11 May 2012 – The previous version of the IMA user’s guide only showed where to install jumpers essential to the operation of each microphone. Unfortunately this number varies, so sometimes you had to add or remove jumpers when changing configurations.
Most configurations call for five jumpers; but one specifies four, and one seven. Changing microphones would be even easier if the number of jumpers remained the same.
The latest version of the decal (reproduced above left) shows where to store/park any “unused” jumpers. Note that these locations vary with each configuration. This scheme even accommodates one optional spare jumper (not included with the IMA kit of parts).
The decal denotes “essential” jumpers with black ovals; unused (non-essential) jumpers with gray ovals; and an optional spare (non-essential) jumper with a white oval.
This suggestion was merged into the user’s guide on 25 July 2012.
3 May 2012 – The photos of the assembled Headers kit – both on our website and in our PDF instructions – show the 4.7 pF cap on the UN-K60XV header “standing” upright. In contrast, the 3 May 2012 version of the Headers kit Quick Start Instruction Sheet (QSIS) suggests that this cap should be installed tilted more than 45 degrees from vertical. Please follow the instructions in the QSIS when installing this cap and position it tilted sufficiently that it extends no higher off the board than the height of the insulating body of P15.
Even standing vertically, the cap will still easily clear nearby K2 components when the UN-K60XV header is install. The only concern is that the cap could be damaged when the UN-K60XV header is not installed in your K2, but is instead parked/stored on the “Foam Home” that’s included with the kit.
If you’ve not yet assembled your headers kit, just follow the instructions in the latest QSIS. If you already built the kit, do not attempt to tilt the cap once it has been soldered in place, since doing so could damage/crack the meniscus on its leads. Instead, make a suitable indentation/hole in the foam immediately below where the cap will reside. Then just be sure to always position the UN-K60XV board on the foam, such that the cap is directly over this location. (You might find it helpful to draw an outline of the board in this position, with a permanent marker.)
20 April 2012 – If you are building a K2 and winding the toroids yourself, then you will surely find this guide useful. It depicts how to evenly distribute the windings over the core diameter, for all of the turns counts you’ll encounter in the course of building a fully loaded K2/100 and a KAT100. It also shows the direction (i.e. over versus under) that the turns must be wound.
In all but one instance, the windings are spaced over 85% of the core and the core is shown actual size.
IMA: When NOT to Externally Bias
9 May 2008 – In a recent Reflector post ➚ Don Wilhelm (W3FPR) wrote …
“Caution: you must know your … micro‑
phone element type – a dynamic element
can be damaged if bias is applied to it.”
The two types of microphones commonly used with amateur radio equipment are electret and dynamic. These terms refer to the principle on which their transducer (element) operates. The output of an electret transducer is inherently low, so electret microphones always incorporate a built-in pre-amplifier.
In contrast, the output of a dynamic transducer is normally sufficient to drive a modern solid-state transceiver directly. Thus, pre-amplified dynamic microphones are rarely encountered.
Regardless of its element type, if a microphone has an internal pre-amplifier it needs to be powered somehow. In amateur radio applications, this power is provided in one of two ways …
Power is applied to the mic AF output line through an external biasing resistor. This method is typical of Elecraft, Heil, and Icom electret microphones. If the optimal value of this resistor is not specified in your microphone’s documentation, then you should request this information directly from the manufacturer.
The pre-amplifier is biased internally either from an internal battery or from power provided by the transceiver. This method is common to Kenwood and Yaesu electret microphones. They put the bias resistor inside the microphone housing, so you should not apply external bias. (Often these microphones will include a DC blocking capacitor in the mic AF output line to protect your radio.)
Dynamic microphones rarely have a built-in pre-amplifier, and most that do are biased internally. However, a very small number of pre-amplified Icom dynamic microphones do require external biasing. If your dynamic microphone does not have circuitry to protect its transducer, then mistakenly applying an external bias will damage it!
The best way to ensure that you are properly configuring the IMA jumpers is to “know” your microphone(s). Yes, our IMA User’s Guide will get you started. However, much of its content is derived from information that has not yet been verified by hands-on testing. So your safest recourse is to know the element type, pin-out, and bias requirements of your microphone(s).
In addition, many other microphones and headsets beyond those described in the User’s Guide can be used with the IMA, provided you know how they are wired.
IMA: Do Not Remove Built-In Spacer
29 February 2008 – In December 2007 we learned that – while removing the remnants of the breakaway tabs – one of our K2 Internal Mic Adaptor (IMA) customers had also mistakenly removed the built-in spacer on the left edge of the Mic Patch Panel board. At that time, we addressed this issue by further emphasizing the importance of this spacer in the IMA Quick Start Instruction Sheet (QSIS). More recently we learned of a second occurrence of this assembly error, prompting us to raise this issue to the level of an app note.
Most likely there was no mention of the importance of this built-in spacer in the beta release QSIS that accompanied our initial (September 2007) IMA deliveries. This spacer ensures that that the IMA cannot slide off the K2’s Mic Configuration header (FP-P1). One customer reported that without the spacer, the entire assembly had eventually worked itself loose. This is more likely to occur if you operate in a high vibration environment with the tilt bail extended. It may also be more likely to occur if you frequently reconfigure the jumpers, due to the resulting lateral forces on Mic Extender socket J1.
If you received your IMA kit prior to January 2008 but have not yet assembled it, you should download and use the latest IMA QSIS to ensure that you don’t overlook this important point during assembly and installation. If you installed your IMA before January 2008, please inspect your Mic Patch Panel board and verify that you did not mistakenly remove this spacer. If you did, then please contact us to make arrangements to replace your IMA.
Headers Kit: Resistance Checks
17 September 2006 – The expected UN-KNB2 (J12) header board resistance measurements are transposed in the Quick Start Instruction Sheet (QSIS) that was included with initial shipments of our new rev. G Headers kit. Our latest QSIS has the correct values, which are reproduced here …
Rev. D Headers PCB: RF-L4 Access
2 September 2005 – An issue has been identified where the rev. D UN-K60XV header board partially blocks the adjustment slot of L4 in the 80/160m bandpass filter (as shown below left).
To alleviate this obstruction, we recommend cutting a small notch in the board (as shown above right). This may be easier to do before populating the board with parts.
Headers Kit: Longer UN-K60XV Pins
30 August 2005 – Do not install the originally supplied “short” male terminal-strip connectors on your UN-K60XV!
An issue has been identified with regard to the male connectors included with your kit. In order to clear bandpass filter inductors L2 and L4, the UN-K60XV requires connectors with longer pins than were originally supplied. Therefore, please use the enclosed connectors with 318 mil contacts for your UN-K60XV.
If you purchased our “Headers PCB” (as opposed to our “Headers Kit”), please note that the UN-K60XV board requires connectors with longer contacts than the other boards.