LFD AUDIO: Dr. Bews discusses LFD Integrated LPCD – the low powered class d

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Hello Dr. Bews. What can you tell us about this new release?

"The cost of the LPCD is for the standard line level version (NO remote control) is £7500, it can be configured to have internal phonostage or internal DAC (192khz/24bit SPDIF only), at a higher price (probably around 10% extra for phonostage and 15% extra for DAC).

I believe that a (SE) version will be available in about 1 year, with more silver wiring and remote control volume, i have made the remote control system, but it uses a active preamplifier which requires different tuning (no time at the moment).

The LPCD actually means: low powered class d, and i have been working on this project for 4 years +. Class D amplifiers are very difficult to implement and i have found that using the technology by International Rectifier, you need to keep the output MOSFET simple and fast (which means limiting the power to a maximum of about 100W-120W). Also the components and the PSU are very important (tweaking a class d amplifier is much more difficult than a standard class A/B amplifier).

To give you an idea of the of the type of requirements, please look at a Japanese company SPEC.

The LPCD uses mono amplifiers (100W)/PSU, but uses one mains transformer. It uses a passive preamplifier section like the NCSE (has silver wire as well), but has different RCA sockets which i have made in the far east (these use a different type of insulation to give a "nicer" sound compared to the usual PTFE and look similar to the WBT 244). The level of sensitivity to decoupling and PSU parts means you need to spend enormous amounts of time tweaking, which most designers will not or can not do.

The reason i have chosen class d, by International Rectifier, is that the designer of the chip (who is Japanese) has engineered in to the sound a more tube like sound, but you can have problems in that the midband can be very good, but the bass is much lower quality (slow and not well defined). You need to "speed up" the sound (helps the bass), but without sacrificing the midband quality.

This project has been worth while, since i have spent much time on PSU components, and this knowledge will filter in all LFD products, I will never get back the R and D costs, but some projects pay dividends in other areas. The LPCD front panel picture shows you the general design and layout (input selector, mute switch, on/off switch then volume). Chassis is similar to the NCSE (back panel looks better than NCSE since the RCA sockets looks far better)."

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