Thetis Microphone Settings

[N7KD]

In the Thetis Transmit settings tab in the Mic section there are radio buttons for "Line" and "Mic" . There are GAIN settings in the Mic section. Do the radio buttons and GAIN settings affect only the Mic mini-phone jack input or do they also affect the "XLR" jack (in reality a 1/4 inch TRS jack)?
Ken
N7KD

[w-u-2-o]

They also affect the balanced mic input (TRS jack).

When selected, the balanced input is switched into the same CODEC input that the unbalanced mic input uses.

Note that the balanced mic input contains its own preamp that has a substantial amount of fixed (non-adjustable) gain.

[N7KD]

Thanks. I am using a dbx 286s preamp to provide phantom power to a condenser mic. The output of the dbx to the G2 is at line level so I don't want to overdrive the audio.

[w-u-2-o]

Gotcha. You still need to select mic to access the balanced input. I'm very curious how it works out for you, please post your results.

[N7KD]

The fact that the balanced input has a lot of gain would appear to restrict its use to microphones a practical matter and does not make sense to me. Balanced inputs (the "XLR" really TRS input on the G2) are often used in audio applications for line level signals out of preamps or mixers at levels of +4dBu (0 on a VU meter) whereas mic outputs are between 1 and 10mV -60 to -40 dBV. Restricting the balanced input to microphones in the Mic input choice and the Line input choice to the unbalanced 3.5mm mic input in Thetis seems strange.

[w-u-2-o]

Yes, sir, I'm with you on that. The gain is very high even for a mic. A switch on the back to change from mic to line gain would have been most welcome. Similarly, adding 48V phantom would also have been desirable.

The good news is that everything associated with the balanced input is contained on a separate circuit card that outputs to the same old CODEC IC on the Saturn SDR board. The card in question is easily modified to achieve whatever gain you want, and even has pinning to accept an external phantom voltage.

See this topic where you can find some relevant discussion as well as the schematic for the balanced input board.

viewtopic.php?f=48&t=4863&hilit=preamp&start=30

[N7KD]

I tried using my condenser mic into the dbx 286s preamp (to obtain the 48V phantom power) and the output of the dbx 286s into the G2 balanced XLR [sic] input with the G2 driving a dummy load. The only way it looks half decent on the Thetis waterfall display is if the input gain of the dbx 286s is turned way down so as to not overdrive the balanced input of the G2 into distortion. As with most amplifiers, operating dbx 286s preamp at the lowest end of the gain structure is not the optimal operating point for the preamp circuit of the dbx 286s and also prevents the effects of the dbx 286s (compressor, enhancer de-esser, expander gate) from triggering. I have not yet tried to increase the input gain and decrease the output gain to see if I can get the output to be low enough so it does not overdrive the balanced audio input stage of the G2 but have the input level high enough to be able to trigger the effects. Having said all of this I may not even want to use the effects but nice to have them available.
I am an old audio guy. I used to do the sound for giant rock n roll concerts all over the US so I am fairly familiar with audio stuff.

[w-u-2-o]

There should be enough processing in Thetis to satisfy an "old audio guy"

Phase rotator, fully adjustable expander/gate with side chain and look-ahead VOX, leveler (compression), main EQ, CFC multiband compressor, post EQ, and adjustable ALC (more compression and look-ahead soft limiting). All multiband stages are 10 band semi-parametric.

What else could you possibly need? Please don't say reverb

IMHO the best way to go is to use a good USB audio interface with the cmASIO facility in Thetis and all of the above processing.

[w9ac]

I use an external hardware leveler/limiter ahead of a USB audio interface to protect its input from periodic sloppy mic positioning. It's set at a low compression ratio until peak audio is reached and is mostly transparent. It's probably not needed with headsets unless one gets carried away during moments of excitement.

Paul, W9AC

[N7KD]

Since I want to use the dbx 286s to provide condenser mic phantom power to me it makes sense to use the effects that are downstream in the dbx signal chain and basically a free bonus. Also I don't think I want to futz around with the preamp circuitry in the G2 to provide phantom power or change the mic/line preamp gain structure at the risk of voiding the warranty. Otherwise the internal Thetis effects are probably very useful.