K2 Internal Mic Adaptor

K2 Internal Mic Adaptor

K2 Internal Mic Adaptor

K2 Internal Mic Adaptor


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 …

  1. Alinco / Kenwood
  2. Elecraft
  3. Icom
  4. Ten-Tec / powered-Yaesu
  5. unpowered-Yaesu

… 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 top cov­er (or op­tion­al KPA100 if it is in­stalled).
  • Re­move the op­tion­al KAF2 or KDSP2 if ei­ther is in­stalled.
  • De­tach the front pan­el sub-as­sem­bly.
Re­move the left side pan­el.
  • If a bi­as re­sis­tor is tack sol­dered to the back of the Front Pan­el cir­cuit board, then un­sol­der it.
  • If the new con­fig­u­ra­tion re­quires a bi­as re­sis­tor, tack sol­der it on the back of the Front Pan­el cir­cuit board (af­ter de­ter­min­ing which two pins of the mic jack to sol­der it be­tween).
  • Re­con­fig­ure FP-P1 – the Mi­cro­phone Jack Con­fig­u­ra­tion head­er – on the back of the Front pan­el cir­cuit board.
Rearrange the jump­ers per the de­cal on the pan­el.
  • Re­at­tach the front pan­el sub-as­sem­bly.
  • Re­in­stall KAF2 or KDSP2 if ei­ther had been in­stalled.
  • Re­in­stall the top cov­er (or KPA100 if it had been in­stalled).
Re­in­stall the left side pan­el.

Latest News

23 July 2013 – Pub­lished re­lease 6F of the user’s guide which in­te­grates app note #9, app note #9, “Six Jump­ers Now Stan­dard”.

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).

20 July 2013 – Re­pub­lished app note #8. app note #8.

20 July 2013 – Re­pub­lished the de­cal. the decal.

19 July 2013 – With the re­lease of app note #9, app note #9, hence­forth the IMA kit will in­clude six jump­ers rath­er than sev­en.

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.

What Others Have Said

Off-Re­flec­tor (di­rect email) com­ments …

DF7TH “… su­perb qual­i­ty …”
GØPKS “… a great bit of en­gi­neer­ing …”
NØXWR “… very clev­er en­gi­neer­ing …”
KB1VBF “… it works great!”
NE1RD “… very cool … quick and easy …”
K5JAZ “… a great prod­uct.”
K6DGW “ … a re­al­ly cool lit­tle add-on …”
KE6US “Very clev­er and nice­ly built.”
AD7GR “… a dream …”
WG7GW “Count me a sat­is­fied cus­tom­er.”
N9RE “It is a great kit.”

Com­ments in the Elecraft® Re­flec­tor ar­chives and eHam Re­views …


Additional comments.

Which microphones does the IMA support?

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 …

  • Alinco : EMS‑3, EMS‑5A, EMS‑10, EMS‑11, EMS‑14, EMS‑42, EMS‑53, EMS‑55, EMS‑56, EMS‑57.
  • Elecraft : MD2, MH2, Proset‑K2.
  • Heil : iCM.
  • Icom : HM‑7, HM‑10, HM‑11, HM‑12, HM‑14, HM‑15, HM‑22, HM‑23, HM‑24, HM‑36, HM‑56.
  • Icom : SM‑5, SM‑6, SM‑8, SM‑10, SM‑20, SM‑30, SM‑50.
  • Kenwood : MC‑42S, MC‑43S, MC‑44, MC‑47, MC‑48, MC‑55, MC‑57, MC‑60, MC‑80, MC‑85, MC‑90.
  • Ten-Tec : 702, 708A, 709A.
  • Yaesu : MD‑1, MD‑100, MD‑200.
  • Yaesu : MH‑1, MH‑10, MH‑14, MH‑15, MH‑26, MH‑27, MH‑31, MH‑31B8, MH‑36.
  • Yaesu : YM‑34, YM‑35, YM‑36, YM‑37, YM‑38, YM‑40, YM‑48.
How does the IMA differ from an external adaptor?

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.

Is there anything the IMA can not do?

Yes, a few de­sign trade-offs were nec­es­sary to make the IMA small enough to fit in the lim­it­ed space.  Spe­cif­i­cal­ly …

  1. The IMA does not per­mit eve­ry sig­nal on the left side of FP-P1 to be con­nect­ed to eve­ry sig­nal on the right side.
  2. The IMA hard­wires two sig­nals di­rect­ly across FP-P1.  This is done “in­ter­nal” to the IMA’s Mic Ex­tend­er cir­cuit board (MEX), such that re­wir­ing ei­ther con­nec­tion would en­tail mod­i­fy­ing the K2.

In prac­tice, the only note­wor­thy con­se­quen­ce of these trade-offs is that the “Fast” but­ton on Yae­su mi­cro­phones can­not be wired.

Is there space for the IMA and the SMT CW tuning indicator mod?

Yes there’s plen­ty of room for both.  (See the pho­to gal­lery below.)  How­ev­er, de­pend­ing on where you orig­i­nal­ly in­stalled it, the SMT CW tun­ing indi­ca­tor might need to be re­po­si­tioned.  For­tu­nate­ly its ex­act lo­ca­tion isn’t crit­i­cal.

Can the IMA be installed in a pre-S/N 3000 K2 that has the A to B upgrade mods?

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.

How might the IMA support fixed-level RX audio for digital modes?

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.

Buy Now

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)
   From stock

* 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).

accepted credit cards

Parts List
  • Two PCBs – Mic Ex­tend­er and Mic Patch Pan­el
  • (3) ⅛ W 5% resistors:  5.6 kΩ; 3.6 kΩ; 820 Ω
  • (6) .100" deluxe jumpers with 30 µ" (30 mi­cro-inch) gold plat­ed con­tacts and 300 mil ta­pered han­dles
  • (3) .100" For­mat Con­nect­ors:
    • 2 × 8 sur­face-mount pass-through sock­et with 30 µ" gold plat­ed con­tacts
    • 3 × 7 through-hole ter­mi­nal strip with 30 µ" gold plat­ed con­tacts
    • 2 × 6 right an­gle through-hole bot­tom shroud strip
  • 3.5" × 2.125" col­or-print­ed self-adhesive decal
  • Col­or-print­ed Quick Start Instruction Sheet (QSIS)
Download (Mic Adaptor Kit) Documentation
See Also

From left to right:  Assembled IMA; Installed IMA; Installed IMA + SMT CW Tuning Indicator; Installed IMA + A2B Mods.
These are thumbnails, click to enlarge (hover for credits).

High-Res PCB Scan
2,000 DPI PCB Renderings
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