Hello all.
I'm very much at the beginning of getting to grips with stuff and have something I've come across which I can't seem to find the answer for. I've got quite a few successful project builds under my belt, but I've recently decided to challenge myself a bit by building a simple tube reverb based on an old guitar magazine project - http://www.musikding.de/images/product_images/popup_images/2897_1.jpg that's less documented than most of the great projects you guys offer.
After very many beginner mistakes(but hey, I'm learning loads!) and lots and lots of reading, I've surprisingly got the thing working! Albeit not ideally...
The reverb sounds very dark, which is something I'd love to ask about and deal with later, but firstly, I've got a rather big problem with buzz coming though. I haven't got access to an oscilloscope so I'm trying to troubleshoot with a DMM and a dc blocking capacitor in series with a speaker as a "probe".
My power rails seem to be in good health. I've got the tube heaters being fed with AC. At the input of the first amplification stage I'm getting a 60mV or so DC reading. Should I read something into this?
Anyway, onto the buzz...
With an 8ohm speaker attached to the spring tank input cable, I'm able to hear what's going on, and the buzz is definitely present. Plugging a guitar lead into the input and monitoring the output, i did some very careful but uneducated poking around.
I found that when i place the tip of the input guitar lead touching the insulation of the black heater wire(from supply to tube), the noise drops substantially. When I touch the insulation of the red wire, it gets a bit worse!
Just to be clear, I'm not poking around and making any electrical contact anywhere in the circuit, I'm placing the tip of the guitar jack against the insulated cover of the heater wire. All heater wires are quite well twisted together, and even so, depending on whether the guitar jack is touching red or black , it makes a substantial difference.
Can anybody please explain/guess what's going on here, and how I might have screwed up? I guess I could cobble together a fix involving some enterprising wire wrapping, but that won't teach me anything about where I'm going wrong.
Unfortunately, I've built the project in a very silly case with the terminal strips at the bottom of the case and the tubes, transformers,choke, jacks and pots on top, so it's not something I can take a photo of easily. I've tried spreading and bunching the various wires(with a wooden spoon) but there is no change in the noise. The only thing that's made a difference has been the guitar lead tip to the insulation of the heater wire as described above.
Because of my immensely stupid case "design", my grounding scheme has also been a bit all over the place and I've been trying various variations of this. My guess is that I'm doing something very dumb here. I've since collected all my grounds and joined them together, along with the case and everything else. My power transformer centre taps go to the ground rail of my PSU terminal strip, which then joins up to star ground, along with all other grounding wires from audio ground, in & out jacks, case, pots etc
Photo attached to show my genius case setup taken from the back...
Any guidance would be massively appreciated.
Thanks, Rob
I'm very much at the beginning of getting to grips with stuff and have something I've come across which I can't seem to find the answer for. I've got quite a few successful project builds under my belt, but I've recently decided to challenge myself a bit by building a simple tube reverb based on an old guitar magazine project - http://www.musikding.de/images/product_images/popup_images/2897_1.jpg that's less documented than most of the great projects you guys offer.
After very many beginner mistakes(but hey, I'm learning loads!) and lots and lots of reading, I've surprisingly got the thing working! Albeit not ideally...
The reverb sounds very dark, which is something I'd love to ask about and deal with later, but firstly, I've got a rather big problem with buzz coming though. I haven't got access to an oscilloscope so I'm trying to troubleshoot with a DMM and a dc blocking capacitor in series with a speaker as a "probe".
My power rails seem to be in good health. I've got the tube heaters being fed with AC. At the input of the first amplification stage I'm getting a 60mV or so DC reading. Should I read something into this?
Anyway, onto the buzz...
With an 8ohm speaker attached to the spring tank input cable, I'm able to hear what's going on, and the buzz is definitely present. Plugging a guitar lead into the input and monitoring the output, i did some very careful but uneducated poking around.
I found that when i place the tip of the input guitar lead touching the insulation of the black heater wire(from supply to tube), the noise drops substantially. When I touch the insulation of the red wire, it gets a bit worse!
Just to be clear, I'm not poking around and making any electrical contact anywhere in the circuit, I'm placing the tip of the guitar jack against the insulated cover of the heater wire. All heater wires are quite well twisted together, and even so, depending on whether the guitar jack is touching red or black , it makes a substantial difference.
Can anybody please explain/guess what's going on here, and how I might have screwed up? I guess I could cobble together a fix involving some enterprising wire wrapping, but that won't teach me anything about where I'm going wrong.
Unfortunately, I've built the project in a very silly case with the terminal strips at the bottom of the case and the tubes, transformers,choke, jacks and pots on top, so it's not something I can take a photo of easily. I've tried spreading and bunching the various wires(with a wooden spoon) but there is no change in the noise. The only thing that's made a difference has been the guitar lead tip to the insulation of the heater wire as described above.
Because of my immensely stupid case "design", my grounding scheme has also been a bit all over the place and I've been trying various variations of this. My guess is that I'm doing something very dumb here. I've since collected all my grounds and joined them together, along with the case and everything else. My power transformer centre taps go to the ground rail of my PSU terminal strip, which then joins up to star ground, along with all other grounding wires from audio ground, in & out jacks, case, pots etc
Photo attached to show my genius case setup taken from the back...
Any guidance would be massively appreciated.
Thanks, Rob