• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

Thunderfunk - big hum?

B

BassBod

Aug 18, 2006
119
1
Bristol, UK
#1
I recently bought a used Thunderfunk here in the UK. It's a TFB550-A, which I believe is the early version of the uprated550, with "the switch" mounted top right.

Its in good condition and working fine, and I think its almost my "ultimate" amp. BUT it has a really loud background mains hum, which makes it pretty much useless in theatre or studio settings. The transformer also makes a fairly loud physical hum, which adds to the problem. I had it looked at and it seems to be just radiated transformer noise being picked up in the preamp.

Has anyone else had similar problems - and what are the options? I've looked around and seen talk of shielded tranformer and "humbuckung" modifications?

I've tried to email Dave Funk (bounced back everytime) and tried a PM here, but so far no luck...any suggestions?

BB
 
#2
I had the same problem with my TFB550A. I emailed with Dave Funk about it, and he came up with the following solution which worked fine with my amp: This is from an email from Dave:

"The fix for the hum is to add a wire from the "sleeve" contact of the headphone jack to the ground lug. Then form the wire (actually form it first to get the length right) over the top of the transformer. The wire should go just off center from the middle. You can listen to the amp through a speaker while you slide it, or you can use a meter or an oscilloscope if you have one. Tune for minimum hum. Then I use super glue to hold the wire in place while I place a large tie wrap around the top of the transforemr to hold it in place. Then I use some silicone caulk on the sides of the transformer. The super glue won't hold when the transformer gets hot. It's just temporary."

Hope this helps,

Bjornar

This is a picture of the mod that Dave sent me.
 

Attachments

  • Tuned Ground Wire.jpg
    Tuned Ground Wire.jpg
    23.5 KB · Views: 198
#4
This is the same fix he told my amp tech when I had problems with the TF420. It brought the noise down to where it should be. These are not dead quiet amps, they do produce a little ssshhh sound that should never get any louder when you turn the volume up.
 
#5
BassBod: The noise level in my TF is now acceptable. I never think about it and it never bothers me in any real playing situation. Usually the guitarists amps are way noisier!

If you want, you can actually measure the noise by measuring the AC voltage at the speaker jack with the volume on zero.
Before I did the fix it was 5.7mV. After the fix it was down to 2.3mV. Still slightly audible, but at an acceptable level. Dave told me he expected it to be around 3.2mV, so anything below that and you should be OK.

Bjornar
 
#6
Thanks for sharing, Bjornar. I believe I noticed this wire over the transformer when I popped the hood on my 550B.

CrashClint said:
This is the same fix he told my amp tech when I had problems with the TF420. It brought the noise down to where it should be. These are not dead quiet amps, they do produce a little ssshhh sound that should never get any louder when you turn the volume up.
Click to expand...

I don't recall noticing this same wire in my 420 but didn't have a noticable noise problem. I wonder if none of the 420's had this hum-tapper or if Dave installed it on an as-needed basis? I would open it up & look, but it's landing on ()smoke()'s doorstep about now. :cool:
 
#7
Thanks for the replies - I've no idea if this wire is already fitted (but I doubt it, from the hum!) so that's going to be the first thing to check out. I'll have it done by someone who's qualified and safe to poke around near transformers.

I'm not expecting it to be dead quiet - its a 20+ year old design at heart, but I would expect the "idle" noise to be around the same as my old SWR 220 or a bit more than the iamp500 (which is really a bit hissy when there is nothing elso going on).

I'm also aware that excessive hum induced into the preamp is going to be there when I use the DI - and I DI from the amp most of the time (either direct or through a passive DI box run from a preamp output)

BB
 
#8
spiritbass said:
I don't recall noticing this same wire in my 420 but didn't have a noticable noise problem. I wonder if none of the 420's had this hum-tapper or if Dave installed it on an as-needed basis? I would open it up & look, but it's landing on ()smoke()'s doorstep about now. :cool:
Click to expand...

The tech that works on my amp called Dave direct and dave emailed him the fix, he called it some kind of choke. It fixed the problem.
 
#15
Thanks to all for your contributions on this one - I've sent the info to my friendly tech, and although he doesn't seem impressed with the "finess" of the suggested fix, I think its about the only option I've got, short of finding a transformer with less noise!

All the best

BB
 
#17
BassBod said:
Thanks to all for your contributions on this one - I've sent the info to my friendly tech, and although he doesn't seem impressed with the "finess" of the suggested fix, I think its about the only option I've got, short of finding a transformer with less noise!

All the best

BB
Click to expand...

No brainer - I'd be following Dave's guidance to the letter and not worry about this tech's impressions. How many killer bass amps has this tech modified, built, and sold? :rollno:
 
#18
xsubs said:
I'm not sure I get your comment Jimmy?
My statement was about the TB community, and the free exchange of valuable information... and the in-depth knowledge that some members are able to share.
Click to expand...
Let me explain a little further. I meant with that list of killer amps you already have, the last thing I'd care about is getting one more. One of those offhand comments late at night that didn't explain itself, you know?
 
#19
The tech is fine, if not high profile (works for many "pro" acts here in the UK, including JPJones, Steve Howe and Jethro Tull). I doubt there is an amp in existence that he hasn't either fixed or modified at some point. His view is that the hum shouldn't really be there in the preamp to be removed - I see his point and pretty much agree. However, it really doesn't matter if the fix works!

BB
 
#20
spiritbass said:
I don't recall noticing this same wire in my 420 but didn't have a noticable noise problem. I wonder if none of the 420's had this hum-tapper or if Dave installed it on an as-needed basis? I would open it up & look, but it's landing on ()smoke()'s doorstep about now. :cool:
Click to expand...

successful landing, and i haven't noticed any noise yet, so i'm staying out of the chassis :):bassist:

...but great to know there is a simple fix should i encounter the issue!
 

Latest posts

Top Bottom
Back