![[a photo of the pedal]](images/fv50h-pedal-small.jpg)
Background
After going to a few live gigs with my plastic piano (Yamaha P45) I struck a common problem: The sound mixer running the instruments far too loud, and drowning out the singers.
Trying to tell someone what volume level to give you is exercise in frustration, not helped by mixers who make large adjustments instead of small ones (that kind of thing has been an on-going problem with various productions, when you ask someone to adjust the level of something, they make 15 dB changes instead of 2 dB adjustments). And it really needs to be adjusted along with whatever other musicians you're playing with, not just by itself. And, even if you can get them to set your level where you want it, they may change things while you're playing. While you should be able to expect a professional operator to get that right, it's another matter with amateurs. And, if your playing is sometimes accompaniment with occasional solos, they probably don't know when your solos are.
My piano only has a limited range of dynamic expression (moderately loud, loud, Jerry Lee Lewis loud, a bit quiet, and no sound coming out at all—I don't see any good reason for a silent output, it doesn't have strings, you couldn't hold a silent chord to resonate with other notes), and other plastic pianos aren't that much better. It may claim to have 16 levels of dynamic expression, used to control four different quiet to loud recording levels in combination. But that (what I described earlier) is about all you can notice, with sudden level changes happening between tiny changes in playing strength. Anyway, piano expression is about the mood of the song, not about competing with other musicians sound levels. You can make some notes stand out, you can make some sweet and gentle, and playing strength alters the tonal quality as well as the loudness. So maladjusting your playing style to play a piece wrongly is not the way to do it, and removes your ability to use dynamics properly.
These days I'm inclined to bluntly say to people who tell you to (inappropriately for your song) play softer or harder to (instead of them setting the mixer levels correctly), “just set up the mixer properly, and don't tell me to play my instrument incorrectly.” I'm long past the point at tolerating people who are crap at doing their jobs, and I don't care how long they've being doing things their way. It doesn't make them right.
My piano has a volume control, but it's a tiny slide-pot, way off on the far-left-hand side, and not something you can adjust while playing normally with both hands. So the obvious simple solution is a stand-alone expression (volume) foot pedal between the keyboard and their sound system (this keyboard has no option to plug one into it). The less obvious solution is to modify the keyboard (if you can) to add external volume control. I can do that, but looking at my piano's service manual, it would be a finicky modification to do. It's volume pot is between 3.3 volts and ground, and putting DC through some pots (even low current) makes them go bad. One day I may attempt it, but I'd need a pedal which moves its pot through a much larger range of movement than this one (more about that below).
Review
Having looked on-line, for volume pedals, I can see there's only a few options. All expensive, some very, and no way to try before you buy. I rang the local music store, and they apparently just had one, this Boss FV-50H. I was a bit dubious, despite the shop keeper's opinion that it would be fine, but took a gamble. I shouldn't have.
What was the problem? It's the high-impedance model. I suspected this may be a problem, but not how much of a problem it actually turned out to be. I'd forgotten how crap high impedance audio equipment is to work with. It's probably been 30 years since I've had to put up with such horribly engineered devices.
High-impedance volume controls only work well between a high-impedance source (such as the raw pickup of an electric guitar) and an even higher impedance input (such as a traditional guitar amplifier, or an effect pedal). And while using short cables. Even then, they have oddball characteristics, as anyone who's played with the pots on their electric guitar knows—they don't just affect the volume level, the tone changes, too.
It could work with a low impedance source, but the side of things that really does need to be high-impedance (in this situation) is the input stage of the amplifier you're connecting to. But seeing as I'm connecting to other people's equipment, that's out of my control. It's most likely going to be to a mixing desk with a medium impedance, via a long cable. And tests at home simulating this showed it didn't work well with those conditions.
Being high-impedance, everything else around it affects how it works. How much volume control it has, and tonal quality. In the wrong circumstances what you get is an unpredictable random tone control. Long and/or crappy cables cause treble-loss due to capacitance. Low impedance inputs load the signal down causing large amounts of signal loss. And device input capacitance loads the treble down, too.
Ignoring that, if they'd had the low-impedance model (FV-50L) which should have suited the purpose I had in mind, what would I thought of the pedal, instead?
It's very expensive and very plastic, exactly the kind of thing that doesn't impress me. Gigging equipment gets a hard life, and it's something operated by your leg and foot, it needs to be robust. There's very little movement in the pedal, making it a finicky thing to use. I can see that it only uses a fraction of the volume potentiometer's range, meaning you're always going to get significant signal loss through it, and not much range of control. Also, I consider that something that sits on the floor should use sealed pots—but this doesn't.
This (below) is what's inside the pedal. The expression pot is 250 ㏀, the minimum level preset pot is 500 ㏀, and there's some tiny 100 nF capacitors going directly from the input to output sockets across the expression pots. So its input impedance ranges from 250 to 750 ㏀, and its output impedance ranges from 750 ㏀ to 0 Ω. That's some horrible variations in bad places of a high-impedance audio circuit.
But since the expression pot is only using a small fraction of its range (about a quarter rotation), it's essentially like this diagram (below). With 35 ㏀ between input and the expression pot. Not very impressive for just a few dollars worth of parts being sold for $169 (Australian dollars, in March 2024).
Oh, and good luck plugging it in correctly under low-lighting levels, with the only labelling being black plastic raised letters on a black plastic background. I loathe that kind of thing, which often means writing texta labels on white sticky tape, or playing around with white paint pens (an alternative is scribbling all around the raised lettering with a white chinagraph pencil, then cleaning off the top of the raised black plastic letters).
Feature-wise, it's two-channel (or stereo). There's a tuner output socket which has a direct connection to one of the input sockets (it doesn't go through the volume control). There's a minimum volume preset—you can set whether the pedal goes from loud down to quiet, or all the way down to mute. It's completely passive, there's no amplifiers in it, so it doesn't need batteries. The footplate (where you put your foot) is 8 by 19 cm. And 5.5 cm high when in the flat position.
If I place it between my piano and the input stages of some of my audio equipment, I get various awful results. Significant signal loss at all times. Significant tone degredation. Not much range between loud and soft. If I switch to the high-impedance mode on my recording equipment's input stage, it just gets worse. So pretty-much useless for my needs.
If I sit it between a music player and my stereo system it works as a reasonably (but not great) very expensive volume control. In my opinion, considering its plastic construction, and only a few cheap parts in it, it shouldn't sell for more than $50, instead of $169.
For keyboard use, you really want a low/medium-impedance model. And actively amplified may be a very good idea, even if it is a pain to need power to a pedal. About the one concern I have with preamplified devices is audio headroom, running things from 9 volt batteries doesn't allow for much. That, and powering it, or dealing with batteries, is a nuisance. But amplified ones ought to bypass the impedance problems of not matching your equipment well (by having a high-impedance input and a low-impedance output), and be able to drive a long cable to an mixer or amplifier.
Some people have concerns about active pedals colouring the sound. While that can be true, it doesn't have to be, only a badly designed amplifier circuit would do that. But using a high-impedance pedal where you should be using a low-impedance pedal (and vice versa) will definitely colour the sound, and not in a good way.
I would expect the low-impedance model should work as I needed, since after the various disappointing trials mentioned above, I pulled it apart and swapped the high-resistance pots for lower-value ones, and made it work. Then set about improving it even further. Though there'll still be a permanent signal loss through it, since mechanically it can only use a small fraction of the pot's rotation.
Coming from an organ-playing background, an expression pedal is usually just a volume control. And that was all that I needed. For synth players and guitarists, an expression pedal can be a control for other aspects of the sound (wah-wah, phasers, and other adjustments to the timbre). This pedal can't be used to do that, you can't plug it into a keyboard simply as a variable resistor to use as a multi-purpose controller (well, not as it stands; but with modification it might be possible to use it that way, though I think that the mechanical movement of the pot by the pedal doesn't vary enough to be useful). The low impedance model may be usable in that manner, and some alternative pedals do offer it as a feature, but this one's only designed to act as a volume control for an audio signal being fed through it.
There are some advantages to it simply being an in-line volume control, in that as well as reducing volume levels (when turned down), it will also reduce any amplifier hiss from the instrument at the same time. Alternatively, an external variable resistor for an instrument with an expression input can do other things. Apart from what I mentioned in the previous paragraph, there's things like dynamic range:
On my piano, its volume control also seems to compress the dynamic range of the keyboard: When you play gentler or harder with its volume control turned down, your playing strength doesn't seem to have as much variance on the output level as when its volume is turned up. And looking into the piano's service manual schematics, I can see that its volume control voltage goes to the microprocessor, not to the audio amplifiers. One day I may try modifying my piano to have an expression input. Apart from the dynamic range adjustment possibly being a useful function, it'd be less of a rat's nest of cabling in and out of the pedal.
I'm very unimpressed with this pedal. Ignoring the impedance problem, it's expensive, plastic, mechanically and electrically flawed (the very limited range of pedal movement—it's a fundamental problem that I can't improve with any modifications). The company making it should know better.
Recommendations
Definitely get the type of pedal appropriate to your needs. High or low impedance, amplified or passive. A volume pedal and/or a variable resistor expression pedal. Find one that seems more robust than this product; the more metal, the better. Find one that's at least as big as your foot, there are some ridiculously tiny ones on sale. And go for one with with a reasonable range of motion, and preferably driving the pot via metal teeth and gears (so more of the pot's rotational range is used, and not plastic parts that will wear out quickly).
I don't think a high-impedance volume pedal between a guitar and amplifier is a particularly good approach, anyway. Since most people using toys with their guitar are probably either using a acoustic guitar with a pickup and pre-amp mounted in the guitar, which should have a low-impedance output, and not need a high-impedance pedal. Also, electric guitarists are probably using their guitar plugged into effects pedals ahead of any expression pedal, and those effect pedals should have low-impedance outputs.
Modifying it to suit my needs
So, what to do about it? I don't think I could take it back, change-of-mind returns only happen at stores that want to offer it, and they had no alternatives in stock. I had a gig I wanted to use it at the next day, and I don't want to be building high-impedance portable pre-amps. So I decided I'd modify the pedal to work the way I need. It's easy enough to take out all the internal components and swap them for something else, and I already had the kinds of parts I need.
One problem I'm stuck with is the limited mechanical range, I can't do anything about that. It's a limitation of the way the footplate pivots on the base, and the simple linkage that they made from it to rotate the pot shaft. The way to do that better would have been to have a gear on the pot, driven by a toothed piece on the footplate. It would have used more of the pot's range, and given a nice friction feel. That's how geared fader controls traditionally worked on vision mixers. And for the footplate to be mounted higher above the rest of the pedal, so that it could pivot further.
I removed the hi-impedance pots and fitted a medium-impedance 10 ㏀ pot, instead. I decided not to replicate their two-pot expression and minimum-volume-level-preset circuit design, just fitting one pot directly between input and output, and rotated the shaft around to the point it gives a reasonable range of volume control.
This simple change immediately made the pedal work more in the manner I needed. So I believe the low-impedance model would probably work okay, if I could only have bought one. Spurred on by this success, I customised things even further.
I'm only feeding a single mixer channel, so haven't bothered (yet) to build a two-channel circuit, and I only had a spare single-gang pot to experiment with at the time. I decided to make the input accept left and right signals from my piano's stereo headphone output (it has no line outputs), summing them together through two 100 Ω resistors. So changed the input socket from TS (tip & sleeve) to TRS (tip, ring & sleeve). This technique will still accept a mono TS jack input, although it will be loaded down to 200 Ω (through the tip's series 100 Ω resistor joined to the ring's, now, grounded 100 Ω resistor). Alternatively, 1 ㏀ resistors may be a better choice if the pedal was going to be used with headphone and line output sources.
Also, I fitted a transformer on the output to give it a balanced output. This helps reduce noise pick-up over long cable lines when connected to a mixer with balanced inputs, and co-incidentally protects your pots and instrument's output stage from inappropriate phantom voltages being shoved up the cable in its direction (should someone use a phone jack to XLR lead). This also meant replacing the output TS socket with a TRS socket, though you can still plug in unbalanced TS jack cables without any problems.
This configuration worked quite well at home and at a gig. But I don't really need to use an expression pedal on the piano at home. Though it's been interesting using it for some experimentation, such as sending a feed to a reverb unit driving speakers at the other end of the room.
An expression pedal on a piano is somewhat like a soft pedal that stays where you set it, but I can just use the piano's master volume control for quiet practicing at home.
Later on I did make it into a stereo version. Keeping the single TRS socket as the stereo input, splitting its left & right signals to a dual-gang pot, sending to two output transformers, going to two TRS balanced-output sockets. With the TRS output jacks cross-coupled via their internal switch, so that a single lead connected to either output socket gets a mono-sum signal, but dual leads get separate stereo signals.