Hum after installing Speedball

[spear321]

My Crack was working fine with virtually no Hum, but after building and installing the Speedball, I have a very distinct hum in both channels, this does not vary when altering the volume, so I think is probably a ground issue though on checking the voltages I appear to have some overvoltage, this is with a 240V transformer in the UK. All the LEDs light up on the boards by the way. Any advice would be grateful, but work on it may have to wait till Monday a bank holiday over here.

the Voltages are as follows:
Mine                 Should Be

1   80.2              75
2   205               170
3   0                  0
4   202               170
5   72                75
6   0                  0
7   113               100   
8   0                  0
9   110              100
10  0                 0
11  0                0
12  0                 0
13  196            170
14  0               0
15  212            185
16  0                 Not stated
17  0                Not stated
18  82              Not stated
19  81              0 ( is this right? as on end of page)
20  0                206 (as above?)
21  232             Not stated
22  0                Not stated 

Have 19 and 20 been transcribed wrong? as 15 at end of one page and 19 at start of next

Thanks Paul

[Grainger49]

Paul,

It is better for those of us who might help to post only those voltages that are more than 15% out of spec.

Please post the spec and your reading.  Just edit (modify) the above post.

Hum is, as you say, most often a grounding problem.  Do try re-wetting the solder joints on the Speedball board and where the wires connect within the Crack.

If all the LEDs are at similar brightness you are good there.  The Speedball circuit is working.

The next thing is you might have caused a non-Speedball related solder joint to go bad.  That will be harder to find.

[spear321]

Thanks Grainger, re edited Post, have to say bit confussed as jumps from one page to next, but 2 and 4 are more than 15% out.

Its late 00:45 here in UK and working tommorow, so will not be able to answer any more questions, till later tommorow.

Will check joints and reflow them, though taking the speedball out after putting it in is not a job I relish, unsoldering is just NOT as much fun as doing it in the first place.

[Laudanum]

There is a sticky near top of this forum page for Crack Manual corrections ...   Terminal 20 should read 0VDC and terminal 21 should read 206VDC

You'll get plenty of help here to sort the hum out when you get back to working on it, so no worries.

[spear321]

Progress sort of...

Check all joints and reflowed U3 where all the earth wires go, of course while bending the big board out the way I snapped the B+ wire so had to replace this ho-hum.

Still had hum, so wondered if it was input wire, disconnected these and hum goes away.

Now we get to tricky bit, I use the passive preamp section of my World Audio Designs KIT6550 as a switching unit to allow me to listen to the CD, tuner etc, with this unpluged from wall I get no hum, but as soon as plugged in (but not switched on) the hum returns,

The crack did not do this before speedballing ( is that a word) any ideas why? Is there any easy fix?

I presume it is some sort of ground loop, do I need to ground lift either the Crack or the WADKIT6550 and if so how?

Help......

Paul

[Grainger49]

Paul,

This says that you have a ground loop.  I don't remember do you in the UK have grounded power cords?  If so can you remove the ground on either the Crack or the KIT6550? 

I don't know why you have hum after the Speedball and not before but we should be able to cure this.  Do remember that hum/grounding problems are among the most elusive.  Still it can be fixed.

[spear321]

Yes UK have grounded power cords

Well I could do what I have now and and leave the KIT6550 not plugged in til I want to use it, but its not a very elegant solution.

If I undid the return (ground) part of the signal interconnect would ths stop the loop? Would I get a signal at all?

I will experiment and let you know as I would prefer to have both Tube amps grounded for safety reasons, and so that they are ready to go (so to speak)

Thamks for the kind words Grainger, and yes I am sure it will get fixed,

Paul

[Laudanum]

Disconnecting the interconnect "ground" and still passing signal depends on the type of interconnect.  If it's a standard coaxial where the shield carries signal, then no, you cant lift it.  If it's a shielded twisted pair, it may already have the shield lifted at one end.  Usually the shield is connected at the source end.  So you could check that and make sure the shield connected end is hooked up at your pre-amp and the lifted end at the Crack.  Actually, should try it both directions.   If shield is connected at both ends, you could lift one end.  Same would hold for a double shielded coax where the outer shield is insulated from the inner shield where the inner shield carries signal and the outer shield doesnt. 

Im not one of the gurus here but I still would suspect something missed or simple.  I dont understand why Speedball would cause it to be more susceptible to hum when it wasnt present before Speedball.

[Grainger49]

The interconnect is tied to the chassis of the Crack.  It is probably also tied to the chassis of the KIT6550.  And somewhere in the KIT6550 the power supply and signal common are tied together.

When the KIT6550 is off but plugged in there is a ground loop or circulating noise.  I am guessing that it is on the ground.  Is it possible that the two pieces, Crack and KIT6550, are not on the same circuit maybe fed from different outlets?  If there is a difference in the ground that the KIT6550 sees and the Crack sees this can cause this problem.  

When the KIT6550 is off only the hot wire is opened.  The neutral and ground are still attached.  Is there a way to lift the ground of the KIT6550 when you turn it off?  Using a DPST power switch maybe.

BTW, I would bet there are other Speedballed Cracks working on 220V in Europe.  The kit has been extremely popular and Bottlehead is shipping everywhere.

[Laudanum]

Grainger, for my knowledge and to help Paul ... can you think of any technical reason why Speedball installation would result in the hum Paul is experiencing where no hum was present prior to Speedball?  Assuming of course that everything is wired prorperly with no connection issues.

[Grainger49]

No, I don't know that it is the result of the Speedball itself maybe a result of the installation.  There might be a ground that got loose in the installation. 

Speedball lowers noise and might boost the gain a little.  Lowering noise might reveal a noise that was covered up before.  I'm not sure of the magnitude of the hum to say it could have been masked by SSSSHHHH noise before.

BTW, lifting the outer conductor on the interconnects will likely cause more hum.

[spear321]

Hi all

Well I unplugged both the Crack and the WAD6550, and tested continuity with a nultimeter between the ground terminal on the electrical plugs and they are connected together with the signal lead in, but not with it not connected, so we are right about it being a ground issue.

I disconnected the return on the interconnect so only the centre signal pins are connected, and hey presto it worked, no hum and sounds fantastic.

I will of course have another look at the crack , as I feel like Grainger that I have probably moved something, but for the time being all I can say is WOW the speedball brings out so much more detail and the bass is better controlled.

I knew my new Astintrew CD player was good, I just did not relise how good until now... My only dissapointment being that I think it loses some of its tubiness and is a bit more upfront now, but i am sure this can be solved by the use of the right tube.

Thanks again

Paul

[Grainger49]

If I understand it correctly, in your configuration now the common for the signal goes through the power cord ground and back up.

[spear321]

Did not think about it but guess you are right, but lets not knock it,

when it lets me listen without a loud hum.

Will have another look under the crack, if any of the common wires were touching the chassis before the first valve cause this?

Paul

[Grainger49]

I agree, listen and look when you have the time.  There are too many of these out there that are described as "Dead Quiet."  Yours can be too.