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Yep, it looks, like very close to “it” design-wise.
http://www.studiomaudio.info/loftinwhite.html
In the way this amp is one of the manifestations of Loftin-White DC-coupled but it has some own things. The driver stage is the Melquiades Tube to keep all 6 channels to have the same “feel”. For this MF only version the 6E6P huge gain is totally not necessary, so it was reduced by using the un-bypassed cathode bias. The removing of fix bas got rid the DC dependency of grid from ground and made easy to remove the buildup of impedance from the driver grid, effectively extending up the amp bandwidth. Also, with the bandwidth helped the redaction of the driver gain that droped the total Miller capacitance… I like the driver stage now: it has no explicit capacitance and with RL input filter it is as “clean” as it theoretically possible to be.
The output stage is very ordinary running the power tube very spearing but the measures were taken do not bypass the cathode cap in a normal way. The solution is very elegant and was advised to me by a friend of mine, who generally helped with the DC coupling and who due to respectable reasons prefers to be anonymous.
The PS is interesting. I source power form my main 400V PS that I jacked up to 114V. The supply is my regular: Schotky full-wave, LCRC with enormous last cap (I think I have 15K by 450V or something like this). The huge capacitance assured kills ripples but most important it decuples PS from the amp. Since the huge cap forms very low filter and the AC from the tube get shorted right here in the cap down to a fraction of hertz. The folks who use 8uF or 20uF capacitance in SET are playing different games. The AC from this tube goes back passing the last cap and at lower frequencies it getting shorted via chokes and rectifiers. Thos people spend days and years learning how rectifiers, capacitors, wires, secondary of transformers affect sound. It all does affect but only because all that unnecessary shit in the AC back path. I hate this and I juts cancel all of it by using the large last cap. As the result my amp very little affected by the “sound” of rectifiers, capacitors, wires and the rest irrelevant things.
The large capacitance does not affect bass negatively, quite in contrary, but it does make HF a bit “harder”. So, what I do? After the last large cap I have a decoupling resistor and a high quality film cap to ground. The impedance of the decoupling resistor is much higher than the filtering impedance of the film cap and way below the operational frequency of the given channel. Here is where the advance of the DSET topology again show itself off: I have perfect DC with a fraction or mV ripples, the DC that acts like a huge buttery but at the same time, my HF channel run own AC to ground via a high quality film caps and do not see that large capacitance behind this film cap. This application was advised to me by Dima, I see a lot of rational behind it and it become my way to do the things for DSET applications.
In the latest revision David Slagle helped me with input filter that roll off 2.9dB and introduces 3.2kHz first order roll off. It is regular voltage decider combined with RL filter. David built the 80% nickel filtering choke or right value with high resonance frequency (18kHz). The choke and the Obbligato Film cap are in the mails and as they arrive I will be able to finish the amp in a final version, to close it up and start to listen it integrated with the rest channels… I will post tonight the draft 18, the latest one. The caT
"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
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