Ampeg SVT3Pro getting hum when I stand too close

[gtlover]

I see a fair amount of damage form well intentioned poking around and especially "reflowing" solder joints.

Relax, it's not like the time I reflowed the solder on the video card in my wife's Macbook by roasting it in the oven.

Also, relax, I didn't do that either, though people on reddit TOTALLY swore that was the fix. Not worried about poking around (already swapped the power amp PCB, see first post) or fixing solder joints (been there, done that).

 

[agedhorse]

If you saw what I see on a regular basis, you wouldn't be quite so dismissive.

 

[frankie5string]

It's coming out your DI because it's being picked up through the pickups and then going all the way through the input on the amp to the DI.
Even though it may take a good pluck to register you bass tone on them, it's surprising how sensitive they are. I was in the studio the other day, with cans on my head between playback and could hear this "tsk tsk tsk tsk"

It was my watch. I wear a battery-operated Timex with hands and a seconds hand. I could hear the second hand "motor" through my pickups. It wasn't even turned up loud. It kept happening because I was reading a book, and had my book in my watch-hand, at a little less than arms-length at about pickup height.

I should try that with my Accutron - it predated Quarts timing and uses a tiny tuning fork. If you put it on a desk, the whole desk hums with it. heheh.

 

[Nevada Pete]

Relax, it's not like the time I reflowed the solder on the video card in my wife's Macbook by roasting it in the oven.

Also, relax, I didn't do that either, though people on reddit TOTALLY swore that was the fix. Not worried about poking around (already swapped the power amp PCB, see first post) or fixing solder joints (been there, done that).

Well, may I just say that among other things I've done in my life I am an experienced electronic technician who has worked both in the music industry including on the big stages, in studio, and also in aerospace and telecommunications. I'm always very concerned to be extraordinarily careful whenever I open up an electronic instrument of any kind to perform work on it. You sound overconfident to me. In electronics, a caviler attitude is just exactly how you get electrocuted (maybe permanently!), or cause damage including catastrophic damage to equipment. Just saying. You really can't be too careful.

 

[dwade]

It's not a cold solder joint if it only occurs based on the proximity of your instrument.

 

[DJ Bebop]

Ampeg SVT3Pro getting hum when I stand too close.
I say...

 

[murphy]

That is the only amp that has always done that with any of my basses
Different studios
Different years
Different amps
SVT3PRO and BUZZZZZZZZ

 

[Throttlejunky]

I've got an old SLM era SVT3Pro that I bought new in the mid-90's. Recently I replaced the power amp board (don't ask) and while it sounds good and loud, I am getting some induced 60-cycle hum if I stand too close.
It's very noticeable in the direct out, and the ground lift doesn't seem to affect it. Upon further experimentation I noticed the following:

-Still happens with different basses, instrument cables, and power cables
-Still happens at different venues (2 different churches and at home)
-Gets louder the closer I get to the transformer
-Gets louder when turning up the EQ gain
-Swapping tubes (all of which recently tested good) has no effect
-Audible in speaker out, and both balanced and unbalanced direct out.

I have checked and re-checked all the connections on the brand new made in asia power amp side and everything seems to be in order. Based on what it does in connection to the EQ gain makes me think there may be a bad connection or solder joint on the preamp.

What sayeth the wisdom of the crowd?

I recently eliminated my annoying hum by using nothing but TRS cables and or XLR connections to the input of the amp from my bass and between pedals. It seems to have worked like a charm. I use three different Fender basses through Markbass amps.

 

[Eddie LeBlanc]

 

[agedhorse]

I recently eliminated my annoying hum by using nothing but TRS cables and or XLR connections to the input of the amp from my bass and between pedals. It seems to have worked like a charm. I use three different Fender basses through Markbass amps.

How do you use an XLR connection to the input of the SVT3pro amp?

 

[dkelley]

This is one of the many advantages to modern well shielded/grounded, small power supply amps.

What you're experiencing is what we all experienced for years and accepted as normal, until companies like Trace came along and reinvented the wheel and we no longer had to live like that.

 

[murphy]

How do you use an XLR connection to the input of the SVT3pro amp?

with your imagination?

 

[agedhorse]

This is one of the many advantages to modern well shielded/grounded, small power supply amps.

What you're experiencing is what we all experienced for years and accepted as normal, until companies like Trace came along and reinvented the wheel and we no longer had to live like that.

Except that Trace never made any "small power supply" or SMPS based amps until Peavey acquired the company.

 

[dkelley]

Except that Trace never made any "small power supply" or SMPS based amps until Peavey acquired the company.

Fair enough. I'll give plenty of due credit to peavey. Doesn't change my point though.

 

[gtlover]

I recently eliminated my annoying hum by using nothing but TRS cables and or XLR connections to the input of the amp from my bass and between pedals. It seems to have worked like a charm. I use three different Fender basses through Markbass amps.

I'm guessing your MarkBass amps are class D? It hasn't been an issue with my PF500, just the 3Pro.
Are you still using standard mono jacks with the TRS cables?

 

[byacey]

I recently eliminated my annoying hum by using nothing but TRS cables and or XLR connections to the input of the amp from my bass and between pedals. It seems to have worked like a charm. I use three different Fender basses through Markbass amps.

I've never seen any basses, amps or pedals with provisions for balanced connections, unless they have been highly modified with transformers, connectors, balanced line drivers / receivers, etc.

Even if they were indeed balanced, the pickups would still produce the same hum when standing close to an AC magnetic field.

 

[BassmanPaul]

I recently eliminated my annoying hum by using nothing but TRS cables and or XLR connections to the input of the amp from my bass and between pedals. It seems to have worked like a charm. I use three different Fender basses through Markbass amps.

Interesting. You must not have basses with onboard electronics as the ring connection has to be grounded in order to complete the power supply circuit. This is done automatically by inserting a TS plug into the output jack on the bass.

 

[gtlover]

I'm always very concerned to be extraordinarily careful whenever I open up an electronic instrument of any kind to perform work on it. You really can't be too careful.

As am I; from time to time I have to do functional QC on electrical control panels, and we are usually running either 230V or 460V - not something you want to get zapped with! I don't like to energize any device I'm working on unless I absolutely have to.
It's the troubleshooting that drives me up the wall, though.

 

[gtlover]

Interesting. You must not have basses with onboard electronics as the ring connection has to be grounded in order to complete the power supply circuit. This is done automatically by inserting a TS plug into the output jack on the bass.

I was wondering the same thing - how would you be able to run a balanced signal through a mono (unbalanced) jack?

 

[BassmanPaul]

I was wondering the same thing - how would you be able to run a balanced signal through a mono (unbalanced) jack?

You have to start with a balanced signal and terminate to a balanced input. Very, very few basses have such a circuit and just as few amps offer a balanced instrument level input.