UncleRobb

Al, what exactly did you simulate? Did you take (DC) resistance, inductivity, and dielectric losses of a (real) capacitor into account? What exactly did you measure and how do you define Q, e.g. AC-resistance/DC-resistance? From what you write, I conclude that you e.g. did not account for dielectric losses. In order to measure the problems introduced by different caps in parallel, you might also want to use some more refined setup. Robert

Perhaps we can agree on that the effect of directionality in wound non-electrolytic caps is an effect for which only those audiophiles may apply who virtually can hear the grass grow and the fleas cough. The two leads of a cap in a non-symmetric network experience different potentials, V, and currents, I, as a function of time, i.e. V(t) and I(t). Thus when a non-ideal cap that itself is non-symmetric with respect to an exchange of the leads is used in such a network, its behavior will (slightly) depend on the direction how it is wired. Non-equivalent capacitors, e.g. a smaller one used to bypass a larger one, have likely different time constants (i.e. T=C*R) which, when they are used in the signal pass, to my understanding, can create some smearing of the audio signal. What do you guys say now? Robert

Gil: Film/foil capacitors are of course non-directional, but, depending on the construction, the two connections can still be different. This is the case for the Hovland Musicaps, which are rolled-up, and the leads to the inner and outer parts of the foil are clearly marked. When these caps are connected in a way that both leads are not equivalent, for example in a CR high-pass filter, then it will make a difference how the leads are connected. Whether the sonic difference is large is another question. When caps of limited quality are used, it might even not possible to hear a difference at all. However, when I spend $100+ on high-quality caps, then I feel that I should wire them in the way the manufacturer recommends. Al: Very funny.... but what can be expected from somebody who puts caps of different values in parallel into the signal path Let the flame war begin... Robert

I made a pair of four 3.3uF/100V Musicaps bundled together to give me 13uF each. After I removed the caps from the xover, I discovered that these are labeled "SPRAGUE, 14.0-150 DC, I2IPI460OR5S2," and they indeed measure 14uF. Damn, I could have had 14uF with two 7uF caps in parallel and saved some money too! Soundwise, the bass now seems dryer and less bumpy (don't ask me why), we (Alice and I) don't notice any change of the midrange, which is as sweet as before, but the treble is less harsh without sacrifying detail. The new caps only have 10 or 20 hours usage and I suspect that they may improve further. Somehow I expected a larger change. Perhaps the original (motor run?) caps are not that bad. Any opinions? And what is the "correct" value for the cap in the highpass filter for midrange and treble: 13 or 14uF? Thanks, Robert

Thanks Rick. Somehow I overlooked this link. I just put the caps into my xover network and I am burning them in. Robert

I have two quartets of bundled 3.3uF/100V Hovland Musicaps waiting to replace the 13uF motor run caps in the A/AA xover networks of my La Scalas. The caps have one lead with clear insulation and the other with a clear insulation with blue stripe. What is the recommended wiring direction? Thanks, Robert

Gentlemen, although I must admit that the name of this thread is indeed a bit provocating, it is not my intent to troll at all. After I read the discussion concerning A and AA type Xovers elsewhere in this Forum, I decided to modify mine such that I can switch between both of them. After I had this done, I found myself to be disappointed by the very flaw that this thread is about. Thus, I believe that this issue deserves some further discussion. And, of course, I am disappointed that I did not find anybody pointing out this weakness of the A type. Finally, since this issue did not give rise to any new discussion in the AA Xover modification Thread, I decided to create this one. Thus, I sincerely apologize if I have hurt anybodys feelings with my wording and I wish to point out that it is not my intent to start a flame war. That being said, can we now go over to the technical/audio aspect? I just measured the threshold voltage for a 1kHz signal fed to my La Scalas with the Xover set to A-type leading to audible distortions. This voltage, 1.5V, corresponds to a power of about 0.15W (assuming a resistive load of 8Ohm). I cannot detect any distortions of the waveform with my scope, nor should my amp produce any significant distortions at this level. Now I still have to respond to the criticism of Mobile Homeless concerning the presence of switches and long wires in my Xover modification. Well, to begin with, my AA Xovers were not exactly designed like a low-current circuit. The components are screwed/glued to some wooden board and the wires are somewhat long and dangling. In some cases, connections are made by screws. Thus I believe that my construction does not lead to a deterioration, especially since the switches are high quality (200V/3A, if I remember right) that should give good contacts. After I learned from Al K. that even the tweeter section in the AA type Xover is a compromise, I am more and more attracted to his construction. I have only two points to criticize and I would appreciate it if Al could reply to this. First, there are a few caps of different values/bypassed in the signal path. To my understanding, due to the different time constants, this may lead to a smearing of the signal and should be avoided. I think that in this case it can indeed be avoided and if caps of a certain value are not available, I would rather bundle caps of the same value. Secondly, I frankly do not understand why it is advantageous to use a transformer to attenuate the squawker signal. Would it not be better to use high quality (e.g. metal film, metal oxide, non-inductive wire wound, tantalum) resistors instead? I could imagine, that these simply were not available at the time PWK designed the Xovers. What do you think? Thanks, Robert

Gentlemen, although I must admit that the name of this thread is indeed a bit provocating, it is not my intent to troll at all. After I read the discussion concerning A and AA type Xovers elsewhere in this Forum, I decided to modify mine such that I can switch between both of them. After I had this done, I found myself to be disappointed by the very flaw that this thread is about. Thus, I believe that this issue deserves some further discussion. And, of course, I am disappointed that I did not find anybody pointing out this weakness of the A type. Finally, since this issue did not give rise to any new discussion in the AA Xover modification Thread, I decided to create this one. Thus, I sincerely apologize if I have hurt anybodys feelings with my wording and I wish to point out that it is not my intent to start a flame war. That being said, can we now go over to the technical/audio aspect? I just measured the threshold voltage for a 1kHz signal fed to my La Scalas with the Xover set to A-type leading to audible distortions. This voltage, 1.5V, corresponds to a power of about 0.15W (assuming a resistive load of 8Ohm). I cannot detect any distortions of the waveform with my scope, nor should my amp produce any significant distortions at this level. Now I still have to respond to the criticism of Mobile Homeless concerning the presence of switches and long wires in my Xover modification. Well, to begin with, my AA Xovers were not exactly designed like a low-current circuit. The components are screwed/glued to some wooden board and the wires are somewhat long and dangling. In some cases, connections are made by screws. Thus I believe that my construction does not lead to a deterioration, especially since the switches are high quality (200V/3A, if I remember right) that should give good contacts. After I learned from Al K. that even the tweeter section in the AA type Xover is a compromise, I am more and more attracted to his construction. I have only two points to criticize and I would appreciate it if Al could reply to this. First, there are a few caps of different values/bypassed in the signal path. To my understanding, due to the different time constants, this may lead to a smearing of the signal and should be avoided. I think that in this case it can indeed be avoided and if caps of a certain value are not available, I would rather bundle caps of the same value. Secondly, I frankly do not understand why it is advantageous to use a transformer to attenuate the squawker signal. Would it not be better to use high quality (e.g. metal film, metal oxide, non-inductive wire wound, tantalum) resistors instead? I could imagine, that these simply were not available at the time PWK designed the Xovers. What do you think? Thanks, Robert

Recently, I modified the type AA Xover in my La Scalas (see the "AA Xover modifcation" thread) such that I can switch it to type A. After Al K. pointed out that for the latter Xover, the tweater still gets -20 dB of a 1kHz signal, I did some measurements and confirmed this value. Thus, when I feed a rather loud 1kHz signal to my La Scalas, in type A mode, the tweeter produces quite some distortions. I find this quite interesting in the light that many in this Forum prefer the A over the AA. Now I wonder how one can speak of improved sound when the tweeter gets a too low frequency signal such that it distorts? Any opinions? Robert

Al, I just did some measurements to find out what signals are output to the squawker and tweeter when a 1kHz harmonic wave is fed into the Xcover network. In type A mode, the tweeter gets a signal that is indeed attenuated by 20dBV. When I remove one tweeter connection, the distortion disappears. In type AA mode, I cannot measure any 1kHz signal coming to the tweeter. By the way, I discovered that my amp generates a 1MHz signal that is also fed to the tweeter. Thus it appears as if the A type Xover lets too low frequencies to the tweeter which, in turn, creates the distortions that I hear. I would not call this high fidelity... Robert

That is great Al! I plan to do some measurement with my 2-channel scope this night after work on the amplitudes of the tweeter and squawker signals. I would not be surprised if one could indeed clearly hear distortions mixed with a pure sine tone that is 20dB louder. With music, this might be more difficult. However, I believe that I hear some distortions here too. Robert

The type A Xover doesn't work for me... Here is what I did: After work, I visited the local Radio Shack to buy some switches and other material for my new project. This is a modification of my type AA Xover such that I can: i) switch off the Zener diode protection; and ii) switch between type A and type AA. The latter is done by a 2-pole switch that: i) removes the 245uH inductor from the network; and ii) deactivates one of the 2uF caps. Additionally, I removed the screw that holds the top board of the 245uH inductor. Both don't seem to be necessary. In type A mode, a 1kHz tone generates a very significant distortion in form of overtone(s). I double-checked my wiring. Everything seems to be OK. It seems to me that for some reason, my amp doesn't like the type A network. Any explanations? Thanks, Robert

Thanks John! I found out that at least in one of my La Scalas, the crossover board is mounted by two 1" screws that are hidden behind the mount of the Zener diodes and the autotransformer. Unfortunately, the woofer leads are too short to allow me to take the board outside the speaker. But I am making progress... Robert

Guy, thanks for sharing your "crossover journey." Somehow, I believe that simpler is better. And although I am sure that Al knows very well what he is doing and although he uses premium parts and he can provide some impressive impendance and phase angle plots, I am not comfortable with the rather complicated ALK crossover. I also do not like having bypassed caps that are in the signal path. I think I modify my type AA with some switches so that I can change it to type A anytime. Robert

Something else: I just had a look at the AA network in my La Scalas and somehow I cannot figure out how the board is attached to the speaker. All I see are several screws that hold the transformer, the inductors, one large cap, and the Zener diodes. Do these (or some of these) also hold the board itself? I hate to open the woofer department to find out more. Thanks, Robert