I'm pleased to announce that we've made some changes for the better to the LDR300. These changes were initially prompted by feedback we received from the LD300 tour unit but as we looked into the original design we decided to also make several additional changes. The net net of all this is an even better sounding preamp.
Here's the summary of the design changes:
1) Deleted the input coupling capacitor - it's now direct DC coupled
2) Added 2-stage internal split voltage power supply with SMPS 1st stage and linear 2nd stage (was previously a 10 V single linear supply)
3) Changed from 12 V to 24 V - 500 ma external power supply input
4) Additional power supply bypass capacitors - Elna Silmac II plus Vishay Polypropylene
We actually went through several iterations before settling on this approach. The output DC offset is almost zero but we kept the output coupling caps to avoid the complications of DC offset protection. The sound is more natural and relaxed and not quite as solid state dry as before. Overall a more pleasing listening experience.
By going with split voltage the PSRR is now huge (meaning VERY quiet) since any noise on the +/- voltage supply will be next to invisible at the near zero volt DC buffer output signal half way between the power rails.
We're waiting for updated production circuit boards at this point.
Once we have production boards we'll be sending out the tour unit for its last few stops and anyone else who may be interested in giving the LDR300 a try - just let me know.