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uBITX - super touchy low end volume #ubitx #ubitx-help

Rob French (KC4UPR)
 

Super excited, just put together my uBITX and love it, though I haven't successfully managed any 2-way QSOs yet.  I've got a few spots on RBN, so I know something's getting out... Anyway...

I've noticed that the volume control (I'm using the stock potentiometer) is super sensitive at the low end.  i.e. As soon as I turn it on, I never turn it more than about 1/4 turn.  And if I go more, it distorts super quickly.  Very small adjustments of the knob change the volume pretty drastically.  I actually wondered if I wired the pot backwards!  But, I checked against the schematic and also this page ( https://ubitx.net/wiring-up-the-volume-control/ ), and as far as I can tell, I've done it right (green, orange, yellow, from L to R).  Any other thoughts?

Thanks!
Rob KC4UPR

Edward Reynolds
 

I’d look at the picture on the HFsignals site uBITX wire up section for volume control and compare your connections with picture. Otherwise no answer other than a bad volume controller. Good luck
Ed de N7SNT 


On Aug 2, 2019, at 6:32 PM, Rob French (KC4UPR) <robert@...> wrote:

Super excited, just put together my uBITX and love it, though I haven't successfully managed any 2-way QSOs yet.  I've got a few spots on RBN, so I know something's getting out... Anyway...

I've noticed that the volume control (I'm using the stock potentiometer) is super sensitive at the low end.  i.e. As soon as I turn it on, I never turn it more than about 1/4 turn.  And if I go more, it distorts super quickly.  Very small adjustments of the knob change the volume pretty drastically.  I actually wondered if I wired the pot backwards!  But, I checked against the schematic and also this page ( https://ubitx.net/wiring-up-the-volume-control/ ), and as far as I can tell, I've done it right (green, orange, yellow, from L to R).  Any other thoughts?

Thanks!
Rob KC4UPR

kg9hfrank@gmail.com
 

Audio taper needed?
de Frank KG9H

On Aug 3, 2019, at 7:26 AM, Edward Reynolds via Groups.Io <n7snt@...> wrote:

I’d look at the picture on the HFsignals site uBITX wire up section for volume control and compare your connections with picture. Otherwise no answer other than a bad volume controller. Good luck
Ed de N7SNT 


On Aug 2, 2019, at 6:32 PM, Rob French (KC4UPR) <robert@...> wrote:

Super excited, just put together my uBITX and love it, though I haven't successfully managed any 2-way QSOs yet.  I've got a few spots on RBN, so I know something's getting out... Anyway...

I've noticed that the volume control (I'm using the stock potentiometer) is super sensitive at the low end.  i.e. As soon as I turn it on, I never turn it more than about 1/4 turn.  And if I go more, it distorts super quickly.  Very small adjustments of the knob change the volume pretty drastically.  I actually wondered if I wired the pot backwards!  But, I checked against the schematic and also this page ( https://ubitx.net/wiring-up-the-volume-control/ ), and as far as I can tell, I've done it right (green, orange, yellow, from L to R).  Any other thoughts?

Thanks!
Rob KC4UPR

Rob French (KC4UPR)
 

Yeah, I thought about that, but from what I can tell, the stock pot is audio taper.  I measure it at a few points w/ my multimeter and it seemed to fit a log profile. 

Jakobus van der Merwe
 

Yes it is a log pot. The human ear hear in a log fashion. Using a linear pot one will notice that, on a dvm you wll notice there is a change in voltage as you turn it up and down in a linear way. Now if the change is relative small, the dvm will show it. But your ears will not detect it. That is why for audio applications a log pot is to be used. The change in resistance at the bottom end is quite small. Going to the higher end the resistance change is quite steep. If you are using for example a 10K pot and and the change in audio level is to harsh to your liking, change it out for say a 20K pot. And here is the reason. Most pots have around a 260° turning angle. So  some simple maths.  10K / 260° = 0.385 ohms per degree. 20K / 260° = 0.077. Ok this is based on a linear pot. But the principal is the same for a log pot. But there is more to it to calculate the exact resistance of a log pot per degree. Also bear in mind that as the resistance of the log pot is not linear, connecting the pot the "wrong" way around. (The 2 outer connections) will effect the responce of the middle connection. How to know if the pot is linear or log. Look on the casing of the pot. The resistance of the pot is written on there. 20K for instance. And followed by an A or B. The A is a log pot. The B is for a linear pot.



Sent from my Samsung Galaxy smartphone.

-------- Original message --------
From: "Rob French (KC4UPR)" <robert@...>
Date: 03/08/2019 16:43 (GMT+02:00)
To: BITX20@groups.io
Subject: Re: [BITX20] uBITX - super touchy low end volume #ubitx-help #ubitx

Yeah, I thought about that, but from what I can tell, the stock pot is audio taper.  I measure it at a few points w/ my multimeter and it seemed to fit a log profile.