OHM KB140 amp problem
- Thread starter burglar
- Start date
Help Support GroupDIY Audio Forum:
When you say the "power cuts out", do you mean that sound ceases to come out of the speaker or that the AC power shuts off, power light goes out, etc.?
It is just the sound that stops. The power light stays on. Sorry, when I posted I thought it was a power issue but it isn't.
The amp has four channels, this problem occurs on all four channels.
The fault does respond dynamically to the input level. With a bass guitar or keyboard, If the playing is very soft it will remain on, if the playing is medium velocity it will cutt out about 2 seconds after playing starts. If playing is hard and the amp cuts out instantly on the transient.
Altering the input level on the amp channels does not change the fault, nor does altering the output. Schematic of amp attached.
The amp has four channels, this problem occurs on all four channels.
The fault does respond dynamically to the input level. With a bass guitar or keyboard, If the playing is very soft it will remain on, if the playing is medium velocity it will cutt out about 2 seconds after playing starts. If playing is hard and the amp cuts out instantly on the transient.
Altering the input level on the amp channels does not change the fault, nor does altering the output. Schematic of amp attached.
Well, it seems clear that the "Overload input mute" circuit is being activated. The question is, is there a fault in the mute circuit or a fault in the output stage which then activates the mute circuit. Check the mute circuit components, as well as D1, R1, and R24 to start with.
s2udio
Well-known member
Check for DC at the power stage output, as this looks like a dc detector circuit, possibly a depleted output transistor or driver.
Also check all the resistor values and diodes around the output stage
Also check all the resistor values and diodes around the output stage
