K2 -- RX audio
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Hi
While trying to improve the K2 RX audio response specially for SSB, I noticed lack of low frequencies, looking at the schematics I find the the LP cutoff is abt 640 Hz, determined by C25, C26 and the 5k vol pot ( this is wheather using DSP or not). By increasing C25 and C26 to 0.2uF (from 0.1uF) the LP cutoff is moved to abt 320 Hz. This makes better sounding SSB signals and also helps in CW mode when copying low pitch signals. To lower the LP cutoff, I soldered 0.1uF SMD caps across C25 and C26 on the control board. To my ears K2 now sounds better..... 73, Matti ps. I use 2.4 kHz X-Tal filter -- Marteinn Sverrisson TF3MA Langitangi 2 Internet: tf3ma [at] raunvis [dot] hi [dot] is 270 Mosfellsbær http://www.raunvis.hi.is/~tf3ma Iceland _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Useful mod Matti. My K2 audio now sounds much rounder.
Gave me something to do while waiting for the next puff of white smoke from Aptos. 73 Stewart G3RXQ On Wed, 31 Oct 2007 16:48:53 +0000, Marteinn Sverrisson wrote: > Hi > > While trying to improve the K2 RX audio response specially for SSB, > I noticed lack of low frequencies, looking at the schematics I find > the the LP cutoff is abt 640 Hz, determined by C25, C26 and the 5k vol > pot ( this is wheather using DSP or not). > By increasing C25 and C26 to 0.2uF (from 0.1uF) the LP cutoff is > moved to abt 320 Hz. This makes better sounding SSB signals and also helps > in CW mode when copying low pitch signals. > > To lower the LP cutoff, I soldered 0.1uF SMD caps across > C25 and C26 on the control board. To my ears K2 now sounds better..... > > 73, Matti > > ps. I use 2.4 kHz X-Tal filter _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Marteinn Sverrisson
All K2'ers
When aligning SSB filters be ware of the low freq cutoff in the audio chain if you are measuring across the loudspeaker terminals. The original RX audio low freq. cutoff (-3db) freq. is approx. 640Hz (with KAF or DSP moduls installed) or 400Hz (with no audio moduls). The cutoff is determined by C25, C26 (on the control board) and the 5kOhm volume control pot (and NE612 mixer output impedance with no audio moduls), C25 and C26 are 0.1uF each and in series with the vol pot which is 5k. This is a high pass filter with abt 640Hz cutoff. So if you are using Spectrogram og Baudline to adjust the low freq points, you will not get the correct setting if you do not know this. To improve the RX low freq range you should change C25 and C26 to 0.22 or 0.33 uF. This affects only the RX audio, and it makes the SSB sound better. In my K2 I put 0.1uF SMD's across C25 and C26, extending the low frequency response to approx. 320Hz. It also helps with SNR when copying low pitch CW signals. just my $.02 73, TF3MA, Matti K2 #2024 -- Marteinn Sverrisson TF3MA Langitangi 2 Internet: tf3ma [at] raunvis [dot] hi [dot] is 270 Mosfellsbær http://www.raunvis.hi.is/~tf3ma Iceland _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Marteinn Sverrisson
I replaced C25 and C26 with .22 uF ceramic capacitors the other evening as
Matti has suggested. It does make a nice difference in the low end. I have the KAF2 filter and am using the standard SSB filter as constructed in Rev E of the KSB2 module. The specs state it is a 2.3 kHz filter. I notice that the coupling capacitors in the KAF2, C12 and C13 are .22 uF devices. I can't help but wonder what changing all four caps C25 and C26 on the control board and C12 and C13 on the KAF2 to .33 uF would do. I don't have enough .33 uF ceramic caps in the junk box or I would try it. Perhaps I will remember to order some from Mouser next time I place an order. I have some polypropylene caps of the right value, but they are a bit to large physically to fit. The audio buffs seem to favor these over the ceramic types as they say they have a better sound to them. Be interesting to see if it would be noticeable. 73, Darrell VA7TO K2#5093 On Wednesday 31 October 2007 09:48, Marteinn Sverrisson wrote: > Hi > > While trying to improve the K2 RX audio response specially for SSB, > I noticed lack of low frequencies, looking at the schematics I find > the the LP cutoff is abt 640 Hz, determined by C25, C26 and the 5k vol > pot ( this is wheather using DSP or not). > By increasing C25 and C26 to 0.2uF (from 0.1uF) the LP cutoff is > moved to abt 320 Hz. This makes better sounding SSB signals and also helps > in CW mode when copying low pitch signals. > > To lower the LP cutoff, I soldered 0.1uF SMD caps across > C25 and C26 on the control board. To my ears K2 now sounds better..... > > 73, Matti > > ps. I use 2.4 kHz X-Tal filter -- Darrell Bellerive Amateur Radio Stations VA7TO and VE7CLA Grand Forks, British Columbia, Canada _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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