Home |
Search |
Today's Posts |
|
Electronic Schematics (alt.binaries.schematics.electronic) A place to show and share your electronics schematic drawings. |
Reply |
|
LinkBack | Thread Tools | Display Modes |
#1
Posted to alt.binaries.schematics.electronic
|
|||
|
|||
schematic for John (from transistor question on SEB)
tempus fugit wrote:
Here's the schematic you were asking about John. This is the section from my amp that is used for remote switching. The original design was to have the 'effects 1+2 footswitch' connected to a mechanical switch, but I wanted to change that to transistor switching so that I could incorporate it into my pedalboard. Where is the LED you mentioned in your post to sci,electronics.basics, "Thanks for the reply John. I'm switching 12v at the collector with 5v at the base. The 12v is coming through a 100K resistor from the previous device, so the current is pretty small. I've found that using a standard (2N2222 type) transistor doesn't quite switch things all the way off ( there is an LED indicator that still glows faintly)." I am assuming that it is something you are adding at the transistor switch replacement part. I also need to see the schematic for all that, to understand what you are testing. If you just wanted transistors to replace the mechanical switches, they could easily be 2N7000 type mosfets or something with even higher resistance, since they only switch the 150 uA current through the 100k resistors in the amp. The harder problem may be keeping the off state leakage current well below something like 15 uA to let the effect be all the way on. If the LED gets involved in this current, it will easily interfere with such a high impedance deal. |
#2
Posted to alt.binaries.schematics.electronic
|
|||
|
|||
schematic for John (from transistor question on SEB)
tempus fugit wrote:
"John Popelish" wrote in message news tempus fugit wrote: Here's the schematic you were asking about John. This is the section from my amp that is used for remote switching. The original design was to have the 'effects 1+2 footswitch' connected to a mechanical switch, but I wanted to change that to transistor switching so that I could incorporate it into my pedalboard. Where is the LED you mentioned in your post to sci,electronics.basics, "Thanks for the reply John. I'm switching 12v at the collector with 5v at the base. The 12v is coming through a 100K resistor from the previous device, so the current is pretty small. I've found that using a standard (2N2222 type) transistor doesn't quite switch things all the way off ( there is an LED indicator that still glows faintly)." I am assuming that it is something you are adding at the transistor switch replacement part. I also need to see the schematic for all that, to understand what you are testing. If you just wanted transistors to replace the mechanical switches, they could easily be 2N7000 type mosfets or something with even higher resistance, since they only switch the 150 uA current through the 100k resistors in the amp. The harder problem may be keeping the off state leakage current well below something like 15 uA to let the effect be all the way on. If the LED gets involved in this current, it will easily interfere with such a high impedance deal. ] Woops. That schem isn't covering enough ground. Here's a bigger chunk. The LEDs in question are marked 'Lead LED' and 'Rhy LED', and are part of the amp itself, not my switching system. Not there yet. The post at the top talks about the effects 1+2 foots witch, but the LEDs are connected to the channel select foot switch. I need to see the experimental transistor circuit you connected to this amp that didn't act as you expected, so I can help you figure out how to fix it. Did you just relocate the Q7 Q8 circuit to outside of the amp? |
#3
Posted to alt.binaries.schematics.electronic
|
|||
|
|||
schematic for John (from transistor question on SEB)
Here's the schematic you were asking about John. This is the section from my
amp that is used for remote switching. The original design was to have the 'effects 1+2 footswitch' connected to a mechanical switch, but I wanted to change that to transistor switching so that I could incorporate it into my pedalboard. Thanks |
#4
Posted to alt.binaries.schematics.electronic
|
|||
|
|||
schematic for John (from transistor question on SEB)
tempus fugit wrote:
The 2 switches in question are the Channel select (at the bottom of the schem - the rest of it is to the left, which I'll post tomorrow - sorry again about that), and the volume boost (closer to the top). The reverb is not switched remotely, since I leave it on all the time. I misposted in saying that it is the effects 1+2 footswitch, since it is in fact the channel select and volume boost (effect 1) that I'm actually working with. The rhy LED is the one that is still (very) dimly lit when I switch. I should also note that when I use a MAX4662 anaog switch (http://datasheets.maxim-ic.com/en/ds...61-MAX4663.pdf) (Ron = 2.5 ohms) that the LED is completely out when switched off. I didn't relocate Q7 and Q8 outside the amp; the LEDs are on the front panel, and if I am correct in their purpose, they are the drive transistors for the LEDs. You mentioned the MOSFETs as a possible alternative - this is what got me posting in the first place, along with the other post about transistors. I had thought of replacing my BJTs with MOSFETs, but then learned that they shouldn't have any voltage on them before they were powered up. SInce the possibility exists that the amp may get turned on before the pedalboard (the switching system), that would put 12v on the drain with no voltage on anything else until the pedalboard was switched on. Looking at the circuit, though (which would be basically the same as my BJT circuit - using a transistor as a switch, only with much higher resistor values) I couldn't see why that would be an issue, since I wouldn't have any voltage at the gate unless I was actually switching the MOSFET on anyway. I've included a partial schematic of my transistor switching circuit. The ones in question are in the lower left. Okay, I think I see what is causing you trouble. When the select switch is closed, there is a 1 diode drop of voltage at the right end of D4. And that one diode drop is applied to the series combination of D5 and the base emitter drop of the two transistors Q7 and 8. If the switch is replaces with a saturated transistor, you add its couple tenths of a volt drop to that diode drop (while it carries the LED current to light D3). So the bases really do not see zero volts, or even necessarily half of the diode + drop. This allows them to both leak just a little collector current. Add either another diode in series with D5, or a base to emitter leak resistor, say, 22k, across Q7 and Q8, to keep them completely off till the full drive comes through. Then any ordinary transistor like a 2N3904 should work in place of the switch. |
#5
Posted to alt.binaries.schematics.electronic
|
|||
|
|||
schematic for John (from transistor question on SEB)
John Popelish wrote: tempus fugit wrote: Here's the schematic you were asking about John. This is the section from my amp that is used for remote switching. The original design was to have the 'effects 1+2 footswitch' connected to a mechanical switch, but I wanted to change that to transistor switching so that I could incorporate it into my pedalboard. Where is the LED you mentioned in your post to sci,electronics.basics, Where is the schematic ? It's not on the news server I'm using. Graham |
#6
Posted to alt.binaries.schematics.electronic
|
|||
|
|||
schematic for John (from transistor question on SEB)
Eeyore wrote:
John Popelish wrote: tempus fugit wrote: Here's the schematic you were asking about John. This is the section from my amp that is used for remote switching. The original design was to have the 'effects 1+2 footswitch' connected to a mechanical switch, but I wanted to change that to transistor switching so that I could incorporate it into my pedalboard. Where is the LED you mentioned in your post to sci,electronics.basics, Where is the schematic ? It's not on the news server I'm using. Graham Here is a copy of the last image he posted. |
#7
Posted to alt.binaries.schematics.electronic
|
|||
|
|||
schematic for John (from transistor question on SEB)
Eeyore wrote:
John Popelish wrote: tempus fugit wrote: Here's the schematic you were asking about John. This is the section from my amp that is used for remote switching. The original design was to have the 'effects 1+2 footswitch' connected to a mechanical switch, but I wanted to change that to transistor switching so that I could incorporate it into my pedalboard. Where is the LED you mentioned in your post to sci,electronics.basics, Where is the schematic ? It's not on the news server I'm using. Graham Here is the PDF converted to gif. |
#8
Posted to alt.binaries.schematics.electronic
|
|||
|
|||
schematic for John (from transistor question on SEB)
"John Popelish" wrote in message news tempus fugit wrote: Here's the schematic you were asking about John. This is the section from my amp that is used for remote switching. The original design was to have the 'effects 1+2 footswitch' connected to a mechanical switch, but I wanted to change that to transistor switching so that I could incorporate it into my pedalboard. Where is the LED you mentioned in your post to sci,electronics.basics, "Thanks for the reply John. I'm switching 12v at the collector with 5v at the base. The 12v is coming through a 100K resistor from the previous device, so the current is pretty small. I've found that using a standard (2N2222 type) transistor doesn't quite switch things all the way off ( there is an LED indicator that still glows faintly)." I am assuming that it is something you are adding at the transistor switch replacement part. I also need to see the schematic for all that, to understand what you are testing. If you just wanted transistors to replace the mechanical switches, they could easily be 2N7000 type mosfets or something with even higher resistance, since they only switch the 150 uA current through the 100k resistors in the amp. The harder problem may be keeping the off state leakage current well below something like 15 uA to let the effect be all the way on. If the LED gets involved in this current, it will easily interfere with such a high impedance deal. ] Woops. That schem isn't covering enough ground. Here's a bigger chunk. The LEDs in question are marked 'Lead LED' and 'Rhy LED', and are part of the amp itself, not my switching system. |
#9
Posted to alt.binaries.schematics.electronic
|
|||
|
|||
schematic for John (from transistor question on SEB)
Tom Del Rosso wrote:
"tempus fugit" wrote in message Here's the schematic you were asking about John. This is the section from my amp that is used for remote switching. The original design was to have the 'effects 1+2 footswitch' connected to a mechanical switch, but I wanted to change that to transistor switching so that I could incorporate it into my pedalboard. I've never seen a transformer like that. Is there magnetic coupling between all the coils? I think the "transformer" you are asking about may be a symbol for a spring reverb unit that includes a voice coil driver at one end and a dynamic microphone at the other. The symbol just shows the two transducers coupled by a bunch of springs. |
#10
Posted to alt.binaries.schematics.electronic
|
|||
|
|||
schematic for John (from transistor question on SEB)
"John Popelish" wrote in message ... tempus fugit wrote: "John Popelish" wrote in message news tempus fugit wrote: Here's the schematic you were asking about John. This is the section from my amp that is used for remote switching. The original design was to have the 'effects 1+2 footswitch' connected to a mechanical switch, but I wanted to change that to transistor switching so that I could incorporate it into my pedalboard. Where is the LED you mentioned in your post to sci,electronics.basics, "Thanks for the reply John. I'm switching 12v at the collector with 5v at the base. The 12v is coming through a 100K resistor from the previous device, so the current is pretty small. I've found that using a standard (2N2222 type) transistor doesn't quite switch things all the way off ( there is an LED indicator that still glows faintly)." I am assuming that it is something you are adding at the transistor switch replacement part. I also need to see the schematic for all that, to understand what you are testing. If you just wanted transistors to replace the mechanical switches, they could easily be 2N7000 type mosfets or something with even higher resistance, since they only switch the 150 uA current through the 100k resistors in the amp. The harder problem may be keeping the off state leakage current well below something like 15 uA to let the effect be all the way on. If the LED gets involved in this current, it will easily interfere with such a high impedance deal. ] Woops. That schem isn't covering enough ground. Here's a bigger chunk. The LEDs in question are marked 'Lead LED' and 'Rhy LED', and are part of the amp itself, not my switching system. Not there yet. The post at the top talks about the effects 1+2 foots witch, but the LEDs are connected to the channel select foot switch. I need to see the experimental transistor circuit you connected to this amp that didn't act as you expected, so I can help you figure out how to fix it. Did you just relocate the Q7 Q8 circuit to outside of the amp? It's getting late so I'll post more tomorrow, but I'll try to answer a couple questions. The 2 switches in question are the Channel select (at the bottom of the schem - the rest of it is to the left, which I'll post tomorrow - sorry again about that), and the volume boost (closer to the top). The reverb is not switched remotely, since I leave it on all the time. I misposted in saying that it is the effects 1+2 footswitch, since it is in fact the channel select and volume boost (effect 1) that I'm actually working with. The rhy LED is the one that is still (very) dimly lit when I switch. I should also note that when I use a MAX4662 anaog switch (http://datasheets.maxim-ic.com/en/ds...61-MAX4663.pdf) (Ron = 2.5 ohms) that the LED is completely out when switched off. I didn't relocate Q7 and Q8 outside the amp; the LEDs are on the front panel, and if I am correct in their purpose, they are the drive transistors for the LEDs. You mentioned the MOSFETs as a possible alternative - this is what got me posting in the first place, along with the other post about transistors. I had thought of replacing my BJTs with MOSFETs, but then learned that they shouldn't have any voltage on them before they were powered up. SInce the possibility exists that the amp may get turned on before the pedalboard (the switching system), that would put 12v on the drain with no voltage on anything else until the pedalboard was switched on. Looking at the circuit, though (which would be basically the same as my BJT circuit - using a transistor as a switch, only with much higher resistor values) I couldn't see why that would be an issue, since I wouldn't have any voltage at the gate unless I was actually switching the MOSFET on anyway. I've included a partial schematic of my transistor switching circuit. The ones in question are in the lower left. Thanks again, and I should have more tomorrow.... |
#11
Posted to alt.binaries.schematics.electronic
|
|||
|
|||
schematic for John (from transistor question on SEB)
"tempus fugit" wrote in message
Here's the schematic you were asking about John. This is the section from my amp that is used for remote switching. The original design was to have the 'effects 1+2 footswitch' connected to a mechanical switch, but I wanted to change that to transistor switching so that I could incorporate it into my pedalboard. I've never seen a transformer like that. Is there magnetic coupling between all the coils? -- Reply in group, but if emailing add another zero, and remove the last word. |
#12
Posted to alt.binaries.schematics.electronic
|
|||
|
|||
schematic for John (from transistor question on SEB)
"John Popelish" wrote in message ... tempus fugit wrote: The 2 switches in question are the Channel select (at the bottom of the schem - the rest of it is to the left, which I'll post tomorrow - sorry again about that), and the volume boost (closer to the top). The reverb is not switched remotely, since I leave it on all the time. I misposted in saying that it is the effects 1+2 footswitch, since it is in fact the channel select and volume boost (effect 1) that I'm actually working with. The rhy LED is the one that is still (very) dimly lit when I switch. I should also note that when I use a MAX4662 anaog switch (http://datasheets.maxim-ic.com/en/ds...61-MAX4663.pdf) (Ron = 2.5 ohms) that the LED is completely out when switched off. I didn't relocate Q7 and Q8 outside the amp; the LEDs are on the front panel, and if I am correct in their purpose, they are the drive transistors for the LEDs. You mentioned the MOSFETs as a possible alternative - this is what got me posting in the first place, along with the other post about transistors. I had thought of replacing my BJTs with MOSFETs, but then learned that they shouldn't have any voltage on them before they were powered up. SInce the possibility exists that the amp may get turned on before the pedalboard (the switching system), that would put 12v on the drain with no voltage on anything else until the pedalboard was switched on. Looking at the circuit, though (which would be basically the same as my BJT circuit - using a transistor as a switch, only with much higher resistor values) I couldn't see why that would be an issue, since I wouldn't have any voltage at the gate unless I was actually switching the MOSFET on anyway. I've included a partial schematic of my transistor switching circuit. The ones in question are in the lower left. Okay, I think I see what is causing you trouble. When the select switch is closed, there is a 1 diode drop of voltage at the right end of D4. And that one diode drop is applied to the series combination of D5 and the base emitter drop of the two transistors Q7 and 8. If the switch is replaces with a saturated transistor, you add its couple tenths of a volt drop to that diode drop (while it carries the LED current to light D3). So the bases really do not see zero volts, or even necessarily half of the diode + drop. This allows them to both leak just a little collector current. Add either another diode in series with D5, or a base to emitter leak resistor, say, 22k, across Q7 and Q8, to keep them completely off till the full drive comes through. Then any ordinary transistor like a 2N3904 should work in place of the switch. Thanks John. So that would take care of the LED not being completely turned off problem, but will the channel it is connected to completely shut off? Or is the channel already completely shut off, but only the LED is partially on? Does the base to emitter leak resistor go from the base of Q7 to the emitter of Q8, or vice versa? Also, do you need to see the rest of the schematic? Thanks again |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
John Deere Question | Home Repair | |||
transistor pinout question,.. | Electronics Repair | |||
Oops schematic mistake on first message. Correction made -- Help. Transistor circuit that connect or disconnect 75ohm terminator for video application | Electronics | |||
PING John Henry: The question of baptism | Woodworking | |||
Transistor question | Electronics |