Recommendations for using analogue output module to play sound

bscohen

Hi!
I have a 8 channel analog output module rev1.1 connected to a r2 state machine and have been trying to play sounds by connecting the module to a speaker with a built in amplifier (Adam A5x). Using this set up I seem limited to producing at most 80 decibels, but when I hook the computer up to the speaker I can easily exceed 100. And have tested the newest versions of both WavePlayer and AudioPlayer. What if anything could explain this discrepancy? I have tested the output using an oscilloscope and it is faithfully reproducing every waveform I give it. I tested different voltage ranges from +-.1V to +-12V without any increase in volume, except for a decrease under +-.2V. Is it possible my speaker simply isn't optimized for the output from the AO module due to an impedance mismatch or something? If so, is there a combination of amplifier and speaker you would recommend for auditory mouse behavior experiments?

Thanks so much for your time,
Isaac

Josh

Hello Isaac,

I'm surprised that you don't get the full output range at +/-12V, and that lower voltages do not result in quieter output. I'm not sure why. It looks like that speaker has "stereo link" and "unbalanced" inputs. Do you see the same result for both?

-Josh

bscohen

Hi Josh!
Thanks so much for your rapid response! I only tested the 'unbalanced' input as the balanced required a XLR cable that I don't have, but given that I can produce a full range of response with the computer I doubt it is the input on the speaker?
Is it possible the analogue output module is not producing enough current even though the voltage is high enough? I should have mentioned that my module is possibly partially damaged as CH1-4 produce tonic negative voltages at -15 through -7 V, but Ch5-8 seem to be working totally normally and I can make them output any waveform I need on the oscilloscope. Until now I have just kept to these channels, but is it possible the module is overworked and not able to produce the current required? When I examined the circuit board I found that part IC5 was too hot to touch. I've provided a picture for reference.
Thx so much!
Isaac!

Josh

Hello Isaac,

IC5 is the digital to analog converter (DAC). It should not output -15V (the power supply voltage), as its maximum output range is +/-12V. It should not be too hot to touch. I suspect the chip has been damaged, and may be drawing too much power from the DC/DC converter.

Ch5-8 use a separate DAC chip, powered by the same DC/DC converter - so it's possible that the broken chip isn't leaving enough power for the second DAC.

-Josh

bscohen

Ah! that makes a lot of sense, in that case is it repairable or do you think we need a replacement?

Best,
Isaac

Josh

Hello Isaac,

Unfortunately it would need to be replaced, and the 8-channel version of the analog output module depended on a discontinued part - Teensy 3.6.

An updated 4-channel version of the module is available, using Teensy 4.1. For your application, the HiFi module may also be a good option.

-Josh

bscohen

Darn! Ok we will probably get the updated version then. Out of curiosity what would happen if I were to use a dremel to cut off the circuitry to the ch1-4 dac?

-Isaac

Josh

I'd be cautious - the board has 4 layers of copper traces, and you wouldn't want to short them together (I'm not sure how cleanly a dremel would cut)

bscohen

Noted! we are definitely going to replace it but I'll let you know if I succeed at tinkering with this one!