Spatial Audio Raven Preamp

As Don mentioned, avoid the thick and crazy-expensive audiophile cables. You have to remember most audiophiles have noticeably colored transistor gear, and use aftermarket products like power conditioners and $5000+ cables to minimize glare, grain, and excessive HF output in their systems. The better approach is using low-coloration electronics and loudspeakers with a smooth response, especially above 2 kHz.

The key spec in any cable, much more important than any other, is capacitance per foot (or meter). Capacitance should be well under 100 pF/foot, preferably much, much less. Inductance *does not* matter unless you are running an AM transmitter (those are RF cables). Inductance does not load down the preamp, but capacitance does, occasionally causing transient instability in a preamp with high feedback. The Raven has zero feedback, but solid-state preamps typically have very high amounts of feedback (40 dB or more), resulting in load sensitivity to the preamp/amplifier interconnect.

The quality of the insulator (dielectric) in the cable also affects the sound, and Teflon is not necessarily the best. It’s the first choice for aerospace applications, and has exceptional DF and DF measurements, but in my experience, may not the best for audio. Various types of plastic all have their own colorations, and the process of fabricating the cable applies mechanical stress to the plastic, which changes its dielectric properties. The more complex the construction, the more complex the coloration, and the longer it takes to settle down (possibly never). Most of all, DO NOT TRUST the reviews you see in magazines or on the Internet.

This question may have been covered, but I have not seen it.  Is the preamp part to part wired? Combo of circuit boards and PTP wiring? Are the tube sockets mounted to circuit boards? 

Most interesting product and thread.  
 

@grannyring The preamp, and the matching amps are point to point wired, yes. The tube sockets are all mounted directly to the top panel in both pieces. The only pcbs are there to hold large film capacitors to facilitate mounting them securely. The regulated power supplies, both high voltage and tube filament, are built on small pcbs, which are point to point wired to the rest of the components. Again, all signal path wiring is point to point with very high quality wire. The power supply wiring is all teflon insulated mil spec copper. Signal path is all copper as well, but there is no teflon insulation in the signal path. There are NO electrolytic capacitors except in the regulated DC filament supplies. The entire high voltage B+ supplies in both preamp and amps are built wtih all film capactitors, all resistors are wire wound.

All parts are chosen so that they are run very conservatively. No part exceeds 60% or so of its voltage or current or temperature rating. For example, the DC filament supplies can deliver 3A of current and in the preamp they provide 1.2A to the pair of 6SN7 tubes. Resistors are run at no more than about half of their power rating anywhere in the circuits. The preamp and amps are designed to last a long time and to survive the odd tube failure without damage to the unit.   You can put your hand on the power transformer of the preamp or amplifiers after hours of use. Even though both circuits are class A, they run at reasonable temperatures and do not stress their transformers at all.

Impressive build and handling of the important details. Thank you for such a detailed answer. I’m very impressed with the quality and design of these products as well as the transparency and comprehensiveness of the responses. You and Larry are to be commended. Thank you.

Let's just say that before building my own tube creations I restored probably 300-400 pieces of vintage tube gear, including about 75-80 citation II amps, over 40 citation I preamps, and many Scotts, Fishers, Sherwoods, Macs, Marantz 8b, etc... I saw what were clearly high quality build practices, and cheap ones too.  I always appreciated the gear that was easy to work on, and hated designs that were difficult to rebuild.   So everything we build is designed so that it is easy to work on should anything ever go wrong.  It is designed so that things are never run anywhere "near the ragged edge".   Tubes are in class A, but still conservatively run and should have long lives.  I want the customer to enjoy the gear for years, and should there ever be a problem, I want the tech to easily be able to swap out a part and have it running again. 

I remember working on Marshall guitar amps for musician friends.   They have a dozen little pcbs, tied together with jumpers cables that all have the same terminals, so that you have to mark each board and cable so you know how to put it together again.  The problem would always be on the bottom board!   So we avoid construction like that.  This gear is a bit complex, but very modular, the layout is neat and clean, and it is designed to be trouble-free.  For example, all AC is on one side of an internal shielding bracket, and all signal path on the other in both preamp and amps.  Star grounding, with strong attention paid to current loops.  No hum!