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Self-contained LIMP jig.
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Re: Self-contained LIMP jig.
Without the protection circuits, you just follow the diagram JR posted above but use the smaller resister instead of the 100 ohm.
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Re: Self-contained LIMP jig.
Originally posted by JasonP View PostThose circuits are for high power testing. Your sound card can't handle the voltage output of the amplifier directly, so it scales down the voltage to a level it can handle. The R1 and R2 function as a voltage divider to do just that. The two zener diodes placed across the sound card input will trip if the voltage is too high, create a short in the circuit, and protect it from possible overload.
If you are doing low voltage testing and have a way to ensure no accidental high voltages reach the sound card (using a DMM to test the output, etc) then you can just use the 16 or 27 ohm resistor setup with the amp output as presented.
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Re: Self-contained LIMP jig.
Originally posted by kevintomb View PostWhat schematic would be used, when using an external Amp?
I plan on using about a 16 ohm resistor.
I see the mention in the manual about using zener diodes, and 2 resistors, but their schematic is confusing. ((Drawing 3.2 and 3.3)) Not sure how they are combining them.
If you are doing low voltage testing and have a way to ensure no accidental high voltages reach the sound card (using a DMM to test the output, etc) then you can just use the 16 or 27 ohm resistor setup with the amp output as presented.
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Re: Self-contained LIMP jig.
Originally posted by johnnyrichards View PostAs far as details, Kenny - just this schematic:
[ATTACH=CONFIG]52566[/ATTACH]
Can't take credit for it however, it is pretty standard. I drew this schematic since some of the examples I found on the interwebz did not make a lit of sense to me, and I actually used a pair of 200 ohm resistors in parallel.
I plan on using about a 16 ohm resistor.
I see the mention in the manual about using zener diodes, and 2 resistors, but their schematic is confusing. ((Drawing 3.2 and 3.3)) Not sure how they are combining them.
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Re: Self-contained LIMP jig.
Thank you Jason. That's exactly what I needed to know. Seems like it's nothing to really worry about. I can't wait to get mine slapped together.
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Re: Self-contained LIMP jig.
The driver I have sitting loose now with the lowest Fs is a Dayton DA270 10" Aluminum. Fs is a mere 30 hz, and using my jig after a little break-in I got T/S matching the published spec nearly on the money.
The accuracy should drop the lower the Fs goes, but I think you'll be fine with drivers that have Fs 20 hz or above, in my experience.
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Re: Self-contained LIMP jig.
Originally posted by johnnyrichards View PostEither of you care to define the Fs limits of this device?
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Re: Self-contained LIMP jig.
Either of you care to define the Fs limits of this device?
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Re: Self-contained LIMP jig.
Originally posted by audioanarchist View PostSo would this not work as well for gathering t/s parameters of a subwoofer with a low fs?
I think it is ridiculous not to use a power amp.
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Re: Self-contained LIMP jig.
So would this not work as well for gathering t/s parameters of a subwoofer with a low fs?
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Re: Self-contained LIMP jig.
Originally posted by Pete Basel View PostIt
seems like they want to hide the performance flaws perhaps in the hopes of having
people believe that there is very cheap hardware to use with their software.
.
Nice job on the jig!
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Re: Self-contained LIMP jig.
Originally posted by bret191 View PostThe no load voltage is 530 mV and with 150 ohms it was at 405 mV on my UCA202. It works kinda ok but I have been looking and came up with this site and pointed me to this same CM2606 as I was using A imm6 and on the UCA202 the input isn't stout enough to get a good mic sig. and the CM2606 is cheaper too.
ridiculous because it hides the low frequency response. And measurements shown by
Jason earlier in this thread found it to be quite bad when loaded with 100 ohms. It
seems like they want to hide the performance flaws perhaps in the hopes of having
people believe that there is very cheap hardware to use with their software.
Interesting that they list the line out output impedance as two ohms, quite good if
their measurement is accurate.
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Re: Self-contained LIMP jig.
Originally posted by JasonP View PostI hooked up my limp jig to the card tonight and ran through two RMAA tests. Here are the results, nothing stellar (as expected) but fine for this kind of testing IMO.
[ATTACH=CONFIG]55752[/ATTACH]
Results on the left are at 50% output, and 100% output on the right. As you can see, nothing special here. The FR is pretty horrible, it starting to roll-off at 100 hz. It is -4 db at 40 and -8 db at 20. However, since LIMP is measuring the difference between channels, FR level isn't an issue at all. Channel matching between right and left is, and this card excels at that. LIMP calibrated with a channel difference of 0.02db, perfect. Tests I made conclude this to work just as well as my ASUS Xonar DX for low level measurement of T/S and impedance. I will not that even at 100% output, my DMM told me it was putting out 0.5 Vrms which isn't all that high. It did not seem to reflect in my measurements comparison in anyway however.
Fs woofers. If the response is fairly flat without the 100 ohm load then it is probably the output coupling
caps and it would help a lot to increase them by a factor of 10. Might not be so easy if they are surface
mount. I think this mod would help a lot.
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Re: Self-contained LIMP jig.
Originally posted by rhodesj View PostCan anyone recommend a small power amp for running impedance sweeps? The headphone out on the UCA202 I'm using rolls off pretty steeply around 20Hz, which isn't really helpful when I'm trying to measure a sub driver, Infinity 1260w, that has an Fs around 23 Hz, so I need solid impedance measurements from at the least 10Hz up.
Don't need a ton of wattage, just flat and clean, and hopefully not too expensive.
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