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. 

Ag insider logo xs@2xwoofhaven1992

@dover 

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

If I had to guess that spec is set to assure near maximum output of the cartridge.  Changing the loading value makes subtle but easily audible changes for many.  I know of several people who routinely load MC carts at 3-5X the internal impedance.  They do this out of sonic preference and not out of ignorance or to thumb their noses at "accepted practice".  I have yet to see a published minimum load that comes anywhere near the <3Ω of the MCCI which precludes their use in general if one were to adhere to the manufacturer's suggestion.

but for those who are more open minded

Odd... it seems to me that insisting one trust a published suggested load over their ears is just the opposite of open minded.

I am not saying that the OP is correct in their 20Ω choice or exactly why that value was chosen.   It may very well be that the 4dB reduction in cartridge output from that cartridge-load ratio may be partially responsible for some additional noise.  The point I was / am trying to make is the disconnect between minimum recommended load and the use of a stage such as the MCCI.

dave

@perkri 

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

 

Please explain where DC would come from. The signal entering the SUT is generated by the cartridge and is a AC signal, there is no way it can generate DC.

 

BillWojo

@intactaudio 

I know of several people who routinely load MC carts at 3-5X the internal impedance.  They do this out of sonic preference

Yes - I have seen this phenomenon myself when I was a high end audio distributor in the 80's. Usually it is psychological, they like an effete sound or rolled off top end because their mother told them off too much when they were young.

Odd... it seems to me that insisting one trust a published suggested load over their ears is just the opposite of open minded.

If you read my earlier posts correctly I suggested he should try the higher loads. The OP has chosen not to try higher loads.

The only reason I took the time to write my post with regards to published specifications and recommended load was to inform the thousands of readers of these forums whom do not post, but might rely on what they read in the thread.

 

apologies to all for veering off topic here....

@dover 

I have yet to se actual measured frequency sweeps from a MC cartridge that show the ""rolled off" top end you suggest above.  Can you point me to some?

The only reason I took the time to write my post with regards to published specifications and recommended load was to inform the thousands of readers of these forums whom do not post, but might rely on what they read in the thread.

I have the same belief.... kinda...  I was just trying to point out to the 'thousands of readers of this thread' that the whole concept of "current injection" flies 100% in the face of blind adherence to the manufacturers minimum load spec.  ie...I see the natural conclusion of your logic to be:  if 100Ω is the minimum <3Ω cannot sound good so it need not be tried.

dave

@intactaudio 

Once again, please read my posts more thoroughly - here is what I posted initially

What I would suggest is get a pair of 470ohm resistors and try running the OC9 straight into your SP14 loaded at 470ohms. This will give you a direct comparison with and without the step up with the same loading. 

The SP14 does not use current injection mode. Your insistence on bringing into the discussion another variable ( current mode ) that is irrelevant to the OP's issues only serves to add more confusion to an already confused OP.