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Audio Amplifier Characterization With VirtualBench

NI Employee

Hello audio fanatics! I am here to share my experiences with VirtualBench.

Every engineer has a hobby. Mine is building high quality audio amplifiers. I do my best to obtain unique sound performances with every new design.

For those who aren't familiar, audio designs become exponentially more complex and expensive for each level of purity you want to reach. From the AC outlet to the speaker set, there is a long way. So I need to understand what goes on with every section of my design, in order to optimize it.

Traditional instruments take time and lot of calibration before you can use them. You're lucky if your instruments can save data to a USB device. My old instruments did not.   Then I used to manually take notes and use Microsoft Excel to analyze signals, create signal relationships, and more. OK, this is part of my hobby but it is really time-consuming. I could use that time for many other things. Life is too short!

scope_fgen_2.jpg


A month ago, I donated my traditional instruments and started using VirtualBench. VirtualBench has all the instruments I need (Scope, Function Generator, Power Supply, DMM, and more) and takes very small footprint in my home bench.

It does not require warm up to use it and offers superior precision. Definitely a great and clean improvement! See below.


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For quick measurements like checking power supplies, transistor bias, filters, and DC blocking stages, I launch the VirtualBench app that is ready to use.With the laptop with LabVIEW installed, I can automate all the integrated instruments to do a Swept Sine FRF test.


It took me few hours from first unboxing to implement an amplifier characterization test system based on shipped examples, and it takes now 30 seconds to characterize my amplifiers, compared to the previous setup that used to take about two hours with lower precision.

It is also possible to use LabVIEW signal processing and mathematics tools to implement other specific analysis.


From 5Hz to 30KHz I got sweet 29dB gain in this particular amplifier, as flat as +/- 0.5dB.


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I am attaching my version of this VI developed in LabVIEW 2013.

Important: Do not forget to use an appropriate load when testing your amplifier. A precise wirewound power resistor will work (4 or 8 ohm). Be careful with heat dissipation in the load.

Hope this can help other electronic designers too. Thanks NI!

Thank you for looking!

Comments
Member

Great use case Bruno!

Congratulations to the case and to the amplifiers you are developing.

Rodrigo Schneiater
Application Engineering
National Instruments Brazil

If this information was useful, please click in the 'KUDOS!' beside.
NI Employee

Hi Bruno, nice showcase for Virtualbench!

Regards!

Guilherme Yamamoto
Field Marketing Engineer
National Instruments

If this information was useful, please click in the "KUDOS"
NI Employee

Very nice job, Bruno. Great application and VI.

Pedro Ivo da Cruz
Engenharia de Aplicações
Member

Very good Bruno! Great shape obtained to!

NI Employee

I want to listen to the Berlin Philharmonics "Also Sprach Zarathustra" with your amp - through my Sennheiser HD650.

NI Employee

Hi Matthi, I can only agree with you. Great masterpiece of music and headphones indeed. These over-the-ear do their job while attenuating outside noise.

Because of their impedance and power, I would use a headphone amplifier instead, with much lower gain and higher output impedance. There are plenty of vacuum tube designs (or traditional PN based ones) out there that meet these requirements with reasonable costs. We do not want to burn your headphone by plugging in a power stage amplifier Take care!

NI Employee

Do you have a recommendation for a good - not too expensive - headphone amp (preferrably with two ouputs)?

NI Employee

Hello Matthi, you should start looking at Amazon searching for "headphone amplifier". You will find many options ranging from $30 to $300 with user reviews.

My personal recommedation is to choose based on your use: If most of your music collection is digital (FLAC, AAC, or other media) choose a model with integrated DAC, 24bit will give you the best digital experience to hook up on any computer. In the other hand if most of your music collection is analog (Records, Cassettes, Reels, Receiver, Guitar or Mic) you would better buy a regular model with just stereo RCA inputs.

It is my pleasure to help, have fun!