...and let me specify I'm looking for something to buy (I know, this is DIYAUdio, but I figure there is probably a lot of expertise here). That also means not like $1000 since this is not a big priority, I just want to do some demonstrations. But...this could be a signal generator or something, so long as it can move a woofer cone at very low frequencies.
The reason for response to DC is I want to be able to drive a speaker/loose woofer at very very low frequencies-like 0.1 Hz or such-to actually watch the cone move back and forth. This means I'm not sure of the drive capability, since I haven't done this in a LONG time. I'm guessing even 10 watts is way enough.
Any candidates? Thanks!
The reason for response to DC is I want to be able to drive a speaker/loose woofer at very very low frequencies-like 0.1 Hz or such-to actually watch the cone move back and forth. This means I'm not sure of the drive capability, since I haven't done this in a LONG time. I'm guessing even 10 watts is way enough.
Any candidates? Thanks!
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You can burn the voice coil if it moves too slow, not recommanded.
Any amplifier will respond to even 1 hz, my poor tube amplifiers clearly move the woofer cone at 1hz through the transformer loss.
I would say some dac's and audio source components limit the output below as per design, but not so the amplifiers usually.
Any amplifier will respond to even 1 hz, my poor tube amplifiers clearly move the woofer cone at 1hz through the transformer loss.
I would say some dac's and audio source components limit the output below as per design, but not so the amplifiers usually.
Basic requirements are:
1/ The amplifier must run on split rail supplies (equal + and - rails). Many fit that requirement.
2/ The amplifier must not use a DC servo.
3/ Any feedback and coupling caps need to be removed (shorted).
4/ You may need a means of trimming DC offset due to '3' above.
A simple chip amp such as a TDA2030 should fit the bill and be easily tweakable to work down to DC.
Adding a series output resistor could be a good safeguard as would a low value fuse to protect the speaker.
You only need a couple of volts drive to move a large cone back and forth.
1/ The amplifier must run on split rail supplies (equal + and - rails). Many fit that requirement.
2/ The amplifier must not use a DC servo.
3/ Any feedback and coupling caps need to be removed (shorted).
4/ You may need a means of trimming DC offset due to '3' above.
A simple chip amp such as a TDA2030 should fit the bill and be easily tweakable to work down to DC.
Adding a series output resistor could be a good safeguard as would a low value fuse to protect the speaker.
You only need a couple of volts drive to move a large cone back and forth.
Why would that be? Can't see any reason for that, as long as you respect the max power rating.
Jan
Exactly, the air flux helps cool down the coil. It is not meant stay still and dissipate 20 Watts in the same position under the magnet.
Even with the capacitors and all this filtering I am sure most amplifiers can push under 1hz signal if it is strong enough at the source, even attenuated it should generate something at the amp output.
Even with the capacitors and all this filtering I am sure most amplifiers can push under 1hz signal if it is strong enough at the source, even attenuated it should generate something at the amp output.
The maximum continuous power rating, not some music power nonsense, with some derating because normal ac operation must be pumping air across the coil and changing the air in the gap
Yes got that. The cooling would help. But as others pointed out, this test should not need max power so would be no real problem.
On the use of an ac coupled amp: if the amps's -3dB point sits at, say, 5Hz (not uncommon), it will still reproduce 1Hz but that is 2 octaves lower so 12dB less sensitivity is 4x attenuation.
For this test it should be OK.
Jan
On the use of an ac coupled amp: if the amps's -3dB point sits at, say, 5Hz (not uncommon), it will still reproduce 1Hz but that is 2 octaves lower so 12dB less sensitivity is 4x attenuation.
For this test it should be OK.
Jan
For a lesson showing people how a speaker works. It's very visual when people can see the cone moving back and forth slowly, and then if you have a DC voltmeter &/or oscilloscope. (A strobe can be cool but not the same thing, not so direct of a demo, and the strobes aren't free). I point out how as the cone moves forward slowly it just pushes air around to the back of the cone. This is why you need VERY low frequencies, or people can't actually see the motion.
At a somewhat higher frequency, maybe 60 or 80, I play music through the speaker in free air. I ask "is there much bass" and the reply is "no." Then I stick the speaker onto a shoebox or such which has a hole the size of the speaker. Suddenly, there is more bass!!!! Due to no cancellation and discussion can ensue.
Yes, little chip amps can be used (see post 3) but you are going to have to be prepared to modify one a little. This is because amps with a response to DC are not normally used for audio, they deliberately have capacitive elements in the signal path to prevent the amp going all the way to DC.
This kind of thing. You would need to remove the (short out) the two caps at the left and power it with a suitable dual rail supply.
Kit 20W Circuit Board LM1875T Mono Channel Stereo Audio HIFI Amplifier Module | eBay
This kind of thing. You would need to remove the (short out) the two caps at the left and power it with a suitable dual rail supply.
Kit 20W Circuit Board LM1875T Mono Channel Stereo Audio HIFI Amplifier Module | eBay
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