Bumble bee ain’t swellin. Resolved

[jimilee]

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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[Cybercow]

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?

[jimilee]

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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[Cybercow]

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.

[jimilee]

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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[Aentons]

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

[Cybercow]

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.

[jimilee]

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.

[Cybercow]

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.

[jimilee]

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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[jimilee]

Anybody got any ideas?


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[benny_profane]

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.

[jimilee]

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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[benny_profane]

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.

[jimilee]

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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