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loss of bass volume in 300 pa amp [message #5426] Sat, 05 February 2005 22:36   kustomrockerbob Messages: 2 Registered: September 2004 Junior Member When I am playing (I use this for my guitar), sometimes my bass volume decreses. It doesn't do it all the time, and only lasts for a second or two. Am I losing a transitor or a cap, and is it in the preamp or output stage? If it is a transistor should I replace all of them while I have it apart? Any info would be helpfull!! Thanks Bob Report message to a moderator

Re: loss of bass volume in 300 pa amp [message #5427 is a reply to message #5426] Sun, 06 February 2005 10:12   chacuff Messages: 11 Registered: January 2005 Location: Gulf Coast Junior Member Bob, There is not enought info to make the determination you are asking for. I certainly would not recommend a shotgun approach to attempting a repair by replacing all transistors or other components. My best guess with what info was given is that you have an intermittent speaker problem. It sounds like they (didn't mention what type) are being driven to excursion and maybe the flexible wire that connects the voice coil to the terminal strip is fatigued and opening the electrical connection causing the speaker to stop making sound until the cone comes back to a position where the electrical connection is restored. This would make sense also if it is a dual speaker cabinet where the two are in parellel with each other and maybe one is in trouble. Hope that helps...Cecil Report message to a moderator

Re: loss of bass volume in 300 pa amp [message #5432 is a reply to message #5426] Sun, 06 February 2005 17:26   kustomrockerbob Messages: 2 Registered: September 2004 Junior Member Cecil, sorry that doesn't help me at all. I am running 2 columns (2 15" KEI and 1 Horn) each. I ran both of them, singularly and both together through my 400 and they were crystal clear, so the speakers are not the problem. Thanks Bob Report message to a moderator

Re: loss of bass volume in 300 pa amp [message #5433 is a reply to message #5426] Mon, 07 February 2005 07:44   stevem Messages: 4733 Registered: June 2004 Location: NY Senior Member If it is just a loss of lows and not a drop in over all volume, and is not produced along with a popping or crackling sound like that of a bad guitar cord, then my guess would be something in the tone circuit. And yes maybe a transistor.Take the amp out of the case try and get it to act up by tapping around with the plastic end of a screwdriver, if not then add a little heat with a hair dryer( not too much) and tap around more, you may be able to locate it down to given area . Report message to a moderator

Re: loss of bass volume in 300 pa amp [message #5435 is a reply to message #5432] Mon, 07 February 2005 09:18   chacuff Messages: 11 Registered: January 2005 Location: Gulf Coast Junior Member Sorry about that....That's the best could do with what I had to work with...I've been a tech for 30+ years so it was not an Newbie answer. Beyond that have you checked your tone controls. If the Bass pot is intermittent it could cause what you are describing. Strike a bass note and rotate the bass pot and see if the change in tone is smooth. A dirty volume pot will cause a scratchy noisey response from the speakers but a tone pot won't always cause that noise just intermittent tone control. I would recommend spraying them with a cleaner designed for that purpose like Deoxit D5 or Radio Shack should have a suitable cleaner. Make sure the label states for cleaning of electronic switches and controls...some cleaners can damage some pots. Hope between that and what Steve has offered helps... Cecil.. Report message to a moderator

Re: loss of bass volume in 300 pa amp [message #5437 is a reply to message #5426] Tue, 08 February 2005 13:02   stevem Messages: 4733 Registered: June 2004 Location: NY Senior Member If you think it may be a trasistor,some of them may be located to close to each other to be narrowed down by the hair dryer tip.In that case use a soldering iron tip on one lead of the suspect transistor for 2 or 3 seconds, but not long enough to desolder it, this can help trace down ones that are going south. Report message to a moderator

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