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Harshness on Normal/Input 2


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7/11/2004 2:31 AM
Bernie Baer
Harshness on Normal/Input 2
Hi folks,  
well I have completed my 5E3, and mounted the chassis in the cabinet. All seems well except when I plug into the 'top right' jack, ie, Normal/2.  
There I get a very, very harsh overtone over the guitar sound. It almost sound like there is something physically wrong with the speaker, kind of a rattling/tearing harsh sound, but the speaker sounds fine on all other channels even at higher volumes.(BTW the speaker is a reissue Jensen P12Q).  
I notice it most when I use a medium attack and the sound seems to be almost an echo or in other words it seems slightly delayed after the chord sounds.  
It also seems to end abruptly. This echo/sudden ending seems to imply that perhaps there is a capacitor involved but I'm not sure.  
Any ideas anyone?  
Thahks, Bernie.
 
7/11/2004 4:04 AM
Bernie Baer

Strange... sometimes it's quite alright. Just now I was playing for a good ten minutes OK, then I flipped the standby switch, waited about 20 seconds, then on again and the harshness started immediately! Played for a few minutes, cycled the standby again, and it was good again?
 
7/11/2004 4:21 AM
jayman

I'd re-flow solder joints on that one jack, just for an obvious easy starter...intermittent nature of it makes me think maybe it's that.
 
7/11/2004 4:38 AM
Bernie Baer

Thanks Jayman, actually I've managed to get it doing it on the Normal/Input1 jack also now, but it only seems to do that on my neck pickup! I'm playing an Epiphone ES-295 with P-90's. Will start checking resoldering soon I guess, the joints look nice and shiny but I guess redoing them is the way to go.
 
7/11/2004 6:19 AM
Bernie Baer

OK I've resoldered all the joints around the jacks, also on the 12AY7 (pins 1,2,3), the junction of the 0.1 uF cap and the 100k resistor, and the 68K resistors (both ends). The harsh noise persists; and now I notice if I hit a double stop with a short sharp attack I get a single 'echo' of the harsh noise, however if I hit the double step fairly gently/slowly I can hear 3 or 4 repeats of the harsh 'echo'. Well I like slapback delay but I'd prefer if it was repeating the original signal!
 
7/11/2004 7:13 AM
Bernie Baer

I resoldered the 0.0047uF capacitor in the tone circuit of the 'Normal' side and I think that may be it. Certainly (for now) the 'echo' appears to have gone, there seems to be some harshness still particularly when using the neck p/up of both my Epi and my Grestch 6120 but maybe I'm just hearing the natural grit of the amp, unaccustomed as I am to 5E3's! It's certainly much better than it was (pretty unbearable before) so I hope that it stays that way.  
Any explanations anybody, as to why that cap may have done that?
 
7/11/2004 11:19 AM
jayman

Good about the echo going away. In thinking about the echo, in some ways, the symptoms of the noise emitted seem not dissimilar, in some ways, to motorboating (runaway oscillation of bass from internal clipping etc., ie., caps are too big in the tone circuit.) Let's hope it stays away.  
 
Now, whatever the harshness problem is, it seems to be revealed under much bass, ie., it appears with the neck pickup using both guitars. Is your speaker mounted really securely to the baffle board, ie., really flush and can't wiggle/rattle? Sure the polarity is right on the speaker wires. (Not meaning to insult in any way; I just like to start with obvious, easy things, and I know, if you're like me, you may have stayed up many bleary-eyed hours, finishing the amp, and could have, being even a normal human -- you're not since you build amps -- overlooked the obvious.)  
 
For example, my amp was all good, except for a little strand of cable shielding touching a tube lug...kept it from firing up (mine only got running about two weeks ago)...I was sleepy, but Bruce troubleshot it and then it fired up, troubleshooting over the phone...but it was an easy, obvious fix after we checked various voltages, and I know you've already done that. You might actually replace that cap just to see if it's a characteristic of maybe one fluke component, but I don't think there should be any of what I would call "harshness" to my ear, especially on the neck pups.  
 
By the way, you may want to tweak your guitar tone caps, once you get the amp all like you want it. I think you'll find that Bruce's amp is a very responsive, "purist" kind of "sport's car" amp, and that you'll get nuance of tone textures even from such small changes that wouldn't be audible with a less better "handling" sports car, or in this case, sports amp.
 

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