Dead End Fx Turbotrem issue with triangle wave (more diagnostics provided)

[spacekid71]

Thanks for mentioning that, I will have a look to see what LEDs and LDRs I have in stock and take it from there.

Do you know what function they have in the Wobulator, and do you think that the vactrols currently in place might be at the root of the triangle wave problem?

[ElectricDruid]

The vactrol's LDRs are providing variable gain in an inverting op-amp. That part is a dual-channel tremolo, basically.

Since the basic gain of the op-amp is set by the 39K input resistor and the 100K feedback resistor, there's no way it's going to be fussy about LDR off resistance. Any much above 1M is just going to be "big" and it won't change anything much. 10M is the same as 30M at this point. The low end will make more difference, since a 10K minimum On resistance will give a different amount of gain from a 30K minimum.

The LED colour/brightness/whatever is important only is as much as it matches whatever the LDR is. Someone might come along and say "Oh, you need an orange hi-brightness LED", but that's only true if you've got the same LDR they had. If your LDR reacts most strongly to green light, you might well be better off with a green LED.

HTH

[spacekid71]

So I have ordered and built out another DFX Turbotrem, and the oscillator circuit is also freezing up when the LFO 1 rate is too slow...

I am aware that I have built out the new Turbotrem with the same components so I am thinking of changing some of the components (Vactrols, J113, BC549C, transformers) to see if the problem lays there.

My first try has been to replace the vactrols with a green diffused LED and an LDR. I have tried both a NSL-5542 LDR (20-40K, 20M) and another LDR (10-20K, 0.5M) but both don't resolve the issue.

When I look at the LEDs, the lights are in sync with the LFO 1 rate which leads me to believe that the vactrols cannot be the cause of the issue.

Next I am thinking of exploring transistors (BC549C, J113) and the Bourns transformers.

It would be great if anyone can suggest another angle to explore.

[Govmnt_Lacky]

So I have ordered and built out another DFX Turbotrem, and the oscillator circuit is also freezing up when the LFO 1 rate is too slow...

I am aware that I have built out the new Turbotrem with the same components so I am thinking of changing some of the components (Vactrols, J113, BC549C, transformers) to see if the problem lays there.

My first try has been to replace the vactrols with a green diffused LED and an LDR. I have tried both a NSL-5542 LDR (20-40K, 20M) and another LDR (10-20K, 0.5M) but both don't resolve the issue.

When I look at the LEDs, the lights are in sync with the LFO 1 rate which leads me to believe that the vactrols cannot be the cause of the issue.

Next I am thinking of exploring transistors (BC549C, J113) and the Bourns transformers.

It would be great if anyone can suggest another angle to explore.

Ensure proper resistor values for R31, R32, R33, and R36. Also double check wiring to and from all jacks (connections, no shorts, no short to GND, etc.)

[spacekid71]

I have done the offboarding wiring for both Turbotrems following along with the build instructions from DEFX,
but maybe I am interpreting them incorrectly.

Do you (or someone else) have a working Turbotrem that I can compare my offboard wiring with?

[Govmnt_Lacky]

Make sure the LFO Trigger jack Sleeve IS connected to GND.
Make sure your LFO Pedal jack Sleeve is NOT connected to GND.

The TurboTrem is a proven build. I have built 2 or 3 in the past (don't have them anymore)

[spacekid71]

Make sure the LFO Trigger jack Sleeve IS connected to GND.
Make sure your LFO Pedal jack Sleeve is NOT connected to GND.

The TurboTrem is a proven build. I have built 2 or 3 in the past (don't have them anymore)

Hi Govmnt_Lacky,

I have verified the LFO trigger and LFO pedal jacks and all looks good but maybe you could have a look at it:





Thanks,

Mart

[Govmnt_Lacky]

The wiring looks ok. The soldering however, needs some work. Looking at the pots in your pictures and where they connect to the PCB, it looks like you have some cold solder joints and the solder is just balled up. Might want to flux all that up and re-heat with the soldering iron to ensure good contact. I believe those are the Rate pots too....

[spacekid71]

Ah okay, thanks for having a look!

I will reheat those solder joints with flux tonight and see if it helps.

[Chillums]

It's hard to tell by the picture but if you don't have pot covers make sure you put something under the back of the pots (like double sided tape) so they're not shorting anything under them.

[spacekid71]

The wiring looks ok. The soldering however, needs some work. Looking at the pots in your pictures and where they connect to the PCB, it looks like you have some cold solder joints and the solder is just balled up. Might want to flux all that up and re-heat with the soldering iron to ensure good contact. I believe those are the Rate pots too....

I have cleaned up all the pots including the RATE pots but it has not resolved the problem.

It is curious how the problem only happens with the triangle wave setting. When I switch to square wave, the oscillations don't freeze when I turn the left RATE knob below 2 o'clock, and the tremelo just continues.

I did check if the pots were shorting against the PCB but they are not even close to the board.

Any other things I can check? I think I will try to swap out the J113 and the transformers tonight to see if that changes anything.

[spacekid71]

Hi everyone,

Tonight I found out that the problem with my DEFX Turbotrem is a faulty J113 jfet transistor. I havent checked the newer Turbotrem that I had built a couple of weeks ago but as it has the same issue, it is most likely the same thing.

I would like to thank everyone who helped me with this, especially Govnmt_Lacky, anotherjim, and ElectricDruid. Two more pedals finished up!

Cheers,

Mart

[Strategy]

Wow, two Turbotrems. Definitely try and play them both at the same time in some sort of stereo setup, you could have Turbotrem #1 modulating one of the stereo channels of Turbotrem #1.
- Strategy

[Govmnt_Lacky]

Glad you found the issue!

For the benefit of others, it would help if you listed the J113 (Q number) from the build that caused the issue.

[spacekid71]

Sure, the issue with the DEFX Turbotrem was caused by Q4. This should be a J113 and I had put one but it turns out that it is faulty.