Noise problem with Rubidium Reverb/DBA Reverberation Machine

[cnspedalbuilder]

Hello, I built the Rubidium Reverb 2.0 from an OSH Park PCB. It's based on the Death by Audio Reverberation Machine. Info on the PCB and schematic here: http://felix.kalium.org/upload/share/builddocs/RubidiumReverb_Builddoc.pdf

I have it boxed with a delay circuit that works fine. The reverb works, but I'm having some trouble with noise. The noise is like a "sshh.." sound, which is different from sounds that I've heard when I've had a grounding issue. It's more like white noise. I don't think it's an offboard wiring issue, as noise disappears when blend is set to 0, but gradually increases as you introduce wet, so it seems to be in the reverb signal path. As an aside, the gain is super high, so once the volume and drive are above the zero point, the pedal cranks up the signal. I originally had the mods for the "more dirt" setting on page 1 but then reverted back to the stock values.  I don't remember if the noise became worse after I reverted it back, because it sat on my desk for a couple of months.

I guess the only other remarkable thing is that I have a few tantalum caps where they suggest electrolytic (C2, C6, C14).

I can post pics of the PCB once I figure out how to get them up, but in the meantime, are there known issues. Thanks in advance!

[PRR]

> As an aside, the gain is super high

Indeed. Over-the-top high, for a reverb. Reverb tanks (modules) always hiss. This module has a relatively high output (unlike a tank). I do not understand why it has a gain of 8 (to 100!!) after the module.

The mixer looks wrong also. Doesn't Blend at zero short-out the dry path? Are you maybe over-cranking the dry path trying to overcome this possible design oversight?

Maybe I am looking at it wrong. See if someone who knows this build has further thoughts.

[BetterOffShred]

My reverberation machine is loud AF.  I've toyed with messing with R6 and R10 (from the glass hero trace) to see if it becomes a little more manageable.  I have never played an original unit but I know guys who have and said it's the same on the real thing. 

[cnspedalbuilder]

@PRR

Indeed. Over-the-top high, for a reverb. Reverb tanks (modules) always hiss. This module has a relatively high output (unlike a tank). I do not understand why it has a gain of 8 (to 100!!) after the module.
The mixer looks wrong also. Doesn't Blend at zero short-out the dry path? Are you maybe over-cranking the dry path trying to overcome this possible design oversight?

I think the blend works, because at low settings I get a lot of what sounds like dry signal, and in fact I don't hear allthat much reverb until about 50%. But even before that point, as I turn towards the wet side, so does the "shushing".

[cnspedalbuilder]

My reverberation machine is loud AF.  I've toyed with messing with R6 and R10 (from the glass hero trace) to see if it becomes a little more manageable.  I have never played an original unit but I know guys who have and said it's the same on the real thing.

Do you get the "shusshing" sound too? Would this go away if cut the gain somehow?

[BetterOffShred]

I have no shushing sound.  The mix is not subtle at I usually run it at like 10 o'clock at most.  The volume and gain usually below 9 o'clock.   The bright mode has strange artifacts.

This design is kind of nuts like most of their other stuff and it kind of does what it does, but the volume inconsistencies are really what make it annoying to me.

[aishabag23]

FWIW, I built three different versions of the Rubidium Reverb, all three are noisy... Too noisy to use, for me at least. I also built the OP-Electronics Spring Reverb kit, which is really similar. Same deal, just too un-stable to use. I finally built the home etched version of the Surfy Bear FET Reverb. It uses a regular-sized tank. It sounds really great, but craps out from the over-heating issue many builders have reported experiencing. Such a bummer, 'cuz it really sounds good to me.

There is a company called One Pot from Mexico that makes a Spring Reverb pedal that uses the little blue Accutronics tanks, like the Ruthenium and OP-Electronics builds. They seem to have it figured out. Wish I could have!

[BetterOffShred]

I built a Ruthenium and it sounded like a squawking bird, so I prodded the wires around to and from the tank and after a few minutes I got it nice and quiet.  Of course you have to dial in the gain trimmer fairly decently. 

One of my 1054s was overheating so I shortened up the tank wires as short as possible and that seems to have cured it. 

As for the reverberation machine,  maybe you should jettison the tantalums and try the electrolytics.. I've never used tantalum.. I know they can be finicky. 

[cnspedalbuilder]

I'll try switching them caps out.

There must be something wrong with my build--It's one thing for the pedal to be noisy in the sense of generating weird sounds, but another to have this loud constant swoosh of white noise!

[cnspedalbuilder]

OK, so I messed around with it some more and the noise appears to only be an issue when the decay pot is set past, say 30%. So it's a weird combination of high blend and long decay times that brings out the worst noise. In one of the modes (dark?) I can barely hear the reverb effect at short decay times, which is probably why I cranked it up. On the other mode, it's pretty nice and springy even with a lower value. So, maybe this is just what it should sound like???

btw: I forgot to mention--I used a TL074 as the op amp, as recommended in the build doc. Could that be increasing the noise?

[duck_arse]

FWIW, I built ..... the Surfy Bear FET Reverb. It uses a regular-sized tank. It sounds really great, but craps out from the over-heating issue many builders have reported experiencing. Such a bummer, 'cuz it really sounds good to me.

sounds interesting. be the one that gets it fixed - start a thread!

[anotherjim]

  That Rubidium scheme! Is it legit?
Wasteful replication of op amp bias networks.
Tone/level suck blend pot. Why not mix the wet signal using the inverting input? The reverb sound doesn't care about inversion.
Treble pre-emphasis in the dry path (C4/R6)?

The tone options going into the brick reverb look interesting, but the rest looks cobbled together from circuit "building blocks" which would explain the provision for a crazy amount of post gain.

[Danich_ivanov]

Something tells me that it all has to do with power supply section, i would try different values for 33r, up to 1k. Also you can try to add a resistor after the regulator, before the cap, in the range of 33r-1k  for example. Full disclosure, i'm not very skilled when it comes to opamps, but if transistor gain stage gives me white noise, in most cases messing around with power filtering solves the issue.

[cnspedalbuilder]

@Danich: I'll check out power supply filtering issue.

That Rubidium scheme! Is it legit?

I think so (?)--I was amused by this thread on Freestompboxes where they traced the schematic. Knutolai said:

Is it just me are DBA kinda bad at circuit design? Why not make a buffered, less noisy reference voltage with the spare opamp instead of individual voltage dividers for each opamp? It would even require less components. This looks like a Also whats up with the volume pot?

[cnspedalbuilder]

Now that I have this thing more or less working without horrible amounts of noise I'm wondering if the circuit analysts out there can advise. There are two problems, which seem to be known circuit issues based on my read of the tagboard effects comments:
1. One of the channels (the sun channel?) has almost no detectable reverb unless you dime the decay pot.
2. Both of the channels darken the tone considerably.

I've seen a few posts talking about resistor substitutions to deal with the first problem. One post said to replace R1 with a 10k or less resistor but to me it looks like that just jacks up the clean signal path.

I don't know how to deal with the second problem but I imagine there's a capacitor somehwhere that can be socketed to improve tone--just don't know which one. Any ideas?

[anotherjim]

What I would try...

Remove C14.
Remove C12, but reuse it so that the blend pot wiper (2) sends reverb to R20. Replace R20 with 100k or keep it at 10k but change C12 to 100n. The blend control is then able to work without interaction with the dry signal path.
Remove C4 and R6 and replace one of those with a wire link (to remove inexplicable bass cut in clean path).
R21 should be the same value as R20 so the gain can at least be set to unity *.

* There is a "thing" popular with noise fans where a reverb is deliberately over-amplified in order to bring up the low-level artefacts in the reverberation tails, but I'm not sure if that is usefully happening here since the clean path must also get lots of gain.

R8, R9 and C3 could be removed and C3 replaced by wire link as IC1b can get it's bias from the output of IC1d - but that's just reducing the BOM and won't notably affect the sound.

[cnspedalbuilder]

@anotherjim, thank you this is very helpful. I hate to be dumb, but I just want to make sure I get what you mean:

Remove C14.

So replace with a jumper right? Or do you mean leave it open?

Remove C12, but reuse it so that the blend pot wiper (2) sends reverb to R20.

Do you mean put a jumper at the C12 pad and then link that capacitor between the blend pot wiper and R20?

Remove C4 and R6 and replace one of those with a wire link (to remove inexplicable bass cut in clean path).

Right now, I'm thinking that the pedal is too dark and that there seems to be treble loss. Wouldn't removing C4 make it worse?

Thanks for your patience and help!

[anotherjim]

The way it's wired, C12 is acting as a treble cut filter on the + input at IC1b pin5. What I propose is to move the reverb path over to the - input pin6. Then C12 is acting as a coupling cap as it should and not cutting treble. To use the -input of the opamp there should be a resistor in series for which the R20 position can be used. The path through C14 to ground is not then required so yes, R14 leaves the job entirely although its solder pad at the R20 end can serve to wire the connection from C12 to.

One thing tutorials miss is that they show all the opamp hook-ups... inverting/non-inverting/differential... etc...
...but they don't say you can have more than one of those connections with the same opamp in use at the same time.
So, essentially, I mean let the clean signal carry on driving the non-inverting + input and the reverb drive the inverting input.
So C1 in that standard circuit above becomes the C12 and R1 is R20 and the input is from the wiper of the blend pot. The dry signal continues as it is to the + input but with the cap C22 (C2 above) removed from that path.

[cnspedalbuilder]

OK it is great to get an explanatio for what needs to be modded, the schematic and idea for the op amp is very cool!

So let me verify that I should definitely
-Remove C12 and C14 [you said R14 above but I'm assuming you mean C14 right?]
-Run the C14 capacitor from wiper to the R20 end of the C14 solder pad.

You mentioned earlier:

Replace R20 with 100k or keep it at 10k but change C12 to 100n.
Remove C4 and R6 and replace one of those with a wire link (to remove inexplicable bass cut in clean path).
R21 should be the same value as R20 so the gain can at least be set to unity *.

Should I still do an R21 mod or change R20 as suggested above? Also, is the C4/R6 mod needed, given that I am trying to restore treble?

All I really want to do is restore treble and get more pronounced reverb on one of the channels (I guess it's the "sun" channel?)

Thanks!

[anotherjim]

Yes, I meant C14.
No need to change anything just because it isn't optimal. C4 & R6 are odd because it's usual to cut bass from reverb return signal to avoid muddiness but not from the dry signal. However, the way the reverb is mixed back with the dry is plain wrong as the low resistance to ground via the blend pot makes the C12 coupling cap into a treble cut.

Once the reverb is feeding into the inverting input via C12, R20, it is a high pass filter which can be used to remove bass from the reverb return. You can change the filter effect to allow more bass by increasing the value of C12. In fact, you could use the 1uF from C14 which would lower the filter frequency to the point that it's passing all signal frequencies.