Volume Knob
zingo
Posts: 11,258
Is it possible to use a wall mount volume knob in a component or passive pre? (link below) If it truly is just 2 channels in and out, shouldn't it work? I like the stepped resistor attenuators, but a decent one is pricey. I'll be buy one eventually, but thought I might try something like this first as an experiment, if in fact it would work since it seem like little more than a mounted pot.
http://www.amazon.com/gp/product/B00009W3IG
http://www.amazon.com/gp/product/B00009W3IG
Post edited by zingo on
Comments
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The answer is, brace yourself for this, NO!
Volume knobs are usually L-pads and not the same construction. Other than that, big clunky contacts and unknown capacitance. -
Zingo, you can pickup lpads (attenuators) at lots of electronics parts houses. Just ask for 'Audio Taper' pots vs 'Linear'. Start between 50K and 100K ohm (for most amps), and you can tweek it from there. You don't need to spend a lot to get good sound. Do a dual mono job, I've built a couple myself.
You COULD use that volume control you linked, if you want to hook the single source directly to your amp, and have the high level outputs (speaker wire) from your amp go DIRECTLY into the control, and back out to your speakers. That's a clusterf#$k route though broham.
Cheers,
RussCheck your lips at the door woman. Shake your hips like battleships. Yeah, all the white girls trip when I sing at Sunday service. -
All good points I was too short sided at the time to think about. Thanks.
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Other than the pic not loading for me, looks good.
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What's your goal on this one, zingo? Just fooling around with stuff, or are you looking to try something passive?
My system's took a real turn lately and has been going in a much simpler direction then before. I've been reading about passive pre's and found this design by Nelson Pass: B1 Buffer Pre Amp. I was going to try building one point to point but psyched myself out. Pass DIY had PCB's for sale, but they sell out so quick it's difficult to grab one. I ended up getting in touch with Tim Rawson through Audiogon, he's gonna build me one so I can give it a whirl. Pretty cheap, too. Just a thought for you....Wristwatch--->Crisco -
My goal is that the pot went out in the integrated tube amp I built. It was a really cheap one, but didn't expect it to go out after 9 months. I might just be replacing that one, but I was also just considering jumping it and building a volume only passive pre like you were saying.
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Does anyone have any experience with a passive preamp without enough gain? I know it is possible to use a passive pre that doesn't go loud enough because the output voltage of the source isn't high enough, but has anyone actually experienced that?
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Well, the left channel of my amp's pot completely quit yesterday and I'm tired of dealing with it. Since I never move the pot, I just took its measurements, 45k and 55k, and I'll going to be replacing it with resistors tonight. I hope it solves my problems and also improves the SQ a tad by removing a pot and it's external wiring. I am also looking into the B1 (thanks strider), and contacted them about being wait-listed for the board.
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Cool. I'm interested in seeing what you come up with. Don't know if you frequent diyaudio.com or not, but here's the build thread for the B1. Get comfortable, though, it's quite a read.
BenWristwatch--->Crisco -
I am a member of the DIYaudio site and that B1 thread is ridiculous! I started reading through it when I was researching the amp, but stopped after a few pages. It looks like a really cool design and the reviews are good too. It's $1000 built, but I'll really be interested to see how much all the parts come to since I'll be ordering the board with the transistors ($40).
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Success! I removed the pot on my amp and replaced it with four 1w resistors; 46.6K, 47.5K, 46.6K, 47.5K. The value of the pot was 100K, and obviously these add up to 94.1, but it doesn't effect SQ. I can't yet comment if SQ was gained by removing the pot, but the highs might be a little brighter and forward; I'll keep listening. It was a VERY easy install and works great for me since I never move my volume knob anyway. And, if I ever needed to change the output volume for whatever reason, new resistors are just pennies away.
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Now that I have a hole in the front of my amp where the pot used to be, I am considering what to do with it. My original thought was a decorative plate or badge of some kind, but I was unsure exactly which direction to go with that. Lately I have been thinking a power light using an LED would be cool. The only problem I am running into is the power. Since the needed voltage for an LED is only 2-4v, I have been considering how to step the voltage down from a given ~110v. My first thought was a resistor, but at that voltage, it would have to dissipate about 1100w of heat, so bad idea (if I did the math right). What's the best way to do this?
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First of all, add a real rectifier diode(400V) in series with the LED to keep it from burning out on the negative half-cycle. Now realize we are at half power.
110VRMS * 5mA(enough for a power light) = 0.55 watts (half of the time)
I would use a 2 watt 22k resistor and a 1n4001(4004 whatever the 400V one is).
This light will blink if you move your eyes around. If you look straight at it, it will appear a solid color. -
Thanks and I'll look into that. I guess I should have thought about the rectifier diode, but I don't always think.
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You have to be aware that LED's have severe reverse voltage limitations.
If you were stringing say 40 LEDs together, then it wouldn't be a problem. With a single LED and resistor, it still shouldn't be a problem. Considering the cost of the rectifier diode, don't take any chances and do the job once. -
With a few hours under the new volume resistors, the amp has a little more high end sparkle, and the noise has been reduced a little with no more pot. However, the best thing I was able to do with installing the volume resistors was reduce the distortion and I'll explain. Before pulling the pot, I hooked up the amp to an oscilloscope and turned the pot up and down until I found the point where I got the most output, yet almost no distortion (as this amps output moved toward clipping, some serious distortion was introduced into the signal). Having found that point, I measured the pot to get the values, then soldered those in as stated above. This ensure that no matter how high I adjust the volume from my preamp, the signal coming from the amp won't distort!
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Shin, I am going to follow your idea of a rectifier diode/resistor combo for the LED, but I'm going to try to pull a little current off one of the heater circuits as long as it doesn't draw too much. The supplied current there is only 6.5v and it would be an easy step down to 2v. But, I will run all this through the oscilloscope first before I make and final decisions.
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Success! I finally ended up using the diode/resistor combo to power and LED for the front of my amp. It works great and I was about to use the 6.5v source from the heaters and that made the install easy. I haven't noticed if the LED effected anything by drawing off that source, but it's such as small draw in current anyway that wasn't expecting anything.
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I've used high intensity red LEDs at 1 mA with great success in the past. Using 6.5 VDC, you would need a resistor of 4.7 Kohm .
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I've used high intensity red LEDs at 1 mA with great success in the past. Using 6.5 VDC, you would need a resistor of 4.7 Kohm .
That's exactly what I did!
You must be able to read minds! (Or do math )
