testing a crossover
that all sounds fantastic Fiesta,ill get on that today,taking photos,ill try draw a schem.but its difficult, but ill do my best,thankyou so much for your help here,its so much appreciated,im sure its some thing simple in the xo,but i cant see it,but it strange how both have gone the same way,caps where all changed out 2 years ago,but ill test them all again. kind regards Mark |
i would also upload some photos, but as this is my first ever use on this site,im not sure how to do thisGo to Virtual Systems page, use the "Create System" to upload photos. https://systems.audiogon.com/ |
I would like to help as I'm an avid bi/tri-amper. I would guess you've checked the cables and wiring to the amp and speakers? I don't know anything about the crossovers in the speakers, is it possible to draw a schematic or shoot some photos? I use an active crossover at the inputs of my amps to limit the frequency range to each driver, tri-amping. Nothing but wire between the voice coils and amp outputs. This configuration virtually eliminates intermodulation distortion, which is most offensive to the ears. I've been bi-amping for 44 years and tri-amping for 41 years. Might be as simple as bad caps in the crossovers you are using. If you would like, I could send a PM to you with my email and you could send me a schematic or photos of your speaker crossovers. I'm positive we can get to the problem without much effort. |
i am using internal xo,which came with the speakers all tests done with power amps disconnected. the problem{ going pop{broken}only happens when the speakers are driven in bi-amp config,and its the amp which is driving the high/mid drivers that blows up . when using only one amp,in bi-wire config,everything works,all be it the sounds quality is slightly off,but i would have thought that to be ok,that why i bi-amp,for better sound quality. to add to this,i changed out the xo caps for better ones two years ago,and after fitting them ,i tested the input speaker terminals for the correct ohms reading and all was good,but something has changed. regards Mark |
Hi Guys,thankyou so much for all your help,but i still dont see a solution to this problem,in my opinion there is shorts in both xos,please see below- LEFT SPEAKER / RIGHT SPEAKER speaker terminals with everything connected on both speakers MID/HIGH 0.0 ohms / MID/HIGH 0.0 ohms BASS 7.9 Ohms / bass 6.8Ohms DRIVER TEST DISCONNECTED FROM X OVER TWEETER 8 OHMS / 7.9 OHMS MID 6.3 OHMS / 6.2 OHMS BASS 6.1 OHMS / 6.0 OHMS CONTINUITY TEST ON X-OVER WITH DRIVERS REMOVED USING DIODE FUNCTION between positive and negative on x over HF 000.2 {dead short} / 000.2 {dead short} MF 000.5 / 000.5 LF OL. / OL. MID HIGH INPUT IP OL. / OL. BASS INPUT OL. / OL. OL. BEING NO CONTINUITY TEST TESTED AT/ON X-OVER SPEAKERS CONNECTED OHMS HF 0.0002 OHMS / 0.002 OHMS MF 0.0001 OHMS / 2.0 OHMS LF 6.4 OHMS / 6.3 OHMS ive also now removed one lead from all the caps on one xo,and tested them with a cap meter,all caps are the correct uf ,within spec,can anyone tell me where to go from here, thankyou again for all your kind help.regards Mark |
@likklegerry - Anymore info from you? Are you using internal passive crossovers? |
The best way I know of to test a crossover is to generate an impedance graph. You can use DATS V2 (or is it now up to V3) or you can build a jig and use Room EQ Wizard’s app for this. But... if you are bi-amping it is possible the two crossover sections are not properly separated. If the voltage in one section can touch the voltage in another, at all then you can cause the amps to fight each other. If the internal crossover is completely separated, including separate grounds internally then no problem. OTOH, if the ground is not separated internally and 1 amp has reversed outputs or balanced outputs then you run into the problem above. |
The formula for parallel resistance is 1/Rt= 1/R1+1/R2+1/R3....If any one or more of the paralleled resistor is 0 ohm, it is a short circuit and the total resistance should be 0 ohm. |
I have a love/hate relationship with puzzles like this. On the one hand I love em because it is nice to think they can be solved if only you know enough. On the other hand I hate em because you never can be sure you are getting the whole story. Like, one train leaves at 30mph, another at 40, how many painters does it take to earn $40? In this case I can't help wondering, how on Earth did two speakers go bad at the same time? In other words maybe zero ohms is a red herring. No trains left the station. Three buckets of paint, and the waitress earned a $40 tip? |
Wilmslow Audio built some fairly complex crossovers, for some of their systems, though I’m not familiar with the Mirage’s. A DMM can easily read impedances, through the inductors in a woofer’s series circuitry. The capacitors in mid/tweet series circuits are another story. I could (easily) be wrong, but: I’d put my money on the speakers/crossovers being OK and something in the amp, or cables/connections: the culprit.
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Got me MC. I think the repair guy missed something.. If it was to heavy a load it will pop a fuse not blow up. Must have one sorry protection circuit. TWICE. I don’t think so.. It’s the amp or PC or RCA or something exclusive to THAT amp.. The input to the amp? It should pop a fuse if it’s on the output side, like a speaker issues, usually. All I know is neg to neg and pos to pos = 1/2 the two numbers added together. 8 ohm top + 6 ohm bottom = 14 ohms /2 = 7 ohms Running neg to pos, to neg to pos, combines the two. 6 ohm bottom + 8 ohm top = 14 ohms. 8 -14 ohms loads on my valve amps are just perfect. They run a LOT cooler and clear as a bell all the way to 100% volume.. I’m likin’ the bass at 8-12 ohms better too, with BIG class d amps. They are 12K amps. 1700 x 2 all day long at 12 ohms bullet proof. Dirt cheap! Get a Behringer NU12000 (NO DSP) move your other amp to the top. Be happy for 400.00 and 10 years.. I disconnect two of the 3 fans and put the last one on a switch. Perfect.. DEAD quiet.. or hook it to 10-12 18" subs.. It will push EVERY one to 120 db. I'm thinkin' 4 new 21" Dayton's with 8 18" passives would be a good bass system .. :-) I like a room that can tenderize meat in a pinch.. :-) |
The formula for parallel resistance is 1/Rt= 1/R1+1/R2+1/R3.... https://www.electronics-notes.com/articles/basic_concepts/resistance/resistors-in-series-parallel.ph... Since he measured almost 8 ohms then the total resistance will be 1/8 ohm + 0 ohm or 0.125ohm. I think we all can agree that is a pretty low resistance and would suck the bass and dynamics out of most amps. What I don't understand is where is the short? And how does the driver manage to still get enough signal to make sound even though there is a dead short? |
Where the heck is George at? You use a single amp and it works with a little less bass. "lack of bass and tightness". NOT no bass. If all the drivers are working and you run the XO in parallel, the reading will go LOWER not higher. Parallel a pair of 8 ohm speakers you get 4 ohms. Put your DMM on the post that reads ZERO and leave it there for a a while. You have to charge the cap (s) with YOUR little battery in the DMM, do you understand? A lot more caps in the band pass than the BASS OX. On the bass side there is usually just a low pass, a resistor for 6 db first order maybe a cap TOO, for a second order 12db.. Get some correct data FIRST then figure out what up.. I’m not 100% sure until I know what the mids and highs read on a DMM. Going from bi-amping to bi-wiring and a single amp tells me there is an AMP problem or the way it’s being wired. A stray single strand or some weird thing like that.. A close look and make sure there is no stray wires touching and you somehow make that happen when you hook that amp back in. You don’t want a strand from one amp touching another. IF the same speaker cables are being used and you're just adding or removing an amp, it sure sounds like an amp issue to me. Less swapping a PC for the one that keeps taking a dump.. You did swap PC right? What else is there? Check the RCAs and XLRs cables for the amp that is acting up. Just swap the silly things.. make sure. Regards |
millercarbon You have a dead short. They worked when connected normally because then the amp sees the sum total resistance including the 6.8-7.9 ohms. But connected bi-wire one amp sees only a dead short and so pop, there she goes.Nope. You're confusing bi-wire with biamplification. They are two different things. In biwire configuration, the amplifier still sees the drivers' total resistance. |
I agree with MC's dead short analysis. Are you b-amping using the passive crossovers inside the speakers, or are you using an active crossover at the inputs of each amplifier? If you are using the passive crossovers in the speakers, then there could be a short in the crossover. But, that doesn't explain why it works when you go back to driving with a single amp. Let me think, and I might have more suggestions once you get back to us. |
You have a dead short. They worked when connected normally because then the amp sees the sum total resistance including the 6.8-7.9 ohms. But connected bi-wire one amp sees only a dead short and so pop, there she goes. The lack of bass and definition is because the dead short results in a total impedance much lower than 6.8. It is simply running out of gas and so what seems strange to you is perfectly normal and expected given the situation. Now it seems something happened to create the dead short. This is what caused the pop and the first amp failure. It seems the drivers are putting out sound or you would have noticed that, and they measure fine. So probably the short is somewhere between the terminals and the drivers. That leaves wires and crossover. Get in there and see. (I hope it is not one of these potted crossover situations....) |
