Hi, this is my first post but have been lurking since 2 months ago, when I bought a non-working Ampeg BA115. After reading through several posts about the amp, I manage to resurrect it and am now enjoying it. I'm not a tech and I don't really know anything about electronics or its theory. Every mention of a component or a type of circuitry in those threads, I have to do a search in google or youtube. I can solder, kind of...and know some components and how to use a multimeter.
I had fun fixing the BA115 that I bought another project: an Ampeg B5R. This is where I definitely bit off more than I can chew.
The amp has a short according to the light bulb limiter...But before I dig deep into the power amp section, the first thing I'm trying to tackle though is the overdrive channel that is always on. The LED indicator for the overdrive channel is also always on. The channel select button doesn't switch the channels. The combine button, on the other hand, turns on the clean channel.
To eliminate that it's a light indicator problem, I've tried connecting the preamp out to a mixer and I could hear that the output is overdriven. I've meter checked four JFETs while on the board and thought they were shorted. I'm now thinking that meter checking these while on the board probably doesn't work. I've replaced those four JFETs: Q6, Q7, Q10, Q11....but the overdrive is still on. Can someone explain how the channel select circuit works on this amp? I've stared at the diagram trying to grasp what is happening but as soon as I think I know how the circuit works, then something else doesn't make sense.
What do I need to check next?
Thanks!
I had fun fixing the BA115 that I bought another project: an Ampeg B5R. This is where I definitely bit off more than I can chew.
The amp has a short according to the light bulb limiter...But before I dig deep into the power amp section, the first thing I'm trying to tackle though is the overdrive channel that is always on. The LED indicator for the overdrive channel is also always on. The channel select button doesn't switch the channels. The combine button, on the other hand, turns on the clean channel.
To eliminate that it's a light indicator problem, I've tried connecting the preamp out to a mixer and I could hear that the output is overdriven. I've meter checked four JFETs while on the board and thought they were shorted. I'm now thinking that meter checking these while on the board probably doesn't work. I've replaced those four JFETs: Q6, Q7, Q10, Q11....but the overdrive is still on. Can someone explain how the channel select circuit works on this amp? I've stared at the diagram trying to grasp what is happening but as soon as I think I know how the circuit works, then something else doesn't make sense.
What do I need to check next?
Thanks!
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