I'm hoping to get a little help diagnosing an issue I'm having with a Sunn beta lead amp. So when hooked up to many different drivers and many different guitars the output is just pure distortion, not like distortion pedal like just broken amp distortion. I have read that this amp has this type of issue due to bad output transistors. I measured them all with my Atlas DCA-55 and they all measured good but I noticed that half of them have been replaced in the past.
Here are some pics
The ones covered with the "92" in permanent marker read 223065/7752, 223056/7752. If the two sets are supposed to be mirrored the it looks like they could be wrong, but I done know. I can't get too much info off of the schematic, I'm having trouble reading it and figuring what transistors are supposed to be there. I saw a pic online and all three on the right bank were identical in that one and in mine they are not.
Here is the schematic http://bmamps.com/Schematics/Sunn/Sunn_Beta_Partial_sm.pdf
Any help would be greatly appreciated! If I should take this to the solid state forum let me know.
Thank you,
Dan
Here are some pics
The ones covered with the "92" in permanent marker read 223065/7752, 223056/7752. If the two sets are supposed to be mirrored the it looks like they could be wrong, but I done know. I can't get too much info off of the schematic, I'm having trouble reading it and figuring what transistors are supposed to be there. I saw a pic online and all three on the right bank were identical in that one and in mine they are not.
Here is the schematic http://bmamps.com/Schematics/Sunn/Sunn_Beta_Partial_sm.pdf
Any help would be greatly appreciated! If I should take this to the solid state forum let me know.
Thank you,
Dan
So I the pic that I found online all three on the right bank were SJ954 NPN and on mine only two are the SJ954 NPN and one is the ECG130 PNP. Could that cause my issue?
Dan
Dan
This is an instrument amp, the discussion belongs here.
You are looking too hard for something esoteric.
ECG130 is NPN, not PNP. Unless someone threw in totally wrong parts and the thing never worked after, I have to think the amp probably was working as you see it for some time before something in it failed. Those are probably all similar NPN power transistors.
Run a sine wave through the amp and scope the output. Both with load and then without load. What does the distortion look like? Is it also distorted when unloaded? If loading causes the symptom, that points to a different cause than if it is always distorted.
Describe the distortion, is it clipped symmetrically? Or is half the waveform missing?
Scope what is coming out of the preamp, could be the preamp is distorting, and the power amp is just amplifying what is sent to it. Are the op amps getting clean +15 and -15?
The power amp, are there unusual DC offsets anywhere?
You are looking too hard for something esoteric.
ECG130 is NPN, not PNP. Unless someone threw in totally wrong parts and the thing never worked after, I have to think the amp probably was working as you see it for some time before something in it failed. Those are probably all similar NPN power transistors.
Run a sine wave through the amp and scope the output. Both with load and then without load. What does the distortion look like? Is it also distorted when unloaded? If loading causes the symptom, that points to a different cause than if it is always distorted.
Describe the distortion, is it clipped symmetrically? Or is half the waveform missing?
Scope what is coming out of the preamp, could be the preamp is distorting, and the power amp is just amplifying what is sent to it. Are the op amps getting clean +15 and -15?
The power amp, are there unusual DC offsets anywhere?
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