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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
intactaudio
307 posts
 

@dover 

the last post in this thread from the OP is below:

@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. 

to which you responded with the text quoted in my first post here where you insisted there must be something wrong with his system.  

I applaud and support the OP's POV that what sounds best is best. I brought current injection into the topic because it is a perfect example on how an amplification method that many find appealing provides a load that is in stark contrast with what any cartridge manufacturer suggests as optimal.  I for one would like to see more discussion about how to reconcile this discrepancy.

dave

 

dover
2,318 posts
 

@intactaudio 

Then why don't you start your own thread on "loading - voltage vs current mode amplification of moving coil cartridges".

Do you understand the difference between voltage and current ?

If you start a new thread there are many knowledgeable folk on the forum who can help you.

 

 

rauliruegas
13,128 posts
 

Dear @dover  : He already did it in this thread and in the cartridge loading one too. I can't understand why came here again with the same topic but is up to him:

 

R.

atmasphere's avatar
atmasphere
12,116 posts
 

Do you not think the cartridge designer and manufacturer knows what they are doing when they recommend a minimum of 100ohms ?

They know that the designer of the phono preamp may not have taken the RFI generated by the cartridge and tonearm cable into account. The 100 Ohm resistor detunes the resonance that they create and so prevents RFI from messing with the preamp.

If I had to guess that spec is set to assure near maximum output of the cartridge. 

The maximum output of the cartridge will be with little or no load. 47K is the industry standard in this regard and qualifies in this regard.

intactaudio
307 posts
 

The maximum output of the cartridge will be with little or no load. 47K is the industry standard in this regard.

the industry standard of 47kΩ was adopted from the MM cartridge world and applied to the MC realm because is first and foremost "does no harm".... until you throw a SUT into the mix that is.  Once a SUT is added the load the cartridge can see can get vanishingly low to the point where you actually start losing gain as you increase turns ratio.  My best guess is that the min load value specified for a cartridge is a value that still assures nearly full specified cartridge output and has little or nothing to do with the sonic behavior of the cartridge.   

What I want to know is why the minimum load value that has to be strictly adhered to in the case of a traditional phono stage can be completely ignored in the specific case of the MCCI with a published input impedance of <3Ω.  

This is completely ON topic since it relates directly to the OP's insistance that a 20Ω load sounds best on his AT-OC9XML.  

dave

 

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