Messages

I have a question about the JC120 preamp circuit like the Paladin. The author has included a Direct Out circuit in this. However, for my use it is not necessary and I will not use it. Can I then omit the part as I indicated below and connect the preamp-out jack directly to R19/R20? That's how it happens in the "original" I think too.

Just took a measurement. I still had a BBD Probe from D_H. So I did the measurements with that.
Output signal from the first BBD.


Measured at the same point but raised the amplitude of the input signal. Here it can be seen that the signal is starting to clip. With BIAS 1 adjusted in such a way that it is cut off equally on both sides.


The same point here, but with an even higher overload.


The following points were measured after the second BBD. Same procedures here too.
Here's a clean signal on the output.


Slightly distorted here.


And here it is again distorted. But still neatly symmetrical.


So I think the bias adjustment is done right?!
Then there are the gain settings. This seems to go well for the first stage. Here I get amplification set to 1x between pin 7 of ic6 and pin 7 of ic7 by means of trimmer Gain 1.
But then Gain 2. So when I go through the next step: "Connect your audio probe to pin1 of IC4_A. Adjust the GAIN2
trimmer until the output is the same or slightly above the volume input of pin7 on IC6." Then here's a difference. Where I measure 3.28V on pin 7 of ic 6 and 1.28V on pin 1 of ic 4.
But when I measure between the NE570 compander on pin 7 and on pin 14, I get it properly adjusted to a gain of 1x by means of the Gain 2 trimmer.
Which of the above methods is correct?

Everything looks correct. Is the effect no working properly? I believe that one has a bipolar cap, doesn't it?


Sent from my iPhone using Tapatalk

Yes, it has a bipolar capacitor in it. C35, 2.2uF and and is in the feedback loop of IC9_B.
I have not tested the pedal yet. I want everything to be set up correctly first. So you still have to set trimmers. I wanted to do this with a function generator and oscilloscope. But unfortunately I can't find any instructions for this on Madbean. I found the link to David Morrin on how to calibrate the EH 7850. However, I don't think that description is entirely clear.
So, does anyone here have a step-by-step description of how to set up the trimmers with the oscilloscope?


Edit:
Just trying to calibrate with an audio probe. Followed instructions as stated in the manual. Then connect audio probe to either pin3 or pin4 or IC6. Then I hear a continuous high-pitched beep. When I measure this with my oscilloscope, I see the following picture. Clock signals look good. There is no signal at the input. But I do see a signal around 8.6 kHz. (On pin 4 this is also the same but I see that my measuring cursor is not in the right position, so it does not measure the full period here)
Pin 3 and 4 do differ in amplitude. I should only measure my delayed signal here, right? In this case I shouldn't measure anything as I have no input connected.

Also tested with input signal. Then I indeed hear a delayed signal on pins 3 and 4. But the high frequency predominates.
Please your expertise.

Yes, I also believe that the power supply is fine now. I also have a stable -15.14V after my 7915. So that's good.
But I've added a video, and there you can see why I still have my doubts. As an example I measure here on pin 3 of the MN3005. Now according to the manual I should measure -9.71V. But as can be seen in the video, it is not stable. This also applies to some other voltages.

https://youtu.be/f6O5aHMeq9Y

Just received the adapter. Without load, it therefore supplies more than 30V.
Once connected, it drops to -27.90V.
Then I am left with a voltage at the input of the 7915 that fluctuates around -20.80V.
A stable voltage of -15.14V remains at the output of the 7915.

Next I want to measure and compare the voltage as shown on page 14 of the manual.
If I then measure on pin 1 of ic2, it continues to fluctuate. Just as mentioned before as it does for the regulator. But at a different voltage. These voltages are not stable.
And this is with a lot of pins.
How have others experienced that?

Could it be that in the original, the input voltage is higher so the problem doesn't occur? In combination with the 240 ohm resistor. Say the input of the 7915 must have -18V. At 40mA, that means the incoming power supply should be -27.6V. Now the Memory Man comes standard with a 24V adapter. Now it is often the case that the voltage with an adapter without load is higher than the specified value. And as the load is, the voltage will also drop slightly. But is it plausible that this voltage is higher than the supply voltage I set with my stabilized power supply? Perhaps with a "real" 24V, the resistance value of R57 will have to be lowered.
I also ordered an original adapter which I will receive next week. I'll see what the power supply does then.

I also tested at -20V input voltage, but the problem still persists. There is a voltage drop across R57 that puts the input voltage of the LM7915 on the edge to output a -15V. I think Brian means the regulator input with the -18V. And not the adapter voltage. Otherwise R57 will have to be adjusted I expect. Well, the problem still persists. For the following tests I have set the supply voltage back to 24V

I have the current limiting fully open. So the full 1A can flow there. But only 40mA is consumed.
I measured with my oscilloscope. Here you can clearly see that after R57 a ripple dances on top of the DC voltage.

This is measured on the incoming power supply.


This is measured at the input of the LM7915. Here you can clearly see a pattern showing the fluctuating. Given the period time, this seems to flow from modulation/clock signal?!


And finally a screenshot of the measurement at the incoming power supply and the input of LM7915. Then the difference is clearly visible.

The problem seems to be with the power input.  Take out all the IC's except the power regulator, and verify the following against the build document:
1. Power is wired correctly, this is a positive ground circuit which can be confusing.
2. You're using the recommended power supply.
3. When you apply power, it's the correct polarity and voltage entering the PCB + and - holes.
4. D1 is the right part number, and installed with the proper polarity.
5. R57 is the correct value.
6. Then check the voltage at the regulator input and output.

The dropout voltage of the 15V regulator is about 17V input, so if that's your input voltage, it's on the edge of dropping out, that's probably why the power is responding to the draw of the circuit.

1. Power is wired correctly, this is a positive ground circuit which can be confusing.
2. You're using the recommended power supply.
3. When you apply power, it's the correct polarity and voltage entering the PCB + and - holes.
Yes, see attached image



4. D1 is the right part number, and installed with the proper polarity.
Yes, a 30V zener diode

5. R57 is the correct value.
Yes, 240R


6. Then check the voltage at the regulator input and output.
They were discussed in my previous post

Okay, here we go. Here are some measurements. To start with all ICs removed.
Then the voltages are stable and appear to be correct.
Then I put IC9 back. Then the voltage fluctuations appear on the input pin of the 7915. The voltage after R57 also drops a bit. However, the voltage is still so high that the voltage on the output of the regulator remains stable at -15V. Then I keep putting an IC back and do another measurement. The voltage at the input of the regulator continues to fluctuate and drops downwards. Until all ICs are inserted. From that moment on, the voltage has dropped so far that the output of the 7915 also fluctuates.

Finally, a measurement was made with all ICs except IC9. Then the fluctuating is gone. Voltage has still dropped too far. Then another test except with the IC8 and IC9. Then you can see that the voltage is rising again.

Basically, the voltage drops as the number of ICs increases. And IC9 ensures, among other things, a varying voltage on the input of the regulator.

Thanks for the quick responses.
The power supply is a well-known (by Dutch standards) Delta Elektronika E030-1. This power supply is known for its good performance. I'm assuming that's not the problem here.

The voltage on one side of resistor R57 remains constant (-24.3V). There is an error on the side connected to the zener diode and the LM7915.
What is the reason for this zener? At a voltage of -24V, this zener will still do nothing, since it has a working voltage of 30V. Doesn't this protect the LM7915 only if the offered voltage is higher than 30V?
Could I remove it for the test?
I will take pictures of the test setup tonight and measure the whole thing without ICs.

Another question. The wires from the chorus/vibrato switch run along the power supply wires. Could this also be of some influence?

The voltage on the input of 7915 regulator is much low. It also seems to fluctuate on the clock signal. I put 24.3V on the power input (it remains stable). After R57 there remains a voltage that fluctuates between -17.58V and -17.84V (with delay knob fully open).
When I turn the delay knob all the way down, -15.13V and -15.35V remain. In short, the voltage after R57 responds to the clock.
When I remove IC9, I am left with a stable voltage of -18.42V to R57. This one is stable.
However, this voltage is still too low if I may believe the manual. This indicates that the voltage on the input of the 7915 must be -25.57V.
So, what's wrong here. Does anyone have an idea?

I managed to file the hole bigger. This allowed me to position the jack higher. Now it should fit just right. I'm still waiting for a few parts and then I can solder the potentiometers. Then I can fit and measure exactly.

I'm working on my Total Recall project. And now I run into the problem that the input jack gets stuck against LM7906. This is of course not the intention.
I can filing the holes for the jacks up a bit, so that I can slide the jacks up a bit. Or I have to extend the LM7906 with wires and move it to another position. Or eventually get a different housing. But it would be nice if it fits in here. I have a BB casing. Are there others who have had this problem?

Tanx!!

Is it possible to share this decal/graphics? The link referenced is dead.