I’m wondering about the common B+ node (at 285V) for V4a and V4b. This might not be a problem here, since there is a reverb spring between the two. Normally it would not be recommended because the signals on the plates of these two tubes are in phase. I wonder if it is possible that there is some positive feedback occurring via the reverb spring?
Might just be worth trying the option of supplying the V4a plate from the 300V node, to see if this has any effect.
Might just be worth trying the option of supplying the V4a plate from the 300V node, to see if this has any effect.
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Hi Malcolm,
When I get home in a couple hours I'll try supplying V4a from the 300V node. I think that the spring reverb tank prevents those signals from actually being in phase with each other, but I'm open to any idea. The recovered signal will have a sum of lightly damped and delayed signals with pretty much any phase possible, so there may be some positive feedback going on. However, the distortion problems exist even when there's no reverb.
When I get home in a couple hours I'll try supplying V4a from the 300V node. I think that the spring reverb tank prevents those signals from actually being in phase with each other, but I'm open to any idea. The recovered signal will have a sum of lightly damped and delayed signals with pretty much any phase possible, so there may be some positive feedback going on. However, the distortion problems exist even when there's no reverb.
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I took a better sound clip to demonstrate that "wandering fuzz" I'm talking about, although its pretty quiet because my roommates are sleeping.
https://soundcloud.com/steeledriver/amp-fizz
In the first bit, I have the pot between V1a and V1b turned up all the way and the rest of the amp turned down quiet enough to pass just that signal clean. You can hear the fizz on that distortion.
In the second bit, I turn that down so V1b isn't overdriven, and turn up the pot at the end of my tone stack to cause further stages in the amp to overdrive. You can hear the same fizz sound on that distortion too. The amp doesn't do that sound when it's clean.
Could that be grid conduction from too much gain/too little attenuation?
https://soundcloud.com/steeledriver/amp-fizz
In the first bit, I have the pot between V1a and V1b turned up all the way and the rest of the amp turned down quiet enough to pass just that signal clean. You can hear the fizz on that distortion.
In the second bit, I turn that down so V1b isn't overdriven, and turn up the pot at the end of my tone stack to cause further stages in the amp to overdrive. You can hear the same fizz sound on that distortion too. The amp doesn't do that sound when it's clean.
Could that be grid conduction from too much gain/too little attenuation?
Hi Guys
Ghost notes are not caused by under-filtering, rather by poor ground and power connection choices that cause intermodulation of the signal by hum and buzz (mains and rectifier noise, respectively). Galactic Grounding as shown in TUT3 cures all of this.
"Fizz" is often an IM issue as well, but the cure above gets rid of it. Fizz can also be caused by an improperly biased output stage. Since you mentioned high-gain, fizz can also be the onset of grid-rectification, fixed by attenuating the signal into the offensive grid. In many cases where an attenuator is already present, its potential to protect the grid is defeated by a cap across the series element, so the fix then becomes adding a true grid-stop. Every tube stage in a guitar should have a grid-stop.
Have fun
Ghost notes are not caused by under-filtering, rather by poor ground and power connection choices that cause intermodulation of the signal by hum and buzz (mains and rectifier noise, respectively). Galactic Grounding as shown in TUT3 cures all of this.
"Fizz" is often an IM issue as well, but the cure above gets rid of it. Fizz can also be caused by an improperly biased output stage. Since you mentioned high-gain, fizz can also be the onset of grid-rectification, fixed by attenuating the signal into the offensive grid. In many cases where an attenuator is already present, its potential to protect the grid is defeated by a cap across the series element, so the fix then becomes adding a true grid-stop. Every tube stage in a guitar should have a grid-stop.
Have fun
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