However, for the 288 compression drivers the L1 terminal is (-) and L2 is (+) because that’s when the sound wave is going towards the listener.

      With the Hiraga-inspired crossover that I use with my A5’s (above), the LF (+) out connects to L1 on the 515 driver, and the LF (-) out connects to L2.

      In the Hiraga-style crossover the LF (+) out becomes the HF (-) out, and LF (-) becomes HF (+).

      So the HF (-) out connects to L1 terminal of the 288 compression driver, and the HF (+) connects to the L2 terminal.

      Anyways, I hope that helps with getting the connections figured out for you!

      Kind regards,

      Jeff

  11. Jeff,

    Thanks so much for the quick reply!

    Just to verify that I understand your description, here are the assignments for the four connections shown on the right-hand side of the Hiraga schematic:

    LP-Out (+) connect to woofer L-1
    LP-Out (-) connect to woofer L-2

    HP-Out (-) connect to 288 L-1
    HP-Out (+) connect to 288 L-2

    (Both L-2 terminals are connected to ground or the negative amp terminal.)

    Please confirm.

    Thanks again for your assistance, and for the great website!

    Brian

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