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Thread: Porter & Davies BC Classic Vibrating Drum Stool System problem

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    Senior Member nevetslab's Avatar
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    Porter & Davies BC Classic Vibrating Drum Stool System problem

    In our Drum Dept Inventory, we have a number of Porter & Davies BC Classic Drum Stools & companion BC-2 Amplifiers to drive them. For those who donít know them, they are a vibrating drum stool, fed usually by the kick drum, either locally using itís mic preamp where you loop the drum mic thru the preamp and on out to the house console, and can dial in the appropriate level where you can feel the kick drum coming up out of the drum stool. Or, it can take a monitor feed from the kick or anything else that has the LF timing of a song.

    We had been using Buttkicker BKA-1000ís and their companion vibration motor-driven stools, though the BC-2 system seems a lot more user-friendly and reliable, though like everything that goes out on tour, they too break down.

    I have one in the shop that had to be put back into working order, and it seemed to work okÖfor about 20 seconds. Sitting on it, feeding it pink noise passed thru a 50hz 1/3 Octave filter yields random amplitude sinewave, with wide min/max dynamicsÖ.14dB or so. Then, the degree of vibration just drops off next to nothing.

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    Internally, thereís a series-parallel lamp array that has PTC thermistor/switches across them between the driving amp and the shaker motor thatís mounted to the wooden base inside the drum stool. Iíve replaced the PTC thermistors with fresh ones from the factory, but still have the same issueÖ.works for about 20 seconds, something must be heating up, and the seat isnít vibrating anymore. The drive signal is still the same magnitude, but watching the AC mains power analyzer, the current draw has dropped way down, reflecting the absence of the higher drive current that had been there before.

    After confirming the amp & the protection lamp/PTC array is all working, by first driving a 4 ohm bass cabinet, and never loosing drive current, then driving a dummy load with the same test signal, watching the waveform, feeling the heat sink temperature continue to rise until it was too hot to leave my hand on it, I began to believe the problem is NOT with the amp system. Gotta be something with the drum stool transducer.

    I put a 1 ohm sense resistor in series with the drum stool transducer, monitored that current with an RMS meter, then monitored the voltage across the transducer with a second RMS meter and manually maintained 10mV across the sense resistor for a 10mA constant current source. The resultant voltage read across the transducer would be the impedance, read in mV / 10. I swept the frequency range from 10hz to 10khz to see what it was. It was a very linear impedance, unlike a loudspeaker where there is the free-air resonance, followed by a wide minimum impedance trough above the free-air resonance, and then continues to climb in impedance in itís inductive range. This started at 4.7 ohms @ 10hz, 5.5 ohms @ 100Hz, 9 ohms @ 1kHz and 34 ohms @ 10kHz, nearly a straight line curve, similar to a shaker table motor impedance.

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    I tried driving it at 1A 50hz, monitoring the voltage across the sense resistor, using a Philips PM2535 system voltmeter, which has a FAST RMS reading mode with a min/max storage system. I only got from 1A down to 970mA over the course of 10 minutes, so that didnít reveal much. I returned to using the 50hz 1/3 Oct pink noise, again using the min/max reading mode, and again, found the drive current dropped off after around 20 seconds. The max voltage out of the amp was over 12V rms, and I got a max current reading of 2.96A, then after it had dropped off, no longer yielding strong vibration, the max reading I got was around 391mA.

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    Finally something being revealed that makes sense. The AC mains current sourcing the BC-2 amp likewise dropped way down from what it was reading when I had full drive current. Seems like there is some internal protection on the seat transducer that isnít working normal. Now waiting to hear back from Tim Porter at Porter & Davies on my findings. We thought for sure it was the PTC thermistors in the lamp array being worn out. Or, something on the power amp or power supply.

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    Butt amp, well now I've seen everything!


    "Motor driven stool" is not a sentence you want to read while having morning breakfast.

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    Senior Member nevetslab's Avatar
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    Quote Originally Posted by drewl View Post
    Butt amp, well now I've seen everything!


    "Motor driven stool" is not a sentence you want to read while having morning breakfast.
    LOL! That didn't dawn on me last night when I wrote the thread.

    Tim Porter's reply this morning was as I had guessed. Though the driver he described being inside the drum throne sounded like the smaller one he had sent a picture of.

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    He requested a photo of the bottom of the seat, and to reach in and unthread the driver he was expecting from the insides of the seat.

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    That wasn't the size of driver I was expecting to find. I'm waiting to hear if this is that larger driver he has made for their seats. I hadn't anticipated getting into the upholstery business to swap out transducers.

    One thing for sure using these seats......better make sure you've had your daily dump before going on stage for a 2 hour set!

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    Supporting Member The Dude's Avatar
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    Quote Originally Posted by nevetslab View Post
    ......One thing for sure using these seats......better make sure you've had your daily dump before going on stage for a 2 hour set!
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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by nevetslab View Post
    LOL! That didn't dawn on me last night when I wrote the thread.

    Tim Porter's reply this morning was as I had guessed. Though the driver he described being inside the drum throne sounded like the smaller one he had sent a picture of.

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    He requested a photo of the bottom of the seat, and to reach in and unthread the driver he was expecting from the insides of the seat.

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    That wasn't the size of driver I was expecting to find. I'm waiting to hear if this is that larger driver he has made for their seats. I hadn't anticipated getting into the upholstery business to swap out transducers.

    One thing for sure using these seats......better make sure you've had your daily dump before going on stage for a 2 hour set!
    So are they on the approved list for breaking up constipation?

    nosaj

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    Senior Member TimmyP1955's Avatar
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    That must be an old seat. The current ones (model 1301TH and 1302TH, depending on I don't know what) have a larger base plate that's green. Remove that and you find the driver - no cloth to remove - mounted with a single center bolt to a piece of plywood that acts as the support for the seat foam. The TT2.8 is the driver that's meant for the P & D BC2 box amp, and the TT6.4 is the driver for the TT6 seat that's meant to be used with standard poweramps.

    Some folks love the P & D, some folks say they don't have enough umph. Instead of the very expensive TT6, the latter group get a Buttkicker "Concert" 2 Ohm driven by one side of a Crown MA3600. The problem with that one is that it mounts well aft of center, so the energy is driven right into the spine. The P & D spreads it out across your bum and your legs, which feels a lot better to me. (If the Buttkicker is mounted under the front of the seat it gets rid of the spinal attack. However you might not be able to father children after a while.)

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    Last edited by TimmyP1955; 12-13-2018 at 03:04 AM.

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    Senior Member nevetslab's Avatar
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    That Gigster seat is their first generation, it turns out. They moved on to TT2.8 & TT6.4 drivers, in a different seat configuration, so we'll have to replace the seat outright. I haven't seen our inventory list on the seats yet. We have the Buttkicker seats as well (with their BKA-1000 amps). I'd guess if we have the more current seats, they'd be the TT2.8 drivers. The driver in this seat that's acting up is doing what they do after they've aged....there's an internal PTC that heats up and drops the vibration level until it cools down. 20 to 30 seconds is about all we're getting out of it before it folds back.

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    I have always thought these types of devices to be very odd. Seems like it is mostly going to be kick drum that comes through them? Is the point for actual monitoring or just to get the drummer to play quieter by making him feel like Bonham even at coffeshop levels? If for actual monitoring is it that the normal monitoring doesn't do enough low freqs?

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    All (most?) musicians can sense music tactilely, not just aurally. I recently saw a platform designed for bassists that contains a transducer. And guitarists, have you ever sat on your cabinet while playing? It's delightful!

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    No thanks.

    Any decent monitor has been enough for me to feel the THUMP of my kick pedals.

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    Quote Originally Posted by glebert View Post
    I have always thought these types of devices to be very odd. - - -
    Me too. In fact, when I first read this thread, I thought that such a device would not improve a drummer's performance or add to the overall band performance. In fact, it may be a distraction to the drummer. Kind of like trying to get some work done with someone who is playing video games on their phone. It may be fun for the drummer but, while the drummer is getting his/her jollies from the seat I suspect that the drumming is not any better and may actually be degraded from the audience's perspective.

    So...some people use a Crown MA3600 to drive the seat? This extraneous equipment brings up the possibility for interesting pranks on the drummer. For instance, feed the seat with a difference source signal. Or add a variable delay between the bass drum mic and the seat amp.

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    Quote Originally Posted by Reader View Post
    Me too. In fact, when I first read this thread, I thought that such a device would not improve a drummer's performance or add to the overall band performance. In fact, it may be a distraction to the drummer. Kind of like trying to get some work done with someone who is playing video games on their phone. It may be fun for the drummer but, while the drummer is getting his/her jollies from the seat I suspect that the drumming is not any better and may actually be degraded from the audience's perspective.

    So...some people use a Crown MA3600 to drive the seat? This extraneous equipment brings up the possibility for interesting pranks on the drummer. For instance, feed the seat with a difference source signal. Or add a variable delay between the bass drum mic and the seat amp.
    Tim Porter was telling me his partner Davies was getting thrown off by the delay in the Buttkicker BKA-1000 and their seat. I hadn't ever set up any of these in the shop with kick drum, mic and mic channel to send it back to the amp to hear/feel what you're playing was IN TIME. I know just a tiny bit of propagation delay in a digital processing chain, getting it back into your head set, or in this case, the drum seat, just totally messes with your head. He couldn't stand the delay in the Buttkicker system, and went on to develop the BC-2 system.

    My church was talking about replacing the bass amp on stage with an active platform so you stand on it and feel your bass instead of hearing it. NOT A CHANCE!! Gotta be able to hear ALL of what I'm playing, which would NEVER pass thru a platform and up into your skeleton for your senses to keep in time.

    Definitely an odd device. I remember hearing a sales pitch from somebody promoting a vibration transducer for the home back in the mid-60's, to make speakers disappear to appease the Mrs, and have the sound come right out of the wall. Sounded terrible, grossly inefficient. I took the amp signal, plugged it into my JBL D130 and blew the socks off that guy, then showed him the door.

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by Reader View Post
    Me too. In fact, when I first read this thread, I thought that such a device would not improve a drummer's performance or add to the overall band performance. In fact, it may be a distraction to the drummer. Kind of like trying to get some work done with someone who is playing video games on their phone. It may be fun for the drummer but, while the drummer is getting his/her jollies from the seat I suspect that the drumming is not any better and may actually be degraded from the audience's perspective.

    So...some people use a Crown MA3600 to drive the seat? This extraneous equipment brings up the possibility for interesting pranks on the drummer. For instance, feed the seat with a difference source signal. Or add a variable delay between the bass drum mic and the seat amp.
    The band I was teching for 2005 tried the new-at-the-time "butt kicker" for the drummer. As far as I'm concerned all it did was add more time to the set up period, and our drummer played terrifically well with or without it. So . . . I s'pose if a drummer wants it, and feels it really does contribute to his performance, then sure why not. Also handy if your drummer needs that kind of feedback, and you really have to keep the volume of his stage monitor low. Otherwise, bolt those butt kickers onto your game chair, movie watching chair, or gang 'em up under seats at special theaters like Universal or Disney to simulate rocket rides & dinosaur footsteps. In the same time frame, I ran across them in use at Las Vegas's Atomic Test Museum, in their simulated A-bomb blast observation theater. Very exciting indeed. Ba-ba-ka-foooom!!! Way kool!

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    I could kind of see it being nice when recording with e-drums to be able to feel something more than what you get through headphones. I actually thought that was the intended application of these.

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    Senior Member TimmyP1955's Avatar
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    It's a small percentage of our clients who ask for one or the other, but some just gotta have it. I'm sure it's nifty when you have a quiet stage with no air being pushed around by speakers.

    We tried the BK amp and it had plenty if umph, but it seemed very source sensitive. When connected to some mixers it was fine. When connected to others it would not power up after completing its start-up self test. (DC offset on the mixer outputs?) An isolation transformer might have fixed that, but between that and the lack of a rack mount kit, we just bought a few more MA3600 beasties over the years.

    (I've been told that Kenny Aronoff uses two Buttkickers on his throne, but I cannot substantiate that.)

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