One Wire Mod Hiss

[metalhead3ecr]

Happy new year everyone! I have shielded all the input wires and put the 68k resistors as close to the tube as possible. My wiring is quite messy. This 50 watter has a PPIMV and a one wire mod like the one Michael R/T uses. CH I volume pot is tolerable with noise. CH II volume pot is fine until the last quarter turn or so.

How do I get rid of this noise other than making a more tidy amp

Here are two videos which should help you understand my issue.

[white noise]

Without tidying up the amp wiring I don't see that sound going away.

[metalhead3ecr]

Without tidying up the amp wiring I don't see that sound going away.

alright, I'll clean things up and report back soon...

[rgorke]

Where are you in your house (presuming you are in your house)? When are you hearing the noise, what time of day?

I build a JTM50 that was dead quiet all day long until the evening and the street lights and other draws on the power in the neighborhood. Try a different outlet. Have you tried it inside a head box?

Does the noise change at all by moving the guitar around? Hard to tell from the video with you playing.

Try to see if external factors are at play. It was an aggravating aspect for me. I could run the amp dimed and it was dead quiet until 7 pm or so in the evening. Then it would hum like yours. I even had the V2 inputs shielded like yours.

[metalhead3ecr]

it's been in various rooms and in and out of aluminum tape shielded head box. Any time of day...I honestly think it was sloppy wiring and the first tube just being driven a little too hard. THe noise resulted only when diming CHII. All three preamp tubes were China's so a little extra noise is expected when dimed i guess.


I plan on cleaning up my work and fixing my grounding and trying it all again...

would like to get it sounding close to the Major Loud youtube guy who's amp can be seen here (was discussed on the forum previously...nothing new) ...his seems fairly quiet

[youtube]https://www.youtube.com/watch?v=W_4pCaG4z8o[/youtube]

[metalhead3ecr]

OK, I rewired the board and cleaned things up. I am so close to determining the cause of this noise issue. I think I have located the source. This video is after I replaced this wire and re-soldered the joints on both ends...Is it a bad pot then? Noise goes away when I move the wire a certain way...not really reproducible though..I'm confused...

https://www.dropbox.com/s/3n73b5pz38ws2 ... 5.MOV?dl=0

[metalhead3ecr]

I replaced the pot with a new one....still noise. Now I'm really confused.

[rgorke]

what wire is that? Have you tried putting in a whole new wire and resoldering it? did you say you switched out tubes?

[metalhead3ecr]

I have replaced the wire several times. I replaced the pot and the results became even less reproducible. I have swapped V1 tube several times (China, JJ, TAD China...all go microphonic). Basically, V1 is very microphonic when the whole amp is dimed and no input jack is being used. I have been tapping around with my "chopstick" and noticed that any wire running to V1 (shielded or not) is picking up noise. When V1 is removed the amp is silent. The noise (as heard in the video) is only hiss. But I am trying to run a similar spec to Michael R/T and his amp is dead nuts quiet...so something isn't right on mine just yet.

[metalhead3ecr]

Still tweaking this thing currently. I added a linear 1Meg pot so as to simulate the 1 Meg resistor that is typically found in the one wire mod. This is my dilemma

If the pot is set to zero (not adding any resistance), then all the tone and all the noise is there.
If the pot is set to 10 (adding 1Meg resistance), then all the noise is gone and all the tone is gone too. Same volume, just dull and boring, no sag and sizzle.

So it seems the noise and tone are both in the audible high end frequency range. Which is a bummer. I could try not biasing V1 so hot with an 820r and up it to a 1.4k or something....but then I loose gain.

Hmm...

Here is a demonstration of the 1Meg pot. https://www.dropbox.com/s/2p1852m9i7yow ... 7.MOV?dl=0

[rgorke]

did I read it right that with no cable in the inputs, there is noise? There should be no noise or maybe some hiss with nothing plugged into the amp.

I had a bad input jack that didn't close all the way. Make sure your jacks are wire correctly. Also, check your voltage on the plate resistors and make sure all your components are the right value. Some folks have had miss marked components or read them wrong.

Finally, make sure the tube socket is wired neatly and there are no unintentional connections between tabs. Your socket may also be bad or damaged.

Does the NFB make a difference? Does the sound change turning the presence control?

[metalhead3ecr]

did I read it right that with no cable in the inputs, there is noise? There should be no noise or maybe some hiss with nothing plugged into the amp.

I had a bad input jack that didn't close all the way. Make sure your jacks are wire correctly. Also, check your voltage on the plate resistors and make sure all your components are the right value. Some folks have had miss marked components or read them wrong.

Finally, make sure the tube socket is wired neatly and there are no unintentional connections between tabs. Your socket may also be bad or damaged.

Does the NFB make a difference? Does the sound change turning the presence control?

Watch the dropbox video. I get massive hiss when trying to implement Michael R/T 's one wire mod. Other than the hiss everything else is working great...

[metalhead3ecr]

Ordered some matched and balanced ECC82 ECC81 and 5751 tubes from eurotubes for V1 and V3 positions. I quickly tried them all out in different configurations and the only difference I am hearing is that the noise is still there...just a lower volume. I'll have to mess with it a bit this weekend. I'm still perplexed as to how people can do this mod without the 1meg resistance and manage to have little to no noise...hmmm

[Colossal]

I get massive hiss when trying to implement Michael R/T 's one wire mod. Other than the hiss everything else is working great...

Hiss is normal. Buzz is not normal. Hiss is shot noise and with that much gain on tap, you are hearing the sound of the stream of electrons boiling off the filament and slamming into the anode.

Curious, what values do you have in your one-wire circuit? You said your amp is a 50. From your video, I can't quite see what is happening on the left, where I would expect the One-Wire to be at the junction of the two 68k/68k input grid resistors. R/T's Major has a shared 820R/330uF cathode and by reversing the coupling caps on each channel as he did, his gain staging is:

Normal Channel input -> 34k/1M ->
820R/330uF -> 2n2 coupling -> Volume II -> 68k/68k -> input to second stage
820R/330uF -> 22n coupling -> Volume I -> 470k/500p peaker over 470k to ground -> input to third stage

Your amp sounds pretty killer though.

[metalhead3ecr]

yea I only have hiss, no buzz. I have been following this layout. Obvious changes for 50watt in the power section..but yeah, my preamp sections are setup like this http://s296.photobucket.com/user/OdieMi ... b.jpg.html