Honey Dripper noise

[RobA]

The 10V side has the two 5.1V Zeners and R42 working as a voltage regulator with R42 limiting the current. So, that could be why it's clean. Three of the IC's tie their power rails at that point (18V side of R42), so the noise could be coming in from anyone of those too.

I think using your bench supply is a really good idea. It could help to confirm or eliminate the LT1054 as the source of the noise.

There is one thing I don't like about the power supply section of the circuit and that's the 9.1V Zener. If your input power is above 9.1V, that Zener can draw a ton of current because there's no current limiting resistor in front of it. It seems that it's there as a protection for something, but everything should be able to take a higher voltage than that. It would make more sense to me for that Zener to be set at a level that is just above what would be expected from a battery/power supply and below the level of half the voltage that the CA3080 can take. So, somewhere around 10V. I don't know if it is really the source of your noise on the power rails, but if it's drawing a ton of current, it might be. You could probe for audio there and see if it's got noise.

Edited: If I've missed something and the level really does need to be held below 9.1V and it does look like the Zener is causing noise, then you could put a current limiting resistor in front of it and that might help. I have a link somewhere that shows how to compute the needed resistor value.

[durian]

I'm think I'm onto something. I just realized none of the op amps have decoupling caps. There are the really large 10uF and 100uF tank caps, but there aren't any small caps at the power pins of the ICs to handle the short, transient loads. I added some 0.1uF caps to the power pins of the op amps and it definitely helped. There's still some noise left, though. I haven't added any to the CA3080's so that's next. I might also add a 1uF cap on the 18V for medium transients.

[RobA]

Yeah, that's a good idea. It does really help to stop noise getting into the audio path. I don't know why, but it's something you don't really see on guitar effects. It's done everywhere on DIY Hi Fi audio. The headphone amp people always do it.

[durian]

Yeah, I'm a digital guy. You wouldn't guess from all my questions, but I do hardware and software for embedded systems. You put 0.1uF caps on every IC. You don't really think about it. You push them off the the side of the schematic so they don't clutter things up, but they're there.

I've still got some noise, but I think I'm headed in the right direction.

[RobA]

Very interesting. I'm from the software world and now learning the embedded side of things -- so many things to learn.

[durian]

I think I've got the noise about as low as I can get it. It's still higher than I'd like, but better than before.

This link, http://brettcave.net/howto/circuits/PowerSupply_DualRail-LT1054-Boosted.pdf, shows an example using the LT1054 as a dual rail, regulated doubler. Most of it isn't needed for this application, but I think Rpf would help reduce noise. We can't really add it to this board without changing the layout, though. The 18V current doesn't really flow out of C19 in this layout. Topologically it is equivalent, but there's not really a path from D13 to C19 and then to the rest of the board. D13 goes to the 18V rail and C19 also sits on the rail, but a bit distant. There's no way easy way to squeeze a small resistor between D13 and C19+. R42 does help clean up the 10V and 5V rails.

So, for other people who've found this thread and are experiencing noise like I was, add 0.1uF (100nF) caps between the power and ground on each of the ICs (except IC6 - the LT1054). Use small ceramic caps and have them straddle the ICs. Solder the cap leads directly to the IC pins. If you take a little care, you'll still be able to remove the ICs from the sockets with the caps attached to the IC.

I also swapped C19 and C20 again. It makes more sense to me to have the larger cap closer to the LT1054. I also added 0.1uF caps across C19, C20 and C17. I put those on the bottom of the board, soldered directly to the larger caps' terminals. Again, use small ceramics that can lie flat against the PCB. I'm not sure these changes added anything, though.

[Matt]

Just did the 100n caps on the ICs as you recommended and it did help with the noise.  Thanks for posting this!

[pedalhealer]

Hi!

I ended my Honey Dripper build, and I have similar problem. If I play the guitar, I hear beside the good guitar tone a "laser-gun" noise. When I pick the strings, start a high frequency noise and then the pitch of frequency is start falling. I'm in trouble....
(sorry for my poor english)