![]() ![]() So for driving low impedance loads where more current is required should do better than the 6SN7. On the other hand, the 6BL7 can dissipate more watts total, 12 vs 7.5. The 6BL7 is only marginally better than the 6SN7 in these tests. One series tests a 6SN7, the other a 6BL7. The tests were done one after the other, not three triodes all in the cct together as in the schematic. Conditions for each test are kept the same, a 300V PS & D% is taken at 10VAC out. So there are three kinds of loads in each series, an ordinary 36.5K load (A), a passive triode biased same as the bottom tube (B) & an active tube on the top (C). When the top tube in these example is passive, load is only One times rp when both triodes are similarly biased. Theory & practice sez the load Rl should be at least 2X rp & preferably 3x or more to reduce distortion. ![]() What effect does the top tube have on the bottom tubes performance sofar as D% is concerned? If we think of it, the top tube in a mu follower forms the load for the bottom tube. I did this work in 1999 as part of a line follower cct investigation. Some Mu Follower Distortion Measurement Results I have several preamps with gain collecting dust (or that eventually will be given away) simply because my builds have enough gain on their own, and are right near the source and other equipment. If you need more build a variation of the above circuit with the direct coupled cathode follower.Ī cathode follower can help in driving cables or tricky loads, but even then they aren't totally necessary. Great way to go for 3-6x if that's what you need, and can drive most any consumer level load/cables. From the 1960s onwards a variety of transistor versions appeared 12,13,1415, but still without the name SRPP applied. Of course, we now use the term SEPP for the more specific circuit arrangement by Peterson and Sinclair. It’s called the cathode follower and it doesn’t amplify sht, at least not in the voltage embiggening sense. 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. I have included three schematics based around a 6SN7 the tube I would like to use. My usual recommendation to folks is to build the 6V6 preamp from Salas' thread. (which also covered circuits like the µ-follower and White cathode follower) or SEPP. Cathode Follower Besides the grounded cathode amplifier, there’s another very common arrangement for a tube that you are sure to run across. Ive built a very basic stereo pre-amp, which is just a gain stage, followed by a cathode follower. In some instances a bit of gain is handy, and I find that something from 3-6x or so works well, and something from 10~15x works well in situations where one is matching mobile devices or running external circuits like a baffle step compensation setup or crossover. Sometimes a transformer if there is funky ground loops in your setup that can't be helped. Oftentimes a simple source selector, volume control, and occasionally balance is all that may be necessary. I think so many people are so focused on having a bunch of gear (commercial, or DIY) that they just want to run a pre or linestage with gain.
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