Tremolo

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Robin28
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Post by Robin28 »

Hello, everyone.

I tried to build a tremolo
An easy build (3 2n5088 and one tl072.)
The tremolo works fine but I Have an Kind of electronic clic synched with the rate.
I checked the schematic a 1000 times, built it a 2nd time with different parts. Same issue.
(i tried as well on a 9V battery)
(i only changed one thing, i used a 1n4003 not a 1n4007).
Help! [smilie=a_damnit.gif]
:D
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Tremolo sound
Audio 1_32.mp3
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stolen
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Post by stolen »

Hi!

There's two options: Either the LFO is coupled to the audio signal via the supply lines or parasitic capacitances/inductances, or the VCA has control signal feedthrough. It's easy to check which one it is; if you disconnect R17 on either end, the LFO is no longer connected to the VCA. If the ticking still persists, it is probably the supply line - we noticed that there's no stabilization cap on 9V in your schematic, adding one could mitigate the problem.

If it's parasitic, it might very well be the leads to the rate knob and the speed toggle; twist them together and give them some distance from the input/bypass leads. If there's a true bypass installed and the ticking is still noticeable when the pedal is bypassed, that might very well be the issue.

In case the ticking is gone with R17 disconnected: is the speed toggle an on/on or on/off/on type? If it's the former, the control signal should be sufficiently smoothened in either setting, if it's the latter, a small (2.2n) capacitor from the base of Q3 to ground might help. Can you check if C3 is not shortened and installed in the correct polarity?

Hope this helps!

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Robin28
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Post by Robin28 »

Thank you for such a fast answer :)

I tried to remove R17, it didn't remove the clicking noise.
I twisted the leads as you said, no improvement neither.
I'm sorry about the stabilisation cap, i did'nt send the entire screenshot. (here it is)

The switch is an on on. (but I don't feel like it' s doing much to the speed.)

Even if removing r17 did change anything I tried to add a 2.2nf cap between Q3 and the ground but and it didn't solve the problem.

I doubled checked the polarity of C3, and it's like in the schematic. (and it's not shortened)
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stolen
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Post by stolen »

Hey!

If removing R17 didn't solve it, then it's definitely parasitic since there is no other direct connection from LFO to signal circuit other than the power supply. The speed switch looks more like a waveform switch to us, not sure how effective it is. Could you send a picture of your full assembly? It is not unlikely a layout/wiring issue.

Experimentally you could reduce the high frequency switching content by adding capacitors in the range of 4.7-47nF between collector and ground for Q1 and Q2 - these will affect the LFO waveform and frequency and may even stop the LFO entirely if too large, but this way large voltage jumps are dampened. The MXR Phase 45 LFO employs that technique with good success, albeit being a totally different topology.

Also we are curious: Where did you get that schematic from? Not sure if we've ever seen a hybrid like this before, and the input section doesn't quite look like it's made for guitar.

It's a bit of a headscratcher, but don't worry, we should be able to figure it out :D!

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Post by Robin28 »

Thanks for all these tips :)

Honestly i've been building compressors, drives and eqs and moding some schematics, but it's my first attempt to modulation.

So I took a schematic that i found on an german electronic website who does DIY kits (cause i wanted to do a easy one to start :lol: ).
As I ordered some other custom PCB I copied the schematic and ordered a PCB for this one without breadboarding it first.
(so the layout is the same that the schematic i sent before)
(here are some pictures , the pcb start to look a bit shitty cause i tried different stuff to solve my problem :) )
(i link you the original schematic that i copied.)
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Post by stolen »

Hi!

We notice that on your PCB a lot of traces run really close together for long stretches, forming sizeable capacitors. Furthermore, the LFO seems to be located right next to the input; it's no wonder that there's coupling. You'd want the LFO to stay as far away from any signal sections as reasonably possible, especially the sensitive input section, and leave space between parallel wires. Also ground copper fills on the other side can help a lot with suppressing interference.

You said you've built that circuit twice, right? Then there's a simple way to see if our assumption is correct: disable the LFO from one of your circuits entirely (for example by grounding one of the bases of Q1/Q2) and only use the VCA section. Then use the LFO from the other board and hook that one up to the emitter of Q3 instead, along with GND and 9V. Keep the boards a few inches apart. The issue should disappear. We know, this is harsh, but board layouts unfortunately need to do more than just connecting the right dots.

If this spatial separation works, and you don't mind sharing, you could post your board layout (raw gerber or kicad preferred) on some filesharing service and we can see if there's some way to hotfix this.

Sorry for the disheartening news.

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Post by Robin28 »

I will try that tomorrow
thanks a lot.
Don't worry, if i learn somthing out of it, it s already great :)

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Post by stolen »

that's the spirit!

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Post by Robin28 »

Hi!
Sorry i Didn’t have time to try What you said before.
I couldn’t mix the two circuits but I mixed it with a breadboard. And you were right ! It solved the problem!

I’ll be more careful with the layout on my next pcb .
Thanks a lot for your help :)

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