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Can I Bench Test an Integrated Amp with Just the FNIRSI 2D15P? | Review Part 2 ~ Real World Testing

Novalux Stereophonic

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FNIRSI sent me this 2D15P free of charge in return for an honest assessment.

Patreon - Learn Audio Repair Differently:
https://novaluxstereophonic.com/join-...

As an Amazon Associate, I earn from qualifying purchases at no additional cost to you. The affiliate links below may include products featured in Amazon promotional campaigns.

🛒 FNIRSI 2D15P Oscilloscope / DMM
https://amzn.to/4dA43hj

🛒 Related tools and accessories:
https://amzn.to/4ftmV41

If you are interested in load testing amplifiers, consider building this simple 8 ohm stereo dummy load.

Build Video:
Build This Simple 8 Ohm Audio Dummy Load f...

Make sure to check the build video description for additional upgrade videos.

Real World Tutorial:
How to Bench Test Amplifiers Using a Dummy...

In Part 1, I covered the technical features, interface, and limitations of the FNIRSI 2D15P.

Part 1 Video Link:
This One Tool Can Start Your Audio Repair ...

In this follow-up video, I put the 2D15P to work in a real bench-testing scenario to see how far a beginner can realistically go using just this one device.

For Part 2, I attempt to fully bench test a vintage Sansui AU-20000 integrated amplifier using only the FNIRSI 2D15P, a dummy load, and basic cables — no full bench of test gear. The goal is to answer a simple question:

Can a beginner meaningfully troubleshoot and evaluate an audio amplifier with this tool alone?

What’s covered in this video:
Initial inspection and safe power-up of an unknown amplifier
Separating and testing the preamp and power amp sections
Using the 2D15P to: Inject test signals, compare left/right channel behavior, Identify dirty controls and switching issues
Square-wave testing of tone controls and filters
Phono stage verification using low-level square waves
Use of an inverse RIAA network to validate phono stage frequency response
Power amplifier testing into dummy loads
Output voltage measurement and power calculations
Identifying the limitations of the built-in sine wave generator
Verifying results with a standalone bench signal generator

Key takeaways:

The FNIRSI 2D15P performs very well for preamp and phono stage testing, especially when using square waves. It makes it easy to:
Compare channels
Spot control issues
Verify overall signal flow
Perform meaningful diagnostic work as a beginner

Where the device falls short is standalone power amplifier testing. The internal sine wave generator lacks the cleanliness and fine amplitude control needed to accurately detect clipping and channel balance at rated output power. In this case, a dedicated signal generator is still required for precise power amplifier evaluation.

Final thoughts:
While I wasn’t able to perform a complete amplifier bench test using only the 2D15P, I came surprisingly close. For someone just starting out in audio repair, this device covers a lot of ground at a reasonable price, with an intuitive interface, solid oscilloscope and DMM functionality, and excellent usability.

As long as you understand the limitations of the signal generator — and plan to add a standalone generator later — the 2D15P remains a strong beginner tool.

Chapters:
00:00 Introduction
00:32 Visual Inspection of the AU-20000
01:29 Setting Up the 2D15P For Audio Testing
03:20 Separating the Preamp & Power Amp for Isolated Testing
04:29 Preamplifier Testing
09:09 Affiliate Link Call Out
09:24 Phono Stage Testing
13:01 Power Amplifier Testing
29:07 Does the D215P Pass the Test? Summary of Results
32:29 Closing Thoughts

YTL086

20 Comments

@NovaluxStereophonic Creator 9 months ago (edited) Pinned

:_Rocket: FNIRSI sent me this 2D15P free of charge in return for an honest assessment.

:_Novalux: Patreon - Learn Audio Repair Differently:
https://novaluxstereophonic.com/join-comment

:_Waveform: Links to products featured in this video can be found in the description.

@philmagnotta5553 6 months ago

Very well done. Natural naration, instead of the constant removal of any/all natural space between words, sentences, etc. Pleasant, sure-footed, honest.

@dirtydon8661 8 months ago

That’s how my bench always looks when I’m testing. No worries. That all in one scope, dmm & gen is tight.

@RanTausi 9 months ago

Hi again, thanks for doing the sec video. Watching now ❤

@EMTdrummer 3 months ago

Firstly, I love this channel... thanks for the attention to detail! Just a thought.... by using a splitter to divide the signal generator output to two channels, you also divide the amplitude which may have contributed to the stepped output issue you discussed... thanks! Dave

@newtechgs7471 9 months ago

What a glorious amp

@Doc_Rocks 3 months ago

As a beginner in this area, I have the Fnirsi 2D15P unit, and being an old fart, I also have a superb AWA Ultra Low Distortion Oscillator G233 - a good old analog sine wave generator. No digital stepping on this one! I have this unit from about 40 years ago, when I was learning how to measure Harmonic and IM distortion using Heathkit distortion analyzers that I built. Sometimes, the old stuff is the good stuff! Very impressed with your narration, that actually has breathing spaces in it, unlike so many channels that edit out every breath so that the watcher becomes breathless trying to take it all in. Duly subscribed - thank you :)

@BobWilson84 9 months ago

Good timing Ben, there’s a AU20k on the bay calling my name! I had to laugh while you made the jumpers for the dummy loads and test leads. It’s 180 out of phase from your ultra fancy patch panel! Great video and a handy little device.

@andyandy4306 9 months ago

Great video… I bought it…I just don’t do as much device checking you do and I’m also a beginner

@jcbritobr 9 months ago

Nice review. Thanks to point the issue in signal generator. Its a nice device yet.

@Richard110173 6 months ago

Perhaps it's a good idea to add an attenuator after the tone generator. That would give you weak signals with higher resolution. For beginners, that seems like a reasonable solution to me. (Or just a potentiometer with, perhaps, an op-amp amplifier.)

@pauledwards2746 3 months ago

Thanks for all the reviews you provide, they are very helpful. Any idea how long the battery life is? Also, are the probes isolated?
Looks like it may be a useful tool for quick field evaluations. The 4.3" screen is better than a smaller handheld. I'm sure this has an 8bit ADC and with the sampling rate the signals aren't going to be very clean so probably not good for any low level noise tracing. But for the price I guess it's not bad. Since the signal generator isn't good at low levels it probably would not work for me. I have a 1968 Fender Super Reverb guitar amplfier (40 watt, 6L6 output tubes) that I'm going to recap and wanted something to test it with after the recap. The input sensitivity for the amp is 1.5V to drive to max output so I need a signal I can vary from 150mv to 1.5. I already have several DMM so I don't need the DMM functions. So at this price point and my needs I would be better off spending more and buying a scope with a 7" display and better specifications. A 70 Mhz digital scope with a 12bit ADC would allow pretty good signal resolution.

@jeremyvonk6853 5 months ago

I stumbled onto your channel while I was looking for reviews of the FNIRSI gear. Your videos are very well done, and your presentation style is great! I'm off to dig through your content to see if I can find anything to help me with my Yamaha CR-620.

@jjptech 7 months ago

Can you make a video on a cheap Signal Generator? I found the TSG3020, maybe that could replace the onboard of the 2D15P and in that way we don't risk any short circuit.

@gunnervine 7 months ago

as a new guy i bought this knowing the flaws. will look at separate signal generator if i get more into the hobby. look forward to a review on their new standalone signal gen. sadly the 2D15P is not available on amazon in australia yet or i would have used your referral. had to order from aliexpress.

@SRSnure 8 months ago

Thank you very much for this review. It's exactly what I was looking for as I'm in the market for an oscilloscope. I particularly appreciate your real-world testing scenario and honest comments. While, for the price, this looks like a very capable device, in addition to the signal generator's shortcomings, I observed that you frequently had to press/adjust several buttons to view and measure the desired data, which would be mitigated with individual test components. For me, at least, I think constant button pushing would get old fast.

That said, specifically for an oscilloscope for testing vintage audio equipment, would you recommend an older, but high-quality scope like a "Tektronix TDS 3012 Color Digital Phosphor Oscilloscope" (available on eBay for <$300) or a new unit something like a "Siglent Technologies SDS1202X-E ($379)" or "Hantek DSO2D15 ($233)"? FYI: I had analog tech training in the early 1970s, but I definitely need a refresher on proper troubleshooting techniques. I plan to repair and restore (re-cap, tune, etc.) analog audio gear from the 70s/80s for my own enjoyment, but want to keep my test equipment investment modest, yet would like it to be reliable.

@Andre-Ocara 2 months ago

Como é a questão de bateria dele? Tem postagens que afirmam que a bateria com o aparelho em modo osciloscópio dura em média, 2 horas em uso continuo. Conseguiu testar a capacidade da bateria?

@wb7ond 6 months ago

Why the square wave assumes those shapes with the tone controls, and phono input. The square wave consists of infinite number of odd harmonics. The highest frequency harmonics are contained in the rising edge, the lows along the top flat top of the square wave. Notice the tall peaks when the (treble) is increased due to the amplification of the higher frequencies that make up the square wave. The rounded corner and slope to the flat is the loss of highs and increase of low frequencies (bass). The bass and treble are working when they distort the appropriate parts of the square wave. Midrange should show normal undistorted square wave. The phonograph record requires special RIAA filtering due to the techniques used to emboss the sound onto the vinyl. To reproduce the sound, special filters manipulate the frequencies so they have proper pleasing high fidelity sound. When he puts the RIAA device in series with the phono input, he is attenuating the frequencies opposite those attenuated in the phono input, and greatly increasing the drive signal. Now with all the frequencies attenuated at the same amounts, you return to the "normal" square wave. You can see the RIAA device schematic on HagTech website.. Understanding why the square wave assumes these shapes allows you to employ the square wave for other testing techniques and predict the o'scope display...

@udosoft-r5i 6 months ago (edited)

If you have some resisitor by hand or better a potentiometer, you could turn up the sg and attuniate the signal down to be used to feed power amp? And a potentiometer and the needed extra wiring is let less cost than an extra sg...