I'll have to try this with my currently developing transistor fuzz-stortion. I've been avoiding clipping diodes as much as possible until I'm fully satisfied with what I'm getting from overdriving my transistors. I fully grasp that voltage gain is the most significant factor when we're trying to generate clipping by exceeding a devices forward voltage, but I've also noticed there's a richness and texture in the final product when there is a nice boost in current included. The simple way I did this in the past was running a ground resistor off the output, and forcing the op amp into Class-A or nearly by doing it, but I imagine there are advantages to adding this current gain stage on the feedback path. With the simple method, it's just a resistor and a bypass capacitor to shunt the noise the method also introduces. I'm just in the practice of establishing as many traits as I can for the project before introducing clipping diodes because 1, I still add other passive components to alter the available voltage that switches them on and 2, in doing so have found using a capacitor so I'm getting a specific corner frequency up/down clipped or bandpass allows for you to get those extra harmonics in the most desired bands and not so obviously reducing output to your load.
A coax cable consists of a central conductor surrounded by insulation which is then covered by the conductive shield (kind of like a cylinder). The shield acts like one plate of a capacitor and the conductor like the other plate. Remember that capacitance is proportional to plate area, so the more area (in this case, the longer the cable), the more capacitance you get. Coax cables are rated in terms of pF of capacitance per foot. A certain cable might be 30 pF/foot. A few inches of cable doesn't have much capacitance, but 100 feet of cable certainly does.
This is great. Would this feedback setup negate thermal runaway on the transistors? Is it still worth putting small emitter resistors on the final stage transistors? Would we still need the biasing diodes? Thanks again, I hope all is well with you.
what about the gain change from adding the push pull circuit in the feedback loop? Does the p-p circut have very low impedance? I'm assuming it does since the output voltage changed very little.
Thanks, this is exactly what I needed to learn for a project with a 5 ohm antenna.
Excellent tutorial ! Dave Jones was talking about ideal diodes and the moved on to talk about the composite amp, so thanks for the TINA demo....cheers
composite amps are clever.
thanks for all the great videos, professor 🙂
I'll have to try this with my currently developing transistor fuzz-stortion. I've been avoiding clipping diodes as much as possible until I'm fully satisfied with what I'm getting from overdriving my transistors. I fully grasp that voltage gain is the most significant factor when we're trying to generate clipping by exceeding a devices forward voltage, but I've also noticed there's a richness and texture in the final product when there is a nice boost in current included.
The simple way I did this in the past was running a ground resistor off the output, and forcing the op amp into Class-A or nearly by doing it, but I imagine there are advantages to adding this current gain stage on the feedback path. With the simple method, it's just a resistor and a bypass capacitor to shunt the noise the method also introduces.
I'm just in the practice of establishing as many traits as I can for the project before introducing clipping diodes because 1, I still add other passive components to alter the available voltage that switches them on and 2, in doing so have found using a capacitor so I'm getting a specific corner frequency up/down clipped or bandpass allows for you to get those extra harmonics in the most desired bands and not so obviously reducing output to your load.
Merci for this nice video. Very interesting, pragmatic and efficient, as far as necessary!
Professor I’m using a JRC 4556 high current op-amp to drive the primary side of a transformer to sweep the Collector Emitter of a transistor.
Thank you
1:27 why does a long run of coax cable have large capacitance?
A coax cable consists of a central conductor surrounded by insulation which is then covered by the conductive shield (kind of like a cylinder). The shield acts like one plate of a capacitor and the conductor like the other plate. Remember that capacitance is proportional to plate area, so the more area (in this case, the longer the cable), the more capacitance you get. Coax cables are rated in terms of pF of capacitance per foot. A certain cable might be 30 pF/foot. A few inches of cable doesn't have much capacitance, but 100 feet of cable certainly does.
@ ohhhh wow thats amazing, thank you!!!
This is great.
Would this feedback setup negate thermal runaway on the transistors?
Is it still worth putting small emitter resistors on the final stage transistors?
Would we still need the biasing diodes?
Thanks again, I hope all is well with you.
Feedback doesn't get rid of thermal runaway here, and yes, include the diodes for lowest distortion.
what about the gain change from adding the push pull circuit in the feedback loop? Does the p-p circut have very low impedance? I'm assuming it does since the output voltage changed very little.
It's inside the feedback loop. With this much negative feedback, the feedback defines the system gain.
Great content! Is there any textbook for reference on op amp current boosting? Thanks!
Yes. My free textbook. See links in the video description above for download as well as inexpensive print versions.
Good explanation. What software package are you using?
TINA-TI, a free version of the TINA simulator, available from ti.com