Artifacts on F#

[njolly]

On my VHT D50 I have noticed these artifacts when playing an F# and a bit less on a G note. I always wrote it off to my phone being in my pocket while playing but after moving my phone away it was still there. I have tried different speakers, cables, and guitars. The noise is less noticeable with OD but still there so I am assuming it's in the first preamp stage or the output stage. I did some upgrades, and mods, but the noise remains unaltered. As part of the changes I replaced the jacks with better quality jacks, replaced the 47uf filter caps with F&T, and replaced the 4 100uf filter caps that were wired in a series parallel setup with a single 330uf/600v. I have no oscilloscope available. Attached an mp3 of the noise and the schematic. Anyone heard/fixed a noise like this before? Any ideas or troubleshooting tips would be most welcome. TIA

[ijedouglas]

I had something similar on my 3rd Gen build. I spent countless hours tracking it down even going as far as replacing V1 tube socket. Nothing worked but I knew there was some type of mechanical oscillation happening on V1 on certain notes. I finally found that if I held the tube shield on V1 it would stop the noise. Obviously not a workable solution but in my frustration I pulled the tube shield and the noise went away. The amp still sounds great and it still has no tube shield

Your issue sounds similar. See if the noise goes away when you hold the V1 shield?

[njolly]

Thanks for the suggestion Ian. Gave that a try but alas no joy.

[Bombacaototal]

Have you tried a different speaker or speaker cab. Have you also tried playing in a different room. If none of the above I would bet it's a cold solder, most likely in the LNFB of the tonestack

[solderhead]

have you checked to be sure that you don't have any AC riding on your DC voltage supply?

[pottedplant]

could it be magnetostriction with the OT? also perhaps a window is rattling or even drywall panels if you're really cranked up and the amp is backed against a wall

actually it may not even have to be very loud if the panel resonance is being matched perfectly by the note, it would vibrate pretty strongly i think

[njolly]

Have you tried a different speaker or speaker cab. Have you also tried playing in a different room. If none of the above I would bet it's a cold solder, most likely in the LNFB of the tonestack

I have tried different speakers but didn't try a different room. I reflowed all the solder joints on the tone circuit and LNFB on V1b. I found one sketchy joint so I thought for sure that would fix it but alas no it did not. Thanks for the ideas. Will try a different room tomorrow.

[njolly]

have you checked to be sure that you don't have any AC riding on your DC voltage supply?

Yes I have. The power supply is really clean and the amp is very quiet in all other aspects. Thanks

[njolly]

could it be magnetostriction with the OT? also perhaps a window is rattling or even drywall panels if you're really cranked up and the amp is backed against a wall

actually it may not even have to be very loud if the panel resonance is being matched perfectly by the note, it would vibrate pretty strongly i think

Quite sure it's not the OT. I changed the amp to use EL34s and ended up replacing the OT with a 50 watt marshall OT from hammond that I had bought a while back for another project I never started. Changing the OT made a big difference to the sound of the am but never altered the artifacts.

Doesn't seem to matter if I play loud or quiet the artifact is still present. Wil try a different speaker in another room tomorrow to make sure. Thanks

[pottedplant]

could it be magnetostriction with the OT? also perhaps a window is rattling or even drywall panels if you're really cranked up and the amp is backed against a wall

actually it may not even have to be very loud if the panel resonance is being matched perfectly by the note, it would vibrate pretty strongly i think

Quite sure it's not the OT. I changed the amp to use EL34s and ended up replacing the OT with a 50 watt marshall OT from hammond that I had bought a while back for another project I never started. Changing the OT made a big difference to the sound of the am but never altered the artifacts.

Doesn't seem to matter if I play loud or quiet the artifact is still present. Wil try a different speaker in another room tomorrow to make sure. Thanks

Ah, okay. I'm sure you're aware of what I'm talking about but just in case you're not a few people have posted about buzzing transformers when using a load box/silently recording their amps cranked. Marshalls especially exhibit this behavior (maybe they are attenuated more often? not sure about if it's actually brand specific/transformer specific). My vintage blackface fender also does it when I crank it up real loud. Here's an example of a marshall doing it: https://www.youtube.com/shorts/m3f_3J59-vI

I just had a thought while searching for a suitable video to share, check your speaker especially down at the bottom for anything that may have gotten in there (like a clipped end from a lead or something). This happened to me a long time ago with some non guitar-related speakers that have pretty open plastic grills. I clipped a lead off of something and it went flying and I didn't see where it went and later on I was using these speakers and there was a crazy buzz coming from one. I suppose it would always buzz in most cases but it could be touching the cone just right to cause a buzz with certain tones. Just to be clear we are talking about the loud buzzing sound in your sound clip no? I hope you find out what's causing it

Just had another thought, could it be a washer? I know some pots/switches have little locating tabs that sometimes people forget to remove and if you tighten one down it leaves a gap between the housing and chassis perhaps?

[alnight]

Does it still do it if you pull the chassis out of the cabinet? It sounds mechanical in the clip, but without being in the room I can't really say. I just last week fixed one of my amps that had an annoying crackle on low F. Pull the chassis out of the cab so you can see everything and poke it with a stick, and it wouldn't do it. Turned out to be a broken resistor lead that was still making pretty good contact. Took a while to find. The resonant freq of the cab is, apparently, F, and would shake it just enough that it would crackle a bit as the note decayed. Quite frustrating. I'm reasonably confident you have something similar as far as the resonant frequency aspect, you just need to find what's shaking.

[Guy77]

Make sure every single wire run that requires a shieled cable has one. Try using a chop stick to move the signal wires in the preamp section and see if the noise goes away.
Be very careful doing this since the voltages here are dangerous.

Cheers
G

[njolly]

could it be magnetostriction with the OT? also perhaps a window is rattling or even drywall panels if you're really cranked up and the amp is backed against a wall

actually it may not even have to be very loud if the panel resonance is being matched perfectly by the note, it would vibrate pretty strongly i think

Quite sure it's not the OT. I changed the amp to use EL34s and ended up replacing the OT with a 50 watt marshall OT from hammond that I had bought a while back for another project I never started. Changing the OT made a big difference to the sound of the am but never altered the artifacts.

Doesn't seem to matter if I play loud or quiet the artifact is still present. Wil try a different speaker in another room tomorrow to make sure. Thanks

Ah, okay. I'm sure you're aware of what I'm talking about but just in case you're not a few people have posted about buzzing transformers when using a load box/silently recording their amps cranked. Marshalls especially exhibit this behavior (maybe they are attenuated more often? not sure about if it's actually brand specific/transformer specific). My vintage blackface fender also does it when I crank it up real loud. Here's an example of a marshall doing it: https://www.youtube.com/shorts/m3f_3J59-vI

The artifact is present even at low volumes without an attenuator so pretty sure the OT is not the issue.

I just had a thought while searching for a suitable video to share, check your speaker especially down at the bottom for anything that may have gotten in there (like a clipped end from a lead or something). This happened to me a long time ago with some non guitar-related speakers that have pretty open plastic grills. I clipped a lead off of something and it went flying and I didn't see where it went and later on I was using these speakers and there was a crazy buzz coming from one. I suppose it would always buzz in most cases but it could be touching the cone just right to cause a buzz with certain tones. Just to be clear we are talking about the loud buzzing sound in your sound clip no? I hope you find out what's causing it
I tried a different speaker/cab in a different room and the issue is still there. The amp is a head so I don't think it's anything loose in the amp either.

Just had another thought, could it be a washer? I know some pots/switches have little locating tabs that sometimes people forget to remove and if you tighten one down it leaves a gap between the housing and chassis perhaps?

Checked today and all the components seem to be secured. Thanks!

[njolly]

Does it still do it if you pull the chassis out of the cabinet? It sounds mechanical in the clip, but without being in the room I can't really say. I just last week fixed one of my amps that had an annoying crackle on low F. Pull the chassis out of the cab so you can see everything and poke it with a stick, and it wouldn't do it. Turned out to be a broken resistor lead that was still making pretty good contact. Took a while to find. The resonant freq of the cab is, apparently, F, and would shake it just enough that it would crackle a bit as the note decayed. Quite frustrating. I'm reasonably confident you have something similar as far as the resonant frequency aspect, you just need to find what's shaking.

Yeah still there if I pull the chassis. I'm slowly replacing the cheap chinese components with better quality parts so I am hoping I will find the problem eventually. Thanks

[njolly]

Make sure every single wire run that requires a shieled cable has one. Try using a chop stick to move the signal wires in the preamp section and see if the noise goes away.
Be very careful doing this since the voltages here are dangerous.

Cheers
G

I'll give this a try over the weekend, Thanks for the idea