Twin Peaks - incredibly loud thumping, much louder than guitar

[lincolnic]

So I finally put my Twin Peaks on the test rig today, and much to my dismay, was greeted with some immediate issues. While the symmetry, shape, tone, and rate knobs all appear to work properly, there's a massively loud thumping sound, much louder than the guitar signal. Turning the depth knob up to around 8 or 9 o'clock seems to trigger it, as does adjusting TR3 or TR4. It was so loud that I immediately took it off the test rig.

Everything is completely stock, no substitutions. VTL5C1s for the vactrols, C22 is socketed and has a 100n in there at the moment. My only thought is that when I soldered the two PCBs together, maybe I had them too close together, and something is shorting out. I was able to slide some cardboard in between them after the fact, but it didn't help (they may be close enough that the cardboard got torn up). But before I do a lot of desoldering I figured I'd ask for help first.

Here are my voltages:

9.0 supply

5532

1. 1.8 - 4.8 varying
2. 3.4
3. 3.4
4. 0
5. 3.4
6. 3.5
7. 2.3 - 5.0 varying
8. 7.1

TL074

1. 4.3
2. 4.3
3. 4.3
4. 8.8
5. 4.3
6. 4.3
7. 4.3
8. 4.3
9. 4.3
10. 4.2
11. 0
12. 2.1
13. 4.3
14. 4.4

TAPLFO

1. 5.2
2. 0.9
3. 2.4
4. 5.1
5. 1.5 - 3 varying
6. 0
7. 1.4 - 3.8 varying
8. 5.2
9. 5.2
10. 3.5
11. 1.8
12. 2.7
13. 2.4
14. 0

I was able to bias B2 and B3 to roughly half of B1 without any trouble (don't remember the voltages offhand and didn't think to write them down, as I did that before listening to anything).

D1 lights up fully when power is applied, but I'm not sure if that's normal or not.

Unfortunately I only have a picture of the main PCB, but I can assure you I've checked the pot PCB and all the resistor and cap values are correct. No photo of the bottom side, obviously. I don't have the momentary tap switch soldered in, would that affect things at all? I feel like it wouldn't, since if the switch isn't being pressed that connection isn't being made anyway, but it's worth mentioning.



The PCBs are just temporarily mounted in the enclosure for ease of testing/photographing. In case anyone's wondering what's going on with the screw holes, I wasn't able to find the nylon screws suggested to hold the boards together, so I just soldered some thick diode legs to the pads instead. I figured since they're not actually connected to anything, it was a permanent enough solution that I could still undo if needed. (As it seems like I'll need to do now...)

[midwayfair]

Is it thumping in time with the effect and does it change when alter the rate, or is it constant?

[Jabulani Jonny]

Yep, had that.  I tamed it by going to at least a 1uf, maybe even a 2.2uf (electro is fine) for C22 and then finely tuning TR3 & TR4.

I got out the thumping and now the Twin Peaks resides on my board.  It's got a hair of noise, but not too bad.  Try switching C22 and really tweaking the trimmers and see where that gets you.   

[lincolnic]

I didn't get to throw it back on the testing rig today, but thanks for the replies. I should have the chance to check it again after work tomorrow.

Jon, I honestly can't remember if it was constant or in time with the effect. What would either of those suggest to you? I'm not even sure where I had the rate knob -- when I turned up the depth just a touch to see if the effect was working, the thumping was so loud it scared me off. I got the same thumping sound when turning TR3 or TR4 up from nothing (as the build doc says to start off). I should mention that the four different modes (black/brown/bass/treble) all seemed to be working properly, as far as I could tell through the noise. So I think my vactrols are good (they came from Small Bear, too). I will gather more data tomorrow.

Jonny, thanks for the suggestion -- not sure if I have any 2.2uf caps floating around at the moment, but I can definitely try a 1uf in the meantime. Will report back.

[Jabulani Jonny]

Jonny, thanks for the suggestion -- not sure if I have any 2.2uf caps floating around at the moment, but I can definitely try a 1uf in the meantime. Will report back.

I can drop one to you if needed.  Let us know how the 1uf and tweaking the trimmers affects the thump. 

[lincolnic]

Well, since my last post here was apparently wiped out, here's what I learned the last time I sat down with this:

1) The thumping changes speed with the rate pot.

2) Changing C22 to 1 uf didn't change anything.

3) The thumping only happens in normal tremolo mode; harmonic, bass only, and treble only modes are all fine.

Since all of the other modes work properly, I believe my vactrols are good and the LFO is fine. Would tweaking T3 and T4 really help get rid of the thump? Seeing as how they control the amount of current getting into the vactrols, I'm slightly dubious -- more current = increased chance of ticking, no? But I'll try it. They're barely turned up now as is.

[drolo]

Hi,

Could you check if you get the thumping in all LFO shapes or just the sharp ones (square, sawtooth etc)?
Your voltages look ok except pin 2 on the taplfo, not sure if it could be related at all but usually pins 2 and 3 both sit at around 2ish volts.

Something else, you mentioned that only the normal tremolo mode has that issue. That is the mode that pulls the most current, since both vactrols are being driven at the same time.

I have actually had a few cases where I would have a very loud thump for no reason and somehow that went away when soldering a small cap (270p) across the volume trimpot. Never really understood why it would do that, why not always and why the cap would stop it, but it did ...

Tip: to avoid the thing being louder than it needs to be and the thump doing any harm, turn the depth fully down and adjust the volume trimpot so that you have equal volume against the bypassed signal.

[lincolnic]

Hi David, thanks for the response. I am getting the thumping in all LFO shapes, though it seems to go away when the shape pot is at either extreme end -- somewhere in the neighborhood of below 9 o'clock or above 3 o'clock.

I'll try reflowing the components connected to pin 2 of the TAPLFO, I don't know why it's showing a low voltage. I'll have to check and see if I have any spare caps to try soldering across the volume trim too. I guess this means I'll be undoing my work connecting the PCBs together...looks like I should've just used regular wire.

Thanks for the tip about adjusting the volume trim, but unfortunately my test rig doesn't have a bypass switch, so I can't really make good use of it.

[destro]

Any luck on fixing this Lincoln? Are you using a testing rig to test it? Guess lfo bleed would not be the case if so. I am in the same situation. Followed setup like you and have loud clicking in blackface mode only.

Is your tap function working properly? Ironically, having same problem as brejna with wonky tap and random mode, but am thinking that may be a chip/programming issue.

Drolo, does that cap go across 1 and 3 on the volume pot?

[lincolnic]

No luck. I actually haven't had the chance to get back to it yet, I haven't even looked to see if I have the right cap to try putting across the volume trim. I've been kind of disheartened by all the trouble, to be honest!

I am testing it on my testing rig, but I don't see why that would make the problem any worse or better. I haven't wired up the tap function yet (figured I'd do so when I boxed the thing), so I couldn't tell you if it's working or not.

I guess it doesn't help that I never really figured out how to set the bass/treble trim pots. Anyone who's got a working Twin Peaks, how did you set yours up? Last time I tried setting them so that the levels were relatively even when the tone knob was at one extreme or the other.

[destro]

Lincoln, try the cap across the volume trim that Drolo suggested! You dont have to separate the boards. Just free solder a cap to lug 2 and the lug on the right close to the two resistors. I used a 100pf. You should also take into consideration that if something is not plugged into the input, it sounds a lot worse than it is. I was still hearing audible thump, but once I plugged my guitar in, it went away.

Drolo, you might consider putting this mod in the notes section of the pdf for the future run of boards coming out. Love your projects, man!

[Scruffie]

Possible suggestion, depending on the origin of the tick, but you could try a 10uF cap with positive to V2 and negative to Vb2.

Also I see on the schematic the 78L05 input has no filtering cap, a 47uF? Positive to input, negative to ground might be worth a shot, same for the other regulator (can't see if it's a 78L05,6 or 8?)

[drolo]

No luck. I actually haven't had the chance to get back to it yet, I haven't even looked to see if I have the right cap to try putting across the volume trim. I've been kind of disheartened by all the trouble, to be honest!

I am testing it on my testing rig, but I don't see why that would make the problem any worse or better. I haven't wired up the tap function yet (figured I'd do so when I boxed the thing), so I couldn't tell you if it's working or not.

I guess it doesn't help that I never really figured out how to set the bass/treble trim pots. Anyone who's got a working Twin Peaks, how did you set yours up? Last time I tried setting them so that the levels were relatively even when the tone knob was at one extreme or the other.

I'm sorry this is giving you such trouble...
About the setting of the bass/treble trim pots, most of the time I leave them fully counterclockwise. Unless I really have a quirky pair of vactrols... then I will set one or the other a little hotter. I think I actually even started using 10k trim pots at some point as usually there is still enough current for the vactrols even so. Trying to set an even volume between bass and treble is really not that easy by ear. A lot of psychoacoustics at play here.
If you wanted to try reducing the current more, you could increase the current limiter resistors R31 + R32 a bit.

Lincoln, try the cap across the volume trim that Drolo suggested! You dont have to separate the boards. Just free solder a cap to lug 2 and the lug on the right close to the two resistors. I used a 100pf. You should also take into consideration that if something is not plugged into the input, it sounds a lot worse than it is. I was still hearing audible thump, but once I plugged my guitar in, it went away.

Drolo, you might consider putting this mod in the notes section of the pdf for the future run of boards coming out. Love your projects, man!

I will do, good idea

Possible suggestion, depending on the origin of the tick, but you could try a 10uF cap with positive to V2 and negative to Vb2.

Interestting, I can't seem to remember having seen this done before. What does this add compared to just having a cap from Vb to ground?

Also I see on the schematic the 78L05 input has no filtering cap, a 47uF? Positive to input, negative to ground might be worth a shot, same for the other regulator (can't see if it's a 78L05,6 or 8?)

When I read this I quickly checked the schematic I had put up on my website and .... WHAT!?! how could I forget the input cap !!
Fortunately, I had corrected that since then it seems ...
You had me panicking for a moment there ... :-)
I guess you were refering to that same schematic.

[Scruffie]

Possible suggestion, depending on the origin of the tick, but you could try a 10uF cap with positive to V2 and negative to Vb2.

Interestting, I can't seem to remember having seen this done before. What does this add compared to just having a cap from Vb to ground?

Also I see on the schematic the 78L05 input has no filtering cap, a 47uF? Positive to input, negative to ground might be worth a shot, same for the other regulator (can't see if it's a 78L05,6 or 8?)

When I read this I quickly checked the schematic I had put up on my website and .... WHAT!?! how could I forget the input cap !!
Fortunately, I had corrected that since then it seems ...
You had me panicking for a moment there ... :-)
I guess you were refering to that same schematic.

Ahh okay yes I was, I did wonder if it might have been a mistake as it seemed unlikely they'd have been missing all this time without someone noticing.

RE the other cap, it's just a tiny bit more stable, I doubt it'll help but it was just an idea. If you've seen a bipolar supply before you've seen it done and as V.Ref is effectively the same thing etc.

EDIT: I also see a NE5532 is being used for the LED drive, that's a current hungry opamp... a LM358 seems like it would be a much more suitable alternative and if the tick is coming from there.

[lincolnic]

Thanks for all the suggestions, guys. I'm not giving up yet! I will keep trying to make this happen, but it's gonna be a little while. I came down with a cold today, and on Wednesday I have a friend arriving from out of town for a few days, so unless I wake up feeling great tomorrow I probably won't be soldering until next week. But I really appreciate all the ideas and all the help!