I am using a second-hand LDS V201 permanent magnet shaker, and would like to use this to test and validate some monitoring equipment. I would like to generate signals suchs as sweep sines, but these do not need to be particularly "clean". I am aware that I need an amplifier to amplify the vibration signals (which we are able to generate) but on contacting the manufacturer, the specific amplifier they recommend (LPA100) costs about £2000. This is above my budget but could stretch to this if necessary.

My questions: What is special about amplifiers for shakers and could I use a less specialised amplifier for this purpose? Is there a "cheap and nasty" way of amplifying my signals?

Specs for shaker and recommended amp attached

Shaker Spec Amp Specs

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    \$\begingroup\$ I think what is special about the amplifier is that the specifications are honest. Driving 5.5A rms into 3.15 ohms continuously is pretty impressive. Don't try to compare that to some audio amplifier that talks about "music equivalent power" or some such nonsense. \$\endgroup\$ – Elliot Alderson Jan 30 '19 at 16:44
  • \$\begingroup\$ Consider a high-power PWM driver. Very efficient. Very "un-clean", with extremely high distortion. However, it is unclear if the shaker could mechanically deal with the high accelerations that would result. \$\endgroup\$ – glen_geek Jan 30 '19 at 16:54
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    \$\begingroup\$ You might be able to roll your own amplifier for less than £2k, but you'd need some real knowledge of what you're doing, much more than we can provide here, and even then you risk getting it wrong and having to replace very expensive parts. Like Elliot says, this is a pretty high-spec amplifier. \$\endgroup\$ – Hearth Jan 30 '19 at 18:17

These amplifiers have a good low frequency response, usually down to DC, which allows testing like the MIL-STD-810 tests that run down to 5Hz, and also shock testing, where a one-sided pulse is applied, and a low ramp in the opposite direction is often used to position the head before the pulse to allow the full travel of the head to be used. If you're only using sine excitation within audio frequencies, a regular audio amplifier would work, though you need to look at the gain variation with frequency - less of an issue if you have a controller that is actively monitoring the EUT amplitude with an accelerometer, but it's not in any case a small amplifier. A pair of car amplifiers in bridge mode might be the cheapest option, because of the limited supply voltage they are generally well suited to driving low impedance loads.

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  • \$\begingroup\$ If DC response is required, it would be wise to de-rate the power amp by at least a factor of two. (200W spec required). A class-B or class-AB output stage's pull-up or pull-down transistors would have to take all the power. For audio use, this power is shared pretty much equally. To prevent slewing distortion, a power amp may have to have some reserve current/voltage - although this "unclean" response seems acceptable by OP. \$\endgroup\$ – glen_geek Jan 30 '19 at 17:00
  • \$\begingroup\$ Thanks for the clarification. That's good news, sounds like an audio amp will be fine for me. Why would I need 2 car amplifiers in bridge mode rather than a single amplifier in bridge mode? Is this simply to increase power? \$\endgroup\$ – Sam L Jan 31 '19 at 16:20
  • \$\begingroup\$ Yes - the output voltage swing available on a single amp would not be able to drive the full power through the coil. These shakers really are nothing more than a heavy duty speaker coil, the rep for one of the systems we had, demoed them by playing Springsteen through them.... Many 2 channel amplifiers have a bridge switch that just feeds an antiphase signal to the second channel. \$\endgroup\$ – Phil G Jan 31 '19 at 17:21

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