leok

The PWM amp listed below is an amp I built based on a Tripath chip similar to the one used in the Sonic Impact T-amp. I built the amp to drive the Forte-IIs I had at the time and thought the combination was great. I've tried the amp on a pair of KLF-30s .. also great. I built a small run of 10 amps and still have two. I use one to drive a pair of RB-5s I'm using as a center channel in an SACD 3.1 system. The amps also do well with my RF-7s. The sound is close to any well designed amp that has low distortion at low power resulting in a smooth, natural sound on efficient speakers such as the Klipsch. It's a little rougher than my Crown D-45 or custom SETs, but not by much. I think they're a lot of fun, sound very good, and are a no brainer when it comes to cost. Leo

Try a sample or two of amplifiers that have low distortion at low power (not all that usual in ss amps). Remove all but essential electronics (phono pre, volume control of some type, and amp). I'd avoid tone controls if possible. Also try a power line rf filter (surge protector won't help the sound, although one may be included with the filter). I suspect your problem is, in the smaller listening space, you're using only a small fraction of a Watt of amplifier power and your amp is not optimized for such low power. lso, line rf may be modulating the audio. Note that a lower power amp, especially ss, is not necessarily good at low power, one has to obtain an amp that is designed to be exceptional at low power. Some possibilities: * one of the lower power PWM or "digital" amps. * the Crown D-45 (or possibly the D75A) * any of several amps recommended by others on this forum. If you find that the amp and/or power filter address your problems, you can begin adding back additional electronics and adjusting amp overall power to suite your final needs. Good luck, Leo

If your problem is RF intereference, which can cause harshness and exaggerated sibilances, there are a few reasonably priced line filters available (usually sold in devices which also provide surge protection). A couple of years ago I purchased two Belkin F5980-TEL, at Staples, for about $80 ea. They are quite effective in removing to RF related grunge from both of my systems. I continue to use stock power cords. A more expensive power "conditioner" may provide additional improvement, I haven't tried one however. I could understand that a power cord that provides its own RF filtering may be an effective solution if another filter is not in use, but it is a rather expensive way to solve the rf problem. Leo

Dean, I'm interested in your impressions of the USD180 (did I spell that correctly?). By the numbers that one should be hard to beat. Leo

JJK, Yes, there IS something else: Pulse Width Modulation. Leo

I have found that once the problems that cause sibilance distortion are removed from a system, most recordings don't exhibit the behavior. Sibilance distortion is virtually eliminated from both of my systems. It does show up on the occasional recording and I don't know if the recordings actually contain the distortion that I hear or they are simply sufficiently difficult to correctly reproduce that residual distortion in my system is the true root cause. Leo

What speakers were you using before? How do they compare? There is the off chance the Heresys need more break in, but nobody's ever mentioned distorted sibilance as a Heresy problem (new or aged). A line power filter might be very helpful. The Belkin F5980-TEL is inexpensive (office supply stores for computer equipment) and effective. If you have an RF interference issue it could impact the sound in the way you describe Leo.

Sibilance is an unvoiced sound people make in speech. Such things as "s" "th" "f" "sh" "ch" are spoken as sibilance. Sibilant sounds are difficult for audio systems because they are tuned,or filtered noise (like pink noise, but more sharply filtered by the mouth) and they tend to expose system distortion. Intermodulation and crossover distortion characteristic of some transistor amplifiers causes sibilances to be exaggerated and rather unpleasant. Feedback, in tube amps, if not done well can also exaggerate sibilances. Efficient speakers such as those made by Klipsch will expose the low power distortion of an amp. Sibilant sounds are some of the lowest power sounds produced by an audio system and we are very sensitive to distortion of those sounds. I doubt the problem is the speakers .. but it can be anything and everything upstream. Leo

Excellent reference and source. Thanks for the tip. Leo

Try using the 4 Ohm output on your amps (if they exist). Leo

I guess putting some angle back on most speakers, even if the object isn't to time align identical drivers, helps project the sound into the listening space and not directly into a piece of furniture. Time alignment of different drivers is way too complex for me. I would expect the phases of adjacent drivers would want to match in the crossover region where they are both most likely to be at some time delay or advance offset from what they are at midband. How does one get them to crossover in phase and stay that way at midband? Then there's the lengths of the horns adding different delays. I have to settle for getting the two identical RF-7 cones lined up, maybe project the Chorus-II up a bit and let Klipsch or Al K. time align the different sections. Leo

I used "AcoustaStuff" which is a plastic, long fiber material. I simply filled spaces with the material. It is light and maintains its volume well. Leo

Erik, Let me know how the fill works out. I would expect it to have a significant impact (good or bad). I'm particularly interested in how it works with the sealed cabinet. (It performed wonders with the passive radiator Chorus-II and destroyed the lower bass in the ported RF-7. But then the RF-7 started out pretty well damped. Leo

Erik, I don't know. I always figured the angled motorboards with different drivers had to do with time alignment, but since the drivers handle different frequencies the problem, or goal, is different than with parallel drivers handling identical frequencies. Nice looking speakers. Leo

Raider, I had completely missed the http://forums.klipsch.com/forums/thread/782250.aspx discussion. Probably, since I wasn't going to mess with the crossover (any more than I already have) I just read it quickly and continued to let the problem nag at me. I hadn't looked at the RC-7 solution very carefully in the past either, because I thought the different low pass frequencies for the cones were simply for frequency response smoothing. I should read more carefully. Very nice technical description of the problem. Leo

Arthur, Absolutely! I actually got the idea when looking at a few of the speakers you mentioned. Yes, people have been doing this for some time. It obviously took me a while to figure out what you and others been doing all along. Leo

If the RF-7 is standing vertically and the listener's ears are in line with the horn, the distance from the lower cone to the ear is greater than the distance from the upper cone to the ear. The two cones are producing exactly the same sounds at exactly the same time, which means the sound from the lower cone reaches th ear after the sound from the upper cone. Technically, this blurrs the sound. By tilting the speaker a few degrees back the cones can be aligned so the sound from each reaches the ear at exactly the same time. It's up to the listener to decide if it's even worth a try, try it if it seems worht it and determine if there is an improvement. I think there is and prefer it. Leo

Rick, The tilt isn't that extreme. However there is much more force on the back feet (or spikes in my case) than front. Leo

I have always wondered what the RF-7 would sound like in a D'Appolito configuration (horn centered between the two cones). As the speaker is designed, the two low mounted cones broadcasting identical information at different distances from my ears has seemed a recipe for phase problems with frequencies above a few hundred Hz. No, I haven't replaced the "motorboard." I decided to align my ears directly between the cones instead of with the horn. I figured the crossover region might suffer a bit, but it's already compromised somewhat because of what it is and the existing RF-7 physical layout and I wanted to hear how things sounded with equal path length from both cones. Instead of sitting on the floor, I have angled the RF-7s back so that a line from my ears to a point between the cones intersects the speaker face at 90 degrees. I like the result. Imaging and recorded room (or hall) ambience are clearer. Lower mid fundamentals are better defined (good for piano and cello in particular, but most instruments seem to have better fundamental definition). The nice clean highs don't seem compromised. I don't know that this would make much difference with loud rock, but for critical sweet-spot listening it's worth a try. Leo

Brendan, A good, and easily read reference is: "Valve Amplifiers" 2nd edition, by Morgan Jones. Publisher: Newnes ISBN 0 7506 4425 7 Leo

Thanks for the nice note Steve. One of my original purposes in making several of the amps was to use them as references. It was satisfying to have this work out that way. Also, good thing you brought this up, because I forgot (very busy week) .. I do have the amp back and in fine shape (the light pipe IS rattling around inside. Too bad you didn't see it with the light pipe in place). Very interesting shrink-wrap around the amp. Leo

Wolfram, Glad to hear the 350Bs are working out. Nice find .. I think Craig was instrumental it passing the word. Leo

The P6D is a very small, 8Watt/chan, stereo, pulse width modulation amplifier. It is similar to a few other 8 or 15 Watt (depending on how they are measured) amps around except that this circuit bypasses the input capacitor that other circuits use. I found that any cap I tried in the input had some kind of sonic signature. So I finally figured out a way to skip the cap altogether. The amp has its own volume control, so I recommend initially taking input directly from a cd player or phono preamp. I developed the amp during my initial search for an amp with low distortion at low power. It's based on a Tripath integrated circuit. The things like about Tripath's pwm is it's quiet, very low in distortion, and neutral to the point of being astonishing. Send me your address (mail on this bb works) and I'll work on getting it to you, with instructions, Leo

Well, If the McIntosh was too laid back (but full enough?) and SET is thin, and the SET sounds the same with a passive volume control, I'd say you are likely to be hearing differences in amps. Something has occured to me in going over this thread. Again, comparing amps within their proper operating envelopes, there are two considerations: 1) technology (ss, pwm, SET, tube pp, etc, and then 2) implementation (or voicing). I wasn't happy with my stock Moondogs. I worked on them until they had the frequency extension and dynamics I think the technology can, and should deliver. But others may think the sound of a stock Moondog is great. The technology provides a platform with certain sonic possibilities: with SET, for me, it's vanishing distortion at very low power. The technology can then be customized to bring out certain characteristics. usually there are tradeoffs, some in cost, some in sound. A differently "voiced" SET may, in Steve's case, do the trick. Maybe he's hearing the "sound" of the traditional air-gapped transformer. Maybe a more expensive transformer or change to ultrapath topology would fill things out .. hard to say. But, for people who can't customize an amplifier, I guess it becomes a matter of trying different amps until the correct one is found. Steve, have you tried a pwm amp? I happen to have a loaner P6D. If you'd like to try it as a reference I'll send it. The nice thing about the P6D is, it is extremely neutral with good frequency extension. Let me know if you'd like to try it. Unfortunately, it's not for sale and I do want it back, but it might give you some ideas about how to procede. Leo A ss amp, or a tube amp with feedback, such as the VRDs, may

Steve, If the McIntosh didn't work (same lack of fullness or was it something else?), maybe it's not the amp at all. Have you tried going straight from the cd player to the amps in stereo only (skip the splitter for now) Does the cd player have a volume control? Otherwise you'll get way more amplitude than you want? Do you have access to a passive volume control? Maybe the preamp is the problem. I did a little research on your amps. Nothing obvious. Within its amplitude capabilities (which is way more than I generally want), it seems bass should be fine. Is the KHorn woofer phased correctly with the upper two drivers? Check how they are wired to the crossover. Did you install the Al K crossovers? Do you have the old ones? In what way was the sound from them different? Based on everything I've read so far in this thread, including your McIntosh comments, I question whether the amp is the issue at all. Leo