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.
Dear friends: Sometimes happens things as what is happening here where several of you keep postng about that SUT when the OP NEEDS NOT any SUT to handle his cartridge. Even if that vintage entry level SUT been in good shape it only can degrades the cartridge signal with out any quality improvement for the LP sound reproduction.
Well, go on on that " party ".
R. | ||||||||||||||||||||||||||||||||||||||||||||||||||
Well this has been interesting, and now the mystery is solved. The prize goes to @mulveling for correctly deducing that when ARC last serviced the SP-14, they soldered 100-ohm load resistors in there. They did know I was using an MC cartridge, but wow it would have been nice if they had said something. Anyway, this explains a lot. Not only does it explain why the SUT behaves as it has, it also explains why when not using the SUT, the cart sounds better when I load the tonearm with 22 ohms than when I load it at 20 ohms, which is the spec for this cartridge. I am definitely not going anywhere near that circuit board with a soldering iron, so there will be no more experimenting with this SUT for me. I'm going to try 25 ohms on the back of my arm, and if I like that sound, start tracing everything I can to find a way to eliminate that last remaining hum. Thanks to everyone who contributed. | ||||||||||||||||||||||||||||||||||||||||||||||||||
NO How many times do I have to post. That is not the spec. The recommended loading for your cartridge is Min 100 ohms. Min means minimum It is not 20 ohms It is not 22 ohms It is not 40 ohms Look at the Audio Technics website if you don’t believe me
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@dover The sheet that came with my cart says 20 ohms. AT has not been consistent with their specs on the OC9 series. More importantly, it sounds better around 20 ohms than at 100. Plenty of people agree with me on this. I'm not going to load it at 100 just because you won't stop yelling at me. I'm going to load it at whatever achieves the best sound in my system. | ||||||||||||||||||||||||||||||||||||||||||||||||||
