Spatial Audio Raven Preamp

I used to think that rules-of-thumb applied to transformers. Well, no. Maybe in the Fifties when they were designed with slide rules, but now you work closely with the designer and their simulation software, followed by a sample build. Model, build, put on the test bench, send the complete set to Don, he re-measures and auditions, and repeat as often as necessary.

The Raven is now on the fifth version of the custom transformer set. As noted by Don, they are optimized for the 6SN7 in balanced mode and the most common range of loads presented by solid-state and vacuum tube power amplifiers.

The secret of transformer-coupled audio design is a close working relationship with the transformer designer. In effect, the circuit is co-designed with the transformer designer.

One of the great things about working with Don is he has good working relationships with key vendors, so we can get custom designs on a timely basis, and we know exactly how they were designed. This lets us further optimize our circuits around the custom parts, rather than work around an off-the-shelf part.

To further the transformer discussion.  We don't need to name companies, but many take a sort of swiss army knife approach with multiple windings that allow for many connection schemes.  Sometimes they work, sometimes they don't.  But they are not optimized for the task.  I auditioned several with exotic core materials and found them to be a bit tipped up in the treble to give hyper detail, but they didn't sound right.  Of course, they look fine on the scope.  Interstage transformers from well known companies would ring at 15KHz or so, or others would run out of steam at 50 Hz and below in our circuit.  We are not talking Hammonds and Edcors here, but very well respected higher end manufacturers.   Our preamp output and amplifier interstage transformers are custom wound and use interleaved laminations of nickel and steel in a proportion that gives very even frequency response and hits the sweet spot balancing detail with proper tonality.  They have full frequency response without any oscillation.  This is based on years of experience by Dave Geren, the designer at Cinemag.  Dave tells me there are only a few sources in the world who can make the cores to his specification.   So a lot of design experience has gone into the transformers used in the 300b project, and as Lynn noted, several iterations for each transformer to get it right.  

Good cores are essential for low distortion.

Capacitive coupling exists between windings regardless of the quality of the transformer. For this reason alone its important for the transformer to be loaded correctly so it expresses its winding ratio without inter-winding capacitance as a parallel element. Otherwise the frequency response won't be flat.

@donsachs @lynn_olson The Blackbird Monoblocks and Raven Pre have over thirty hours on them and how sweet they are. Great job gents.

But darn it Don right you are about the Khorns and lower base. Running Roon I have even gone into the paramedic equalizer (a sin?) and boosted the lower hertz but still compared to my other system w/ a pair of Sonus Faber Guarneri Evolution’s speakers (faster sounding than Khorns) the base is flat verses the aliveness and vibration of a nice walking bass line. Low piano notes should vibrate too. “Grandmama's Blues” by Cyrus Chestnut on the "Earth Stories” album is a great test track https://open.qobuz.com/track/2003813  or even “Ham Hocks and Cabbage” by the Christian McBride Trio https://open.qobuz.com/track/10462550. Lower Tom drums also not quite there.

The low mids..heck all the rest (room still not treated and it’s boomy ) get ‘er done. Your gear is great and my contact over at Spacial has provided great service.

I have to consider if’s my streamer adding/subtracting to the bass quandary. I’ll swap out my other streamer and dac.

@wsrrsw

It will not be the amps unless something is wrong with them or you have a bad tube. The easy test is to move them to your other system. Your Sonus are 86 dB, 4 ohm. Not the best load, but the blackbirds will drive them and that will tell you if the amp has issues. Khorns have limited bass below about 45-50 Hz. It falls off like a stone. They are what they are..... They do other things quite well. The crossovers can be upgraded if you have not, but the physics of the speaker in that cabinet are what they are.. the spec is 33 Hz, but that is - 4dB. It is an incredibly easy load for the amps. If you have the patience, put the preamp and amps in front of your other speakers and see if you are satisfied with the bass. I suspect so. If not, then you may have a tube that didn’t ship well. My guess is it is a combo of the Khorn and the room they are in.

The first thing people say when they hear the Raven and Blackbirds is how amazing the bass is.... and your speakers are trivial to drive.  The amps hardly know they are connected.