Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: tony321owen on January 18, 2020, 06:29:07 pm

Title: RF noise, hiss and hum in high gain preamp design. Cures?
Post by: tony321owen on January 18, 2020, 06:29:07 pm

Ive been building amps with higher gain preamps which means noise is a bigger issue...

How does one go about defining and curing these issues?
 
any tricks to designing an amp that uses a high gain preamp and that can be played loud with single coil guitar pickups with minimal noise?

Title: Re: RF noise in high gain preamp design. Cures?
Post by: PRR on January 18, 2020, 09:33:53 pm

Why do you say "RF noise"? Then say buzz? There is also hiss.

First figure out what kind of crap you have. (The sound gives clues.)

There's nothing the amplifier can do about room crap that gets directly into the pickup.

Title: Re: RF noise in high gain preamp design. Cures?
Post by: tony321owen on January 18, 2020, 10:03:13 pm

is the noise that gets worse with single coils sound to you like RF interference?

 My amps are always noisier at my home when compared to other places i have plugged them in. My latest amp is worse than the rest when using single coils. just wondering if people have advice on common cures. here are some symptoms from my recent ac-15 style build...

With a single-coil pickup plugged in, there is a nasty noise that almost disappears when changing to a Humbucker or noise cancelling pickup..

IM trying to define my noise terms so bare with me...

This type of noise disappears with the guitar cable unplugged or if the guitar is plugged in with the volume knob down. It becomes unplayably bad at about 5 on the volume knob.   

With nothing plugged in, as I turn up the volume towards ten, a loud hiss appears. From five to ten it's very audible and becomes a nuisance.

With volume at 0 there are two types of hum though they are not terribly loud.. maybe 60cycle and 120cycle.. neither makes the amp unplayable but obviously they are not ideal!

reverb knob makes hum louder as do treble and cut controls...

Ive been documenting my build on here

https://el34world.com/Forum/index.php?topic=24358.msg276016#msg276016

just though I would start this thread with hopes people would chime in with their knowledge.. 
 

Title: Re: RF noise, hiss and hum in high gain preamp design. Cures?
Post by: d95err on January 19, 2020, 02:12:45 am

The thread you linked to seems to be about an AC15 build. I assume that is not the high-gain build you’re talking about here.

Please post the current schematic here instead.

Title: Re: RF noise, hiss and hum in high gain preamp design. Cures?
Post by: tubenit on January 19, 2020, 06:50:21 am

I responded to some of this in your other thread.  I do not consider an AC-15 to be a high gain amp.

With respect, Tubenit