Added an SUT...not sure I understood this

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.

@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.

@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 

Sounds to me as if the SUT is wired backwards. If it were me to verify this I would grab a few adapters and hook it up 'backwards' and see if the gain increases. If it does, I'd send the unit back for repair and if not in warranty, have a local tech fix it.

OTOH getting to the bottom of the hum thing might be a good idea too. SP-14s are older ARC preamps if memory serves (and a quick search says it was introduced in 1989...) - when was the last time the filter capacitors in it were replaced?

If the answer is 'never' then it would be a good idea to get it serviced out. Its old enough that filter caps (including those in the DC filament supply) can be failing. Failing filter caps have a way of eating power transformers in older gear and you really don't want that happening! It smells terrible and you can expect a transformer like that to be really expensive if you can even find it.

@woofhaven1992

Your observed behavior is entirely consistent with the MM phono input load being much lower than 47K ohms. I know you said it was recently serviced by ARC and therefore should not deviate for spec, but mistakes do happen - it’s possible they sometimes add say a 100 - 500 ohm resistor in there for users who want to direct-connect MC cartridges? Triple-check that your tonearm is free of all the loading resistors you’ve used before.

Perhaps also measure the phono input with a multimeter (make sure your cartridge is disconnected from the chain when measuring). 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 (with no other significant distortions) is demonstrated. If you can borrow another SUT, that would be a good sanity check right now!

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.

This will give you an idea of what's inside.

BillWojo

@intactaudio 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.

getting back to the OP.... He seems to state that he expects 6-8dB of gain in place of the nearly 20dB that a 1:10 suggests.  He then says he is getting the opposite effect which I take as less gain.  

for the OP.

In sticking with just the 40Ω (1:10) tap.  Does the gain increase, decrease or stay the same compared to the same cartridge directly into the MM input?

dave

The EAR MC-3 and MC-4 also use that "tap / coil ohms" labeling, and I hate it lol. There is no "standard" for what actual dB gain or ratio these ohm labels correspond to. And they generally assume a traditional iron coil former (efficient), but cartridges with the same coil impedance can have wildly different output levels (or vice versa) depending on design - look at Benz’s LPS (ruby plate former) with 38 ohm coils providing 0.34mV output, versus My Sonic Labs with 1.4 ohm coils for 0.5mV output!

This kind of taps labeling works better for tube speaker amps, because almost everyone has either 4 ohm or 8 ohm speakers, and gain matching isn’t as crucial there (adjust your preamp volume accordingly, to an extent).

For a SUT, labeling either the gain ratios OR dBs is much more useful. On my EAR MC-3, the taps: 4 ohms, 12 ohms, 40 ohms correspond to (I think, roughly): 4 ohms = 28x (+29dB), 12 ohms = 18x (+25dB), and 40 ohms = 10x (+20dB).

I think this tap labeling was used only to help its users avoid the most minimal amount of math calculations: match your cartridge's coil spec to the tap, and hope the SUT designer had your cartridge's relative design / efficiency in mind.

Vinylzone, I think you’re correct about the labeling of the SUT inputs, but in this case the best choice is the 40 ohm inputs despite the fact that 12 ohms ( the internal R of the cartridge) is closer to 3 than to 40. That labeling custom can be very misleading. “40 ohms” results in a 1:10 step up, which is what is needed here. The 1:10 voltage step up will give you an input Z of 470 ohms. That would be about 10X the internal R of 40ohms. So the label really only means that pair of inputs is ok for cartridges that have a 40 ohm R or lower than 40 ohms. I am glad that “logic” is no longer used.

A Schiit Mani 2 ($150) with its mc gain setting probably will sound better than the SP14 phono/SUT combination.

@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.

Your tx is 1:10. Take what the input resistance is at the phono preamp - it should be 47k, and divide it by 100 (10 squared). That is 470 ohms if you have 47k. This number should be at least 10 times the internal resistance of the cartridge. I suspect the input resistance is less than 47k and you are pinching the current. Remember ohms law - current is a relationship between voltage and resistance. I have several SUTs and it is worth noting a that even when the correct resistance is applied, the apparent loudness does not follow the voltage. It’s misleading. 2.5mv and 5mv just sound the same in terms of loudness.
 

 If the goal here is to chase down a hum, and if the tx solved this, sounds like a grounding issue. Try reworking the grounds. Ground the TT to the phono only. Try a star ground. Try shielded cables. Try shielded cables with the shield only landed on 1 side and switch the side the shield is landed on between the TT and the phono pre. try to disconnect all grounds and use a loose ground wire to touch the outside of the rca connections. Ground hum finds a path of least resistance to ground and goes there. Usually this is whatever has the largest power transformers. 

The lower the ohm rating on a tap the higher the gain.  As a rule of thumb, you should use the tap that most closely matches the internal resistance of your phono cartridge.

Please omit “gel reader “ from my last post. I have no idea where that came from. Should read “47K or higher” load resistor. Nearly all MM phono stages use 47K standard.

Raul makes a good point, but if you’re determined to use a SUT then you must use a low gain phono stage (40 to <50db) with a 47K or gel reader load resistor.

In my experience it will be a bad result relying on downstream gain (20dB line stage) to make up for the lack of a proper MC headamp or SUT. Such preamps, with a normal MM stage (e.g. 44dB in your case) plus enough line stage gain to "make up" for MC’s needs were very specific to that bygone era. These days having that much gain in a tube line stage (usually from 12AX7 tubes) is just asking for noise issues.

OP, you did the right thing seeking out a SUT to help your MC cartridge, unfortunately I suspect you’re right that something might be wrong with it.

@rauliruegas Yes I have been using the SP14 with no SUT for some time, and the sound is great except for a touch of hum just at the level of the noise floor. I decided to fiddle with this SUT as a way of addressing that problem, which otherwise has been  persistent despite lots of attempts to address it, including having ARC work on the pre-amp twice.

You are correct that through the SUT I lose some resolution,  although I was blaming that on the crappy built-in output cable. I figured I could find a way to replace that but maybe I should, as you say, forget it.

Dear @woofhaven1992  : For that cartridge you don't need to use any SUT. The SP 14 spec MC sensitivity is 0.25mv and your cartridge has an output 0.4mv, repeat you don't need any SUT and obviously not that low quality Denon that was a vintage entre level Denon line.

You need to read the SP 14 very carefully to make the rigth set up/gain for your SP 14 stand alone and check for every system link to avoid any hum/noise developed.

You are in the wrong path with a SUT, jus forgeret and focus on your whole system with that cartridge.

Regards and enjoy the MUSIC NOT DISTORTIONS,

R.

@mulveling Thanks.  Clearly there is something wrong with this SUT.  There's no possibility of wiring it backwards since it has a built-in output cable and two sets of RCA jacks for inputs.

You are right about the gain on my line stage.  When playing from a digital source, my light fixtures start rattling before I reach the 10 o'clock position.

Make sure your inputs and outputs to the SUT are not reversed! I've done this before. I've also accidentally stacked two SUTs, which actually goes backwards in gain (due to really bad loading). Double and triple check all connections. In your setup, that SUT should give you an extra 20dB of gain which is HUGE and absolutely noticeable. There's no way you should be pegging the volume unless something is seriously wrong. That line stage has 20dB of gain! That's an awful lot. You should be having the opposite problem - you should be able to hit 95dB relatively low on that volume control - like below 12 o'clock, for sure. 

Well, as I said, I removed the load resistor when I installed the SUT.  Thus, the SUT is driving my preamp's 47k ohm input impedance without modification.  The pre-amp was just serviced and spec'd out by ARC, so I know there's no chance its impedance or gain are other than as designed.

It sounds like everyone agrees with me on what adding the SUT should result in, both in terms of gain and tonality.  It's just that is not what is happening.  

What mulveling said.  There is only one correct way to terminate the SUT, with a 47K ohm load (or higher in some rare cases for special reasons) across the secondaries and input to an MM phono stage.  With a SUT that has a 1:10 turns ratio (like yours), this will have the cartridge "see" a 470 ohm load, which is OK for 99% of LOMC cartridges.  It's really simple.  Don't overthink it.

The cartridge likes to see a load impedance that is at least 10 times its internal impedance or greater.  Your cartridge has an internal impedance of 12 ohms, so you are fine with a 470 ohm load.  (Greater than 10X ratio is acceptable.)  The load seen through a SUT is equal to the value of the phono load resistance (47K ohms) divided by the square of the turns ratio (10-squared = 100).  Hence the cartridge sees 470 ohms (47,000/100).  Your cartridge puts out 0.4mV at the standard stylus velocity.  So the MM phono stage will see 4mV, which is perfect for driving any typical MM phono stage.

You absolutely need to ensure you’re loading a SUT at 47K. Any less load resistance than this, and you’ll start throwing away gain, as well as encouraging other distortions. Your talk of 40 ohm, 22 ohm resistors makes me nervous you’re adding a heavy load to the SUT. If the SUT ratio is chosen properly for your cartridge, then 9 times out of 10 the natural reflected load from the SUT directly into a 47K ohm MM input works out "fine", with no need for additional loading on its primary or secondary.

@dweller the SP14 has a built-in phono stage.

@noromance the SP14 does not have an MC setting.  The expectation was that one would either just crank up the gain or use SUT or headamp.

@jasonbourne52 I wish I had someone else in my orbit with an SUT to borrow, but my audio clan is very anti-vinyl, so no joy there.  It's good to know my expectations were not crazy.

The AU-320 has a built-in cable for output, and maybe I can find someone who can solder in a set of jacks instead, since the cable is pretty generic.

Yes, the standard 47K mm input on the SP14 should work fine.

Why the loading resistor? Plug the SUT into the MM input.