Background hum

[deltaunit]

Apologies for the slight thread-jack.

When I turn on the crack with the E80CC in I get a inrush type hiss in the right channel, then it dies down completely before the same happens on the left a second or two later (but the hiss stays at a noticeable level). Is this indicative of something?

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?

I quite liked the sound of it and am considering replacing it, is it a lost cause though or just a bad experience? My other tubes seem perfect fwiw.

[2wo]

Might try cleaning the tube pins, Scotchbrite works well. Then insert and remove the tubes 5 or 6X to clean the sockets.

Delta, try leaving the tube running for a few days, see if the hiss cooks off...John 

[MarkG]

I just finished my speedball upgrade yesterday and with the exception of soldering one of the 2907A transistors where one of the 2222A was suppose to go everything is working. I discovered my mistake shortly after doing it and set it right. However, my amp is no longer as "black" quiet as it was before. There is definitely a low background hum that seems to be unaffected by the volume control and a pronounced buzzing that comes in between 75-100% volume. I've had a good look and most of the ground contacts and the soldering seems solid. Any thoughts on where I should start to troubleshoot?

Thanks.

Mark 

[Doc B.]

If the transistors got power before the mistake was discovered,  I would start by replacing the 2N2907 and 2N2222 that were installed in the wrong places. They may have been damaged and that could be creating the noise. Other than that the other idea would be to go over all of the new solder joints that were created with the upgrade with a hot iron and reflow them.

[Grainger49]

If you didn't power it up before swapping the transistors rewet all the solder joints for the Speedball upgrade connections to and from the circuit and to and from the circuit board first.  If that doesn't help then try the boards themselves.

[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.