300b lovers

When I was having a Bespoke Valve Input/Output Phonostage Built for me.

The designer builder was running two builds parallel, with the only differences being one had more RCA Inputs and my one had a Single RCA Input.

The Designer Builder invited me to listen once more to the design, but I could not get my head around it, there was still too much perception of weight, which was a a assessment put forward during the demo's done prior to what was supposed to be the final demo' prior to completing. 

I told the designer/builder, it was time to introduce Foil Resistors and Alternative Cap's. After some toing and froing, we got there in principle. Z Foils and a selection of Copper Foil Cap's was bought in.

The impact these had on the Sonic was from my assessment something very very special, even the designer /builder was on board and had their eye on this as a Upgrade Package on the Phon's if they were to be produced in increased numbers My later investigations which resulted in the addition of Vintage Tubes selected as a outcome of Tube Rolling experiences, was the addition that is the Cherry Garnish on Top.

The Tuning/Tweaking has the capacity to produce a sonic that is very different in the attraction/likeability generated to a earlier version. 

@pindac   Exactly my friend, exactly.   Once the power supply is right,  all the operating points are right and there is some serious listening, then the tuning begins.   We are almost there...

@atmasphere  very interesting Ralph. What are some amps you’ve heard with high feedback that you’ve enjoyed? I’ll have to check them out.  I’ve seen the measurements for the Purifi and its distortion is incredibly low, to the point it’s at the limits of what the AP analyzer can measure. It does have raising distortion in the treble but if I had to surmise, it is most likely low order as I find the purifi a touch sweet in the treble. I do run it without an input buffer as my preamp is up to the task of driving the Purifi module directly. 
I have yet to hear the new Gan stuff that is specifically designed for audio. I know yourself and AGD specifically designed yours for audio applications unlike many of the other brands. Are you guys going to be at the pacific audio fest? I’d love to come hear your Class D amps and hear how it compares to the 300b statement monos. 

@cloudsessions1

Are you guys going to be at the pacific audio fest? I’d love to come hear your Class D amps and hear how it compares to the 300b statement monos

That would be terrific!! Even if not heard in the same system. Still worthwhile to hear the GAN class D amplifiers and how they compare with the new 300b push-pull amplifiers. My sense is that Don and Lynn’s amplifier is something quite special.

Charles

Pindac has described the stage Don and I are at now: tuning the subjective balance ... there are a couple of nodes in the circuit where parts selection is quite audible, and we’re fine-tuning that.

I wrote an email to Don a couple of days ago that this topology is uniquely susceptible to parts coloration at the critical nodes. You get the same parts sensitivity in non-feedback SET amplifiers, but the much lower distortion of this circuit, compared to SET, exposes parts coloration more vividly. Fortunately, the right parts are available and are not super-exotic.

The circuit is inherently transparent, so there is almost nothing we can do to take that away, nor would we want to. But subjective tonal balance can be adjusted at the critical nodes. Surprisingly, the tuning has no effect on measurements, since topology, operating points, gain structure, tube loading, and bandwidth all remain the same.

Cloud Sessions asks a good question. Why does it sound this way? The best I can give is:

1) The circuit avoids both local and overall loop feedback, so there are no issues with hard clipping (transient overshoots in the FB network), stability margin (running out of gain and/or phase margin at high frequencies), or sensitivity to load reactance (which decreases phase margin and increases settling time after a large transient).

2) There are no differential stages to current-limit when one tube saturates or clips, taking the other tube along with it ... instead, the paired PP-mode tubes are functionally in parallel, helping each other out when the opposite-phase tube saturates or clips. Avoiding series-mode operation has a big effect on subjective dynamics. No SRPP’s, no split-load inverters, no long-tail pairs, no cathode followers.

3) Last but not least, each stage is individually optimized as much as possible for intrinsic linearity over the audio band. This is a matter of optimizing loads and minimizing the effect of Miller capacitance on the preceding stage.

Interestingly, Class D amps are free of Class AB transition artifacts, so there’s an entire class of coloration that just isn’t there. The big issue for Class D is nanosecond precision of timing for the pulse-width modulation (Class D is pulse-width-modulation, akin to FM, and not PCM), and insensitivity to reactive loads affecting the PWM modulator.