Hi all,
I have built the DeadEndFx Turbotrem and most of it seems to be fine except for the triangle shape. I have indicated the path that doesn't seem to be working on the schematic. I have also made a video to illustrate the issue. Any help would be great.
(https://i.postimg.cc/CRzyTz17/turbotrem-build.jpg) (https://postimg.cc/CRzyTz17)
Schematic: (https://i.postimg.cc/yWRVM3wP/turbo-trem-diagnose.png) (https://postimg.cc/yWRVM3wP)
Video: https://drive.google.com/file/d/1ZEjflX3k6r_vhyk5GshDNh353fP5xwUf/view?usp=sharing (https://drive.google.com/file/d/1ZEjflX3k6r_vhyk5GshDNh353fP5xwUf/view?usp=sharing)
DEFX build document: https://drive.google.com/file/d/1zfFb6p8sl1gLMdpkSlTrNNS-i0e7dZRp/view (https://drive.google.com/file/d/1zfFb6p8sl1gLMdpkSlTrNNS-i0e7dZRp/view)
At a guess, I'd say there's something wrong in the switch wiring that's causing the triangle output to be tied to some static voltage and is killing the LFO.
Certainly I'd start by making sure that all the soldering around that rotary switch is really clean and there's nothing that's shorting to the ground plane or anything else. A tiny little blob of "lost solder" would be enough to do it. With the power off, scrape the gaps between the tracks clear with a small screwdriver bit to make sure that you've got gaps where you should have gaps.
HTH,
Tom
I have cleaned around the rotary switch area including IC4, but the triangle wave still doesn't function. I have now also taken out the rotary switch and I am manually connecting pin C to pin 10, but it still doesn't change anything.
When pin 12 is connected to pin C (square wave selection), pin 7 of IC4 is showing the voltage going up and down in sync with the left LED. When pin 10 (triangle wave selection) is connected to pin C, pin 7 of IC4 reads 2.4V constantly. In both scenarios IC4 is getting 9V power.
Anyone have any more ideas on what I can look at? I can provide more readings if it helps.
Does the square wave work? Really, the square depends on the triangle which is enabled by a JFET. Bad JFETs happen all too often but a good one is normally conducting and stopping the cap C19 from charging and discharging. To get the triangle running the JFET needs to be switched off, so what voltage do you have on Q5 collector? It will be 0v to switch it off and run the triangle. What is connected to R39 off to the right of the snippet?
Yes, the square wave works fine. The voltage on the Q5 collector is 7.1 mV independent of the setting being selected (square or triangle). This doesn't seem right based on what you said as it should be 0V for triangle to work.
The pins indicated on the schematic snippet are related to two sockets, the LFO pedal socket, and the LFO trigger socket. I have attached another image that shows the offboard wiring. Pad 13 is connected to the LFO Trigger socket and the silkscreen indicates TRG on it. Pad 10 and 12 are connected to the LFO Pedal socket and pad 11 grounds to the enclosure.
I can provide additional info if needed.
Your help is much appreciated!
(https://i.postimg.cc/KkdWTBLY/turbo-trem-diagnose-offboard.png) (https://postimg.cc/KkdWTBLY)
I think the triangle must be working. It and the squarewave are two outputs of the same oscillator. IC4 pin7 is Triangle and IC4 pin1 is Square. This is a common oscillator circuit using two opamps known as a "Function Generator" if you want to read up on it.
Check there is continuity between IC4 pin7 and the two contacts it feeds of the Shape switch.
Thank you for identifying that the LFO is a function generator, I will have a look at it tonight.
There is continuity between pin 7 of IC4, and pin 9 and 10 of the rotary switch.
When I measure voltage on pin 1 and pin 7 of the IC4, I see the following:
1. Square wave mode
Both pins are showing fluctuating voltages between 3V and 6V that seem in sync with the LEDs going on and off.
2. Triangle wave mode
Both pins show a constant voltage and the light from the LED also remains the same.
Pin 1: 7.7V
Pin 7: 2.4V
Quote from: spacekid71 on January 23, 2023, 04:43:36 PM
There is continuity between pin 7 of IC4, and pin 9 and 10 of the rotary switch.
This is good!
Quote
When I measure voltage on pin 1 and pin 7 of the IC4, I see the following:
1. Square wave mode
Both pins are showing fluctuating voltages between 3V and 6V that seem in sync with the LEDs going on and off.
This means the LFO is working, at least in this mode. That means there's nothing fundamentally wrong with it.
Quote
2. Triangle wave mode
Both pins show a constant voltage and the light from the LED also remains the same.
Pin 1: 7.7V
Pin 7: 2.4V
In this mode, the LFO stops working for some reason. The Shape switch seems to be ok, or at least you said you'd checked it out and it seemed to be all soldered cleanly. Could the problem be the mode switch? In the triangle mode, the triangle is supposed to only be connected to IC3 via R25/100R. Is it possible there's some other connection being made there? Could the switch have been fitted the wrong way around? (is that possible?) Are the Mode and Shape switches identical? Could they have been reversed if not?
It still seems to me most likely there's something shorting the LFO out in the triangle mode. The question is finding it!
Quote from: ElectricDruid on January 23, 2023, 07:06:58 PM
In this mode, the LFO stops working for some reason. The Shape switch seems to be ok, or at least you said you'd checked it out and it seemed to be all soldered cleanly. Could the problem be the mode switch? In the triangle mode, the triangle is supposed to only be connected to IC3 via R25/100R. Is it possible there's some other connection being made there? Could the switch have been fitted the wrong way around? (is that possible?) Are the Mode and Shape switches identical? Could they have been reversed if not?
It still seems to me most likely there's something shorting the LFO out in the triangle mode. The question is finding it!
Both the Shape and Mode switches are 3P4T rotary switches and they are installed the correct way around, I double-checked them. As far as I understand, in triangle mode, the triangle connects through R25 and R24 to pin 2 of IC3, and also through pin 4 and pin A of the Mode switch to pin 3 of IC3. Pin 2 and 3 of IC3 being inputs and pin 1 being the output.
I measured pin 1 of IC3 and in Square wave mode, the voltage is fluctuating. In Triangle mode the voltage stays at 2.5V continuously...
Are you sure that R34 is a 10K resistor and not a 1K?
^ That's a very good one to check. The triangle amplitude will be very low if R34 is too small but the squarewave could still appear. Conversely, R29 could be too large and have the same impact. It's the balance between these two resistor values that sets the amplitude of the triangle wave but the squarewave is always going to have full amplitude.
Thanks anotherjim and Govmnt_Lacky! I will check these resistors and report back. Hopefully they are wrong and it will fix the issue. 8)
Quote from: spacekid71 on January 24, 2023, 09:05:00 AM
Thanks anotherjim and Govmnt_Lacky! I will check these resistors and report back. Hopefully they are wrong and it will fix the issue. 8)
Looking at the pic you uploaded, I am not so much concerned about R29 as it looks to be the correct value of 15K (Brown, Green, Black, Red) however, the R34 resistor "could be a 1K (Brown, Black, Black, Brown). It should be Brown, Black, Black, Red.
Quote from: Govmnt_Lacky on January 24, 2023, 10:58:25 AM
Looking at the pic you uploaded, I am not so much concerned about R29 as it looks to be the correct value of 15K (Brown, Green, Black, Red) however, the R34 resistor "could be a 1K (Brown, Black, Black, Brown). It should be Brown, Black, Black, Red.
I just unsoldered R34 and checked its value, and unfortunately it measures in at about 10K. I must admit that the colors are very close between the Brown and the Red, I couldn't tell the difference by looking at it. Any other parts that I should check?
Quote from: spacekid71 on January 23, 2023, 04:43:36 PM
When I measure voltage on pin 1 and pin 7 of the IC4, I see the following:
1. Square wave mode
Both pins are showing fluctuating voltages between 3V and 6V that seem in sync with the LEDs going on and off.
2. Triangle wave mode
Both pins show a constant voltage and the light from the LED also remains the same.
Pin 1: 7.7V
Pin 7: 2.4V
Jim, Lacky,
It's not that the triangle wave is low in volume, it's actually *stopped*, as evidenced by the quote above. In triangle mode, even the square signal goes dead - the LFO stops oscillating.
What could that switch be doing that's killing the oscillation?
I diagnosed a bit more tonight and the triangle wave is not completely dead it seems. Hooray!
When I turn the LFO-L-RATE knob (B100K) to 2 o'clock or further, the triangle comes alive! If I turn the knob back down below 2 o'clock, the IC4 pins show a constant voltage again (Pin 1: 7.7V, Pin 7: 2.4V) and the LEFT LED goes dim.
Another thing I noticed is that 2 o'clock and further both LEFT and RIGHT LEDs are on, and when below 2 o'clock, only the LEFT LED is on dimly.
It does seem that in triangle mode, the oscillations are being killed...
Well, the circuit is proven so we should start by checking things:
- Check proper values of R29 through R39, C18 through C21.
- Check to make sure that Q4-Q6 are correct and in their proper locations
- Verify the Mode and Shape rotary switches are making good and proper contact
(When the A-pole is contacting Pin 1, then B-pole should be on Pin 5... C-pole should be on Pin 9. As you rotate the numbers should move up 1 with each rotation)
- Verify that you have a Linear taper pot (B-taper) for the LFO Rate pots
- Verify you have Vref voltage on IC4 Pins 2, 5, 9, and 12.
- Verify you have Vref voltage on Mode rotary Pins 1-3
- Swap out IC4 and retest
- Swap out IC3 and retest
Just a thought. Are the rotary switches the Alpha type 3P4T? If the turn limit tab washer was in the wrong hole giving 4 positions at the wrong end of the 12 possible positions these have, what do the contacts make to, if at all?
Quote from: Govmnt_Lacky on January 25, 2023, 07:18:24 AM
Well, the circuit is proven so we should start by checking things:
- Check proper values of R29 through R39, C18 through C21.
- Check to make sure that Q4-Q6 are correct and in their proper locations
- Verify the Mode and Shape rotary switches are making good and proper contact
(When the A-pole is contacting Pin 1, then B-pole should be on Pin 5... C-pole should be on Pin 9. As you rotate the numbers should move up 1 with each rotation)
- Verify that you have a Linear taper pot (B-taper) for the LFO Rate pots
- Verify you have Vref voltage on IC4 Pins 2, 5, 9, and 12.
- Verify you have Vref voltage on Mode rotary Pins 1-3
- Swap out IC4 and retest
- Swap out IC3 and retest
Thank you for the list of things to check, Govmnt_Lacky, I will have a look at this and report back.
Quote from: anotherjim on January 25, 2023, 10:07:38 AM
Just a thought. Are the rotary switches the Alpha type 3P4T? If the turn limit tab washer was in the wrong hole giving 4 positions at the wrong end of the 12 possible positions these have, what do the contacts make to, if at all?
These are the Alpha 3P4T switches but I have checked that the switches are the right way in and that the turn limit tab washer is properly in place (both in position 4 of 12).
I did have a problem earlier with the Mode switch where I had overturned the nut too much and it broke the rotary switch. For this reason I have replaced both rotary switches to make sure that they function properly.
One thing I did wonder though. I have all isolated TRS sockets for this build and in the build document it uses TS sockets for all sockets except the input socket. Would this cause any potential issues? I am wanting to check this with you because both the LFO pedal and the LFO trigger sockets are hooked into the LFO. Just a thought I had in the back of my mind for a number of days so I thought it would be better to check.
Quote from: spacekid71 on January 25, 2023, 11:04:10 AM
One thing I did wonder though. I have all isolated TRS sockets for this build and in the build document it uses TS sockets for all sockets except the input socket. Would this cause any potential issues? I am wanting to check this with you because both the LFO pedal and the LFO trigger sockets are hooked into the LFO. Just a thought I had in the back of my mind for a number of days so I thought it would be better to check.
The short answer is NO
As long as you wired the TRS jacks in accordance with the build doc (Sleeve connections to Sleeve/Tip connections to Tip) then you should be OK. I have built many of these and always used TRS jacks in every position with no issues. The big thing to note is that the LFO Pedal Sleeve and Sleeve Switch and LFO Trigger Sleeve and Sleeve Switch do NOT make contact directly with the enclosure (as well as the Sleeve connection of the Right Stereo Out)
As an aside, you may want to verify your soldering of the LFO Pedal and Trigger wiring at the PCB. Just make sure nothing is shorted where it ISN'T supposed to be.
Quote from: Govmnt_Lacky on January 25, 2023, 11:33:06 AM
The short answer is NO
As long as you wired the TRS jacks in accordance with the build doc (Sleeve connections to Sleeve/Tip connections to Tip) then you should be OK. I have built many of these and always used TRS jacks in every position with no issues. The big thing to note is that the LFO Pedal Sleeve and Sleeve Switch and LFO Trigger Sleeve and Sleeve Switch do NOT make contact directly with the enclosure (as well as the Sleeve connection of the Right Stereo Out)
As an aside, you may want to verify your soldering of the LFO Pedal and Trigger wiring at the PCB. Just make sure nothing is shorted where it ISN'T supposed to be.
Just wanted to clarify the grounding that is going on before verifying that the sockets aren't shorting out.
I have a wire running from the enclosure (attached with a screw and nut) to the enclosure GND pad (LFO pedal socket - middle pad), and all sockets are plastic so they don't come in direct contact with the enclosure. But the enclosure GND is connected to the power jack GND (I checked with continuity) and through that to the GND of the input and outputs. Is that correct?
When I check continuity on the LFO pedal socket I get the following:
Without a cable plugged in:
GND to SCN: yes
GND to TIP: yes
TIP to SCN: intermittent
With cable plugged in:
GND to SCN: yes
GND to TIP: no
TIP to SCN: intermittent
I guess this makes sense as without the cable, the tip is being shorted to ground so it has no effect on the LFO?
What is "SCN"?
Quote from: Govmnt_Lacky on January 25, 2023, 08:51:20 PM
What is "SCN"?
I just checked using continuity and it gives me the following silkscreen to schematic mapping:
TIP -> PAD 12
GND -> PAD 11
SCN -> PAD 10
Not sure what SCN would stand for but maybe SCAN?
Quote from: Govmnt_Lacky on January 25, 2023, 07:18:24 AM
Well, the circuit is proven so we should start by checking things:
- Check proper values of R29 through R39, C18 through C21.
- Check to make sure that Q4-Q6 are correct and in their proper locations
- Verify the Mode and Shape rotary switches are making good and proper contact
(When the A-pole is contacting Pin 1, then B-pole should be on Pin 5... C-pole should be on Pin 9. As you rotate the numbers should move up 1 with each rotation)
- Verify that you have a Linear taper pot (B-taper) for the LFO Rate pots
- Verify you have Vref voltage on IC4 Pins 2, 5, 9, and 12.
- Verify you have Vref voltage on Mode rotary Pins 1-3
- Swap out IC4 and retest
- Swap out IC3 and retest
- I have gone through the resistors and capacitors by visually confirming their values and they check out.
- I have verified that Q4 is the J113 and that Q5 and Q6 are BC549C transistors. They are also the right way around based on the silkscreen.
- I have used continuity to check both the Mode and Shape switches to make sure that pins correspond to correct poles.
- I have checked that both LFO rate pots are B100K.
- I have checked on the specified pins of IC4 and the Mode switch that they have the VREF voltage of 4.30V from pin 1 of IC1.
- I have swapped out IC3 and IC4 multiple times and the triangle wave just won't behave.
I have made a new video to illustrate the triangle mode problem: https://drive.google.com/file/d/1f8QkTaSL3imUIGuzdfav6-vwStCFjt_C/view?usp=share_link (https://drive.google.com/file/d/1f8QkTaSL3imUIGuzdfav6-vwStCFjt_C/view?usp=share_link).
Quote from: spacekid71 on January 25, 2023, 04:16:06 PM
When I check continuity on the LFO pedal socket I get the following:
Without a cable plugged in:
GND to SCN: yes
GND to TIP: yes
TIP to SCN: intermittent
With cable plugged in:
GND to SCN: yes
GND to TIP: no
TIP to SCN: intermittent
I guess this makes sense as without the cable, the tip is being shorted to ground so it has no effect on the LFO?
Are you talking about the LFO PEDAL jack -OR- the LFO TRIGGER jack? YOu should not see GND on the Tip of the LFO Pedal jack at all.
Quote from: Govmnt_Lacky on January 25, 2023, 08:51:20 PM
What is "SCN"?
"Screen", I would guess - e.g. the shield on a shielded cable.
Maybe. Don't know whether that makes sense with the connections given.
Well, sure Scrn=Screen=Sleeve is the "S" in TRS, but for control/switching it can be anything that's safe. Doesn't have to be an audio cable shield/ground/0v.
I don't like the PCB having wire pads at a minimum distance apart. Stranded wire can hide broken strands that pop out and short to a neighbour. Unless you're going to use crimped connectors, solid wire is a better choice. Anyway, the only thing I'd look for there is shorts between the wires to the control pedal jack. The LFO trig needs to ground normally so that shouldn't be an issue.
Quote from: Govmnt_Lacky on January 26, 2023, 07:03:56 AM
Are you talking about the LFO PEDAL jack -OR- the LFO TRIGGER jack? YOu should not see GND on the Tip of the LFO Pedal jack at all.
(https://i.postimg.cc/sGJX6mtj/offboard-wiring.png) (https://postimg.cc/sGJX6mtj)
The continuity info that I provided was for the LFO Pedal jack. I think I should redo the offboard wiring, starting with the LFO Pedal and LFO trigger jacks, it looks like that could be killing the oscillation.
Is there a reason that it would only kill the oscillation in triangle mode when the rate is below 2 o'clock?
Quote from: spacekid71 on January 26, 2023, 11:36:14 AM
(https://i.postimg.cc/sGJX6mtj/offboard-wiring.png) (https://postimg.cc/sGJX6mtj)
The continuity info that I provided was for the LFO Pedal jack. I think I should redo the offboard wiring, starting with the LFO Pedal and LFO trigger jacks, it looks like that could be killing the oscillation.
Is there a reason that it would only kill the oscillation in triangle mode when the rate is below 2 o'clock?
Perform this quick test:
- Remove all plug from any jacks on the pedal
- Set Left Rate pot to center
- Set Right Rate pot to center
With your Multimeter on Continuity or Resistance check, place Black probe to Ground lug. With the Red probe, check ALL 3 of the solder points on the Left and Right Rate pots.
You SHOULD NOT get continuity or a direct short to Ground on any of them.
EDIT: Just to make sure we are on the same page, based on your build you sent pics of.... your LFO Trigger jack is on top of your pedal above the LFO Rate pots.. The LFO Pedal jack is above the Depth pots.
Quote from: Govmnt_Lacky on January 26, 2023, 01:36:37 PM
Perform this quick test:
- Remove all plug from any jacks on the pedal
- Set Left Rate pot to center
- Set Right Rate pot to center
With your Multimeter on Continuity or Resistance check, place Black probe to Ground lug. With the Red probe, check ALL 3 of the solder points on the Left and Right Rate pots.
You SHOULD NOT get continuity or a direct short to Ground on any of them.
Thanks Govmnt_Lacky! I am in Canada and I am currently working but I will have a look at this when I have some dedicated time.
Quote from: Govmnt_Lacky on January 26, 2023, 01:36:37 PM
Perform this quick test:
- Remove all plug from any jacks on the pedal
- Set Left Rate pot to center
- Set Right Rate pot to center
With your Multimeter on Continuity or Resistance check, place Black probe to Ground lug. With the Red probe, check ALL 3 of the solder points on the Left and Right Rate pots.
You SHOULD NOT get continuity or a direct short to Ground on any of them.
EDIT: Just to make sure we are on the same page, based on your build you sent pics of.... your LFO Trigger jack is on top of your pedal above the LFO Rate pots.. The LFO Pedal jack is above the Depth pots.
I have tested continuity between the ground lug and the solder points on both RATE pots, and there is no continuity for any of the solder points to ground.
There is continuity between both pads of the LFO trigger socket. When retesting the LFO pedal socket, I am unsure what is happening.... With the pedal powered on, I get continuity between GND and TIP (not good), NO continuity between GND and SCN, and intermittent continuity between TIP and SCN. When the pedal is turned off, there is no continuity between any of the three pads. I am probably doing something wrong...
I have made an image that shows the PCB pads on top of the photo of my build and I have indicated which socket is which, I hope this helps.
(https://i.postimg.cc/kDdB8mv9/turbotrem-lfo-sockets.png) (https://postimg.cc/kDdB8mv9)
Do not test continuity in a circuit with its power on. It will clash with the DMMs own probe voltage if the circuit is powered.
To properly test sockets, check continuity with a plug fitted and test to the plug contacts or the other end of a suitable cable fitted with that plug.
The LFO trigger socket has a switch contact used opposite the tip contact. This contact breaks when a jack plug is inserted and makes when it isn't. Have a look at what happens to the contacts when a plug is fitted in and out - you should see the movement that works the switching.
So, the tip is grounded with no plug fitted and that will allow the LFO to work. When a footswitch pedal is attached, the socket ground is removed from the tip and it's then up to the external footswitch to ground the tip or not.
The LFO speed pedal socket connects an external potentiometer in an expression/volume pedal to the LFO rate pot, so it will depend on the setting of the rate pot how much a fault on the pedal socket will affect it.
Quote from: spacekid71 on January 27, 2023, 12:13:31 AM
When the pedal is turned off, there is no continuity between any of the three pads. I am probably doing something wrong...
This is correct with NO power applies (as Jim said) and with the LFO PEDAL jack.
Lets try to call in reinforcements....
The issue with the triangle wave is still not fixed..
I did some more investigation on IC4 to see what voltages are like when the triangle is working and isn't working. Here are the values:
rate below 2 o'clock (triangle wave not working)
IC4
1 7.81V
2 4.31V
3 4.37V
4 8.59V
5 4.30V
6 4.30V
7 2.06V
8 1.44V -> 6.04V *
9 4.31V
10 2.05V -> 8.73V *
11 0V
12 4.31V
13 4.31V
14 1.72V -> 5.23V *
rate above 2 o'clock (triangle wave working)
1 4.17V -> 4.41V *
2 4.29V
3 4.13 -> 4.17V *
4 8.56V
5 4.29V
6 4.29V
7 4.04V -> 4.06V *
8 1.2V -> 7.56V *
9 4.29V
10 1.99V -> 8.99V *
11 0V
12 4.29V
13 4.29V
14 3.37V -> 8.56 *
* voltage constantly changing, values to give an approximation
Hi everyone,
I have been continuing to investigate the triangle wave problem. So as far as I understand, the Turbotrem circuit has two waveform generators, LEFT and RIGHT. It uses one TL074 to generate both LEFT and RIGHT waveforms and for each it generates square and triangle waves. Now when I am in Tremulant mode using the triangle shape, there are oscillations when the LEFT rate knob is passed 2 o'clock, otherwise it is a static voltage.
So this morning, in the static voltage scenario, I thought I would see if the RIGHT waveform generator is having any effect on the LEFT one freezing up, so I shorted the RIGHT triangle (pin 14 on IC4) to ground. The result was that the LEFT triangle waveform started to work as intended.
Looking at the schematic, it seems that the only way that the RIGHT waveform generator is being used and connected in the whole circuit, is in the Dual Tremulant mode, in which it connects through pin A of the Shape switch to pin 5 of the Mode switch. It seems odd then that it would have any effect in Tremulant mode.
I am using a IC socket for the TL074 and thought maybe there was a short there. I checked but the only connections are the pins 2, 5, 9, 12 which are connected to VREF. Finally, I did some measurements directly on the LEFT rate pot in various positions to illustrate the oscillator lock up (which I attached as an image).
I hope someone will be able to point me into the right direction. Any help would be appreciated.
(https://i.postimg.cc/kVb0tkLh/L-Rate-Measurements.png) (https://postimg.cc/kVb0tkLh)
Everything about this just screams that there is either an incorrect resistor value somewhere in the circuit -OR- the rate pot(s) are the wrong value or taper :-\
Could the rate pot just be faulty?
Thanks Lacky. I will do a sweep of the resistor values in the whole circuit, and perhaps take out the pots and check their values as well.
I was thinking that the two vactrols have LDRs in them so if they are faulty, that could also mess the circuit up resistance-wise. Do you know what function the vactrols have the circuit? I have attached images of both places where the two vactrols are used. I also spoke to Matt Harrison (GiveUsYourBones) by email yesterday and he had built the Turbotrem and experienced some issues because of the vactrols.
(https://i.postimg.cc/xqdyZtZ8/turbotrem-vactrols-1.png) (https://postimg.cc/xqdyZtZ8)
(https://i.postimg.cc/fS3dRg4v/turbotrem-vactrols-2.png) (https://postimg.cc/fS3dRg4v)
Quote from: spacekid71 on February 13, 2023, 08:46:06 AM
I was thinking that the two vactrols have LDRs in them so if they are faulty, that could also mess the circuit up resistance-wise. Do you know what function the vactrols have the circuit? I have attached images of both places where the two vactrols are used. I also spoke to Matt Harrison (GiveUsYourBones) by email yesterday and he had built the Turbotrem and experienced some issues because of the vactrols.
Any time I have built a Lovetone-like project, I have always used LDRs and LEDs. Not vactrols.
In this case, with the TurboTrem (Lovetone Wobulator) you need to use either Diffused Green or High-Brightness Clear Green (NOT Superbright) LEDs and 10-30K On/20M Off LDRs.
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?
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
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.
Quote from: spacekid71 on April 26, 2023, 12:51:43 PM
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.)
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?
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)
Quote from: Govmnt_Lacky on April 26, 2023, 02:02:25 PM
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:
(https://i.postimg.cc/0z0NvMQT/offboard-wiring-lfo-trig-lfo-pedal.png) (https://postimg.cc/0z0NvMQT)
(https://i.postimg.cc/8JJD7jpP/turbotrem-lfo-trig-lfo-pedal-wiring.jpg) (https://postimg.cc/8JJD7jpP)
Thanks,
Mart
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....
Ah okay, thanks for having a look!
I will reheat those solder joints with flux tonight and see if it helps.
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.
Quote from: Govmnt_Lacky on April 27, 2023, 01:13:34 PM
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.
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
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
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.
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.