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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. 

Ag insider logo xs@2xwoofhaven1992
dover
2,273 posts
 

@woofhaven1992

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.

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

Cartridge & Stylus
Frequency Response 20 - 47,000 Hz
Channel Separation 27 dB (1 kHz)
Vertical Tracking Angle 20 degrees
Vertical Tracking Force 1.8 to 2.2 g (standard 2.0 g)
Stylus Construction Nude square shank
Recommended Load Impedance Min 100 Ohms
Coil Impedance 12 Ohms (1 kHz)
DC Resistance 12 Ohms
Coil Inductance 25 μH (1 kHz)
Output Voltage 0.4 mV (@ 1 kHz, 5 cm/sec)
Output Channel Balance 1.0 dB (1 kHz)
Stylus Shape Microlinear
Cantilever 0.28 mm Ø nude boron
Static Compliance 20 x 10 – 6 cm / dyne
Dynamic Compliance 16 x 10 – 6 cm / dyne (100 Hz)
Mounting 1/2” centers / Threaded
Cartridge Weight 7.6 g
Dimensions 17.3 (H) x 16.8 (W) x 25.7 (L) mm
Accessories Included 1 non magnetic screw driver
1 brush
2 washers
4 pairs of mounting screws: 5mm, 8mm, 10mm, 12mm
1 plastic protector
Body Material Aluminium
Model AT-OC9XML
Stylus Size 2.2 x 0.12 mil
Terminal Pins Brass
Wire Used for Coil PCOCC (Copper by Ohno Continuous Casting process.)
Ag insider logo xs@2x
woofhaven1992 OP
65 posts
 

@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. 

dover
2,273 posts
 

@woofhaven1992 

The sheet that came with my cart says 20 ohms.

I don't believe this. All OC9's are recommended 100ohm minimum. I used to sell them. If it sounds better at 20 ohms, there must be something wrong with your system.

Perhaps you could post a picture of the sheet you are referring to.

 

 

lewm
13,363 posts
 

You came here for help, and several knowledgeable people have tried to help. You ought to be open minded about accepting advice, since you clearly do not have an in depth understanding of what you’re doing. There’s nothing wrong with that, unless you continue to insist on many of your misconceptions. Dover pasted the spec sheet here, so you can see that the minimum load R is 100 ohms. At 20 or 22 ohms the cartridge ought to sound weak and dull, because a large fraction of its output would be lost to ground and high frequencies would be rolled off. The fact that you found 100 ohm load resistance in your unit proves you’ve been connecting the SUT to its MC inputs, because there’s no way ARC would have installed 100 ohms at MM inputs. So if you put your SUT away, just directly drive your MC inputs and sayonara. Like Raul said.

lewm
13,363 posts
 

By the way, when we speak of MM inputs vs MC inputs, those are euphemisms for low phono gain (usually 40 to 50db) vs high phono gain (usually >60db). Also with your SUT set at its 40 ohm mode(1:10 ratio), and into those 100 ohm resistors, the load seen by the cartridge is 1 ohm! 

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