LP125M SE upgrade

[Big Dog RJ]

G'day maties, greetings from down unda.

Finally received the monoblocks on Friday and was playing well at my dealers place, prior to picking up just to make sure both were working perfectly. Hauled them into the car and drove home. Installed them and powered up... upon turn on, straight away there was a significant low level hum coming from the right channel.

Mostly heard from the bass panels of the CLX's. When the right monoblock is turned off this hum goes off immediately. Turn it back on and there it is...

It does not attenuate or rise as playback levels are adjusted, just a flat low level hum, which can be heard from the listening position. The wifey says she can't hear it... unless she staples her ear to the CLX's bass panels, ah! Then she hears it. As in my case I hear it pretty well, very sensitive hearing you see...

Never had this sort of hum issue before, even at our previous place and in our new place, prior to sending the amplifiers for a final SE upgrade. They were always dead quiet, zero noise. Probably one of the quietest systems I've experienced.

I then re-dressed the cables, interconnects and power cords, just making sure nothing was touching. Also realigned the power connections going into the Nordost Qbase8. Starting with Primary Earth for the preamp followed by both monoblocks on either side, followed by the rest of the gear and ending with the CLX's being plugged into the far outer AC outlets on the power board.

It was getting pretty late about 4:30am, so I haven't powered up the amplifiers since... too tired.

My chief CJ tech is saying to conduct the following:

1. Swap monoblocks; L to R & R to L and see what happens.
2. Swap interconnects on the main outs from preamp to power amplifiers and see what happens.
3. Change Input tubes on the one that's causing the hum. This should sort it out.

I've never thought an input tube may be the cause of any such hum or interference. Anyway, I've got spares so I might swap tubes.

Just wanted to get any of your valued advice as to how I should go about finding the cause...
Other than that the SE upgrade with all those added high quality parts was definitely worth it! The overall sound is a couple notches even higher. It's as if a completely new set of monoblocks have been installed.

Was also wondering if it's just an Input tube and not any other tubes, driver/phase inverter or output tubes?

Oh well, I hope to find the problem out soon, so that those fine tunes can be enjoyed!

Best, RJ

[admin]

Is the hum around 60 hz? May be a ground loop. Very common, I've had them in my system before.

Edit: I just remembered you are on the other side of the world where the toilet water swirls the opposite direction. A ground loop hum would be 50 hz for you.

[AnotherJohnson]

I’d be most suspicious of interconnects... but you say you’ve checked them.

After that, plug them both, and the preamp, into the same outlet.

Not likely a tube failure ... but reseat them all. Sounds like you’ve done that too.

[Big Dog RJ]

Thanks for the suggestions maties,

I'll give it a retry this Friday, as I'm not off until then. Been pretty flat out as Melb/ Vic state went into lockdown again... hence, people are starting their favourite activity of panic buying. We're only in lockdown for just 5 days, these chaps can't over it

Regarding the re-seating of tubes, yes my chief tech suggested this, especially on the input tube. Said to take it out and place back in. I'll do that again if the hum persists.

Will report back on Friday night.
Best, RJ

[roberto]

RJ, wolf mate,
Disconnect the input cable and turn the amp on. If you have the 60Hz, it is the amp that is causing it. The small tubes are culprit to produce odd noises like 60Hz...swap small signal tubes. Do one by one...chasing hum is sometimes difficult.

A hug, woof woof,
Bobby.

[Big Dog RJ]

Yes, I will do that. Infact, I'll try out a few things in sequence and see how it goes. I'm sure I'll figure it out because before these amplifiers were absolutely dead quiet. Something is definitely causing that right channel to hum along...

Thanks mate, appreciate the advice.
Cheers, RJ

[Big Dog RJ]

Very pleased to report, the hum is gone!
Replaced both Input and Driver tubes and very fine results.

So now, I've got no new spares of the M8080, rather the much older original pair of Mullards that are still good! I'll have to order in a few more sets of those Mullards as I guess all the bumps and rides in hauling these monoblocks up state would have caused some travel sickness... As Eve Anne once rightly pointed out, tubes don't like to travel, especially air freight. So keeping that in mind, I need to order a few spares.

BTW, the monoblocks are sounding superb! I just made a post under the MF2550SE tab. Cheers to all, appreciate all the help.
Big woof, RJ

[admin]

Glad to hear it was an easy fix. Enjoy the music!

[Big Dog RJ]

Maties, I must confess something I just realised only now.
This is what happens when you install gear and connections after midnight, especially around 3am!

I had apparently mixed up the R & L inputs from CD player to Preamp!!! Damn, how could I have missed that...?

Remembering what AJ said about checking the interconnects, Robbo advised to remove one, Admin also mentioned to check the grounding etc., I did check all these in sequence, swapped tubes, swapped amps, did push ups plus cart wheels... I hadn't checked the inputs on the preamp!

After all these decades of highend experience, a simple low-end approach of getting the interconnects right was not done. How pathetic! Even the wifey mentioned this and I replied that dept is all good, yeah right.

Now, more than happy to report the quietness is even quieter, absolutely dead zero silent, as it should be, plus zero hum from all sides.

Phew! What a relief. So, without getting into a major tragic turn of events, as you all suggested, first things first, check the bloody interconnects!

Much appreciated all, and a mighty woof'n.
Best, RJ
Keep safe all

[AnotherJohnson]

My experience is that 75% of the time, if the unit was good before you moved it, then the interconnects are the likely culprit. We’ve all been there.

Great that you sorted it out! Congratulations!

[Big Dog RJ]

The fix of hum was short lived!

The hum came back and more so a loud pop! Whenever a light/fan switch was on & off in the wash room!...?
Why that darn light switch? And only that switch, no other switch in the house... how on earth could that light switch interfere with the audio, especially when it's supposed to be on a dedicated line wired to the mains board... or is it?

So, just yesterday on Thurs morning, I called in the experts to have a look and diagnose the problem. They checked each AC outlet around the house, they checked each CB on the mains board, also checked the dedicated AC line for the system and all was well. Then they disconnected the dedicated line and ran an entirely separate line from mains board to the audio system on a separate 20amp outlet, just to check what's the fuss about. It turned out to be the right channel monoblock!

That particular monoblock has something probably come loose or touching inside, underside or on the board somewhere, which is causing the hum and loud pop static charge whenever that darn light switch is activated. So they replaced the switch and the fan, now that works super fine but that loud pop is still very much there and it follows that one monoblock... so it's gone back up state for another service.

Until then, I'm enjoying the big bold & the beautiful MF2550SE, marvellous!

So, as I'm enjoying every bit of finesse from this big beauty and the CLX's are also enjoying every bit of that mighty fine level of control, total grip and effortless drive, the musicality is just as satisfying as CJ's tube gear. Everything is very apparent and extremely well balanced, highs, mids and formidable bass lines, it's all crystal clear and very easy to follow, even on complex passages.

So what am I missing on the tube gear compared to this, the good wife asked. And there it was! That added soundstage depth and full 3D holographic imaging presence that is a hallmark of CJ's tube amplifiers. That's what I'm missing and craving for, in addition to that lush magical midrange, which is highly addictive it's so hard to give up.

Cheers to all! Best woof'n RJ

[roberto]

Tu-be or not? Are you feeding the amp from a separated AC wall outlet? Yes, I understand that you have a dedicated AC line from the house AC distribution box. What you are having is a ground loop. Something is wired different. An AC dedicated cord is adjacent to the cord of the fan.

You can't imagine what the electricians have done, even having a diagram of what to do.

Or,
1) Did you swap the amplifiers? No? Swap them.
2) Is the same bad mono block after you did make the swap ? Yes? Mono block has an AC issue. Check inside the polarity of the primer transformer.
3) If now is the other mono block with the problem, then it is your dedicated AC line. Just guessing, there could be a mixed cords between the wall and the AC female wall outlet that it is giving a problem. You are chasing your own rabbit tail.

Happy listening!

[Big Dog RJ]

Happy to also report that the monoblock has been fixed!

It was not any ground loop issue, no AC line issue, no mix up in wiring, no issues with other AC outlets or switches, transformer issue... none of those whatsoever!

It was a loose soldering joint under one of the tube sockets, and a loose wire near one of the Teflon caps that were just recently upgraded. The soldering on those ends had virtually come off... and thus was causing the hum and loud static pop whenever that monoblock was having an issue, relaying an electrical feedback into the mains grid and onto whatever switches that were close to that dedicated AC line.

All perfectly working and picking up the amplifier on Friday as well.

It's a good thing to note down these symptoms so that in the future if anyone was to experience the same thing, they must get the amplifier checked, especially when there's a significant hum along with a loud static pop coming from the AC grid feeding that power amplifier. This is something serious and must be attended to immediately. A hum coming from only one channel is not always a ground loop issue. We only assume that since it's pretty common, especially with monoblocks. However, in this case it was far more than that.

Something to think about and worth taking notes.

Cheers maties, and enjoy those fine tunes!
Big WOOF! RJ

[roberto]

Enjoy those fine tunes RJ. It is great to know that it was a simple thing too!

Happy listening! Woof,woof!

[Big Dog RJ]

Thanks Robbo mate.

Infact, after a brief chat with the head service tech further on the topic of soldering, it was also a loose solder joint at the amplifier's RCA input in relation to a ground wire coming off, so due to this the hum occurred.

The loud static pop was due to another soldering issue as mentioned earlier. Anyway, all fixed now and picking up on Friday. Cheers maties!
RJ

[Big Dog RJ]

Ah! G'day maties,

Finally, picked up the monoblocks today, plus phonostage and TT rig, all connected up and playing beautifully!

I must say, those Teflons, Vishay resistors and all the upgrades and adjustments made have been well worth the investment. The performance is a stunning one, just superb!
Couldn't really be happier at this stage or need anything more, really.

Now my system is complete.

Cheers to all and a big woofty woof'n!

Oh, and do enjoy those fine tunes!
RJ

[admin]

Lookin great! Just a nice clean setup with some "holy grail speakers". Enjoy.