The Q used as a buffer amp

[4krow]

  It has been a long time since I have built a Quickie. Now, a new question comes about for it. What would have to be changed in the circuit to render the Q to a 1:1 buffer?

[cpaul]

Search this forum for cathode follower.  http://bottlehead.com/smf/index.php?topic=1221.msg28432#msg28432  This idea isn't fully fleshed out, but if you read between the lines you should be able to give it a try.  I have intended to try this myself for a while but other projects are higher up on the list.

Cheers and good luck.  Report back if you try it!

[4krow]

  There is no doubt that your idea is worthy of a trial. Trouble for me is that I am not of the level of electronics experience that I am able to design such a circuit. Like many others, I try the very simple stuff like changing out parts of the same value within the existing Q circuit, or something equally easy to accomplish. There are a few 'aha' moments now and then, but to do more than that, it is wise for me to have a ready to assemble kit, or at least, a detailed set of instructions to follow.
 I have, in the past tried a cathode follower that was designed by John Broskie. The quality of the circuit was certainly enviable, but the sound was not as popular with me as the Quickie. Also, the circuit used 6NS7 tubes if I recall, and required much higher voltages, transformer, etc, that made it quite more complicated than the Q. Shortly after making a few of these kits, I returned to the Q for the sound that I so admired.

[cpaul]

That was Dr. Toobz's idea but I hope to try to breadboard a circuit to see how it works.  Cathode followers are likely to sound different from the standard Quickie design, and I'm not good enough to predict what might happen.  Do read through the short thread a few times, though, b/c it's pretty simple.  Take out the resistor/CCS/choke (whatever you have) at the plate, replace the resistor and cap currently at the cathode with what came out of the plate (well, not the CCS as that requires a bit of a rebuild), then move the output wires that go to the output RCAs (and WERE also at the plate) to the cathode (between the socket pin and the resistor or choke you moved).  I think that is all, though I should double check.  Not a substantial change as far as work goes, and as easy as the Q is to build.  Do ask questions as you go, though, so I and others can help keep you on track.

I'm likely to try the choke in the cathode when I do it, but maybe start with a simple resistor.

[Paul Joppa]

The stock Quickie is a buffer with a maximum gain of about 2.2 (7dB). If you turn the volume control down 7dB, then it's a unity-gain buffer.

Cathode followers use feedback to control the gain, but that gain is always less than unity. For the 3S4, that gain is about 0.8 (-2dB).

[4krow]

Thank you gentlemen, I will definitely these things into consideration when the time comes. I am also considering a regulated AC power supply, but that is another thread altogether.