... a
bit Suffolk|
Users are sometimes a little confused what the InTNaT does. Its job is to sum a crossover's outputs, do it differentially, and provide some protection for the NaTKiT and PC. The
InTNaT sums a crossover's outputs so they can be tested in one
operation.
When testing crossovers you are squirting the output of a power amplifier, perhaps even a mighty power amplifier, into the NaTKiT via maybe a single reactive component. It has never happened yet but if something did go wrong the InTNaT would sacrifice itself and save the NaTKiT and PC. The InTNaT v1.0 Passive is a four channel, five channel capable, interface for production testing passive loudspeaker crossovers. The interface provides summing differential inputs so that a crossover's outputs can be summed and tested in one pass. The inputs are differential and so detect open circuits in any common line of test unit's outputs. The mains fuse is externally accessible but gain setting is by an internal DIL switch to prevent accidental adjustment in use. There is no power switch for the same reason. The interface is particularly suited to the NaTKiT1 production test system. INSTALLATION Installation is just connecting up and setting the gain. Connect the speaker leads from your power amp to the Red and Black 4mm sockets on the NaTPmP's rear marked FROM AMP. These sockets connect directly to the Red and Black 4mm sockets marked TO XOVER on the NaTPmP's front.
Connect the crossover's outputs to the 4mm sockets on the InTNaT's front panel marked A..D. How the crossover outputs are plugged should be documented to ensure each test unit is connected in the same way. The prompt file facility of the NaTKiT1 test software is there for just this sort of thing. Connect the male 3 pin XLR connector on the InTNaT's rear, ie the interface's output, to the NaTKiT's input, ie the mono 3.5mm socket. The InTNaT's output is NOT balanced. The pin identity is pin 2 live (positive polarity) and, 1 and 3 return (ie screen, shield or earth). Connect mains to the IEC socket and the red LED should light. (If the LED does not light then either the LED is faulty, the interface is faulty, or the mains fuse has blown. The 20mm mains fuse is in the IEC mains connector on the rear of the interface and should be 250mA anti-surge.) Now set the InTNaT's overall gain using the internal 4 way DIL switch. When using a NaTKiT with the interface set the gain so that there is no visible sign of clipping when doing a sweep, and that Rng? does not appear at the bottom right of the response graticule. If there is clipping the gain is too high, and if Rng? is visible the gain is too low.
SWITCH POSITIONS X = Don't Care
THE FIVE CHANNEL CAPABILITY The InTNaT v1.0 Passive does not have 5 channels as standard because it makes the front panel very crowded and this may intimidate and confuse an inexperienced operator. But the InTNaT v1.0 Passive is 5 channel ready and NaTCH can easily upgrade the interface for you. CONNECTING TO THE InTNaT You will need some form of "jigging" to connect your test units to the interface. Hooking up is easily the longest part of testing a crossover so the process justifies some thought. Perhaps some car battery sized croc clips or Safeblocs (those things for connecting bare wires to the mains) mounted on some MDF. |
You
might get some result like in this sketch. You would expect the high pass
output to be lower than the low pass because tweeters are usually more sensitive
than bass drivers. What quite will happen in the crossover region will
depend on the particular crossover.
Some users have products that mostly sum like our sketch above but the
odd model goes through the crossover transition smoothly. When testing
these oddities they purposely connect one output out of phase to get a response
with a suck out like the others and so not worry the operator! This is not an unreasonable thing to
do as the NaTKiT
tests comparatively.
... if
there were an open circuit in the common line of the low pass section then there
would still be a path as shown by the red link; and the crossover wouldn't show
as faulty, but ...
if you use
differential
amplifiers then there is no common path and the open circuit is detected.
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