babadono Posted March 1, 2014 Share Posted March 1, 2014 Craig, Do you have it hooked up as "Volume Control" below? Eric 1 Quote Link to comment Share on other sites More sharing options...
mustang guy Posted March 1, 2014 Author Share Posted March 1, 2014 Craig, Do you have it hooked up as "Volume Control" below? Eric beats me. The ground wire is nowhere near the pot. Think of it this way. One hot wire in, and on wire out that is being influenced by the resistance of the rotary potentiometer. With an ohmeter, the potentiometer is indeed causing up to 10Kohms resistance to the out wire. Quote Link to comment Share on other sites More sharing options...
babadono Posted March 1, 2014 Share Posted March 1, 2014 ah...... well, the ground wire is necessary if you are trying to make a volume control. Sounds like you have it hooked up like a "variable resistor" from the diagrams although you may not have two of the terminals tied together. It will still act like a "variable resistor" using only 2 of the 3 terminals. So if I understand correctly how you have it wired, you have added a 10K variable resistor in the output of a preamp going into the input of an amplifier. Since the input impedance of the amplifier is considerably higher than the 10K pot, typically about 50K, the 10K pot even when it is adjusted for maximum resistance is only dropping the input voltage to the amp by one sixth. Five sixth of the signal is still getting to the amp. Did you say the pot has no effect? None whatsoever? If the input impedance of the amp is even higher then it is getting even more of the signal. Is this making any sense? Quote Link to comment Share on other sites More sharing options...
mustang guy Posted March 2, 2014 Author Share Posted March 2, 2014 My problem is I don't know what the 1, 2, and 3 represent in the above schematic. What I do understand is In, Out and GND. Based on the way I have this wired and not understanding the above numeric representations, I can only guess I am not wired in any of the above ways. One wire in and one wire out. Could you explain what the 1, 2 and 3 represent? Quote Link to comment Share on other sites More sharing options...
mustang guy Posted March 2, 2014 Author Share Posted March 2, 2014 I found it here: http://m.wikihow.com/Wire-a-Potentiometer I definitely had it wrong. I never would have guessed this wiring scheme. I wired it based on simple experimentation with an ohmeter. Did you know that the resistance between 1 and 2 goes up, the resistance between 2 and 3 goes down? I thought it was simply two ways of wiring it. 2 in and 1 out or 2 in and 3 out. I hate reading instructions. Instead I like to figure things out. In fact, that is the one thing I like to do most. It's my passion. Now with your help, I have learned something very new. In my mind it seems counterintuitive. I will report back when I get back to the shop. Thanks again! Quote Link to comment Share on other sites More sharing options...
Don Richard Posted March 2, 2014 Share Posted March 2, 2014 You want it wired as a voltage divider (potentiometer) so as to control the signal through it. Quote Link to comment Share on other sites More sharing options...
babadono Posted March 2, 2014 Share Posted March 2, 2014 Craig, Cool that you are learning something new, I love learning new stuff. I do not agree completely with the info at that wiki page, it is not entirely correct. The signal should not be injected into the wiper(pin 2) because when the pot is turned to pin 1 it will short the signal to ground. This maybe OK for electric guitar pickups but it is not OK for electronic amplifiers. If you are trying to make a volume control between a preamp and a power amp it needs to be wired like the diagram "volume control". Pins 1 and 3 are the ends of the resistive element in the pot. The resistance between them will not vary, just like any fixed resistor. Pin 2 is the wiper, it travels along the resistive element between 1 and 3 as you turn the shaft. When turned completely CW or CCW the total resistance will be between the wiper (pin 2) and one of the other terminals and conversely there will be 0 ohms from the wiper to the other terminal. Now since this is an audio taper pot it matters how you hook it up because when the pot is adjusted to its middle position there will be approx. 10% of the resistance from the wiper to one of the ends and 90% to the other. So what you need to do is adjust the pot to its middle position and read the resistance from the wiper to the ends. The terminal that reads approx 1k ohm (10% of 10K) is terminal 1, the one that reads 9k is terminal 3. Wire the output of the preamp to terminal 3, and the ground to terminal 1. Wire the input of the amp to terminal 2 and its ground to terminal 1 also. Then you will have a volume control. Eric Quote Link to comment Share on other sites More sharing options...
mustang guy Posted March 3, 2014 Author Share Posted March 3, 2014 (edited) Works like a charm now! As it turns out all I needed to do was solder a GND to terminal 1 or 3 or whichever... I know what they did in the wiki. When they say 'in' them mean in to the amp, and 'out' was out from the preamp. Talk about bass-ackwards thinking. Edited March 3, 2014 by mustang guy Quote Link to comment Share on other sites More sharing options...
mustang guy Posted March 8, 2014 Author Share Posted March 8, 2014 FYI, I was getting a good bit of distortion, so I posted a question on the diy tube forum. I have been told that 10K is nowhere near enough resistance for a tube tuner. I am now discerning just how much resistance to use. I may need as much as 1m, but I think it will be somewhere between 100k and 500k. Quote Link to comment Share on other sites More sharing options...
babadono Posted March 9, 2014 Share Posted March 9, 2014 Craig, Hmmm...I must admit I am a little confused. What is this "volume control" doing now? It is now on a tuner output? Is there any possible way that you could update your schematic? Eric Quote Link to comment Share on other sites More sharing options...
mustang guy Posted March 11, 2014 Author Share Posted March 11, 2014 Sure. The device is now an amp selector with discreet volume controls. Here is a link to the diyaudio thread. Quote Link to comment Share on other sites More sharing options...
babadono Posted March 11, 2014 Share Posted March 11, 2014 Read through that whole thread. Seems like there are some smart and helpful blokes over there. I am not a "tube guy". Studied them in school back in the day but have not really had any real world (work) need for them. Thanks for updating your schematic, looks like you have the pots truly hooked up as volume controls now. So the tube gear is highly sensitive to the load placed upon it by the pot. Have you installed the 500Ks yet? I think the 500K/360pF combo is going to affect the high freq response. Quote Link to comment Share on other sites More sharing options...
mustang guy Posted March 12, 2014 Author Share Posted March 12, 2014 No, haven't bought the pots yet. I agree about the LPF issue with the capacitance and the resistance in parallel. I have no idea how to calculate the frequency, and I didn't have any bites at DIY either. Do you know how to calculate it? It might be in the MHz range or something... Quote Link to comment Share on other sites More sharing options...
mustang guy Posted March 12, 2014 Author Share Posted March 12, 2014 (edited) I found it. You were right.... Here is the site with the calculator for RC (resistor/capacitor) passive filters. http://www.ekswai.com/en_lowpass.htm With a 360pF capacitance of the 6 meters of coax, and the potential resistance of 500K in the volume control, the LPF would be 884Hz. Man that puts a damper on things. How in the blazes do people work around this problem? update: Here is a schematic of an RC Filter. I may be wrong, but I don't think coax capacitance between sources qualifies as a capacitor to ground. I don't think there is an Rc Filter in this passive. Edited March 12, 2014 by mustang guy Quote Link to comment Share on other sites More sharing options...
babadono Posted March 14, 2014 Share Posted March 14, 2014 Yep, the signal will be down 3db at 1/2piRC. And yes the capacitance of the cable per foot is from the center conductor to the shield so it is from the signal to ground. So the cap/ft times the length of the cable can be thought of as equal to a capacitor that size to ground. Quote Link to comment Share on other sites More sharing options...
mustang guy Posted March 14, 2014 Author Share Posted March 14, 2014 I have a new way of doing it thanks to the knowledgeable folks over at diy. I have already built a small box with two 500k pots. What I will do is place the box right beside the tuner, and I will disconnect the existing 500k pots inside, and run a short wire to the box and back, thereby making the trim pots forward facing. I will take some pics. It should work well. I am thinking of using CAT5, as it has the 4 pairs I need, and it is twisted pair for noise reduction. Should work like a charm. Quote Link to comment Share on other sites More sharing options...
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