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