Hi everyone, I have been visiting this interesting forum for a long time to look for solutions and ideas. Now I'm looking for the schematics to build two types of NON-digital amplifiers. The first of high power (500 - 1000W RMS), the second more modest (10 - 20W RMS and possibly with single power supply), neither of the two amplifiers are intended for listening to the audio, but rather to drive a coil to generate a magnetic field in sine wave to make some experiments with frequencies. The most important thing is the frequency response which should start at 1Hz and go as high as possible (possibly over 100Khz). I have tried searching the internet, but most amps have specs that start at 20 Hz, (though they can probably go lower). Since you are eating amps for breakfast in this forum, I thought you could help me with my research.
Your help will be greatly appreciated.
Thanks
Your help will be greatly appreciated.
Thanks
A single supply amplifier will not work well for this application, due to the several
DC blocking capacitors required.
DC blocking capacitors required.
@FauxFrench,
since I will build the coil the impedance could be from 2 to 8 ohms, let's say 4 to stay average, about the power I still don't know exactly if I will need all 1000 watts, but to lower could be always possible.
@Rayma
I have built a single supply amplifier that works very well for this application, the only problem is that it cut everything below 12Hz, and I just need to go lower, but if you say that the dual supply is mandatory to reach the goal, I will take a look at it.
since I will build the coil the impedance could be from 2 to 8 ohms, let's say 4 to stay average, about the power I still don't know exactly if I will need all 1000 watts, but to lower could be always possible.
@Rayma
I have built a single supply amplifier that works very well for this application, the only problem is that it cut everything below 12Hz, and I just need to go lower, but if you say that the dual supply is mandatory to reach the goal, I will take a look at it.
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Absolutely, without a DC blocking capacitor. You do not want to see how big a DC-blocking capacitors you need to transfer 1000W in 2 Ohm at 1Hz.
The impedance is quite important for the choice of amplifier chip(s) to use if you want 1000W. One very likely candidate is the TDA7293 that can easily be connected in parallel such that the total can handle an impressive current down to 0Hz (DC). You will need quite a heatsink or more likely a good heatsink with a fan. All this is doable. Do you have experience in making DIY amplifiers?
Many amplifier designs are potentially going to work at DC, except that the input network often has a capacitor to block DC, sometimes the feedback network has a DC blocking capacitor. In theory bypassing these components will make a DC amp.
Any amp with a DC servo is problematical, the DC servo acts to drive DC gain to zero. Bypassing such a servo circuit is usually possible, although you have to understand how it works to be confident of doing this right.
Many/most commmercial audio amplifiers have explicit protection against DC (and very low frequency) on the outputs to save loudspeakers in the event of a fault. Again this is something that could be bypassed typically.
Note that an amp not designed for DC may have thermal issues if used directly with a DC offset, as the heat generation is then not shared equally by the output devices - you may have to derate the output power to allow for this.
BTW why not "digital amplifiers"? (do you mean class D by that?)
You don't happen to be a scientist/government spy/submarine communications developer/vlf US defense contractor for shipboard weaponry ?
Dont live by the sea ---beached whales ---no? good but plenty of advice in those areas ---if you can find it.
As FauxFrench says it wont be cheap to build (heavy current demand).
If I am not mistaken VLF transmission was experimented on and equipment built pre-WW2 I am sure Wireless World had patents published in their magazines of that era.
Dont live by the sea ---beached whales ---no? good but plenty of advice in those areas ---if you can find it.
As FauxFrench says it wont be cheap to build (heavy current demand).
If I am not mistaken VLF transmission was experimented on and equipment built pre-WW2 I am sure Wireless World had patents published in their magazines of that era.
Very interesting chip... since you say that can go down to dc, and looking at the datasheet, the minimum supply voltage is +-12V I could try to use it even for the "little" ampli" since I have the supply that is 24V, I could split it.
Because of the switching frequency, that it is not audible, but can be perceived by the body...
And the application is not for VLF transmission, but for generating a closed magnetic field, (although it can transmit), and no... nothing to do with government 🙂
Adapting any audio amplifier for DC or near DC response is quite trivial, assuming you start with a typical directly coupled amp. If you are not capable that nor of designing your own amp then you should buy a commercial laboratory amplifier. Attempting to build an amplifier that you don't completely understand is a recipe for grief and failure.
Lab Amplifier
Lab Amplifier
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Two power supplies SMPS in series are required.
Amplifier chips 3886, 7293 and even 2030, 1875 (with amplification BJT or MOSFET) or in bridge switching are suitable.
It is also necessary to solve the problem of generating an ultra-low-frequency signal.
The switching frequency of a Class D amplifier is effectively filtered with the right design.
The output capacitor (and others) cut the LF response, and would have to be very large,
unreasonably so (well over ten times larger). Even a servo on a dual supply circuit,
would be problematic. You need an all DC circuit, with good input stage DC offset and drift.
There are some, even the Pass F5 for example, for the low power amplifier.
Firstwatt F5 amplifier v3 - diyAudio Guides
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With a minimum supply voltage of +/-12V, you are not going to get 500W even in 2 Ohm. Ohms law apply. Four TDA7293 in parallel can handle 25A so high power is possible, if not in SE-configuration then in BTL-configuration. The power supply may be more expensive than the amplifier itself and eventually constructed with lead batteries.