2. analog
  3. 178923-132572

Added an SUT...not sure I understood this

I just added a Denon AU-320 step-up transformer in between my AT-OC9XML cart and my ARC SP-14 preamp.  I am glad that the (relatively quiet) hum that had been present before is now gone...and I mean gone...since that was what motivated me to add an SUT.

However:

I sort of expected that I would also experience a noticeable increase in gain.  Specifically, using the 40-ohm (10X) tap, I would have expected maybe a 6-8 dB increase in volume, and more with the 3 ohm tap.  I am not hearing that, and in fact am getting the opposite effect.  This means I actually have to peg the volume control if I want to achieve 95 dB levels at my listening position, something I rarely, but still occasionally, do.

Also, I removed the 22-ohm loading resistor upon connecting the SUT.  I noticed previously that a 40-ohm loading still had the cart sounding pretty bright.  But with no loading and using the 40-ohm tap, things sound natural.  I sort of expected I was going to need to add a 40-ohm resistor (at the tonearm) to achieve the same loading.

All of this confuses me; I'm happy so far with the sound yet perplexed.  Perhaps some good Samaritan here will be able to explain why I am hearing what I am hearing.  in the meantime, I'm just going to enjoy my quieter background. 

woofhaven1992

Showing 2 responses by perkri

perkri
926 posts
 

Seems to me, you have DC in the signal. DC will not pass through the transformer(s), which is why the hum is going away

 

perkri
926 posts
 

@rauliruegas

 

Just finished building a Hiraga Super 30 watt Class A amp

500VA transformer, followed by 192KuF of capacitance in the power supply

Toroidal transformer hums on start up, had to instal a Hypex Soft Start board so as to manage the inrush of current on start up as the magnetic field stabilizes.Humming stops once warmed up.

In an SUT, traditional transformers are used, and the discussion had to do with electrical hum, and not physical hum.

The reason the hum goes away when the SUT is added is because the DC in the signal isn’t passing through the transformer.

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