wuemura

Hi audioguru, Tell me something, do you know what is happening with this sample? http://www.sendspace.com/file/f2fh8j (1.2Mb) Looks like the sound is cracking up at the both ambience channels, the voice channel is fine, this is one of the "special situations" because the circuit works great with others CD's, there is no variation at the virtual ground so the problem is not there, adjusted the levels and opamp gain with no success, try to use signal levels at 500mv but no change. I did change the CD player with 3 different models and again with no success. The CD is original and analysing the signal without the circuit it shows that it is no clipping or distortion in it. Following the signal it get bad before and after R2 and R25, removing R5 and R22 the signal became good before and after R2/R25, but at the output of the opamp's the sound is very bad and loud. So i try to buffer after R2 and R25 and use a 100K resistor at the opamp output but with no success. Do you have any idea what is causing this? Thanks

Do you still have SQ vinil records? I was reading a page about Quadraphonics here, maybe you will like. I've never heard any type of vinyl records that uses technology like that, SQ, Quadradisc, Q4, Quad-8, Quadraphonic Stereo etc. http://en.wikipedia.org/wiki/Quadraphonic But i know from some friends that this type of equipament was very expensive, the price that you paid at the time you could buy a new car, so he said. So, i did a real life test of the circuit in my car, it worked out fine but had problems with the old Ace of Base CD, i was getting peaking at high frequency on the ambience channels. Looks like the problem was the power amp load, measuring the virtual ground again there was fluctuations. So i came up with the changes attached. I've found more information about virtual ground and opamp here: http://tangentsoft.net/elec/vgrounds.html With that changes and using the virtual ground as negative reference i do get a stable +6.04V and -6.00, the voltage used in the circuit is 12.04V, at the R1/R2 divider the voltage is 5.99V. The circuit looks stable now.

Hi audioguru, Sound like mission accomplished to me. ;D I enjoy listen to this haffler in my car, and you told me that you have build one your self right? Thank you again audioguru.

So, here is the sample with the double buffer configuration and all the changes. http://www.sendspace.com/file/0syxro (2Mb) The distortion was noticed at the beggining when there is something that sound like a pipe organ, moust of the time there was a distortion. But with the new virtual ground it sounded great now.

Hi audioguru, I'm using a comercial PSU (regulated at 12V/1A), i know that is is very stable, and i'm sure that the problem is the virtual ground, it has to be stable at 1/2 Vcc or i will get the distortion problems, messing up with the values shows that. But your virtual ground solution works very well! I'm doing some tests here with a dozen CD's that i have and the distortion and clipping are gone for good. I did change some values because using a double buffered virtual ground change some aspects of the circuit, what was good because all the CD's that i've tested worked out fine. The design that i came out is attached in this message and belive me, is good, the audio output got a little louder than before using 2 virtual ground buffers, so i've changed the circuit input resistors from 51K to 62K. The solution that you gave work fine with standard RCA levels like 1Vpp, i did a small headphone amp using your virtual ground and and work it out fine (using a simple TL072 like the cmoy one), no noise or distortion, if some one try to build a pocket headphone amp this is the way to go. With the signals that my circuit will work with the attached schematic work best. I did not made further tests with the values but R1 and R2 can be 12K. I will record and upload a new sample, this one has a guitar at the back, this is one of the songs that had the distortion at the high tones of this guitar, now is tight.

So, moment of truth. I've made a few tests with exacly same components as your virtual ground design, it was almost. I pushed the circuit limits by the way, so instead of 2.3Vpp signal i use a 5.0Vpp signal to push it to the limit and to meet the specifications that i will work with. Using this signal i get distortion at high notes and fluctuations over virtual ground point, this is good because it will work with signals from about 1Vpp to 3.3Vpp. So i start to play with the resistor dividers, Increase the two 100K to something like 330K i get a bad distortion, getting this value to about 48K it will work nice but not at the level that i need, sounds very good but it will distort with some specific conditions from the source. Using 22K get's better but still distorting a little bit. Lowering to 4.7K if there is a high voice for example the voice sound os ambience do a strange vibrato effect in some very specific type of music. 6.8K is the exact value that will give me a rock stable virtual ground, 10K work also, but 6.2K is how low we can get with that high RCA level. Using the headphone it sounds perfect clear, but in very specific conditions and paying atention there is a low level not easy to notice some kind of "granulation fade out" for very short period, again, only in very specific conditions. Since i'm using a TL072 that is a dual opamp, i will try to double buffer the virtual ground and see what it does.

Ok, i will made the changes with your circuit, just give me a minute to work this out.

Hi audioguru, Yes, it was Elvis Presley, the recording was made live at the show from the sound board at 08/12/1970, the original has that distortion and noise, the Buzz, Hum and Shhh. I did not know that the 22nF could overload the opamp but i tought it wold atenuate the high frequency around 17.5Khz acording with my tests, so i could remove this capacitors, change the circuit to see how things work out, if the tweeters start to pop out again i could try 10nF instead. One thing that i have also noticed is the turn on time, using a pair of 100K resistors make the sound crack when the circuit is turned on using 22uF/100uF, changing to 220uF/100uF it gets around 3.5 seconds for the opamp start operating at full. Changing from the two 100K to 4.7K and 220uF/100uF the turn on time is less than a second, and changing the capacitors to 22uF/100uF it makes the turn on even faster but it decrease the bass response. I will use the TL072 because i have a bunch of it, i will adapt the "Phanton Ground" without the capacitors to the ground, build a new prototype and i post here the results, ok? Thank you

I will design the "phanton ground" using a TL072, do you think that this will be enough to make the virtual ground more stable and avoid the distortion?

Doing frequency analysis response, changing the eletrolitic capacitor from 220uF to 22uF i get a decrease at bass response, sound looks like a dry high frequency and a dull midle to bass response, changing back to 220uF gives a more natural flat sound

Hi audioguru, Changing that R12/13 from 4.7K to 100K makes the sound worse, at the center channel for example, Elvis voice start to crack up soon as he start singing, i used the same 2.3Vpp signal, when we get near to the end all channels has a huge distortion like a guitar overdrive. The capacitor load at the output (22n) is needed because of the power amp, otherwise the tweeter start to click and pop out, maybe i could use a bigger ones like 100n. The condition becomes normal if i use again 4.7K in R12/13, but keep the changes in the eletrolitic capacitors.

Hi audioguru, So your sugestion is to increase the resistor values to 100K, decrease the capacitors values and remove the 100K bias resistor? But there is a problem, if i remove the 100K bias resistor i will short the input channels messing up with the effect, right? The buzzing distortion at the brass horn instruments was in the original CD, including the "buzz and Hiss" noise. I will make the changes and see what it does. Thank you.

Hello audioguru! How are you, you big dog (or duck) ;D Thank you, it was not an easy task and i wont let it go that easy ;) I love learning this stuff. 8) So, what you think about the new circuit, it was a brain burning task, you have more experience than me in that area. tell me something, if i do the circuit by Analog Devices, do i need to keep biasing the opamp inputs? Thank you.

Hello esp1, how are you? Thank you for your reply The aplication note AN581 (Download here) show a similar circuit with the CA3140. But i really worry about is if this buffered virtual ground will or could hold a 5Vpp RCA signal to prevent audio clipping. At this sample: http://www.sendspace.com/file/3fxm5w (2.06Mb) I use a 2.3vpp signal with the configuration of the schematic, using the 4.7K resistor voltage divider, and as the sample show this is the circuit limit, anything higher than that start to have small clipping. Thank you.

Hello guys! I was talking with audioguru some time back about my hafler circuit (schematic attached), it was clipping and i did know exactly why, we exchange some ideas and i choose to let it go. I've never used the center channel and when i did the quality was very bad, the overall sound got even worse since i've added 2 more TL074, so i redesign the center channel block, but after building the prototype clipping was worst than before in all channels. So it was not the signal, it was not gain but i've find out that the clipping problem was related with the virtual ground, i was using a pair of 10K resistors to make a voltage divider and every time the sound clipped i got oscilations at that point. Doing my research i've found this information: http://headwize.com/projects/showfile.php?file=opamp_prj.htm There may be times, though, when a virtually-grounded dual supply has a tendency to "rail" when the resistor-type voltage divider cannot maintain the virtual ground at 1/2 Vcc. Such cases may occur when the opamp draws too much current or input signal (for example, a high boost equalizer) pushes the opamp into heavy clipping and power supply is unable to recover. Changing the R12/13 to 4.7K did a huge increase in sound quality, audio now was cristal clear again, so i thought. Here is a audio sample (8Mb, sorry if is too big): http://www.sendspace.com/file/l79kos If you hear it with headphones you will notice the audio clipping, not that much, i recomend that you play with your audio card balance to hear what each channel is doing, left channel is the center channel or voice and right channel is ambience. Analyzing the virtual ground i get a very smal oscilation when the audio clip. Good, now i know what is going on with the circuit and why is clipping. I've found a circuit in a old magazine that use a CA3140 and a few components, the question is, this circuit can or could make the virtual ground to be more stable? Or should i consider design a full symetric supply based on SG3524? My goal is to keep this small because there is alot of components already, and if the CA3140 solution work out there is no need for me to use the SG3524 that will need a dozen more components. Thank you guys!

Hey AN920 nice circuit, thank you for your reply. But come on, don't do this!!! Let me wrap my hands and hold my self and use my mantra "I dont want to build this!, I dont want to build this!" ;D ;D ;D Let me ask you something, there is a way to make your circuit work with 8 led's so it will make a true Knight Rider! I have about 10 circuits builded, i think this will be another one, finger crossed!

Ok, when i get some free time i will try to mess up a bit more with this project. Thank you Audioguru! By the way, you can move the file to the project section for others to build their own board of the project, inside there is a schematic, board design ready to print and the Eagle Project.

But the effect is only the fade out correct?

Hello Audioguru, long time no see! Yep, i know that, but sometimes you have that feeling that "it might work out". I've done long time ago the basic CD4017/NE555 with some power transistors and light bulbs (i said bulbs not bubs ;D ) used in brake light, and it work like you said, when the light shuts it fades slowly making a nice effect. What catch the eyes is not that coming and going effect, but the impression that is a devil traped inside that scaner, you know, like an evil bull with red eyes impacient, looking at you, coming and going just waiting the right moment to get you. Is THAT effect that i want to build and reproduce in a small proportion with led's. This circuit is not that all bad, comparing with this simple CD4017/NE555 (2CI's) this 7CI's project has a is very smooth movement as you can see in my video. But, an true Knight Rider scaner has 8 light and not 9 like this one, i think it should be ease to fix this project. But Audioguru tell me something, to get this effect with led's, it could be done with 47uF or 100uF eletrolitic capacitors right? Connecting then in series to ground so the acumulated energy in the capacitor will discharge slowly and so the led will have a fade effect right? For thouse that want to build the project i've included in this message the board and schematic. PS:Rename the extension from .zip to .7z

Hello All! I've build this "Nite Rider Lights" http://www.electronics-lab.com/projects/automotive/011/index.html http://www.electronics-lab.com/forum/index.php?topic=1427.0 Made a few changes in the project to meet my needs, R3 100R, R2 1K, C1 10uF. By the way, i dont know why i get dragged to projects like this because at the end it will work the same, this one need 7 CI's and a simple CD4017/NE555 do the same effect. So, here is a video of the project working: http://www.youtube.com/watch?v=OYyYeOvRzm0 My question is, how hard is to use this circuit to make a true Night Rider scanner like this: http://www.youtube.com/watch?v=-5Ktks-1RjM

Good to hear (read) that! Thanks!

I see signal loss at input 1-2 and 3-4 because it has to pass by 3 CD4053 (150R*3=450R), the input 5-6 has only a total resistence of 300, so i fear that this could mess up with the signal even if it is buffered at the output, like diference in signal at input 1-2/3-4 and less at input 5-6, but i can compensate this by adding 3 150R resistors at the output of the IC3 (pin 4, 14, 15). Any way, i need to build this first and test latter. I will search for this debounce circuit, thanks!

Hi audioguru, No, no, i will not work with RGB just component video (Y'PbPr). My monitor can handle component video (Y'PbPr) and 1080i signals. This structure is just the basic connection to work with video, the audio block still missing in there. But before i build the design to the audio block i have to solve the video block first, that is why i ask for a good opamp video buffer because of the loss of signal when it pass by the CD4053 internal switches. Maybe i have some where a schematic for the circuit of the pushbutton using the CD4017. But, the basic idea, do you think it will have too much signal loss?

So here is the basic structure (is not ready yet), so this could be more easy to explain. The first output of CD4017 will have a inverter 74xx to make sure that all CD4053 are reseted (LOW), so all CD4053 is in X0/Y0/Z0 position, this will be channel 1 Using a push button to change state of CD4017 output 1 (HIGH) will make IC1 switch from X0/Y0/Z0 to X1/Y1/Z1, all other CD4053 stay at the same position, , this will be channel 2 Changing the state again from CD4017 output 2 (HIGH) will make IC4 switch from X0/Y0/Z0 to X1/Y1/Z1, IC2 hold position, this will be channel 3 CD4017 output 3 (HIGH) will make IC2 switch from X0/Y0/Z0 to X1/Y1/Z1, IC4 hold position, this will be channel 4 CD4017 output 4 (HIGH) will make IC5 switch from X0/Y0/Z0 to X1/Y1/Z1, IC3 hold position, this will be channel 5 CD4017 output 5 (HIGH) will make IC3 switch from X0/Y0/Z0 to X1/Y1/Z1, IC5 hold position, this will be channel 6 When the CD4017 start counting again, it will send a LOW signal to all CD4053 to reset and go back to channel 1 again. So, this is what i was thinking, i'm open to suggestions. To make this more easy: Channel 1 IC1 X0/Y0/Z0 IC4 X0/Y0/Z0 IC5 X0/Y0/Z0 Channel 2 IC1 X1/Y1/Z1 IC4 X0/Y0/Z0 IC5 X0/Y0/Z0 Channel 3 IC2 X0/Y0/Z0 IC4 X1/Y1/Z1 IC5 X0/Y0/Z0 Channel 4 IC2 X1/Y1/Z1 IC4 X1/Y1/Z1 IC5 X0/Y0/Z0 Channel 5 IC3 X0/Y0/Z0 IC5 X1/Y1/Z1 Channel 6 IC3 X1/Y1/Z1 IC5 X1/Y1/Z1

Hi audioguru, The idea to use the CD4017 is to use this logic sequence to trigger different CD4053 on the way, for now is just a concept. Since i will use 6 inputs: 1) The first block will switch the signals( inputs 1-2, 3-4 and 5-6). 2) Second block will work with the logic of the signals since is only one output i have to disconnect the output of 1-2 and connect the signal from 3-4 and so on. The CD4017 will solve in a simple way all that mess. 1) Output CD4017 0 (NC) & 1 (trigger from input 1 to 2). 2) Output CD4017 2, trigger another CD4053 to change from output 1-2 to 3-4 And so on, i think i will need 5 CD4053 and maybe a inverter (74xx) to make all the logic work out. What do you think? I will make a basic schematic of this.