An integrated Tube amp and possible GIANT killer???? the MP-301MK2

Lyndon · « **Reply #40 on:** 9 May 2011, 03:27 pm »

John,
Did you have some issues (hum) when you purchased those Eico amps back when you were living in the States?
Lyndon

JohnR · « **Reply #41 on:** 9 May 2011, 03:31 pm »

Hi Lyndon, not that I recall. Those however were vintage gear and I'd apply different criteria to them and generally assume that power supply cap replacements are needed.

...

Why do you ask? (You have a good memory!

PS. I still have a pair of Eico HF-30s and an HF-87. All needing something or other of course

Lyndon · « **Reply #42 on:** 9 May 2011, 03:34 pm »

I so wanted those monoblocks you found! I picked up an Eico ST-40, not as pretty, and still have it running in my bedroom system. It does have a slight hum when there is no source playing, but it has a great sound.
If you were still in the San Fran area, I would tell you to attend those Burning Amp Festival. I would love to chat with Nelson Pass for a few minutes.
Lyndon

eclein · « **Reply #43 on:** 9 May 2011, 03:41 pm »

JohnR--I just feel horrible because some folks went and got these or ordered them and now this whole thing is happening--the hum from hell!!!!

It sounds like a grounding thing but I'm not knowledgeable enough about amps, etc.. to know exactly--it is a drag, and I'll figure it out.

JohnR · « **Reply #44 on:** 9 May 2011, 03:45 pm »

Well Ed, you know, caveat emptor and all that. I thought I read in the linked thread that the chap was willing to take them back. It is a tricky issue, when it shows up.

Ericus Rex · « **Reply #45 on:** 9 May 2011, 03:56 pm »

Ed,

Next time the hum comes around, go to all the tubes and give them a good tapping with your fingernail. See if the hum stops or somehow changes. If no change happens, then grab the top of each (using gloves) and 'rock' the tubes in a circular motion in the tube sockets. Do this with the amp on and let us know if you experience any change. My guess is that the tube sockets are not properly engaging the tube pins. This would explain why it gets worse for you after 7-8 hours (thermal expansion).

eclein · « **Reply #46 on:** 9 May 2011, 04:11 pm »

Ericus- I'll try that but I can say that the tubes fit the sockets very well, tight, not loose at all. When I read your sentence about moving them around in a circular motion the first thing I thought was "the tubes are in there so tight thats going to be difficult".

Right now today as I type I can't hear any hum until the music stops or I'm sitting right up on the amp, I listen very nearfield-like 6' from center of the two speakers. The speakers are about 6-7' apart and I'm sitting 6' back using the triangle setup (I can't find the right words here)....you know what I mean.

I love the sound of the amp and will figure out whats up with it but in the meantime I'm enjoying some tunes!

Ericus Rex · « **Reply #47 on:** 9 May 2011, 04:50 pm »

There are probably 7 pins for each socket. It would only take one to be ill fitting for problems. The other 6 could still be tight and make it seem that the tubes fit very well in the socket. This method may also reveal a solder joint problem at the socket.

I spent about 2 hours reading all 24 pages of the head-fi thread this morning

. I sounds to me that Garry is just making sure the tube newbies (many on that thread) aren't expecting tubes to be as quiet as SS stuff. Noise within a foot or two of the speaker should be expected from an amp at this cost. If you're hearing any tube noise (rush, hiss or hum) at 6 feet then you certainly have a problem and I'm sure he'll take it back as he said many times in the thread. It's just a real bummer that you'd lose the shipping. Sounds like quality control issues in China.

eclein · « **Reply #48 on:** 9 May 2011, 05:01 pm »

I'm going to just play music through it for the next couple weeks and then re-evaluate because Like I said it sounds excellent. Like right now I've got Lee Ritenour/Larry Carlton CD playing and I'm fully into it!!! LOL...toe tapping the whole nine yards....so I'm just gonna listen for awhile. If its bad it will still be bad in a couple weeks then I'll decide what to do, this amp was a gift so I'm just grateful to have it at all and I'm not complaining at all if this is the way its going to be I'll be fine with it.
Ericus- I'll do the tube thing you suggested later and let you know what happens, if they find me charred to a crsip you'll know it was the tube sockets...LOL!!!!!

Quiet Earth · « **Reply #49 on:** 9 May 2011, 05:29 pm »

*******I don't think wiggling the tubes around while the amp is on is a good idea, proceed at your own risk of damaging the amplifier and yourself.*******

Ed, in the earlier cheap tube integrated thread I asked you about the heat problem. Can you tell us if the AC power transformer is running extremely hot or is it just the total amplifier package in general that seems hot. If it's mostly the AC transformer then it may be possible for the designer to understand why the unit hums. I can think of a couple of reasons, but you need to say if the AC power transformer is burning hot or not.

eclein · « **Reply #50 on:** 9 May 2011, 05:52 pm »

OK.....Is it the big square thing behind the tubes*** Because that gets really hot, as does every other part.....look under astricks

monsterbill · « **Reply #51 on:** 9 May 2011, 05:58 pm »

Quote from: Quiet Earth on 9 May 2011, 05:29 pm

*******I don't think wiggling the tubes around while the amp is on is a good idea, proceed at your own risk of damaging the amplifier and yourself.*******

+1 on this point. While a lot of folks use this method for diagnosis, I understand that ironically one way to *create* a tube problem is to mess around with the tubes when they're hot. Don't give MP an excuse not to refund your money.

eclein · « **Reply #52 on:** 9 May 2011, 06:04 pm »

Actually I wasn't going to do that, it seemed very risky to me. Today right now I have like a minor hum, only can be heard when music is paused. It sounds to me like a grounding problem???? Changing all the tubes made it 80% quieter......

monsterbill · « **Reply #53 on:** 9 May 2011, 06:14 pm »

Ed, could be a grounding problem inside the unit, a wire too close to the transformer or the transformer humming. Really hard to nail this stuff down, but if it's happening with a large # of units at objectively unacceptable levels it's a design issue.

However, to eliminate external causes, you can try (1) lifting the ground on the PC (use a cheater plug, but dont keep it this way) , and (2) playing it with different sources or no source (but never play it without speakers/headphones plugged in!).

Ericus Rex · « **Reply #54 on:** 9 May 2011, 06:55 pm »

As a long-time tube owner I'm just trying to help guys.

Quiet Earth · « **Reply #55 on:** 9 May 2011, 08:14 pm »

Quote from: eclein on 9 May 2011, 05:52 pm

Is it the big square thing behind the tubes

I didn't see any internal pics of that particular model on their website so I can't tell if it's a cover for the AC mains power transformer or if it's a cover for the two audio signal output transformers, or if it's a cover for all three.

A couple of things crossed my mind, just thinking out loud if that's OK. (This is not a diagnosis.)

1. I noticed on their website that the AC input power spec is listed as 100-110V. This makes me wonder if the AC power trannie is having trouble dealing with United States 117 - 123 volts that many of us seem to have in our homes. Normally this wouldn't be a too much of a concern but,

2. This is a low priced amp so maybe (MAYBE!) the AC power transformer is already at its maximum capacity and the higher AC input is causing the variable hum, especially as your incoming ac may go up and down during the day.

3. It's possible that the power supply design is ambitiously over-taxing the transformer with too much capacitance after the rectifier, although I do realize that this has a solid state power supply, but still..... you never know. We would need a schematic or a peek inside to talk about that issue. It's probably better to run it by the designer first.

4. There is a lot of activity stuffed into that small package. Just having the power supply very close to the tubes and also close to the audio output transformers might be part of the problem. Again, a layout possibility.

Edit and addendum :

5. I see the term "worldwide use" next to the ac input spec. Does this model have a switch mode power supply? If it does, then disregard my comments about the AC power transformer.

monsterbill · « **Reply #56 on:** 9 May 2011, 09:26 pm »

Quote from: eclein on 9 May 2011, 06:04 pm

Changing all the tubes made it 80% quieter......

Ed, did you change to lower output tubes? If so, maybe this fact could help Ericus/Quiet Earth with their generous diagnostic posts. If not, maybe the stock tubes are the issue, either because they need more break-in or are faulty.

My 2 cents are that you should run this on a system you don't listen to and go back to your MP 301 v1 for a few days. If the hum is audible from your listening position after burn in, return it to MP for evaluation. Garry will either fix it (Yay, problem solved), or tell you that this amount of hum is "normal" (Boo, but then you can just get your friend's money back and get something else).

eclein · « **Reply #57 on:** 9 May 2011, 09:34 pm »

Bill....I don't know if they are lower output tubes, you mean you can get tubes that put out more signal than others can???

I talked to my guy Jon at thetubeshop.com and sent him the list/grid with replacement tubes and asked him for Mullard EL34 tubes I knew he had, and then he also had some RCA's that fit the pre-amp part (Not sure of the exact size of those or the output of any of them)

Quiet Earth- Good suggestions but I need to get a torx wrench set or whatever to open up the case and look....

Quiet Earth · « **Reply #58 on:** 9 May 2011, 09:45 pm »

Ed,

Please don't open the unit up for me to try and diagnose over the internet. I don't want you to void your warrantee, or get yourself hurt, or cause any more damage to the unit if it is unnecessary. I was really just trying to give you some more ammunition for a better discussion to have with Gary.

I was just wondering if you or (anyone else) knew about the power supply because you mentioned hum and hot temperatures in the set of problems. I saw one user on that thread that you linked said his transformer covers were not hot to the touch at all. He is using the 230V version. Maybe someone in China is putting in the wrong ac power transformer. (I saw a post where they also substituted the wrong ac cord, so you never know.)

Ask Gary about it.

monsterbill · « **Reply #59 on:** 9 May 2011, 09:57 pm »

Quote from: eclein on 9 May 2011, 09:34 pm

Bill....I don't know if they are lower output tubes, you mean you can get tubes that put out more signal than others can???

Yes, just like lightbulbs. I'm a lightweight when it comes to tube lore, but I seem to recall that Garry said that EL34s have a higher output than 6L6s, which doesn't really explain why you would hear less hum with the EL34.

Anyway, if Garry's offering to help, I think you should take him up.