This is a review and detailed measurements of the Sound Town ST-UPDM4C four (4) channel professional amplifier. It was purchased new by a member and drop shipped to me. It costs US $540.
As you see, there is a bit of style to this amp with the front panel. This is a straight amplifier with no DSP:
The fans came on immediately and made moderate amount of noise (much quieter/lower pitched than many small fans like this). As you see, input is XLR and output is speakon connectors.
I was very pleased to see Audio Precision analyzer graphs in the manual. They were quite tiny and hard to read but made me hope that the design was verified through such.
Sound Town ST-UPDM4C Measurements
The tests you see are all performed using Channels 1 & 2 on one side. Let's start with our dashboard:
SINAD is below average of all amplifiers tested by 4 dB but for a Pro amplifier, it is not bad:
But there is more going on here. There is broad set of noise between 2 and 4 kHz. I shut off the signal feed to it and was very surprised to find this noise component:
Seems like some square wave with harmonics buzzing around internally that is bleeding into the amplifier. Not good.
That noise limited the signal to noise ratio:
It also showed up in multitone test:
Notice how the ends of the spectrum has reduced levels which indicates non-flat frequency response:
Not only do we have (speaker) load impedance dependency but we are missing the lows as well below 40 Hz or so. As such, you can't use this amplifier for subwoofer duty.
Amplifier is rated at huge wattage so I was shocked to see so little output with 4 ohm load:
I am used to seeing power exaggeration in pro amplifier specs but this is in entirely different class.
Strangely, I got identical amount of power into 8 ohm load:
Is there some kind of limiter in the unit? There must be. See what happens when I change frequencies:
See how the curve goes up but then starts to go backward below 1 kHz? That is electronic limiter in action.
Finally crosstalk was very poor:
Conclusion
I have hardly seen any audio device show issues in every test I run but here we are. I don't understand what is going on here. How can they have analyzed the performance using AP yet have so many issues left on the table? Did they design change post those measurements? This is the frequency response from the manual:
It shows flat response to 20 Hz. Notice the date is 2003. Is it really that old of a design?
Anyway, I can't recommend the Sound Town ST-UPDM4C.
-----------
As always, questions, comments, recommendations, etc. are welcome.
Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
As you see, there is a bit of style to this amp with the front panel. This is a straight amplifier with no DSP:
The fans came on immediately and made moderate amount of noise (much quieter/lower pitched than many small fans like this). As you see, input is XLR and output is speakon connectors.
I was very pleased to see Audio Precision analyzer graphs in the manual. They were quite tiny and hard to read but made me hope that the design was verified through such.
Sound Town ST-UPDM4C Measurements
The tests you see are all performed using Channels 1 & 2 on one side. Let's start with our dashboard:
SINAD is below average of all amplifiers tested by 4 dB but for a Pro amplifier, it is not bad:
But there is more going on here. There is broad set of noise between 2 and 4 kHz. I shut off the signal feed to it and was very surprised to find this noise component:
Seems like some square wave with harmonics buzzing around internally that is bleeding into the amplifier. Not good.
That noise limited the signal to noise ratio:
It also showed up in multitone test:
Notice how the ends of the spectrum has reduced levels which indicates non-flat frequency response:
Not only do we have (speaker) load impedance dependency but we are missing the lows as well below 40 Hz or so. As such, you can't use this amplifier for subwoofer duty.
Amplifier is rated at huge wattage so I was shocked to see so little output with 4 ohm load:
I am used to seeing power exaggeration in pro amplifier specs but this is in entirely different class.
Strangely, I got identical amount of power into 8 ohm load:
Is there some kind of limiter in the unit? There must be. See what happens when I change frequencies:
See how the curve goes up but then starts to go backward below 1 kHz? That is electronic limiter in action.
Finally crosstalk was very poor:
Conclusion
I have hardly seen any audio device show issues in every test I run but here we are. I don't understand what is going on here. How can they have analyzed the performance using AP yet have so many issues left on the table? Did they design change post those measurements? This is the frequency response from the manual:
It shows flat response to 20 Hz. Notice the date is 2003. Is it really that old of a design?
Anyway, I can't recommend the Sound Town ST-UPDM4C.
-----------
As always, questions, comments, recommendations, etc. are welcome.
Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
