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Post by cfidave on Oct 2, 2019 12:36:20 GMT -7
I have a pretty noticeable hiss in my 2007 Carmen Ghia Head. Happens with nothing plugged in as soon as I crack the volume knob. It gets louder as I increase volume and pulling the phase inverter tube stops the hiss. It is NOT the tubes as I have tried several known to be quiet tubes in both the preamp and power amp locations with no change. It appears to be preamp related. Looking inside the chassis I see no bad solder joints, chop sticking preamp and phase inverter wires has no effect. I have cleaned and re-tensioned the tube sockets, cleaned the volume, tone pots, and cleaned input and output jacks. I am thinking it could be the volume pot itself, or a bad resistor in the preamp section. I have never run into a bad volume pot, and there is no crackling or static when turned. Can anyone think of anything else that might cause this?? Thanks for reading.
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Post by purpletele on Oct 2, 2019 15:26:41 GMT -7
I have a pretty noticeable hiss in my 2007 Carmen Ghia Head. Happens with nothing plugged in as soon as I crack the volume knob. It gets louder as I increase volume and pulling the phase inverter tube stops the hiss. It is NOT the tubes as I have tried several known to be quiet tubes in both the preamp and power amp locations with no change. It appears to be preamp related. Looking inside the chassis I see no bad solder joints, chop sticking preamp and phase inverter wires has no effect. I have cleaned and re-tensioned the tube sockets, cleaned the volume, tone pots, and cleaned input and output jacks. I am thinking it could be the volume pot itself, or a bad resistor in the preamp section. I have never run into a bad volume pot, and there is no crackling or static when turned. Can anyone think of anything else that might cause this?? Thanks for reading. I have limited experience but a POT has never created a hiss. I have had pots create a bit of static and also pop with a bad wiper losing the signal, but I don't recall having a hiss. I'd say it's possible but unlikely on the Pot causing the hiss. On a 12 year old amp, you may have loose connection on one of the pots, in fact that is probably a good thing to check. The hiss may be from a ground that isn't solid, which could be the POT connection to the chassis. Try tightening the few POTs that you have. That's all I can think of right now. BV |
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Post by cfidave on Oct 2, 2019 16:03:03 GMT -7
Hey, thanks. Like you, I never had a bad pot do anything but cause static, so that probably is not the problem. I did check all pot connections, they seem perfect. I also re-tightened the pot to the chassis and cleaned behind the pot. I am going to check preamp voltages to see if any coupling caps are leaking D.C. I doubt that would cause hiss, most likely hum.
Speaking of hum, this amp has zero hum, just the hiss, which unfortunately is so bad that I can't use it for my situation. Too bad the tone is great.
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Post by bgkyt1 on Oct 3, 2019 8:53:56 GMT -7
are the jacks tight? does it still hiss badly if a cord is plugged in the input jack?
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Post by Mark (Basement Enthusiast) on Oct 3, 2019 10:02:12 GMT -7
cfidave, if it is a tube problem (not sure that it is, but worth checking) Doc has some very good info on all that here: drzamps.com/info/faq-troubleshoot/And if it's something else--such as the other suggestions above of "loose pots or jacks"--then you'll see all about how to tackle that here:
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Post by cfidave on Oct 4, 2019 3:52:36 GMT -7
Thanks guys, as I said it is not a tube problem, and all jacks and pots are tight and clean. In talking with Z-Repair what I am hearing is the actual noise in the tube itself due to the gain factor of the amp. My options are to adjust the gain by lowering the plate load resistors and/or using a lower gain V1 tube like a 5751 or even an AT7. The other option is to add the master volume mod . In other words I am told that this is normal for Carmen Ghia. I don't have another amp like the Ghia with just volume and tone, so I can't compare. My Cure is dead quiet, as are my Fenders.
Not sure what I am going to do, the tone on the Ghia is wonderful, but the hiss is very distracting.
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Post by purpletele on Oct 4, 2019 6:48:09 GMT -7
Thanks guys, as I said it is not a tube problem, and all jacks and pots are tight and clean. In talking with Z-Repair what I am hearing is the actual noise in the tube itself due to the gain factor of the amp. My options are to adjust the gain by lowering the plate load resistors and/or using a lower gain V1 tube like a 5751 or even an AT7. The other option is to add the master volume mod . In other words I am told that this is normal for Carmen Ghia. I don't have another amp like the Ghia with just volume and tone, so I can't compare. My Cure is dead quiet, as are my Fenders. Not sure what I am going to do, the tone on the Ghia is wonderful, but the hiss is very distracting. Please try the lower gain tubes, you will still have a killer tone. |
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