And we're off...
Konut the tour LDR300 is headed your way and should arrive by Tues/Wed next week.
A little info on the tour unit.
The tour LDR300 is a converted LDR3.V25. What that means is the LDR3 had been used here off and on for the past year and as such is not a brand new unit although it's been upgraded with our new OLED display. Consequently, the rear panel on the tour unit still says LDR3.V25 even though the internals have been modified to include the new SSB.V1 Rev A solid state buffer board which has been integrated with the V25 controller. Thus the only real difference between a production LDR300 and the tour LDR300 are purely cosmetic.
The tour LDR300 includes the optional upgrade to a Belleson SuperRegulator which has specs claiming 110 dB noise suppression compared to around 80 dB using the stock TL317 regulator. The tour LDR300 also includes the option upgrade to VCAP 3.3 uF OIMP output caps which are about as large a physical cap as will practically fit into the current buffer board. From very recent testing I've bumped up the input caps to 4.7 uF WIMA MKP polypropylene caps which are now the stock caps of choice until such time as we discover a better alternative.
The LDR300's buffer utilizes slightly more than 3,000 uF of power supply filtering which is arguably total overkill since it draws maybe a total of 25 milliamps of primary power. The filter caps are ELNA Silmic II silk capacitors which in my view are some of the best electrolytic audio capacitors available today. One of the goals for the LDR300 was to have as dead quiet an output as the unbuffered passive signal. Subjectively I think we accomplished that but I look forward to getting the opinion of others as they give it a try.
We spent way more time than I'd planned on trying out various makes/models of transistors in the buffer module. We listened to several MOSFET as well as JFETs. In the end it was no contest when we finally tried out the LSK170 JFET made by LinearSystems in California. It not only sounded the best but its noise specs are remarkably low. The buffer modules are plug-in so if we find something better down the road it would a simple matter of yanking the current modules out and plugging in new ones.
One of the areas that I spent quite a bit of time futzing with is the power-up/turn-on/turn-off/power-down logic and protection. The goal was to avoid any noticeable power/turn on/off transient bump at the speakers. I'm confident we succeeded at this. One of the consequences is there's an extra long delay...sometimes upward of 20 seconds...from the time you plug power into the preamp, and subsequently turn it on after it boots up, before the preamp outputs connect to the buffer and goes live the first time. Assuming you keep power connected to the unit, then during subsequent normal turn on/off there's only a 10 second delay before the buffer unmutes. Buffer output isolation is done via LDRs and not relays. There are no relays in the signal path. Note that if you abruptly remove power from the preamp before first turning if off normally, you'll probably see a very brief but non-violent in/out excursion in your woofer cone but absolutely no pops or bangs.
The tour LDR300 has dual outputs. The outermost (closest to edge of rear panel) pair of outputs are the buffered outputs. The second inner pair of outputs carry the unbuffered passive preamp outputs. If you're curious how different (or similar!!) the preamp sounds as a passive vs. buffered this can very easily be done by manually moving your interconnects between these 2 pairs of output jacks.
In keeping with our lean approach to paper manuals and such, you can find plenty of current info on the preamp controls in section 2.2 of our online documentation which can be found via the link below. The controls are fairly straightforward now that we've changed over to the menu driven OLED display. https://www.tortugaaudio.com/support/product-documentation/?section=oled-v25-control-menu
Enjoy the LDR300. Give it a good workout. Thanks for participating. And let us all know what you think.