J. Rockett Audio Designs - Lemon Aid  [traced]

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gigelmargel
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Post by gigelmargel »

TWSpedals wrote: 15 May 2021, 07:48 Have you considered depletion mode MOSFETs like the LND150?
No, because I don't have ones. Maybe I will try to find ones.

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gigelmargel
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Post by gigelmargel »

Manfred wrote: 15 May 2021, 07:52 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.
Thank you very much, Manfred!
I will try to find some BF256B here or I will buy some 2N5485.
How do you run the simulation?

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gigelmargel
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Post by gigelmargel »

This is the layout that I used, very kindly designed by fuzzhead from http://dirtboxlayouts.blogspot.com/. Many thanks, fuzzhead! :applause:

Rockett Lemon Aid.png
Boost switch it's not wired as in the layout (Boost SW2&5) is one row below.

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gigelmargel
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Post by gigelmargel »

I've just tested it with BF256B (I remembered that I have 4 in a amp simulator), but no change...same squelch!!! :roll:

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Post by Manfred »

How do you run the simulation?
I use an obsolete Version of Multisim.
I've just tested it with BF256B (I remembered that I have 4 in a amp simulator), but no change...same squelch!!!
What DC-voltage values did you read using the BF256B?

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Post by gigelmargel »

What DC-voltage values did you read using the BF256B?
Battery: 8.85
FET 1 (GSD): 0 V / 2.6 V / 7.6 V
FET 2 (GSD): 0 V / 2.8 V / 7.6 V
Collectors of second 2N3906 from every pair: 6.20 V / 5.47 V

Thank you, Manfred!

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Post by Manfred »

gigelmargel wrote: 16 May 2021, 08:39 Battery: 8.85
FET 1 (GSD): 0 V / 2.6 V / 7.6 V
FET 2 (GSD): 0 V / 2.8 V / 7.6 V
Collectors of second 2N3906 from every pair: 6.20 V / 5.47 V
Thanks, Gigelmargel
I should not trust everything.
I looked at the model data of the BF256B where it says BC264 in the header.
I ran the simulation with the BC264C and got the same values.
This BC264C is unfortunately also not available at trustworthy dealers, so in the end really only the 2N5485 remains.

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Post by gigelmargel »

Thank you very much, Manfred!
I will recheck all, because I think that I made a mistake. I can't understand why the circuit squelches, because, only from my experience (without a serious electronic knowledge), I never saw a FET (or other transistor) squelching like a synth because it's unbiased. With all the FETs that I tested it, all the pots and switches works OK, but the guitar is barely audible because of the squelch. Mainly, this squelch appears when I made some shortcuts between output and input.
Meanwhile, I will try to buy some 2N5485 :)

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Post by bmxguitarsbmx »

You should be able to use any FET. You will need to re-bias. The thing about series feedback designs is that biasing it up is like a circular process. The current through the Jfet controls the current through the 2n3906, which adds a voltage to the FET source, which changes the current through the j-FET. Stick it on the breadboard and let it rip. Might even be as simple as changing emitters resistors. I don't know!

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Post by gigelmargel »

I measured almost all my FETs (including some BF245B which I found that are a good replacement for BC264C) and I found two 2N3819 that are very close to 2N5485 specifications: IDSS around 3mA (2N5485 has a minimum of 4mA, but I didn't find one) and VGS(off) around 2V (2N5485 has between 0.5 and 4V). Unfortunately, only the same squelch :slap:

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Post by gigelmargel »

Hello, again!

I bought some 2N5485 from banzai, but the effect didn't work. To be clear, it makes the same squelch as when I used other FETs. The voltages are almost the same as the ones with BF256B.

I think that it could be a problem with the layout, even I checked it 10 times :(

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Post by gigelmargel »

I rechecked the vero and my build and both seems to be OK. Could someone to recheck the schematic?
Thank you a lot!

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Post by TWSpedals »

Sadly I don't have the pedal with me anymore. But I went over the PCB enough to know I didn't make mistake in the trace. That being said I'm not going to rule out that a value somewhere could be incorrect. So someone else who has access to the original pedal will have to wade in here, untill that happens it appears it's a deadend for now unfortunately.
Have a nice day!

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Post by TWSpedals »

gigelmargel wrote: 05 Jul 2021, 04:14 I rechecked the vero and my build and both seems to be OK. Could someone to recheck the schematic?
Thank you a lot!
Just a thought, looking at your voltages again. Is the 2.2uF in the tone control leaky? That Q3 collector voltage is low. That 1.5K between your Q1 source and Q3 collector, maybe try increasing that too.
Have a nice day!

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gigelmargel
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Post by gigelmargel »

TWSpedals wrote: 05 Jul 2021, 06:19
gigelmargel wrote: 05 Jul 2021, 04:14 I rechecked the vero and my build and both seems to be OK. Could someone to recheck the schematic?
Thank you a lot!
Just a thought, looking at your voltages again. Is the 2.2uF in the tone control leaky? That Q3 collector voltage is low. That 1.5K between your Q1 source and Q3 collector, maybe try increasing that too.
I will check as soon as I will have some time...

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Post by gigelmargel »

Using 2 pieces of 2N5952 I obtained exactly the voltages posted by TWSpedals...unfortunately, the squelch is the same...I have no idea what to o do...

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