thoppa

Thanks for the advice - I had not considered this at all ! Maybe I should modify the output op amps in the DAC to form a Linkwitz-Riley crossover instead of adding another circuit ? On the second point, I doubt I will disconnect the HF crossover. I'm too scared of connecting an amp straight up to a sensitive compression driver. I realise I won't get all the gains I hope for and there might be phase issues if I dsconnect the LF one but not the HF one, but there we are. Peace of mind is a factor that I cannot ignore. Many thanks again, Tom

Hi, The bi-amping efforts progress...and then get immediately stuck.... So I'm now thinking to get a DAC that has great op amps - then maybe I can add another op amp circuit of the same quality to do an active crossover; easy and not much worse for noise, distortion etc. I'll also try a first order passive line level crossover (once I find out the input impedance of the amps), and of course, a fool's bi-amp too. Thing is, I've got to wait - my speakers are still settling in and that will take a full month before they can be eliminated as a variable. Anyway, first step - I opened them up - very well damped (with the foam egg-box-style stuff) inside for a reflex cabinet. Also well-braced. Coloured black too. Nice. Caps are custom coated with a Klipsch logo. The crossover is a second order butterworth with, I think, polyester caps. The circuits are entirely separate. The HF goes into a 5W 11RJ resistor, then to a small cap (can't read the value because of the glue and positioning) which is about a 3uF I think. After this the signal goes on to the horn via a 68uF 100VDC cap. A 0.36mH air core inductor with, I think 18AWG wire, is wired in parallel to the horn. The LF signal goes into a 1.4mH iron core coil, also 18AWG, then to the drives which are wired in parallel. A large cap (again, can't read) is wired in parallel. Shame about the iron core but hey ho. An aire core replacement with the same resistance would be huge and need something like 40metres of 16AWG. I don't fancy making that so the iron core will stay ! So now I'm confused - 1.4mH @ 8 ohms is 1286Hz crossover. 1800Hz, the stated frequency, would mean the drives are 11 ohms at the crossover frequency. 11 ohms for two drives in parallel ? 22 ohms each ? Hmmm, my maths must be wrong...? I also opened up my Edirol - the controller is fine and there is a 60Mhz clock, the DAC is okay; AK4114 (24bit/192Khz, dynamic range 108dB, S/N108dB, THD+N -94dB) but then the op amps - horrors NJM2100. I'd expect this in a crappy discman or something. So now I'm looking for someone in HK that can replace them with opa2134s (I think...) Anyway, I'm stuck until I can work out what's what with the crossover frequency and impedances - little help anyone ? Cheers, Tom

Why not just use the volume controls on the amplifiers and reduce the number of parts in your signal path? The only parts in the signal path is a lenth of wire. One lenth for each section of the crossover, which attaches to the drivers. To get +3db with the LF, 0db change with the MF, and -3db with the HF. My implementation was to tri-wire using the 8ohm tap to the LF, 4ohm tap to the MF, and 2ohm tap to the HF. The 8ohm tap has twice the turns of the 4ohm tap, twice the voltage, +3db. The 2 ohm tap has half the turns of the 4 ohm tap, valf the voltage, -3db The amp is rated at 135 watts per channel. So what's the result ? What benefits have you experienced ? Any drawbacks ? Please tell me if you think it was worth the effort ! Most of the bi-amping stuff says I should bypass the speakers internal crossover but there is no way even on a sunny day that I'm gonna open up my new Klipsch - they haven't even settled in yet. Incidentally, they are really loosening up. They sounded much harsher out of the box than the demo models in the shop and I was concerned about acoustics but actually my Klipsch and I are getting on very well indeed. The horn is very impressive and the 5.25" drivers exceeded my hopes. I'm made up, as they say back home. Cheers

Hi, I fully appreciate and agree with your comments re. bandwidth. I did a year of Physics at uni, incl. a course in electronics so I did circuit theory, Norton's Thevenin's and all that. We might not be on the same page but at least I have an idea about what book you're using.....Before work took over I used to build amps and speakers as a hobby. Sadly, I have forgotten almost all of my learning experiences and only recently had the chance to ease off work and get back to my first love ! Anyway, I don't claim to know or understand more than just the basics. It may well be my assumptions that are clouding my thinking. I've done some more reading on the fool's thing - seems the phrase was coined by a guy trying it with tubes. The consensus seems to be that it provides only minor improvements (intermodular distortion ? not sure what this is...) so it isn't worth the cost, given themeagre benefits. Interestingly though, no-one says it won't provide some benefits and is a class above simple bi-wiring, which does next to nothing it seems. As you know I'm sure, class-T is totally different from other forms of amp because it uses PWM, amplifies this, pumps in current, filters out the clock. This results in low output impedance, high damping , high efficiency, low distortion. So perhaps some of the theories that apply to linear and tube amps might not be valid for class-T ? I know class-T has only started to become popular but I thought someone must have tried out all the 'old theories' on the 'new technology' if you see what I mean. I am also completely open to finding the best and simplest solution; within a budget. I am aiming to build a sytem for around US$1200, not incl the PC. So far I have spent US$540 on the Klipsch, US$250 on the amps, US$150 on the DAC (which is dead - taking it back...), $80 on the soundcard. I am not interested in ultimate SPL - what I am searching for is awesome dynamics and soundstage - which is why I bought the Klispch. My souncard is ASIO but two channel. I have an old SBlaster Extigy which is 6-channel but it also re-samples to 48Khz and claims it is 24 bit but actually upsamples from 16. I don't want to use it but I could, just to experiment with the Foobar dsp digital crossover for bi-amping etc. Here's a link to it - http://xover.sourceforge.net/ I read abut a Linkwitz-Riley active crossover that is 24dB/octave and, although as you say phase shifts, they are 360 degrees (or 180...I forget ..) so the soundstage won't be seriously affected. Anyway, thanks again for keeping on at me - I'm on a learning curve.... Do you bi- or tri-amp ? Cheers,

Problem solved ? I didn't want passive bi-amping 'cos of the phase shifts, or active 'cos of more circuits, noise, distortion (albeit small if I pay enough). I really wanted a digital filter thingamy and was thinking of getting a DSP to go in my DAC. However it seems there is a plugin for Foobar that creates a high pass and low pass channel for the left and the right channels - four channel output and bit perfect I hope. So now I need to play with this and if it works I need a new soundcard and maybe a second DAC. Not the cheapest option but at least it is an option. So if anyone out there is looking for a digital crossover to bi-amp....the answer is Foobar. ....maybe. Signing off, Tom

Yo, Energy = power x time. No mystery. Why patronise ? Transient = power x very short time = energy An amp is only any good if it can deliver transients while also delivering a continuous load. So it needs energy of two kinds - continuous load and transients. Bi-amp for transient response. You won't know it works it unless you do some serious testing. I don't plan to, so I hoped to find someone who has/will. It's just for fun for me. What did Klipsch engineers say ? Actually came to this forum to find out if anyone knew about class-T....heck. Cheers, Tom

OOps, just realised I said white noise. I meant the pink kind....although purple is more my colour....matches my ...er.....

Thanks for the ongoing debate ! [] I'll try to explain myself another way. Dynaudio (can I mention them here ?) pulse test their drives at 1KW for a millisecond or something and they like to tout that their drive does not distort with transients like this that are far above the rated power; they rate them at 150W or so; a continuous load. Amplifiers are also capable of transients far above their continuous rating. How would this be possible if output voltage is going to be the same ? What do you mean by this ? I think it is never the same but always varying, unless I'm listening to white noise (otherwise known as thrash metal. ...[]) Music (not thrash trash - but a full orchestra or something) is about dynamics - I think fool's bi-amping allows better dynamics because the amp is not working so hard; it's sharing part of the load with another amp. The frequencies determine the amount of energy needed to push the driver and because the drivers are pushing different volumes of air, more energy is needed for an LF driver than a HF one; about 80/20 of the total output power for a 2Khz crossover. Would you dispute this ? I think the greatest benefit of bi-amping will be found in HF because that will become very lightly loaded and have tons of headroom for transients. The LF, by contrast, will only get maybe 20% more energy to play with so the increase in transient response will only be a few dBs; but just 3dBs is a doubling of the pressure level and that means twice the volume on a transient. If I get that I will be so happy - it'll be a huge difference for just US$110. I completely agree that it is a very complicated matter because amplifier output impedance, damping factors, heat, and slew rates also have to be considered. It is why I am curious about using class-T for bi-amping. I can't find anyone posting on this topic. They are much more efficient amps so I can almost ignore heat losses I hope. However, I have no real data about their ouput stage because it is quite different from tubes and linear amps - it's via hand-wound air-core coils and they are bridge-tied load too. So what I'm saying is, if you still don't see what I'm saying, then no worries, my class-T bi-amping 'research' will continue ! Enjoy your tunes ! Cheers, Tom

Hmmm....not sure I agree. I tend to think of these things in terms of energy; voltage and current together make power = energy. If I disconnect one driver I'm releasing energy for the other (because less current will be used for the same voltage so the power use goes down) hence more power available for the remaining driver (assuming it doesn't just turn into heat). What often happens in power supplies is the voltage dips a little with high current drains and pulses. So in theory the extra energy available should add a little volume (very little probably - I expect only 1 dB) but it will allow more headroom for dynamics, which is actually what I'm after - a system that can really punch. It's why I like the idea of 5.25" drivers. Anyway, just MO. The proof of the pudding...

Well I'm gonna be a fool and try anyway. I'm too much of a 'purist' to add components when I reckon the amps will be quite happy. Actually, there's plenty of punch and drive with just one amp but what the hey....I'll have fun trying. I bought a pair of RF-52s (HK$4200 = US$540 incl some cables) and have spent the whole weekend discovering previously unheard details ! Awesome ! I did an SPL test (very approx) and they produce bass all the way down to 20Hz but it only really kicks in at 40Hz. 70Hz and 150 Hz are both a dB or two up. So I suspect the driver's free air resonance is around the 70Hz area and the cabinet helps extend this almost an octave. Pretty good design work if you ask me. I also found out I can't hear over 15Khz. I'm only 37. Too many discos... I think you will get the most bang for your buck by going with a quality receiver. The Denon AVR's actually have great preamps - just find one with analog preouts on the back and you're good to go. Can't justify the moula on a power stage I'll never use - gonna demo some Chinese DACs and a Musical Fidelity and see what takes my fancy.

Thanks for the replies ! I think the thing to do is buy the speakers, run them in, get used to them and then try a fool's bi-amp and see if my ears can hear any difference. I'll be sure to let you know if the amp designer or Tripath know a technical answer in the meantime. Still, now I have an excuse to buy a new pair of speakers and spend hours on the sofa......! Cheers,

hello speakerfritz - thank you for the post ! I don't think I was very clear - sorry - I have eight class-t amps - they work in pairs as btl amps - so I have four btl amps, 20 watts each. 80w total. So this would be 20w for the HF speaker input and 20w for the LF speaker input for each of a pair of speakers. Obviously it is a tad weedy on paper but in reality, 20 watts into an efficient speaker is quite tasty, especially a distortion-free 20 watts. Plus there's the argument about high-power amps heating coils etc etc. I digress. Because the crossovers are low(ish) at 1.8Khz on the speakers I'm lusting after, I reckon fool's bi-amping would mean about 20% or more power available for the LF stage and an HF stage that never ever gets near distortion output levels. I have no argument with the comments above about this power turning into heat because of very high impedance in the crossover reacting with the output stage of some amps, nor that fool's bi-amping is not suitable for tube amps. But I wonder if this applies to BTL amps ? and how about class-t amps with high damping factors and awesome thermal efficiency ? and, of course, BTL class-t amps ! Class-t stuff is quite new and quite different from the norm so I wonder if the rules are different for this kind of setup. So will this extra 20% add a dB or two to the headroom or just keep me cosy on a cold night ? Is it even worth trying ? I noted above that it was said Klipsch Techies were saying bi-amping was the way to go until someone from MacIntosh said no thank you. Does anyone know where I can find this discussion ? It doesn't seem to be in this loverly forum. Incidentally; I read in another thread that a $10,000 music setup blew people away with RF-52s so I'm definitely leaning that way now too. Quite excited in fact....sad eh ? Thanks for reading, Cheers !

Hi, Can I jump into this conversation and ask if you have tried class-t (hybrid digital) amps with bi-amping ? I am using class-t amps from DIYparadise 'cos they have very low distortion and sound sooo sweet - rich and detailed. They are what has prompted to upgrade my whole system. However their max output is around 20 watts as a bridge-tied load so bi-amping, fool's or passive, is the way I am inclined to go for just a bit more headroom and complaints from the neighbours. I'd rather not add components so a fool's bi-amp set up really intrigues me because I don't think the power would be lost in heat. As far as I know, they don't suffer the heat problems of linear or tube amps and have very good damping (they are very efficient so they don't even need a heatsink at full output - incredible but true). Is it still fool's bi-amping if it works ? Also I'm planning to buy either RF-52s or RB-61s - both can be bi-wired/bi-amped I believe ? Do the RF-52s really go as low as 34Hz ? They're 5.25" after all. Is it weak output in the bass ? If anyone has listened to these in a decent room and has an opinion please let me know what your experience was. Finally, now completely off the thread (sorry) but can anyone recommend a modestly priced (a few hundred US$) DAC for 24bit 44.1khz signals ? Thanks to all, Tom