300b lovers

I heard, and liked very much the Songer fieldcoil speakers I heard at Capital Audiofest.  I believe the dipole driver speaker and the more conventional box speaker were the same price, even though it appears that you get much more with the dipole version (two-way instead of a single driver).  Both sounded quite good to me.  It would be interesting to hear them more or less contemporaneously with my other show favorite--Charney Audio full range systems (higher efficiency than the Songers so even more low-powered SET friendly).  

I am glad I followed this, am in search of a new line-stage and the Raven looks like a good prospect. I have simple needs with only one RCA and 1 XLR input and same with outputs. I will pair it with my VAC Renaissance 70/70Signature amp and XLR into my Legacy Audio Focus XD’s. Saw the Raven design on a You tube show Video.

Coming back to Earth, I heard the Purifi Class D amplifier at the show. Quite good, and free of the usual transistor Class AB metallic coloration. The Raven preamp would make an excellent match for the Purify, since it is very transparent, has plenty of drive current, and is also an ultra-quality ground and RFI isolator. It might seem like an odd pairing, but for somebody that needs cool-running Class D power, the combo would probably work really well.

However ... the way the Raven is configured now, it can only drive one output at a time, either XLR or RCA. Well, technically it can drive both at once ... no harm is done to the circuit or any parts ... but the load is then unbalanced, with more cable capacitance on one side than the other. So the amp with the balanced inputs will receive a signal that doesn’t quite match at high frequencies.

This is probably true of other preamps with XLR and RCA outputs ... unless the literature comes out and says it has independent and isolated output sections for each set of outputs, you should assume the RCA is simply connected to one side of the XLR output. If that is so, then the added capacitance of the RCA cabling, plus the input capacitance of the RCA power amp, will unbalance the XLR output.

I should also mention when a transistor power amp is turned off, the input section of that amp is not isolated from the cabling, and the turned-off input transistors can create a nonlinear load for the preamp. Once it’s on again, feedback and power is restored, and the amp operates as specified. But when it’s off, best not to have another amp connected in parallel.

This is an important difference between tube power amps and transistor power amps. The input grid of a turned-off tube amp just sits there with a few pF of capacitance from the tube socket. Nothing else happens. It would take hundreds of volts to arc-over the tube, or break something in the input section.

By contrast, the base or gate of the bipolar or JFET transistor has a nonlinear input capacitance that remains when the power is off, and there is serious risk of damage if a 20 volt transient comes by ... this is a real hazard with conventional cap-coupled tube preamps and their associated turn-on thump. (The Raven is transformer-coupled and cannot pass DC transients, but there’s a small click when the VR tubes snap on, but small enough that even the most delicate Lowthers would not be harmed.)

@lynn_olson

"However ... the way the Raven is configured now, it can only drive one output at a time, either XLR or RCA. Well, technically it can drive both at once ... no harm is done to the circuit or any parts ... but the load is then unbalanced, with more cable capacitance on one side than the other. So the amp with the balanced inputs will receive a signal that doesn’t quite match at high frequencies."

I wonder if this is an issue since the XLR’s are just driving the bass, however this happens with in the internal crossover in the speaker. I spoke with Don on the phone today, getting clarification from Legacy how this works with RCA and XLR together in bi-amp.

Lynn makes note of hearing Purifi Class D amps at the show in a favorable way.   I did hear Atma-Sphere's new GaN mono amps driving the the Tekton Moabs and I thought they sounded excellent.  I could easily see a synergy between the Raven and Ralph's mono amps and I personally would require a tube preamp with any amp I might choose to use.  That Ralph has made such a move to Class D technology after decades of being a tube designer/manufacturer ought to make the audio community sit up and take notice.  What I heard of his $5500 amps was very impressive.  Of course, let your ears be the judge.

I am luxuriating with Don's DS2 preamp and his new 300b monos driving my now run-in Cube Audio Jazzon speakers.   I am enjoying the sound in my room to a degree that I have never experienced before.  From morning to night...