Hum Neutralizer

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Riffmonster
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Hum Neutralizer

Post by Riffmonster »

Hi guys,

I stumbled upon this video as I had some hum in an my 18 Watt Superlite TMB:

https://www.youtube.com/watch?v=epQUVJ--JZY

I tried it on my amp and it did reduce the hum quite a bit, however, not completely. What are your thoughts on this "mod"? Anybody else tried it?
I could not try the amp loud yet, but do you think the tone has changed?

Thanks and best regards!
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JMPGuitars
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Re: Hum Neutralizer

Post by JMPGuitars »

That appears to be a modified version of elevated heater wiring. I'm not sure what connecting it to the PI cathode does, but I didn't really watch the video yet. This method likely only gets rid of hum due to the heater wiring.

If you're still having hum/noise issues, it's more likely lead dress, grounding, or possibly not paying attention to the direction of capacitor foils, or a million other things that can add to amp noise.

Which version Superlite TMB did you build?
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TriodeLuvr
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Re: Hum Neutralizer

Post by TriodeLuvr »

This technique has been used commercially for many years, although I've never seen it applied to the phase inverter. Here's a Stromberg console amp from the '60s:

Image
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Re: Hum Neutralizer

Post by Riffmonster »

Thanks for the replies guys!
I was aware of heater elevation too, but this method of noise canceling was new to me. And to be honest, I did not fully understand the logic behind it as explained in the vide. The way I understood it was that ALL hum getting into the power stage can be cancelled by it and not only heater hum (as opposed to common heater elevation). I guess I was mistaken.

Josh, it is just the regular Superlite TMB (newest version from the downloads here). I recycled used parts and had to make some tradeoffs due to very short wire lengths of the transformers I used. This has led to suboptimal lead dress.
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Re: Hum Neutralizer

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Riffmonster wrote:
Thu 12/17/20 1:40 pm
This has led to suboptimal lead dress.
I would say that's probably your answer right there. If the leads are too short, you can extend the leads and double heat-shrink tube the connections. That's fine as long as you're not planning on selling the amp. That said, I would be surprised if it's all in the PT area causing your noise. BTW- this is one reason why I stick with solder lug PTs. Harder to avoid on OTs, but wires can still be extended if done correctly.

Post some build photos so we can take a look. Also a sound sample so we can hear the issue.
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Re: Hum Neutralizer

Post by crgfrench »

Rob Robinette has a good note about Humdingers on his site.
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Re: Hum Neutralizer

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JMPGuitars wrote:
Thu 12/17/20 4:49 pm
Riffmonster wrote:
Thu 12/17/20 1:40 pm
This has led to suboptimal lead dress.
I would say that's probably your answer right there. If the leads are too short, you can extend the leads and double heat-shrink tube the connections. That's fine as long as you're not planning on selling the amp. That said, I would be surprised if it's all in the PT area causing your noise. BTW- this is one reason why I stick with solder lug PTs. Harder to avoid on OTs, but wires can still be extended if done correctly.

Post some build photos so we can take a look. Also a sound sample so we can hear the issue.

You are right. I have to make the leads of my OT longer so I can place my board better with regards to the tube sockets. I have rather long leads to the PI tube from the board and they cross wires of the power tube socket. I will fix that and if the problem still remains post some pictures. Btw, the hum is tolerable but I still like my amp as quiet as possible. I will keep you updated, thanks!
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Re: Hum Neutralizer

Post by TriodeLuvr »

Riffmonster wrote:
Thu 12/17/20 1:40 pm

You are right. I have to make the leads of my OT longer so I can place my board better with regards to the tube sockets.
I often re-purpose vintage transformers that have been removed from older gear. The leads are almost never long enough. I just mount a terminal strip directly under the transformer and wire all the leads to that. Then I add new wiring to the terminal strip. Looks neat and solves the problem.

Jack
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Re: Hum Neutralizer

Post by Riffmonster »

TriodeLuvr wrote:
Fri 12/18/20 10:15 am
Riffmonster wrote:
Thu 12/17/20 1:40 pm

You are right. I have to make the leads of my OT longer so I can place my board better with regards to the tube sockets.
I often re-purpose vintage transformers that have been removed from older gear. The leads are almost never long enough. I just mount a terminal strip directly under the transformer and wire all the leads to that. Then I add new wiring to the terminal strip. Looks neat and solves the problem.

Jack
That is actually a smart idea, thanks for the tip!

I did rework the amp a bit today. I moved all tube socket one position to the PT direction after making the leads of my OT a bit longer. This made it possible to shorten most wires going from the board to the tube sockets. The hum is significantly lower now, when you play at bedroom level you can basically not hear it. There is a bit of hum and white noise when I turn it up, but I think it is not too bad.

I attach you two photos. It is not a neat looking amp, I know. As I said it was made from parts I used years ago over an over again. If you have some tips for making it even more quiet, please go ahead. I could, for example, try carbon comps on the PIs. Thanks
You do not have the required permissions to view the files attached to this post.
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Re: Hum Neutralizer

Post by JMPGuitars »

Riffmonster wrote:
Fri 12/18/20 12:23 pm
I did rework the amp a bit today. I moved all tube socket one position to the PT direction after making the leads of my OT a bit longer. This made it possible to shorten most wires going from the board to the tube sockets. The hum is significantly lower now, when you play at bedroom level you can basically not hear it. There is a bit of hum and white noise when I turn it up, but I think it is not too bad.

I attach you two photos. It is not a neat looking amp, I know. As I said it was made from parts I used years ago over an over again. If you have some tips for making it even more quiet, please go ahead. I could, for example, try carbon comps on the PIs. Thanks
Carbon comps are the noisiest option. They're only beneficial at the PI plates. If you want less hiss, metal film are the best option.

But I doubt it's the resistors from the look of the build. Your lead dress is a mess, and you should chopstick it a bit. Sloppy lead dress = noise.

Your heater wires are also an issue. They should all be tight together, including the separate runs going between the tubes. For example, both connections to Pin 9 on your preamp tubes should not be separated. Use a zip tie to join them if you need to. I twist and heatshrink.

Thanks,
Josh
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Re: Hum Neutralizer

Post by Riffmonster »

Thanks Josh, those are good tips!
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Re: Hum Neutralizer

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Riffmonster wrote:
Fri 12/18/20 12:23 pm
TriodeLuvr wrote:
Fri 12/18/20 10:15 am
Riffmonster wrote:
Thu 12/17/20 1:40 pm

You are right. I have to make the leads of my OT longer so I can place my board better with regards to the tube sockets.
Tube Town parts? I recognize the silicon wires
I often re-purpose vintage transformers that have been removed from older gear. The leads are almost never long enough. I just mount a terminal strip directly under the transformer and wire all the leads to that. Then I add new wiring to the terminal strip. Looks neat and solves the problem.

Jack
That is actually a smart idea, thanks for the tip!

I did rework the amp a bit today. I moved all tube socket one position to the PT direction after making the leads of my OT a bit longer. This made it possible to shorten most wires going from the board to the tube sockets. The hum is significantly lower now, when you play at bedroom level you can basically not hear it. There is a bit of hum and white noise when I turn it up, but I think it is not too bad.

I attach you two photos. It is not a neat looking amp, I know. As I said it was made from parts I used years ago over an over again. If you have some tips for making it even more quiet, please go ahead. I could, for example, try carbon comps on the PIs. Thanks
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Re: Hum Neutralizer

Post by crgfrench »

JMPGuitars wrote:
Fri 12/18/20 12:48 pm
Carbon comps are the noisiest option. They're only beneficial at the PI plates. If you want less hiss, metal film are the best option.
I use metal films, but if you were inclined to use CC and believe RG Keen, they would be OK on the PI plates in a non-NFB amp like the 18 Watter, and on the output tube grids too. And also at the first stage plate, which Keen says is "ideal".
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Re: Hum Neutralizer

Post by JMPGuitars »

crgfrench wrote:
Sat 12/19/20 12:38 am
JMPGuitars wrote:
Fri 12/18/20 12:48 pm
Carbon comps are the noisiest option. They're only beneficial at the PI plates. If you want less hiss, metal film are the best option.
I use metal films, but if you were inclined to use CC and believe RG Keen, they would be OK on the PI plates in a non-NFB amp like the 18 Watter, and on the output tube grids too. And also at the first stage plate, which Keen says is "ideal".
Yeah, we mostly use the same stuff.

But for other people's reference:
http://www.geofex.com/article_folders/c ... oncomp.htm

http://www.aikenamps.com/index.php/resi ... -it-matter

I thought Merlin had a thing about it too, but I can't find it.
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Re: Hum Neutralizer

Post by Riffmonster »

Thanks guys. I implemented a proper star ground and the hum is gone now.
I did not do the heater elevation in the end. Maybe I will try the carbon comps on the PI plates, but I am quite how it sounds now. This showed me once again how important proper grounding an lead dress is.
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