Celsius Preamp - White Noise?

[coltonius]

Aloha. I just finished the Celsius Preamp last night, and it's a lot of fun with plenty of gain (volume) on tap! Preamps aren't typically my thing, but I've heard plenty of great feedback on the PastFX and Triungulo versions and decided to take a whack at it.

The problem is, there's a ton off white noise that persists in just about every situation:

- onboard Gain knob in any position (worse at higher settings)​

- no guitar plugged in​

- guitar plugged in, guitar Volume all the way down​

- toggle up or down (with or without transistor inline)​

- with or without buffer in front (for the purposes of this test I used both a JFET buffer and the buffered bypass in a Centaur clone)​

- swapped IC​

As you can see below it's a pretty straightforward build. The astute among you may notice a few values that seem off, but I've cleverly split some values I didn't have with a parallel resistor under the board (eg., two 3k in parallel to create a 1.5k).

So the big questions are:
Is this normal behavior for the build? I understand there's a metric ton of volume and gain available.
Is there any way it can be mitigated?

Thanks in advance for the help, guys.

 

[carlinb17]

I would take a look at your joints… the foot switch appears to have some very long legs that can be shortened(lugs 8 and 9 almost appear to be touching.) I would definitely reflow everything and see how it sounds from there.

 

[coltonius]

I would take a look at your joints… the foot switch appears to have some very long legs that can be shortened(lugs 8 and 9 almost appear to be touching.) I would definitely reflow everything and see how it sounds from there.

They are touching, that's how I wired it- so there's less that can fail (mechanically) when the pedal is bypassed.

I've never seen a few extra mm in wire length cause a problem like this (across hundreds of builds), but I did ask for help so I'll give it a shot.

 

[giovanni]

Those two pins don’t need to be touching but I don’t think that’s causing any problem.

 

[fig]

Did you try another charge pump? Maybe an SCPA instead?

 

[carlinb17]

I’m confused, so you

View attachment 29709
Those two pins don’t need to be touching but I don’t think that’s causing any problem.

I think he said he did that intentionally but it will cause problems like you said

 

[giovanni]

I’m confused, so you

I think he said he did that intentionally but it will cause problems like you said

In bypass, those two pins are connected, so no problem. When the pedal is on, the output gets connected to the bottom pin which is floating so it shouldn’t be a problem.

 

[carlinb17]

Your right it would be floating when open, I guess I just don’t like the idea of adding an extra wire connection just one more thing…

 

[coltonius]

View attachment 29709
Those two pins don’t need to be touching but I don’t think that’s causing any problem.

They don’t need to, but they are.. on purpose. That’s the output wire mechanically connected to pin 3, the same as pins 1 and 6 are connected to ground the input.

It’s wired that way as an “extra” failsafe to prevent the footswitch from causing noise or protection against failure because there’s only one pole breaking the connection during switching (pins 2 and 3). It would be the same as me wiring the output from 8 directly to 3..

Please don’t mistake my low post count for a lack of experience.

 

[coltonius]

Did you try another charge pump? Maybe an SCPA instead?

It's an SCPA alright. The “CPA” part is continued on the second line of text.

 

[coltonius]

To help us get past the footswitch fixation, here's a slightly different wiring method used by Skreddy which illustrates the single break between Input and Output via a jumper between 4 and 9 in this case. Hopefully we can return to the issue at hand, not what seems to be an "odd" choice in wiring compared to what others do.

 

[carlinb17]

They don’t need to, but they are.. on purpose. That’s the output wire mechanically connected to pin 3, the same as pins 1 and 6 are connected to ground the input.

It’s wired that way as an “extra” failsafe to prevent the footswitch from causing noise or protection against failure because there’s only one pole breaking the connection during switching (pins 2 and 3). It would be the same as me wiring the output from 8 directly to 3..

Does nobody else see the value in doing this? Please don’t mistake my low post count for a lack of experience.

I don’t assume due to any amount or lack of a post count what someone’s experience is. While I have seen footswitches wired in the diagram below yours was a modification of that and you were having issues with your circuit so that’s why i brought it up. Best of luck

 

[coltonius]

I don’t assume due to any amount or lack of a post count what someone’s experience is. While I have seen footswitches wired in the diagram below yours was a modification of that and you were having issues with your circuit so that’s why i brought it up. Best of luck

Thanks. I do have a few things to try based on the suggestions you and others have made.

Swapping the charge pump IC for the same (TC1044SCPA) and for a TC7660 yielded no change. I’m going to reflow solder joints and shorten the leads from board > footswitch this afternoon in hopes that either or both help.

This may be one of those things where it’s a feature of the preamp though, as it’s so freakin loud!

 

[Bricksnbeatles]

I was planning on building my Celsius last week, but I don’t have the right pot value on hand, so it’s on hold. Once I have mine together I’ll report back on if I have a noise issue too

 

[coltonius]

Reporting back:

I re-flowed solder joints, changed the Gain pot from A50k to A100k, and shortened the leads between the board and footswitch.. No dice.

I did find this veroboard project with comments that seem to corroborate what I'm hearing with the elevated noise floor. Perhaps I will revisit this later and add Master Volume, diode clipping, and a switchable input buffer (as PastFX and Triungulo have done), but until then I'll be waiting on pins and needles for @Bricksnbeatles 's build report!

 

[Wizardofwoz66]

Reporting back:

I re-flowed solder joints, changed the Gain pot from A50k to A100k, and shortened the leads between the board and footswitch.. No dice.

I did find this veroboard project with comments that seem to corroborate what I'm hearing with the elevated noise floor. Perhaps I will revisit this later and add Master Volume, diode clipping, and a switchable input buffer (as PastFX and Triungulo have done), but until then I'll be waiting on pins and needles for @Bricksnbeatles 's build report!

Did either of you end up figuring this out? I built mine, the noise floor is kind of high in the low gain mode, but almost unusable in the high gain mode. There's an extremely loud persistent whine in the high gain mode (almost as loud as the signal level itself when playing), curious if anyone has thoughts on this.

 

[carlinb17]

Did either of you end up figuring this out? I built mine, the noise floor is kind of high in the low gain mode, but almost unusable in the high gain mode. There's an extremely loud persistent whine in the high gain mode (almost as loud as the signal level itself when playing), curious if anyone has thoughts on this.

Can you start a new thread including pictures, how it’s powered, and where it is in your signal chain?

 

[Wizardofwoz66]

Can you start a new thread including pictures, how it’s powered, and where it is in your signal chain?

I can, but I think it's a bit unnecessary lol. It's on an isolated 9V one spot wall wart with nothing else in the signal chain, so I don't think either of those should be the issue. I've built enough pedals and this is simple enough that I don't think it's a build issue, was mostly just curious if either of you had figured the issue out.

 

[MichaelW]

This pedal is inherently noisy. Initially, I was able to live with it but then I notice I put it on my shelf ad haven't used it since.

I didn't bother trying to figure out why it was noisy. Not sure if @coltonius got any further with his. Shame because it's a great sounding boost.

 

[coltonius]

This pedal is inherently noisy. Initially, I was able to live with it but then I notice I put it on my shelf ad haven't used it since.

I didn't bother trying to figure out why it was noisy. Not sure if @coltonius got any further with his. Shame because it's a great sounding boost.

@Wizardofwoz66

That was my conclusion as well. Mine is currently in pieces since I disassembled it with the intention of adding some useful mods:

• Master Volume
• Clipping Diodes
• pre-boost buffer (I’m using a K-style)

Since the current knob effectively sets the Gain, I’m hoping a MV will help tame the circuit a bit. I haven’t been in a huge hurry since it’s such a quirky circuit. Perhaps I’ll wrap it up this week, though, just to get it out of the projects pile!