tremulus pain in the backside...

[jamesymurray]

sorry to be bringing up old stuff here, 
ive just finished my vero tremulus from Torchy's layout, and i have a few questions that i cannot seem to find answers for.

I'm not using the fine pot at the moment, i can always add it in afterwards. I have now got Speed 3 going to where Fine 1 should be on the board.
I'm also using an LDR/LED combo for the optoisolator section.

On powering it up, it seems that both LED's are working correctly, and the controls seemingly affect the led's in the right way.
However, the effect is very weak and only slightly noticable. Could this be due to the responsivity of the LDR, or has anyone got a good result with them?

Another thing that strikes me as odd, is that when the battery is disconnected, the clean guitar signal still gets through.

I've checked over the layout countless times, and made sure there are no bogus jumps between strips. Everything looks alright.

many thanks

jamesy

[Barcode80]

i'm assuming you wired for true bypass. if you did, the bypass is just a bridge between the in and out cable. this means you get clean signal whether the effect is powered or not, provided you have it switched to bypass.

[jamesymurray]

I dont have the switch or any bypass wired in at the moment, just straight into the effect.

j

[jamesymurray]

I've checked over the schematic numerous times, everything is as it should be (or so it seems)

By process of elimination, the LFO half of the circuit seems to be working correctly, so the problem must lie with the TL072.
I have now noticed that even when the op-amp is removed, the clean guitar still gets through. Been debugging this now for 12 hours, might just call it quits.

jamesy
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[petemoore]

  Why not take voltage measurements of the pins around where you think the problem is?
  and Audio probe...
  Approaching the fault from all possible angles makes it harder for it to remain illusive.
  It sounds as though you have the LFO working the LED's and..only things left are get sound to the LDR, then recover gain after...IIRC...
 

[$uperpuma]

Audio probe sounds like it would be useful in this situation... you can follow the signal path as shown on the schematic... it helped me when troubleshooting my lune...http://www.diystompboxes.com/pedals/debug.html

[jamesymurray]

Good suggestion there, I've had a probe around it, and ive marked out on the layout what I have found.
The black and grey route is the audio path from input to output.

I probed it without the chip in at first, and then with the TL072 installed. The results were the same.



I get signal through on pins 1,2,6 &7 of the chip.

baffling...

jamesy
x

[$uperpuma]

a common mistake with Vero seems to be not cutting the traces that need to be cut... just another thought to throw in...

[Ge_Whiz]

An op-amp circuit will usually pass a signal when unpowered - with or without the chip in place - because it will go through the feedback resistor from input to output. You've checked that the supply is reaching the op-amp?

Keep checking - you'll find it in the end.

[jamesymurray]

My DMM is dead at the moment, so I have only had my trusty resistor/LED probe to have look around with. There is power on all the pins that there should be. However, when i probe with the LED on the track inbetween the LDR and the bottom pin of the trimpot, the LED flashes in time with the LFO LED's, but the variation is only very slight on the LDR side.
Could it just be that my LDR is rubbish for this application and that it takes too long to respond when the LED is off?
It's the same LDR as those used in the Easyvibe, which worked like a charm.

jamesy

[jamesymurray]

My DMM is still dead so I have had to makedo with an analogue one.

I swapped over the LED /LDR combo for a silonex optocoupler this morning, the problem still persists. The signal is just passing through the LDR side and not being affected.

I have taken some voltages from the pins of the TL072 with the chip in and no signal through.
The voltages are pretty rough as the analogue meter isn't very accurate

Reading direct from the battery ~ 8.5v

Pin1 ~ 8v
Pin2 ~ 5v
Pin3 ~ 0v
Pin4 ~ 0v
Pin5 ~ 0v
Pin6 ~ 8v
Pin7 ~ 8v
Pin8 ~ 8v

Please someone help me!!! I've checked over the layout near on 100 times and still cannot seem to pinpoint the problem.

jamesy
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[jamesymurray]

To try out, i have just replaced the 10k trimpot with a 100k trimpot.
Now, using the audio probe, i get a slight tremolo sound on pin2 and a deeper tremolo sound on pin1. The thing that is confusing is, is that this is is all before the LDR. There is no signal at all after the LDR.

jamesy
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