FS: Raven D/A-preamp with RAKK DAC, Lundahl iron, 6N6P

[zigzagflux]

Lot of nice features in this one box.

Power Supply:
Lundahl 1683 power transformer, 1685 choke in both rails, highly optimized for low noise, low ring, and transient-free. 6DE4 damper diodes with scope-optimized snubbing on the transformer secondary. Very clean ripple. Snubber grade 1uF polypropylene first cap followed by motor run capacitor. Coupled with the cascode CCS into the gas regulator makes for a really clean regulated B+. Close mounting makes for small loop area for low radiated noise.

Bus bar grounding with intelligent layout of raw PS, regulated PS, and signal star points. Transformer coupling on input and output completely eliminates ground loops.

K&K / Raleigh Audio RAKK DAC II with two LL1572 spdif xfmrs, switch selectable inputs. K&K upgraded 12V power supply. All 60 Hz iron arranged for greatest spacing between signal path for low hum pickup.

Current output of D/A feeds a dual 60 ohm I/V stage using Vishay VTA bulk foil resistors. Riken ohm series resistors to Goldpoint 50k stepped attenuator.

Matched 6N6P triodes for gain stage are perfect application. Low Rp drives the output transformer with no problem, no resonance. AC heaters work very well, no audible hum. Elevated to 40VDC. Shielded twisted pair from transformer to heaters (dedicated split bobbin transformer for heaters) for RF immunity. Ceramic caps right at heater pins.

Designed for LL1689AM/PP output transformers, which have been removed. You could place non-amorphous in if you want to save some money, or any other mfgr. Extremely low output impedance of around 60 ohms with this topology means you can drive just about any high capacitance cable you want over long distances. Balanced and unbalanced outputs can be used simultaneously if desired.

Copper foil applied to inside of wooden chassis for extra shielding. Bonded to the Front Panel Express top plate, with chromated surface for conductivity. All hardware is flush mounted on the top side for clean look and easy polishing. Steel/Mu metal shield installed between PS and signal portion for additional magnetic shielding.

FFT attached. Distortion around 0.004% at 1 kHz. Low noise floor. If you are overly particular, you could pursue DC heaters to get rid of that last bit of 60 Hz, but it is not audible at full volume.

To just add up the cost of the significant components:
LL1683 $200
LL1685 $100
120uF motor run $40
RAKK DAC II $350
Goldpoint $150
Teak wood $50
Top plate $150

Looking to sell (includes a set of tubes) for $1000 including shipping anywhere in the cont. US. Outside the 48, contact me for shipping.

[Dufus]

Did you payed 150$ for the Front Panel Express top plate?

[zigzagflux]

Paid $171.31 in October of 2009. Attached is what you would pay today (plus shipping). Having countersunk holes throughout is where quite a bit of this cost comes from. Also, 3mm aluminum.

Oh yeah, all hardware is stainless steel. I have had cheap steel hardware oxidize on me over time with previous projects, so I only build with SS. No, it has nothing to do with the magnetic properties removing precious ground side electrons from the aether.

I don't have exact numbers, but when I consider all the details, this project cost me well over $2500 in addition to my labor.

I have taken a different approach with my current preamp (DCX2496 into 6-channel active volume control) hence my choice to sell this one.

[zigzagflux]

I'll entertain offers, or else start parting it out and selling individually.

[JohntheRevelator]

Hi ZZF,
How much do you think replacement OPTS cost for the preamp. I love your work and it would break my heart to see you take it apart, however I don't "need" another preamp but thinking about it for a second system. NICE BUILD! Patrick

[zigzagflux]

You can get brand new LL1689 from K&K Audio for $140 each, or go amorphous for $325 each. I have both flavors, and can't say I hear huge differences between them, but I am able to measure just a tad lower distortion with amorphous in the midrange (we're talking a few dB in what is already -120 dB).

You should contact Kevin Carter at K&K. Great guy, he knows a lot about transformer coupling with tubes. He will likely tell you the 1689 is the transformer of choice for this topology.

This preamp will drive anything you give it with no complaints.

[zigzagflux]

Okay, some interest but no takers.

Taking offers on individual parts.

[djn]

It would be a REAL shame to part this out. Great work!!!