Vibrating Ampeg PCB, save me from madness.

[ahpook]

I've tracked down the buzzing sound thats been bugging me (a polite understatement) when I play my V4B at reasonable home volume - it's the back edge of the the preamp board.

 

The board is supported by 3 nuts secured by star washers onto threaded stand-offs set in the chassis (they're a bit loose as I'm mid-fiddle), and the unsupported spans are about 8" long. The back of the board is about 4mm off the chassis.

 

My plan is to reseat the board and retighten the pots to see if I can make it sit better, but failing that....any ideas ? The buzz is right on G. ( G...buzz, G....buzz, G....buzz.  Ahpook screams in Lovecraftian horror)

 

Some silicone/neutral cure/sealant stuff, mid span ? Thin washers between the board and the standoffs ?

 

Any ideas would be gatefully received 👍

[Reggaebass]

I’m not an expert in these things but would a small rubber washer under the star stop it vibrating 

[ahpook]

8 minutes ago, Reggaebass said:

I’m not an expert in these things but would a small rubber washer under the star stop it vibrating 

 

I'm going to give it a go ! I'm just hunting for a small bagful of washers I know I have somewhere - small bag, not the tidiest of workspaces

 

 

Edited November 8, 2023 by ahpook

[ahpook]

Couldn't find my washers, but I raided Mrs. Pook's bike stash which has a generous assortment of nuts, bolts and washers for her bike renovations.

 

I'm going to see how I get on with sandwiching the board with nylon washers. I can test it without putting the chassis back in the enclosure (which is a boon as it's not an easy thing to shift around) ...fingers crossed !

[Lfalex v1.1]

If it's any consolation,  my SVP-PRO loves to vibrate at 50Hz. Think it's mains induced vibration from the transformer in my case. 🤪

[ahpook]

16 hours ago, Lfalex v1.1 said:

If it's any consolation,  my SVP-PRO loves to vibrate at 50Hz. Think it's mains induced vibration from the transformer in my case. 🤪

 

Oh yes, mind did too...like a substation !

 

I found a folded piece of thin card on top of the transformer provided just the right amount of shimming between it and the chassis to tame it a touch.

 

Silly idea to mount the transformer to the PCB rather than the chassis IMHO - I reckon it's physically noisier and eventually the stress ruins the PCB. Mine's pretty much an ornament now, as the tracks round the transformer are in such a bad state.

Edited November 12, 2023 by ahpook

[ahpook]

🌻

 

Double post, so here's a pretty flower instead

 

Edited November 12, 2023 by ahpook

[tauzero]

Are the stand-offs secure at the chassis end?

[ahpook]

54 minutes ago, tauzero said:

Are the stand-offs secure at the chassis end?

 

Yes, rock solid.

 

Update: The nylon washers tamed the vibration a lot, they could only go on the top of the board as there was a grounding pad on one of of the stand-offs. Still a slight noise, but much more ignorable. Huzzah.

 

However, I've decided that the amp needs a decent service. It's working and sounding great, but by the looks of it it's not been touched in 25 years, so I'm dropping it off for a thorough check-up thus week - something that my maintenance skills aren't really up to.

 

It's Trace Elliot fun for a short while, whilst it's having it's holiday

 

Thanks for the help folks !

 

 

 

 

Edited November 13, 2023 by ahpook