Amp hums excessively, but only with single coils?

[elipsey]

Hi,

I built an AA1164 Princeton Reverb clone for my uncle using a Weber chassis and circuit board kit (but with better parts), and a standard layout and grounding scheme from the original schematic and pictures of vintage examples. He told me that it works well with hum-bucking pickups, but hums excessively with his Strat and Tele, more then with his other amplifiers. Because he lives in a different town than me, I arranged a conference call with a guitar playing friend to help diagnose this.

My friend brought his own vintage Princeton ("Tuxedo" 6G2) with him to my uncle's home and reported that it had noise but was noticeably quieter with the same single coil guitars connected. I advised that this might not be an "apples-to-apples" because of gain, tone stack, power, speaker efficiency etc., but promised to investigate further. My friend and uncle are both experienced working musicians, and deemed the noise to be excessive.

Are some amps noisier with single coil pickups than others? What can I do to address this?

Thanks

[Enzo]

I look at it this way, If your humbuckers don't hum and your single coils do, the only thing that changed between the two examples was the pickups, not the amp. Sounds like the amp is not the problem.

Does it help to stand back from the amp as far as possible? In other words, does moving closer and farther from the amp with the guitar make the hum louder anad softer? And does the hum change if you face different directions with the guitar? Power transformers make a magnetic field which sensitive pickups can well pick up. Perhaps your amp has a stronger transformer field than the other one.

[octal]

One other thought- because of the generally higher output of a humbucker, you're going to running the amp at lower gain/volume settings to get an equivalent SPL "volume". So, if the amp did have an internal hum issue in the early gain stages, it might be less noticeable with humbuckers, simply because the signal/hum ratio is more favorable with a higher output pickup, thus masking the hum more.

[elipsey]

I look at it this way, If your humbuckers don't hum and your single coils do, the only thing that changed between the two examples was the pickups, not the amp. Sounds like the amp is not the problem.

Does it help to stand back from the amp as far as possible? In other words, does moving closer and farther from the amp with the guitar make the hum louder anad softer? And does the hum change if you face different directions with the guitar? Power transformers make a magnetic field which sensitive pickups can well pick up. Perhaps your amp has a stronger transformer field than the other one.

They tried standing at the length of the cable, but they said it made no difference, which I found suprising.

I know What you mean about how the test with the humbucker seems diagnostic. I'm trying to keep an open mind and help solve the problem.

My friend thinks this might be an unusually noisy environment; he said there is a lot of computer and electronic stuff in the practice space. They told me that the other amps they tested with (AC4TV and non-reverb princeton) were quieter.

I'm not sure if this is a fair comparison because those are both smaller and both have one knob tone controls, so I suppose that they have less volume, less gain stages and less treble. When we started the conference call for testing, the amp I built had the treble turned up to 9, and the volume was pretty cranked too.

I think there are also some solid state or modeling amps there and I'm wondering if they could have built in noise gates, or other noise counter measure that aren't present in vintage gear, like snubber caps. I emailed to ask what model these are, and I'm awaiting a response.

[elipsey]

One other thought- because of the generally higher output of a humbucker, you're going to running the amp at lower gain/volume settings to get an equivalent SPL "volume". So, if the amp did have an internal hum issue in the early gain stages, it might be less noticeable with humbuckers, simply because the signal/hum ratio is more favorable with a higher output pickup, thus masking the hum more.

This is a good point. We tried turning the amp volume and treble all the way up with a humbucker connected, and it wasn't noisy. I'm pretty sure the preamp is quiet. We also checked with the reverb cranked, and that made a little bit of noise, but nothing close to the single coil hum.

[jbltwin1]

Is the bridge grounded?

[elipsey]

Is the bridge grounded?

Good call, I'll have them double check that with a meter.

I installed the pickups so if it's not, I'm embarrassed. I'm guessing it's OK though, because they found similar noise with a telecaster. For what it's worth I think the strat is HSS with a no-load tone pot, and the middle single coil is not connected to a tone pot. I wonder if that makes the noise slightly worse...

EDIT: The humbucker in the same guitar is quiet though, so I don't think that's it...?

[TimmyP1955]

If the Strat has a 5-Way switch, and has the correct pickup set (and wired rightly), positions 2 and 4 will be humbucking. Have him see if those positions are quiet. (Here in the shop, a Strat in 2 or 4 is quieter than a LP/SG/335 in any position - though sometimes you have to face the right direction :-)

[olddawg]

It's an age old problem. There are a couple of clubs that I can't use my Strat at all. One has a gas station next door with a lot of fluoresce lights. One has a big step down transformer out back. Triac dimmers on stage lighting cause big problems. Bar refrigerators cycling! Many times I have to keep the switch in 2 or 4 position or the volume off, then when the band starts (hopefully) the hum is buried in the mix, especially if I'm using a boost pedal. Shielding the cavity can help if you don't loomake a ground loop. And yes, some amps have more hum with Strats than others, especially at high gain. A single coil pickup will always be prone to hum.

[big_teee]

You can make a strat a good bit quieter.
Which helps on noisy locations.
Make sure the pickguard has heavy foil on entire bottom side.
Make sure all the metal components read continuity to the foil, and the ground side of the jack.
Use shielded cable from the jack to the volume control.
Another extreme measure, is to replace the pickup leads with shielded cable, grounded on the switch or pot end.
You can also replace the pickups with low wound blade buckers.
They are really quiet and sound pretty strat like.
GL,
T

[Leo_Gnardo]

Make sure the pickguard has heavy foil on entire bottom side.

I recommend copper foil shield, pickup and control cavities too. It's easy to solder ground wires to copper, and bridge sections of copper foil with solder. Some brands claim they have conductive stickum on the back, I don't trust it. When sections are soldered together you know for sure. Some folks have good luck with conductive paint, me not so much.

Found one I'd worked on @ 15 years ago, on youtube. Even the pickup bolts are grounded, in an effort to stop snap noises from static discharge. "Got some weird harness apparatus!" sez Seymour, referring to the single coil strat pickguard. Well, it worked a treat, so did the same artist's regular stage guitar. Jump to 5:15 to see. Link:

https://www.youtube.com/watch?v=ofK6LdgfcTQ

Note, I did NOT do the funky milling & drilling. Yikes! It was like that when I met it.