I've reflowed a half dozen times, I've checked components about that many times. Voltages on the right top are off and it won't swell, what am I missing?
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Did you do the stock build or follow the variations found page 7 of the build document? (Opamp substitutions? Opto-Coupler used? FETs used? 20K trimmer or 22K resistor? Value of C25? (Although the C25 question is likely not part of the problem.)
I have a VFE Bumble Bee in build queue, and while I've not yet gotten to the building part, I have been researching all the info I can find on the SG-1 circuit. There is a lot of concurrence that the following parts (numbers based on the schematic of this particular build) should be closely matched:
• R17 & R32 (4K7 Ω)
• C20 & C21 (1µF)
• D3 & D4 (1N914)
• R33 & R34 (100k Ω)
• Q6 & Q7 (2N3904)
What are the actual measured voltages for your 2N3904 Qs?
Quote from: Cybercow on May 24, 2020, 10:49:53 PM
Did you do the stock build or follow the variations found page 7 of the build document? (Opamp substitutions? Opto-Coupler used? FETs used? 20K trimmer or 22K resistor? Value of C25? (Although the C25 question is likely not part of the problem.)
I have a VFE Bumble Bee in build queue, and while I've not yet gotten to the building part, I have been researching all the info I can find on the SG-1 circuit. There is a lot of concurrence that the following parts (numbers based on the schematic of this particular build) should be closely matched:
• R17 & R32 (4K7 Ω)
• C20 & C21 (1µF)
• D3 & D4 (1N914)
• R33 & R34 (100k Ω)
• Q6 & Q7 (2N3904)
What are the actual measured voltages for your 2N3904 Qs?
Wow, I didn't realize the pictures didn't post. Fixed. Voltages are listed, trim pot used. Madbean stock.
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I don't see your measured voltages listed anywhere. However in the photo, I do see two questionable solder joints - lower-right area and mid-lower-center area. (Circled in red.)
And considering there are several socketed components, (always a good idea), have you ensured all the legs of those devices are sitting snuggly in their respective sockets? Sometimes, I have to "wrinkle" the ends of the legs a bit to get them to fit snuggly.
Quote from: Cybercow on May 25, 2020, 01:51:35 AM
I don't see your measured voltages listed anywhere. However in the photo, I do see two questionable solder joints - lower-right area and mid-lower-center area. (Circled in red.)
And considering there are several socketed components, (always a good idea), have you ensured all the legs of those devices are sitting snuggly in their respective sockets? Sometimes, I have to "wrinkle" the ends of the legs a bit to get them to fit snuggly.
Hey thanks , I'm sorry about that, I don't know what's wrong with me tonight. I chose the voltages as one of the uploads. I got it this time. I'll run over those solder joints again, thank you.
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Hmm, I haven't built this one yet and so I haven't studied it very much but the build doc talks about the trim pots being used to bias the jfets so it seems where you have the trim pots(s) set may affect those voltages that are off. Not sure, just throwing it out there
One of the things I've noted about this (and some other VFE build docs) build document is that the PCB nor the build docs identify the part numbers - only the values. The only way to assure one is correctly referencing (correlating) any specific part between the schematic, the PCB and\or the build document images, is to do some circuit-tracing. Which a is PITA. At least the one image with the blue & red traces is helpful in that regard.
Quote from: Cybercow on May 25, 2020, 11:11:12 PM
One of the things I've noted about this (and some other VFE build docs) build document is that the PCB nor the build docs identify the part numbers - only the values. The only way to assure one is correctly referencing (correlating) any specific part between the schematic, the PCB and\or the build document images, is to do some circuit-tracing. Which a is PITA. At least the one image with the blue & red traces is helpful in that regard.
I agree. I was just thinking about that. I just sat here and looked at that diagram and compared it to the picture. I still don't see any wrong parts.
Quote from: Aentons on May 25, 2020, 07:52:33 PM
Hmm, I haven't built this one yet and so I haven't studied it very much but the build doc talks about the trim pots being used to bias the jfets so it seems where you have the trim pots(s) set may affect those voltages that are off. Not sure, just throwing it out there
While the 20K trimpot does indeed adjust the FET (Q2) in this circuit, the off-voltages are exhibited by what appears to be the 2N3904 transistors in the detection section of the circuit (Q5, Q6 & Q7) as indicated in jimilee's posted voltage readings. There seems to be no simple tweaking for the 2N3904 transistors.
Of the 3 trimpots on this PCB, the 20K is for the rough swell adjustment; 50K for the bass adjustment; and 100K to fine tune the swell adjustment.
Quote from: Cybercow on May 26, 2020, 01:04:37 PM
Quote from: Aentons on May 25, 2020, 07:52:33 PM
Hmm, I haven't built this one yet and so I haven't studied it very much but the build doc talks about the trim pots being used to bias the jfets so it seems where you have the trim pots(s) set may affect those voltages that are off. Not sure, just throwing it out there
While the 20K trimpot does indeed adjust the FET (Q2) in this circuit, the off-voltages are exhibited by what appears to be the 2N3904 transistors in the detection section of the circuit (Q5, Q6 & Q7) as indicated in jimilee's posted voltage readings. There seems to be no simple tweaking for the 2N3904 transistors.
Of the 3 trimpots on this PCB, the 20K is for the rough swell adjustment; 50K for the bass adjustment; and 100K to fine tune the swell adjustment.
Yep. I'm starting to wonder if the b100 pot is bad. It seems to be the only common denominator, but I'm not sure if I'm in the right track.
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Anybody got any ideas?
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Have you tried a different JFET? I believe the device there has a pretty narrow operating window. That may be why your voltages are off. Check out some of the discussions in re the slow gear for the particulars there. Also, what is the emitter voltage for Q4? The build doc says 0v, but that should be ~1/2Vcc.
Quote from: benny_profane on May 26, 2020, 10:54:26 PM
Have you tried a different JFET? I believe the device there has a pretty narrow operating window. That may be why your voltages are off. Check out some of the discussions in re the slow gear for the particulars there. Also, what is the emitter voltage for Q4? The build doc says 0v, but that should be ~1/2Vcc.
Yep, I checked. The 5457 measures 3.1, above the 1.75 mark, but would the 5457 and the 3809s measure property?
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Quote from: jimilee on May 26, 2020, 11:35:35 PM
Quote from: benny_profane on May 26, 2020, 10:54:26 PM
Have you tried a different JFET? I believe the device there has a pretty narrow operating window. That may be why your voltages are off. Check out some of the discussions in re the slow gear for the particulars there. Also, what is the emitter voltage for Q4? The build doc says 0v, but that should be ~1/2Vcc.
Yep, I checked. The 5457 measures 3.1, above the 1.75 mark, but would the 5457 and the 3809s measure property?
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I'm not sure what you're saying here. Can you test the Vgs of the JFET? I'm pretty sure you're looking for Vgs ~= 1.25–1.5V.
Quote from: benny_profane on May 27, 2020, 12:08:38 AM
Quote from: jimilee on May 26, 2020, 11:35:35 PM
Quote from: benny_profane on May 26, 2020, 10:54:26 PM
Have you tried a different JFET? I believe the device there has a pretty narrow operating window. That may be why your voltages are off. Check out some of the discussions in re the slow gear for the particulars there. Also, what is the emitter voltage for Q4? The build doc says 0v, but that should be ~1/2Vcc.
Yep, I checked. The 5457 measures 3.1, above the 1.75 mark, but would the 5457 and the 3809s measure property?
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I'm not sure what you're saying here. Can you test the Vgs of the JFET? I'm pretty sure you're looking for Vgs ~= 1.25–1.5V.
Sorry, yes. The VGS measures 3.1. Would that stop the 3904 trannies at the top on the right and the one below it from measuring properly? I've got more 5457s on order.
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Like benny said the proper VGS of Q2 is critical to make the effect work. But, I don't think using one out of spec for the build will throw off voltages for the 2n3904 at all.
Worse comes to worst, I might be able to dig up a proper spec'd 2n5457 for you if your new batch doesn't pan out.
Quote from: madbean on May 27, 2020, 12:29:48 AM
Like benny said the proper VGS of Q2 is critical to make the effect work. But, I don't think using one out of spec for the build will throw off voltages for the 2n3904 at all.
Worse comes to worst, I might be able to dig up a proper spec'd 2n5457 for you if your new batch doesn't pan out.
Thanks to you both. I really didn't think it would but I don't know how the two effects are configured to work with each other.
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JimiLee - "Sorry, yes. The VGS measures 3.1. Would that stop the 3904 trannies at the top on the right and the one below it from measuring properly? I've got more 5457s on order. "
The FET Vgs needs to be between 1.25 and 1.5 as indicated in the build docs. But the poor FET performance should not be responsible for the incorrect voltages of the trigger sensor section BJTs (2N3904s). What are the voltage output of the switching board PCB? It should be a dual rail at ±15v. Have you verified that?
Quote from: Cybercow on May 27, 2020, 12:57:17 PM
JimiLee - "Sorry, yes. The VGS measures 3.1. Would that stop the 3904 trannies at the top on the right and the one below it from measuring properly? I've got more 5457s on order. "
The FET Vgs needs to be between 1.25 and 1.5 as indicated in the build docs. But the poor FET performance should not be responsible for the incorrect voltages of the trigger sensor section BJTs (2N3904s). What are the voltage output of the switching board PCB? It should be a dual rail at ±15v. Have you verified that?
I have, but I didn't write it down. I'll get it to you in a bit. I was wondering about that.
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Quote from: Cybercow on May 27, 2020, 12:57:17 PM
JimiLee - "Sorry, yes. The VGS measures 3.1. Would that stop the 3904 trannies at the top on the right and the one below it from measuring properly? I've got more 5457s on order. "
The FET Vgs needs to be between 1.25 and 1.5 as indicated in the build docs. But the poor FET performance should not be responsible for the incorrect voltages of the trigger sensor section BJTs (2N3904s). What are the voltage output of the switching board PCB? It should be a dual rail at ±15v. Have you verified that?
The v+ is 8.05 and the v- is -7.45.
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Quote from: jimilee on May 27, 2020, 01:49:57 PM
The v+ is 8.05 and the v- is -7.45.
OK, the supply seems fine. (I mis-stated the ±15v previously, it should be closer to ±9v like you have.)
Q5 seems to have near enough correct voltages, but Q6 & Q7 are far too low. Those 2N3904 collectors (Q6 & Q7) should be at around 5.9v. Did you set the switch in the middle position, the Mix control all the way counter-clockwise and the other controls centered?
What voltages do you get when you remove the 2N5457 & 2N3904s (Q6 & Q7) from their sockets? Please try that and report your voltages.
Quote from: Cybercow on May 27, 2020, 03:20:32 PM
Quote from: jimilee on May 27, 2020, 01:49:57 PM
The v+ is 8.05 and the v- is -7.45.
OK, the supply seems fine. (I mis-stated the ±15v previously, it should be closer to ±9v like you have.)
Q5 seems to have near enough correct voltages, but Q6 & Q7 are far too low. Those 2N3904 collectors (Q6 & Q7) should be at around 5.9v. Did you set the switch in the middle position, the Mix control all the way counter-clockwise and the other controls centered?
What voltages do you get when you remove the 2N5457 & 2N3904s (Q6 & Q7) from their sockets? Please try that and report your voltages.
I knew what you meant with the voltages, its all good.
Yep, switch is in the middle and voltages don't change with the 5457 removed. The only way I can get the voltages to change is with the 100k trim pit.
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Did you remove Q6 & Q7 (2N3904s) also? The ones with the low voltages?
And something is definitely wrong if the 100K Tweak trimmer is changing the voltage on the collectors of Q6 & Q7. C4 is supposed to isolate them from ground.
Quote from: Cybercow on May 27, 2020, 03:48:13 PM
Did you remove Q6 & Q7 (2N3904s) also? The ones with the low voltages?
And something is definitely wrong if the 100K Tweak trimmer is changing the voltage on the collectors of Q6 & Q7. C4 is supposed to isolate them from ground.
I didn't remove them no. Are you talking about to check the 5457 after they're removed? When I turn the tweak trimmer all the way down, the 5457 and q6 an 7 voltages are where they should be. So C4 is the isolater, the 2.2u
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JimiLee - that 2µ2 cap is actually C14. I was referring to C4 (0.68µF) - it's always connected. C5 & C4 are actuated via the toggle switch. And never mind the bit about pulling the FET or any transistors. The following should help.
Have you gone thru this part of the setup procedure (#4 from page 7)? - - - - "4) To set up the swell effect do the following: set the switch in its middle position, the MIX knob all the way counter-clockwise and all other pots to their middle position. Leave TWEAK in the center and the 20k trimmer all the way down. Now, adjust the 20k trimmer clockwise until you hear notes start to swell up in volume. Continue adjusting it until the volume of the swell matches your input. From there, you can adjust the TWEAK trimmer to re-tune. In my build, the 20k is set at about 11 o'clock and the TWEAK trimmer pretty much in the middle."
What occurs to me is that the voltages are to be measured with the above mentioned settings. Mind you please, that this is an assumption on my part as it is not clear at what settings things should be when measuring the voltages.
So, if you're getting proper voltages on the collectors of Q6 & Q7 with the 20K trimmer turned all the way down (counter-clockwise), then you should be able to get it swell by following the instructions in #4 on page 7 as noted above.
Quote from: Cybercow on May 27, 2020, 06:20:09 PM
JimiLee - that 2µ2 cap is actually C14. I was referring to C4 (0.68µF) - it's always connected. C5 & C4 are actuated via the toggle switch. And never mind the bit about pulling the FET or any transistors. The following should help.
Have you gone thru this part of the setup procedure (#4 from page 7)? - - - - "4) To set up the swell effect do the following: set the switch in its middle position, the MIX knob all the way counter-clockwise and all other pots to their middle position. Leave TWEAK in the center and the 20k trimmer all the way down. Now, adjust the 20k trimmer clockwise until you hear notes start to swell up in volume. Continue adjusting it until the volume of the swell matches your input. From there, you can adjust the TWEAK trimmer to re-tune. In my build, the 20k is set at about 11 o'clock and the TWEAK trimmer pretty much in the middle."
What occurs to me is that the voltages are to be measured with the above mentioned settings. Mind you please, that this is an assumption on my part as it is not clear at what settings things should be when measuring the voltages.
So, if you're getting proper voltages on the collectors of Q6 & Q7 with the 20K trimmer turned all the way down (counter-clockwise), then you should be able to get it swell by following the instructions in #4 on page 7 as noted above.
Yep, did the setup thing. Lemme ask you this, Brian said I didn't have to use a polarized cap for the .68u. Not doing so would then not isolate anything from ground if I'm right.
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JimiLee - no. The 0.68µF cap will DC isolate whether it is polarized or not.
If you did the setup thing, then, (IMO) the only thing(s) left to look at is the original postulation I made where "matching" those specific components in the sensor trigger section are crucial.
As a recap, those specific components to match are:
• R17 & R32 (4K7 Ω)
• C20 & C21 (1µF)
• D3 & D4 (1N914)
• R33 & R34 (100k Ω)
• Q6 & Q7 (2N3904)
I'll keep my eye on this thread just see what else you might discover. I have little else to offer at this point.
Quote from: Cybercow on May 27, 2020, 07:16:00 PM
JimiLee - no. The 0.68µF cap will DC isolate whether it is polarized or not.
If you did the setup thing, then, (IMO) the only left to look at is the original postulation I made where "matching" those specific components in the sensor trigger section are crucial.
As a recap, those specific components to match are:
• R17 & R32 (4K7 Ω)
• C20 & C21 (1µF)
• D3 & D4 (1N914)
• R33 & R34 (100k Ω)
• Q6 & Q7 (2N3904)
I'll keep my eye on this thread just see what else you might discover. I have little else to offer at this point.
Thank you for all of your help.
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Have you been able to accrue any progress on this pedal? Anything new to report?
Quote from: Cybercow on May 28, 2020, 05:47:07 PM
Have you been able to accrue any progress on this pedal? Anything new to report?
Nope, not yet.
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Quote from: madbean on May 27, 2020, 12:29:48 AM
Like benny said the proper VGS of Q2 is critical to make the effect work. But, I don't think using one out of spec for the build will throw off voltages for the 2n3904 at all.
Worse comes to worst, I might be able to dig up a proper spec'd 2n5457 for you if your new batch doesn't pan out.
I feel like R17 and the resistor below it are swapped the build doc, am I wrong? The schematic and your numbering of the boardhas r17 4.7k below the 1n cap the silkscreen has the 39k there.
Quote from: jimilee on June 01, 2020, 07:47:39 PM
I feel like R17 and the resistor below it are swapped the build doc, am I wrong? The schematic and your numbering of the boardhas r17 4.7k below the 1n cap the silkscreen has the 39k there.
JimiLee - Wow! Great catch! That does look like they are swapped between the schematic, the parts ID image and the silkscreen. R17 (4K7 in the schematic & BOM) does indeed go to the emitter of Q5 (2N3904) - according to the red & blue trace image. And R20 (39K) is supposed to feed the base of Q5 (2N3904). But the silkscreen has those two resistors R17 (4K7) and R20 (39K) interchanged. That would certainly foul the swell. If there's a 39K resistor on the emitter of Q5 and a 4K7 resistor on the collector of Q5, the whole detection circuit is out of balance.
The 39K resistor should be above the 4K7 resistor where the part ID image says R17 & R20. Still, the silkscreen on the PCB is correct - with the 4K7 resistor going to the emitter. So I would not put that much stock in the part ID image. I think the Part ID image may off for those two resistors.
What value do you have on top position (referring to those two resistors)?
Brian covered this in the setup part of the build doc but there is a slight discrepancy in the patreon bundle notes that I though I might point out just in case.
The vfe bundle notes state:
"do not install the JFET trimpot. Instead, install a jumper between the left-middle pin of that trimpot and its bottom pin. Use the TWEAK trimpot to fine tune the swell response"
So, it looks like you put a jfet trim pot there, and in your pic it looks cranked all the way over to pin 3, which I think is all the way up. Make sure its all the way down to start.
Also, not sure this matters either, just throwin it out there... the 3362 datasheet says:
-----------------------------
Absolute Minimum Resistance
.................................... 1 % or 2 ohms
(whichever is greater)
-----------------------------
https://www.mouser.com/datasheet/2/54/3362-776956.pdf
So, you are not starting at zero, you are starting at 200 ohms minimum.
Did you try swapping the JFET for one in the range indicated? I may have missed it if you did.
Quote from: Aentons on June 02, 2020, 12:03:13 AM
Brian covered this in the setup part of the build doc but there is a slight discrepancy in the patreon bundle notes that I though I might point out just in case.
The vfe bundle notes state:
"do not install the JFET trimpot. Instead, install a jumper between the left-middle pin of that trimpot and its bottom pin. Use the TWEAK trimpot to fine tune the swell response"
So, it looks like you put a jfet trim pot there, and in your pic it looks cranked all the way over to pin 3, which I think is all the way up. Make sure its all the way down to start.
Also, not sure this matters either, just throwin it out there... the 3362 datasheet says:
-----------------------------
Absolute Minimum Resistance
.................................... 1 % or 2 ohms
(whichever is greater)
-----------------------------
https://www.mouser.com/datasheet/2/54/3362-776956.pdf
So, you are not starting at zero, you are starting at 200 ohms minimum.
Nope, I missed the part where he says not to use the trimpot, use a jumper. On page 7, he says to use the trimpot. Where did you say that was again?
Quote from: Cybercow on June 01, 2020, 09:27:53 PM
Quote from: jimilee on June 01, 2020, 07:47:39 PM
I feel like R17 and the resistor below it are swapped the build doc, am I wrong? The schematic and your numbering of the boardhas r17 4.7k below the 1n cap the silkscreen has the 39k there.
JimiLee - Wow! Great catch! That does look like they are swapped between the schematic, the parts ID image and the silkscreen. R17 (4K7 in the schematic & BOM) does indeed go to the emitter of Q5 (2N3904) - according to the red & blue trace image. And R20 (39K) is supposed to feed the base of Q5 (2N3904). But the silkscreen has those two resistors R17 (4K7) and R20 (39K) interchanged. That would certainly foul the swell. If there's a 39K resistor on the emitter of Q5 and a 4K7 resistor on the collector of Q5, the whole detection circuit is out of balance.
The 39K resistor should be above the 4K7 resistor where the part ID image says R17 & R20. Still, the silkscreen on the PCB is correct - with the 4K7 resistor going to the emitter. So I would not put that much stock in the part ID image. I think the Part ID image may off for those two resistors.
What value do you have on top position (referring to those two resistors)?
I have a 39k in the r17 position instead of a 4.7k
Quote from: benny_profane on June 02, 2020, 12:54:43 AM
Did you try swapping the JFET for one in the range indicated? I may have missed it if you did.
Not yet, I was working on getting my voltage right. The Jfets that came on Saturday were all below Spec. I figured I'd try to get the voltages right before I put too much more into the jfets. I've been working on some other stuff in the mean time.
Brian's build doc (page 7) has this:
-----------------------
3. Peter recommended not installing the 20k trim and using a fixed 22k resistor in its place. Don't do this. Use the trimmer! I built two Bumblebees, one with the resistor and one with the trimmer. I could not get the swell to work using the fixed resistor method (and that was with a pre-tested 2n5457). IMO, the 20k trimmer is essential to getting this to work optimally. It may be he used JFETs with a very narrow cut-off range and was able to get away with the fixed resistor. But, my experience was different.
4. To set up the swell effect do the following: set the switch in its middle position, the MIX knob all the way counter-clockwise and all other pots to their middle position. Leave TWEAK in the center and the 20k trimmer all the way down. Now, adjust the 20k trimmer clockwise until you hear notes start to swell up in volume. Continue adjusting it until the volume of the swell matches your input. From there, you can adjust the TWEAK trimmer to fine-tune. In my build, the 20k is set at about 11 o'clock and the TWEAK trimmer pretty much in the middle.
-----------------------
In the notes that came with VFE board bundle that was sold on the VFE website and Patreon, Peter says:
-----------------------
"do not install the JFET trimpot. Instead, install a jumper between the left-middle pin of that trimpot and its bottom pin. Use the TWEAK trimpot to fine tune the swell response"
-----------------------
Brian said his first one didn't work with a 22k fixed resistor and that's why he recommend using the trimpot, but he may have just misread where Peter says to use a jumper
Quote from: Aentons on June 02, 2020, 02:07:31 AM
Brian's build doc (page 7) has this:
-----------------------
3. Peter recommended not installing the 20k trim and using a fixed 22k resistor in its place. Don't do this. Use the trimmer! I built two Bumblebees, one with the resistor and one with the trimmer. I could not get the swell to work using the fixed resistor method (and that was with a pre-tested 2n5457). IMO, the 20k trimmer is essential to getting this to work optimally. It may be he used JFETs with a very narrow cut-off range and was able to get away with the fixed resistor. But, my experience was different.
4. To set up the swell effect do the following: set the switch in its middle position, the MIX knob all the way counter-clockwise and all other pots to their middle position. Leave TWEAK in the center and the 20k trimmer all the way down. Now, adjust the 20k trimmer clockwise until you hear notes start to swell up in volume. Continue adjusting it until the volume of the swell matches your input. From there, you can adjust the TWEAK trimmer to fine-tune. In my build, the 20k is set at about 11 o'clock and the TWEAK trimmer pretty much in the middle.
-----------------------
In the notes that came with VFE board bundle that was sold on the VFE website and Patreon, Peter says:
-----------------------
"do not install the JFET trimpot. Instead, install a jumper between the left-middle pin of that trimpot and its bottom pin. Use the TWEAK trimpot to fine tune the swell response"
-----------------------
Brian said his first one didn't work with a 22k fixed resistor and that's why he recommend using the trimpot, but he may have just misread where Peter says to use a jumper
Ah, thank you for that, I bet I've read this doc 100 times and missed it.
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Quote from: madbean on May 27, 2020, 12:29:48 AM
Like benny said the proper VGS of Q2 is critical to make the effect work. But, I don't think using one out of spec for the build will throw off voltages for the 2n3904 at all.
Worse comes to worst, I might be able to dig up a proper spec'd 2n5457 for you if your new batch doesn't pan out.
Can I buy a couple of those trannies from you?
Quote from: jimilee on June 09, 2020, 02:05:36 PM
Quote from: madbean on May 27, 2020, 12:29:48 AM
Like benny said the proper VGS of Q2 is critical to make the effect work. But, I don't think using one out of spec for the build will throw off voltages for the 2n3904 at all.
Worse comes to worst, I might be able to dig up a proper spec'd 2n5457 for you if your new batch doesn't pan out.
Can I buy a couple of those trannies from you?
I'm doing a bunch of the VFE builds all at once right now too, including the BB and tractor beam. I'm gonna try to solve some of these jfet woes by getting 100 J113's from Mouser for $13
https://www.mouser.com/ProductDetail/ON-Semiconductor-Fairchild/J113?qs=ljbEvF4DwONIvgQL%2FiOeMA%3D%3D
Do you have access to a reliable instrument to measure JFET characteristics or a test circuit? I had no issue finding an in-spec 2n5457 from the SBE devices. I also used the trim pot rather than the fixed resistor.
Quote from: benny_profane on June 09, 2020, 04:10:46 PM
Do you have access to a reliable instrument to measure JFET characteristics or a test circuit? I had no issue finding an in-spec 2n5457 from the SBE devices. I also used the trim pot rather than the fixed resistor.
Yes I do. I ordered some, but they were all crap. I have a bounced off matches ones, but they're around 3.0. What are sbe devices?
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Quote from: Aentons on June 09, 2020, 03:40:47 PM
Quote from: jimilee on June 09, 2020, 02:05:36 PM
Quote from: madbean on May 27, 2020, 12:29:48 AM
Like benny said the proper VGS of Q2 is critical to make the effect work. But, I don't think using one out of spec for the build will throw off voltages for the 2n3904 at all.
Worse comes to worst, I might be able to dig up a proper spec'd 2n5457 for you if your new batch doesn't pan out.
Can I buy a couple of those trannies from you?
I'm doing a bunch of the VFE builds all at once right now too, including the BB and tractor beam. I'm gonna try to solve some of these jfet woes by getting 100 J113's from Mouser for $13
https://www.mouser.com/ProductDetail/ON-Semiconductor-Fairchild/J113?qs=ljbEvF4DwONIvgQL%2FiOeMA%3D%3D
Will j113s work?
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I asked about the J113 for phasers here:
https://www.madbeanpedals.com/forum/index.php?topic=31196.msg300928#msg300928
Well, I don't know for sure if it will work in the BB, but I am going on the assumption that all that matters is we want an N-channel jfet with a Vgs(off) value between 1.4-1.5V. And since the drain and source pins are interchangeable on these, all you have to do is turn them around for the right pinout.
From the respective datasheets:
Vgs(off) Min/Max
J113 -0.5V / -3.0V
2N5457 -0.5V / -6.0V
2n5952 -1.3V / -3.5V
So, its seems like the J113 is not only usable for the BB, but it will also be easier to match them for phaser usage.
Someone please correct me if I am wrong
I got the right 5457, it's all about the 5457. Carry on.