J. Rockett Audio Designs - Lemon Aid [traced]
- TWSpedals
- Breadboard Brother
Had one of these in for repair today.
Traced it out and found it had a very interesting current mirror topology. I'm not going to pretend to know what exactly is going on here but it's probably the most original gain stage in a pedal I've seen in a while. It's worth noting that there is no filter cap or polarity protection at all.
The pedal is loud, very clean, very stiff, and a little sterile which makes sense with the hifi/SS amp theory being utilised here. I don't find the cut switch useful at all. The pedal feels at home to me pushing an amp or drive pedal.
Have a nice day, Tom.
Traced it out and found it had a very interesting current mirror topology. I'm not going to pretend to know what exactly is going on here but it's probably the most original gain stage in a pedal I've seen in a while. It's worth noting that there is no filter cap or polarity protection at all.
The pedal is loud, very clean, very stiff, and a little sterile which makes sense with the hifi/SS amp theory being utilised here. I don't find the cut switch useful at all. The pedal feels at home to me pushing an amp or drive pedal.
Have a nice day, Tom.
Have a nice day!
- gigelmargel
- Resistor Ronker
Hello, Tom!
Looking at the schematic, I am not sure that I understood the connections of the boost switch (I am not very good at reading schematics).
Please, can you write the numbers of the boost switch pins on the schematic? Usually, I saw that the pins of this kind of switch are numbered in this way:
1 - 4
2 - 5
3 - 6
I assume that in one position only the 1.5uF is connected, in the middle position no cap is connected and in other position only the 10uF is connected, but I am not sure (it seems to me that the 10uF is connected in parallel with the 10uF).
Thank you very much!
Looking at the schematic, I am not sure that I understood the connections of the boost switch (I am not very good at reading schematics).
Please, can you write the numbers of the boost switch pins on the schematic? Usually, I saw that the pins of this kind of switch are numbered in this way:
1 - 4
2 - 5
3 - 6
I assume that in one position only the 1.5uF is connected, in the middle position no cap is connected and in other position only the 10uF is connected, but I am not sure (it seems to me that the 10uF is connected in parallel with the 10uF).
Thank you very much!
- TWSpedals
- Breadboard Brother
My mistake. This is the actual layout. I don't know why they put the 10u and 1.5u in parallel, it's not much of a jump up in value from 10ugigelmargel wrote: ↑10 May 2021, 09:07 Hello, Tom!
Looking at the schematic, I am not sure that I understood the connections of the boost switch (I am not very good at reading schematics).
Please, can you write the numbers of the boost switch pins on the schematic? Usually, I saw that the pins of this kind of switch are numbered in this way:
1 - 4
2 - 5
3 - 6
I assume that in one position only the 1.5uF is connected, in the middle position no cap is connected and in other position only the 10uF is connected, but I am not sure (it seems to me that the 10uF is connected in parallel with the 10uF).
Thank you very much!
Have a nice day!
- gigelmargel
- Resistor Ronker
Thank you very much, Tom! It's very clear now and as I supposed
I think that I will use a simple 1P3T instead of 2P3T because, as you said, there is a small difference between 10uF and 11.5 uF.
I think that I will use a simple 1P3T instead of 2P3T because, as you said, there is a small difference between 10uF and 11.5 uF.
- bmxguitarsbmx
- Cap Cooler
Pretty cool circuit! My hat off to a company trying something.
- gigelmargel
- Resistor Ronker
I finished my clone, but it's not working. Only a strong synth-like squelch. All pots and switches seems to work. I used 2N5484 instead of 2N5485 (no chance to find ones here). This could be a problem?
- TWSpedals
- Breadboard Brother
They do have different VGSoff value ranges so that may be an issue. If there's any external DC on the input that may also be a factor (maybe use a decoupling cap to be sure for now. I'll double check the schematic as I still have the pedal with me, though I don't think there's any errors beyond the boost switch one I corrected.gigelmargel wrote: ↑11 May 2021, 12:26 I finished my clone, but it's not working. Only a strong synth-like squelch. All pots and switches seems to work. I used 2N5484 instead of 2N5485 (no chance to find ones here). This could be a problem?
Have a nice day!
- gigelmargel
- Resistor Ronker
I have some doubts regarding the Cut switch: in one position the resistance from gate of 2N5485 to ground is 10K and in the other one is around 100K. Both are much lower than the value of 1M that I usually saw in other schematics (but it's possible that I am wrong, because I don't have many knowledges about electronics).
If you can and/or if you have time, maybe you can post the voltages of the transistors. Thank you very much!
If you can and/or if you have time, maybe you can post the voltages of the transistors. Thank you very much!
- TWSpedals
- Breadboard Brother
Cut switch is correct, I'm aware it's not the standard values for a JFET gate, as I said I don't see much point in it.gigelmargel wrote: ↑11 May 2021, 20:05 I have some doubts regarding the Cut switch: in one position the resistance from gate of 2N5485 to ground is 10K and in the other one is around 100K. Both are much lower than the value of 1M that I usually saw in other schematics (but it's possible that I am wrong, because I don't have many knowledges about electronics).
If you can and/or if you have time, maybe you can post the voltages of the transistors. Thank you very much!
Voltages for the FETs are as follows
FET 1: Gate = 0V, Source = 2.5V, Drain = 8.6V
FET 2: Gate = 0V, Source = 1.9V Drain = 8.5V
Have a nice day!
- bmxguitarsbmx
- Cap Cooler
Series feedback amplifiers are tough to bias up sometimes. I'm almost thinking these would need to be matched FET's. Though, getting the right part number may get you close enough.
What is the voltage at the output transistors (2n3906)?
The FET drains will be locked at essentially the forward voltage of the 2n3906. (Supply voltage - (diode drop + the emitter resistor voltage drop))
What is the voltage at the output transistors (2n3906)?
The FET drains will be locked at essentially the forward voltage of the 2n3906. (Supply voltage - (diode drop + the emitter resistor voltage drop))
- gigelmargel
- Resistor Ronker
Thank you, Tom!TWSpedals wrote: ↑12 May 2021, 15:24Cut switch is correct, I'm aware it's not the standard values for a JFET gate, as I said I don't see much point in it.gigelmargel wrote: ↑11 May 2021, 20:05 I have some doubts regarding the Cut switch: in one position the resistance from gate of 2N5485 to ground is 10K and in the other one is around 100K. Both are much lower than the value of 1M that I usually saw in other schematics (but it's possible that I am wrong, because I don't have many knowledges about electronics).
If you can and/or if you have time, maybe you can post the voltages of the transistors. Thank you very much!
Voltages for the FETs are as follows
FET 1: Gate = 0V, Source = 2.5V, Drain = 8.6V
FET 2: Gate = 0V, Source = 1.9V Drain = 8.5V
My voltages are the following (bolded):
Battery: 8.85 V
FET 1: Gate = 0V / 0V, Source = 1.45V / 2.5V, Drain = 7.83V / 8.6V
FET 2: Gate = 0V / 0V, Source = 1.87V / 1.9V, Drain = 7.87V / 8.5V
My voltages seems to be closed to yours, excepting the source of FET 1. I tested and the squelch is present at the source of FET 1, so maybe I will find the error
- gigelmargel
- Resistor Ronker
I wrote on the schematic all my voltages:
- gigelmargel
- Resistor Ronker
I have no chance to find 2N5485 herebmxguitarsbmx wrote: ↑12 May 2021, 17:01 I'm almost thinking these would need to be matched FET's. Though, getting the right part number may get you close enough.
I will search in datasheets for a closer equivalent.
- TWSpedals
- Breadboard Brother
The voltages at the collectors of the 2nd and 4th 2n3906 transistors in the unit I traced are as follows:
Q3: 5.75V
Q6: 4.3V
Hope this helps you. Though I do fear that it's a case of starting with the right FETs and going from there.
Q3: 5.75V
Q6: 4.3V
Hope this helps you. Though I do fear that it's a case of starting with the right FETs and going from there.
Have a nice day!
- gigelmargel
- Resistor Ronker
It seems that you are right, Tom
Thank you very much for your help!
- gigelmargel
- Resistor Ronker
I replaced the 2N5484 with other FETs (BF256 and 2SK30A), but with no luck. I got the same squelch. I recheck all for 2 times and it seems to be OK.
- Manfred
- Tube Twister
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I ran a simulation with some JFET types, only the 2N4221 and the 2N3822 came with the DC voltage values close to the read values with the 2N5485,
the diffrences were about 15% to 20%. Unfortunately, the two types are difficult to get and if then at very high prices.
There seems to be no suitable replacement type for the 2N5485.
the diffrences were about 15% to 20%. Unfortunately, the two types are difficult to get and if then at very high prices.
There seems to be no suitable replacement type for the 2N5485.
- Manfred
- Tube Twister
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I just ran another simulation with the BF256 you have ruled out and found that the BF256B gives the same DC voltage values as the 2N5458.
BF256A and BF256C did not work.
Due to the large variations of the JFETs even in the same selection group, one must select the appropriate types.
BF256A and BF256C did not work.
Due to the large variations of the JFETs even in the same selection group, one must select the appropriate types.