Spatial Audio Raven Preamp

Any info on your power amps? Input sensitivity (volts RMS to clip the amp) and input impedance should tell the tale.

Transistor amps (with feedback) are typically 1~2 volts to clip amp, and input impedance is typically 10K to 22K.

The Bruno Putzey Class D modules are designed so they need they need about 10V drive and an input impedance of 6300 ohms. This non-standard input is intentional; it gives the third-party amp designer the freedom to design an input stage that has the tone color they want: op-amp, solid-state discrete, or vacuum tube.

My speakers are 89dB sensitivity and the volume on my Raven preamp at a "comfortable" listening level is 35.  Need those amp specs or something is amiss.

The Bruno Putzey Class D modules are designed so they need they need about 10V drive and an input impedance of 6300 ohms

Actually if you want to be safe you should expect to drive 2000 Ohms rather than 6K or higher. Typically an input buffer will provide roughly 12dB of gain and allow an input impedance of more like 47KOhms. That would put the total gain in the region of 22-25dB which is plenty for most speakers.

True. I surmise leaving the input section of the Bruno Putzey modules as they are was a deliberate design decision on Bruno’s part. The modules are an almost-complete power amp, but are incompatible with existing RCA and XLR interfaces, due to the low input impedance and medium-level voltage drive requirements.

The OEM is then free to add as much or as little sonic flavor as they like. If they are catering to the ASR crowd, there are superb op-amps these days with truly exceptional measurements (they also sound good). If the OEM is up to a challenge, they can design a discrete transistor circuit, but it is very unlikely it will match the specs of the best modern op-amps. The days of the evil 741 and the mediocre 301 are long gone. The 5532/5532 is very old, dating back to 1979, but is still seen in pro gear. And if the OEM wants to earn the contempt of the ASR folks, they can use one or two vacuum tube stages, which will increase the distortion of the Putzey module a hundred or a thousand-fold.

True. I surmise leaving the input section of the Bruno Putzey modules as they are was a deliberate design decision on Bruno’s part. The modules are an almost-complete power amp, but are incompatible with existing RCA and XLR interfaces, due to the low input impedance and medium-level voltage drive requirements.

@lynn_olson If you simply design an instrumentation amplifier that is balanced and using good opamps, it will work just fine. It seems to be a bit of a testament that so many class D products using Bruno's modules fail at this task thru no fault of the modules!! You don't need much gain either (2 is fine) so you stay well within the requirements of modern opamps, allowing them to be completely neutral. Even then, despite the low distortion of the opamps, they will dominate the distortion character of the finished amp.

The power supply requires special attention as well. Class D amps can go from almost no load for a power supply to quite a heavy load, so the power supply has to be overbuilt if you want the design to be musical!

It is the variables of the input buffer and power supply as to why you read so many disparate experiences that audiophiles have with class D amps.