Amplifier for Function Generator needed (500 mA) - Page 1
Forum section: electronics / testgear

author: HighVoltage
author_rank: Super Contributor
timestamp: September 22, 2018, 01:02:24 pm
content: I am looking for a simple amplifier to gain the current output of a Keysight function generator.- Voltage output: 10V PkPk- Current output: 500 mA- Max Frequency: 100 kHzWhat do any of you use?What is of the shelf available?Any recommendations?I found the LPA01 from Newtons4th but what else is available that will not break the bank?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 22, 2018, 01:38:26 pm
content: Almost any audio amp circuit or buffer IC will do.Building, or off-the-shelf, plug and go?Tim

author: HighVoltage
author_rank: Super Contributor
timestamp: September 22, 2018, 01:56:45 pm
content: Thanks, This is for official use and I need an amplifier with datasheet that can be calibrated.So, DIY is not applicable for this project.I just came across the RIGOL PA1011, a 10W Power Amplifier for around $ 400May be this can work.

author: maukka
author_rank: Unknown
timestamp: September 22, 2018, 02:06:42 pm
content: Cheaper alternative but only up to 50kHz:https://www.ebay.com/itm/FeelTech-DC-power-amplifier-module-amp-driver-For-DDS-Function-signal-Generator-/132059122895

author: JohnPi
author_rank: Regular Contributor
timestamp: September 22, 2018, 02:15:50 pm
content: Does anyone have any experience with that one ? Is it current limited ? Is there just a stereo amplifier inside the box ?

author: Kleinstein
author_rank: Super Contributor
timestamp: September 22, 2018, 03:50:03 pm
content: Quote from: JohnPi on September 22, 2018, 02:15:50 pmI don't think they would use a stereo amplifier - more like a mono audio amplifier chip. It may be a more modern one to get at least a reasonable speed and have some protection. For just 50 kHz there is no need to do it different.

author: TurboTom
author_rank: Super Contributor
timestamp: September 22, 2018, 09:19:24 pm
content: What about the EvilAmp?30Vpp and 10A up to 10MHz (probably got to use a PL239 as the output connector...)Just kidding, this would be way beyond your requirements and it's not available as a finished unit. But it may be interesting for some anyway. It's based on ten cascaded LT1210 wideband power opamps that have been matched for offset voltage. The PCB is single sided aluminium substrate. To be able to design the whole unit on a single-sided board, I had to use the substrate (and the underlying heat sink) as the ground plane. That's why there are so many M2 screws holding the assembly down. Each of these screws provides a ground connection. Proper heat sinks are underway and the power supply still needs to be designed. Currently I'm running it off a Lab supply but that's marginal for the substantial power demand of this amp. So far, everything's really looking good and the unit performs as designed. I've got to complete the new PSU soon to be able to test it at full grunt... Once finished, I may publish some more detailed design information in case someone wants to duplicate itCheers,Thomas

author: JohnPi
author_rank: Regular Contributor
timestamp: September 22, 2018, 09:52:34 pm
content: Quote from: Kleinstein on September 22, 2018, 03:50:03 pmThe pictures show OUT+ and OUT-. My guess is that it uses a stereo audio amplifier in a bridge configuration; but I'd like to know how this is configured, and if it works well (ringing, slew-limiting) and if there is short circuit protection.

author: Wolfgang
author_rank: Super Contributor
timestamp: September 22, 2018, 11:33:21 pm
content: Hi,have a look at the Jim Williams Appnote "High Speed Amplifier Techniques".He describes some amps with +/-10V output, frequency from DC to a few MHz and 1A output.Another interesting note is "Gain Stages for Monolithic Amplifiers" by the same author.I built some of those and they are stable and fast.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: September 24, 2018, 04:25:17 am
content: Quote from: TurboTom on September 22, 2018, 09:19:24 pmCool! I could use something like this

author: DaJMasta
author_rank: Super Contributor
timestamp: September 24, 2018, 04:41:18 am
content: Maybe you could find a low frequency, high power RF amp rated for +33dBm output power instead? I don't know of a lot of premade options for this kind of amp, but perhaps one of these inline RF amp modules would qualify for being characterized and otherwise official.

author: TurboTom
author_rank: Super Contributor
timestamp: September 24, 2018, 05:53:47 am
content: Quote from: DaJMasta on September 24, 2018, 04:41:18 amProblem with these RF amps is they don't go down to DC and they are rather limited regarding the load impedance (usually 50 Ohms). If it's got to be something off-the-shelf, @HighVoltage's best chance are probably the mentioned Rigol power amp or it'sSiglent counterpart SPA1010.If a DIY solution would be an option, a single LT1210 will easily match the requirements. The difficulty with the high-power, parrallel solution that I'm conducting is that virtually all the components have to be matched (LT1210's for offset voltage, possibly for impedance at the feedback input and maybe also open loop gain, feedback resistors for very low deviation within one set so the gain of the ten paralleled amps is matched as accurate as possible). Only this way it is possible to use resistive summing up of the outputs (0.33 ohms in series with each output) without much cross currents. Supply voltage has to be very close to the limits for the device (it's planned to use +-17.5V) to reach the desired output voltage swing and it's got to be accurately regulated (probably a switcher with a linear post-regulator)It seems the prototype performs quite well but the project has been on a hold for some time due to other duties. PSU design is a little awkward but I've got some ideas how to get where I want. Since it's a hobby project, something I always wanted to make, I'm not in a hurry and eventually it will be completed. So far, if I need to use the amp for some testing, I simply hook it up to a lab supply and strap it to a larger heat sink and that's it. And one can virtually fry anything attached to it...

author: capt bullshot
author_rank: Super Contributor
timestamp: September 24, 2018, 06:06:08 am
content: There's some amplifiers by Toellner, e.g. the TOE 7607https://www.toellner.de/amplifiers?pf=67&pi=70And the TOE 7741 power function generator:https://www.toellner.de/products?pf=61&pi=65For homebrew stuff, I've made a simple amplifier using the ADA4870 chip.

author: HighVoltage
author_rank: Super Contributor
timestamp: September 25, 2018, 09:00:28 am
content: Thank you all for the suggestions.I most likely will order the RIGOL Amplifier for Euro 400 it seems reasonable and has good specs.I came across another one that also has great specs, made by Clever ScopeCleverscope CS1070-https://cleverscope.com/products/CS1070- 0 - 52 MHz- 1A output current on a 1 Ohm impedance- But the price of 1150 EURO seems steep

author: tautech
author_rank: Super Contributor
timestamp: September 25, 2018, 10:02:59 am
content: Did you miss the mention of this one earlier by TurboTom:https://store.siglentamerica.com/product/spa1010-10-watt-amplifier/Seems a good bit cheaper.

author: HighVoltage
author_rank: Super Contributor
timestamp: September 25, 2018, 10:07:18 am
content: Ohh, thanks, I will have a closer look in to the Siglent SPA1010Which one to trust more, Rigol or Siglent?

author: capt bullshot
author_rank: Super Contributor
timestamp: September 25, 2018, 10:13:52 am
content: Quote from: HighVoltage on September 25, 2018, 09:00:28 amInteresting, looks like a box with the ADA4870 and some clever circuitry inside.

author: tautech
author_rank: Super Contributor
timestamp: September 25, 2018, 10:18:50 am
content: Quote from: HighVoltage on September 25, 2018, 10:07:18 amI've never seen one or had one on my bench so I can only work from the specs and the manual that TurboTom has already linked.You'll work it out to which is the best to suit your needs.

author: HighVoltage
author_rank: Super Contributor
timestamp: September 25, 2018, 10:32:31 am
content: While searching for the Siglent SPA1010, I came across this:Low Cost Function Generator Amplifier DIYhttps://www.dmcinfo.com/latest-thinking/blog/id/9462/low-cost-function-generator-amplifier-diyBased on the OPA541 Audio Amplifier35 V and 10Ahttps://www.digikey.de/product-detail/en/texas-instruments/OPA541AP/OPA541AP-ND/251157

author: 21KUZY073
author_rank: Contributor
timestamp: December 16, 2022, 05:10:03 pm
content: Did you test your amplifier? Bandwidth and so on... Have you some picture from oscilloscope?

author: BeBuLamar
author_rank: Super Contributor
timestamp: December 16, 2022, 06:25:58 pm
content: Quote from: T3sl4co1l on September 22, 2018, 01:38:26 pmAudio amplifier can have bandwidth more than 20kHz but may not reach 100kHz without some loss.

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 16, 2022, 07:35:36 pm
content: Quote from: 21KUZY073 on December 16, 2022, 05:10:03 pmthis is 4 years old thread... what took you so long to ask? today we have few $20 FG buffer from china that can go MHz. i recently built one using basic class AB amplifier that about 0.1dB flatness to 300kHz that i will later aim to be able to source/sink 5-10App current...

author: mawyatt
author_rank: Super Contributor
timestamp: December 16, 2022, 10:48:53 pm
content: Here's a few that are more up to date, just do search and you'll find lots of related discussions.https://www.eevblog.com/forum/projects/precision-opamp-power-stage-to-increase-v-and-i-out/msg4433602/#msg4433602https://www.eevblog.com/forum/testgear/awg-buffer-amp/msg3368650/#msg3368650https://www.eevblog.com/forum/testgear/cheap-diy-high-powervoltage-awg-buffer-amp/msg3449784/#msg3449784https://www.eevblog.com/forum/testgear/hv-buffer-amp-for-awg/msg3623953/#msg3623953Best,

author: gamalot
author_rank: Super Contributor
timestamp: December 17, 2022, 05:17:58 am
content: This post reminds me that I have two OPA549M that I bought on ebay for 10AUD/pc about 5-7 years ago, maybe it's time to test if they are genuine.

author: coromonadalix
author_rank: Super Contributor
timestamp: March 12, 2025, 03:39:45 pm
content: reviving this threadcheck apex products, they have some high voltages op ampsour company want to push an sig gen output to high voltage(s) levels with low current, some variable 50 60 hz ac source ...PA93 PA98 seems very capable ...no affiliation