Hi all,
After my research, I couldn't find my particular issues or questions. I hate to bother people for answers because I prefer to study and figure it out myself but I'm such a novice when it come to newer solid state.
So I've been working on my amp for a while now. When I bought it I noticed a hum in the right channel. I replaced the four filter caps, eight feedback (I believe) caps and six electrolytics on the two driver boards. I left the mylars alone. I then left the amp on the bench for an hour( no input and 8 ohm 20 watt load) continuously bringing the bias back down to as close to 50 mv as possible. This seems way to long. I'm lost as to what would cause this. While playing music fairly loud, the heat sinks are hot and temping close to 120. Is this to hot?
As for the hum I have the DC offset at .7 and .9 so the issue is somewhere else. I did find from research that a possible cause could be a Zener diode or mosfet on the input stage. Looking at the schematic it looks like that would be Q1,Q2,Z1 if I'm correct. Any confirmation would be greatly appreciated. As much as I love my research, I just want to get back to listening to music!
Other than those issues, the amp sounds awesome.
Regards, doug
After my research, I couldn't find my particular issues or questions. I hate to bother people for answers because I prefer to study and figure it out myself but I'm such a novice when it come to newer solid state.
So I've been working on my amp for a while now. When I bought it I noticed a hum in the right channel. I replaced the four filter caps, eight feedback (I believe) caps and six electrolytics on the two driver boards. I left the mylars alone. I then left the amp on the bench for an hour( no input and 8 ohm 20 watt load) continuously bringing the bias back down to as close to 50 mv as possible. This seems way to long. I'm lost as to what would cause this. While playing music fairly loud, the heat sinks are hot and temping close to 120. Is this to hot?
As for the hum I have the DC offset at .7 and .9 so the issue is somewhere else. I did find from research that a possible cause could be a Zener diode or mosfet on the input stage. Looking at the schematic it looks like that would be Q1,Q2,Z1 if I'm correct. Any confirmation would be greatly appreciated. As much as I love my research, I just want to get back to listening to music!
Other than those issues, the amp sounds awesome.
Regards, doug
I’ve had other similar amps that would hum slightly with no input connected, yet we’re fine when playing.
Maybe this will help if you haven’t seen it already;
Adcom GFA-5500 - Manual - Stereo Power Amplifier - HiFi Engine
Maybe this will help if you haven’t seen it already;
Adcom GFA-5500 - Manual - Stereo Power Amplifier - HiFi Engine
Phase,
Yes I do have that downloaded. Kept adjusting bias back down to 50 for an hour which seems to long. DC offset is .7 and .9. The hum is through the right speaker. I will need to put it back in and compare to a test tone.
Mr. Snell,
If grounding is fine then may the right channel BR is bad.
Yes I do have that downloaded. Kept adjusting bias back down to 50 for an hour which seems to long. DC offset is .7 and .9. The hum is through the right speaker. I will need to put it back in and compare to a test tone.
Mr. Snell,
If grounding is fine then may the right channel BR is bad.
Have you installed an RCA grounding plug into the problem channel, does this change the level of the hum?
Power everything off and remove the RCA cables or shorting plugs and speaker cables. Measure the resistance between the speaker ground and chassis ground. It should be around 4 - 5ohms on each channel. They do not usually go bad but if it measures a lot lower for some reason then you may need to replace the CL40 thermistor in the power supply. If you had to replace it I would use a CL60 which would give you more like 10 ohms of isolation between chassis and circuit grounds.
Power everything off and remove the RCA cables or shorting plugs and speaker cables. Measure the resistance between the speaker ground and chassis ground. It should be around 4 - 5ohms on each channel. They do not usually go bad but if it measures a lot lower for some reason then you may need to replace the CL40 thermistor in the power supply. If you had to replace it I would use a CL60 which would give you more like 10 ohms of isolation between chassis and circuit grounds.
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