This channel will (hopefully) show people electronics in a way that perhaps isn't really considered very much anymore. I started this channel around the subject of vacuum tubes but it has evolved into a mix of solid state and valve electronics. Most of it is analog, but sometimes contains elements of basic digital logic. I showcase projects, circuits and theory that I've put together. I usually try to explain things that would normally require a bit of digging and background knowledge to find otherwise. My goal is simply to remind people how fascinating electronics can be.
With the volume control all the way up, about 500K ohms with the balance pot centered. With the volume turned all the way up and the balance pot all the way to one side, it would be close to 0 ohms for the nulled out channel and 1M ohm for the other. This design is actually not good for an input stage because it really needs to be buffered. If you take out the balance pot, the input impedance simply becomes 1M ohm for each channel as usual.
What's the frequency of the sine waves? Also, what transistor did you use? I don't think you mentioned that. I plan to adapt the circuit to RF and quite like the idea. The way I see it, it's essentially a phase splitter (transistor part), where you then have adjustable RC filter for the signal recombination. I think at higher frequencies the values for R and C are going to become a problem. Perhaps less if you use PCB and SMD components. Still, most standard inductors and capacitors have quite low Self Resonant Frequencies (~10MHz) so above that you need the more expensive RF components. Perhaps there is an alternative to using the RC filter.
Great video, exactly what I was looking for my own DIY Wah bypass switch!👍 I know about the 4053 that might be a newer version? But thinking of only doing a bypass I guess a 4966 would be more likely the way to go?
The CD4053 is not newer, it's a 3-throw version of the CD4051. The CD4052 shown here is the 2-throw version. The CD4066 is basically just four separate single-pole single-throw switches. For your pedal, likely any of these would work, but I know some pedal designs need multiple poles for the switch. In that case the CD4052 or CD4053 would be needed. Do put some zeners or some kind of protection on the input and output of the circuit though, these CMOS switches are not immune to static.
The input and output are approximately equal and are something like 550mV peak-to-peak in this video. It doesn't really matter though, as long as your peak-to-peak signal is within ~4.7V, it shouldn't clip.
How was gain Calculated where A=0.97, I understand that, how did find the value of re = 26ohm , and Capacitor value for bootstrapped to have high impedance.
There is an equation for re that is a function of emitter current and temperature. That number should be taken with a grain of salt since it can be as high as 42 ohms or as low as 21 ohms for a given current depending on what you take to be the ambient temperature. For 42 ohms the gain would be something like 0.96 instead of 0.97. The capacitor value should be set to pass all frequencies above 1Hz at the input impedance of the stage before bootstrapping. This is the impedance of the voltage divider which is about 13K, in parallel with the input impedance of the base, which is ~150K for an Hfe of 150. The 150K base impedance swamps the 4.7K resistor because it can change +/- 30% or more depending on the transistor Hfe and temperature. For a 10uF cap, this gives a rolloff of just under 1Hz.
@@thetuberoaster8321 bootstrapping the input to have greater Rin ( input impedance) . Your circuit on the first page. Your out is comming what is your collector right. So what is your gain ? With high impedance. What is your input Ac voltage : 20mv Vpp ? I am really trying to understand what's going on your video. What is the benefit of having high impedance if I am not doing audio. I am building a 3 stage amplifier CE- CE-CC. What's your thoughts on that.
@@Tankzim.z The gain is approximately Rc over Re. The intrinsic emitter resistance changes that slightly but in this case it is almost 10. The output impedance is roughly Rc which is 10K. The input impedance without bootstrapping would be dominated by the base bias network, making it hard to get anything above 10s of Kohms. Bootstrapping allows this input impedance to be at least and order of magnitude higher. This is sometimes useful for when you can't afford to load down the preceding circuit. If you have one CE stage driving another, the first will be loaded by the input impedance of the second. This will cause the gain to drop and the distortion to increase somewhat. The more obvious solution is to use a FET, but for low-noise applications this may not be feasible. This technique allows you to use a regular BJT with its benefits but without its usual trade-off of low input impedance. The input sensitivity of this amp is something like 400mV before clipping. You can tweak the biasing and the gain to change the operating point to make the input sensitivity whatever you like. The three stage amp you are talking about - the CE-CE-CC amp - allows you to split the gain between two stages, which is better in terms of distortion. The CC output will make the output much lower impedance than a normal CE amp, allowing the amp to drive heavier loads without increased distortion or loss of gain.
I know I'm late to the party but wanted to say thanks for posting your research on this. I downloaded the pdf manual and added this to my list of things to build.
great video! I'm in an aerial robotics class where we are learning the math behind a lot of stuff including this. It's neat to see all the variables we have been talking about come to life a little bit in your circuit!
I should have said in the video that this series only represents one part of the cycle of the waveform. For multiple cycles the Fourier series more accurate since it shows sine components cancelling. The (infinite) series itself does not converge but 1/n does converge to zero as n goes to infinity. As n becomes infinitely large the amplitude of the nth component becomes infinitely small. As the number of terms approach infinity the wavy saw slope becomes smooth. The waves in the middle gradually cancel out as many terms add together. This is very similar to the behavior of a square wave. In real circuits, the high frequency components cannot be infinite in number because the circuit cannot respond at infinitely high frequencies. Those components would then have amplitudes of zero and therefore not matter. It is in some ways akin to integrating 1/n. Technically, the slope only approaches zero so therefore the integral can be infinitely large. Generally, the integral is taken over some convenient bound so that this integral is finite and predictable. (Like computing radioactive decay or heat transfer.) If the circuit is part of a digital system where there is a DAC, there will be aliasing and low-pass filters to prevent the aliasing. If you look at a digitally generated square or saw tooth wave on an oscilloscope you will see little waves instead of a flat line. The closer the filter rolloff is to the fundamental of the wave being generated, the more pronounced this effect is. This is due to those high frequency components being filtered out.
As I understand it, it ultimately produces a bucking voltage for your input signal so it's seeing a much higher impedance when it appears across the new input resistor networks. The coupling capacitor prevents the input device from seeing D.C., and the input device is more effectively transferring it's voltage. This was in fact, helpful, but I still need to put more work in. 11 years since I was in college and I haven't done the math for about 8 years. 😩 *I suppose for use in guitar distortion where my goal is to overdrive the transistors and not involve diodes whatsoever, this is another path for me to explore soon after finishing current designs.* I ultimately increased my base voltage divider values by a factor of approximately 550x, which created a massive increase on input impedance and my gain in fact went through the roof. Surprisingly, the really high resistor values aren't giving me noise issues so I'm safe on the simpler path in this example, but everything is ultimately a piece of the puzzle to better performance as we progress.
TBH I don't actually know where that comes from. It has also been a long time since I've looked at this circuit. The book shows the expected Vcc²/2xRl but then later it also shows Vcc²/8xRl for the same output stage calling it maximum average output power.
All this nonsense is useless this was solved back in the 1980's with midi signals switching audio relays it was solved back then and has worked till 2023. No professional uses hard contact switching with multiple outputs and inputs, one of the biggest problem is the industry of using Midi audio switching has always been at a Pro level area so the boards are not easy to find as kits. Custom Audio ( the Bradshaw Switching system dude) basically had a monopoly on the Midi to Audio switching boards. Even in 2023 there is no kit available you have to build the system yourself, Voodoo Labs is a hit and miss with these smaller switching systems. Basically the only way to properly switch and mix audio inputs to outputs is using Midi Signals on a floor controller. This solves many problems as Midi is opto and the relay switches ramp up and down so you never hear any pops or hiss. I am still dumbfounded how in 2023 that no Musical audio corp has taken over this area since hardware is so cheap these days to do this. Literally a 20 in-20 out midi audio switching rack and floor controller should cost less than $500 these days but yet nothing out there, not even Behringer is in this area which is very suspicious.
excelent video thank you that circuet might by usefull for pick up coils in distributor I am plagued for years with my hei ignition system basicali that thing has no advance or retard option for ignition timing very usefull circuet how ever Im not shure if it wuld work on my circuet I did in the past use only 500k pott betwean pick up + lead and input on the 4 pin gm ignition module and indead it was nearli 180° out of phase fiering how ever I did not use voltage deviders or capacitora engine run crapy honestli but it did fire at exaust stroke engine did run at exauat stroke how ever after half houer cranking engine and the problem by my was I used speaker wire was an fool didnt have any non resistive leads. Only problem I have I dono what resistor value to chuse or capacitors or resistors the pick up coil is mostli based on voltage and high frequency I ques around 33hz up to 333hz max thats how much is rated the 555 timer in the ignition module it uses the mc 3334 ic chip set . So any suggestions what transistor potentiali wuld work on that set up or activateing or useing that circuet with an darlington power transistor???
Hi! Great project! I want to refactor my JCM800 EL84 SE amp into PP based on ECC82 or ECC99. Please tell me how you recalculated preamp cathode resistors for lower anode voltages and which anode voltages were your reference? Thanks!
It's been a long time, but I remember getting the datasheet with the characteristic curves for the 12AX7 and plotting loadlines for the anode load to find the cathode resistor. I wanted to keep the gain relatively the same so I kept the 100k anode load resistor. I wanted the anode voltage to be just above half of the available HT voltage. Ohms law gave the required anode current in order to make that happen. I settled on a desired grid voltage of something like -1.5V. Tying the grid to ground and putting a resistor of 1.2K between the cathode and ground yielded ~1.6V. The second stage is biased colder for some reason at something like -3V near cutoff. I do not remember the reason for this nor the reason for why the two input stages were so different. I do remember trying to emulate the real superlead circuit and keep the bias voltage and anode current ratios as similar as possible. The bypass caps are different between channels because one is the bright channel with less bass and the other is the normal channel. I think I did recalculate those values as well using the standard -3dB RC filter equation. The stage after the volume control is biased the same as the normal channel input stage. (The bright channel is the one with the bright cap on the volume control). I do not remember changing anything in the cathode follower driving the tone stack. I may have left it the same. The tone stack is literally cut and paste from the original. I'm pretty sure the phase splitter long-tailed pair stage was also original. The only thing that I changed was the feedback resistor in the presence knob circuit since the output stage had a different amount of gain. I did this experimentally and settled on 47K but I might have been able to go lower. The output stage I had to change the grid leak resistors to something lower to drop the gain a little and added big grid stopper resistors to hopefully knock down RF and prevent oscillation. I'm pretty sure the 12AU7s in the output make way more voltage gain than El-34s do. This causes the amp to compress the sound a bit too much at full volume. The sweet spot is about 2/3 of the way up. You could probably decrease the gain somewhere and make it more manageable. I could not tell if this excessive compression was due to the power transformer sagging, the output transformer saturating, or the gain issue.
The negative terminals of the power supplies are not directly connected to ground. There are separate ground and negative terminals. I connected the two power supplies in series and the connection point of the + and - I took as ground for the device. It's no different than connecting two batteries in series.
Hello. Do you happen to have a corrected schematic I could use to build this?! I bought ten of these tubes looking to build a headphone amp with, but the schematic I found doesn't have all values listed😢 thank you so much if you happen to be able to help!
The original one that inspired this build came from the oatley electronics kit. The link is in the description. The schematic is listed there as a pdf download which you can look at for reference. Or you can just use the schematic I provided and change the front-end volume control to your liking.
anyone have any troubles with pop/clicks when switching between audio sources? I'm using a different IC but it is also an analog spdt meant for audio switching applications, but i get pops when switching.
If you make the emitter resistor lower than 4.7k, it will amplify the signal, but it will also phase shift it more since. The signal from the emitter will be lower than that of the collector, therefore it will act upon it less. As you change the 50k pot, the signal will change phase but also amplitude, arguably making it less useful.
As far as I know the 12AU7 was not designed for 12V operation. Datasheets give operation at 100 and 250V. Operating the tube at these voltages you may get a lot more out of it. Ecc86 on the contrary was specifically design for 12V operation. It was use primarily in car radios. Tuning of a regenerative radio requires the use of both hands, one for the tuning control and one for the regeneration control. At first you increase regeneration until a light hiss is heard through the speaker and then you turn the tuning control. As the tuned frequency changes you may need to adjust regeneration accordingly. I have build 2 regenerative radios so far , one for the MW band and one for the SW band. I’m on the way to build another one that will be mobile. The tubes are the 2V/ 60mA filament types and the HT is 180V. A DC to DC converter will supply the HT.
im using a CD4017 as the 1 to 4 counter to indicate current input with leds and have to figure out the 2 bit counter for the cd4052 A/B selectors (i dont have any D flip flip). Everything is getting along for this project thanks to you!
Hi, what voltage good in Plate and Grid ? In my version, I am using 22V, then 180k ohm resistor for Plate and Grid, so I get only 8V in these position. In addtion, I am using cathode bypass resistor for Cathode with 140ohm for auto bias. Can I remove 180k resistor to upgrade voltage to 22V for Plate and Grid ? Because in 6418 tube datasheet I found that class A mode should be 15-22.5V for grid and plate
is there a single and dual channel version of this (for smaller layouts space available) and can it avoid click and pops in the audio when the switch occurs?
since these stereo pots are meant for stereo use I think you just got the connections the wrong way for one channel, i.e. swap pin 6 and 4 and it should be ok... Actually from your pcb layout I don't quite get how you connected any of the channels and your balance trimmer...
An aluminum case would help noise. However, PCB has power planes on both sides that shield the traces to some degree. Also, the gain of the circuit is rather low, which helps. The shot noise of the tube and the thermal noise of the resistors are nearly as loud as the mains hum anyway.
I replied to another comment similar to this which you can also look at. You can solve for RC in the equation but the trick is making the phase shift range large enough but useful. A 180 degree phase shift is not practically possible because it can only occur when the term for arc tangent is infinity. The best you can do is something like 176 or 178 degrees. If you solve for a phase shift much higher than 176, the range of the pot becomes really nonlinear and it does not sweep the phase range in a way that is useful. I'd recommend plugging in 176 degrees for the phase shift and the desired frequency to then solve for RC. This will correspond to the max value of the potentiometer. The 0 degrees phase shift condition is of course simple. When the pot is turned down it will go to 0 ohms or near enough making the phase shift nearly 0 degrees.
You need a decoder circuit to turn the binary coded decimal logic back into normal counting numbers again, unless you want your LEDs counting in binary. For two inputs this is easy, all you need is an inverter. For four inputs, you need a 2 to 4 decoder chip like the SN74LVC1G139 which will give an output for each LED. The outputs are active low (inverted logic) so you will need to switch the low side of the LEDs to make one light up for each input selection.
@the tube roaster - can you plz help how to select stereo and dvd which has 6 channels like front, left, surround left, surround right and centre. I can using relay but it would be. Much expensive, need 5 relays so thought once I select dvd, output should give 6 channel instead of stereo output(right, left)
You can use two CD4053s together to get six channels that can switch between two sources. The 4053 has three separate single-pole double-throw switches inside. You can tie the input select pins together so they all switch at the same time. To accommodate more sources, you can add another pair in parallel and use the inhibit pins to select which pair passes the signal. The logic circuit might need to be modified however.
