stereo amplifier

[lou123]

Hi everyone- I have an LDS v101 electromagnetic shaker. The recommended power amplifier to run it is the PA25E from LDS, which is now sold by Bruel and Kjaer and is far too expensive for me to buy.

I am looking for a cheap alternative amplifier that will run the shaker, I have been advised that if I match the impedance then a normal stereo amplifier would do the job.

Can anyone advise on this and the spec that the amplifier would need? and perhaps even recommend a cheap model that would do? I attach a picture showing the spec of the recommended amplifier, and the details of the v101 shaker.

Help much appreciated!

 

[BobK]

The impedance of the device is shown as 3 Ohms. The kind of amps people us in car stereos for the subwoofers can typcially drive down to a 2 Ohm load, so I think you should look at these as a cheap solution. You would need to provide 12V power which you can also get fairly cheaply.

Bob

 

[lou123]

Thank you very much for your prompt reply! Do you mean this type of thing? The Kicker DX Series Amplifier, 1 x 250W from Halfords:


http://www.halfords.com/webapp/wcs/...uctId_823881_langId_-1_categoryId_265874#tab2


My concern is that I might damage the electromagnetic shaker since its a very expensive piece of kit. I have a 12V desktop power supply already which I suppose would do the trick.

 

[BobK]

I misspoke when I said to get a subwoofer amp. This one, at least, filters out everything above 200Hz, so that is not good. You just want a full-range amp. Try to get one that does not have that much power since the suggested amp only has 45W.

Any audio amp that can drive a 2 Ohm load would be okay.

Bob

 

[lou123]

Hi Bob, sorry to post again- I think I've found two that are suitable:

http://www.jlaudio.co.uk/xd200-2-car-audio-xd-amplifiers-98260
http://www.powerbassusa.com/xax-2160fd-2-ch-mini-amp

I can't seem to find any that are lower than 100W at 2 ohms, only ones that are not full range. Of the two I am in favour of the JL Audio one since it goes down to a slightly lower frequency. Can you confirm that this might be ok? Do you think hooking one of these up to the shaker would be a complicated job?

 

[KrisBlueNZ]

Hi Lou. I'm not Bob, but I'll answer now and Bob can correct me if necessary.

I think either of those amps will be fine. You will want to disable any low-pass or high-pass filtering, and you'll need a 12V DC power supply that can provide a few amps. Since you won't be running the amps (edit: I mean amplifiers, not amperes) anywhere near their limit, your power supply won't have to meet the full requirements specified by those amplifier makers.

 

[lou123]

Thank you very much for the advice

 

[lou123]

Hi- so I purchased the amplifier and it works well with the shaker so I am very pleased. The shaker manufacturer recommends that I limit the current going to the shaker at below 1.5 amps. They also told me to stick below 10V, which I am doing.

My question is, how do I limit the amps going to the shaker? There doesn't seem to be a setting on the amplifer to do this and I am worried about damaging the kit. To be honest i'm not even sure how to measure the amps going to the shaker with a multimeter!

I am running it all from a 12V car battery. The link below shows details of the amplifier, and the v101 shaker details are in the first message of this thread.

http://www.jlaudio.co.uk/xd200-2-car-audio-xd-amplifiers-98260

Any help appreciated, I will post this in the main forum too in case you don't see it!

 

[KrisBlueNZ]

Hi- so I purchased the amplifier and it works well with the shaker so I am very pleased. The shaker manufacturer recommends that I limit the current going to the shaker at below 1.5 amps. They also told me to stick below 10V, which I am doing.

Great!

My question is, how do I limit the amps going to the shaker? There doesn't seem to be a setting on the amplifer to do this and I am worried about damaging the kit. To be honest i'm not even sure how to measure the amps going to the shaker with a multimeter!

I guess, with a fast-blow fuse. The main reason would be to protect the shaker against a fault in the amplifier (or the signal generator that feeds it).

Personally what I would do is this. Put a fuse in series with the feed from the amplifier to the shaker. Start with a 1A fuse. (Always use fast blow fuses.) Run the shaker with a heavy load, and at maximum amplifier output and maximum battery voltage. If the fuse blows, go to the next rating upwards, and repeat until the shaker runs continuously with maximum load and maximum amplifier output and maximum battery voltage. Then optionally go to the next fuse rating upwards again, in case the fuse rating you're using is borderline. At least, keep some spare fuses ready that are rated higher than the rating you're using.

I'd expect that the shaker will draw more current as it gets older, as various parts deteriorate slowly. So you may need to increase the fuse rating at some stage in the future.

I will post this in the main forum too in case you don't see it!

Don't do that. It's part of this thread. Perhaps a moderator will merge them.

 

[lou123]

Hi, thank you for your reply

I fitted a fuse in series. A 1A blew straight away and I now have a 1.5A quickblow in, and its running fine. I also measured the current with an avometer in series, it seems that the shaker is drawing less than 600 mA current at all frequencies, so i'm not entirely sure why the 1A fuse blew. Also I expected the shaker to draw more current when playing lower frequencies than high, but it seems they are roughly the same. But anyway, better safe than sorry with the 1.5A fuse i guess.

Feeling a lot more confident that i'm not going to damage the shaker now at least!

 

[KrisBlueNZ]

Great! Nice work