dmbaer
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How to Build a Good Quality (Yet Inexpensive) Monitor Volume Control
As promised, I'm reporting back on my efforts to find a passive volume control for my monitors. It took a little experimentation, but I found a nice solution that was fairly inexpensive and not too hard to build. My first attempt used a stepped attenuator from EBay. It cost a little under $50 including shipping. I don't have the link handy and couldn't find one currently listed (only some more expensive units). The idea behind the stepped attenuator vs using a stereo potentiometer was that, in theory, the stepped attenuator offers a great deal more accuracy in terms of both channels having the same resistance at all settings. Unfortunately I took some advice from an electronics web site that proved to be bad. The advice was to use a pot with a max. resistance that's 20% of the monitor input impedance. My monitors have a fairly typical input impedance of 20K, and the closest match was a 10K stepped attenuator. It worked, but only the last third of the rotation had any sound at all. The other issue was that this particular device was hella difficult to soldier (in fact, it looks like I fried at least one resistor in the process, even though there was no audible damage). Next I did what I should have done in the first place. I picked up a cheap 100K stereo pot from Radio Shack for $3.50. This was a much better fit in terms of loudness throughout the range. Having found the right resistance, I tracked down a quality pot here: http://angela.com/alpspotentiometerbluevelvet100kstereo.aspx It cost about $25 with shipping. I tested with my inexpensive multimeter, and for whatever it's worth, the resistance of each channel matched dead on at a variety of positions. Although easier to soldier than the stepped attenuator, this was still no piece of cake. There's probably some tool or technique I don't know about. But I got it working and it sounds great. The circuit is simple. For each channel you have a two-conductor cable that goes to the sound card and another two conductor cable that goes to the monitor. The four wires from the two cables get connected to the three connections on the pot. Although it's probably obvious, let me add that you should set your software volume control to max once the external volume control is in place. Here are the specifics on what goes with what. If you're using the same pot as I did (the one from the link above), the terminals are as follows. If you're looking at the front of the device (shaft pointed at you) and the connection posts are on the bottom side, the leftmost post is "ground" for both monitor and sound card, the center is the hot monitor connection, the rightmost the sound card hot connection. By ground, I just mean the connection that goes to the outer cylinder for an RCA plug or the long shaft portion of a quarter inch plug. Hot means the connection that goes to the center shaft of an RCA plug or the tip of a quarter inch plug. If you use a different kind of pot, you might need to figure out which connection post is which. For that you'll need a multimeter to measure resistance. Find the two connections for which resistance doesn't change when you turn the shaft. One of those is ground and the other is the hot sound card connection. The third post is the hot monitor connection. Turn the shaft fully counter clockwise. Measure the resistance between the hot monitor connection and the other two posts. The one that shows zero resistance between it and the hot monitor connection is the ground.
post edited by dmbaer - 2011/04/18 14:20:01
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batsbrew
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Re:How to Build a Good Quality (Yet Inexpensive) Monitor Volume Control
2011/04/18 14:48:57
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AT
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Re:How to Build a Good Quality (Yet Inexpensive) Monitor Volume Control
2011/04/18 15:14:55
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TC has their controller. It was selling for $80 and everything I heard about it was good. One of the local studios had it hooked up in lieu of their SSL that was being fixed. The owner/engineer moved it from his B room and was quite pleased with it.
@
https://soundcloud.com/a-pleasure-dome
http://www.bnoir-film.com/ there came forth little children out of the city, and mocked him, and said unto him, Go up, thou bald head; go up, thou bald head. 24 And he turned back, and looked on them, and cursed them in the name of the Lord. And there came forth two she bears out of the wood, and tare forty and two children of them.
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batsbrew
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Re:How to Build a Good Quality (Yet Inexpensive) Monitor Volume Control
2011/04/18 16:24:17
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plus, you can do other things with it....
Use it as a passive line level control for extension speakers.
Use it in back of a tube preamp and control in/out level combinations without overloading your other gear.
Line Level Control for output to prevent clipping. Use it between mic preamp and the inputs of your A/D converter.
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ohhey
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Re:How to Build a Good Quality (Yet Inexpensive) Monitor Volume Control
2011/04/18 19:21:08
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dmbaer
As promised, I'm reporting back on my efforts to find a passive volume control for my monitors. It took a little experimentation, but I found a nice solution that was fairly inexpensive and not too hard to build.
My first attempt used a stepped attenuator from EBay. It cost a little under $50 including shipping. I don't have the link handy and couldn't find one currently listed (only some more expensive units). The idea behind the stepped attenuator vs using a stereo potentiometer was that, in theory, the stepped attenuator offers a great deal more accuracy in terms of both channels having the same resistance at all settings. Unfortunately I took some advice from an electronics web site that proved to be bad. The advice was to use a pot with a max. resistance that's 20% of the monitor input impedance. My monitors have a fairly typical input impedance of 20K, and the closest match was a 10K stepped attenuator. It worked, but only the last third of the rotation had any sound at all. The other issue was that this particular device was hella difficult to soldier (in fact, it looks like I fried at least one resistor in the process, even though there was no audible damage).
Next I did what I should have done in the first place. I picked up a cheap 100K stereo pot from Radio Shack for $3.50. This was a much better fit in terms of loudness throughout the range.
Having found the right resistance, I tracked down a quality pot here:
http://angela.com/alpspotentiometerbluevelvet100kstereo.aspx
It cost about $25 with shipping. I tested with my inexpensive multimeter, and for whatever it's worth, the resistance of each channel matched dead on at a variety of positions. Although easier to soldier than the stepped attenuator, this was still no piece of cake. There's probably some tool or technique I don't know about. But I got it working and it sounds great.
The circuit is simple. For each channel you have a two-conductor cable that goes to the sound card and another two conductor cable that goes to the monitor. The four wires from the two cables get connected to the three connections on the pot.
Although it's probably obvious, let me add that you should set your software volume control to max once the external volume control is in place.
Here are the specifics on what goes with what. If you're using the same pot as I did (the one from the link above), the terminals are as follows. If you're looking at the front of the device (shaft pointed at you) and the connection posts are on the bottom side, the leftmost post is "ground" for both monitor and sound card, the center is the hot monitor connection, the rightmost the sound card hot connection. By ground, I just mean the connection that goes to the outer cylinder for an RCA plug or the long shaft portion of a quarter inch plug. Hot means the connection that goes to the center shaft of an RCA plug or the tip of a quarter inch plug.
If you use a different kind of pot, you might need to figure out which connection post is which. For that you'll need a multimeter to measure resistance. Find the two connections for which resistance doesn't change when you turn the shaft. One of those is ground and the other is the hot sound card connection. The third post is the hot monitor connection. Turn the shaft fully counter clockwise. Measure the resistance between the hot monitor connection and the other two posts. The one that shows zero resistance between it and the hot monitor connection is the ground.
Thanks for the post, I have a HiFi preamp in my stereo that needs a new pot, that one looks like the one that's in there but I wasn't sure on the value. Humm.. I wonder if one of those would fit in my M-Patch 2 ?
post edited by ohhey - 2011/04/18 19:26:05
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tarsier
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Re:How to Build a Good Quality (Yet Inexpensive) Monitor Volume Control
2011/04/19 10:30:55
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Thanks for the update. My problem is that I need a multichannel volume control for surround work, preferably something to handle 7.1. There's nothing inexpensive in that realm.
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batsbrew
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Re:How to Build a Good Quality (Yet Inexpensive) Monitor Volume Control
2011/04/19 11:13:56
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JayJayVee
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Re:How to Build a Good Quality (Yet Inexpensive) Monitor Volume Control
2011/05/05 18:42:48
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Here is an excerpt from my book Sound Recording Advice. I throw it out here to help any Cakewalker who is trying to build some outboard/physical line level master Volume Faders. I grabbed this text from my book's Word file which unfortunately does not have the pictures embedded. If you need pix, then email me separately at soundadvice-at-johnvolanski.com. You can use these at the output of any unbalanced line level analog audio output (mixer, sound card, tape deck, effects box, etc.) and control the level of volume going into the next stage (such as another high input impedance analog audio device or a power amp driving your monitors). John Volanski -- [color=#000000 size=3 font="bookman old style"]MASTER FADERS [size=3 font="bookman old style"] At one point in time, I put together a custom mixer for my home studio using some Teac Model 10 mixer modules. A warehouse in Los Angeles was selling new in-the-box mixer modules for $30 each, marked down from list prices of $150 to $525 for each module. For about $200, I put together a 16 x 4 stereo mixer with a cue and an effects loop, plus 24 monitor channels. This mixer served me well for many years. One of the shortcomings of this mixer was that it didn't have a pair of linear slide pots to serve as the master output faders. During the final mixdown from multi-track to stereo master, I was forced to use the rotary input level pots on my stereo master deck to handle the fade out at the end of a song. If you've ever tried to twirl two rotary volume pots to have the audio fade at exactly the same rate in each channel, then you know what a pain this is. Another problem I had was lack of volume control on the send to the power amplifier that drove the monitors in my studio. If your studio also suffers these kinds of shortcomings, or if you just need a set of linear pots that you can insert anywhere in a low-level audio chain, read on. My solution to this problem was to build a remote box to house two master faders. Ideally, the requirement is to have two long-throw, audio taper, linear slide potentiometers situated near each other, so that stereo fade outs can be accomplished easily with one hand. [size=3 font="bookman old style"]The first hurdle is to find some pots that fit those requirements. Apparently, linear slide pots are not a popular item, because few distributors that I know sell them. I ordered some from Mouser Inc. ( [size=3 font="bookman old style"]http://www.mouser.com). To order a catalog, contact them at (800) 346-6873 or Fax (817) 804-3899. Be careful to purchase only audio taper potentiometers, not linear taper. Don't be confused here; the slide action of these potentiometers is along a linear track, but the rate of change of the resistance along that track varies logarithmically, as does the perception of loudness by human ears. If you use linear taper pots in this application, you'll find that most of the sensitivity of the pot (as perceived by your ears) occurs over a relatively small range of the pot's excursion, thereby making it unsuitable for use in volume control circuits. Mouser part number 312-619A-10K would be a good choice. The schematic for this circuit is quite simple. The input signal attaches its center/hot conductor to the top of the pot and its ground/shield conductor to the bottom of the pot. The output signal attaches its center/hot conductor to the wiper of the pot and its ground/shield conductor to the bottom of the pot. Basically, the master fader allows the audio signal to pass through unaffected when the slider is at the top of its travel (zero resistance) and begins diminishing the amplitude of the signal as the slider is moved to the bottom of its travel (maximum resistance). Also note that there are no active electronics associated with these pots, therefore impedance matching is not preserved, and there is no gain. The longer the throw (travel) of the fader, the easier it is to have a smooth fade out. The pots I bought have a 2-inch throw. If you can find a pot with a longer throw, by all means use it. A 3-inch throw is a good length for a mixer fader pot, but they are tough to find. The impedance value of the pot can be any value between 10kW and 100kW, with 10kW being a good target value. I used RCA jacks for the input and output connectors. Radio Shack is a handy source for these connectors, but you can get them at any electronics parts supplier. Radio Shack part number 274-322 contains 4 RCA connectors on one bakelite panel for under two dollars, or you can use individual RCA jacks as I did. Mounting the individual RCA jacks is easy with a drill. In order to keep hum and noise to a minimum, proper shielding and proper grounding procedures should be followed. Use a metal case for the project, if you can. The case should be grounded, so that it acts as a shield against magnetic fields radiating from other equipment that can induce hum into your circuit. You may find that the case you have is anodized, and this anodizing treatment prevents the metal of the case from conducting electricity. You will need to scrape off the anodizing and use a star washer, if you want to make good metal-to-metal contact with the case. Use a "star" ground approach for all ground connections. That is, there should be a central point to which all ground wires connect within the box. You can bus the four ground connections together on the RCA phono jacks. This then is the center of the ground star. For the cabling from the pots to the RCA jacks, use sections of shielded cable. I just cannibalized an RCA patch cable and cut it into short sections for this application. Solder the shield of each cable section that runs between the RCA connectors and the slide pots at the ground star end, but not at the potentiometer end; just solder the center conductor of the cable to the pot. Refer to ***Figure X for the locations of the potentiometer connection terminals. Note that if you use a metal case, it's not absolutely mandatory to use shielded cable for inside connections, though I still recommend it. If you use a wooden or plastic case, you should definitely use shielded cable, however. The partially assembled slider pots are shown in ***Figure AA. Probably the most difficult part of this project is slotting the case for the wiper handle to slide back and forth. Unfortunately, there doesn't seem to be any easy way to do this, unless you happen to own a sheet metal shop. The method I have generally used involves using a jigsaw to cut a thin slot in the case. I mark off the limits of travel of the wiper handle on the top panel of the case. To do this, use masking tape, as it will also serve to protect the finish on the case. ***See Figure Y. At the top limit of travel of the slider, I drilled a series of small holes that allow the jigsaw blade to be inserted into the panel to cut the slot. Then, I drilled a set of holes for the mounting of the pot. ***See Figure Z. When you are cutting the slot with the jigsaw, be careful not to run the jigsaw past the two points that mark the maximum wiper travel limits, or you'll run the slot into the mounting holes for the pot, which will cause much wailing and gnashing of teeth. I used a nibbling tool (refer to ***Figure P) to clean up the slot for the wiper travel. The prototype master faders that I built are shown in ***Figure BB and **Figure CC. Now that you've got the master faders built, where do they go? Insert them in the signal chain between the master output of the mixer and the input to the mixdown (master) tape machine as shown in ***Figure DD. Remember that these faders can only reduce the signal level; they can’t increase it. Typically, the input circuitry of your mastering tape machine will not mind that its inputs are grounded when the master faders are all the way down. If it does react strangely, add a small series resistor in-line with the output signal of each fader; 10W should be sufficient. Remember, never short the output of a preamp or amplifier circuit directly to ground. (The output transistors of many amplifying circuits are protected from sizzling as a result of the large currents which flow during a direct short to ground, but you may be unhappy to discover that your amp, preamp or mixer is not properly protected to sustain a direct short of this nature.) You can also use the master faders between a CD player (that has no volume control on the preamp output) and a straight power amp, or even the output of a mixer or sound card that connects to your power amp or amplified monitor speakers. Another application for the master faders is to use them to regulate the output level of a SMPTE or FSK code generator device that you are using to stripe a synchronization track on a multi-track tape deck. I always try to record the SMPTE track with the lowest (yet still reliably solid) level I possibly can to prevent it from bleeding into the adjacent audio track on an analog multi-track tape deck during subsequent recording or playback. However, don’t record it so low that the synchronization becomes unreliable upon playback. I use one channel of the master fader to regulate the record level during a “practice run” while I monitor the output with another SMPTE time code reader. When the signal gets too low, the SMPTE reader will lose lock and drop the sync; I boost the level sufficiently beyond that point, and then go back and stripe the tape for real. This approach has worked every time for me! By the way, always stripe the synchronization time code onto an edge track of the tape (e.g., track 8 of an 8-track machine), as this will minimize the amount of cross talk into adjacent channels (signals bleeding from one track into another track). [size=3 font="bookman old style"]
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JayJayVee
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Re:How to Build a Good Quality (Yet Inexpensive) Monitor Volume Control
2011/05/05 18:46:52
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Ah nice, I see when I pasted the Ohms symbols into the text above, it shows up as a "W".
All those values for the pots should be in kOhms.
JV
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Twigman
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Re:How to Build a Good Quality (Yet Inexpensive) Monitor Volume Control
2011/05/06 06:14:09
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batsbrew
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Re:How to Build a Good Quality (Yet Inexpensive) Monitor Volume Control
2011/05/06 10:28:22
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 ALL YOU NEED.
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Twigman
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Re:How to Build a Good Quality (Yet Inexpensive) Monitor Volume Control
2011/05/06 11:45:14
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John6528
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Re:How to Build a Good Quality (Yet Inexpensive) Monitor Volume Control
2011/05/06 11:49:07
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jeez... I had an old mixer laying around so I just use that. Seems to work ok but kind of overkill and big on my desktop.
John
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JayJayVee
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Re:How to Build a Good Quality (Yet Inexpensive) Monitor Volume Control
2011/05/06 16:15:54
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The ATTY looks to be about $100 USD and the SM Pro Nano Patch + looks to be about $60 USD.
However, if you've got no significant money to spend, then I spose you build your own.
JV
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