# Big Static Hiss - but only on B



## Beach Bob (Sep 12, 2009)

I recently built a Trinity 18w kit and its been working pretty good. However, I took the amp to a buddy's last night and whenever he plays a "B" thru it with some attack, a staticky hiss starts to build up. The longer the note is sustained, the louder the hiss. I can even pull the plug from the guitar and the hiss will continue.

This is happening on both inputs on both channels. Based on that, I think I can rule out anything in the pre-amp section. But other than that, I'm really confused as to what to look for. 

Any ideas on what to check?


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## keto (May 23, 2006)

My first guess would have been loose parts, a nut or something, followed by a possible tube problem - have any others you can swap out and test?


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## LydianGuitars (Apr 18, 2013)

I would check all the tubes, connectors and solder joints


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## zdogma (Mar 21, 2006)

?parasitic oscillation. I remember reading about this type of problem with certain blues junior amps where the oscillation caused hiss only with certain notes.


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## Beach Bob (Sep 12, 2009)

I got some time to try to work this out this morning. Plugged the amp into the speaker on a buddy's Traynor. Absolutely no sign of the problem. Pulled things apart and resoldered everything to do with the speaker in my amp and solved 90% of the issue. Unfortunately...still leaves 10%

So, I'm pretty certain that the problem is in the speaker; all joints have been resoldered.. is possible that its an issue internal to the speaker? (12" Eminence Private Jack)


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## jb welder (Sep 14, 2010)

Yes, it could be the speaker. If so, you should be able to verify it by hooking it up to a different amp and playing the same note.
However, if it is a combo amp it could also be that the speaker vibration is causing something to vibrate in the amp. Is it a combo amp or is the speaker separate?
Combo's are much more susceptible to problems such as bad solder or microphonic tubes. Amps with such problems will often sound ok when the internal speaker is disconnected and an external cab. is used.
One of the first things I would try would be to get the noise happening, then try holding on to the tubes one at a time (with a rag or something) to see if the noise is related to vibration of a tube.


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## Beach Bob (Sep 12, 2009)

jb welder said:


> Yes, it could be the speaker. If so, you should be able to verify it by hooking it up to a different amp and playing the same note.
> However, if it is a combo amp it could also be that the speaker vibration is causing something to vibrate in the amp. Is it a combo amp or is the speaker separate?
> Combo's are much more susceptible to problems such as bad solder or microphonic tubes. Amps with such problems will often sound ok when the internal speaker is disconnected and an external cab. is used.
> One of the first things I would try would be to get the noise happening, then try holding on to the tubes one at a time (with a rag or something) to see if the noise is related to vibration of a tube.


It is a combo amp... I guess I'll have to find some heat proof gloves to try and hold tubes. Thanks for the suggestion.


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## Wild Bill (May 3, 2006)

Beach Bob said:


> It is a combo amp... I guess I'll have to find some heat proof gloves to try and hold tubes. Thanks for the suggestion.


Not suggesting you don't know what you are doing but is there any chance you have mis-wired the output connections?

I'm thinking two possibilities. One is that the phasing of the speaker output wires is wrong - the wires are reversed. This would make the negative feedback loop through that 100k resistor from the speaker lead back to the phase inverter a POSITIVE feedback loop!

If there is enough feedback this is easy to spot - the amp squeals like a stuck pig! If there is only a little bit you get symptoms like you describe - hissing and/or ringing on notes.

The cure is to reverse the speaker output wires.

The other possibility is that you have a 16 ohm speaker on a 4 ohm tap. This will give a sky high plate load. Most of the time the amp won't care but once in a blue moon it causes fizzy problems.

Those are the only things that come to this old brain at the moment.

Good Luck!

Wild Bill/Busen Amps


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## WCGill (Mar 27, 2009)

I doubt there's any relationship between negative voltage feedback in the amplifier and speaker polarity. Different manufacturers even vary in polarity amongst themselves, JBL and Jensen being two that come to mind that are opposite to most. How do you even know if the pickups in the guitar are in phase as well? The mojo for the older Tweed amps was the out-of-phase Jensen speakers, but Marshall used in-phase Celestions and had some pretty heavy mojo too. It *may* sound different, but it may very well be that old demon "psychoacoustics".


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## Wild Bill (May 3, 2006)

WCGill said:


> I doubt there's any relationship between negative voltage feedback in the amplifier and speaker polarity. Different manufacturers even vary in polarity amongst themselves, JBL and Jensen being two that come to mind that are opposite to most. How do you even know if the pickups in the guitar are in phase as well? The mojo for the older Tweed amps was the out-of-phase Jensen speakers, but Marshall used in-phase Celestions and had some pretty heavy mojo too. It *may* sound different, but it may very well be that old demon "psychoacoustics".


Wasn't thinking about different speakers, WC. I was thinking about the fact that this is a kit he built himself. It is not speaker polarity that determines the phase of the feedback. It is the phase of the speaker wires coming from the output transformer. Swap the green and the black wire for yourself!

I noted that when he fed the amp to a different speaker the problem was reduced but not eliminated. That made me think the problem could be speaker load sensitive. This of course would not change the phase of the feedback but if the feedback was already wrong a different load could make changes in how the problem appeared.

I agree it's a long shot but hey! This seems to be a long-shot problem.

Wild Bill/Busen Amps


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## Beach Bob (Sep 12, 2009)

The amp is at a buddy's... hopefully I will have time to swing by tomorrow night.

The output transformer is wired correctly and I have the resistance set properly... I'm 100% certain of that.

I am not 100% certain that the wiring between the speaker and the jack isn't crossed. I'll have to take a look at that. After Wild Bill's first response, I hoped this might be the issue; his second response makes me think it doesn't matter.

Bill - To clarify... the problem disappeared completely when feeding a different speaker. It moderated out pretty good after resoldering the speaker connections, but still remains.


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## Wild Bill (May 3, 2006)

Beach Bob said:


> The amp is at a buddy's... hopefully I will have time to swing by tomorrow night.
> 
> The output transformer is wired correctly and I have the resistance set properly... I'm 100% certain of that.
> 
> ...


Well, if feeding a different speaker killed the problem, wouldn't it make sense your problem is the speaker?

Wild Bill/Busen Amps


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## WCGill (Mar 27, 2009)

Wild Bill said:


> Wasn't thinking about different speakers, WC. I was thinking about the fact that this is a kit he built himself. It is not speaker polarity that determines the phase of the feedback. It is the phase of the speaker wires coming from the output transformer. Swap the green and the black wire for yourself!
> 
> I noted that when he fed the amp to a different speaker the problem was reduced but not eliminated. That made me think the problem could be speaker load sensitive. This of course would not change the phase of the feedback but if the feedback was already wrong a different load could make changes in how the problem appeared.
> 
> ...


Swapping the primary wires will give positive feedback for sure, swapping the secondaries will probably only change the phase, or polarity of the speaker.


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## Wild Bill (May 3, 2006)

WCGill said:


> Swapping the primary wires will give positive feedback for sure, swapping the secondaries will probably only change the phase, or polarity of the speaker.


Either swaps the phase coming back, WC! Try it! I've done it many times!

Wild Bill/Busen Amps


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## WCGill (Mar 27, 2009)

Against my better judgement I did swap the secondaries on my Princeton Reverb and not knowing which was which, I heard zero difference.


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## jb welder (Sep 14, 2010)

As far as I know, when you have squeal from OT being out of phase, either method will cure it (swapping primary leads around or swapping secondary leads around). 
However, you can only swap the secondary if it is a single tap output. If you have multiple taps, swapping the secondary leads is not feasible. So it's a good idea to leave some extra wire length when wiring up an OT, in case you need to swap the leads around you don't want to have to splice in some extra wire.
Most people prefer to swap the primary as it leaves the color of the speaker jack wires looking "proper".
You could also swap the leads going from the phase splitter to the power tube grids.
All that being said, this is theoretical and I have not tried the experiment which WCGill did.
What I'm wondering is: are you saying that for your Princeton Reverb, swapping the primary leads will make it squeal, but swapping the secondary leads will not?
If it's not too much trouble, could you try both? If you can introduce squeal by swapping the primary, you should be able to remove it by then swapping the secondary.


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## WCGill (Mar 27, 2009)

Hi JB,
Indeed, swapping inputs to the PI will result in the same wailing and gnashing, changing speaker leads, not so much. I won't swap the primaries on my Princeton because I don't feel like tearing down the amp and I know what the result will be. That's why I prefer to build AC30's, no chance of getting the wires hooked up backwards.  I can't believe no one has done this. I would encourage someone else to try it, maybe their results will be different.

*Update*- I guess I'll have to eat crow on this one as I only reversed the speaker leads, which of course will not do anything to the feedback loop. Fawlty logic. My bad.


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## Wild Bill (May 3, 2006)

WCGill said:


> Hi JB,
> 
> 
> *Update*- I guess I'll have to eat crow on this one as I only reversed the speaker leads, which of course will not do anything to the feedback loop. Fawlty logic. My bad.


How does it taste to you, Mr. Gill? I've eaten so much of the damn stuff over the years I'm starting to develop a taste for it! :food-smiley-004:

Wild Bill/Busen Amps


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## WCGill (Mar 27, 2009)

You know, the whole time I've been thinking "Why would reversing the speaker leads give positive feedback?" I guess I should have been reading instead of writing or as I tell my kids "listening instead of talking". Crow is part of my nutritional plan on a regular basis, the taste, well....largetongue


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## Wild Bill (May 3, 2006)

WCGill said:


> Crow is part of my nutritional plan on a regular basis, the taste, well....largetongue


My doctor always comes up with things I'm supposed to either eat or not eat.

Some years ago I simplified his instructions, while accurately obeying them. 

I just don't eat anything I like! I also eat only what I don't like!

He says I will live at least 10 years longer. Man, it sure feels like it!

Wild Bill/Busen Amps


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