Ampeg SVT3Pro getting hum when I stand too close

[DJ Bebop]

450 volts is a swift and efficient teacher of respect, and where not to stick your fingers.

 

[byacey]

Beaker is my underdog hero!

 

[DJ Bebop]

Then you won't have the same problem as the OP, because the SMPS has an inherently low hum field.



That they worked at all is sheer luck. Often with pedals, the ring mist be shorted to the sleeve to allow the pedal to power up. If the output jack uses a TRS jack with the ring tied to sleeve, this will work, but most do not.

Your MarkBass with the XLR input is the exception to the rule regarding inputs, the OP's amp does not have a balanced input.

I didn't understand how he is doing this either. I guess he has this:
Invalid Link Removed

 

[gtlover]

450 volts is a swift and efficient teacher of respect, and where not to stick your fingers.

The only time I got zapped was on 115V and once was enough. I've lost a couple of meter leads, though.

 

[agedhorse]

I worked regularly with 480/277Y in my industrial controls engineering work, as long as you follow the rules and safe work practices, it's not a big deal.

Where things get dangerous is where folks who do not understand the details and differences between the different systems, and make assumptions without thinking through the scenarios, or people who are careless and like to wing it (ie: cowboy techs) often make a mistake that's less forgiving at the higher voltages. Same for folks who don't understand short circuit current ratings and fault current profiles.

 

[Nevada Pete]

Yeah, 450 volts is dangerous enough, and you will see it in vacuum tube gear such as radio transmitters. Even a 12AX7 in a microphone preamp, though, can have plate voltages around 300 volts DC which can be very dangerous. But in an industrial motor panel which is going to be three phase there's some massive current behind that 440 / 450 / 460 volts. Short circuits and fero-resonance effects can explode with the force of dynamite upon energizing a circuit! Be my guest. I'll steer clear, thank you.

 

[gtlover]

Did some further checking - all the jacks are functioning normally, no bad contacts or solder joints that I could find. No obvious bad grounds. Triple-checked all the connections to the new PCB, especially the transformer.
However, when I used my old Ibanez, which is still the original single coils and no shielding, I discovered a significant amount of hum is coming from the fan. I confirmed this by (briefly) disconnecting the fan. Not sure what to do about that. It's never been sonically quiet but the hum was never a problem like this before.

 

[agedhorse]

Hum intruded via a fan rarely if ever changes with the position of the bass.

 

[gtlover]

Hum intruded via a fan rarely if ever changes with the position of the bass.

Any other ideas from your experience on root causes or possible solutions? Something as simple as swapping out an inexpensive component?
Mostly I'd rather not have to mute myself every time I need to tweak my EQ or adjust the stage volume. I'm about ready to build a Faraday cage for it.

 

[DJ Bebop]

Hum intruded via a fan rarely if ever changes with the position of the bass.

Could it be the crossover? The F HUM

 

[gtlover]

Could it be the crossover? The F HUM

Highly doubtful; I would think if the crossover inductor was getting crosstalk from any source inside the amp, the hum would be constant. The hum increases as I move my bass closer to the amp, and experiments with unshielded single coils yield highest hum in the vicinity of the power transformer. As noted above, that hum is noticeably lower with the fan disconnected. Actually at a tolerable level at that point, but not a good idea for any more than the few seconds at low volume that I tested. Between the tubes and the mosfets, there's a fair amount of heat.

 

[DJ Bebop]

Highly doubtful; I would think if the crossover inductor was getting crosstalk from any source inside the amp, the hum would be constant. The hum increases as I move my bass closer to the amp, and experiments with unshielded single coils yield highest hum in the vicinity of the power transformer. As noted above, that hum is noticeably lower with the fan disconnected. Actually at a tolerable level at that point, but not a good idea for any more than the few seconds at low volume that I tested. Between the tubes and the mosfets, there's a fair amount of heat.

Kiddin'! that was a joke, I repeat, that was a joke
See this post, there's your answer Ampeg SVT3Pro getting hum when I stand too close

 

[gtlover]

Kiddin'! that was a joke, I repeat, that was a joke
See this post, there's your answer Ampeg SVT3Pro getting hum when I stand too close

Well played sir, well played.

 

[byacey]

Hum intruded via a fan rarely if ever changes with the position of the bass.

An AC boxer fan could kick up a little bit of electromagnetic noise, but nothing compared to a large power transformer core. I wonder if the original poster is using some single wound coil pickups that are overly sensitive to noise?

 

[SteveIII]

I started using a separate preamp and set my amp as far away as my cables allowed. Put both pickups on or turn down the volume when you go near the amp. I'm toying with the idea of humbuckers but really like my single coil sound. Im using a gk700rb-ii but having the same hum issue

 

[agedhorse]

Any other ideas from your experience on root causes or possible solutions? Something as simple as swapping out an inexpensive component?
Mostly I'd rather not have to mute myself every time I need to tweak my EQ or adjust the stage volume. I'm about ready to build a Faraday cage for it.

No, an experienced tech might be able to rule in or rule out specific causes though.

A DC fan can induce noise into the power supply, which then gets coupled into the audio circuitry, but generally this is unrelated to the bass.

 

[gtlover]

No, an experienced tech might be able to rule in or rule out specific causes though.

A DC fan can induce noise into the power supply, which then gets coupled into the audio circuitry, but generally this is unrelated to the bass.

I tracked down a local tech who has a good reputation, so I may take it in and see what's what.

It's just annoying that it was never this bad with the old power amp PCB, even with old single coils and unshielded passive controls. Now even my Lyte, which is active with 2 humbuckers, gets a buzz. Doesn't matter if I'm touching the strings, ground lift makes no difference.

 

[agedhorse]

There may very well be a new problem that was caused by the work that was done.

 

[Throttlejunky]

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.

You are much more knowledgeable about this subject than I, but I've attached two pics one of my pedal board and one of my amp input(yes class D amp). The bass output is not balance and its running wireless via a Shure GLXD16 to the input on the board. The final pedal (Big Muff Deluxe) on the board has XLR output which I connect to the XLR input of the amp (pictured). All patch cables on the board are balanced cables. Anyway, the noise I had when I was using non XLR amp input and non TRS cabling is completely gone, reduced to a low hiss. Even when I switch on the distortion box, just a hiss sound. All electronic devises plugged into the same strip.

 

[agedhorse]

Luck is defined as a blind squirrel finding a nut.