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Good afternoon everyone!
Perhaps maybe, someone on here, can tell me how to fix my Musical Paradise MP-401 single ended tube amplifier.
Here's my question.
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I opened up the amp, and took a closer look at it.
Among trying to figure out what kind of preamp tubes that I can use in it, I'm also trying to figure out how to get it to quit humming.
A good high-end amp, has virtually no noise floor.
But if the amp has too high of a noise floor, it's going to defeat the perpis of reproducing music the way it's supposed to be heard.
The object is, to get the amplifier out of the way, and let the music flow threw it, as if the amplifier isn't even there.
But if you have things going on like hum hiss and other noises, that's not going to happen.
So, how do you get rid of that humming noise?
This is the problem that I'm trying to solve.
The only two things that I see going on inside the amp is, there are two wires that could be cozzing the problem.
One of the wires, is an earth grounding wire, that's attached to the chassis via a lug nut on the bottom of one of the output transformers.
I removed that wire, and capped it off with a piece of black electrical tape.
I done this to keep from cozzing any short cerkets.
But this didn't stop the amp from humming.
The other wire, is a teel green wire, running from the power transformer, and going straight to the negative poles of both the right and left speaker terminals.
I know that, there is a technical reason for Musical Paradise putting that wire there, but it's unknown as to what that reason is.
I've been working on vacuum tube electronics sense I was a five-year-old little boy.
But I've never seen anything like this before, until now.
Also, there is a switch in the back of the amp that's marked, "105, 215."
This means that, this amp will work just about, anywhere in this world.
Here at my house, my household voltage, is 125V-AC.
I tried switching the voltage switch to 215V mode, just to see what the amp will do.
But before I tell you what happened, perhaps I'd better tell you about my other discovery first.
I took all of the tubes out of the amp, then turned it on.
I was thinking that, it wouldn't hum threw the speakers without its tubes being in it.
Boy was I ever wrong about that!
Because the amp still hummed, even without the tubes being in it anymore.
But now when I put the tubes back in the amp, this is when I started playing with the voltage switch in the back of it.
When the amp was switched to 215V mode, the humming stopped.
But when I switched the amp back to 105V mode, the humming noise came back.
Oh, I know that, while plugged in to 125V-AC, and operating the amp in 215V mode while plugged in to 125V, it's not going to operate the way it's suppose to operate, because at this point, I've cut the voltage in half.
Let's just say that, this amp puts 450V-DC on the plates of its tubes.
But I have the amp plugged in to 125V, but operating in 215V mode.
Instead of 450V-DC, I am now hitting the plates of its tubes with 225V-DC.
Sure, this will work with some amps, if that's all they really need.
But if the amp is suppose to have a B-plus voltage of 450V-DC, you can't get that from a power transformer that's sat up to have 215 volts going in to it, from 125 volts.
But as I stated above, when I put this amp in that mode, the humming noise, went away.
Just only switching the amp back to 105V mode, brought the humming noise back.
If you're like me, then you want that humming noise gone for good.
But how do you make that happen with your current household voltage?
This is the mystery that must be solved.
The question is, how do you go about doing that?
Follow Ups:
That hummed when I first got it. I tried all the normal stuff to get rid of it, I only was able to reduce it.
I remembered looking at a Audio Note Phono preamp kit instructions showing each ground from the input connectors going directly to the pcb and not connected together like you show in the pic. Even Counterpoint did this very grounding thing. After I redid the grounds to have each one connect directly to the PCB in my Musical Paradise, the hum was all gone.
Maybe you can try this and see if that helps take it away or reduce it.
The puzzling part of what you said when you switched the voltage. Try using a Variac and set the voltage to 110 VAC on the variac and see what happens. When you bought the amp from MP did yo tell Gary what your line Voltage was?
Good morning Cougar!
To answer your question, no.
I bought the amp used from Sounds Classic.
This amp is 16 years old.
I'm quite sure that, this is an oversight on Mark's part.
I'm thinking about calling him this up coming week, to ask him about it.
And to answer some questions that someone else asked me on here, I at first drove the amp from my iPad, via my Earman Angel portable headphone amp/DAC.
I wanted to see what this amp sounded like, when fed DSD files.
But then I tried it with my Presonus Quantum ES-4 audio interface with my computer providing the digital audio signel.
I heard the hum from my Avantone Pro CLA-10 studio monitors, as soon as the music stopped.
I wanted to know where I was geting that humming noise from.
And so, I disconnected all audio sourses, and listened to it that way.
I don't own a variack as of yet, but I do own a power oscillator transformer.
I thought that I could get rid of the hum that way.
But I was wrong about that.
I also thought that I could get rid of the hum by disconnecting the earth ground wire from the power inlet.
But that didn't work either.
I was curious, and so, I tested the amp without its tubes, the hum was still there.
The only other audio sourse that I used, was my NLS digital talking book player, with an NLS cartrage, with lots of wave files on it.
But sense both it and the Earman Angel both operates on rechargible batteries, one would think, there won't be any humming noise.
But, that didn't happen that way.
Because, the amp still hummed.
product with point to point wiring, all the products I have purchased and seen on line have had PCB's inside that have nice neat layouts and connections.
The more I look at the pic you posted it looks like there are several cold sold joint on the wiring.
If this is around 16 years old and IF those are the same original caps in there, they could need to be changed. I would get back with the guy who sold that amp to you.
Good morning Cougar!
I thought about that, and I think I will do that.
Because usually, he recaps stereo receivers, power amps, preamps, and other audio gear before he posts it on his website for sail.
Too bad he won't be open tomorrow, but I can call him Tuesday and ask him about that.
do any mods or repairs to this amp?
Good morning Cougar!
To answer your question, it doesn't look like Mark done anything to it.
Because usually, he does go over everything and checks for anything that mite be problemadic.
Perhaps this is an oversight on his part.
When he opens up at 10:AM CT tomorrow morning, I will call him and ask him about this amp.
mechanical like from the transformer, or through the speakers?
Good morning Ozzie!
Yes, the hum is threw the speakers.
But what I don't quite understand, is this.
It hums threw the speakers, even when the tubes had been removed from the amp.
This is the very first time that I've ever encountered this.
But never in 47 years of doing this kind of work.
That is, until now.
And for the one that asked about the wires, the one that I disconnected, was an earth ground wire that's connected to the power inlet.
And where I disconnected it at, was an O-lug on a bolt held down to it, by a lug hex nut.
That's how I disconnected it, and capped it off with black electrical tape.
The teel green wire, looks like it's running in to the grounding speaker terminals from the power transformer.
I did shoot a picture of the inside of the amp thoe.
I'm just trying to figure out how to upload it to the site so that, you all can see what I'm talking about.
for the "upload image" line. Click on the "choose file" link to the right of "upload image", and your photos should appear. Then click on the photo and select "preview message" below to make sure the photo appears in your post. The photo will appear first in your message. If you want to change that, that will be another procedure. Others may have better suggestions, but that's how I do it.
Good morning everyone!
Ok, here goes nothing.
I'm phrasing it this way because, I have no eye sight above lights and shadows.
Everything I do via any digital device, all has to be done threw text to speech converters.
On my computer, I use JAWS.
On both my iPhone and iPad, I use Voiceover.
I had to take the amp outside in the yard.
This is so that, I could use the sunlight in order to be able to shoot the inside of the amp.
I had to email the picture from my iPhone, to my computer.
If only I could use a USB cable to cut and paste pictures from my iPhone to my computer.
My wife, can do a lot of things with the mouse.
But sense I can't see well enough to do that with the mouse, the keyboard of my computer happens to be my best friend when it comes to this kind of a thing.
So, please be patient with me.
I will give it a go.
OK, that's a good photo, but not large enough for real troubleshooting.
I can see that the amp is grounded at the speaker outlets and there is one ground wire that goes into the amp probably to the cap at the top left. From there it goes to more caps and at that point it is lost. I can't see the AC power inlet and if the unit is grounded through the power cord as it should be. I can't see where the audio input is grounded or the input tubes where there cathodes are grounded. There is just not enough information; but there is the appearance of multiple ground loops.
So, at this point I would reconnect anything you have disconnected and find a technician or audio hobbyist in your area to help with the diagnosis.
Good afternoon Palustris!
The only wire that I disconnected, was an earth ground wire that was attached to one of the output transformers, via a bolt and nut.
The wire is turminated by an O-lug.
And that wire is coming in from the IAC power inlet.
But on the primary side of the output transformers, they each have two wires.
One is going to the plate of each one of the output tubes, and the other wires are going to the B-plus power supply.
I mean B-plus voltage.
But on the secondary of the output transformers, there are three wires each.
One is ground, the other two are 4ohms, and 8ohms per channel.
But wouldn't that choke get rid of hum too?
I have a much larger amp then this one, that also has a choke in it too.
it is equally the same age as this one.
But it's push-pull.
Two KT77 tubes per channel in that one.
And after 16 long years of service, I've never once heard that amp hum.
But that one, is my Eastern Electric M-520 amp.
But the one that I uploaded a picture of, is the inside of my Musical Paradise MP-401 amp.
This is the one that I'm trying to figure out.
I also read somewhere on the net that, "heavy filtering, can make single ended tube amps stop humming."
But it didn't say how.
I guess you have to use more caps?
The problem is not the wire that grounds the amp by the power cord. That should be connected or the amp won't be grounded.
You never answered my question: is anything connected to the amp such as a CD player?
Has this amp ever worked without hum? Is this a new problem? How old is this amp?
The problem is probably not insufficient power supply filtering; there are plenty of capacitors unless the amp is old and the caps have dried out. The problem appears to be a ground loop.
Good morning Palustris!
I don't know if you saw my last few posts, but I did tell Cougar about all of this.
But sense you asked, no.
The amp hummed, as soon as I unboxed it, and hooked it up.
The amp was made in 2008.
So there for, this amp is 16 years old.
I drove the amp via my iPad, and Earman Angel portable headphone amp/DAC.
I wanted to see what this amp sounded like, when fed DSD files.
Aside from that, my Presonus Quantom ES 4 audio interface, with the computer providing the digital audio signal.
And later on, my digital talking book player, with NLS cartrages that have 16bit, 44.1KHZ wave files.
But either way, I couldn't make the humming noise go away.
I did call and spoke to mark about it yesterday afternoon.
When I told him about the part where and when I removed the tubes, and still heard the humming noise, it stumpped him.
But I told him about that problem, sense he was the one that sold it to me.
I think he's gonna make arangements for me to send it back to him, so that, he can check it out.
But I also thought about something.
If the primary side of the output transformers are wired up wrong, wouldn't that be causing the humming noise problem too?
Thanks in advance!
Good morning Ozzie!
Yes, the hum is threw the speakers.
But what I don't
There are three different forums dedicated to tube audio. A message there might get more response.
There are more mysteries in your post than there are clues.
Does the amp have a grounded power cord and if so, is the incoming green ground wire connected securely to the chassis? Is the amp connected to anything other than speakers?
Is the signal ground connected to the center tapped secondary of the power transformer and are they both connected to the chassis ground?
Your two mystery teal green wires that connect to the output transformers: are they connected to the primary or secondary of the power transformer and are they connected to the primary or secondary of the output transformer? The wire you disconnected: was it connected to the primary or secondary of the output transformer.
The output transformer secondary's ground should go to the respective input tube's cathode ground on each channel; the input tube's ground should be the "quiet" end of the ground buss which should be connected directly to chassis ground. Without a schematic it is hard to know how this amp was wired. Photos of these areas would probably help.
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