jelt2359

First post here, been lurking a while but I'm a huge fan of Pete's (Doug's too, for that matter), here's some info I got from Pete via PMs, and Todd was okay with me reposting it so I thought I'd share. The Sangaku has more "single-ended triode" sound (mostly second harmonic distortion), for a more tubey presentation than his previous hybrids. This is a result of the way the Nutube's circuit was designed. Nonetheless, his tube amps do tend to have broadly similar sonics- in short, there is a "house sound", a certain harmonic mix that he shoots for, typically by moving the operating point of the first tube stage. Some other differences between the Sangaku and the previous Apex hybrids: The new amp has much more output voltage driving capability than any of the previous hybrids; and also the lowest output impedance. Part of this is because of the Nutube- it only uses milliwatts of voltage. At the same time, the power supply voltage on the Sangaku is much higher (+/-18V, vs. 12V or 10V) to provide bigger output swing. The output stage is also different from the Peak/Volcano. The Peak/Volcano had a discrete MOSFET buffer. In the Sangaku, however, Pete has moved back to using power opamps. According to him the Peak was more of an experiment to see how well he could do without an opamp, but he's since decided that power opamps are better. He knows that some will argue that this is a less 'pure' approach, but he's made his choice- they dissipate less power, are smaller, and perform better. He's implemented these power opamps with CCS loads on them to keep them in class-A operation at low signals. Nonetheless, when driving lots of current, the output still goes into class AB operation. The CCS keeps more bias current flowing, which reduces any crossover distortion, an issue most problematic with small signals. Finally, the Sangaku is not DC coupled, but it's -3dB point is very low (single-digit Hz).