[vortrex]

Doesn't the fact that the hum goes up and down with the volume control imply the cartridge is the culprit?  I've never experienced a ground loop hum being volume adjustable.

To be sure it's not the phono stage unplug the tonearm cable and turn everything on.  If the hum is gone then your culprit is ahead of the phono section; either the cartridge (are the leads secure?) or the SUT, or their cabling.  If the hum is still there then your phono pre, or its cabling, or its interaction with nearby power supplies is likely the demon.

hum/noise is there with the TT disconnected.

hum/noise is there with phono stage connected and inputs shorted.

NO noise/hum using a CDP.

NO noise/hum with nothing connected to the inputs of the integrated.

it's not the table or the SUT.

[vortrex]

I thought vortrex already isolated the TT from the variables, leaving the phono stage and possible grounding issues, or hum pickup from AC, RFI, transformers, or other sources?

that is correct.

[*Scotty*]

vortrex, I suspect you need to send the Chinook back to Manley Labs and have them verify that the phono stage meets its claimed signal to noise ratio of 84dBu at the 45dB gain setting. When the inputs of the phono stage are shorted the only thing left for your integrated amp to amplify is the residual noise the phono stage has. If Manley determines that the Chinook does indeed meet its S/N specs then you have a definite case for having too much gain in the integrated amp.
Scotty

[vortrex]

My K&K phono stage sounds the same though...

[*Scotty*]

Do both phono stages have similar S/N specs? If so then it might be worth while to put some kind of attenuation on the incoming signal from the phono stage, this simultaneously reduces both the signal and the noise from the phono stage.
Scotty

[roscoeiii]

Do both phono stages have similar S/N specs? If so then it might be worth while to put some kind of attenuation on the incoming signal from the phono stage, this simultaneously reduces both the signal and the noise from the phono stage.
Scotty

But *Scotty* how do you account for the lack of this issue with vortrex's previous amp and the K&K phono stage? For me signs point more and more to an interaction between both phono stages and the amp. The title of the thread is jumping out at me again: "Too much gain?"

[vortrex]

I have some 12db attenuators that I think were delivered today.  I'll throw those in as a test to see if it makes a difference.

[Ericus Rex]

If you're using shorting plugs remove them all.  If not, best of luck to you b/c I'm outta ideas.  I suspect Roscoeiii is on the right track though.

[roscoeiii]

I suspect Roscoeiii is on the right track though.

That's something I don't get to hear enough. 

Though on the Vinyl Circle, orthobiz talks about being "Roscoe'd" when I post about an LP that he doesn't know about that seems interesting enough to buy...

[vortrex]

If you're using shorting plugs remove them all.  If not, best of luck to you b/c I'm outta ideas.  I suspect Roscoeiii is on the right track though.

not using any shorting plugs, only used one that Manley had me make for testing.

[vortrex]

I added the 12b attenuators and things are much better.  there is still a slight hum that is audible with ear close to speaker or at listening position with the volume cranked way up (no music playing) and most of the noise is gone.  with these attenuators in I'm at 59db using the SUT.  the KAB calculator says I should be at 61db and their generic chart says .15mv to .30mv = 60db and .30mv to 1.0mv = 53db.  I wouldn't mind losing a few more db in case I switch carts down the road.

[roscoeiii]

Is it possible to decrease gain by tube swapping? Sometimes it is possible to replace a 12AX7 with a 12AT7 or 12AU7. Check with the dealer or manufacturer on that though...

Or maybe it is possible to do that some other way inside the amp.

[vortrex]

Is it possible to decrease gain by tube swapping? Sometimes it is possible to replace a 12AX7 with a 12AT7 or 12AU7. Check with the dealer or manufacturer on that though...

Or maybe it is possible to do that some other way inside the amp.

I've replaced the 12AX7 with 5751's, which are supposedly 30% less gain.  that really made no difference other than sounding better (NOS tubes).

[vortrex]

I contacted Line Magnetic in China and asked them about changing the sensitivity of my amp.  They said it was simple, change out two 1M ohm resistors for 470 ohm.  Now since I know little to nothing about how the electronics actually work, can someone explain how lowering the resistance will make the input less sensitive?  I also emailed them back to make sure they really meant 470 and not 470k, since it seems like a fairly large drop from 1M.
     

[Quiet Earth]

Hmmm....  without seeing a schematic of your amp I think we would be guessing about the resistor change. 

Before you pick up a soldering iron, it would be nice to know these answers from Line Magnetic :

1. What is the sensitivity reduced to with the resistor change?
2. What is the new input impedance with the resistor change?

Sounds like the pads on the input of the amp helped. Just out of curiosity, what value did you pick?

Don't feel bad about the 5751 not helping,,, I've never heard significantly less gain out of them either.

[vortrex]

those questions are out to LM now, it usually takes a couple days for them to respond.  they've been very helpful, I never thought I would get a reply.  there messages are fairly terse though.

they were 12db pads.  those helped with the unwanted noise, but not much for the volume control sensitivity.

[vortrex]

new update here, as I am losing my mind...

I added yet another phono stage into the mix and still have the same issues!  The new (Zesto Andros) phono stage is well known to be dead quiet.  I'm now running at 65db with no SUT.  The KAB calculator recommends 62db so this should be spot on.  I still have horrible hum and white noise.  Since this has been 3 high quality phono stages, various output levels, and the same results, I say this cannot be a phono stage issue.  BUT, since my amp works with a CD player just fine that kind of throws me for a loop as far as blaming the amp.

I've disconnected the cable TV line as it comes off the street, shut off every breaker in the house but the circuit I am on, removed anything else from the wall on that circuit, and none of that made a difference.  I've replaced all the tubes in the amp and the three phono stages, no change.  Below you can see all the setups I have tried, all sound roughly the same.  The LM amp does have the high input sensitivity of 250mv, is that being overdriven by the output of the phono stage?

1st:
Denon 103R -> Amadeus -> A23 cable -> A23 SUT (26db) -> A23 cable -> 38db MM K&K phono -> A23 cable -> LM

2nd:
Denon 103R -> Amadeus -> A23 cable -> A23 SUT (26db) -> A23 cable -> 45db MM Chinook phono -> A23 cable -> LM

3rd:
Denon 103R -> Amadeus -> A23 cable -> A23 SUT (26db) -> A23 cable -> 45db MM Chinook phono -> A23 cable -> 12db attenuators -> LM

4th:
Denon 103R -> Amadeus -> A23 cable -> 60db MC Chinook phono -> A23 cable -> LM

5th:
Denon 103R -> Amadeus -> A23 cable -> 55db MC Zesto phono -> A23 cable -> LM

6th:
Denon 103R -> Amadeus -> A23 cable -> 65db MC Zesto phono -> A23 cable -> LM

[roscoeiii]

How was 55dB gain on the Zesto vs. 65dB?

[vortrex]

How was 55dB gain on the Zesto vs. 65dB?

65db sounds better and has less hum.

[roscoeiii]

Interesting. That to me would suggest that the amp is the issue there. Though the CD player mystery remains perplexing.