Members denimboy Posted January 15, 2009 Members Share Posted January 15, 2009 (*This post is also on amp forum but since I prefer you guys I give it a try*) I got this 1986 Fender The Twin (red knob) which has been really noisy lately. I get this issshh coming from the amp as soon as I switch the Bypass off. There is only a Fender Telecaster plugged into it. I get the noise whatever input I use and at any volume level. Impedance match is well set and speakers seem fine. The circuit is very clean and no visible breaks. I'm thinking it might be a leaky capacitor. I would start by replacing the filter caps in power supply. Any suggestions? Here is the schematic diagram:http://www.schematicheaven.com/fenderamps/the_twin.pdf I can record the amp for the need. Can take guts pictures too. Your help is appreciated. I'm into second year of audio electronics repairing school. I can do it myself with some help. Link to comment Share on other sites More sharing options...
Members chisa Posted January 15, 2009 Members Share Posted January 15, 2009 take it to a tech Link to comment Share on other sites More sharing options...
Members denimboy Posted January 15, 2009 Author Members Share Posted January 15, 2009 bump Link to comment Share on other sites More sharing options...
Members andreas Posted January 16, 2009 Members Share Posted January 16, 2009 I'm no amp guru, but bad filter caps will usually produce hum and/or motorboating, not hiss. I'd start looking at the preamp tubes, starting with the input stage and working my way towards the power amp. Link to comment Share on other sites More sharing options...
Members denimboy Posted January 16, 2009 Author Members Share Posted January 16, 2009 I agree. Filter caps would bring hum. However I've been told that issh can be cause by leaky caps. I will start by repalcing power tubes (which seems very old) and since the isshh is not volume dependent, its my best shot for the moment. Link to comment Share on other sites More sharing options...
Members Byronamatron Posted January 16, 2009 Members Share Posted January 16, 2009 Resistors hiss, particularly when they drift high. Not volume dependent= something after the volume knob I think. Don't start with the filter caps (or any amp repair) unless you are positive you will not be killed in the process. Link to comment Share on other sites More sharing options...
Members justintee Posted January 16, 2009 Members Share Posted January 16, 2009 i have an amp at present that's causing a similar problem.. i would describe it as white noise, even... and i suspect it could well be a tube problem, as suggested above... if you have spare tubes swap them around - tedious but it may be a fix as simple as that.. but if the noise level is the same at whatever volume or gain setting, might be more than the tubes, which would warrant an tech consult. Link to comment Share on other sites More sharing options...
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