leok

In the May 2002 Stereophile magazine, there is a review if the Quicksilver Audio "Horn Mono Amp." It's an amp designed for use with horns. I found the review interesting. Of note is the designer's use of feedback (a lot of feedback). Not what one would expect, but his remarks about higher gain resulting in more noise make sense. I removed the feedback in a very similar amp to get rid of the noise. It didn't occur to me to increase it instead. Anyway, I thought this would be interesting for readers of this forum.

Steve, Why not try a simple attenuator. Creek makes a nice one with remote control for about $300. It's the OBH-12. Creek also makes couple of nice phono preamps, OBH-8SE for mm and OBH-9 for mc. The OBH-8SE is all class A .. no op-amps, and is not harsh. auduioadvisor.com has them, and a few additional Creek passive preamp type offerings. If you don't need the gain, no matter how good an active preamp is, it's just adding distortion. good luck.

TBrennan, Audioholic, Thanks for the responses. You've provided references in areas where information is hard to find. The fact is I'm not completely sold on tubes myself, but between what I have built and what I've heard at stores (including the NADs of my own that I finally gave up on) I havn't had much for comparison. By the way, JoshT, the NADs I have are not the latest or greatest from that manufacturer. I was particularly interested in the Tripath comparisons. I've been trying to figure out how to compare My Tripath design with exactly the amps that TBrennan mentioned. What I listen to mostly is the Tripath. I don't have a more conventional ss design that comes close: none of the amps you mention, for example. For a change, I hook up the KT66 design, and am working, with mdeneen's help on an improved phase splitter for it. Thanks, again leok

Folks, JoshT, You're make a good point. I generalize. I have done some amplifier design and am an electrical engineer by profession. Starting from a clean sheet of paper, with the objective: create an amplifier for my Forte IIs and RF-7s, I have yet to figure out how to begin with either the bipolar or FET transistor, although I use them daily in less demanding applications (that includes just about everything except audio amplification). They are inherently non-linear and require massive feedback (FETs not quite as non-linear). I do acknowledge that effective transistor amplification of sub-Watt applications can be implemented, but it is very difficult .. certainly beyond me. I have implemented 2 successful designs, one using the Tripath TA1101B IC and the other using tubes. Both the Tripath and tubes are inherently linear. I believe, the result of the fundamental problem is, for the Klipsch application, there are a lot of very bad transistor amplifiers and a few good ones. There are a lot of reasonable tube amplifiers and a few bad ones. So, when people ask, I try to steer them into a region where I think they are more likely to achieve success. I try to encourage people to at least audition a low distortion @ low power amp with a Klipsch speaker, before concluding that horns are harsh. JoshT, I think you are already there. You're looking at some pretty nice amps and confronting the problem where it resides, in the amp. I don't know about techguy13. So before he decides he can do better with B&W and a run-of-the-mill transistor amp, I wanted to steer him towards an amp that would give him a better understanding of what he is really trading. So, the question is, how do we steer someone who asks "why do my Klipsch speakers sound harsh?" or "what kind of amp should I use?" to an amp that will reveal the strengths of the Klipsch speaker, not the weakness of the amp?

The comparison between the B&W and Klipsch sound more like a comparison between efficiencies. I suspect that the reason the Klipsch speaker(s) sound more harsh is that they operate at lower power where the (I am guessing) high powered amplifier that was used, contributed more distortion. Compare a B&W driven by a transistor amp and Klipsch driven by an SET and the harshness will probably come from the B&W. In order to perform a fair comparison, the amplifier distortion should be the same at the powers used for each speaker. With a transistor amp, this is generally not possible. Thansistor amps have considerable distortion at low power. When I auditioned a set of RF-7s, which I now own, I brought my own amp to the store because they did not have an amp with low distortion at low power. The sales reps were shocked. They had never heared Klipsch speakers sound so natural and image so well. For me to achieve the quality of sound I have with my RF-7s and a good low powered amp, would cost thousands of additional dollars were I to use B&W speakers. I suggest that a good amp for Klipsch speakers would have 20W or less, probably use tubes or would be solid state class A.

I think we should be asking you. Really, I don't know the amp. I am interested in your impressions, since, If I understand your post, you have already purchased the amp. Also, what are you normally using as an amp? Generally tubes will sound smoother because they produce less distortion, at the sub-Watt level Klipsch speakers require for normal operation, than do many transistor amplifiers. You may notice that difference. If you do, and like it, then what you have probably learned is that you prefer lower levels of low power distortion. That's important to know .. especially with a nice set of speakers like the 78 cornwalls. How DOES it sound?

Neandertal, If you want to do your speakers and ears a favor, use a high quality cap such as the Hovland 2.0uF film/foil polyprop. available at http://www.madisound.com/. I use Hovland in my Fortes and RF-7s. I think they're an improvement on stock. They are expensive, but I think Klipsch speakers are easily worth the upgrade. good luck

JoshT, I looked up the Cary SLI-80 to see if I could get some idea why you might find the sound "glary and thin." The first two things I noticed were excess power and feedback. Excess power, even in a tube amp, opens the door for noise and distortion that may be a small part of the amp's total output, but since you're only using a few watts, if that much, is a larger part of the power you're using. Feedback contributes to the noise and distortion. I noticed that the AE-25 refered to above by deang is a no feedback design. It is also triode, push-pull (do I have that right deang? This kind of amp is smoother than one using ultra-linear, feedback, or both. Also, the power of the AE-25, base model seems to better match your Heresys. deang's offer looks good. Since you mentioned the sonic problems that smaller, no-feedback amps address, I suggested trying the amps I have, which are no feedback, class A, PP .. pretty close to the AE-25. It may tell you whether or not that is a direction in which you want to move. I hope that helps clear up my earlier posts.

Hello JoshT Sorry, I wasn't clear. I was thinking you could try the Heaths just to hear that type of amplification and get another tube reference. The Heaths aren't for sale. The Tripath amp is a completely different technology. You might like it .. I think it's great. Again, I wasn't thinking of selling one, but, in that case I could probably work one up if you really wanted one. First, however, you might want to just listen, with no pressure to buy. leok

JoshT, I have a couple of amps you might be interested in trying. One in a pair of Heath W5Ms I've rewired to class A PP (KT66), triode mode, no feedback. Also, I have a Tripath TA1101B implementation (TA1101B is an integrated circuit made by Tripath). I live in Waltham If you're close by, maybe we could work something out.

tbabb, That's a classy little amp, and I'm beginning to suspect, one of the best. It's an interesting combination of technology (pentode pp), scale, component quality, and overall design. Mobile provided a pointer to the schematic recently, and it was not at all what I expected. I'd love to hear one of those. Is this your first tube amp? If so, it's a double treat: tubes and one of the best. Enjoy it. leok

TroyTN, I have the speakers pointed directly at the listening position. I think it minimizes contributions from the room and lets me hear the on-axis characteristic of the speaker. This can also be the most difficult, because it is the most revealing of imperfections. But I think when it works, the image is what the recording engineer intended. BWM, The XLO Test/Burn-In Cd is a great idea. I think I'll give it a try. I get real tired of wondering, when something doesn't seem right, if it's me or it. Thanks.

BWM, I own a set of RF7s that I've used with several amplifiers. Generally, the speaker is so good I treat it as a reference. I also own Forte-IIs, which I enjoy, but I think are a bit more colored. I have upgraded crossover components in both sets of speakers and damped the horns. I don't think I can spend much time in the room with either speaker at 5 Watts. I doubt I've ever put over 3.5 Watts through the RF7s .. so power isn't a problem. Currently I'm using an amp that uses two KT66s in a push-pull arrangement, all class A, all triode, no global feedback. I experimented with an SET configuration using a single KT66 and loved it. But the KT66 and transformer I have are not optimized for SET so I moved on to the current setup that is much like parallel SET, taking advantage of a transformer's ability to add currents with inverted phase. I think the RF7 is one of the best speaker buys available, and certainly a good match for a good SET.

kenratboy and atom, What's so silimebaggy about Monster. Their entry-level Litz-type constructions are not particularly expensive and seem to work well .. certainly better than zip. If the individual strands are not insulated then that's a problem, but I think they are. The 12 GA on Parts Express looks fine, but I can't tell if the individual strands are insulated. Individual strand insulation lowers high freq. impedance (even as low as 20KHz). I have a set of RB5s and I switched to Kimber 4TC. I thought the hf improved and bass was damped more effectively. In the end, however, I think "dry and hard" sounds more like transistor nonlinearity or crossover distortion than hookup wire. atom, do you have access to a tube or class A transistor amp? Klipsch speakers are very sensitive to what an amp puts out. If it's music, it's good. If it's distortion, then you hear it.

Chris, Nice job with the amps and description. Do any of you: Chris, mdeneen, homeless, NOS440 think, in addition to bias, the EL84s may have an advantage in that they are mated with a smaller output transformer? The repolarization energy is lower and there will be less, here it is again, crossover distortion. I have been looking for a high quality 10 watt push-pull transformer to check this out. Just a thought. I wish MagneQuest would build a Cobalt 10W PP. Homeless, I think you've given the Eico HF-81 a new life. I certainly won't pass one up, even if all that's left is the output transformers. leok

Several items here .. I'll go in reverse order: gamer, The dynamat is to damp horn resonance. I believe it is effective. Instrument timbres are cleaner, and more uniform from note to note. It seems particularly effective with woodwinds. I cut pieces to fit all of the horn surfaces. firejim, I'm glad the post helped. I think the RF7s, are overlooked by many classical listeners, because they haven't heard them driven properly. This is generally true of all horn speakers, but I think the RF7 is quite an achievement. mdeneen,I'll pursue the measurements. What you describe is where I'm starting to bog down in my SET investigation, and investigation into improvements in general. I'm beginning to suspect I'm running out of low hanging fruit. I'm not going to spend $2K and 2 months of building without listening, and 2A3 SETs aren't that easy to just borrow for a while. I do have access to distortion specs for the Tripath TA1101B. They look very tube-like. Below 5 Watts, THD+N is under .03%. Above 5 Watts the distortion goes through the roof. See Tripath.com. Go to the site map and look under data sheets. TA1101B is the first one, I think. (If you go to the TA1101B product page, the data sheet there is for an eval. board, which is also interesting). My circuit is much like the data sheet version except I have the input DC coupled. Also, I use nicer components that they do on their demo.

mdeneen .. your note reminded me of an additional factor. 5) Room Treatment: To reduce reflections from my rather low ceilings, I have 1ft x 1ft panels of acoustic absorbing material protruding like square baseball caps from the top of the RF7 cabinets. I have also absorbed reflections from a brick fireplace adjacent to the right horn. Except for casual listening, I always remove the grills. Amp distortion .. I don't know. I considered taking a few distortion analyzer measurements, but considering the very low level of the amplifier output signal I anticipated a measurement quagmire that could quickly become larger than the set of audio questions the measurements are to shed light upon. Being told that I'm much more tolerant of even than odd harmonic distortion has added to my uncertainty. Perhaps you could suggest a measurement setup that you consider effective, and I will attempt to perform the measurement. For the benefit of others reading this post: what mdeneen and I are refering to here is the problem of measuring audio excellence. Actually, I suspect both of us know we're not really talking about that, but casual readers might not. mdeneen, I'll try to contact you by email so we can work out some of the protocol.

Since last Thanksgiving, when I purchased a pair of RF7s, I've been tinkering with both the speakers and amplification to achieve a particular goal for which I believe the RF7s are well suited. That goal is the reproduction of classical instruments, especially small, chamber ensembles, in a way that the instruments sound natural and the soundstage is well defined and stable, and at amplitudes that are similar, in my living room, to amplitudes I experience in live performances. Having finaly achieved that goal I want to thank members of this BB for their generous help, and encouragement. This is a difficult and subjective task that requires exchange of some fact and mostly opinion. Since opinion is easily criticized, I consider it particularly valuable. Finally, as a result of this BB, I am becoming aware of stereo sound capabilities that are well beyond my initial goals. Following is a list of what I found most critical, generally in order of impact, to the success of the project. Certainly, for others, the list might be different. 1) Speakers: The RF7 is a remarkable speaker. For $2200/pair, they are beyond remarkable. I don't know of a better deal today, in any product. They are capable out of the box, and respond very well to nominal modifications. 2) Amplifier: I listen to these speakers at a fraction of a Watt. I doubt I have ever put more than 3.5 Watt peaks into them. Low distortion at very low power is very important for both the natural and the imaging parts of the objective. Two types of amp: tube amplifiers and a custom switching amp based on the Tripath TA1101B have been succesful. Both of these amps avoid the nonlinearity and crossover distortion that plagues transistor designs at low levels. Elimination of global negative feedback provides a tremendous improvement in the upper harmonics. Many amps are available with this "feature" (or lack of it). 3) Speaker Modifications: I applied Dynamat "Extreme" to the horns and upgraded the crossover components. Replacement crossover components are Hovland Musicaps in series with the horn and Solen air core inductor in series with the cones. Also, I substitued Solen metalized polyprop. caps in parallel with the cones and in the RLC circuit that parallels the horn. The Solen caps, in the parallel circuits, which I changed just recently, made these already smooth speakers much smoother. I suspect that, at my low listening levels, the reduction in dielectric absorbtion, provided by the Solens, addresses something similar to crossover distortion produced by less expensive stock caps. If you upgrade the crossovers, don't skip the parallel circuits. 4) Speaker Connection: There was a link, somewhere on this BB (I can't find it now) to an article that recommended, for improved imaging, NOT bi-wiring, for tube amps (that also applies to my Tripath amp). The logic, from an engineering viewpoint was reasonable, so I tried it. My speakers have always been bi-wired. So I re-installed the metal jumpers and tried a single Monster MCX-IS set (Litz bundles wrapped around a "flux tube") to each speaker. The imaging improved. Instruments now clearly stay in position, but there is a feeling of air, or space around each one .. they have become so distinct. Also, the overall sound of the RF7s became more crisp .. just enough of that "dryness" I find so appealing in my Forte IIs. Beyond my initial goals: Well, there is the elimination of global negative feedback that I mentioned in the Amplifier paragraph. Next, I am in search of an opportunity to try a high quality Single Ended 2A3 or 300B amplifier. I need to hear Cornwalls (with Alnico magnets) driven by a 2A3 SET because I've heard so much about that setup. Finally, I'd love to hear a set original Klipsch corner horns with an Al Klappinger crossover, driven by a very high quality tube amp. Meanwhile, the music I hear in my living room has the magic I remember from when I first heard "high fidelity" tube sound in 1960. But now it is much more natural sounding, and it's stereo.

Last weekend I was rewiring, for the 10th or 12th time, the Heath W5Ms my wife gave me for Christmas a year ago. She said "Oh my, the gift that keeps on giving." I showed her the picture of the dustpan full of ST70 parts. Now I border on conservative. What's this going to be? PP triode output? What will you do in front of that? I can't wait. Clipped and Shorn, maybe you said, but I missed it. What are the lucky speakers?

mdeneen, Both speaker and resistor are wired to the output taps of the output transformer (all external connections). Different configurations were fun and educational. They were done along with discussions on this BB with mobile, arco, & Conductor. Following is text from a note I wrote then: ----------------------- Based on the above discussions, I tried a few experiments with my 2 Heath W5Ms. The amp is normally configured as ultra-linear with KT66s biased dissipating just over 20 Watts each, at idle. One of my Sovteks died so I had only a set of Valve Art tubes which seemed to lack high frequency capability. I had re-wired the g2 directly to 400V dc to operate in tetrode mode, which is designed to reduce Miller capacitance and improve high freq. response. This worked, but there was clearly some distortion at the high end. Mobile strongly recommended the triode configuration, so I tried it; connecting g2 to the anode. I had expected high frequencies to vanish, but they didn't. Much of the high end distortion also vanished. What was left was some swirly sounding stuff on the "S"s. Mobile even more strongly recommended single-ended triode so I disconnected the signal input to one of the KT66s (leaving it in to balance the bias into the output transformer). This was very good. In fact, this was much better than I would have thought. The sound was cleaner, more articulate, and the swirly stuff was gone. At this point, what I had was very much like a big operational amplifier, with a voltage gain of 10, and a single-ended output. This is a really cool thing and one would do well to stop there. But Mobile also mentioned that single-ended triode with no global feedback is worth a try, and there are plenty of reviews that agree. Also, there is plenty of engineering that agrees. So I removed the first gain stage and phase splitter (which wasn't helping anyway). The results were very remarkable except that the KT66 had absolutely no local feedback and was scrambling the high end again. So I re-connected the ultra-linear connection to give it some negative feedback (why the triode connection doesn't do this is a mystery to me). This is a tradeoff between high end distortion and upper mid. detail. I'm sure this is the starting point for a real single ended triode amp. The point for me is I have never heard anything that comes close to this. ---------------- Since then I ran across an idea on the Plitron (transformer) webpage which featured push-pull output, triode connection, class A, no global feedback, and a little local feedback via 10 Ohm Cathode resistors. Initial gain and phase splitter were carbon copy of the 12AU7 circuit already in the Heaths. This, for me, has been the most successful arrangement. What I had wanted to address here was lack of dynamic capability of the set hookup. I just don't think the KT66 and Peerless transformer adapt that well to set operation. With the set connection, when sound became complex and loud it would loose definition. With the push-pull setup, full orchestra remains clean, with stable imaging. The final change has been to swap ECC88s in for initial gain and phase splitting (there was some very minor bias adjustment for this) instead of the 12AU7s. his change was impressive. Everything sounds more real and the very high end is very clean. One reason I pushed for this last change was a disk I have of Andrew Manze and Richard Egarr (violin and harpsichord) playing Handel's violin sonatas. These period instruments deliver a load of upper harmonics that can get real screachy if distorted. The ECC88s realy cleaned up their harmonics. This is probably the first time I've heard my recordings of period baroque instruments sound right. I heard Manze and Egarr live a few weeks ago, and what I have now is reasonably close. I use RF-7s and I think they're great. I have Forte IIs also. I think the RF-7s sound more natural, but I'll never give up the Fortes. Crossover components for both speaker sets have been upgraded (air core inductors and Musicaps). I'm aware that a pair of Cornwalls and a real s.e.t. might sound better, but I don't have those. not yet anyway.

Something to take into consideration when matching a speaker to a tube amp is how the load changes the loadline on the output tube(s). Especially in the no-feedback applications, the slope of that line has an impact on linearity. One thing that can be done with 8 Ohm (nominal) horn speakers, because they are so efficient, is to attach them to the 4 Ohm output transformer tap, and then add a 32 Ohm resistor at the 16 Ohm tap. With this setup, the output tube sees only half of the impedence change/frequency of the speaker and the tube load line remains optimized. At the same time, the speaker sees a lower impedence source. I've rewired my Heath W5M in several different configurations, including stock, set, and no-feedback class A push-pull. In all cases the configuration I described provides a cleaner sound.

A few observations on tubes: Any tube function, preamp, phase splitter, or power can have a significant impact on the sound. The way a tube is used can also have an impact: for example, I found that Sovtek KT66 sounded better in ultralinear mode than Valve Art. However, when I rewired the amp to use the output tubes in triode mode, the Valve Arts were much better. Both of those companies make EL34s .. so, If I were to guess, I'd say Ultralinear > Sovtek .. Triode > Valve Art. Art Audio uses Valve Art. does that help? I've been using a real nice collection of 12AU7s that I thought were E.German. From what I can tell, the European tubes tend to be better suited to audio. Recently I've used http://www.thetubeshop.com and http://www.halfin.com/shop/index.htm. both have some nice NOS and are very responsive. (halfin may appear expensive, but I've found their quality to be good .. so in the end thay're not expensive.) The 12AU7 will be an ECC82, 12AX7 will be ECC83 (I think). You probably know that. good luck.

MBM135, I've been using Forte IIs for a long time .. I bought mine new, just after they hit the market. For years the brightness puzzled me. I think I know what's going on now. The Forte II is very efficient. Even if you're playing them at over 100dB, it is likely most of the high frequency energy (where you're hearing brightness) is drawing a fraction of a watt from your amp. If your amp is solid state it probably delivers substantial distortion at a fraction of a watt (transistor amps are usually rated at full power only, for a reason). What distortion does is produce a bunch of additional frequencies that are sums and differences of all of the harmonic frequencies that should be there. This adds a whole lot of intense trash in the upper midrange. Tubes tend to be linear by construction and tube amps are less likely to have a thing called a crossover region at lower powers. As a result, tube amps tend to produce a lot less of that harmonic and intermodulation distortion that you're hearing. Try to borrow a very good transistor amp (class A if you can find one .. see other threads in this "2 channel" section) or a tube amp. I have used a Dynaco ST70 with the Fortes and it was a good match. I happened to be particularly impressed with Fleetwood Mac's "Go Your Own Way" from "The Dance" with that particular setup. I currently use, with the Forte IIs, a homemade amp based on the Tripath TA1101B chip which uses a modified pulse width modulation output. Its distortion at 1/8 Watt is .07%. With my RF-7s I use either the Tripath amp or a tube no-feedback push-pull triode class A design. It's low level distortion seems to be even lower. The Forte II is a real classic. Enjoy it.

Barista, Some excellent, rather minimalist, baroque: Handel Complete Violin Sonatas Andrew Manze violin Richard Egarr harpsichord harmonia mundi 907259 If you like that: Pandolfi Complete Violin Sonatas same performers harmonia mundi 907241 These are very well performed and recorded, and the music is fascinating and beautiful. This isn't anything like orchestral music .. 1 violin and 1 very small harpsichord. Both of them are loosely strung, very woody sounding baroque instruments. I use a tube amp and RF-7s. The sound is wonderful. I believe these instruments are especially good on the reference series speakers because most of what you hear comes out of that big square horn. Only the fundamentals use the woofers for the most part.

Hello jjhaz, Maybe low freq oscillation due to feedback problems. I wouldn't have expected it with the Dynaco, but there are many factors involved. Try a different impedence hookup for the speakers (If they are connected to the 8 Ohm tap, try the 4 Ohm tap). The amp may be experiencing positive feedback at some low frequency and is oscillating. Usually changing something in the output circuit calms things down. Other possibilities: very long speaker wires, grounding problems .. try grounding the amp chassis to the preamp chassis. Good luck.