JonM

I've been in touch with the original manufacturer of the transformers (Custom Coil in Zanesville, Ohio) and they found replacements I think in inventory, though they are missing the bell covers. I am still working with them on getting things arranged (which may involve making new covers, or using the ones from my transformers). They have been very helpful - will let you know how it turns out.

I know I sounded like a ding dong in my last posting, but frankly I looked a couple of years ago when the amps originally failed, and there was no hint of Custom Coil. Their web site must be relatively new. They appear to be a small shop, and small businesses are often the last to "webify".

I appreciate all the feedback (no pun intended). I, too, am completely baffled that both went at the same instant. But that's what makes me think it was something in the AC feed. They were both protected by 2 amp fast blow fuses on the primaries, and I'd have thought that would have prevented any currents needed to do real damage. They were, I admit, plugged into a Tripplite surge protector/AC filter (not a UPS), and I wonder if some weird resonance started in the surge protector's circuitry at a very high frequency that...no, the windings of the transformer would be a high impedance to that...oh, I really am baffled! I determined it's a short in the primary by the very simple test of disconnecting *all* the secondaries, putting in a new fuse, and plugging it in. Pff - fuse blows instantly. The preamp is fine - everything else works with a different power amp. Nothing else that was being fed by the same surge protector that day was damaged (I no longer use it - I can't say it's guilty, but I'd rather not find out by damaging something else with it). I guess getting the transformers rewound is a possibility, but I was hoping to find a way that's less expensive. And yeah, the Mk IV uses a different power transformer than either the Mk III or the ST 70. My transformers were made by "Custom Coil" (marked on the case) DING DING DING!!! I just did a google search and found Custom Coil is still in business, in Ohio. Time to drop them an email. Thanks guys - it wouldn't have occurred to me to look if I hadn't had this exchange with you. I'll let you know what happens when I talk to the folks at Custom Coil!

I'm asking this here just because this seems to be the forum with the most Dyna postings. Maybe one of you can help. A year or two ago both of my Dynaco Mk IV amps (they're the 40 watt mono ones, sort of half a Stereo 70) suffered the exact same catastrophic failure at the exact same instant. The power transformers shorted out! One moment they were quietly playing Sunday morning background music, the next moment there was silence. I cannot for the life of me figure what happened (weird harmonics on the power line?), but the primaries of both shorted out (yup, I disconnected all secondaries and plugged them in, and the fuses still instantly blew), and I am still looking for replacements. Any idea whom to contact? I tried Magnequest, and Hammond - the usual suspects. No luck - either the wrong voltages, or no bias voltage tap, or simply the wrong dimensions to fit the chassis. The rest of the amps are in beautiful condition, and I like the sound (not as sweet as my ST-70, but still very listenable), so you can imagine I'd love to find new transformers and get these units running again. As they are now, they are collecting dust. :-( Any ideas are much appreciated. I'm using SS to feed my Khorns for now, and I know they'd like to be tube-fed again :-)

Okay, so I've been away for a while, and I come out of the proverbial basement to see that Klipsch has released the long awaited updated Klipshorns! I have found only one review of the new Khorns, and it is VERY positive. Has anyone here heard them? How do the new tweeter and squawker sound? Who actually makes the new drivers? Anybody thinking yet of updating their existing Khorns with the new drivers? My 1976 Khorns are doing great, thank you very much, so I can easily resist the upgrade fever. But it's good to see the old masters back in production. Paul should feel proud, wherever he is :-)

The 150 was a derivative of the 400. And it was perhaps Dyna's best sounding SS amp. I built one in 1975 - still have it, sometimes I pull it out and turn it on. Still sounds pretty good. The 120 was a mid 1960's design, very early SS. I have two of them, and they are bright and hard sounding. Of interest only for their historical significance. The picture above is of a 120 chassis with someone else's circuit. For one thing, it has a modified power supply. Note the power supply in the pic is unregulated +/- whereas the Dyna 120 used a regulated single ended power supply and big output capacitors to block the DC from the speakers. I can't see the pic as I type this, but I don't recall seeing the output caps, either, so this is a Dyna 120 chassis with someone else's circuitry installed. It might be gawdawful, or it might be fine, but it's not a Dynaco, 120 or 150.

Oh, yeah, it was hum radiated by the transformer. When I moved it away from the amp by a few feet, the hum went away. I could change the hum level by reorienting the transformer. I couldn't mount the transformer on the same wooden block as the rest of the amp without the hum being unacceptable. That's why I say a transformer with better shielding and a lower radiated hum field is needed. If I'd known how bad the RS transformer was, I'd never have bought it. The input impedance of the IC is 20 kohms, set by resistors internal to the chip.

I have no idea what commercial amps may use this part. It's low powered, so maybe boom boxes (or headphone circuits?). It's been out since '96 (the date on the spec sheet from Philips), and NTE makes a substitute, so it must have some users or they would have stopped production. It's probably lurking out there in more places than we realize :-) (I have seen places selling the part alone for about $6, for those who really want to roll their own.)

Paul Klipsch said it - What this country needs is a good 5 watt amplifier. Well, I think I've found a pretty good one, at a terrific price. Velleman, from Belgium, is known for their electronics kits (boy, who else makes electronics kits anymore?). Tube and solid state, some are fairly well regarded. They make little kits, too, ones with almost no parts, no cases, you provide the power supply - really, experimenters' kits. The one I built is based around the Philips TDA1521 power amplifier module, really two high fidelity power amplifiers on a chip. Velleman takes this module and adds a little circuit board that carries a full wave rectified power supply (with 9400 mF capacitance - not bad), input blocking capacitors, an output load (I assume to keep the amp stable at RF), and a big heat sink. You provide the power transformer, the input and output connectors, and a case if you really feel like it. Velleman's part number for the kit is K4003. Velleman makes some pretty bold claims for performance (2x10W at 8 ohms, 0.07% THD at 1 KHz/1 Watt, 98 dB S/N, FR 7 Hz to 60 kHz), so I downloaded the Philips datasheet, which is a bit more conservative (0.15% THD at 6 watts, 20-20 kHz power bandwidth) but which gives a full set of fairly impressive curves, especially when you consider it's all done, for both channels, in an IC not much bigger than a couple output transistors. (Oh, it even has a turn on/off pulse suppression, so there's no thump in your Khorns when you turn it on or off!) So for $35 I bought one. (I could have paid less mail order, but immediate gratification was a priority :-) The kit comes with instructions in half a dozen languages, but assembly was a snap. It would be hard to mess this one up unless you really rush it and are simply careless. I mounted the amp on a scrap piece of pine - literally just held to the wood by a piece of copper wire across the heat sink. Inputs and outputs are via 22 GA copper bell wire. (See the attached picture - you can just make out the wood block, which was painted white, on top of a sheet of white cardboard.) Simple, expedient, fast and cheap. I wanted to hear what this thing could do! I tried powering it with a $10 Radio Shack transformer (part #273-1512B - 25 VAC CT, giving two 12 VAC feeds, exactly what Velleman recommends and right at what Philips suggests), but that (cheap) transformer radiates such a hum field that I had to keep it several *feet* from the amp to keep the hum out of the music. Not practical. So I found a +/- 20 VDC supply that used to run some piece of office elctronics (a printer or router or something). I hooked it up to the same connections as the AC transformer. (So what if the DC gets "rectified" again in the amp's power supply? - that's no problem!). 20 VDC is near the 21 VDC upper limit of the supply voltage that Philips recommends in its data sheet, but it's within spec, so I think I'm okay. (And it's well within the K4003's filter capacitors' 25 VDC rating.) Result? Ahh, quiet! In fact, putting my ear up to my Klipschorn tweeters, I hear virtually zero noise. I have to strain to hear anything! No hum, no hiss, no buzz - that's good. (Truthfully, when I moved that hummy transformer far enough away, the amp was equally quiet, so you don't need an outboard DC supply for a good S/N ratio, just a transformer with a low radiated hum field.) This is the quietest amp I have ever heard through my Khorns. Power is plenty - only 60 ma of DC current was being consumed by the amp while playing at normal volumes (30 ma on both the + and - power feeds), so it looks like about 1.2 watts is going into the amp from its supply. Even if it's 100% efficient (which you know it isn't), I'm using less that a tenth of its output at what I consider to be full volume! And because of that, the heat sink never gets above room temperature. The heat sink Velleman provides is plenty - way over kill - when driving something as efficient as a Khorn. Well, better safe than sorry. But what about the sound of music? Well, I've been using a stock Dyna ST-70, which gave me a sweet, slightly warm, and *very* listenable sound. The TDA1521 is clearer, more detailed, cooler without being dry or "transistory". Voices are very clear and smooth, instruments are well defined, front to back layering is the best I've heard to date on my Khorns. The lows are full and natural, less tubby and warm than with the Dyna; the highs are extended and clear. Purcussion instruments have a clarity and bite I never heard through the Dyna - they sound more "there", more real through the little Velleman. It's not perfect - there does seem some very slight roughness in the upper mids - the curves in the data sheet imply a class B output stage, and maybe I'm hearing a hint of grittiness from the crossover distortion often associated with no bias current in the output stage. But it's very subtle, and in reality, I may just be hearing imperfections in recordings (or my preamp, a 20 year old APT Holman) previously masked by my Dyna. So am I happy? You betcha! It was inexpensive, easy to assemble, runs cool, seems completely reliable (the chip even thas two different thermal protection circuits and overload and short circuit protection!), incredibly quiet, and sounds really quite good. It goes to show that sometimes good things do come in small packages. Well done, Velleman! (Oh, and it will probably stay on that piece of wood - I get such a hoot out of seeing that tiny amp driving those huge speakers!) PS - If you decide to build this, one thing Velleman left out that you'll need - transistor heat sink grease. I happened to have some, but not everyone does. And in my kit, the insulator between the IC and the heatsink had to be carefully trimmed to make slots for the heat sink's mounting bolts to pass through. These are both nits, but for a beginner, they may be confusing.

Sold. The buyer will use them w/ K-horns for a home theater. Should be fun! (Bob, feel free to delete this thread.)

Soundog's right. I used the Advent woofer because it fit (same screw holes and everything) and because I had a pair lying around. The Heresy cabinet is about the right volume (i.e., about the same volume as an old larger Advent), and the fact that it isn't as rigid or air tight as it should be didn't stop my experiment. I dropped the mid/high output by changing the autoformer connections - made for a better balance with the less efficient acoustic suspension woofer. The result was okay, but hardly great. I got more lows, but the midrange blending wasn't as good as it could have been. I didn't try too hard playing with different crossovers (the choke and capacitor in the woofer circuit will affect things a lot), and I didn't go out looking for other woofers (I was playing around and didn't want to spend anything if I could help it). But that's one beauty of the Heresy - you can get inside so easily to play around. A fun way to experiment and learn.

Chris - Thanks for the kind words - I guess being an "engineer's engineer" means tinkering and playing! It was an Advent woofer, and it was an experiment. It worked, sort of. I've heard tons of commercial speakers with a better bass/mid blend than my Heresies had with the Advent woofers (no surprise - I really was just playing around). But they did have a low end that stock Heresies don't. The Heresy cabinet is about the right volume for a woofer like the Advent's - getting that blend right with the midrange is the challenge! My restored-to-stock Heresies are for sale. (My K-horns get all the attention, and the Heresies are getting lonely :-) See separate note for details & pics.

Had trouble posting these - sorry!

Well, it's time. Time to put my Heresies up for sale. I simply never use them. Heresy I's. Oiled walnut, original woven cane grills, original risers. Serial numbers 164Y523 and 164Y524. K22K woofer, K53K squawker, K77M tweeter, all original. Grills are perfect, drivers are perfect, one cabinet has small nicks (see H5.jpg - a nick on the front right edge a few inches down from the top) and dark water marks on the top (see H3.jpg). I damped the squawker horns with mortite, stuffed the cabinets with polyfill, and dropped the tweeters 3 db by moving their connection to the autoformer. All mods are completely reversible, and I even left instructions inside the cabinets how to restore the factory original tweeter connection. Apologies for the quality of the images - it's the best my little camera can do. But the speakers really are in excellent condition. $400 obo plus shipping from Boston area. Will have MBE pack. Contact me at jon_mechling@hotmail.com This message has been edited by JonM on 02-23-2002 at 10:18 AM

If I remember (after reading all the other replies), the original complaint was that the Heresies were too bright. This is hardly a new complaint. I was surprised nobody's suggested taming the tweeter by moving its connection on the autoformer in the crossover. I did this on my Heresy I's, dropped the tweeter by 3 dB, and it made a world of difference. They're still a bit thin sounding (no bass - we all know that), but that excessively bright high end was brought back under control. I'm sorry Ben doesn't like his Heresies - he spent a lot of money for them. I hope something as simple as room placement and taming that tweeter can do what he wants. But not everyone likes the Klipsch sound. Maybe Ben's one. (Especially if he likes the Paradigm Studio 60's - superb speakers, and simply very different from Heresies.) Welcome to life. This message has been edited by JonM on 02-02-2002 at 05:16 PM

I have a C30 (love it). I don't think the Y adapter will work the way you want - I think it'll simply parallel the L and R outputs and you'll get mono. (The C30 doesn't have as many bells and whistles as the 32 or 33, so its internals may be a bit different, but I am pretty sure McIntosh does not drive its outputs separately - they are the same point electrically just controlled by the front panel switches.) You could do something with op amps (acting as buffers so a mixed center won't make the main channels mono), or even just drive another preamp off the second set of outputs and do the Y adapter at its outputs. Or put 10k-50k resistors in series with the outputs, combine the other end of those resistors, and use that to drive a center channel amp. Depending on the sensitivity of the center channel amp and speaker, the level may or may not be appropriate for your needs. The second preamp idea gives you its volume control to adjust the center channel level - that's probably the way to go. This message has been edited by JonM on 02-02-2002 at 04:39 PM

That silver wire is called "tinsel" (because that's what it looks like). Very unusual for it to fail, but it is where alot of flexing is done as the cone moves in and out. Any good, stong cement (like epoxy) would do what you want - add mechanical strength to the solder at the back of the cone where the tinsel connects. Don't use too much or get it on too much of the rest of the tinsel - you want that to be able to flex. If that doesn't work, you may be looking at ordering a new woofer from Klipsch. Good luck!

Before you change anything, you should listen to them long enough to determine what, if anything, in their sound you want to change. Mike's right - there are a lot of possible modifications. You can drop the tweeter level with a change to the crossover wiring. You can put rope caulk on the backs of the horns to possibly tame some mechanical resonances. You can stuff the cabinets with fiberglass or polyfill to possibly change the low end extension. You can actually replace the woofer with either a Klipsch replacement or some other manufacturer's, depending on the sound you want. You can brace the cabinets. You can change the internal wiring, or even port the enclosure. Some of these changes may improve the sound, some may make it worse, some may make no perceptible difference. The typical approach is to stick to changes that are reversible if you don't like the results or decide to sell the speakers (which are usually worth more in original condition). The Heresy is a great platform for this sort of experimentation - open and accessible. Have fun, and let your ears be your guide. This message has been edited by JonM on 11-20-2001 at 09:50 AM

The Klipsch parts list (printed 5/7/01) shows the K52K as the midrange used in the Heresy, Cornwall, KLF20 and KLF30. The Cornwall II is shown as having the K57K squawker. My Heresies have the Heresy II squawker, which just tells me Klipsch had started moving to the new midrange before they made the model change. My guess is that they transitioned among drivers as inventories depleted. I'd bet that the Cornwalls with the K52 driver (good picture!) are as shipped from the factory. Frankly, I've never seen another company use different drivers and crossovers like this without changing the product designation. But maybe (I'm guessing here and looking for comments) the horns have a greater effect than the actual drivers so they figure it didn't matter that much. So I'd look elsewhere for the muffled sound problem.

For those who care, I'll try to attach a little picture of one Heresy with an Advent woofer installed (yes, that's a K-horn directly to the right). I really like the sound of the acoustic suspension woofer and those horns. Believe me, I am as surprised as anyone!

Are you sure the squawker was a K52K? I've been inside a pair of mid-1980's Cornwalls, and the squawker was a K57. It's hard to read the blue stamped lettering sometimes - Al Klappenberger had to help me figure out what squawker I was looking at. Regardless, by that time Klipsch had started to transition away from the K55 to alternative squawkers for the Cornwall and Heresy. They are not necessarily better or worse than the K55. In my listening to a pair of Cornwalls versus my K-horns, I thought the K-horns sounded muffled compared to the Cornwalls. The K-horns had that BIG sound, and dynamics in the lows that the Cornwalls couldn't touch, but the mids and highs seemed brighter in the Cornwalls. Could have been the drivers, could have been the Type B crossover that was in the Cornwalls, could have been room acoustics and speaker placement. So many variables. I passed on the Cornwalls - just too big for the space I live in. But I think you should keep experimenting with placement, toe-in, height (put the Cornwalls on stands?), etc. Last resort, look at the mid and tweeter hookups to the autoformer - you can increase their levels by changing the taps that feed them. that can make huge differences in the sound!

Chris, you sweet talker you. (That does not mean I want to be on any island with you, unless they have one helluva nice golf resort :-)

I'm with discorules on this one. His test lengths were unrealistic, and his test signals were 10 kHz square waves, whose first harmonic is above most people's ability to hear (let alone their higher harmonics, and to get a square wave, you need a lot of them!). He glibly said a 1 meter cable's problem will be 1/100th the 100 meter cable's, but that means its reflection will come 100 times sooner, and let's see his oscilliscope show *that* on the waveform's leading edge. In fact, in any normal length of cable at any normal audio frequency, the wavelength of the signal in the cable is much greater than the length of the cable itself, and such mismatches can be ignored. The theory of transmission lines is well known (I studied it in school many years ago, and it was old stuff then). The author (affiliated with an engineering school, if I remember) should have known that at audio frequencies and in normal cables of a few meters, this simply doesn't apply, and the factors you need to look at really are the lumped constants of the preamp output impedance, cable R, L and C reactances, and the following power amp's input impedance. I.e., it's a simple RLC filter. (And his solution to a nonexistent problem was to add additional electronics - another op amp or two. A previous Stereophile had a more convincing article saying how except for two particular designs, all common op amps are bad for the sound. Gotta love it - if you were looking to Stereophile for consistent guidance, forget it.) What bothers me is that Stereophile pubishes this sort of stuff apparently without technical review. But then Jonathan Scull, their senior editor, never claimed to be technical. A scholarly journal it ain't - Audio used to be, but now all we have really is the Journal of the Audio Engineering Society, and that's way above most people's heads (including mine most of the time).

When you rope caulk your squawkers, try this. Do one, then from the front of the speaker (with the grill removed) tap the inside of the horn (not way inside toward the back - don't take a chance damaging the diaphragm!) with a small screwdriver, pencil, anything hard you can tap it with to get a "tick" sound. Then do the same with the squawker you haven't damped, and listen for the difference. I damped my Heresies (which have the plastic horn on a K53 driver), and was surprised at the difference. (I'm a natural skeptic.) The damped horn was much deader and sounded much less "plasticy" when I tapped it. I even heard a difference between two layers of caulk and just one layer - again, the one with two layers was acoustically more dead. That's what convinced me that the rope caulk really will damp out resonances that might be excited by signals from the driver. I'd be real curious to hear your results - do the metal horns ring with a metallic quality the way the plastic ones sound plasticy? (I damped the metal horns on my K-horn squawkers, but the grill cloth kept me from doing the tap test.)

FWIW, I actually ran measurements on a Cornwall crossover, very similar to the Heresy crossover (bigger capacitor to the squawker, which goes a little lower than the Heresy's). Each autoformer tap is 3 dB down from the previous one. Tap Level 5 Input 4 -3 dB 3 -6 dB 2 -9 dB 1 -12 dB On the Heresy, the original squawker connection was at tap 2 and the tweeter was at tap 3. I dropped the tweeter initially to 2 to make it more balanced with the squawker, then dropped both of them to 1, to even them out with the inefficient woofer. Note that Cornwall has the squawker and tweeter one tap higher in level, to keep up with its more efficient woofer.