# QA401 **URL:** https://forum.quantasylum.com/c/qa401/7.md [Latest](https://forum.quantasylum.com/latest.md) · [Categories](https://forum.quantasylum.com/categories.md) --- ## [About the QA401 category](https://forum.quantasylum.com/t/about-the-qa401-category/16)
**Author:** [@matt](https://forum.quantasylum.com/u/matt)\ **Replies:** 0
Discussion related to the QA401 Audio Analyzer. --- ## [Measuring noise](https://forum.quantasylum.com/t/measuring-noise/53)
**Author:** [@handsome](https://forum.quantasylum.com/u/handsome)\ **Replies:** 8\ **Last updated:** [October 26, 2026, 2:24pm UTC](https://forum.quantasylum.com/t/measuring-noise/53 "2026-10-26T14:24:28Z")
HI there, I am thoroughly enjoying using my QA401 - great hardware! I would like to know what are the best parameters for measuring/quantifying amplifier noise? I prefer unweighted measurements and use a 20-20 000Hz b… --- ## [Noise and Root Hz (RtHz) Display Options](https://forum.quantasylum.com/t/noise-and-root-hz-rthz-display-options/152)
**Author:** [@matt](https://forum.quantasylum.com/u/matt)\ **Replies:** 3\ **Last updated:** [July 26, 2026, 7:06am UTC](https://forum.quantasylum.com/t/noise-and-root-hz-rthz-display-options/152 "2026-07-26T07:06:55Z")
This is an elaboration for a question sent to support since it’s easier to post graphics here: You often hear people talking about the “noise floor” of their measurement. And when the report it, they kind of eyeball the… --- ## [Measuring Compressor Response](https://forum.quantasylum.com/t/measuring-compressor-response/73)
**Author:** [@matt](https://forum.quantasylum.com/u/matt)\ **Replies:** 5\ **Last updated:** [October 24, 2025, 3:44pm UTC](https://forum.quantasylum.com/t/measuring-compressor-response/73 "2025-10-24T15:44:45Z")
A customer writes wondering how to measure a compressor transfer response for compressor output versus input response. That measurement can be made with the AMP Gain and Distortion plug-in, shown in the plug-in menu here… --- ## [Reloading FR Traces into GraphTool](https://forum.quantasylum.com/t/reloading-fr-traces-into-graphtool/131)
**Author:** [@handsome](https://forum.quantasylum.com/u/handsome)\ **Replies:** 5\ **Last updated:** [October 7, 2025, 2:32pm UTC](https://forum.quantasylum.com/t/reloading-fr-traces-into-graphtool/131 "2025-10-07T14:32:04Z")
Hi Matt, Is there any way to load a FR trace into graph tool without having to run a sweep first? Whenever I load a saved FR trace, the X-axis displays as linear? --- ## [QA401 Right Channel Noise Problem?](https://forum.quantasylum.com/t/qa401-right-channel-noise-problem/244)
**Author:** [@Buckskin](https://forum.quantasylum.com/u/Buckskin)\ **Replies:** 21\ **Last updated:** [August 22, 2025, 3:47am UTC](https://forum.quantasylum.com/t/qa401-right-channel-noise-problem/244 "2025-08-22T03:47:59Z")
I just finished building a pre amp and decided to get some measurements from my QA401. All seems well, except the right channel is showing significantly more noise than the left. After much swapping of cables, I think … --- ## [Problem measuring notch filter](https://forum.quantasylum.com/t/problem-measuring-notch-filter/363)
**Author:** [@ceulrich](https://forum.quantasylum.com/u/ceulrich)\ **Replies:** 15\ **Last updated:** [January 28, 2025, 5:31pm UTC](https://forum.quantasylum.com/t/problem-measuring-notch-filter/363 "2025-01-28T17:31:23Z")
I am new to this forum, so if this post blows up, please bear with me. I am working with a 1 KHz passive notch filter. The design is based on the Hall Network as described in a paper by Kuhn (https://www.kennethkuhn.co… --- ## [THD+N calculations for tones less than 100Hz?](https://forum.quantasylum.com/t/thd-n-calculations-for-tones-less-than-100hz/1466)
**Author:** [@chrichap](https://forum.quantasylum.com/u/chrichap)\ **Replies:** 15\ **Last updated:** [July 23, 2024, 5:12pm UTC](https://forum.quantasylum.com/t/thd-n-calculations-for-tones-less-than-100hz/1466 "2024-07-23T17:12:55Z")
Hi Matt, While measuring some class-D subwoofer amplifiers with my QA401, I noticed that when I use a tone less than 100Hz, the THD+N calculation seems to omit the THD components, leading to measurements where THD appea… --- ## [QA401 on MacBook Pro M3 parallels](https://forum.quantasylum.com/t/qa401-on-macbook-pro-m3-parallels/1294)
**Author:** [@Pgamb](https://forum.quantasylum.com/u/Pgamb)\ **Replies:** 2\ **Last updated:** [March 14, 2024, 8:06am UTC](https://forum.quantasylum.com/t/qa401-on-macbook-pro-m3-parallels/1294 "2024-03-14T08:06:50Z")
Hi All, is there a way to have the QA401 working on MacBook Pro M3 parallels (Win 11 pro)? the software works but the usb drivers are not installed properly and there is no communication with the device (other USB perip… --- ## [Where is the phase curve on frequency response?](https://forum.quantasylum.com/t/where-is-the-phase-curve-on-frequency-response/1252)
**Author:** [@jipihorn](https://forum.quantasylum.com/u/jipihorn)\ **Replies:** 4\ **Last updated:** [February 27, 2024, 7:53pm UTC](https://forum.quantasylum.com/t/where-is-the-phase-curve-on-frequency-response/1252 "2024-02-27T19:53:06Z")
Hello, I got a QA401 and try to use it, but I have some problems I can not solve. The ergonomics are weird, especially as I’m used to Audio Precision stuff. I’ve been trying to get frequency response for tuning a regul… --- ## [QA401 max input voltage relative to ground?](https://forum.quantasylum.com/t/qa401-max-input-voltage-relative-to-ground/1175)
**Author:** [@gvl](https://forum.quantasylum.com/u/gvl)\ **Replies:** 4\ **Last updated:** [January 16, 2024, 5:16am UTC](https://forum.quantasylum.com/t/qa401-max-input-voltage-relative-to-ground/1175 "2024-01-16T05:16:15Z")
Max input voltage for the QA401 is spec’d at 26dBV with the attenuator enabled or 6dBV without. I understand this is the voltage across the +/- inputs. What is the max allowed voltage on inputs relative to the analyzer g… --- ## [Measuring high voltages using a scope probe. Safely](https://forum.quantasylum.com/t/measuring-high-voltages-using-a-scope-probe-safely/1049)
**Author:** [@Chicago](https://forum.quantasylum.com/u/Chicago)\ **Replies:** 13\ **Last updated:** [January 7, 2024, 10:14am UTC](https://forum.quantasylum.com/t/measuring-high-voltages-using-a-scope-probe-safely/1049 "2024-01-07T10:14:00Z")
I have built an “oscilloscope emulator” front end for my QA401 that: Provides the AC line 3rd prong ground connection that all scopes provide Properly terminates oscilloscope probes at both AC & DC (one Meg + the usua… --- ## [QA401 Programming Commands](https://forum.quantasylum.com/t/qa401-programming-commands/267)
**Author:** [@ggorman](https://forum.quantasylum.com/u/ggorman)\ **Replies:** 11\ **Last updated:** [November 23, 2023, 1:54pm UTC](https://forum.quantasylum.com/t/qa401-programming-commands/267 "2023-11-23T13:54:41Z")
It seems very easy to control the 401 with tractor but what about a list of commands like most all other lab equipment manufactures have. I’ve done lab automation for years but I do not see anything straight forward he… --- ## [QA401 input stage question](https://forum.quantasylum.com/t/qa401-input-stage-question/1018)
**Author:** [@Chicago](https://forum.quantasylum.com/u/Chicago)\ **Replies:** 4\ **Last updated:** [September 26, 2023, 6:34pm UTC](https://forum.quantasylum.com/t/qa401-input-stage-question/1018 "2023-09-26T18:34:21Z")
Hey there Matt, hope all is well. Question about the analyzer input impedance. 100K @ AC and an open circuit at DC, correct? Thanks! --- ## [measure input max](https://forum.quantasylum.com/t/measure-input-max/969)
**Author:** [@jumpod](https://forum.quantasylum.com/u/jumpod)\ **Replies:** 2\ **Last updated:** [August 11, 2023, 5:27am UTC](https://forum.quantasylum.com/t/measure-input-max/969 "2023-08-11T05:27:44Z")
I want to measure input headroom at 1Khz how many dBUs does a measuring device such as an isolator have to do? --- ## [Where is add measurement in QA1.92](https://forum.quantasylum.com/t/where-is-add-measurement-in-qa1-92/967)
**Author:** [@pwm](https://forum.quantasylum.com/u/pwm)\ **Replies:** 2\ **Last updated:** [August 8, 2023, 7:33pm UTC](https://forum.quantasylum.com/t/where-is-add-measurement-in-qa1-92/967 "2023-08-08T19:33:38Z")
Where can I add a measurement in QA1.92? I would like to add a power measurement with a specific load impedance. --- ## [Noise spectral density measurement](https://forum.quantasylum.com/t/noise-spectral-density-measurement/914)
**Author:** [@1audio](https://forum.quantasylum.com/u/1audio)\ **Replies:** 2\ **Last updated:** [July 2, 2023, 8:32pm UTC](https://forum.quantasylum.com/t/noise-spectral-density-measurement/914 "2023-07-02T20:32:15Z")
Matt added the V/rtHz capability to the UI some time ago, possibly from my request. I just had the need to use it and ran into some confusion. I believe it will work the same in the later versions as well. I have two wa… --- ## [QA401 DC voltage at inputs?](https://forum.quantasylum.com/t/qa401-dc-voltage-at-inputs/726)
**Author:** [@rjmmusic](https://forum.quantasylum.com/u/rjmmusic)\ **Replies:** 7\ **Last updated:** [February 8, 2023, 8:03am UTC](https://forum.quantasylum.com/t/qa401-dc-voltage-at-inputs/726 "2023-02-08T08:03:49Z")
In the process of debugging and measuring a circuit of mine, I discovered that my QA401 is leaking DC out of its inputs, which is a bit surprising. The left + input is reading about 0.38V from tip to ground, and the righ… --- ## [QA401 UI Recommendations](https://forum.quantasylum.com/t/qa401-ui-recommendations/763)
**Author:** [@M2Circuits](https://forum.quantasylum.com/u/M2Circuits)\ **Replies:** 2\ **Last updated:** [December 14, 2022, 8:39pm UTC](https://forum.quantasylum.com/t/qa401-ui-recommendations/763 "2022-12-14T20:39:51Z")
I’ve had the QA401 for a few years now and have been enjoying it. However, there are still some things that I would like to recommend for the UI of the software. I wish that there were some more options for the graphs l… --- ## [Notch Filter Hardware REVC](https://forum.quantasylum.com/t/notch-filter-hardware-revc/60)
**Author:** [@matt](https://forum.quantasylum.com/u/matt)\ **Replies:** 11\ **Last updated:** [October 18, 2022, 6:20pm UTC](https://forum.quantasylum.com/t/notch-filter-hardware-revc/60 "2022-10-18T18:20:08Z")
In a previous post (here) a new oscillator and notch filter were discussed as a tool for the lab. The third revision of the board has been built and measured. This post documents the measurements of new board. Please rea… --- ## [SMPTE IMD (mental problem)](https://forum.quantasylum.com/t/smpte-imd-mental-problem/745)
**Author:** [@bklein](https://forum.quantasylum.com/u/bklein)\ **Replies:** 2\ **Last updated:** [October 6, 2022, 6:27pm UTC](https://forum.quantasylum.com/t/smpte-imd-mental-problem/745 "2022-10-06T18:27:39Z")
The SMPTE IMD approach is described in the QA401 manual as well as in the QA40x and IMD Measurements dedicated report. I am having mental trouble comparing the two examples and then addressing the method to my test plat… --- ## [BNC to RCA adapters](https://forum.quantasylum.com/t/bnc-to-rca-adapters/549)
**Author:** [@anchan](https://forum.quantasylum.com/u/anchan)\ **Replies:** 6\ **Last updated:** [September 13, 2022, 12:10am UTC](https://forum.quantasylum.com/t/bnc-to-rca-adapters/549 "2022-09-13T00:10:12Z")
Hello, I’m still using a QA400 on a windows 7 machine. Waiting patiently to upgrade to the 403. It’s a great piece of gear! Anyway, my question: Is it ok to use regular bnc to rca connectors like below to measure the o… --- ## [Attenuator for high RMS signal tests](https://forum.quantasylum.com/t/attenuator-for-high-rms-signal-tests/569)
**Author:** [@Fralippo](https://forum.quantasylum.com/u/Fralippo)\ **Replies:** 3\ **Last updated:** [August 2, 2022, 1:19pm UTC](https://forum.quantasylum.com/t/attenuator-for-high-rms-signal-tests/569 "2022-08-02T13:19:53Z")
Hello everybody, this is my first post on the QA forum about my great QA401 analyzer. I’m an italian audio tube DIYer and, although I had been told that it was not created to be used for high voltage devices, I bought i… --- ## [Measure HV Power Supply Ripple & Noise](https://forum.quantasylum.com/t/measure-hv-power-supply-ripple-noise/186)
**Author:** [@dbotich](https://forum.quantasylum.com/u/dbotich)\ **Replies:** 10\ **Last updated:** [May 23, 2022, 10:05pm UTC](https://forum.quantasylum.com/t/measure-hv-power-supply-ripple-noise/186 "2022-05-23T22:05:11Z")
Can the QA401 be used to measure ripple and noise of a HV DC power supply as used in a typical tube power amplifier? In the 300-600 VDC range. If yes, how would this be set up? --- ## [QA401 Trouble reproducing Manual page 50](https://forum.quantasylum.com/t/qa401-trouble-reproducing-manual-page-50/678)
**Author:** [@bklein](https://forum.quantasylum.com/u/bklein)\ **Replies:** 3\ **Last updated:** [April 29, 2022, 9:39pm UTC](https://forum.quantasylum.com/t/qa401-trouble-reproducing-manual-page-50/678 "2022-04-29T21:39:56Z")
Ok, I’m brain dead. I am trying to duplicate the testing on page 50 of the manual. What is the trick with zoom. I can’t reliably zoom. I can try over random places of the main waveform and sometime it works, most ti… --- ## [How to test a codec (eval board) with QA-401](https://forum.quantasylum.com/t/how-to-test-a-codec-eval-board-with-qa-401/670)
**Author:** [@bklein](https://forum.quantasylum.com/u/bklein)\ **Replies:** 4\ **Last updated:** [April 20, 2022, 4:43pm UTC](https://forum.quantasylum.com/t/how-to-test-a-codec-eval-board-with-qa-401/670 "2022-04-20T16:43:12Z")
I have a QA-401 and wish to test 4 different ADI codec boards: ADAU1772, ADAU1787, ADAU1701MiniZ, and SSM2603. Am I kind of on my own doing this as the QA-401 doesn’t have a serial audio data path. If I test A/D \> D/A,… --- ## [Testing DACs with QA401 generated \*.wav files](https://forum.quantasylum.com/t/testing-dacs-with-qa401-generated-wav-files/593)
**Author:** [@Chicago](https://forum.quantasylum.com/u/Chicago)\ **Replies:** 20\ **Last updated:** [April 4, 2022, 8:57pm UTC](https://forum.quantasylum.com/t/testing-dacs-with-qa401-generated-wav-files/593 "2022-04-04T20:57:04Z")
Hi all, just getting into some DAC testing and not getting the results I expect. Take a look - what am I doing wrong here? Thanks. --- ## [Anybody selling their QA401/QA402?](https://forum.quantasylum.com/t/anybody-selling-their-qa401-qa402/525)
**Author:** [@philipte](https://forum.quantasylum.com/u/philipte)\ **Replies:** 13\ **Last updated:** [March 29, 2022, 2:40am UTC](https://forum.quantasylum.com/t/anybody-selling-their-qa401-qa402/525 "2022-03-29T02:40:35Z")
hello! we are in need of a few more QA401 or QA402. is anybody interested in selling theirs? we pay list price ($449/$499) and take care of the shipping to our office in Sweden. if you have one available, feel free to… --- ## [Estimated DUT THD](https://forum.quantasylum.com/t/estimated-dut-thd/642)
**Author:** [@a14352](https://forum.quantasylum.com/u/a14352)\ **Replies:** 5\ **Last updated:** [March 27, 2022, 12:03pm UTC](https://forum.quantasylum.com/t/estimated-dut-thd/642 "2022-03-27T12:03:40Z")
Got an idea for a possible feature in the QA401 for excluding QA401 inherent THD. Would it be possible to add a feature that calculated pure DUT THD based on relatively simple math. I know from the cable industry that i… --- ## [RIAA phono stage testing: Headroom / overload](https://forum.quantasylum.com/t/riaa-phono-stage-testing-headroom-overload/583)
**Author:** [@Chicago](https://forum.quantasylum.com/u/Chicago)\ **Replies:** 9\ **Last updated:** [February 8, 2022, 3:48am UTC](https://forum.quantasylum.com/t/riaa-phono-stage-testing-headroom-overload/583 "2022-02-08T03:48:24Z")
Hi all- I’ve been working on several phono stages lately and have discovered a nice headroom test that capitalizes on how the QA analyzers work. The 401 & 402 use a flat drive signal to excite the DUT, and subtracts ou… [Next page](https://forum.quantasylum.com/c/qa401/7.md?page=1)