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"Noise" on all Inputs of PrimaLuna EVO 400 Integrated Amp / Recording Provided...


JeffLebowski
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Hey Guys,

So, on the weekend my amp started to make a sound when the volume button was turned down to zero and it was present on all the different AUX inputs.

 

What does this sound like to you? The amp/tubes? Electrical Line issues? 

At the 28 second mark, I turn off the amp and you hear the lovely crackling sounds of the tubes lol.

 

Thanks so much,

Cheers

 

https://www.dropbox.com/s/0dwdb6veo5mmafr/New Recording 12.mp3?dl=0

 

 

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How long have you had the amp Jeff?  Is it under warranty?  Is the retailer near by?  Seems like with the problems you have reported it may be time for another set of eyes and ears.  That's a bit of money to spend and it not sound right.

 

I have the PL Dialogue Premium HP.  Just changed out the two tubes Fido is referring to (V11& V12) with some nos tubes from the 50s produced in Holland.  Burning in as I type.

 

Good luck with getting it squared away!

 

 

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2 hours ago, Fido said:

Sounds like a bad preamp tube to me. Most likely one of the two center preamp tubes.

Yes I would agree. Sometimes it is really gone by cleaning the pins of the tube and put it into the socket twice when the amp is switched off. It happens in my amp often with changing seasons once. Can you change/swap the tube with her sister from left to right and check if the hiss moves with the change or is this Prima Lune amp designed in a way that the faulty position tube is a stereo tube for both channels in its stage of the circuit design, as one can use a tube for two mono stages of one channel or doing the same job in parallel for the left and right channel being a double triode.

If it is a one channel tube and the hiss remains on the very channel after swapping the tubes then the faulty part could be a small electrolytic cap like it is used as a cathode accelerator if this is the right term in English. But I would think it is the tube itself.

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Sounds to me like arcing, that crackle and pop, bacon in frying pan sound when a resistor starts to internally arc. Could also be just a bad solder connection arcing or even a tube/tube socket.

 

This often happens to plate load resistors especially if chosen near it's limits. Many engineers feel it is ok to run a resistor near it's dissipation limit, I will say depends on application but for a high quality amplifier a good engineer will choose plenty of headroom, I like at least 5x preferably 10x. For example you have a plate load resistor dissipating 100mW, I personally would use a 1 watt plate load resistor (1 watt) but 1/2 watt (5x) would be ok. I have seen way too often 2mA of current on a 100k plate load resistor, this dissipates 400mW and they use a 1/5 watt resistor. Yes technically it is within the maximum limits but depending on the temperature coefficient it could change values drastically and also fail sooner. 

 

If you are careful around high voltage open her up and poke around with chopsticks until you hear the arcing noise become worse. Wiggle everything you can and keep one hand behind your back or in pocket while doing this.

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On 11/10/2021 at 9:44 AM, Fido said:

Sounds like a bad preamp tube to me. Most likely one of the two center preamp tubes.

 

So, finally had time today to do a re-arranging of tubes.

What I did was move the two preamp tubes in the middle (Number 11 and 12 or 3/4 to make it easier) to the right channel sockets 13/14 (5/6).

The rattling, crackling sound went away and it isn't dead quiet like before but there is a real negligible hum.


Please help me with this if you could....guys....we have two pre-amp (gain) tubes in the centre slots and two driver tubes on each side of those pre-amp tubes.

What would cause noise in the first place? 

Could a faulty driver tube cause it? Only a faulty pre-amp tube? (not looking at the power tubes) 

Or, could any/all of them cause it?

 

If it is the two centre tubes only then I guess I should put them back switching the positions they were in. Left to right and right to left as the noise was mostly from the left channel. 

 

To add to it, when I was about to do the swap, I  gently grabbed the tops of all the tubes(driver included) and made sure they were set in place and discovered that the 9 and 10 sockets were definitely loose and the 13 was slightly loose. The rest were  totally solid.

 

Confused in Canada lol.

 

Again, thanks for all the help here guys.

Any suggestions welcome.

I just want to fix this and move on and listen to my records and stream music.

 

Cheers

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I would take the humming seriously. I am not a technician, so other members should be able to say something more about it. But a hum could be an indication that something is wrong with the power supply. E.g. a power supply capacitor or a diode. I don't want to scare you but you should check this. Maybe it is just a badly shielded cable.

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whenever I had any noise in my evo 400 it was always quickly resolved by switching out the center 2 preamp tubes and basically it only took unplugging them and plugging them back in. My Brimars became noisy after about 6 months but replacing them with the stock Primaluna preamp tubes immediately returned the amp to its previous quiet clean sound.

 

Some people might suggest to spray the tube sockets and tube pins with Deioxit but that wasn't required in my circumstance.

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Thanks again for all the help guys.
I want to re-state something I said earlier which was entirely wrong.
Being new to tubes, I stated that 3 of the front tube sockets were loose. They are not loose, but rather the tubes are loose fitting in the sockets. I thought it was the socket moving but it is the tubes easily moving when I wiggle the tops of them.
I do feel the appropriate amount of shame.

But is it normal to have loose tubes? The rest are pretty solid up front and the power tubes are in there like cement.
BTW, the front tubes are in the sockets all the way.

Here is a 12 second video of the loose tubes:

Dropbox - Valve Movement.MOV - Simplify your life

Cheers and again, I am sorry I stated the wrong thing.

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I doubt it is the actual sockets but anything can happen, if it is just the female part of the socket you can use small jeweler screw drivers or better a dental or mechanics pick and re-tension the sockets to fit tight again. You can also have a bad solder connection to the tube sockets that after removing and installing has altered the connection.

 

Since all of your front end tubes are 12AU7, it sounds like you took the two high gain tubes (3&4) that are the most crucial to noise and swapped them to tubes 5 and 6 which are phase inverter and driver where noise is less critical to the circuit. The first stages have more gain and also any noise is multiplied by gain further down the line. So it sounds like to me you have a noisy 12AU7 tube that you moved to a less critical section of the circuit hence the noise is less than what it was. I recommend putting the tubes back to how they were originally and while the amplifier is on tap the side of each tube with a chopstick or wooden pencil, this may make the noisy tube easier to find and just replace it. Also while it is on give each preamp tube a wiggle and listen for noise, do not pull it out of the socket just gently rock it side to side in the socket.

 

So probably just a noisy microphonic tube, these amps have the autobias feature which I have seen many fail and have to be repaired, you may just want to bring it to a good tech to have the whole thing looked over while it is in there.

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  • 3 weeks later...
On 11/10/2021 at 2:56 PM, captainbeefheart said:

 I like at least 5x preferably 10x. For example you have a plate load resistor dissipating 100mW, I personally would use a 1 watt plate load resistor (1 watt) but 1/2 watt (5x) would be ok. I have seen way too often 2mA of current on a 100k plate load resistor, this dissipates 400mW and they use a 1/5 watt resistor. Yes technically it is within the maximum limits but depending on the temperature coefficient it could change values drastically and also fail sooner. 

I have used a 4x multiplier for many years and never had a resistor fail.

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I listened to your recording, and what I heard is very similar to dusty/dirty tube sockets.  Loud cracks and pops are in my experience akin to inadequate connections, but I'm familiar with Prima Luna, and can say with confidence that soldering-related issues are, at the very least, not likely.   The workmanship on Prima Luna Products, which are wired point-to-point, is among the very best available.

 

"I doubt it is the actual sockets but anything can happen, if it is just the female part of the socket you can use small jeweler screw drivers or better a dental or mechanics pick and re-tension the sockets to fit tight again. You can also have a bad solder connection to the tube sockets that after removing and installing has altered the connection."

 

I'm sorry, but............. ATTENTION!

 

I have seen instances here on this forum over the past 20 years (which is when I became a member), where people with very little or absolutely no experience working with high voltage circuits have been badly shocked by either poking around inside an energized amp in order to move wires around, soldering in a live amp (an alarmingly ignorant thing to do -- even for an experienced technician, etc.

I agree that tightening the female socket pins with a dental pick or similar tool might help.  HOWEVER (sorry for the all-caps, but it's necessary).  There is a structure in a tube referred to as the plate or anode.  That is where the high voltage on a tube resides.  If one happens to be using a conductive tool for pin re-tensioning, even if the component is turned off, this represents a seriously dangerous safety hazard.   I've been working-on and building tube equipment for a long time, and must confess to have made stupid mistakes -- simply from being in a rush, or too confident (Lots of that here on the forum)...or careless, or whatever.

 

I've said this over and over again here:  EVEN IF A COMPONENT IS TURNED OFF AND UNPLUGGED IT IS STILL POSSIBLE TO RECEIVE A POTENTIALLY LIFE-THREATENING ELECTRICAL SHOCK FROM THE CHARGE STORED IN POWER SUPPLY FILTER CAPACITORS.  IF THE POWER SUPPLY DOES NOT MAKE USE OF A BLEEDER RESISTOR ON ITS OUTPUT, WHICH WILL ALLOW CAPACITORS TO GRADUALLY RELEASE THEIR CHARGE, ONE PUTS ONESELF AT SERIOUS RISK FOR ELECTROCUTION.  

 

There is another way to quickly bleed down capacitors before doing any work, however I'm just going to leave out the details of that.  Leave the work to someone who knows how to work on this stuff.

 

So, what CAN be done in this case?  With the amplifier off, try removing and reinserting each tube in its socket a few times.  If the sockets have exposure to normal house dust (if they are covered or shielded), simple dirt can very often cause some of that gritty, scratchy sound in your recording.  This is a problem I have frequently, despite lots of dusting, and it can help.

 

If you have hum, that involves some extra investigation, and often depends of whether the frequency of the hum is 120Hz or 60Hz.

 

Hoping you solve this problem, although my main concern here was not so much the noise you have, but rather wanting to once again highlight the importance of safety when working on this stuff.  Passive crossovers are totally different animal.

 

I remember once, many years ago here, when one very confident member called another equally confident member a CHICKEN (good grief) for not being willing to solder inside a tube amp while it was plugged in and powered on.  The story ends with the member who owned the amp and wanted to work on it returning to the forum to share how he had gotten an absolutely enormous zap when his soldering iron accidentally touched one end of what happened to be a..... plate-load resistor.

 

Be Careful.

 

 

 

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Henry said: "First thing to check is connections, all connections tubes and input cables. Cleaning the pins of tubes and sockets is always advisable. Many different products available. Always consider connections before digging deeper or replacing tubes."

 

Excellent advice, particularly with male tube pins.  I use those green abrasive pads for the pins.   

 

SOCKETS:  IF YOU OWN AND KNOW HOW TO USE A MULTI-METER, CHECK FOR RESIDUAL DC BEFORE DO ANYTHING, MAKING SURE THE AMP IS UNPLUGGED AND TURNED OFF.  IF YOU DON'T KNOW HOW TO MEASURE FOR STORAGE CHARGE IN BIG CAPACITORS, LEAVE IT TO SOMEONE ELSE WHO DOES.  IF THERE IS STILL DC PRESENT, DON'T TOUCH.

 

Apologies again.  Know and respect your limitations!

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The first lesson on working with tube equipment. One hand in pocket. The 2nd lesson one hand in pocket. There are serious voltages inside a tube amplifier. Like Erick I have worked on and built many tube amplifiers, love the sound, and I am still respectful and follow the rules working on such gear. Again one hand in pocket and drain those filter caps first thing. 

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7 minutes ago, henry4841 said:

Again one hand in pocket and drain those filter caps first thing. 

Yes!  Thank you!  It's so important.

 

In case someone might be wondering why:  One hand in a pocket helps prevent a potential charge from going through the heart - and possibly stopping it.

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