figuringstuffout
Well-known member
- Joined
- Dec 10, 2011
- Messages
- 45
So I'm again screwing around with tube compression and have run into an issue that requires someone way more intelligent and experienced than my novice self.
A while back I was dealing with a crosstalk issue that was sorted out with a better grounding scheme, but this time I am having a distortion issue than is driving me nuts.
See attached schematic.
NOTES
1. The gain makeup stage sounds great
2. The compression sounds awesome
3. Yes I am using a 12ax7 for the LED driving...why? Cause I have zero knowledge about transistors or opamps.
4. The grounding is following a star scheme
5. The 680pf is there because if it isn't more distortion bleeds through to the signal
6. The 68k resistor to ground is as small as it is otherwise the distortion making its way to the signal is really loud
7. B+ rail includes a choke, 100uf caps, resistors, and three separate B+ taps....one for each gain stage in the schematic
QUESTIONS
1. Looking at the schematic, what are the obvious flaws that I should know if I knew what I was doing?
2. The 12ax7 is distorting often, even with no gain reduction happening, and I can't figure out how it is seeping into signal coming out of the compressor. If I drastically lower the gain of the 12ax7 then the distortion seeping through goes away, but then there isn't enough voltage to drive the LED, rendering this unit useless as a compressor.
3. Is there a way I can maybe up the voltage gain on the LED circuit in such a way that it doesn't distort the signal? If I can get enough voltage going to that LED without distortion then my issue will go away. I can only get enough voltage to the LED currently when the 12ax7 is pushed to distortion.
Thanks for the help!
A while back I was dealing with a crosstalk issue that was sorted out with a better grounding scheme, but this time I am having a distortion issue than is driving me nuts.
See attached schematic.
NOTES
1. The gain makeup stage sounds great
2. The compression sounds awesome
3. Yes I am using a 12ax7 for the LED driving...why? Cause I have zero knowledge about transistors or opamps.
4. The grounding is following a star scheme
5. The 680pf is there because if it isn't more distortion bleeds through to the signal
6. The 68k resistor to ground is as small as it is otherwise the distortion making its way to the signal is really loud
7. B+ rail includes a choke, 100uf caps, resistors, and three separate B+ taps....one for each gain stage in the schematic
QUESTIONS
1. Looking at the schematic, what are the obvious flaws that I should know if I knew what I was doing?
2. The 12ax7 is distorting often, even with no gain reduction happening, and I can't figure out how it is seeping into signal coming out of the compressor. If I drastically lower the gain of the 12ax7 then the distortion seeping through goes away, but then there isn't enough voltage to drive the LED, rendering this unit useless as a compressor.
3. Is there a way I can maybe up the voltage gain on the LED circuit in such a way that it doesn't distort the signal? If I can get enough voltage going to that LED without distortion then my issue will go away. I can only get enough voltage to the LED currently when the 12ax7 is pushed to distortion.
Thanks for the help!