High Power Amplifier - Page 1
Forum section: electronics / testgear

author: steaky1212
author_rank: Regular Contributor
timestamp: September 20, 2017, 02:55:41 pm
content: Hi,This is probably going to be fairly niche, but here goes...I currently have a product that I drive a 200Hz signal 12Vpkpk into a 70R load. I need to do some extended lifetime tests whereby I overdrive this, but I don't have the capability.I would be looking at AT LEAST 4x the input voltage. What sort of amplifier would I need?Audio ones are only for low impedances (8-16R), and most RF ones seem to spec a much higher minimum frequency.Thanks,Steaky

author: edavid
author_rank: Super Contributor
timestamp: September 20, 2017, 03:00:56 pm
content: Quote from: steaky1212 on September 20, 2017, 02:55:41 pmYou are misunderstanding the specifications, audio amplifiers work fine into a higher impedance load. Just get a big audio amp, or a less big audio amp and a big stepup transformer.

author: b_force
author_rank: Super Contributor
timestamp: September 20, 2017, 03:01:33 pm
content: The fact that audio amplifiers are only for 8-16 ohm doesn't mean they can't be used for higher impedance.In fact, the impedance of a loudspeaker can easily reach 70ohms.So if I understand you well, you need an amplifier which can deliver 4*6=24Vpeak (48Vpkpk).There are plenty of amplifiers capable of doing that.Depending on the circuit you can even go for a bridged amplifier.(depending if you want to measure things)With 24Vpk (=17 Vrms) at 70ohm you only need to have around 4Wrms or 8Wpeak

author: nfmax
author_rank: Super Contributor
timestamp: September 20, 2017, 03:03:14 pm
content: An audio power amplifier will have no trouble at all with a 70? load. The power rating is usually 'Watts RMS' (!) into 8?, so you should find a 70W to 100W amplifier more than adequate. But buy a good quality, (semi-) pro one, rather than a cheap domestic receiver type, which is unlikely to take kindly being driven continuously over an extended period.

author: David Hess
author_rank: Super Contributor
timestamp: September 20, 2017, 05:05:02 pm
content: Quote from: steaky1212 on September 20, 2017, 02:55:41 pmI am not sure if you mean 12 volts peak into 70 ohms or 6 volts peak into 70 ohms but the former is 170 milliamps peak and the later is 85 milliamps peak.A small audio amplifier can handle it easily. So could an operational amplifier with a simple external two transistor class-B emitter follower output stage. There are some power operational amplifiers which could be used also.

author: _Wim_
author_rank: Super Contributor
timestamp: September 20, 2017, 08:02:14 pm
content: You could also use a Kepco power supply. The BOP-series and BHK-series (using the back terminals) can be wired as an amplifier (probably many other models also) from DC to (for some) 20kHz. And off course you can use them as a normal power supply also.I have a BOP-36-5 and a dummy load that can be wired for 70 ohm. If you want me to test something to see the dynamics, feel free to ask.This one might be interesting to you (identical model as I have):http://www.ebay.de/itm/Bipolares-Labornetzgerat-m-Leistungsverstarker-von-KEPCO-BOP-Spannung-36V-5A-/232491699716?hash=item362195ce04:g:h5UAAOSwhYdZviQhEdit: missed the fact that you needed at least 4x input voltage, so this +-36 supply will not handle that. But there are lots of other choises..

author: _Wim_
author_rank: Super Contributor
timestamp: September 20, 2017, 08:08:06 pm
content: P.S: do not buy such a supply if you like "quiet" instruments, these contain very noisy fans...

author: shteii01
author_rank: Frequent Contributor
timestamp: September 21, 2017, 09:29:45 am
content: Um... LM386 works with speakers that are 4 to 32 Ohm. I am actually going to wire one to 32 Ohm 0.5W speaker. So that 16 Ohm thing is something that you are imposing on yourself.