quickie hum

[aragorn723]

Hi,

I'm having some Quickie hum problems, and am wondering if the tubes could be the issue?  After swapping them left to right, there is no difference in hum.  The hum is not so bad out of my main amp, but with the B&W ASW 600 sub I just added, the hum is very pronounced (out of the sub).  Is there a way to fix this?  Thanks,

Dave

[Bonzo]

If the hum somewhat change when you put your hand on the tube it should be a grounding issue.
Try to ground the output of the quickie to the chassis of your main amp, but beware if you have a chip-amp (some issues have been reported on this forum!).
Hope it helps.
Ciao!

[cpaul]

Does the sub have it's own plate amp?  If so, what is the input impedance?  If it's down around 20k or less, that may be the issue.  If so, not sure what you do about that.  May be possible that there are gain issues with the sub too?  I was running a chip amp and had hum problems.  The issue, though, was with the chip amp.  My thread about it is just below this one.

[aragorn723]

The sub has a 150w plate  amp.  The input impedance of that is 22k.  Would the impedance situation be better if I used a splitter on the Quickie's output (one to the amp, one to the sub)?  Right now the output of the Quickie is going to the sub's rca inputs, and an rca cable is hooked up to the sub's outputs that runs the amp.  Thanks,

Dave

[cpaul]

Hey Dave,

I hope better minds than mine will chime in.  I'm guessing that if you split the output, you'll still get hum from the sub, and it may not help at all.  But it's an easy enough experiment, especially if you have those RCA splitters. 

Did you use the same amp before with Quickie and NOT have hum problems?  If so, then I'd guess the impedance mismatch with the plate amp may be at issue.  Again, not sure what to do.  If it were possible to modify the plate amp with a higher impedance, I suspect the issue would be reduced or even resolved.  Alternatively, if you're adventurous with the Quickie, you might consider modifying it into a cathode follower.  Take a look here http://bottlehead.com/smf/index.php?topic=1221.msg8462#msg8462.  You'll need to know what you're doing, but it ain't rocket science either. 

Note this will reduce gain overall but should also give you better drive and impedance mis-matches shouldn't be a problem.  I really don't know for sure if this would solve your problem, so I'm curious what others will say.

[2wo]

You could try using the high level inputs on your plate amp and taking the signal from the output (speaker) of your main amp...John

[rif]

I installed and grounded tube shields.  Removed all traces of hum

[Natural Sound]

I installed and grounded tube shields.  Removed all traces of hum

Cool! That would indicate some type of EMI/RFI present in your listening environment. Glad you got it sorted out.

[aragorn723]

I installed and grounded tube shields.  Removed all traces of hum

Cool!  That might be the answer.  Were you able to put them over the existing sockets?

Dave

[aragorn723]

Also found this socket/shield combo:

http://www.thetubestore.com/Parts-Accessories/7-Pin-Sockets/7-Pin-Tube-Socket-with-Shield

Will that work with the existing socket holes, and does that help with microphonics too?

Thanks,

Dave

[rif]

Will that work with the existing socket holes, and does that help with microphonics too?

I think those are the ones I purchased. They won't work with existing sockets - the shield needs something to attach to something.  It's difficult to see in the picture,  but you can see a cylinder extending up.

Nope, doesn't help with microphonics.

-david

[Paul Birkeland]

Is your sub plugged in to an outlet that's different than the power source for your sources?  The speaker level inputs (if present) should cure the issue.  You can also run a wire from the metal plate of the plate amp to your amplifier's chassis to attempt to address the loop.

[aragorn723]

Hi Paul,

The entire system is plugged into the same outlet with surge protectors.  I'll have to try the speaker level inputs next.  Thanks,

Dave

[aragorn723]

I installed and grounded tube shields.  Removed all traces of hum

Where are the batteries on your Quickie?  A separate chassis?
Dave

[rif]

Where are the batteries on your Quickie?  A separate chassis?
Dave

Underneath the chassis. The d-cells are mounted to the top plate. The 3 x 12V packs are attached to a bottom plate I made

-david