++++++++++++++++++ See also: Headphones K2 AF Gain Mod ++++++++++++++++++ Date: Sat, 1 Dec 2001 21:05:11 +0100 From: "Sverre Holm - LA3ZA" Subject: [Elecraft] Audio level The observation from the K2 team in the CQWW on the better and louder sound level when taken from the external speaker jack rather than the headphone jack, solved the problem I always had of too little audio level. As said it is probably the combination of my headphones, impedances and so on. This observation deserves its place among the tips given some time ago on how to improve the output level (was it 25 ways?). I've investigated several of them, but none of them had this effect (I did not try those that had side-effects like poorer intermodulation performance and so on). - - Sverre, LA3ZA - ----------------- www.qsl.net/la3za - -----Original Message----- From: owner-elecraft at qth.net [mailto:owner-elecraft at qth.net] On Behalf Of Cady, Fred Sent: 30. november 2001 15:34 Subject: [Elecraft] Report on K2s in the CQWW A criticism of the audio sound was that it sounded somewhat "tinny" and one operator observed the sound was more full when plugging the Heil Pro headset into the external speaker jack in the back. This effect maybe due to the 82 ohm resistors in the front panel headphone jack circuit that are not in the circuit for the external speaker. Another operator would like to have more audio level as he had the AF gain cranked wide open most of the time. +++++++++++++++++++ Date: Sat, 1 Dec 2001 17:31:17 -0000 From: "Santa Fe" Subject: [Elecraft] headphone audio level I observed low audio level with Heil Pro-set headphones. Older Heil headsets are 200 ohms. Use headphones that match the impedance for which the K2 is looking, about 35 ohms. Further, there are more sensitive and less sensitive headphones. The K2 audio amp does not have the power of a stereo system. I have used two different headphones that provided a HIGH level of success. AKG K100, 35 ohm impedance and 103 db sensitivity. Sennheiser HD-500, 35 ohm impedance and 105 db sensitivity. Both result in outstanding audio, and the AF gain gets set to about ten o'clock. I like not challenging the audio stage. Don't need any added noise from there. 73, Fred W5YA # 700 +++++++++++++++++++++++ Date: Tue, 4 Dec 2001 17:48:05 -0000 From: "Santa Fe" Subject: [Elecraft] Re: K2 Audio > the K2 needs much more audio. Even with a good pair of headsets, I > run the AF gain at 3 o'clock. I keep trying to share this... I don't know enough engineering to help with too much else. My K2 runs AF gain about 10 to 11 o'clock, though it did run at 3 o'clock with Heil Pro-set. There are two reasons. A good set of phones is almost always much less sensitive. On some websites you can get the specs from a phone. The AKG K-100 I bought for the above result says 103 db. The HD-500 Sennheiser says 105 DB and they are better. Both are about 35 ohms. I don't know the sensitivity of the Pro-set but i would bet they are around 97 db, and they are about 200 ohms. Have no concern about the phones being wide range. I do not hear any more high frequency hiss in the quality head set than in the narrow range communication phones. Get a sensitive low impedance head set and you will be happy with the audio gain of the K2 with phones. More gain to drive less sensitive phones would mean more power consumption. 73, Fred W5YA # 700 ++++++++++++++++++++ Date: Tue, 4 Dec 2001 17:33:57 -0800 From: "Ron D' Eau Claire" Subject: RE: [Elecraft] K2 Audio Jim wrote: > ...the K2 needs much more audio. Even with a good pair of headsets, I > run the AF gain at 3 o'clock. The S meter action seems marginal, > too, which > my indicate an overall receiver sensitivity problem. That indicates something very wrong with your K2. My K2 ran, as first built, with the audio gain almost against the minimum volume stop at all times when using headphones (35 ohm Labtec Model LT-820). A lot of other ops on the reflector reported the same situation. Gain control was good on the speaker, although I rattle the windows if I turn it past half (12 o'clock) on a decent signal. Recently the Elecraft gang came up with a fix to a design issue in the audio gain control that provided a more natural characteristic curve to the gain control function. Now my audio gain sits at about 9 o'clock in normal operation. The gain at higher levels is unaffected by this mod. So the K2 design includes a lot of audio gain. That said, there have been ops who complained about low audio. Haven't seen any comments lately, but you are not the first. I don't know what the fix for that was though. Your comment about marginal S-meter operation sounds like a real clue to something wrong in the r-f section, assuming you have calibrated the S-meter per the instructions. Ron AC7AC K2 # 1289 +++++++++++++++++ Date: Tue, 04 Dec 2001 18:16:17 -0800 From: lhlousek Subject: Re: [Elecraft] Re: K2 Audio My problem has been too much audio from my K2. Until I did the AF gain pot mod I couldn't turn it down far enough. Now I run at about 9:00 o'clock with headphones or speakers. It even puts out enough speaker volume using it mobile. Is there a lot of unit to unit variation in audio output? Lou W7DZN ++++++++++++++++ Date: Tue, 4 Dec 2001 19:01:08 -0800 From: "Garth Hitchens" Subject: Re: [Elecraft] Re: K2 Audio Another thing to keep in mind: The front headphone jack of the K2 has some pretty signifcant resistors in series with each headphone (82 ohms) with some 2.2uf caps to ground. This significantly reduces both the audio level and wideband noise level going to headphones. If you plug into the BACK of the k2, (the external speaker jack), you get the full, unfiltered output of the audio amp, which is quite a bit louder. You'll need to use a mono-to-stereo converter if you do that with stereo headphones. Having said that, my rig seems pretty "normal" as far as audio gain assuming that I run the preamp above 10mhz. I usually run 10:00 to 12:00 on the AF gain, sometimes 1:00 or 2:00 if band is very quiet and signals are very weak. Garth KG7GA > > the K2 needs much more audio. Even with a good pair of headsets, I > > run the AF gain at 3 o'clock. ++++++++++++++++ Date: Tue, 04 Dec 2001 21:18:34 +0000 From: Paul Hendershott Subject: Re: [Elecraft] K2 Audio ....In the spirit of beating a dying horse (not quite dead yet), I have had great success with Sony's MDR-7506's. I rarely need to adjust the AF gain pot past just 15% beyond minimum gain when using them. In fact often I have them all the way down and still can hear the stronger stations! When I first got my K2 on the air, I bought a $6 pair of walkman-type headphones from RS. I needed at least a 12 o'clock - 3 o'clock setting most of the time with that $6 pair.... so I would conclude from my very un-scientific test - get a good pair! Again, I have heard no better than these Sony's ( lots of articles about them on the web and from other ham's, too!) On the other hand.... Using the K2 speaker, I wish it had more audio. I plan on using my K2 as my main station rig, so I wouldn't mind buying a good audio-amp/station-speaker set up. Would anyone have a recommendation on this? 73 Paul KB9YVP ++++++++++++++++++ From: "Rick Shindley" To: "elecraft digest" Date: Thu, 7 Mar 2002 14:23:17 -0600 Subject: [Elecraft] audio amplifier/speaker/headphone impedance matching People sometimes are confused about impedance (Z) matching. They mistake the need to do so at rf frequencies with the conventions used at audio frequencies. At rf, power transfer is maximized when the load impedance matches the source impedance. In the audio realm, maximum power transfer occurs when the source impedance is zero! That is what is termed the "dynamic impedance" characteristic of an audio power amplifier's output. The coupling medium at audio frequencies is not coax, waveguide, or open wire feedline. No need for that. An old lamp cord works just fine. (Note: that's why MFJ doesn't make an audio SWR bridge!) At audio frequencies, power transfer becomes essentially the same as with resistance voltage divider circuits. At such low frequencies, the reactance component of "impedance" is very low and resistance dominates the mathematics. The output "impedance" of an audio amplifer is essentially zero Ohms. All the output voltage from the amplifier appears across the speaker terminals. Basically, the amount of power transferred to the speaker from an ideal amplifier is dependent only upon the ability of the speaker to receive it (voice coil resistance, magnet strength, cone size, etc). Placing a 16 Ohm speaker in place of a 4-Ohm speaker won't hurt the amplifier, it just will result is 75% less audio power from the speaker! If you want the same power from the 16 Ohm speaker as before, you would have to double the voltage to it somehow. This is what goes on in public address systems. They use an amplifier with high current drive capability, and cause it to output audio RMS voltages of 70.7 volts. Any amount of power can be retrieved off the 70.7 V audio "bus" by way of a step down transformer at each speaker. Want more power at a given speaker? Just move the voltage tap up more on the local speaker's transformer secondary! No "impedance matching" going on there! It's very much the same as electrical power distribution in communities. No Z matching going on there, either. The zero Ohm source impedance of most audio amplifiers assures that the speaker voice coil will be forced into position with authority. That means low acoustic distortion. If the amplifer had a non-zero output impedance, the voice coil would not accurately track the voltage signal and acoustic distortion would result. Rick KC0OV K2 1360 ++++++++++++++++ Reply-To: From: "Sverre Holm - LA3ZA" To: "'elecraft digest'" Subject: RE: [Elecraft] audio amplifier/speaker/headphone impedance matching Date: Thu, 7 Mar 2002 21:47:14 +0100 -----Original Message----- >From: elecraft-admin at mailman.qth.net [mailto:elecraft-admin at mailman.qth.net] On >Behalf Of Rick Shindley >People sometimes are confused about impedance (Z) matching. They mistake the >need to do so at rf frequencies with the conventions used at audio frequencies. .... >The zero Ohm source impedance of most audio amplifiers assures that the speaker >voice coil will be forced into position with authority. That means low acoustic >distortion. If the amplifer had a non-zero output impedance, the voice coil >would not accurately track the voltage signal and acoustic distortion would >result. >Rick KC0OV >K2 1360 ------------------- This is an interesting topic that is raised here. I have often wondered about the practice used in most ham equipment of using series resistors to feed the headphones (e.g. separate 82 ohm resistors to feed the R and L headphones in the K2). It does make the output short-circuit proof. But what are the side-effects? Does it cause the headphone to ring at some undesired resonance frequency? Could it distort CW, by distortion I mean color it with some unknown frequency response which is the effect of the design of the headphone and the series resistor? At the very least we don't get the advantage of damping the headphone coil with the low output impedance of the amplifier. Any comments? 73 Sverre Sverre Holm, LA3ZA Asker, Norway (59.8N, 10.4E) --------------------------------- www.qsl.net/la3za ++++++++++++++++ Reply-To: From: "Sverre Holm - LA3ZA" To: "Elecraft at Mailman. Qth. Net" Cc: "'Rick Shindley'" , "'David A. Belsley'" Subject: RE: [Elecraft] audio amplifier/speaker/headphone impedance matching Date: Fri, 8 Mar 2002 00:43:12 +0100 The main concern is that of damping of the headphone vibrations. After it has been excited, the membrane will keep on oscillating unless it is being damped by the low output impedance of the audio amplifier. This is common practice in audio engineering. One computes the ratio of the load impedance (e.g. 8 ohms), and the output amplifier's impedance (say 0.1 ohm) and finds a damping factor of in this case 8/0.1 = 80. If the resistance of the cable adds say 0.3 ohm, the system has been compromised because now the damping is reduced to 8/(0.1+0.3) = 20. My concern is the effect of adding 82 ohms to the output impedance of the output amplifier. We are talking of a minor effect here, but I think the idea that was brought up by Rick's (KC0OV) posting is worth pursuing. If there is something we can learn from the audio people that can improve overall sound quality, then why not? Sverre Holm, LA3ZA Asker, Norway (59.8N, 10.4E) --------------------------------- www.qsl.net/la3za +++++++++++++++++ Reply-To: "Bob Lewis (AA4PB)" From: "Bob Lewis (AA4PB)" To: "'elecraft digest'" Subject: Re: [Elecraft] audio amplifier/speaker/headphone impedance matching Date: Thu, 7 Mar 2002 20:51:37 -0500 > If the resistor is pure R and no X, it should have > no effect on frequency response. But the headset has X which means it represents a lower impedance at lower frequencies. There could be more drop across the resistor at lower freqs than at higher frequencies and that could affect the frequency response. As a practical matter the difference in response is probably not enough to notice. ++++++++++++++++++ Reply-To: "Bob Lewis (AA4PB)" From: "Bob Lewis (AA4PB)" To: "Elecraft at Mailman. Qth. Net" Subject: Re: [Elecraft] audio amplifier/speaker/headphone impedance matching Date: Thu, 7 Mar 2002 20:57:31 -0500 I think damping factor is more of a concern in LF drivers (10 or 12 inch) operating at very low frequencies (i.e. base response) than it is in a small headset. I doubt that the headset (especially a communications type headset) has enough mass to have its response effected very much by damping factor. +++++++++++++++++ From: "Gary O. Lyons" To: Date: Sat, 25 May 2002 22:24:43 -0700 Subject: [Elecraft] K2 Headphone Output >I find myself using the K2 volume control at max when listening to weak >CW signals. Has anyone played around trying to increase the headphone >output on the K2? Earl, If you're experiencing low audio with your current headphones check their impedance. The K2 is designed for 32 ohms and will produce low output with the typical 4-8 ohm "communications" phones. I initially experienced the same problem with my K2. I now use a pair of Labtec 820 phones and rarely move the AF gain beyond the 9 o'clock position. If you experience the same low audio problem through the speaker then the most likely problem is crosswiring at the remote speaker jack. 72/73, Gary/NQ7T ++++++++++++++++++ From: "Barry Simpson" To: Subject: FW: [Elecraft] volume increase needed. sorry forgot to mention I have a K2 Date: Wed, 26 Jun 2002 11:34:13 -0000 Hi My simple solution to the same problem is to put a small piece of two and a half inch inside diameter plastic pipe with a right angle bend on top of the K2 speaker grille. Point the outlet towards you and bingo a huge increase in the volume. There's nothing wrong with the K2 audio output - it's just that the speaker faces upward. I use the same solution with my TS2000 for the same reason - not very pretty but totally effective. 73 Barry VK2BJ K2 1781 +++++++++++++++++ From: "Don Brown" To: "Steve & Anne Ray" , "Elecraft" Subject: Re: [Elecraft] Volume increase in the K2 Date: Thu, 27 Jun 2002 09:10:13 -0500 Hi This is an option however all computer speakers are not created equal. I = have found some of them do not like to work in close proximity to RF fiel= ds and will buzz when keying the transmitter. This problem seems to be wo= rse on the type with built in power supplies rather than the wall wart ty= pe. This is usually caused by improper RF bypassing of the rectifier diod= es in the power supply. If you can open the speakers up you could try a .= 01 UF across each rectifier in the power supply. I have tested a set of Edirol speakers made by Roland and they work fine.= Not cheap ($100) but nice speakers with 10 watts per channel in wood cab= inets. It has a 2 channel mixer so two radios could be connected at the s= ame time. =20 http://minidisco.com/minispecs/edirolma10a.html Don Brown KD5NDB ----- Original Message ----- From: Steve & Anne Ray Sent: Wednesday, June 26, 2002 11:58 PM To: Elecraft Subject: [Elecraft] Volume increase in the K2 Well just for the heck of it, I plugged in my computer stereo speakers in= to the headphone jack of the K2. The speakers are nothing fancy, but they a= re amplified and I could get more volume then I would ever need. ++++++++++++++++++++ From: "ZOOM" To: Date: Thu, 27 Jun 2002 23:29:54 -0400 Subject: [Elecraft] My K1 Hi all; With all the discussions on getting more audio out of their rig, I thought I would share a pic of my K1 and its power supply speaker combination I built. A jack goes from the headphone jack to the speaker for nice loud audio. Works great and I think looks pretty good as well. The audio is directed to the operator instead of sending it to the ceiling. This is my field day set-up. I have one of my small spinner attachments on the K1 knob for easier and fast tuning. http://valveman.tripod.ca/K1.jpg Regards, Robert VE3RPF ++++++++++++++++++++ Date: Sun, 21 Jul 2002 13:16:42 -0400 From: jbg144 at netscape.net To: elecraft at mailman.qth.net Subject: [Elecraft] RE: Low audio output Problem solved: A bit of signal tracing (and good luck) revealed a cold solder joint at pin 5 of U11 (the product detector, no less). A touch of the iron, and the audio is MUCH better. Thanks for all of the suggestions 73 Jeff NY1P ++++++++++++++++++++ From: "Steve & Anne Ray" To: "Elecraft" Date: Wed, 23 Oct 2002 21:19:36 -0400 Subject: [Elecraft] Raspy Receive Audio and Transformers Just a note, as I had followed the Elecraft advice and kept my power supply (Astron 10A) more then 18 inches from the K2 to avoid the magnetic field affecting the K2. Well, last night I was on and the received audio was crackling and raspy, all the CW signals sounded like they were about RST 573. Needless to say the horrible thought went through my mind on what had gone wrong with the audio. Found out the problem relatively quickly, I had moved my old Heath Digital Clock to within 5 inches of the K2. I did not think that this would be a problem as the power supply for the clock only draws 600 mA. Moving the clock back to its regular position about a foot away cured the problem. Just hope this helps someone else. 73, Steve Ray K4JPN ex K1VKW EM82ep Warner Robins GA Elecraft K2 1422 Heath Fan HW-101, HW-8 +++++++++++++++++++ From: "Wolf-Ruediger Juergens" To: Subject: Re: [Elecraft] K2 #2857 2. Part complete - but audio to low Date: Sun, 15 Dec 2002 08:53:49 +0100 Organization: Privat > Signals are strong but I think audio is to low. AF-Gain is 12 o'clock and with > full RF-gain and Pre on it's not so bad but my K1 is much louder. Found the reason, D3 was installed in the wrong direction. After setup the filters several times, the audio level is much better now. I will setup again all filters using spectrogram after finished the next assembly part. 72 de Wolf, DL2WRJ ++++++++++++++++++ From: "Bob - AG5Q" To: , Subject: Re: [Elecraft] RE: Speaker for K2 - Low audio Date: Mon, 3 Feb 2003 11:20:32 -0600 Hi Bruce, If you have the KAF2 Audio Filter, you can increase the audio by changing R9 to a larger value. Something in the range of 20K to 33K will help. 73/ Bob - AG5Q ++++++++++++++++++ Date: Tue, 11 Mar 2003 14:22:34 -0800 To: elecraft at mailman.qth.net From: Eric Manning Subject: [Elecraft] K2 Rev A - weak audio - one more time I'm one of many K2 Revision A builders who thought my audio was a bit feeble. Well, it wasn't the audio at all - it was overall receiver gain too low - caused by the AGC threshold set too low and thus holding down the gain too much. I tried a simple test from the instructions for upgrading to K2 Rev B. You tune to a quiet band - I used 28 MHz when the band was dead- and turn off the AGC by pressing AGC and PRE/ATT together. If the noise level rises, the AGC was reacting to noise and holding the receiver gain down when it shouldn't, namely when there is no signal present. Mine rose between 1 and 2 S-units, by ear, when I turned off the AGC. The fix is to replace R1 [51K] of the control board by a pot set at 51K and then reduce the resistance just enough to let the noise level with AGC on approach or equal the AGC-off noise level. If you turn R1 down way too much the receiver gain will fall way off. If you turn it down a bit too much the S-meter LEDs will all remain dark when you try to re-set S meter HIgh and S-meter low, which you must do [manual p 84] . I turned it down just enough to bring up the noise level but not enough to prevent calibrating the S-meter. Just a small adjustment of the 100K pot I used. Happiness - the receiver sounds much louder on weak signals and the S-meter is livelier. I used a 100K trimmer pot soldered to little pigtails made from wire clipped from resistors, and I left it in the circuit, perpendicular to the board, with some scotch tape on the case to prevent it touching. It's a tight fit but seems OK. Or, you can measure the pot value and put in a fixed resistor of same value. -- Eric Manning VA7DZ VE3DPV K2 #2561 "Pauline" +++++++++++++++++++