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I've had some breakthrough success lately in finding and fixing some persistent noises in my amp that has been an issue since it's birth. I've also swapped out the OT back and forth between the Heyboer I had custom built and an edcore. I finally settled on the Heyboer for no good reason other than, they both sound fine and I don't want to replace the output transformer any more.
The amp is really getting close to being left alone so it can be played and judged a success or scrap.
With some of the more distracting issues which were previously causing the instability out of the way and solved, I was still getting some 60 cycle hum and a little buzz at idle. I've heard worse, in other high gain amps, certainly, but I wanted to see if I could knock it down.
It for sure was being generated in the first two tubes, because the balanced part of the amp is dead quiet with those pulled. I was pretty certain that it was heater noise coupling through, so I set up to run them on a DC circuit and see if there was any improvement. I disconnected the AC feed to V1 and V2, and connected them in parallel to a 6V Lantern battery, which was a total waste of time, considering that even though I bought it a day earlier, it was expired in january and totally trashed.
I needed to improvise, and began to rummage around our benches for a wallwart supply. Obviously, my chances of finding 12V DC were going to be much better than finding 6.3V DC , so I rewired the 12AX7s for 12V heater operation (which is easier anyway) and connected them to an adjustable voltage wallwart supply. I set it for 12V, checked the wiring and tested the voltage to make sure it was built correctly and working right.
I powered it back on, and waited for the amp to warm up. The noise I was hearing earlier was nearly all gone, and resulted in a pretty dramatic improvement.
The obvious solution was to run those tubes off a DC heater supply. Using 4 schottky diodes, I constructed a bridge rectifier with a 5600uF high quality cap, 1.5R dropper, and a final 10000uF filter which supplied the two tubes with 6.2V DC.... and it was a disaster. Probably noisier than the AC heater arrangement, and buzzier too.
I figure that the 12V DC heater was a better arrangement to start with, but fact that it was isolated from the existing AC heaters was also helpful.
Therefore, what suggestions do you have that would meet the criteria of clean, isolated 12V (12.6V) DC and is reasonably small enough to install as a retrofit. I do have some space on the top of the chassis for a separate filament transformer for a linear supply, but a switching supply will give me the benefit of more options. so I'm open to both
The amp is really getting close to being left alone so it can be played and judged a success or scrap.
With some of the more distracting issues which were previously causing the instability out of the way and solved, I was still getting some 60 cycle hum and a little buzz at idle. I've heard worse, in other high gain amps, certainly, but I wanted to see if I could knock it down.
It for sure was being generated in the first two tubes, because the balanced part of the amp is dead quiet with those pulled. I was pretty certain that it was heater noise coupling through, so I set up to run them on a DC circuit and see if there was any improvement. I disconnected the AC feed to V1 and V2, and connected them in parallel to a 6V Lantern battery, which was a total waste of time, considering that even though I bought it a day earlier, it was expired in january and totally trashed.
I needed to improvise, and began to rummage around our benches for a wallwart supply. Obviously, my chances of finding 12V DC were going to be much better than finding 6.3V DC , so I rewired the 12AX7s for 12V heater operation (which is easier anyway) and connected them to an adjustable voltage wallwart supply. I set it for 12V, checked the wiring and tested the voltage to make sure it was built correctly and working right.
I powered it back on, and waited for the amp to warm up. The noise I was hearing earlier was nearly all gone, and resulted in a pretty dramatic improvement.
The obvious solution was to run those tubes off a DC heater supply. Using 4 schottky diodes, I constructed a bridge rectifier with a 5600uF high quality cap, 1.5R dropper, and a final 10000uF filter which supplied the two tubes with 6.2V DC.... and it was a disaster. Probably noisier than the AC heater arrangement, and buzzier too.
I figure that the 12V DC heater was a better arrangement to start with, but fact that it was isolated from the existing AC heaters was also helpful.
Therefore, what suggestions do you have that would meet the criteria of clean, isolated 12V (12.6V) DC and is reasonably small enough to install as a retrofit. I do have some space on the top of the chassis for a separate filament transformer for a linear supply, but a switching supply will give me the benefit of more options. so I'm open to both
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