divie23
Head-Fier
- Joined
- Aug 25, 2001
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Hey Guys,
I've been trying to figure this problem out for several days now but seem no closer to solving it. However, I have carefully observed its effects. Some of the following may sound incredibly tedious so I hope I explain it all nice and simple!
Firstly I'll explain the amp I've built. It's basically a buffered CMoy using OPA637s and a single BUF634 per channel.
In essence the amp when initially switched on produces a buzzing kind of a sound in both channels. However, after about 2 minutes it gradually fades to silence and the amp functions perfectly. Also, the buzz only seems to occur when the Pot is set to a minimum (maximum resistance) and decreases in volume as the Pot is increased, and finally ceases when the resistance of the Pot is zero. My timing of the buzz is when the Pot is left at full resistance.
Removing the buffers from the amp and making it a voltage gain amp only removes this buzzing completely. And likewise removing the gain stage and leaving simply the buffers in also removes the turn-on buzzing completely as does removing either a single Op Amp OR a single buffer while leaving the others intact. Make sense?? I hope so! The same is true when I remove an Op Amp and a buffer from a single channel and feed the signal raw through it but amplified through the other channel.
I suspect it's a power supply issue but I can't see how it can be. I mean I'm using a virtual ground driver with 2 BUF634s, about 400/500 microfarads per rail in capacitance (aluminium electrolytics), a 24V regulated mains supply which is rated at 300mA. The current draw which I measured sometime ago was approx. 60mA.
Can anyone offer me some suggestions as to how to tackle this please?! I mean I've spent close to £150 on this amp and this is really testing my patience to the point where I feel like smashing the thing!
Divie
I've been trying to figure this problem out for several days now but seem no closer to solving it. However, I have carefully observed its effects. Some of the following may sound incredibly tedious so I hope I explain it all nice and simple!
Firstly I'll explain the amp I've built. It's basically a buffered CMoy using OPA637s and a single BUF634 per channel.
In essence the amp when initially switched on produces a buzzing kind of a sound in both channels. However, after about 2 minutes it gradually fades to silence and the amp functions perfectly. Also, the buzz only seems to occur when the Pot is set to a minimum (maximum resistance) and decreases in volume as the Pot is increased, and finally ceases when the resistance of the Pot is zero. My timing of the buzz is when the Pot is left at full resistance.
Removing the buffers from the amp and making it a voltage gain amp only removes this buzzing completely. And likewise removing the gain stage and leaving simply the buffers in also removes the turn-on buzzing completely as does removing either a single Op Amp OR a single buffer while leaving the others intact. Make sense?? I hope so! The same is true when I remove an Op Amp and a buffer from a single channel and feed the signal raw through it but amplified through the other channel.
I suspect it's a power supply issue but I can't see how it can be. I mean I'm using a virtual ground driver with 2 BUF634s, about 400/500 microfarads per rail in capacitance (aluminium electrolytics), a 24V regulated mains supply which is rated at 300mA. The current draw which I measured sometime ago was approx. 60mA.
Can anyone offer me some suggestions as to how to tackle this please?! I mean I've spent close to £150 on this amp and this is really testing my patience to the point where I feel like smashing the thing!
Divie