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i have a early pulsescan detector and ive added a volume control of 1k to the vco board and its ok but there is a back ground tone present and very noticeable when the volume is turned right down...it sounds like the tx frequency...i had the same problem a few years ago when i did the hammerhead project...any idea's on how to cure this problem ????
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circuits 'analog' and 'digital' must be splitted. additional capacitors on power lines, 'star' power supply traces, all
those is a way... advanced electronics guys know that good. but Eric did all himself. that i see...
ive added a volume control of 1k to the vco board
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volume control done ON POWER line of the VCO is more advanced way. you get automaically simple RC filter.
but you and other guys are following only 'standart' DIRECT way in-head.. our problem we are not able to turn the brain when we need... -
Hello kt...Ive never had this problem with any of my surf pi projects but only with the hammerhead and the pulsescan...maybe N channel based pi detectors are more prone to this problem...maybe someone could be more precise on this problem so i can get the audio nice and clean.Comment
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I've encountered this problem before. It was due to the audio (555) IC picking up noise from the TX output. I found that some 555 timers were more susceptible to this than others, and simply swapping the IC could fix the problem. Other times it was necessary to add a grounded shield wire around the audio oscillator. You may also be able to get rid of the background hum by repositioning the wiring within the enclosure. If the background noise wasn't there before, then (in your case) it's probably due to pickup by the volume control wiring. Have you tried using a shielded cable?Originally posted by daverave View PostComment
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Hi George...to be honest i just used non screened wires to the volume control....sounds like it maybe the problem.Comment
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Maybe you could try changing value of pot to something lower, put a 1k resistor in parallel with pot just to see what effect if any on hum.Comment
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Just had a look at old superscan schematic, kt315 is right, the volume is done on power line of vco by varying output of lm337 with reference to 0 volts via a 10k pot.Comment
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Hello banner...when i adjust the frequency control the problem also changes so its got to be pick up from tx...ive also had to boost the audio output to drive my piezo headphones and im going to make an external amplified speaker for the pulsescan...i didnt want a built in speaker as my control box is waterproof type so a plug in one is better for me...im not sure now what to do about the tx noise problem...maybe as george said it could be that i need to screen the wires.Comment
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Hi daverave, how does this detector perform? Can you share pics? Is it a tdi?Comment
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Hi dbanner...my pulsescan is almost like the tdi pro without the fine ground control...which i guess is not really needed on the beach....ive only just completed this project but i tested it in air with my 9ct gold wedding band and i got about 20" whisper which is about 3" better than my best surf pi...an old english nickle half crown 22" whisper...i got the pulse delay down to 8 uS which i can use on dry sand...overall im very happy with the pulsescan...and in my view gs 5/tdi is the best detector that eric designed.Originally posted by dbanner View PostComment
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Very cool. Can you please tell me which schematic you used.Comment
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mine is the original pulsescan tdi/gs 5 issue 2...the schematic posted on here is i think issue 1 and is incomplete without audio section and i believe errors in the schematic.Comment
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capacitor helped
took my pulsescan apart today and spent several hours trying to sort this tx audio noise problem....i tried screened cable but not that...and in the end only a 1000 uF capacitor across the supply reduced the tx noise...i cannot still not understand why the capacitor helped cause in the pulsescan the large electrolytic 4700 uf should have been more than enough to reduce the noise....detectors sometimes can be a pain in the butt.Comment
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try temporary connect a cap above every chip, on its power lines pins, and find a place where noise reduses.Comment
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i did try some caps on the +5v/-5v lines for the vco pcb but made no difference...i cannot understand why a pulsescan board would have this problem being a commercial detector...i wonder how whites got around this problem in their later detectors...the hammerhead design has the same problem but i never got this with surf pi detectors...i will take on board your advice kt 315 about caps around each ic
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