Help needed with MC hum issues and SUT recommendations

vinyl_guy · « **on:** 14 Mar 2010, 03:41 pm »

Hi vinyl lovers,

I could use some help with hum issues and SUT advice for my new Lyra Skala. The Skala's internal impedance is 5.5 ohms and the output voltage is .5 mV. My pre amp has a phono stage based on the Art Audio Vinyl Reference. The MM gain is 45 db and the MC gain is 65 db. There is a selector switch that allows me to select loading of 47k, 1k, 300, and 100 ohms for each set of inputs. My turntable is an SME 20/2 and the arm is an SME IV.Vi. The cartridge I was using before the Skala is a Sumiko Blackbird, a high output (2.5 mV) MC that I used with the MM inputs without any hum or noise issues.

When I use the MC inputs, there is a loud hum coming from the speakers which both the pre amp designer and cartridge dealer believe is due to grounding issues. The hum is loudest at 47k loading and decreases as I lower the loading to 100 ohms. I don't fully understand electrical current flow and issues associated with grounding, but I think I read somewhere that it can be difficult to isolate. Is a device like the Ebtech Hum-X a possible solution? http://www.ebtechaudio.com/humxdes.html

When I use the MM inputs, the hum disappears, but I don't feel like I am getting all the Skala is designed to deliver. Plus I have to turn the volume knob up very high to obtain normal listening levels.

So, I figure I either need to solve the hum issue with the MC inputs or buy a SUT to use with the Skala and the MM inputs. I would appreciate your ideas/advice on how to solve the hum issue with the MC inputs and whether you think going with an SUT might be a better way solve the problem. Also, any recommendations on an SUT will be appreciated.

Thank you,

Laura

Wayner · « **Reply #1 on:** 14 Mar 2010, 03:47 pm »

What table/and or arm combo are you running?

Wayner

vinyl_guy · « **Reply #2 on:** 14 Mar 2010, 03:50 pm »

The table is an SME 20/2 and the arm is an SME IV.Vi. I have edited the original post to include this info.

Thanks Wayner

Blackmore · « **Reply #3 on:** 14 Mar 2010, 04:07 pm »

Hey Laura,
My MC cart just got mailed back to Japan for some diagnostics and will be gone for a month. Do you want to try my K&K SUT while it's gone? Set up for 180 ohm and has 18 or 24 dB of gain. Also has some jumpers to change the way ground is established (I think that's right) This would let you try SUT and see if it changes the grounding problem.

Either way, I don't need it back for a while.

rollo · « **Reply #4 on:** 14 Mar 2010, 04:46 pm »

Question. Is the TT grounded ? The arm ? also check the wires from cart. to arm. Sometimes they loosen and cause hum. Any tubes ? if so replace them and try again. What puzzles me is in MM mode no hum. Good luck.

charles

vinyl_guy · « **Reply #5 on:** 14 Mar 2010, 06:42 pm »

Quote from: rollo on 14 Mar 2010, 04:46 pm

Question. Is the TT grounded ? The arm ? also check the wires from cart. to arm. Sometimes they loosen and cause hum. Any tubes ? if so replace them and try again. What puzzles me is in MM mode no hum. Good luck.

charles

Charles, thanks for the suggestions.

The only ground associated with the TT/arm is the phono cable ground (Cardas Golden Reference) and it is attached to the ground screw on the back of the pre amp. I have listen with and without the ground wire attached. Without the ground wire attached and no radio or TV on in my house, I picked up a basketball game boradcast (MM inputs) through the speakers. I reattached the ground wire and the speakers were silent.

The pre amp/phono stage is all vacuum tube and I recently replaced the phono stage tubes, but not the line stage tubes. I will check the wires to the cart

Wayner · « **Reply #6 on:** 14 Mar 2010, 08:21 pm »

First, the amount of gain on an MC compared to an MM is tremendous. That said, location of your power amp in relation to your turntable is critical, as the transformers in the amp will give off tremendous magnetic fields that may be mistaken for cartridge hum. It's making your cartridge hum, but for other reasons (other then being grounded properly). So, how far away is your power amp?

Wayner

vinyl_guy · « **Reply #7 on:** 15 Mar 2010, 06:05 am »

Quote from: Wayner on 14 Mar 2010, 08:21 pm

First, the amount of gain on an MC compared to an MM is tremendous. That said, location of your power amp in relation to your turntable is critical, as the transformers in the amp will give off tremendous magnetic fields that may be mistaken for cartridge hum. It's making your cartridge hum, but for other reasons (other then being grounded properly). So, how far away is your power amp?

Wayner

Wayner,

The power amp is on the bottom shelf and the turntable is on a 4" maple block sitting on the top shelf of a SolidSteel 6.4 stand. This picture from my systems page and gallery shows the TT, then pre amp/phono and then the power amp on the stand. http://www.audiocircle.com/index.php?action=systems;area=browse;system=1140
The CD rack on the right is 6' tall.

Laura

Wayner · « **Reply #8 on:** 15 Mar 2010, 11:44 am »

It looks like the amp is far enough away. Do you have headphones? It would be an interesting test if you had the phones on while having the table on (no LP spinning) and see if the hum disappears when you shut the power amp off. This would eliminate it as a big suspect.

If that doesn't do it, do you have any kind of wall wart close by, say plugged into a power strip? What is that little light for the turntable powered by?

Wayner

Ericus Rex · « **Reply #9 on:** 15 Mar 2010, 12:20 pm »

To take what Wayner is saying one step further your pre could also be picking up these magnetic fields. I once had a similar noise coming out of speakers that disappeared once I moved the pre 1 more shelf away from the amp. Unplug everything but table,pre and amp (and whatever else is absolutely necessary) and see if noise goes away. If not, make sure there are no power supplies or other types of transformers near your preamp or cartridge. Last ditch effort: move these three components as far as possible from each other (still with all other components unplugged) and see if that makes a difference. If any of these suggestions work then it's just a matter of finding out which component is the 'corruptor' and moving it more out of the way.

Best of luck!

JuanR · « **Reply #10 on:** 15 Mar 2010, 01:56 pm »

The same just happens to me,I had the same tuntable ,cartridge and preamp. for some time, few days ago I turn on the turntable and got a loud hum ,I did check cables ,ground ,tubes ,even I changed to mm output, and the problem was only with mc,to make the story short, I changed the outlet and the hum is gone,probably bad power from the street or an appliance or other divice in the house was doing that.

Listens2tubes · « **Reply #11 on:** 17 Mar 2010, 01:27 am »

The recommended load impedance for the Skala is 100 ohms or higher which translates to using the 100 ohm setting on your preamp. The internal impediance you refer to is used when matching a transfomer (SUT) to the cart.

vinyl_guy · « **Reply #12 on:** 17 Mar 2010, 01:35 am »

Quote from: Listens2tubes on 17 Mar 2010, 01:27 am

The recommended load impedance for the Skala is 100 ohms or higher which translates to using the 100 ohm setting on your preamp. The internal impediance you refer to is used when matching a transfomer (SUT) to the cart.

Thanks. I appreciate the clarification. I'm going to uplug everything and start connecting one peice of equipment at a time to see if I can isolate the ground hum. I'm also going to try Mark's K & K SUT and see how the Skala sounds going thrugh the SUT.

Listens2tubes · « **Reply #13 on:** 17 Mar 2010, 01:37 am »

LUCKEEEE

The K&K stuff is awsome!

vinyl_guy · « **Reply #14 on:** 17 Mar 2010, 02:00 am »

Quote from: Listens2tubes on 17 Mar 2010, 01:37 am

LUCKEEEE The K&K stuff is awsome!

Thanks. I just read a good review in a past issue of Stereophile

neobop · « **Reply #15 on:** 17 Mar 2010, 02:01 am »

You might try running a ground wire from your preamp to amp. Sometimes that works.

vinyl_guy · « **Reply #16 on:** 17 Mar 2010, 02:06 am »

Quote from: neobop on 17 Mar 2010, 02:01 am

You might try running a ground wire from your preamp to amp. Sometimes that works.

thanks. I'll try that

Delacroix · « **Reply #17 on:** 17 Mar 2010, 03:23 am »

On the off chance your cables are part of this, try playing around with the layout of the cable from table to phono stage. I get a hum when one of the cables from my VPI arm comes within a few inches of the other -- by repositioning alone, I can cure hum.

Failing that, try a power cord like one of the PS Audio line where the ground can be lifted -- not the most elegant solution but it cured a pre/power amp hum for me when nothing otherwise so easily would.

Just passing on what worked for me.

vinyl_guy · « **Reply #18 on:** 17 Mar 2010, 06:23 pm »

Quote from: Delacroix on 17 Mar 2010, 03:23 am

On the off chance your cables are part of this, try playing around with the layout of the cable from table to phono stage. I get a hum when one of the cables from my VPI arm comes within a few inches of the other -- by repositioning alone, I can cure hum.

Failing that, try a power cord like one of the PS Audio line where the ground can be lifted -- not the most elegant solution but it cured a pre/power amp hum for me when nothing otherwise so easily would.

Just passing on what worked for me.

Thanks. I have a couple of PS Audio power cables.

I really appreciate the ideas. I am going to tackle the hum issues this weekend and I will let everyone know what I find. It might help somone else in the future.

Wayner · « **Reply #19 on:** 17 Mar 2010, 06:58 pm »

No one person has all the answers, but as a collective group, there is some awesome brain power here, at your disposal. The vinyl world can offer many rewards, but to get there sometimes has many roadblocks and potholes. Some of our posts may lead you in the wrong direction, others in the right direction. Hard to diagnose a problem "over the phone".

We'll all help you get there.

Wayner