FWIW I was using my jig again today for a while and it's barely warm to the touch. The only part that seems hot is R1. I may want to put some kind of heatsink on R1 now that I've held my finger on it for a little while and pushed down harder to find out that it is hot to the touch (not painful though).
At this point, I'm only using the jig as an amp - I've been waiting on the guide to explain how to use it to measure impedance, but that hasn't been done yet? Or did I just miss the post/thread with that?
At this point, I'm only using the jig as an amp - I've been waiting on the guide to explain how to use it to measure impedance, but that hasn't been done yet? Or did I just miss the post/thread with that?
Hi Andrew,
Sorry for the rather long delay in responding.
The chipamp is the only component that should get just slightly warm. It should be attached to the metal backplate (no insulator needed).
The LED dropping resistor was sized for a 12 VAC supply. The LED should be fine with a bit more current, even though it is rated for 20mA (I believe).
April, that took a while.
The LED resistor needs some explanation. I use the recommended transformer voltage.
It allows the resistor to run far too hot and the LED passes far too much current, at that recommended voltage.
With no inputs nor outputs inserted, why does the Zobel and the chip run hot?
The LED resistor needs some explanation. I use the recommended transformer voltage.
It allows the resistor to run far too hot and the LED passes far too much current, at that recommended voltage.
With no inputs nor outputs inserted, why does the Zobel and the chip run hot?
I just ran mine for 10 minutes or so - R1 got up to about 40*C, so a little warm. R5 (Zobel) didn't get warm at all and the chipamp mounting plate didn't get much above ambient.
You have a point about R1 Andrew, I originally had this at 1K but changed it to 750 to give ~20mA to the LED. This is pushing the resistor beyond its power rating (1/4 watt). With that said, it will probably not be an issue for intermittent use (what this jig was designed for) and is in a non-critical part of the circuit (power on LED). It would be best to change the R1 value to 1K or more (or to 1/2 watt) if the jig will get continuous use.
ok, I see what you did combining the Lin and Rin to a single stereo jack. Makes sense. Now, if I'm using a sound card with a built-in microphone preamp, I'm assuming the jig will still work. In this case, make sure that Rin is connected to the sound card input and just don't connect anything to the jig's mic input. Also, why is the mic in a TRS jack, with the ring going to directly to BP3_4?
I think I'm going to need a pair of stereo mini to 2xTRS cables to get this thing going.
I think I'm going to need a pair of stereo mini to 2xTRS cables to get this thing going.
Greeting! 
The top design consideration for this jig was that it be convenient to use. Eliminating the switches of the Wallin jig, building in an amplifier that can drive a speaker during frequency response testing and using the same format of connecting cable as the typical soundcard (stereo mini jacks) go a long way to realizing this goal.
After the jig has been constructed, there are a couple of items that are needed to calibrate and facilitate operation:
The first are 2 resistors - one that is ~4 ohms and one that is ~16 ohms. The important thing about these resistors is that you know their exact resistance. Measurement with a reliable meter should be good enough. These are used to calibrate the software (Speaker Workshop or some other impedance measuring software). The Wallin jig has these resistors mounted internally and they are switched in and out as needed. I found that the calibration process was brief and did not warrant the added complexity of a switch.
The second is a set of cables, single conductor with a banana jack on one end and an alligator clip on the other. You'll need 2 of these and they are used to connect the jig to a device under test (DUT), such as a driver, an inductor, a capacitor or a resistor. Having one Red and one Black is handy.
Hi,
As explained above, you'll need external resistors for calibration. The internal reference resistance is the 3 parallel 30 ohm resistor (making a very accurate 10 ohms)
Hi,
I'll start up a new thread soon (yes, I promise!) that runs through initial setup of the jig, calibration and basic impedance measurement usage with Speaker Workshop.
The top design consideration for this jig was that it be convenient to use. Eliminating the switches of the Wallin jig, building in an amplifier that can drive a speaker during frequency response testing and using the same format of connecting cable as the typical soundcard (stereo mini jacks) go a long way to realizing this goal.
After the jig has been constructed, there are a couple of items that are needed to calibrate and facilitate operation:
The first are 2 resistors - one that is ~4 ohms and one that is ~16 ohms. The important thing about these resistors is that you know their exact resistance. Measurement with a reliable meter should be good enough. These are used to calibrate the software (Speaker Workshop or some other impedance measuring software). The Wallin jig has these resistors mounted internally and they are switched in and out as needed. I found that the calibration process was brief and did not warrant the added complexity of a switch.
The second is a set of cables, single conductor with a banana jack on one end and an alligator clip on the other. You'll need 2 of these and they are used to connect the jig to a device under test (DUT), such as a driver, an inductor, a capacitor or a resistor. Having one Red and one Black is handy.
Hi,
As explained above, you'll need external resistors for calibration. The internal reference resistance is the 3 parallel 30 ohm resistor (making a very accurate 10 ohms)
Hi,
I'll start up a new thread soon (yes, I promise!) that runs through initial setup of the jig, calibration and basic impedance measurement usage with Speaker Workshop.
It is best to use a mic and preamp that plugs into the "mic in" jack. The mic in jack has a switch internally that disconnects the amp output from the Line In jack (Right channel) and connects the mic input. The left channel gets a reference signal direct from the amp via the voltage divider formed by R10 and R11.
There was some confusion earlier about this Mic input as my original version has a mic preamp inside. This input accepts a 2 conductor mini jack and it needs to be a preamplified mic, not a mic that can plug direct to the Mic in on a soundcard. I should have changed the label of this input to "Mic Preamp In".
Hi,
Sorry, I can't give the Gerbers at this time.
I will have kits available soon and I have boards on hand now. Send me a PM if you would like one.
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