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K100-2 Hiss [message #27969] Mon, 25 January 2021 15:45 Go to next message
hgibson is currently offline  hgibson
Messages: 3
Registered: July 2016
Junior Member
I know, I know, one more post about Hiss. I have an all original blue sparkle ser # 21338 with original cable, foot switch and manual with vinyl near mint except one very small, you guessed it, cig burn on top. I replaced power cord to 3 prong, kept the original for some fool who might want to put it back. All other components are the original. So I want to know what is acceptable hiss. I have heard that these amps had some hiss when new? I am looking for a baseline decibel reading for hiss that most would assume to be acceptable. Example, place iphone with decibel app mid speaker height, 2 feet in front, volume knob 1/2 way up with bass, treble centered and reverb off. Seems like this would be good information to use to determine where your amp is in terms of acceptable hiss. If you should not have any then I guess this is a mute (ho hiss) point. Looking forward to thoughts. Hugh Gibson, Vermont.

Hugh Gibson
Re: K100-2 Hiss [message #27972 is a reply to message #27969] Tue, 26 January 2021 05:57 Go to previous messageGo to next message
stevem is currently offline  stevem
Messages: 4357
Registered: June 2004
Location: NY
Senior Member
Due to widely veering efficiencys of different speakers , and how old the speakers Magnet may be , a test done like that would not be valid, not to mention that control pots have a 10 to 15% resistance tolerance to them!.

I will try and come up with a better way for you to test out results and get back to you.

Do you have a digital voltmeter?

[Updated on: Tue, 26 January 2021 05:58]

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Re: K100-2 Hiss [message #27973 is a reply to message #27972] Tue, 26 January 2021 09:51 Go to previous messageGo to next message
hgibson is currently offline  hgibson
Messages: 3
Registered: July 2016
Junior Member
Good Morning, Thank you for your response. First I want to know if I should have any hiss at all, if not then I need to troubleshoot. If hiss at some level was inherent in the Kustoms when built, well I dont need to do a thing. That is what I was trying to establish. For starter reference, Speakers are original Kustom G12a. I have noticeable hiss at 1/2 volume, increasing with volume and increases significantly when increasing reverb. When both are turned all the way up, hiss abundant and I pick up a local radio station. Unfortunately the music from the station is better than what i am playing. Razz You have a valid point on too many variables using decibel level as I described to troubleshoot. I was using that method to establish if hiss level needed attention at all. In any case my answer to your question is yes, I have digital mutimeter, 2 year degree in Electrical Engineering, but most of that was lecture , book learning, it would have helped to actually troubleshoot something in lab. I can read a diagram, crank calculus, solder like a pro but lost in signal tracing. Hands on failure of higher Ed. I do like a logical approach to troubleshooting and not solution by replacement. Since Hiss is so prevalent in Kustoms it begs for someone to lay out a step by step procedure for troubleshooting. Thank you for your time. Hugh, Vermont

Hugh Gibson
Re: K100-2 Hiss [message #27974 is a reply to message #27969] Wed, 27 January 2021 14:07 Go to previous messageGo to next message
stevem is currently offline  stevem
Messages: 4357
Registered: June 2004
Location: NY
Senior Member
While I am working on your testing procedure of the hiss issue I can tell you the old factory mod /!fix for getting rid of radio station pick up.
The fix is to add a .005 cap followed by a 47k resistor to ground off of the hot of both input jacks.
Re: K100-2 Hiss [message #27975 is a reply to message #27974] Wed, 27 January 2021 15:01 Go to previous message
hgibson is currently offline  hgibson
Messages: 3
Registered: July 2016
Junior Member
Thanks for the radio station squelch tip. Cool

Hugh Gibson
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