Members SykoJr Posted September 6, 2010 Members Share Posted September 6, 2010 Hey guys. I found this schematic ( http://www.triodeel.com/comp1.jpg ) on the interwebz and decided to build it, since it is pretty simple in comparison with other tube compressor designs. But before I actually laid my hand on any hardware I decided to run some SPICE simulation, And good thing I did cause it seems that this thing does not work as intended. The thing should be basically voltage controlled voltage splitter (the right half of the right tube together with the 470k resistor) which is controlled by the DC voltage generated by the right half of the 1st tube which is running as a diode. I get the whole idea, but the problem is that if i want to see some change of resistivity of the splitter tube I will need negative voltages on the tube's grid. The problem is, that the control voltage is positive no matter what I do. I'm a tube noob, so please if you have any advice - bring it on. Thaks. Link to comment Share on other sites More sharing options...
Members normh Posted September 6, 2010 Members Share Posted September 6, 2010 The spice models for tubes need work. As an example, I modeled my Vox AC4TV amplifier. When run through the spice simulator it does not work. The amplifier and the model are simple. The working product is sitting next to me but the spice model indicates that it does not work. Epic fail when it comes to tube models. Spice simulations and models are only guesswork when it comes to a working product and all spice models should be taken with a grain of salt. The transistor and IC models are better. However, even the solid state models need to be examined. As an example here, I designed lm386 two watt amplifier in a high dollar program, Multisim. When I worked the bugs out and built the amplifier I kept blowing the IC's. It took some work and trouble shooting to come to the realization that Multisim failed to take into account the maximum power dissipation of the op amp.'s. Not hard to remedy, but a nuisance. Link to comment Share on other sites More sharing options...
Members SykoJr Posted September 6, 2010 Author Members Share Posted September 6, 2010 The spice models for tubes need work. As an example, I modeled my Vox AC4TV amplifier. When run through the spice simulator it does not work. The amplifier and the model are simple. The working product is sitting next to me but the spice model indicates that it does not work. Epic fail when it comes to tube models.Spice simulations and models are only guesswork when it comes to a working product and all spice models should be taken with a grain of salt. The transistor and IC models are better. However, even the solid state models need to be examined. As an example here, I designed lm386 two watt amplifier in a high dollar program, Multisim. When I worked the bugs out and built the amplifier I kept blowing the IC's. It took some work and trouble shooting to come to the realization that Multisim failed to take into account the maximum power dissipation of the op amp.'s. Not hard to remedy, but a nuisance. Well... totally not the answer I was hoping for, but thanks anyway. Link to comment Share on other sites More sharing options...
Members SomeoneYouKnew Posted September 6, 2010 Members Share Posted September 6, 2010 The thing should be basically voltage controlled voltage splitter (the right half of the right tube together with the 470k resistor) which is controlled by the DC voltage generated by the right half of the 1st tube which is running as a diode. I get the whole idea, but the problem is that if i want to see some change of resistivity of the splitter tube I will need negative voltages on the tube's grid. The problem is, that the control voltage is positive no matter what I do.I can see that without even using spice. The right half of the first tube is functioning as a diode with capacitive coupling of the signal from the cathode follower circuit of the triode on the left. The cathode on the right can never be negative, only positive. This signal is then routed to the grid of the left triode of the second tube. Again, a cathode follower. Its cathode can only be positive. This signal is DC coupled to the grid of the grounded cathode amplifier of the right triode. It either conducts hard or harder. It's always in saturation with the grid more positive than the cathode. I suspect there is an error or errors in this circuit. I can't imagine it working at all. In addition, there is no buffering of the input signal. So this will be lossy. The output can never be greater than the input in amplitude and the output impedance will be quite high. I think I'd dump this and look for a different circuit to start with. Link to comment Share on other sites More sharing options...
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