Transformer Rattle & Hum issue - Dynakit ST-70

[brilliantblue]

Hi everyone. I'm a bit concerned about a behavior that my Dynakit ST-70 exhibits. It has a slight "whoomp" when powering up or down. There may also be a continuous low level hum. I hear these sounds with the volume down, and they aren't coming through the speakers, but right off of the chassis. I can also feel a slight vibration right at start-up and shut-down

I read a bit about Lamination Rattle and such at (no affiliation) PS Audio - Why do transformers hum? : Frequently Asked Questions & More
but I'm wondering if any of you have experienced this issue and have insight on a) how detrimental to the amp's health it is, if at all, and b) remedies for the problem. Thanks in advance for your input.

 

[DavesNotHere]

tighten up all of the transformers' and inductor's lamination screws

 

[DF96]

a) probably no harm done
b) use an inrush limiter (plenty of discussion on here - use search tool)

 

[brilliantblue]

Will do, as soon as I'm at home again. As often seems to be the case, once I ask a question I tend to find the information I'm asking for online, as though the asking unveiled the search results I was seeking all along. If tightening doesn't cure the problem, I may soak it in some acrylic varnish and let it dry a few days. And/or perhaps some rubber grommets to suppress vibrations.

 

[brilliantblue]

DF96 - thanks for the tip on the inrush limiter - I'll look into it.

 

[brilliantblue]

Tightening the bolts to the chassis did help remove most of the "whomp". Though the bolts were not "loose", I was still able to get 1/4-1/2 turn out of each without damaging effort. I think I will leave it there for now, as the top of the PT is coated and I don't think the issue warrants breaking that seal.

I've not totally checked out the rest of this amp. As I've read that this kind of noise can be worsened by heavier loads, I should probably make sure that nothing downstream is putting undue stress on the transformer. The amp sounds great, but is basically stock. I will post an update when I've had the chance to give it a thorough going over.

Thanks for the replies!
Jeff