# 403 I/o connections to xlr **URL:** \ **Category:** QA40x\ **Created:** [August 24, 2023, 7:28pm UTC](https://forum.quantasylum.com/t/403-i-o-connections-to-xlr/988 "2023-08-24T19:28:54Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Deadcap](https://avatars.discourse-cdn.com/v4/letter/d/74df32/32.png) [@Deadcap](https://forum.quantasylum.com/u/Deadcap)\ **Post date:** [August 24, 2023, 7:28pm UTC](https://forum.quantasylum.com/t/403-i-o-connections-to-xlr/988/1 "2023-08-24T19:28:54Z")
Hi first post here. Got the Q403 and happy with it. I am trying to fit it to my lab environment witch is audio repair lab and need to make the unit balanced xlr connectors and since I am mesuring mic pre amps there is allways the fear that connecting the Q403 output to MIC in with +48V on culd dammege the d/a’s outputs… Do you think I shuld build it a breakout box with dc blocking caps on the outputs? Has anybody done it before? Those caps need to be very big in value (4700uf) in order to match the -3 db point planned on the 403’s inputs… I will be happy to hear your thoats on that. Thanks. Oded ---
**Author:** ![matt](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@matt](https://forum.quantasylum.com/u/matt)\ **Post date:** [August 25, 2023, 1:23am UTC](https://forum.quantasylum.com/t/403-i-o-connections-to-xlr/988/2 "2023-08-25T01:23:19Z")
Hi @Deadcap, The danger for the QA40x inputs and outputs is when 10 mA or more is flowing. A +48V phantom supply is usually provided through a 6.8K. So, the max current that can flow is around (48-14.5)/6800 = 4.92mA. Is your phantom power provided through a 6.8K or so? Thanks, Matt ---
**Author:** ![Deadcap](https://avatars.discourse-cdn.com/v4/letter/d/74df32/32.png) [@Deadcap](https://forum.quantasylum.com/u/Deadcap)\ **Post date:** [August 25, 2023, 7:51pm UTC](https://forum.quantasylum.com/t/403-i-o-connections-to-xlr/988/3 "2023-08-25T19:51:55Z")
Thanks for the fast and accurate answers Matt 🙂 Ok I guess you have calculated the +48v - rail voltage threw the protection diodes to +vcc on the outputs? Anyway its good to know they exist there… I encounter 99% of the time 6.8k resistors for Fantom power which I believe to be a standard. Is 10ma the max current threw the out’s protection diodes? Thanks Oded ---
**Author:** ![matt](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@matt](https://forum.quantasylum.com/u/matt)\ **Post date:** [August 28, 2023, 2:07pm UTC](https://forum.quantasylum.com/t/403-i-o-connections-to-xlr/988/4 "2023-08-28T14:07:05Z")
Hi @Deadcap, yes, the 10mA is what the protection diodes can sustain. These diodes are in the OPA1612 opamps, so you can read more about them in the OPA1612 spec. Parallel to the opamp’s steering diodes, there are other discrete steering diodes on the board that steer the current into TVS devices that are bias “on” around 12-13V. Those can handle a 100mA continuously, and 1A surge. The discrete circuits, due to inductance, are more of a second line defense rather than front-line. So, the 10 mA should drive your analysis. ---
**Author:** ![Deadcap](https://avatars.discourse-cdn.com/v4/letter/d/74df32/32.png) [@Deadcap](https://forum.quantasylum.com/u/Deadcap)\ **Post date:** [August 29, 2023, 8:12pm UTC](https://forum.quantasylum.com/t/403-i-o-connections-to-xlr/988/5 "2023-08-29T20:12:52Z")
Dear Matt thanks for those details it is useful to know when I am operating safely with the 403 as I am connecting this instrument to all sorts of other instruments at the lab all day long… On an other subject, Today I have connected the 403 in my lab for the first time and saw that the oscillator is not operating continuously I have connected it to an oscilloscope and saw that the sine wave has a short interrupt at about each second and this interrupt is synced with capturing speed of the analyzer… I need the oscillators to be a steady sine wave during fft work. It is a critical matter to me especially when measuring compressors that have dynamic behavior highly depended on input signal changes… ---
**Author:** ![Moto](https://avatars.discourse-cdn.com/v4/letter/m/2bfe46/32.png) [@Moto](https://forum.quantasylum.com/u/Moto)\ **Post date:** [August 30, 2023, 4:49pm UTC](https://forum.quantasylum.com/t/403-i-o-connections-to-xlr/988/6 "2023-08-30T16:49:22Z")
Use the Idle button. That will make it continuous. ---
**Author:** ![matt](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@matt](https://forum.quantasylum.com/u/matt)\ **Post date:** [August 31, 2023, 1:04pm UTC](https://forum.quantasylum.com/t/403-i-o-connections-to-xlr/988/7 "2023-08-31T13:04:08Z")
Hi @Deadcap, if you need a constant sine, you can use the IDLE button in the Run/Stop group (below the RUN button). When pressed, if you are not making measurements, then a constant sine will be generated at the GEN1 settings (freq and amplitude). If amplitudes are changing during FFT operations, the FFT result is really hard to interpret. For this reason, there are a few plug-ins and methods that can help. Please see the links below: > **[Amp Dynamics](https://github.com/QuantAsylum/QA40x/wiki/Amp-Dynamics)** > > Releases (no source) for the QA402 and QA403 Audio Analyzer. - QuantAsylum/QA40x > [@Measuring Compressor Response](https://forum.quantasylum.com/t/measuring-compressor-response/73/3): > > Hi @AudioGarden, the scales are almost always fixed in dB. The plots you see above with white background are automated measurements and if you are measuring THD(N) then the left axis will shown dB and the right axis will show %. In the analyzer (dark background) you can switch between dBFS, dBV, dBU, and dBR. The dBFS is useful if you want to understand your measurements relative to full scale on the converter. The dBR is, of course, relative measurements. You can also switch between freq domai… > [@QA40x Release 0.997](https://forum.quantasylum.com/t/qa40x-release-0-997/406): > > Release 0.997 adds the following: Settings A settings menu has been added (Edit-\>Settings). For now, there are two settings, and both are related to acquisition. Latency Compensation Latency compensation allows you to work with DUTs that have path latency that exceeds 30 mS or so. While a normal analog amplifier has virtually zero latency (measured in microseconds), digital amps and especially bluetooth-connected gear can have latency in excess of 30 mS. Setting the prebuffer to a l…