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Post subject: What's that noise? (Humming on Hot Rod Deluxe II)
Posted: Thu May 19, 2016 3:50 am
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It's been bugging me for ages and I really need to get it sorted.

When I mic up my HRD I get a range of hums and buzzes depending on where I place the mic (SM57). Also, if I put my head near the back of the amp I can hear a buzzing.

Here's some examples:
https://soundcloud.com/user485777105/ho ... 7-mid-left
https://soundcloud.com/user485777105/hot-rod-buzz-clip

Any ideas what could be causing these noises? I can't record anything :(


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Post subject: Re: What's that noise? (Humming on Hot Rod Deluxe II)
Posted: Thu May 19, 2016 5:09 am
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sounds normal to me, all my tube amps have an idle hum, some more so than others, I guess a lot depends on things like filter caps and other internal parts that wear down with use.

you're probably not going to hear that when what ever your playing / recording starts.


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Post subject: Re: What's that noise? (Humming on Hot Rod Deluxe II)
Posted: Thu May 19, 2016 8:21 am
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You have fluorescent lights hanging overhead?


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Post subject: Re: What's that noise? (Humming on Hot Rod Deluxe II)
Posted: Thu May 19, 2016 9:28 am
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BMW2002Ti wrote:
You have fluorescent lights hanging overhead?


+1

All possible sources of extraneous RFI in close proximity to the amp AND the guitar need to be identified and isolated or removed. That's the fluorescent tubes Steve mentioned plus TV sets, computer monitors, video-game consoles, electric motors, and cell phones.

Should these measures prove fruitless, investigate your cables (guitar, patch, mic) and consider upgrading to products that provide better shielding against RFI/EMI.

Arjay

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Post subject: Re: What's that noise? (Humming on Hot Rod Deluxe II)
Posted: Thu May 19, 2016 2:04 pm
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Thanks for the input so far.

Just to confirm, I have tried this in numerous locations, turned off any electrical devices/lights in the area and unplugged any inputs to the amp but the noise remains.

Last year I also replaced two of the smaller preamp tubes (whilst aiming to lower the overall volume).


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Post subject: Re: What's that noise? (Humming on Hot Rod Deluxe II)
Posted: Fri May 20, 2016 12:55 am
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Follow up - I've just tried a few things but still have the noise:

1) Re-seated all tubes for snugness and checked over visible solder joints and cable connections. Nothing was loose.

2) Removed/swapped tubes v1 v2 v3. I have GT-12AX7 in V1, 12AT7EH in V2 + V3. If I remove any and try the amp, there's no noise but it won't play. Various combinations of tubes have the same noise.

3) I turned off pretty much every electronic device and light in the house but noise remains.

4) If I disconnect the speaker jack the background hiss disappears but the electrical buzzing remains. I have identified this to be coming from the main circuit board area when I take the back off.

5) I have checked bias and set to 71ma (previously 73ma) - Doubt this is related though.

Any other suggestions?


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Post subject: Re: What's that noise? (Humming on Hot Rod Deluxe II)
Posted: Fri May 20, 2016 9:48 am
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If you remove V1 and the hiss n hum go away, that is in the V1 or the jack grounds. Look closely at the soldering on the jacks.

The mechanical buzz when the spaeker is disconnected is from the power transformer. Check all bolts and chassis screws for tightness, including the choke and OT.
Silicone glue at the base of the transformers can help chassis buzzes
A loose lamination in the PT can also cause a buzz. Spray it with clear laquer and let it soak into the laminations.


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Post subject: Re: What's that noise? (Humming on Hot Rod Deluxe II)
Posted: Fri May 20, 2016 10:27 pm
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It may be a 60 cycle hum coming from an appliance in the house, or some other part of the electrical system. A tube amp (as well as recording gear) will pick up all kinds of stuff if the house wiring is not perfect. My HRD hums a little bit more than my Egnater Tweaker 15 head, both of which are plugged into the same outlet.

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Post subject: Re: What's that noise? (Humming on Hot Rod Deluxe II)
Posted: Sat May 21, 2016 5:21 pm
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Retroverbial wrote:
BMW2002Ti wrote:
You have fluorescent lights hanging overhead?


+1

All possible sources of extraneous RFI in close proximity to the amp AND the guitar need to be identified and isolated or removed. That's the fluorescent tubes Steve mentioned plus TV sets, computer monitors, video-game consoles, electric motors, and cell phones.

Should these measures prove fruitless, investigate your cables (guitar, patch, mic) and consider upgrading to products that provide better shielding against RFI/EMI.

Arjay
I had a bothersome low hum that would just come and go. Frustrating. One day when the amp was very quiet, I left the room and came back and there was the dreaded hum. Then bingo! I had just turned on this tiny quiet personal desk fan in another room. Hard to believe that was the source. I guess there are ways to block those things without shutting down the house and neighborhood, but they don't worry me much.


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Post subject: Re: What's that noise? (Humming on Hot Rod Deluxe II)
Posted: Sat May 21, 2016 6:41 pm
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LawFlow wrote:
I guess there are ways to block those things without shutting down the house and neighborhood, but they don't worry me much.


A power conditioner may help.

Arjay

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Post subject: Re: What's that noise? (Humming on Hot Rod Deluxe II)
Posted: Tue Jun 28, 2016 3:16 am
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I just realised that if I use the drive channel, the noise is dramatically reduced (but still very faint). What would this suggest?


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Post subject: Re: What's that noise? (Humming on Hot Rod Deluxe II)
Posted: Tue Jun 28, 2016 8:26 am
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Using my plain-o logic, I would guess a component in the power section leaking power at that point in the circuit. Maybe something slightly out of spec. Has the issue gotten worse in the clean channel over time?
Taking all the tube covers off may help, if its RFI related; well those are seriously just a pita.


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Post subject: Re: What's that noise? (Humming on Hot Rod Deluxe II)
Posted: Tue Jun 28, 2016 9:50 am
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When you switch in the drive channel, it adds circuitry for the boost. You would think the hum would go up.
But it also switches out the normal volume control. If that reduces the hum, the problem is likely in that circuit. A cold joint on C19, R9, R6 or K1 could be the culprit. In terms of what's most likely, I would guess a broken solder joint on the ground of the normal channel volume control.
The controls and relays involved are usually very reliable, The solder joints are not. Many RFI problems are caused by cold solder joints. The crack becomes a lead crystal that rectifies the incoming interference, making it audible.
With the age of your amp, I would just have the whole thing resoldered. After 5 or so years of shaking the board, its considered a normal maintenance. Kinda like tightening all the bolts on yer dirt bike after a few races..


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Post subject: Re: What's that noise? (Humming on Hot Rod Deluxe II)
Posted: Tue Jun 28, 2016 10:20 am
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TimsAudio wrote:
Kinda like tightening all the bolts on yer dirt bike after a few races..


Dude! You used to race dirt bikes? I remember redoing the piston rings after every weekend. My last bike:

Image


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Post subject: Re: What's that noise? (Humming on Hot Rod Deluxe II)
Posted: Wed Jun 29, 2016 1:55 am
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I know! Start a third thread about the same topic, because, really, two aren't enough. :roll:

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