+++++++++++++++++++ See Also K2 AF Gain Mod +++++++++++++++++++ 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: Fri, 23 Mar 2001 13:04:59 -0400 From: "Michael Harris" Subject: Re: [Elecraft] K2 Noisy AF Gain pots Hello, > The AF Gain pot on two K2s I have in my shack both are noisy when changing > the AF Gain while listening to a signal. Has anybody noticed this and/or had > any luck improving them with pot cleaner? Been there, got the "T" shirt. I have had to replace the AF gain pot on #1400. There doesn't seem to be any way to get lub into the pot. I Elecraft did replace it and I did send the removed pot back to Gary just in case he wanted to look into it. It has been suggested that the two links R18 and R19, 0 ohms, be replaced by 1.5kohm resistors, apparently part of the original design. I use a pair of Sony MDR-V150 headphones which are very sensitive (and inexpensive) and consequently run the AF gain at a very low setting, just off the bottom stop. We have a very quiet household. I have noticed that a little noise is creeping into the replacement pot. Hopefully replacing the links with resistors will shift the gain pot setting further up the track. This mod I plan to do when I open the box up again when installing the newly ordered noise blanker. At the same time I might do the PSK31 mods, however, having never used the K2 on SSB yet, Kenwood MC-43S microphone on order (lost sale to Elecraft), I might leave it stock until I have. I did suggest some time ago that it might be interesting to see how many K2's have suffered an AF gain pot problem. Nothing came of it. Don't feel shy, having been in the telecom/electronics business for 30+ year I know I didn't abuse the pot on installation. Regards to all Elecrafters, Mike VP8NO GQRP-10148 (GD18BH) IOTA SA-002 K2 #1400 Who didn't work D68C ++++++++++++++++++++++++++++++++++++++++++++++++ Date: Fri, 23 Mar 2001 13:07:17 EST From: MikeN2JZ at aol.com Subject: Re: [Elecraft] K2 Noisy AF Gain pots In a message dated 3/22/01 7:05:45 PM Eastern Standard Time, LHLOUSEK at aol.com writes: << The AF Gain pot on two K2s I have in my shack both are noisy when changing the AF Gain while listening to a signal. Has anybody noticed this and/or had any luck improving them with pot cleaner? Luigi >> Luigi, I had the problem too. It appears that the product detector has more audio output on some K2s than on others. Consequently, some of us are operating our K2's with the audio gain control near the bottom. I replaced the audio gain pot twice and the problem eventually returned. I would highly recommend not replacing the pot but rather replace the two jumpers with 1.5KOhm Resistors in the product detector output path. That solves the problem nicely. Another alternative is to back off the RF gain control to about 12 o'clock and adjusting the AF gain to a comfortable setting. I find that lately 40 meters has been quite noisy and using the controls in this way helps to a very significant degree. If you do replace the audio gain pot be careful not to lift the pads (PC board traces) on removal...the posts that support the pot have very little clearance in the PC board holes. Make sure you remove all the solder and don't let the board get too hot....It's tricky. When you install the new pot Gary Surrency recommended that you file down the audio pot leads in order to facilitate getting them in the tight PC board holes. That is good advice but I didn't have a file handy so I took a pair of sidecutters and cut the ends to a point. That also worked very well. Good luck. Again I would advise against replacing the pots as the resistor fix works just as well. Regards, Mike N2JZ ++++++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Fri, 23 Mar 2001 14:13:14 -0500 From: "David A. Belsley" Subject: Re: [Elecraft] K2 Noisy AF Gain pots Michael: One way to place the AF gain higher in its range is to keep the RF gain less than wide open. Many like to keep the RF gain wide open to get "accurate" S-meter readings; but that is an oxymoron. At least on cw, you often benefit by putting your AF gain quite high and controlling volume by reducing the RF gain. This can reduce noise, qrm, and agc pumping, and it can help smooth out qsk. I don't 'do' ssb, so I can't speak directly whether this would be a good idea for ssb as well, but I understand from others that it is. Only AM really benefits from running the RF gain wide open and controlling volume with the AF gain. best wishes, dave belsley, w1euy - --On Friday, March 23, 2001 1:04 PM -0400 Michael Harris wrote: > Hello, > > >> The AF Gain pot on two K2s I have in my shack both are noisy when >> changing the AF Gain while listening to a signal. Has anybody noticed >> this and/or > had >> any luck improving them with pot cleaner? ++++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Fri, 23 Mar 2001 16:45:05 EST From: LHLOUSEK at aol.com Subject: Re: [Elecraft] K2 Noisy AF Gain pots MikeN2JZ writes: << I would highly recommend not replacing the pot but rather replace the two jumpers with 1.5KOhm Resistors in the product detector output path. That solves the problem nicely. Another alternative is to back off the RF gain control to about 12 o'clock and adjusting the AF gain to a comfortable setting. >> Luigi writes: Assuming the inputs to the AF amp are reasonably high impedance it looks to me that adding the two 1.8 K resistors would cut the max audio by about 40 % ( 2.3dB). Hardly noticeable and should move the bottom of the range of the AF gain control up quite a bit but I still get pot noise even in the middle of it's range. mike.harris at horizon.co.fk writes: <> Luigi writes: I've been looking at the schematics trying to figure this stuff out so correct me if I'm wrong on the following: It looks to me that lowering the RF gain (really post-filter IF gain) lowers the loop gain in the AGC circuit which will reduce the effectiveness of the AGC circuit. Reduced effectiveness would certainly reduce AGC pumping and probably improve QSK as well. Turning the AGC off would make an even bigger improvement. As an experiment turned down the RF gain control to about 12 o'clock and compensated by turning up the AF gain control and the reduction in the effectiveness of the AGC was immediately apparent. The level of the desired signal varied much more then when the RF gain was full on and the audio gain was reduced. Turning down the gain anywhere in the signal path should be equally effective at reducing atmospheric noise and QRM unless it's a dynamic range issue in which case the gain should be turned down early in the signal path with the preamp off and/or attn in. To reduce internally generated noise that might be making a weak signal difficult to copy it is best to keep the signal big compared to the internally generated noise throughout the signal path (gain high at the front end, preamp on) and turn down the gain at the very end (AF gain). Turning down the RF gain (post-filter IF gain) would not be as effective as turning down the audio gain. TIA Luigi ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Date: Sat, 24 Mar 2001 08:31:58 -0800 From: "Ron D'Eau Claire" Subject: RE: [Elecraft] K2 noisy volume control Dave, G4AON wrote: "The normal reason for a noisy control is there is DC on the pot. I tried looking around the circuit diagram and couldn't work out where it went..." What? There is someone else out there who gets cross-eyed looking at that schematic? Ah, for the days of the 7-tube rig all on one page... ... anyway, the volume control goes to the VOL1 and VOL2 points at pins 2 and 3 of AF Amp U9 on the Control Board. It gets there by way of P1 to J8 on the r-f board which feeds the lines from the Front Panel board to the Control Board where the audio amp is. It would appear to have some d-c on it, but I haven't looked at the innards of U9. Okay... I swore I wasn't going to say it, but I have a noisy volume control too... and it's my second one... and I don't feel like pulling the noisy one out AGAIN!... and I have one of the K2's with lots of audio gain so I normally run the audio control near the minimum when the r-f gain is all the way up... The comment by Dave, W1EUY and others about running the K2 with the r-f gain backed down is a very good idea in my book too, especially on noisy band. When the band is at all noisy the AGC makes the noise level sound like it's competing with the signals. Whenever the station you are copying pauses, the AGC hauls that noise level right up there so it's as the same volume as the station. Defeating the AGC by turning down the r-f gain (and turning up the a-f gain) often makes the QRN just go away, and the signals stand out loud and clear above a much quieter background. Besides, I trust the accuracy of a signal report given by someone who is listening to my signal and deciding how strong it is with a practiced ear much more than most "S-meter" readings. Ron AC7AC K2 # 1289 ++++++++++++++++++++++++++++++++++++++++++++++++ Date: Fri, 29 Jun 2001 19:34:23 -0500 From: Tom Hammond =?iso-8859-1?Q?N=D8SS?= Subject: Re: [Elecraft] S-meter & AGC Question Folks: For what little it may be worth... and BEFORE you hit the control with ANYTHING liquid, try cycling the control a dozen or more 300+ degree rotations (lock to lock). Quite often, if the problem's nothing more than dust, a bunch of rotations will clear away the dust (or accumulated carbon particles) and render the control usable for another lengthy period of time. Cleaning sprays should only be used as a last resort as they also tend to flush away that lubrication that gives the controls their 'silky' feel... additionally, the may also remove any conductive lubrication that might be on the pot material itself. If you DO consider a cleaner, find one which leaves no oily residue. A quick test is to spray a small spot onto a piece of white typing paper. When the spot dries, it'll probably leave a slight ring where the liquid was... IF the remaining spot is more translucent that the paper itself, chances are that the cleaner left an oily residue. If it left only a ring, but no translucency,then it's probably OK to use if you must. FINALLY... remember that some cleaners will MELT PLASTIC!!!!! ONLY spray the control if you can ensure that none of the cleaner will touch ANY of the buttons or other controls. I'm still probably forgetting to warn of something.. but I'm sure others will pick me up before I fall completely on my face. Maybe... hopefully. As always, dissenting opinions are most welcome. 73 - Tom Hammond N0SS At 06:38 PM 6/29/01, you wrote: >At 08:31 AM 6/29/2001 -0400, David A. Belsley wrote: >>Jay: >> Your problem is almost certainly a noisy rf control. As you turn it, >> it is momentarily opening, which will indeed cause the s-meter to go >> full scale. I had a similar problem and tried various cleaners, but >> eventually had to replace the pot (which is not that bad a job). My pot >> was not dirty; it had actually deteriorated and had numerous small >> pieces of plastic float about inside, which caused the slider regularly >> to lift from the composit. >> >> Get a new pot from Elecraft. > >Mine has just started to get noisy. Is it possible to restore it, at >least for awhile, using a spray contact cleaner? > > >73, Chas, W1CG ++++++++++++++++++++++++++++++++++ Date: Sat, 20 Oct 2001 10:47:12 -0400 From: "Bob Lewis \(AA4PB\)" Subject: Re: [Elecraft] Still Noisy after All These Mods - AF gain pot I've got an original FT K2 with the original volume control pot. It gets noisy but by making a number of full sweeps with it the problem goes away for a while. I think perhaps either some sort of film or dust perhaps builds up and must be cleaned off. If it were actual wearing of the resistive coating I would suspect that it could not be fixed by "exercising" the pot. I also suspect that the same problem exists in the other pots but they are not so sensitive because there is no audio going thru them for you to hear. Eventually, if they become bad enough, they may exhibit some problems as well. I personally would rather have seen PC mount pots with a threaded bushing and nut that attaches to the front panel to avoid the "wobble". That by itself may not have fixed the noise problem. Perhaps a more expensive sealed pot could be used for the volume control on future models (K3 or whatever). +++++++++++++++++ Date: Sat, 20 Oct 2001 12:06:44 -0400 From: "David A. Belsley" Subject: Re: [Elecraft] Still Noisy after All These Mods - AF gain pot I guess I would like to give the other side of this issue. I have (knock on wood) had no trouble with my AF gain pot. It has worked fine for nearly two years. I did have a noisy RF gain pot which seemed internally to self distruct shortly after I completed the K2. I replaced it, and it's been fine ever since. At the time I did this, I also added nylon washers between the control knobs and the front panel. These washers have all but removed any play in the shafts and physically prevent any excessive torque being applied by sideways pressure on the knobs and shafts. I'm not positive that they are a help, but they appear to be. Many people unconsciously press the knobs to one side as they turn them, and this has got to increase wear and tear. I was able to find black ones of the same diameter as the K2 knobs, and they look just fine in place. I would also add that I see no relation at all between the issue of a noisy AF control pot and the KAF2. The audio amp and its volume control follow the filter in the circuit. best wishes, dave belsley, w1euy ++++++++++++++++++ Date: Sat, 20 Oct 2001 19:04:17 +0100 From: "DeniGm3skn" Subject: Re: [Elecraft] Still Noisy after All These Mods - AF gain pot > Hi Gang > > The volume control in my K2 (#1892) went noisy after only two weeks use, so > those suggesting rough handling, smoking, etc. should look for another > cause. > --- snip --- > My volume control on K2 1188 seemed to be noisy from almost new, although it was possible to clear it by sweeping the full range of the pot several times. Elecraft sent me a new pot but I never did get round to changing it, I did fit a nylon washer behind the knob to support the spindle and I'm sure that helps. Now the problem has entirety disappeared so perhaps it' s a matter of bedding in the track to wiper. 73 Deni GM3SKN +++++++++++++++++++ Date: Sat, 20 Oct 2001 11:47:28 -0700 From: "Ron D' Eau Claire" Subject: RE: [Elecraft] Still Noisy after All These Mods - AF gain pot Rod, WA9GQT, wrote: > I really do like my K2 & am having lots of fun with it, but > the AF gain pot is a real joke. I am on my 2nd AF gain pot even > after trying resistors instead of jumpers. I thought this gain > issue would have been resolved with the KAF2(which I have). After my recent comment about having had two AF gain pots go bad on me in just over a year, including one of the 'new and improved' versions Gary sent me, I heard privately from a couple of other ops having the same problem. Clearly, there is a problem either with the part or with the design. The last time this issue came up one op suggested that it is a bad design to have d-c flowing through these pots because it degrades the contact between the wiper and resistance element. I've no personal experience with that issue, but clearly there is something "killing" the audio gain pots in a significant number of K2's. My K2 lives a life of luxury, BTW, sitting on my operating desk. It has not been out in the field where it can get knocked about or exposed to dirt. Still, the AF Gain pot has become nearly useless in the area where I normally want the audio gain set. Ron AC7AC K2 # 1289 +++++++++++++++++ Editor's Comment - The following entry speculates that the position of the wiper when soldering in the pot MAY be responsible for the noisy section of pot travel.... Sounds possible... +++++++++++++++++ Date: Sun, 21 Oct 2001 10:02:48 EDT From: CEMILTON at aol.com Subject: Re: [Elecraft] Still Noisy after All These Mods - AF gain pot In a message dated 10/20/01 20:31:53 PM Eastern Daylight Time, mike at rioux.org writes: > list of noisy AF pots. Not a smoker, rig sits in shack, rig > used 3-4 times a week > and all weekends (when the XYL runs out of 'honey doos'). Happens at the > low end of the > pots travel. > Mike W1USN K2 #1964 Mike, I've been following the elecraft "story" for several weeks and I hope to purchase a K-2 when the "amp" module is finalized. This means ------ I do not own a K2 nor have I seen the component in question. But, I repair/restore boatanchors as part of the hobby and I wonder if the heat from soldering the pot in might be part of the problem? Perhaps the resistive deposit is becoming hardened (each end of the travel) while the wiper connection would only transfer heat to a very small portion of the deposit. Some comments reflect "no problems" while others are just the opposite. And I can only presume the pot offered is from the same manufacturer. Of course the pots may not be from the same "run" so there is another variable and one that could point to a manufacturers defect. Its just a thought and maybe something that might get others pointed toward a solution. When I receive my kit, I think I'll use hemostats in/around this particular component. Anyone else have thoughts abt this? Thanks for the BW W4MIL Chuck ++++++++++++++++++ Date: Sun, 21 Oct 2001 10:38:22 EDT From: WA9GQT at aol.com Subject: [Elecraft] Noisy AF gain pots Hi All! Thanks for all the messages! By the way I also am a non smoker & have never had my K2 in a dusty environment. The pot only acts up at low levels. Chuck W4MIL may be onto something about heat affecting the pot during soldering! Again, I want to say that I really enjoy the K2 but this is something that should have been resolved by now. Hopefully something can be done to address this problem. For those of you that are curious about this problem, just look back into the archives to see various comments & mods. 73, Rod WA9GQT K2 #1900 ++++++++++++++ Date: Sun, 21 Oct 2001 08:59:18 -0600 From: "John A. Evans - N0HJ" Subject: Re: [Elecraft] Noisy AF gain pots Nope - my RF pot (I have the AF all the way up and use the RF for level control) acts up in midrange. I am also a non-smoker and the K2 spends its time on my desk, mostly. Sweeping the range helps for a period of time, too, so I suspect it is just a contact or film issue. 72 - john - n0hj - contemplating the purchase of a four band K1 for backpacking. +++++++++++++++++ Date: Sun, 21 Oct 2001 08:55:39 -0700 From: "bob baxter" Subject: Re: [Elecraft] Still Noisy after All These Mods - AF gain pot I'm starting to get worried now. Old 922 has been setting here for the better part of 2 years now and the AF pot hasn't made a sound. Yes, I do have it turned on. Bob Baxter AA7EQ Bisbee, Az ++++++++++++++++ Date: Sun, 21 Oct 2001 10:26:41 -0700 From: Wayne Burdick Subject: [Elecraft] AF gain pot We're very much aware of the problem with the AF GAIN control on some K2s. This has been a high-priority issue for myself and for Gary (our customer service engineer) ever since it first came up. I wanted to let you know what we're doing to try to correct it. Once we solve the problem, you'll be the first to know, and we'll be sending any needed replacement parts to affected parties ASAP. Meanwhile, we apologize for the inconvenience and really appreciate your patience. Thanks to some recent comments on the list, we now have even more data. For example, it's clear is that the problem is statistically much more likely to occur with newer K2s. Some time ago, we started shipping pots with a metal bushing to make the shafts feel "tighter," and this seems to be when noisy pots became an issue. We've tried pots from four different manufacturers in the past two years. Each type has its advantages and disadvantages. Some have bushings, some don't, but at the time we selected the present unit, all of the samples we tested were functioning very well. The present problem could be related to one particular batch. Those of you who have an AF gain control that is conspicuously "noisy" could help us out by sending the following information directly to me (NOT the list!): 1. Your K2 serial number 2. Whether your AF GAIN pot has a metal bushing or not (you may need to pull the knob off to see it, but you do NOT have to remove the front panel) 3. Whether it was noisy from the beginning, or if it took some time (how long?) to develop the condition. (Please be as succinct as possible so I can quickly compile the data.) We have sent all noisy pots that Gary has removed from front panel boards back to the manufacturer for analysis. They have sent us some preliminary data, but we're still in the thick of this discussion and we're comparing results to their published quality standards. At our request, they sent us samples of new, custom pots with a double-screened resistive element and a different (supposedly more reliable) wiper contact material. We are presently life-testing these, and with any luck, they'll be much more robust. As for the AF gain circuit itself: First, there is no DC on the pot. The voltage at the inputs to the LM380 is 0 volts, and it is isolated from the MUTE circuit by low-leakage capacitors. The standing current through the pot is 0 mA. Still, we are exploring all possible minor changes to the volume-control circuit to see if there's any way to reduce the audible effect of pot nonlinearities. Please send any further comments only to me. I'll be keeping everyone informed on the issue. 73, Wayne N6KR ++++++++++++++++++ Date: Mon, 22 Oct 2001 15:41:23 EDT From: Unifiedtx at aol.com Subject: [Elecraft] AF Gain Pot I have just installed a black vinyl washer between the knob and front panel. I don't know if this is a permanent fix for the scratchy pot, but for now it has completely eliminated all scratchiness. Be sure that the washer goes over the bushing ridge and is positioned flat against the front panel. I went to the hardware store and bought a washer with a quarter inch hole and took a round rat-tail file to enlarge the hole. The overall diameter of the washer is no bigger than the diameter of the knob, so it is virtually invisible. +++++++++++++++++++++ Date: Mon, 22 Oct 2001 13:26:02 -0700 From: Wayne Burdick Subject: [Elecraft] seeking orphaned AF gain pots If you have a noisy AF gain pot that you've removed from your K2, please send it to us for testing. We'll use your pots to confirm the results of what appear to be very promising lab tests. Please send them to: Elecraft Gary Surrency 1326 N. Laveen Dr. Chandler, AZ 85226 Thanks in advance! Wayne N6KR +++++++++++++++++++++ Date: Mon, 22 Oct 2001 15:17:04 -0700 From: "Ron D' Eau Claire" Subject: RE: [Elecraft] AF Gain Pot Roy, W4WFB wrote: > I have just installed a black vinyl washer between the knob and > front panel. > I don't know if this is a permanent fix for the scratchy pot, but > for now it > has completely eliminated all scratchiness. I tried pulling out lightly and pressing inward lightly on the AF Gain while rotating it in the scratchy region. Pulling out made no difference, but if I press gently (maybe 50 grams) while rotating the scratchiness is gone. Something I hear in my work a lot is, "It's not a design issue, it's a training issue! They don't know how to use it properly. Train the customers right and they won't have trouble!" Ron AC7AC K2 # 1289 ++++++++++++++++ Date: Mon, 22 Oct 2001 21:06:22 -0700 From: Wayne Burdick Subject: [Elecraft] AF gain pot update We have plenty of data now, and I wanted to say thanks to all those who responded. We're testing a circuit modification that looks promising. If you have a very noisy AF GAIN pot and would like to volunteer to try the mod, please let me know (directly -- NOT to the list, thanks). 73, Wayne N6KR ++++++++++++++++++ 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 ++++++++++++++++ Reply-To: From: "Ron D'Eau Claire" To: , Subject: RE: [Elecraft] Scratchy Pot Syndrome Date: Tue, 27 Aug 2002 16:21:35 -0700 Before getting starting this fall on the KPA100, I've wanted to install the scratchy pot mod to get that out of the way first. ... In other words, can the pc board be separated by only removing the knobs and encoder hardware without removing these wires? ... I'm wondering if the overall gain is going to be negatively impacted? . Frank, W4FMS K2 #1608 _______________________________________________ It's been a long time since I made the mod, but I'm quite sure that you do not have to remove the encoder. You simply remove the nut that holds it to the front panel and the encoder is held by the short leads to the board while you do the work on the board. The total gain of the K2 is NOT affected by the mod. What happens is that the behavior of the volume control takes on a logarithmic characteristic. That is, the gain increases more slowly at the lower end of the range and then increases more rapidly as you approach the higher end of the range. That way it SOUNDS to your ear like the control is more "linear" because the sensitivity of your ear to the change in level is also logarithmic. The maximum noise your K2 will make is not changed. Ron AC7AC K2 # 1289 ++++++++++++++