output circuit Cathode follower, minimum 10k Ohm load. it may well reduce the output impedance but that is not the same thing at all.Īpologises for 'teaching my grandmother to suck eggs." but not everyone understands this enough when they examine a circuit. It features the famous 6SN7 octal vacuum tube, and all vacuum tube rectification using the 5AW4. so the use of CF configuartion or feedback (local or global) doesn't give the stage anymore ability to drive current into a load. Im curious if theres any evidence that the grid of the follower seeing full B+ at startup is actually a problem. FOR SALE This auction is for ONE bare PCB. ![]() This is clearly seen by looking at the V/I curves (plate curves) of the valve at the chosen operating point and then plotting where the input signal moves it from that operating point. DIY PCB BOARD OTL Tube Headphone Amp Aikido White Cathode Follower 6SN7 6BX7 - 30.00. One thing people need to understand is that regardless of configuration or feedback a valve cannot deliver current into or volts accross a load that goes outside of that permtted by the valves intrinsic V/I regime. Run the beastie with high curent and it will sound good. like run the input at low Av to reduce the Millar capacitance and load it with a choke loaded CF second stage. ![]() Of course it probably sounds OK in an all valve system where it isn't asked to drive long cables or low input impedance but then why use this design as there are recognised much simpler ways to get good sound out of a 6SN7. Please, any suggestions would be most welcome. I have been looking but cant find anything - Either OTL or TX output, I dont mind, I would think that the 6sn7, especially in parallel would have enough juice to supply my Sennheiser HD650. in short its a horrible application for a 6SN7. I have an abundance of 6sn7 family tubes and I wish to make a headphone amplifier using ONLY the 6sn7 throughout. It really doesn't use the 6SN7s stregths (exceptional linearity when lightly loaded but run hot) and walks into its weaknesses (high Rp, relatively high input capacitance, poor current drive capability) the feedback doesn't change the V/I regime the valve is operating under and just exposes it to more current demands that it cannot meet so adding to the TID that the feedback introduces. ![]() I've been trying not to comment on the design as I think it is horrible. It's in some of the 40s and 50s textbooks too - so it has a certain pedigree that runs from before the 80s revival diy scene. It has weak bass, and although I havent measured it with a spectrum analyzer, Id swear there is a dip in the upper bass register. JRB defines the meaning of plate (anode) follower and why it has been used. Ive built a very basic stereo pre-amp, which is just a gain stage, followed by a cathode follower.
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