Added an SUT...not sure I understood this

@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.

@woofhaven1992 

Here is what you need to know -

Your Audiotechnica AT-OC9XML has an internal impedance of 12ohms and voltage output of 0.4mv

Therefore it needs to see a load higher than 100 ohms ( as per specs ).

When you ran the OC9 straight into the SP14 with a 40ohm loading resistor you would have strangled the sound.

Now the AU320 step up.

The 3ohms and 40ohms on the front panel refer to the cartridges internal resistance - NOT the loading.

With the 3ohm input, the gain is 36x which means the cartridge will see a load of 36ohms. The SP14 phono will see 14mv. The sound should be awful because the cartridge at 12ohms cannot drive 36ohms, and the FET based front end of your phono is probably overloading.

With the 40ohm input on the AU320 the gain is 10x which means the cartridge will see a load of 470ohms which is fine, the phono input will see 4mv which is perfect.

Adding loading to transformers can be a minefield, therefore I would suggest you run the AU320 into the SP14 phono at 47k without any additional loading resistors .

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. You might find the SP14 phono with the OC9 at the correct loading may be fine. Of course the additional step uphill add gain if you need it.

@mulveling 

I know we all suspect the SUT is bad, but I’m not sure how a SUT can even go bad such that this negative-gain behavior 

I’ve already explained to the guy the 3ohm tap on the AU320 has a gain ratio of 36 and the 12ohm ATOC9 will see a load of 36ohms. Furthermore the FET based phono on the SP14 will see 14 volts - this would explain his results - cartridge cant drive 36ohms and the SP14 is probably overloading with 14 volts into a fet. It will sound like c**p.

I doubt there is anything wrong with the AU320 - it is behaving as I would have expected running into the SP14 FET based phono.

Previously he was running the 12ohm ATOC9 into the SP14 loaded down to 40ohms which is too low and probably killing the sound.

With the 40ohm input on the AU320 the gain is 10, the phono sees 4volts which is pretty much bang on where he needs to be.

@atmasphere

I’ve already explained to the guy the 3ohm tap on the AU320 has a gain ratio of 36 and the 12ohm ATOC9 will see a load of 36ohms. Furthermore the FET based phono on the SP14 will see 14 volts - this would explain his results - cartridge cant drive 36ohms and the SP14 is probably overloading with 14 volts into a fet. It will sound like c**p.

I doubt there is anything wrong with the AU320 - it is behaving as I would have expected running into the SP14 FET based phono.

Previously he was running the 12ohm ATOC9 into the SP14 loaded down to 40ohms which is too low and probably killing the sound.

With the 40ohm input on the AU320 the gain is 10, the phono sees 4volts which is pretty much bang on where he needs to be.

@woofhaven1992

Connecting to the 40 ohm tap results in less gain that connecting the cartridge directly to the MM input. On the front panel of the SUT, there is a selector to bypass the transformer, to use the 40-ohm tap, or to use the 3-ohm tap, and the gain achieved by each of these is exactly the opposite of what you would expect:

Bypass - loudest, 40-ohm tap - quieter, 3-ohm tap - quieter still.

I’ve explained to you above why running into the 3 ohm tap doesn’t work - the load is too low for the cartridge and the high gain likely overloads the SP14 phono.

The 40 ohm input on the AU320 should work - your results suggest there could be a dicky joint with your cables or the AU320 input. This is unlikely because both channels would have to have the same fault to explain your results.

You need to check your SP14 measures 47k on the phono input and that you have no other loading resistors in the chain when using the SUT.

The other question I would ask is there any evidence some moron hasn't tried to modify the AU320 - these are generally very reliable units - I have never seen one fail.

@billwojo 

Sounds like something is wrong with your AU-320. There is a strong probability that the switches are in a need of cleaning, not an easy job.

I’ve already explained to the guy the 3ohm tap on the AU320 has a gain ratio of 36 and the 12ohm ATOC9 will see a load of 36ohms. Furthermore the FET based phono on the SP14 will see 14 volts - this would explain his results - cartridge cant drive 36ohms and the SP14 is probably overloading with 14 volts into a fet. It will sound like c**p.

I doubt there is anything wrong with the AU320 - it is behaving as I would have expected running into the SP14 FET based phono.

Previously he was running the 12ohm ATOC9 into the SP14 loaded down to 40ohms which is too low and probably killing the sound.

With the 40ohm input on the AU320 the gain is 10, the phono sees 4volts which is pretty much bang on where he needs to be.

@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

@intactaudio 

He hasn't solved his problem, although he now knows why the SUT did not work ( there was a 100ohm loading resistor already in the SP14 ),  I believe the last post I saw was that he still had hum issues.

He is not using a current injection stage.

Apparently he is going back to loading at the tonearm 25ohms, which means that given there is already a 100ohm loading resistor in his SP14 that he is effectively loading his 12ohm cartridge at 20ohms. If you think this is a good idea - good luck to you.

I really don't care what the OP does - but for those who are more open minded, I have set up plenty of OC9's over the years - in most instances where customers were using solid state phonos ( excluding current mode ) I found optimum loading usually around 400-470ohms.

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

@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.

@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. 

@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.

@intactaudio 

Obviously you haven't got a clue so I'll explain it to you - actually here's a quote from JCarr

The loading resistor value is placed across the phono cartridge's output terminals, which means that any output voltage produced by the cartridge will be forced to flow through the load resistor in the form of current. The higher the load resistor value is, and the farther the net impedance is from the cartridge's internal resistance, the less current will be produced. Conversely, the lower the load resistor value is, and the closer the net impedance is to the cartridge's internal resistance, the more current will be produced.

IMHO, the only time that forcing the cartridge to produce more output current could be justified is when using it into an IV phono stage. Since this kind of phono stage converts input current into output voltage (and is more or less oblivious to input signal voltage per se), it would make sense to feed an IV phono stage with as much input current as possible. An IV phono stage, however, possesses de facto a low impedance input node that receives the output current from the cartridge as a series element (without needing a separate load resistor). This is not how a normal loading resistor works with a typical voltage amplification stage, since there the separate load resistor bleeds the current from the cartridge into ground (thereby wasting that energy). Also, IV phono stages sound qualitatively different to voltage amplification phono stages., and part the reason is that undoubtedly the cartridge is forced to operate into a zero-ohm load (or some other values that is quite close to the cartridge's internal resistance).

In other words comparing the resistive load in a current mode mc input to the the resistive load in a voltage gain mc input is like comparing apples and oranges.

If you cant understand what JCarr wrote, and don't understand the difference between voltage and current then I cant help you any further.

@intactaudio 

Lets get back to the simple question I asked....  If going well below a cartridge manufacturers load is not recommended, how can we reconcile the use of transimpedance amplification or in your case a load that is 1.7X the cartridge internal impedance?

It is my belief that when specified by the cartridge manufacturer the load value range would relate to the behavior of their cartridge and not in response to the unknown capabilities of what follows. 

This is where you go wrong. Loading down a MC produces more current and less voltage. ( explained by Carr above ).

Therefore whether the mc phono input is voltage mode ( as in SP14 ) or current mode  is vitally important because in voltage mode loading down the MC reduces voltage going into the voltage based phono and reduces overall gain.

With a current mode phono, loading down increases current and hence increases overall gain.

I cannot fathom how you cant see the difference between increasing gain and reducing gain.

@woofhaven1992 

Looks like you've got the wrong cartridge.

You claimed to have an ATOC9XML

Paoerwork here

Note the recommended minimum load is 100ohms as I posted.

The paperwork you have posted appears to be from the ATOC9ML/II which is a different cartridge. 

However the 20 ohm recommended minimum loading referred to is the minimum recommended loading when using a step up transformer. The recommended loading for a head amp is 100 ohms. See see up instructions #6.

Here is the paperwork for the ATOC9ML/II

In your case your SP14 has a FET based front end, not a step up transformer, and the recommended minimum load is 100ohms.

@intactaudio 

I concur with lew and it makes no sense to me how a loading a cartridge can have different "ideal" values for different amplification types.

Wrong. That is not what @lewm said. He said -

I’ve never understood why the minimum load can be acceptably different for the same cartridge with vs without a SUT in the circuit. 

Lewm was comparing active mc amplification vs SUT's.

You really do need to read posts more carefully, unless you are deliberately misinterpreting posts.

It is clear from your conclusion that you do not understand how current mode and voltage mode gain stages work, and I would suggest if you are genuinely interested then you should do some study - there are plenty of high schools that run after school programmes that are excellent.

@woofhaven1992 

You remain incorrect, however, about the correct loading with the SP14, which contains neither a head-amp or an SUT built in.  

Wrong. The SP14 has a FET based input at the front end of the phono stage., Its same principle as a head amp. Correct loading is 100ohms minimum as per the manual.

I don't have an issue if you prefer 25ohms, thats your ears. I post so that others reading can get the best out of their cartridge using the minimum loading as recommended by the manufacturer. My own experience with setting up many OC9's of various types in multiple systems is that around 400ohms is optimum and it is clear that you have no interest in even trying alternative loading.