Background hum

[MarkG]

Thanks for the quick replies. I discovered the mistake while I was still building the boards, about 10 seconds after I'd soldered the wrong one in place and clipped the leads. Oh well, lesson learned. Check twice, solder once. After reflowing the solder joints on the new connections that seems to have solved the worst of the hum. I still have some buzz at the top end of the volume but it isn't where I do my listening so I can live with it.

With the music going, it sounds great. iMac > MusicHall Dac25.2 > Crack > Beyer DT-990 (250 ohm)

Thanks again for a great kit, I feel another expensive hobby coming on.

Mark.

 

[Grainger49]

Be certain to move the iMac away from the amp as all computers create noise.

 

[deltaunit]

I've noticed that in general when I power on one channel usually comes up first and also when powering down, I guess this is normal? Could the E80CC have suffered in some manner because of this?

Is this normal behaviour? I'm wondering if the E80CC because of it's slightly different requirements to the E82CC's might actually be fine and maybe it's something else, especially as the hiss starts quite loud in the right channel then reduces to nothing and then starts up in the left channel and reduces to a quiet level. It's like it is repeating but doesn't get enough something to reduce the left channel down all the way...

I'm hung up on this tube now. I'm concerned if I buy another, it will just do the same. Tx

 

[Grainger49]

Yes, one tube heating and coming on faster than the other is normal. If you have two slower tubes in the same channel, like in a Paramount, it is even more dramatic.  

If you don't get sound in 10s that isn't normal.

Deltaunit, you might have a fellow Bottlehead in your town.  If so you might not have to buy a tube to check it out.

 

[deltaunit]

Thanks Grainger, I'm based in the UK, Bristol to be exact, so it might be a long shot but if there's anyone with a E80CC in the area - get in touch!

I'm thinking I just wasn't aware of the hiss at first, it is quite quiet and negligible against daytime noise (I also didn't plug my HDs in until after it was on to be safe so wouldn't have heard the rushing sound) so I probably just missed it at first. It was sold as being 100% though so I've just contacted the seller, just to see what comes of it.

Has anyone had a totally silent E80CC I wonder? Hope so, I'm on a mission now!

 

[Paul Joppa]

... a pronounced buzzing that comes in between 75-100% volume...

This is often a sign of RF interference; the upper range setting on a log taper volume control provides the highest impedance at the input grid and the greatest susceptibility to electric field capacitively coupled noise. In some cases it is actually television signals, at 30Hz (US) frame rate with lots of harmonics. Light dimmers, cell phones, electric motors, various appliances that you or the neighbors may be using, are other possible sources. Just a thought.

 

[MarkG]

Yes, that would make sense given where the amp is located and the rats nest of AC, computers, home theater gack and general crap that is in that part of my apartment. Thanks again for the help.

mark.

 

[fullmetal]

Replaced the 12AU7 and...silence! Thanks for the help!

 

[Viktor]

So even without the speedball upgrade the amplifier is supposed to be dead quiet? Because mine still gives of a low hum though it is impossible to hear when there is music playing as there's almost always some kind of background hum on the records themselves...

 

[Laudanum]

So even without the speedball upgrade the amplifier is supposed to be dead quiet? Because mine still gives of a low hum though it is impossible to hear when there is music playing as there's almost always some kind of background hum on the records themselves...

Have you tried a different source, like perhaps a CD player just to check?  I assume you're spinning vinyl since you stated "records".  Im far from being an expert but my Crack is stock, no speedball, only an Alps blue velvet pot and Mills resistors in place of the stock cements and it is dead quiet, no hum no hiss. My source is a digital music player and I recently added an old AH Tjoeb CDP as well and it is quiet with both.  I may be off base but I would think that eliminating the source itself as the culprit would be a logical first step.

 

[Doc B]

Hi Viktor,

Does the hum go away when you turn the volume down all the way? What headphones are you using?

 

[Viktor]

Hi! No the hum doesn't go away when I turn it down, it is basically constant regardless of volume level. I'm not using vinyl at the moment, feeding it from the computer with a music streamer II. Also, I'm using HD650 headphones. Maybe it is something with the tubes, I don't know if I can muster going through all the solderings either.....And since all the measurements were correct it is a bit confusing!

 

[Doc B]

Low hum levels aren't always directly correlated to bad solder joints. I would suggest trying different tubes if you have not done so already, as my hunch is that is the most likely source if the hum.  There is also a small chance that the amp is picking up the hum from a power transformer on a nearby piece of gear - if there is another power trans nearby.

 

[Viktor]

Ahh, okay! Unfortunaly I don't have any other tubes nearby, I'll see if it is possible to pick some up here in Sweden and try them out as well!

 

[Grainger49]

Viktor,

Doc supplies nice and new tube sockets with his kits.  But who knows when they were made.  There might be a little dirt/tarnish in the tube sockets.  Try removing and re-inserting the tubes 6 or 7 times to see if this cleans both the tube pins and socket.  It is easy, quick and often effective for noise.

 

[Viktor]

You have given me that advice several times no and I still haven't done it properly.... Of course I have taken them out and put them back in I think at least four times in total. Maybe I should also try with some de-oxidation/grease/super-duper oil as well. I have one here at home that I've used on contacts in my computers with success so maybe that could be worth a try also. I'll report back with my findings!

Thanks for all the help, most helpfull forum ever!

 

[Laudanum]

Viktor, Ive never been to Sweden but I would suspect that it's possible that one of the musical instrument retail stores would sell some new production tubes ... if there are any close to you.  12AX7 seems to be most popular pre-amp tube in newer production tube guitar amps but you never know.  Maybe worth a shot to make some phone calls. 

 

[Viktor]

Yesterday I took the big tube out and cleaned the pins for a bit then put it back in. The background hum was the same but I still listened to some music then all of a sudden all I can here is static, I was very afraid I'd destroyed my HD650 but fortunaly they seem ok. Then when I tried to turn the amp back on and listened with my SR60 ( my test headphones from here on ) there were no static at all and everything worked as before. I'm getting very vexed by this irregular behaviour, today I'm going to go trough the solderings once again as there is one part that I did a bit weir, its two of the connections for the 6080 where I put one wire to the bottom hole and the other one above, I don't think this should be a problem by maybe it is worth a try to put the both trough the same hole.... We'll see how it goes.

 

[Grainger49]

Viktor,

You have two problems, the background hum and the crackling noise.

There are a number of things that can cause hum.  A ground that is not well soldered becomes an "Ohmic" connection.  That can be checked by touching up all the ground connections.  

Another thing that might cause the background hum is the AC heaters to the tubes.  They should be twisted well and flat against the top plate.  The heater wires should be routed so they cross the signal wires at a 90 degree angle.

A loose ground or signal wire in your interconnects can cause hum... see the list goes on.  Have you checked with the inputs grounded?  (I think, can't remember all the posts in this thread, I think that your hum doesn't go away when the volume is all the way down.  That eliminates anything upstream of the volume control.)

The noise might be the tube, swapping it for another, one at a time, can eliminate that.  You will most likely roll tubes soon anyway so check the "Tube Rolling w/Crack" thread.  It is always good to eliminate the tubes as the source of a problem.

 

[Viktor]

Greatful for all the advice! I did a small checkup today and resoldered some connections including the first ones I did, seems a bit lower now but not completely gone. Are the ground connections the ones with black cable? I know that the ground often is black but not completely sure in this case!

Okay the cracking popping sound is still there though and the background hum is there as well. I think I'll order some new tubes and test those before doing anything further so I can rule that part out at least.