Got this sucker fixed. It was a bad gain/overdrive pot.
First I tried a 12AU7 tube. Colored the sound a little but no real overdrive sound. Next tried a 12AT7 tube. A bit more gain so some overdrive punch but still not enough. Finally plugged in a 12AX7 tube. Now were talking! But very noisy (hiss and hum). That won't fly for me and not sure a metal case and better wiring techniques can completely fix that. No joke, if I touch the foot switch with my finger I can hear a local AM radio station.
My plan is to stick with the 12AT7 tube and play around with different gain stage plate resistors and maybe even change the gain pot value.
Also seems like I'm getting unneeded gain from the output plate follower stage. I have the output stage volume pot at only 10%. Might try rewiring it so that it's a cathode follower topology (no gain). I seem to remember Marshall amp's gain stage drive into a cathode follower stage. Need to google some schematics to verify.
Good to hear you found the problem! Does this use a grid stopper on either of the stages? That and maybe a very small cap to ground might help keep FR junk from creeping in. You could also play around with the load resistor on the second stage. Not sure what that might do to the tone, but you could clip lead something in there just to try it.
Not sure on what value cap would work on that design. The phono stage I'm playing with doesn't have a cap on the input, but he did use 1K grid stoppers.
It's not clean. There I saved you the time of getting out the scope.
I have been using the Mean-Well DDR15 on many projects that require a clean dc voltage. these will give you 75mvpp ripple. My measurements say that they are much better than the spec sheet says. This will also open up some securities in that the power supply can now be a broad range of wall wort and the DDR15 will make sure that is it a consistent voltage. https://www.mouser.com/ProductDetail/MEAN-WELL/DDR-15G-12?qs=sGAEpiMZZMv0DJfhVcWlK0%2BNBIYn4O1XIOt%2Bj1Qupp447ikeOa2LzQ==
Just as a heads up for those unaware, there is a filter for smps at diyaudio called amyalice, and while its only rated at 3a and won't work for most amplifier projects, it's excellent for line level builds.
I added the grid stoppers. That fixed the issue with picking up RF but the overall noise is still there. It's got to be the smps. I have all the parts I need to build a linear power supply with good filtration and a TS2812 voltage regulator.
Comments
Look like CDE version of Sprague Orange Drop.
InDIYana Event Website
Two Orange Drops and one Nichicon polyester metal film.
Just plugged my Fender strat in. Obviously something wrong. Nothing but noise. Maybe a bad pot, tube, or solder joint. I'll get it sorted out.
My man on the orange drops
Grounding issues maybe?
Youll dial it in by tonight Im sure . Youll figure it out
Thinking my next build- for the 3rd order HP on the tweeter, I just have to use a stack of Orange Drops. I saw a good video on orientation:
Naw... watching the Steelers play the Ravens right now.
Got this sucker fixed. It was a bad gain/overdrive pot.
First I tried a 12AU7 tube. Colored the sound a little but no real overdrive sound. Next tried a 12AT7 tube. A bit more gain so some overdrive punch but still not enough. Finally plugged in a 12AX7 tube. Now were talking! But very noisy (hiss and hum). That won't fly for me and not sure a metal case and better wiring techniques can completely fix that. No joke, if I touch the foot switch with my finger I can hear a local AM radio station.
My plan is to stick with the 12AT7 tube and play around with different gain stage plate resistors and maybe even change the gain pot value.
Also seems like I'm getting unneeded gain from the output plate follower stage. I have the output stage volume pot at only 10%. Might try rewiring it so that it's a cathode follower topology (no gain). I seem to remember Marshall amp's gain stage drive into a cathode follower stage. Need to google some schematics to verify.
Good to hear you found the problem! Does this use a grid stopper on either of the stages? That and maybe a very small cap to ground might help keep FR junk from creeping in. You could also play around with the load resistor on the second stage. Not sure what that might do to the tone, but you could clip lead something in there just to try it.
Great suggestions Tom! No, no grid stoppers resistors on either stage. I didn't even think about that!
Maybe a 10 nF cap to ground on the first stage grid?
Not sure on what value cap would work on that design. The phono stage I'm playing with doesn't have a cap on the input, but he did use 1K grid stoppers.
Yeah for me usually 1k on preamp grids and 100-200 on power tubes. That'll be my first attempted fix. Thanks again for reminding me about that.
Also power supply filters. Your taking the signal from the plates.
True. Hard to say how clean that smps wall wart is without busting out my scope.
It's not clean. There I saved you the time of getting out the scope.
I have been using the Mean-Well DDR15 on many projects that require a clean dc voltage. these will give you 75mvpp ripple. My measurements say that they are much better than the spec sheet says. This will also open up some securities in that the power supply can now be a broad range of wall wort and the DDR15 will make sure that is it a consistent voltage.
https://www.mouser.com/ProductDetail/MEAN-WELL/DDR-15G-12?qs=sGAEpiMZZMv0DJfhVcWlK0%2BNBIYn4O1XIOt%2Bj1Qupp447ikeOa2LzQ==
https://www.meanwell.com/webapp/product/search.aspx?prod=DDR-15#1
Just as a heads up for those unaware, there is a filter for smps at diyaudio called amyalice, and while its only rated at 3a and won't work for most amplifier projects, it's excellent for line level builds.
I added the grid stoppers. That fixed the issue with picking up RF but the overall noise is still there. It's got to be the smps. I have all the parts I need to build a linear power supply with good filtration and a TS2812 voltage regulator.