+++++++++++++++++++++ See Also K2 Noisy AF Gain Pots +++++++++++++++++++++ Date: Wed, 31 Oct 2001 17:05:27 -0800 From: Wayne Burdick Subject: [Elecraft] K2 AF GAIN control circuit modification Some K2 owners have reported noise or other audible artifacts during rotation of their AF GAIN potentiometers. We have found a way to modify the circuit that eliminates the noise completely, without replacing the pot. This change also provides dead silence when the AF GAIN control is fully counter-clockwise, while the original circuit may have a small amount of leak-through in this position. About 10 K2s have been modified, all with excellent results. The modification takes an hour or so. Instructions can be found at the links below (your choice of PDF or HTML): http://www.elecraft.com/Apps/K2_AF_pot/K2_AF_gain_app_note.pdf http://www.elecraft.com/Apps/K2_AF_pot/K2_AF_gain_app_note.htm Note that this modification is optional. It need not be done unless you have objectionable noise when rotating the AF GAIN control. 73, Wayne N6KR +++++++++++++++++++ +++++++++++++++++++++ Date: Tue, 30 Oct 2001 01:19:06 -0500 From: "Terry" Subject: [Elecraft] Re K2 Noisy Pot Hello to All: I have just finished the vol control mod and it works great so far. My control was very noisy and this seems to have corrected it. Took a little over an hour to do. Thanks to Wayne and all the help we all got on this problem.. 73 Terry VE3TKF +++++++++++++++++++++++ Date: Tue, 30 Oct 2001 07:48:37 -0800 From: Eric Swartz WA6HHQ - Elecraft Subject: Re: [Elecraft] Re K2 Noisy Pot The application note will be uploaded to the web site later today. We will post a notice here when it is up. 73, Eric WA6HHQ ========== Steve Banks wrote: > I guess I missed the 'vol control modification.' Where/what are the > details? > K0PQ > K2 S/N 1599 ++++++++++++++++++++++ Note: Entry Containing Mod to fix problem was put at the beginning of this file.... ++++++++++++++++++++++ Date: Wed, 31 Oct 2001 21:39:20 -0800 From: "Ron D' Eau Claire" Subject: [Elecraft] AF Pot Mod Being one of the chronic suffers of the 'scratchy audio pot' syndrome I installed the new mod that is posted under Builders Resources on http://www.elecraft.com. I works great! The audio gain control is now smooth and QUIET. The proof that it was the circuit and not the pot is in the fact that it does NOT involve changing the 'noisy' pot. My old scratchy pot is now whisper quiet in the new circuit. But, and this is the reason I am posting this, the characteristic of the gain control is radically altered. It now WORKS like an Audio Gain control, with a smooth, gradual taper down to virtually dead silence at the minimum stop. In other words, it is not just quiet, but has much better 'feel' when used as well. More of what I expect when a turn an audio gain control. For that reason, I would recommend that modification to anyone with a K2, regardless of whether their pot 'sounds' scratchy. My hat's off to the Elecraft team for another great 'fix' and great customer support. Ron AC7AC K2 # 1289 +++++++++++++++++++++ Date: Thu, 1 Nov 2001 22:11:48 +1300 From: "Ron Willcocks" Subject: [Elecraft] K2 Vol control mod I downloaded the Builder's resource note regarding the K2 volume control mod tonight and have since done the mod. The worst part of the whole proceedure is cutting the earth bridges on pin3 of P3 and pin3 of J1.....not much room to get in there, but could be worse I guess. Anyway.....the effort was work it. No more scratchy volume control at the lower end of it's travel, and the volume indeed now does turn right down to zilch. The instructions are precise and are accompanied by clear pictures Thanks Wayne and team... Cheers......Ron ZL1TW +++++++++++++++++++++ Date: Thu, 01 Nov 2001 07:02:09 -0600 From: Tom Hammond =?iso-8859-1?Q?N=D8SS?= Subject: [Elecraft] AF Pot Mod Tom: >A question for the collective. Will/does/can this mod reduce the audio >level? Nope. >Wayne stated that you would have to turn up the volume control from the >previous normal location. Is this due to lower audio levels or due to >different non-linear response from the pot, with the same audio output? Merely a slight shift in the level relative to rotational change of the knob. >Actual mod results and comments welcomed for this question. The mod works, and quite well. If you're satisfied with the way your pot works, then there is no reason to perform the mod, BUT keep it handy in the event that you might need it down the line. The three main benefits (I believe) from the mod are: 1) No more scratchy noise at the far CCW end of rotation, IF you had the problem in the first place. 2) Signals will no longer be heard when the pot is fully CCW. 3) The AF Gain pot acts more like a normal pot, wherein there is not as much volume increase during the first 50% of rotation, so you can achieve a smoother lo-level adjustment. If you wish to avail yourself of ANY of these benefits, then, by all means perform the mod. If these 'benefits' are not a concern, and there is no need to perform the mod. The mod DOES require that you have access to a nice SHARP blade, with which to sever the PC board lands in several spots. Probably the most difficult cutting point(s) will be at pin 3 of RF-P1 and FP-J1 where grounding lands must be cut on BOTH sides of these two pads (but ONLY on one side of the PC board). The other lands should be pretty easy to cut. The wiring of the mod is easy to accomplish. In step 4 of the Control Board mod, Wayne recommends using a piece of solid bare wire. I believe this recommendation is because the wire is so short and an attempt to tack-solder a INSULATED wire of this length might result in melting of the insulation. This having been said... IF you use bare wire, BE SURE to elevate the wire a small bit above the PC board (but no more than 1/16" (1.6 mm) to help ensure that it doesn't short out to the PC board itself. Another possibility might be to use some wire-wrap wire OR a short length of PRE-TINNED enameled wire. When I performed the mod, I used some #22 solid, tinned and insulated wire I liberated from a length of 100-pair telephone cable. I cut the wire to length and stripped only about 1/16" of insulation, KNOWING that when I pre-tinned the wire before installation the insulation would recede a bit more. Then I formed the wire to exactly the shape I wanted, carefully (and quickly) tinned the ends, laid it in place against the points where it was to be installed, and hit it briefly with a bit of heat... and maybe just a 'touch' of additional solder. You DO want to have a bit more solder at these 'jumper' points to ensure that you have something there to HOLD the wire ends in place. Wayne emphasizes that all wires should be as close to the PC board as possible (with the noted exception of the BARE wire in the CTRL PANEL mod). This is to help prevent unwanted noise pickup on the AF GAIN line. 73 - Tom Hammond N0SS +++++++++++++++++++ ate: Thu, 1 Nov 2001 11:02:34 -0500 From: "Ken Wagner" Subject: [Elecraft] AF GAIN CONTROL MOD Good morning all: I have done the mod and I like it. Do have a comment, though.... In the Instructions, Front Panel Board, Step 4: After the trace is cut between the center and left pin of the AF control, "....resistance between the two left-most terminals is now about between 4 and 6 kohms." Mine measures about 9.5 kohms, and after chasing the lines on the schematic around the barn a couple of times and then checking the parts list, that looks to be OK... *IF* the R3 control provided is a 10K pot rather than a 5K pot. 920 has a 10k pot. 73, Ken Wagner K3IU K2 #920 +++++++++++++++++ Date: Thu, 01 Nov 2001 11:01:27 -0800 From: Wayne Burdick Subject: [Elecraft] Re: AF GAIN mod: resistance measurement Ken, Thanks for catching this. We have used both 5 k and 10 k pots, so the resistance measurement in question will be either around 4-6 k or 9-11 k. It isn't critical; the tolerance on the pots is about +/- 10 %. 73, Wayne N6KR Ken Wagner wrote: > > Good morning all: > > I have done the mod and I like it. > > Do have a comment, though.... > > In the Instructions, Front Panel Board, Step 4: After the trace is cut > between the center and left pin of the AF control, "....resistance between > the two left-most terminals is now about between 4 and 6 kohms." Mine > measures about 9.5 kohms... ++++++++++++++++++++= Date: Thu, 1 Nov 2001 20:01:49 -0700 From: "Ken Lotts" Subject: RE: [Elecraft] AF Pot Mod Great Mod! My K2 had developed an annoying lack of low audio. Zero position on the volume control equated to almost normal listening when using headphones. I was not very optimistic about how this mod would work for me. BUT.. After this *simple* mod.. Total Silence! plus Zero scratchiness! Thanks Elecraft! Ken Lotts aa7jc Sierra Vista, AZ +++++++++++++++++++ Date: Mon, 05 Nov 2001 14:44:28 -0600 From: Tom Hammond =?iso-8859-1?Q?N=D8SS?= Subject: [Elecraft] K2 AF GAIN MOD DOCS - FINALLY READY FOR PRIME TIME Wow... it's about time, right? I finally got with the program (got some sleep and wasn't in a hurry) and, with Wayne and Lou's assistance, I got it right this time... amazing! This PDF file is a complete set of the K2 AF Gain Pot Mod DOCs. Including Wayne's step-by-step instructions, PC board pictures, Wayne's drawing of the new AF Gain circuit (schematic), and the revised K2 Front Panel and Control Board schematics, also included are the RF Board connector inter-wiring changes. That should pretty well cover it. The file (738kB) can be currently downloaded from my DOWNLOAD page at: http://home.earthlink.net/~n0ss/k2_af_gain_mod.pdf With any luck, it'll appear on the Elecraft web site soon and you will be able to download it from there. But until that time, I'll make it available on my site. Again, I apologize for having caused several of you to either not be able to access the file when I said it would be there, and then to download it, only to find that it was in error. Enjoy. 73 - Tom Hammond N0SS ++++++++++++++++++ Date: Fri, 09 Nov 2001 10:29:01 -0600 From: Tom Hammond =?iso-8859-1?Q?N=D8SS?= Subject: [Elecraft] ERRATA - AF Gain Pot Mod Folks: Thanks to the sharp eye of Ken Wagner, K3IU, a (fortunately) small error has been caught in my PDF of the K2 AF Gain Pot Mod. The capacitor which connects BETWEEN pins 2 & 3 of U9 (LM380N-8) was inadvertently labeled C25 and shown as .002. In actuality, it should be labeled C27 and shown as .022. I have made the correction in the PDF and uploaded a new version to my web site. Thanks for your patience with my ineptness this month.. so far... and the month's still young, think of what I could do! Oh yeah... the URL for the new file is: http://home.earthlink.net/~n0ss/k2_af_gain_mod_v3.pdf And it's only about 288kB instead of the 730+kB it was previously... found more aggressive compression settings in Adobe Acrobat, with no significant loss in resolution!!! 73 - Tom Hammond N0SS +++++++++++++++++++ Date: Sat, 10 Nov 2001 10:58:40 -0600 From: Tom Hammond =?iso-8859-1?Q?N=D8SS?= Subject: Re: [Elecraft] K2 AF Gain mod - Tom's PDF file David: >Many thanks to Tom for his enthusiasm in producing the K2 circuit >details. >and finally printed it out as a permanent record. > >Can you confirm please, Tom, that the final K2 circuit includes the >Sidetone mod that was necessary to use the KIO2 ? The K2 AF Gain Mod info includes NO MODS other than those for the AF Gain mod. KIO2 mods are a completely different thing and were not addressed in the AF Gain mod docs. Tom N0SS +++++++++++++++++++ From: "Joe Malloy" To: , Subject: RE: [Elecraft] Scratchy Pot Syndrome Date: Tue, 27 Aug 2002 19:11:28 -0400 Hi, Frank. To answer your questions: 1. Yes. No removal of wires is necessary on the front panel board to do the mod; 2. My audio was as you describe before the mod; since doing it, I now have to turn my pot up to maybe the 10 o'clock position for normal volume. (Recently I've made a little "director" out of the list-recommended CD jewel case at about a 45 degree angle from the plane of the speaker - works nicely!). The amount of audio hasn't changed much, if at all; just the usefulness of the audio control. I recommend the mod: I thought I had a dirty pot and was amazed with the smoothness of things afterwards! 73, Joe, W2RBA +++++++++++++++++++