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What I don’t understand is if the voltage between pin 6 and ground is too high, does that not signify part of the problem? Doesn’t that mean the power aspect of the circuit is wrong? Also
, maybe I have a bad part and it is driving us crazy. Part of me says to start over on a Pcb and eliminate the breadboard issues.
maybe I should try with the other op amp I have, on the existing breadboard. I do realize I’d have to adjust the pin wirings Many options. Maybe start over on pcb and follow the video Bertus mentioned? Although having done this five times now, I can’t be getting it wrong each time.
, maybe I have a bad part and it is driving us crazy. Part of me says to start over on a Pcb and eliminate the breadboard issues.
maybe I should try with the other op amp I have, on the existing breadboard. I do realize I’d have to adjust the pin wirings Many options. Maybe start over on pcb and follow the video Bertus mentioned? Although having done this five times now, I can’t be getting it wrong each time.
I agree that the recording has no distortion. It sounds like the entire "overdrive circuit" is simply a piece of wire.
The gain control should make the sound like a piece of wire with no distortion when shorted to extremely distorted when turned to 500k ohms.
The wrong voltage on the opamp output might completely disable the opamp, so again the entire circuit might be simply bypassed with a piece of wire.
Did you measure the voltage at the connection of R32 and R33 and at the green wire feeding pin 3 of the opamp??
The gain control should make the sound like a piece of wire with no distortion when shorted to extremely distorted when turned to 500k ohms.
The wrong voltage on the opamp output might completely disable the opamp, so again the entire circuit might be simply bypassed with a piece of wire.
Did you measure the voltage at the connection of R32 and R33 and at the green wire feeding pin 3 of the opamp??
Have you checked the voltages that @Audioguru pointed you to?.
Stay with the breadboard. You can solder the circuit on pcb when you have it working.
Also, what voltage have you got on the input of the opamp?.
Martin
Stay with the breadboard. You can solder the circuit on pcb when you have it working.
Also, what voltage have you got on the input of the opamp?.
Martin
Voltage from R32 to ground. 4.47
Left leg of R33 to ground. 4.4
Right leg of R33 to ground. 8.9
Pin 6 to ground. 7.8
Pin 3 to ground 7.77
I alos notice that when i measure stuff and the pins move slightly, the readings quiver and go to zero.
As I have a variable power supply, is it worth dialing down the voltage there and aplying it directly to the op amp to see if it solves the issue? I'd have to know what voltage to apply and to where. In other words, let the variable power supply do the work of the step down part of the circuit?
Left leg of R33 to ground. 4.4
Right leg of R33 to ground. 8.9
Pin 6 to ground. 7.8
Pin 3 to ground 7.77
I alos notice that when i measure stuff and the pins move slightly, the readings quiver and go to zero.
As I have a variable power supply, is it worth dialing down the voltage there and aplying it directly to the op amp to see if it solves the issue? I'd have to know what voltage to apply and to where. In other words, let the variable power supply do the work of the step down part of the circuit?
bertus
Moderator
Hello,
Read this page:
https://e2e.ti.com/blogs_/archives/b/thesignal/archive/2012/11/27/the-unused-op-amp-what-to-do
There you will see this picture:
Bertus
Read this page:
https://e2e.ti.com/blogs_/archives/b/thesignal/archive/2012/11/27/the-unused-op-amp-what-to-do
There you will see this picture:
Bertus
ok...so i have replaced the op amp with the 4558D. I now have:
Pin 1 as out
Pin 2 as - In
Pin 3 as + in
Pin 4 as Ground
Pin 8 as Vcc in
I am using this datasheet:
https://components101.com/ics/lm4558-dual-op-amp-pinout-datasheet
Bertus- i read the article you asked me to, but it is too technical for me to understand. What I got from it, is there is a way to wire the second op amp so that functions as a unity gain buffer, but from the article, i cannot decipher what to do to make it do that.
When I plug the guitar in to the circuit as is (without solving the second op amp issue). I think i hear a distorted signal, but there is too much buzz to make it out. Probably because I have to deal with the other side of the op amp?
Pin 1 as out
Pin 2 as - In
Pin 3 as + in
Pin 4 as Ground
Pin 8 as Vcc in
I am using this datasheet:
https://components101.com/ics/lm4558-dual-op-amp-pinout-datasheet
Bertus- i read the article you asked me to, but it is too technical for me to understand. What I got from it, is there is a way to wire the second op amp so that functions as a unity gain buffer, but from the article, i cannot decipher what to do to make it do that.
When I plug the guitar in to the circuit as is (without solving the second op amp issue). I think i hear a distorted signal, but there is too much buzz to make it out. Probably because I have to deal with the other side of the op amp?
Update- i noticed that i forgot to change the connection to C3 so that it gores to Pin 1. Once I did that, I could hear distortion. However, there is still too much buzz and i notice that if my hand goes close to certain components on the breadboard, the buzz gets more intense or weakens as I move away. Ideas?
By the way. I now beleive that we were dealing with a faulty op amp and I could have built that circuit over and over with the same bad results. So, the lesson i am learning is that when good people are giving you advice, and you're following it and still it does not work, it must be a bad component.
By the way. I now beleive that we were dealing with a faulty op amp and I could have built that circuit over and over with the same bad results. So, the lesson i am learning is that when good people are giving you advice, and you're following it and still it does not work, it must be a bad component.
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Have you connected pin 6 and 7 together?.
Amp B inverting input and amp B output?
Martin
Amp B inverting input and amp B output?
Martin
Audio buzzing is caused by each long messy breadboard wire (including the wires on resistors and capacitors) is an antenna that picks up the 50Hz or 60Hz from the electricity wires all over your home or business. That is why the circuits I make on stripboard are compact and tidy.
Also, the wires from the guitar to the preamp and from the preamp to the power amp must be shielded audio cables.
The wire from the gain control pot to the opamp -In is especially sensitive to picking up interference. This wire should be VERY short. Maybe the housings of the gain control and volume control pots should be connected to the circuit ground as shields.
Also, the wires from the guitar to the preamp and from the preamp to the power amp must be shielded audio cables.
The wire from the gain control pot to the opamp -In is especially sensitive to picking up interference. This wire should be VERY short. Maybe the housings of the gain control and volume control pots should be connected to the circuit ground as shields.
Thanks for the observations. Here si where I am:
Martin- i have now connected pins 6 and 7 and it has made a difference.
Bertus: I would like to better understand the treatment of the second op amp, but I don't think i am there yet. Things like unity gain must be second nature yto you and oyhers who have experience, but it is not something i understand- yet.
Audio Guru- now that we are close to having the kinks worked out, it may be time to consider going to pcb. You're right- the breadboard, while useful, creates a lot of issues.
I have attached a sound file of what I am sounding like now. You can clearly hear that we have achieved distortion. However, it seems short lived, as though it cuts out. Maybe it is the breadboard artifacts?
Here is how it sounds (hopefully, I have linked ina. way that allows you to hear it)
https://drive.google.com/file/d/1zHaiFEdGY81rQGR2NWb_XEB1hPI3GpZY/view?usp=sharing
Any other suggestions prior to my moving to PCB mode?
Thanks to all for hanging in with me.
Martin- i have now connected pins 6 and 7 and it has made a difference.
Bertus: I would like to better understand the treatment of the second op amp, but I don't think i am there yet. Things like unity gain must be second nature yto you and oyhers who have experience, but it is not something i understand- yet.
Audio Guru- now that we are close to having the kinks worked out, it may be time to consider going to pcb. You're right- the breadboard, while useful, creates a lot of issues.
I have attached a sound file of what I am sounding like now. You can clearly hear that we have achieved distortion. However, it seems short lived, as though it cuts out. Maybe it is the breadboard artifacts?
Here is how it sounds (hopefully, I have linked ina. way that allows you to hear it)
https://drive.google.com/file/d/1zHaiFEdGY81rQGR2NWb_XEB1hPI3GpZY/view?usp=sharing
Any other suggestions prior to my moving to PCB mode?
Thanks to all for hanging in with me.
I have a suggestion.
Watch this video from EEvlog
Martin
Watch this video from EEvlog
Martin
Thanks again. I watched the video last night. I think I understood half of it...which is good for me. He kind of lost me when he began talking about virtual ground, but I did get the concept that it happens during the non inverting loop.
I think i now know how to create a buffer loop. It involves connecting the output to the inverting input. So I now understand why Martin suggested I connect Pin 6 to 7. (Inverting input of the second op amp to the out of the second op amp).
Now, i'll admit, I don't know the function of a buffer loop. Is the function simply to keep the second op amp "busy" so that it does not create noise or issues? Or, does the buffer serve a particular purpose beyond that? The video did not say.
Bertus- thank-you. Why is Vref, in this case, the the point between R32 and R33? (I feel like a 2 year old asking the why questions, but that's how I am learning. ;-)
Thanks to all. I don;t see any reason why I should not try this on a PCB now. I plan tpo use a socket for the op amp, so I can easily switch it out if one becomes damaged. As I mentioned , I've got about 100 of the 4588Ds.
The reason why i'd like to proceed, is because I noticed that on the breadboard, even touching a part of it causes other jumpers to move within their holes, and produces noise, shorts etc. I'd like to hear this circuit in a "solid" state. I plan to reintroduce the tone control too. you will recall we took it out,m when I was encountering issues. We now know it was a bad op amp.
I think i now know how to create a buffer loop. It involves connecting the output to the inverting input. So I now understand why Martin suggested I connect Pin 6 to 7. (Inverting input of the second op amp to the out of the second op amp).
Now, i'll admit, I don't know the function of a buffer loop. Is the function simply to keep the second op amp "busy" so that it does not create noise or issues? Or, does the buffer serve a particular purpose beyond that? The video did not say.
Bertus- thank-you. Why is Vref, in this case, the the point between R32 and R33? (I feel like a 2 year old asking the why questions, but that's how I am learning. ;-)
Thanks to all. I don;t see any reason why I should not try this on a PCB now. I plan tpo use a socket for the op amp, so I can easily switch it out if one becomes damaged. As I mentioned , I've got about 100 of the 4588Ds.
The reason why i'd like to proceed, is because I noticed that on the breadboard, even touching a part of it causes other jumpers to move within their holes, and produces noise, shorts etc. I'd like to hear this circuit in a "solid" state. I plan to reintroduce the tone control too. you will recall we took it out,m when I was encountering issues. We now know it was a bad op amp.
The gain control sets how much distortion is produced by the diodes, because a diode conducts when the voltage across it tries to be more than about 0.7V and the gain control sets the opamp gain from 1 (unity gain) when the gain pot is a short circuit between the opamp output and its -In to a gain of 501 times when it is turned to produce 500k ohms between the opamp output and its -In. The distortion is also depending on how loud you play the guitar.
Good to know. I can't wait to hear how this turns out once I have solid connections. I will report back.
hevans1944
Hop - AC8NS
About breadboards versus printed circuit boards... the purpose of a breadboard is to prove or verify the operation of a particular circuit configuration, whereas the purpose of a printed circuit board or PCB is to implement in a reliable manner the operation that was proven or verified on the breadboard.
As hobbyists we are almost always involved with one-off prototypes, not production circuits, so even if PCBs are "dirt cheap" (which they are from China), we may not want to go that route. Lots of room for error in translating a breadboard to a PCB, and rework to correct errors is never any fun. There are many alternatives to PCB construction that are just as reliable. For example, @Audioguru favors stripboard (as do I) which consists of parallel strip conductors alternating with insulating strip spaces, with holes drilled all over the stripboard left and right and up and down on 0.1-inch centers. Some stripboard will have all of those holes plated through with a thin layer of tin-plated copper applied to the wall of each hole, some with pads at each hole on both sides of the stripboard... real fancy, that, and it does make component soldering somewhat easier, but really cheap stripboard with copper pads only on one side also works just fine. A quick swipe with a fine Scotchbrite pad will remove any corrosion on the non tin-plated copper pads for easier solder wetting of the pads.
As hobbyists we are almost always involved with one-off prototypes, not production circuits, so even if PCBs are "dirt cheap" (which they are from China), we may not want to go that route. Lots of room for error in translating a breadboard to a PCB, and rework to correct errors is never any fun. There are many alternatives to PCB construction that are just as reliable. For example, @Audioguru favors stripboard (as do I) which consists of parallel strip conductors alternating with insulating strip spaces, with holes drilled all over the stripboard left and right and up and down on 0.1-inch centers. Some stripboard will have all of those holes plated through with a thin layer of tin-plated copper applied to the wall of each hole, some with pads at each hole on both sides of the stripboard... real fancy, that, and it does make component soldering somewhat easier, but really cheap stripboard with copper pads only on one side also works just fine. A quick swipe with a fine Scotchbrite pad will remove any corrosion on the non tin-plated copper pads for easier solder wetting of the pads.
