I built an amp a couple threads ago, in my "help choose a guitar amp to build" thread.
Was just using an old, cheap woofer. I put better speakers on it, and all the fun is over.. Lots of noise.. (old speaker didn't go high enough in frequency, and was inefficient)
I cleaned up most of it and the amp is silent other than a slight hiss when the input is grounded. Also, there's a volume control between the input and LTP, and w/ that volume down, the amp is silent.
But, with nothing plugged into the input the amp makes a loud buzzing.
I'm not sure what's normal w/ a high gain instrument amp, so I'll just list some symptoms..
Moving the input jack changes the buzzing, and in some places it almost goes away. In other places it's deafeningly loud. (jack is connected via ~5inch shielded cable, and not mounted to a chassis yet).
Playing an MP3 player through the amp doesn't have any noise, as long as the player is powered on. When it's powered off, it's as if the cable is unplugged.
W/ a guitar plugged in, it's silent when the guitar volume is down (because it's shorted to ground), but I get a lot of noise through the guitar. It's even got EMG active pickups, which should be quiet.
I've got an old Gibson lap steel w/ P90's, and those, the plucked strings and the noise are about equal!
To me the symptoms seem odd.. If this were a hifi amp, I'd think it was silent, as mp3 and cd players hooked up work fine.
But, w/ the guitar... noise..
My other amp is an old Magnetone, which doesn't have a lot of gain.. The same type of noise is present, but well below the volume of the instrument.
Oh, and the noise.. W/ nothing plugged in, and the input not grounded, it's all sorts of random noise.. Changes frequency, volume, etc.
W/ the guitar plugged in it's consistent.. I guess I could call it a buzzing sound, increases evenly w/ the volume.
I completely rebuilt the input stage a few times today.. Replaced all the antique carbon comp resistors I was using, cleaned up messy solder blobs, and replaced everything again! no changes.
Any ideas? Is the amp likely the culprit, or is it ok since it's quiet when the input is shorted or a cd/mp3 player is connected?
Was just using an old, cheap woofer. I put better speakers on it, and all the fun is over.. Lots of noise.. (old speaker didn't go high enough in frequency, and was inefficient)
I cleaned up most of it and the amp is silent other than a slight hiss when the input is grounded. Also, there's a volume control between the input and LTP, and w/ that volume down, the amp is silent.
But, with nothing plugged into the input the amp makes a loud buzzing.
I'm not sure what's normal w/ a high gain instrument amp, so I'll just list some symptoms..
Moving the input jack changes the buzzing, and in some places it almost goes away. In other places it's deafeningly loud. (jack is connected via ~5inch shielded cable, and not mounted to a chassis yet).
Playing an MP3 player through the amp doesn't have any noise, as long as the player is powered on. When it's powered off, it's as if the cable is unplugged.
W/ a guitar plugged in, it's silent when the guitar volume is down (because it's shorted to ground), but I get a lot of noise through the guitar. It's even got EMG active pickups, which should be quiet.
I've got an old Gibson lap steel w/ P90's, and those, the plucked strings and the noise are about equal!
To me the symptoms seem odd.. If this were a hifi amp, I'd think it was silent, as mp3 and cd players hooked up work fine.
But, w/ the guitar... noise..
My other amp is an old Magnetone, which doesn't have a lot of gain.. The same type of noise is present, but well below the volume of the instrument.
Oh, and the noise.. W/ nothing plugged in, and the input not grounded, it's all sorts of random noise.. Changes frequency, volume, etc.
W/ the guitar plugged in it's consistent.. I guess I could call it a buzzing sound, increases evenly w/ the volume.
I completely rebuilt the input stage a few times today.. Replaced all the antique carbon comp resistors I was using, cleaned up messy solder blobs, and replaced everything again! no changes.
Any ideas? Is the amp likely the culprit, or is it ok since it's quiet when the input is shorted or a cd/mp3 player is connected?
+1 for input jack extra connections shorted to short input when no jack is present.
Could be poor screening in the guitar. Or maybe bad connection in the guitar.
Those guitar pick up coils will pick up everything if not screened properly.
Guitars like the zero volt line grounded otherwise the guitar screen becomes an antenna.
Could be poor screening in the guitar. Or maybe bad connection in the guitar.
Those guitar pick up coils will pick up everything if not screened properly.
Guitars like the zero volt line grounded otherwise the guitar screen becomes an antenna.
I'm not using a shorting jack... Thanks! I feel a little better now, because shorted, it's almost silent (just a little hiss, which I think is normal).
I chased ground loops all day.. I was using an old chassis, and originally left things grounded to the chassis as they were.. But now everything is star grounded to the first cap.
Well actually, I have the ef86 cathode and 'rg' and the input socket (so the guitar) all connected in one spot, and that junction connects to the first cap.. It's probably wishful thinking this will make a difference, but I'm heating up the soldering iron now..
I chased ground loops all day.. I was using an old chassis, and originally left things grounded to the chassis as they were.. But now everything is star grounded to the first cap.
Well actually, I have the ef86 cathode and 'rg' and the input socket (so the guitar) all connected in one spot, and that junction connects to the first cap.. It's probably wishful thinking this will make a difference, but I'm heating up the soldering iron now..
Glad you sorted (shorted 
) it .
Guitar pickups are noisy little buggers, because they pick up all electromagnetic fields present.
Saying "they are EMG" just by itself does mean that much.
a) there are passive EMG which behave like any other pickup.
b) even if active, a single coil type is a noise catching machine
Humbuckers do the same, but since both coils are out of phase, they (mostly) cancel it out.
Only "humless" guitars are those which have properly mounted and shielded piezo pickups which by necessity are also active.
And yet they hiss a little.
) it .Guitar pickups are noisy little buggers, because they pick up all electromagnetic fields present.
Saying "they are EMG" just by itself does mean that much.
a) there are passive EMG which behave like any other pickup.
b) even if active, a single coil type is a noise catching machine
Humbuckers do the same, but since both coils are out of phase, they (mostly) cancel it out.
Only "humless" guitars are those which have properly mounted and shielded piezo pickups which by necessity are also active.
And yet they hiss a little.
So, rewiring the input grounding on my amp made no difference.
The EMG's are active.. They(emg) suggest not grounding the bridge, and whoever installed them did not ground it.. So, I rewired the guitar and grounded the bridge and grounded the conductive paint in the cavities. It made a little difference, but not much.
I'm getting a pair of passive humbuckers for xmas, so will have some more experimentation to do then.
I need to see if I can find another guitar or amp to test with as a comparison.. Or maybe even just bring my guitar and amp to a different less urban location, and see if it's quiet.
The EMG's are active.. They(emg) suggest not grounding the bridge, and whoever installed them did not ground it.. So, I rewired the guitar and grounded the bridge and grounded the conductive paint in the cavities. It made a little difference, but not much.
I'm getting a pair of passive humbuckers for xmas, so will have some more experimentation to do then.
I need to see if I can find another guitar or amp to test with as a comparison.. Or maybe even just bring my guitar and amp to a different less urban location, and see if it's quiet.
It's coaxial.. I did try two cables, but both are the same coax style.
I'll pick up a shielded cable to try.
Hey, different topic real quick..
I just realized I don't need a negative supply to add a source follower after my ef86, do I? I've only used them to drive negatively biased power tubes, in the past.. But here, the signal is well above 0v.
So, just a mosfet, 100r gate stopper, and 220k on the source, right?
(My schematic is no longer complete.. The tone controls are between the ef86 plate, and .047uf coupling cap.. I'd insert the mosfet directly after the plate, and before the tone controls)
I'll pick up a shielded cable to try.
Hey, different topic real quick..
I just realized I don't need a negative supply to add a source follower after my ef86, do I? I've only used them to drive negatively biased power tubes, in the past.. But here, the signal is well above 0v.
So, just a mosfet, 100r gate stopper, and 220k on the source, right?
(My schematic is no longer complete.. The tone controls are between the ef86 plate, and .047uf coupling cap.. I'd insert the mosfet directly after the plate, and before the tone controls)
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Yeah, the proposed mosfet topopology will work fine, just make sure to chose a mosfet with low CRSS (capacitance gate to drain)
More here: http://www.irf.com/technical-info/appnotes/mosfet.pdf
Perhaps George (tubelab) or Anatoliy (wavebourne) will suggest suitable mosfets based on their experience. Mine is limited to DN2540 in cascode ccs and mu-followers and I use low rp tubes with them. (Their CRSS is way too high for use here IMO)
Perhaps you could even use a cascoded follower to reduce the effect of CRSS, and then you could use commonly available DN2540.. I would run enough current through it to get relatively high transconductance, perhaps 3 - 4mA or more.
More here: http://www.irf.com/technical-info/appnotes/mosfet.pdf
Perhaps George (tubelab) or Anatoliy (wavebourne) will suggest suitable mosfets based on their experience. Mine is limited to DN2540 in cascode ccs and mu-followers and I use low rp tubes with them. (Their CRSS is way too high for use here IMO)
Perhaps you could even use a cascoded follower to reduce the effect of CRSS, and then you could use commonly available DN2540.. I would run enough current through it to get relatively high transconductance, perhaps 3 - 4mA or more.
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LND had the lowest crss out of anything I had on hand, so I patched one in.. (Pretty cool, I built it 'dead bug' style, and it only takes up about a square cm in total, w/ the resistors and all)
It didn't help w/ the noise.. It made my tone control circuitry much less like an antenna if it's not grounded, but w/ all the pots grounded, it was fine anyway.
I found a really long guitar cable in my collection.. First, I turned everything off.. All wifi, all PC's, all lights, unplugged tv's, etc.. No change in the noise through the guitar..
Then I walked all around my house, and I found a plane of quite! It runs along the length of my house, and is only about as wide as the guitar itself.... But if I hold the guitar there.. it's quiet!!
What a mess our environment is! (at least mine). I'm in the middle of a big residential area.. I can't think of where so much interference would come from.. No big transmission towers or big HV lines running anywhere around here...
It didn't help w/ the noise.. It made my tone control circuitry much less like an antenna if it's not grounded, but w/ all the pots grounded, it was fine anyway.
I found a really long guitar cable in my collection.. First, I turned everything off.. All wifi, all PC's, all lights, unplugged tv's, etc.. No change in the noise through the guitar..
Then I walked all around my house, and I found a plane of quite! It runs along the length of my house, and is only about as wide as the guitar itself.... But if I hold the guitar there.. it's quiet!!
What a mess our environment is! (at least mine). I'm in the middle of a big residential area.. I can't think of where so much interference would come from.. No big transmission towers or big HV lines running anywhere around here...
I'm afraid this is over my head, and I've tried to self-educate w/out much luck.. (I'm assuming you meant "note the difference" and not "no difference")
The standard diagram for a follower (on guitar amp forums) uses an irf820, which is enhancement mode.
The LND150 and DN2540 are depletion.
I added the LND to my circuit, wired in just like the irf820 diagrams. So, gate connected to the input tube plate (w/ a gate stopper). Source connected to a coupling cap, to the next stage, and large value resistor to ground. Drain connected to b+.
It works... as in, it passes a signal.. But that's all the testing I've done.
I know that can be improved several ways..
But, should something be different, even for the most basic follower circuit, w/ depletion mode?
That is correct. I have used LND150's as followers in exactly this way. I usually use a 100K for the source resistor.
Wiring the LND directly to the plate of a high gain tube may lead to oscillation. Add a resistor in series with the gate, and slip a ferrite bead or two over the wire between the resistor and the gate.
If the noise in your amp sometimes turns on and off abruptly it may be oscillation. Try a small (100pF) cap from grid to ground on the EF86.
No need for that
Those are big negative icons for Ecologists but really what causes the interference bothering you is magnetic field, and those depend on current, not voltage.
In the middle of a residential area?
Then you have big fat power cables passing hundreds of amperes (all combined) real near you, as little as a few feet, probably under the floor or embedded in walls.
Proof is that you found a nulling point (even more, a line) within your environment.
FWIW I make battery powered Guitar amps and one favorite trick of mine is, when I'm on tour with some Rock Band and we stop the bus in the middle of nowhere to, huh, fertilize the land or something, then I make the guys pull some amp and guitar outside, play a little, then pull the guitar plug and touch the tip with my finger.
Eerie no hum !!!
Just some click or pop (meaning some static electricity is being discharged).
It's so counter intuitive that guy's jaws drop and they think I'm playing some kind of trick
FWIW I make battery powered Guitar amps and one favorite trick of mine is, when I'm on tour with some Rock Band and we stop the bus in the middle of nowhere to, huh, fertilize the land or something, then I make the guys pull some amp and guitar outside, play a little, then pull the guitar plug and touch the tip with my finger.
Eerie no hum !!!
Just some click or pop (meaning some static electricity is being discharged).
Hmm, that's a good story, and says a lot about urban areas.
Well, changes changes changes..
Found a slightly loose pot on the guitar.
Think I had a bad cap on the ef86 screen.. I tacked a new, grounded 10pf cap to it, and it got much quieter. (hiss went down, and very faint radio station pickup went away)
Changed the 12ax7 ltp to 12at7, for a little less gain
Added plate to grid feedback, of 200k resistors between the 6v6 plates and the 12at7 plates.
I did that all at once... Then tested again, and it's much better! Still a little too much hiss, but the amp is a 'rats nest' of wires and not enclosed. Once I build the final copy, I'm sure that will be better.
The loud buzz from the guitar is also much lower now. Still picking up the same interference (still have the same quiet line through my house), but it's an acceptable level now.
I made a VVR, and it's fun! I may label the knob "extra distortion".
No need for that
Those are big negative icons for Ecologists but really what causes the interference bothering you is magnetic field, and those depend on current, not voltage.
In the middle of a residential area?
Then you have big fat power cables passing hundreds of amperes (all combined) real near you, as little as a few feet, probably under the floor or embedded in walls.
Proof is that you found a nulling point (even more, a line) within your environment.
FWIW I make battery powered Guitar amps and one favorite trick of mine is, when I'm on tour with some Rock Band and we stop the bus in the middle of nowhere to, huh, fertilize the land or something, then I make the guys pull some amp and guitar outside, play a little, then pull the guitar plug and touch the tip with my finger.
Eerie no hum !!!
Just some click or pop (meaning some static electricity is being discharged).
It's so counter intuitive that guy's jaws drop and they think I'm playing some kind of trick
I have made similar experience with my home-brewed battery-amps. Furthermore, I bought an ac magnet field meter. With that meter it is easy to find electric power wires under the pavement of the streets. Or the magnetic field below hi-voltage lines. Even in the forest there was a significant level, I assume these are ground currents. All this relates to a big city in Germany. On my holidays in the nowhere in Ireland I checked this with the same meter. Levels were a decade lower than in Germany, even in close vicinity to the local power station.
On the other hand, noise pick-up is not exclusively magnetic. The battery amp trick will even work in an urban environment due to the fact that this amp is not connected to the mains thus there is no significant leakage current that you finger can ground when touching the tip. Worst current leakage is obtained when connecting the battery amp to a charger that does not connect the amp to protective earth.
And the electrostatic-field may cause noise as well in a badly wired guitar using bare wires.
I recommend grounding the bridge to avoid any clicking sound when touching the strings.
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