Hum Neutralizer Circuit For Tube Amps

Have a hum in your guitar tube amp? Like everyone else? Want to get rid of it? This hum neutralizer circuit is based on a concept in the Radio Design Handbook. This circuit is a noise cancellation concept. I elevate the ground and then use the previous stage to invert the signal and then the hum is canceled out in the power tube. Very nice solution and it only costs the price of 1 resistor, a few inches of wire and installation time.
This video explains the problem, why some common fixes are not 100% effective, the oscilloscope image of the problem and then explains the remedy.
This is now a standard feature to all my vintage circuits.
Original Work, Copyright 2015 James D. Whiteside, II all rights reserved, For consideration only, no reproduction without prior permission.

[@richardleerodgers5303]

Awesome video!!! I have been designing Vacuum tube guitar amplifiers for 28 years since getting my Degree in Electronics. I was a guitarist and loved their tone and dynamics there was little academic emphasis on tubes during formal education most of my knowledge I gained searching out "Old Timers" and discovering the Radiotron Designer's Handbook 4th Edition, which I notice you reference is a "Goldmine" It's nice to see somebody knowledgeable! Best Regards

[@stormriderkaos]

Someone likely mentioned this in the comments already but... faulty old filter capacitors are definitely a source of hum in tube amps and not a rare issue in vintage tube guitar amps.

[@ryanybos]

Now here's some good usable knowledge thank you Jim !

[@jedishaw6771]

Great info! Thanks for doing the video!!

[@robertholley2195]

bless you mr whiteside

[@kevinbeckenham3872]

Thank you for explaining how get rid hum, in my ferrograph series 4 valve reel to reel tape recorder

[@Joshua-to5bl]

Awesome amazing masterful!

[@deuce-way1440]

I still have hum in my push pull build using this setup, any other tips for dc elevated heaters?

[@xaz7088]

could it be done in a PI to PP output stage?

[@dumpsterchicken6287]

I have a question. My output tube cathode has the parallel resistor/capacitor, but not the other resistor to the cathode. Can I attach R hum directly to the cathode? Thank you.

[@Attic-Toy-Design]

Excellent video. Could you please explain how to get rid of hum on the Marshall 18 watt lite amp from preamp? Thanks .

[@deepblueharp]

The most common solution to that amp is to elevate the heater. There are several schematics online showing how. Basically, it involves connecting the heater centertap to the cathode of the power tubes. That raises the heater centertap to the bias voltage of the power tube and quiets the residual hum.

[@davidbolus]

Great video and tutorial - thank you very much for the information. How would you handle a fixed bias push pull circuit such as a Princeton 6g2 layout? Any suggestions regarding the Inversion and injection point into the 2 power tubes?

[@deepblueharp]

Thanks for watching. It is a solution for single-ended amps only. Because: Rule 1: PP configurations are hum canceling circuits. Rule 2: The PP tubes have grounded cathodes, which makes the PP configuration absolutely & positively deathly quiet. If not, then 1) one or both of the tubes is/are getting old, 2) the power filter caps on the 5Y3 are suspect or 3) the preamp tubes are the problem: old tubes or the connection to the input jack is creating a hum (ground loop issue).

[@davidbolus]

@@deepblueharp Makes sense - thanks for the response!

[@johnston.scott64]

I believe this would be applied to the output power amp section. I have a hybrid Marshall. A 12AX7 preamp with a solid state output. I'm not quite sure if rewiring the preamp with a triode tube would produce any quantifiable results.

[@deepblueharp]

A solid state output has other issues, so this isn't applicable. Also, a triode power tube is much less prone to hum and should not need this neutralizer in most cases.

[@pipercherokee8598]

Would the same steps apply to trying to diagnose 180Hz hum? Not entirely sure where it is coming from, but it is present with all knobs at minimum and nothing plugged in. The hum then increases with the REVERB knob, even with volume at minimum. Interesting. And, it is present even if the reverb tank and footswitch are disconnected entirely. Thoughts? '65 Princeton Reverb clone. Thank you, your channel is very informative!

[@deepblueharp]

Please send me an email (see my KZbin channel). I am going to need some more information and maybe a sound clip for analysis.

[@NickAnanas]

Hi, very interesting technique. I wonder why does V2 has two resistors, is to implement correctly? because usually there is only one resistor with a capacitor. Secondly, does it need the filter capacitor on the cathode resistor or it will still work without the capacitor? Thank you

[@deepblueharp]

On the cathode: one resistor is 1 ohm to take a direct measurement of the current the other sets the bias. The cathode does not need a bypass capacitor for this to work.

[@NickAnanas]

@@deepblueharp thank you!

[@CraigHollabaugh]

Nice work, there's multiple things going here, raising the filament supply, adding feedback to V1's cathode which might contain 60hz because of filament raising, and not introducing phase shift with coupling capacitor. Getting out my tattered RDH4 now to see what it says. I'll keep your handy dandy tip ready for future designs. Thanks

[@dcbluez4883]

Putting a 12.6vdc regulated heater circuit would also help also. At least on the preamp section. Power tubes 6.3vac no problem since they cancel out.

[@dcbluez4883]

Even if there is a voltage rise on V1 cathode this could be adjusted back down with resistor value changes on the V1 cathode and or plate resistor.

[@dcbluez4883]

Very nice idea. I will give it a shot. From what I can see from your schematic is coming off V1 cathode, use a 470K to the cathode of V2, or power tube. Is this correct? Would like to see the waveform after the resistor is added. Thanks much

[@lroy730]

Great Video. I've ben using similar cicuits for years. In some amps I can even get a boost on some frequencies... Funny how most well know Amp Mod Guru's don't know anything about Noise Canceling Inverting Loops. These work well and you don't need to add a big cap.

[@fisherterrell714]

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[@eugenejavion8686]

@Fisher Terrell Flixportal :)

[@fisherterrell714]

@Eugene Javion Thanks, I went there and it seems to work =) Appreciate it!

[@eugenejavion8686]

@Fisher Terrell Happy to help :D

[@christopherchirico8170]

It works! Thank you for posting. I have one question though. Could you put a variable 20k resistor in place of the Rhum?

[@deepblueharp]

+Christopher Chirico Yes, you can if you have space. Thanks for watching and I am glad it worked for you.

[@christopherchirico8170]

HI, I am going to try the 20k pot today. I just wanted to clear up something first, If you have time. I did not have a center tap on my 6.3 v secondary and used the 2 x100ohm to create one. This center tap lead would then go to the wiper on the pot and the 1 and 3 would go to the respective V1 and V2 cathodes directly on the tube pins. Correct?

[@jfrheavy1]

hi your video help me a lot, but my circuit only have preamp, can i do it whit only 12ax7? ( sorry for my English I'm peruvian )

[@deepblueharp]

+Jonathan Fernandez yes.

[@thatsfunnyjimmy1351]

How would you use this technique on a class AB push pull tube amp where the cathode is grounded on the power tubes ?

[@deepblueharp]

I had this question sent to me last week and I have had time to think about it more. I really wouldn't suggest doing this with power tubes of a AB amplifier. The cathode will need to elevated and the RC filter needs to be rated for 7 watts. However, it can be done. The cathode of the power tube needs to be elevated to 2VDC to 5VDC and a resistor (10W rated) connected from the cathode to the output of the preamp (generally the second stage). It is the preamp that is normally the source of the hum that needs corrected. So... What would be better is to elevate the ground on the preamp section. Connect the centertap of the 6.3VAC filiment to the RC filter of the preamp second stage (it is normally at 1VDC). Then connect a resistor from there to the cathode of the first stage of the preamp.

[@martynshaw7214]

@@deepblueharp can you do a schematic for this

[@Echo_III]

Sir, let's say I want to use oscilloscope on my computer (PC software). Can I hook amp an amp (Speaker taps) to a PC? How one can do that?

[@deepblueharp]

No, you cannot hook your PC to an amp or any other high voltage device. It will require an interface that will isolate your pc from the devices (like the amp or speaker). The isolation devices will output safe voltage levels for the pc (under 5 volts). I have no recommendations for you. I use an oscilloscope that has outputs to send to a pc to safely acquire data.

[@Echo_III]

Okay, thank you. Any advice about parameters which good oscilloscope should have?

[@deepblueharp]

I would suggest looking at the Hantek HT6022BE20MHz 6022be PC based usb digital storage oscilloscope's specifications. Also, it is really inexpensive.