Elecraft didn’t offer their own microphone when Wayne ➚ designed the K2, so he made it easy to configure the pin-out of the K2’s mic connector for other vendor’s microphones during initial assembly. Or more precisely, it’s easy to configure if you already purchased the KSB2 option, given that the Mic Configuration Header isn’t included with base K2/10 kit of parts! Once the KSB2-supplied 2×8 DIP header has been installed, gaining access to it again requires partially disassembling the front portion of the radio. Also, there’s no provision for inserting a bias resistor should your microphone require “external” biasing.
Our Internal Mic Adaptor (IMA) is a tiny circuit assembly – consisting of two multi-layer boards – that fits snugly in the half-inch gap between the K2’s Front Panel and Control boards. Once installed the IMA more-than-dramatically simplifies the task of configuring the K2 for the five …
… most common 8-pin Foster mic connector pin-out schemes.
In addition to “rewiring” the pin-out, an external bias resistance can also be “inserted” – with seven jumper-selectable choices available ranging from 820 to 10k (Ohms). At least 66 popular (8-pin Foster connector) microphones are supported, including all Alinco, Elecraft, Heil, Icom, Kenwood, Ten-Tec, and Yaesu models.
The single word that best describes the extent to which the IMA simplifies the task of reconfiguring the K2 to support this wide variety of microphones – is “indescribable”. The table below illustrates the difference the IMA makes.
|Standard SSB K2||SSB K2 + IMA Upgrade|
|Remove the left side panel.|
| ||Rearrange the jumpers per the decal on the panel.|
|Reinstall the left side panel.|
22 July 2013 – Republished the jumper configuration summary sheet.
21 July 2013 – Republished the QSIS (to change the number of jumpers in the parts list).
13 June 2013 – Published release 6E of the user’s guide, which corrects the Yaesu MH-27 jumpering instructions. (The MH-27 was mistakenly listed under both of the Yaesu configurations.)
1 September 2012 – Published release 6D of the user’s guide. Most of the changes are related to the revised QSIS.
31 August 2012 – Republished the QSIS. The new version is formatted for 2-up printing on legal-size paper.
12 August 2012 – Published release 6C of the user’s guide. There are numerous small improvements, but no single change is particularly significant.
9 August 2012 – Published release 6B of the user’s guide. Two of the images are now sharper, and several “broken” links have been fixed.
7 August 2012 – Release 6A of the user’s guide has been published. The most notable changes are: (A) the addition of “background” information for readers who are not familiar with the K2; and (B) the addition of eight more known microphones (two Icom models and six Alinco models).
25 July 2012 – Version six of the user’s guide has been published.
Frequently Asked Questions
The IMA supports all microphones offered by: Alinco; Elecraft; Heil; Icom; Kenwood; Ten-Tec; and Yaesu manufactured with an 8-pin Foster mic connector. The list of supported microphones includes …
The IMA can be quickly reconfigured for any one of the seven most common 8-pin Foster pin-out + bias resistance schemes, whereas an external adaptor is typically custom fabricated for just one. Multiple external adaptors would be a better choice if you intend to use your K2 interchangeably with several mics having different pin-outs or biasing requirements. And obviously an external adaptor would be required for a microphone having a different style connector than the K2, such as an RJ45, RJ25, or RJ11 jack. An external adaptor would also be necessary for a microphone with different MIC3 (DOWN) or MIC7 (GROUND) wiring, since these signals are hardwired on the IMA’s Mic Extender board.
Something else to consider is that frequently reconfiguring the IMA jumpers will eventually wear off the gold plating from both the internal jumper contacts and the jumper block “posts”. However, in normal use this won’t be an issue since all connectors and jumpers have 30 µ" (micro-inch) gold plated contacts which are rated for at least 100 insertion ⇄ removal cycles.
Yes, a few design trade-offs were necessary to make the IMA small enough to fit in the limited space. Specifically …
In practice, the only noteworthy consequence of these trade-offs is that the “Fast” button on Yaesu microphones cannot be wired.
Yes, although it may be necessary to reposition some of the “sidetone mod” components which you tacked onto the back of the Control board. Depending on the length of their leads and the required repositioning, it may be desirable to replace some of those components with new ones, or to extend their leads.
In this photo you can see that rather than repositioning the sidetone mod components, Phil has covered the bottom portion of the IMA’s Mic Patch Panel board with electrical tape to insulate it from them.
You could add RX audio support on the K2’s Front Panel circuit board, then the IMA would route the signal to the mic connector. Referring to the IMA schematic, the best way to do this would be to put RX audio on the “DOWN” pin on the K2 Front Panel circuit board, which in turn is hardwired to MIC3 on the Mic Extender board. This way it will always be on MIC3 no matter how you configure the jumpers.
This would require that you also cut the existing “DOWN” signal trace on the K2 Front Panel circuit board to disconnect it from FP-P1. Please contact us if you require further assistance.
The internal mic adaptor kit is currently out of production, pending sufficient interest for a possible next production run.
First, you may wish to review …
|Replacement IMA 2nd-Generation Decal (with self-adhesive backing)|
* The applicable shipping and handling (S&H) charge for your QTH will be added to your invoice at checkout. 8.625% state sales tax will also be added (for New York residents).