Single coil buzz louder in certain amps?

[bryan999]

Hello all,
I've lurked here a little bit in the past but never took the time to post anything until now. I just finished an amp I was building, and noticed that it is strangely more sensitive to single coil hum than alot of fenders I have played.
I tried isolating the input jack and running the cable shield to ground through a .022 cap and though that did help, the problem is still there.

anything I should maybe try to get the amp less sensitive to that buzz?

It's dead silent with humbuckers...

thanks!
-bryan

[Darkbluemurder]

Bryan,

Unfortunately you did not tell what amp you built. Is it higher gain than a Fender? Then your observation is normal.

Cheers
Stephan

[bryan999]

sorry about that!

It's basically an early marshall preamp with a fender 100w output stage (6L6 in pushpull). I run it on a 4x12 most of the time so it get's pretty loud and ballsy, but with my king of the britains pedal the hum is horrendous. My grounding scheme is pretty good, with each section of the preamp being stargrounded to the input jack and the powersupply and output section getting grounded near the IEC inlet... no chassis grounds other than at the powersupply end and input jack end. I just feel like maybe i'm missing something?

If anything could potentially make it better i'm all ears!
-bryan

[LOUDthud]

Grounding at the power supply and the input jack is an invitation for trouble. However, if the amp is silent when the single coil guitar is unplugged, I would say it's OK. You said the noise was acceptable with a humbucking guitar, is the noise just more noticable with the single coil guitar because you turn the gain up? With what you have done so far, I would try to duplicate your results with another single coil guitar.

[CaseyJones]

Grounding at the power supply and the input jack is an invitation for trouble.

How so? Generally that's the way it's done.

but with my king of the britains pedal the hum is horrendous.

Tell us about that pedal. I'm not familiar with that one. Does it have its own power supply or just a battery?

[LOUDthud]

Grounding at the power supply and the input jack is an invitation for trouble.

How so? Generally that's the way it's done.

There are many misconceptions about grounding. Obviously, Leo Fender used seemingly random chassis grounds and it worked fairly well for years. But, Leo's amps never had the over the top gain like the amps discussed here. It seems like everyone that has built more than one amp has their own way of connecting grounds. I don't want to say that there is one and only one way to do it right, but there are many ways to do it wrong. I think most people would agree that some form of star grounding produces good results.

I've never seen an amp of this complexity that was totally star grounded at one point. There are only so many wires you can get into one eyelet or so many ring terminals you can get onto one transformer bolt. I could be wrong, post a picture. In this case, the amp has been described as having two star grounds and two chassis connections so, as in most real life situations, there is some deviation from the ideal. I don't know enough about the amp yet to say if this is a problem or not, but it could be. How the two stars are connected will shed some light on this.

[jjman]

Most Fenders, at least BF/SF’s scoop the mids a good amount. You have no buzz with HB’s and lots of buzz with single coils. It sounds like your amp’s EQ favors the “buzz range” of frequencies more than an average Fender would. If it’s dead quiet with HB’s I would think your grounding is fine.