Tuesday, 30 October 2007
The above is the schematic design for the DRD45 power supply. This was done using PSU Designer II. The above shows a residual 'noise' of around 6 mV, which with a 510 V gives a noise dB of around -98dB. This of course ignores the higher harmonics generated, but makes a good starting point. The design calls for a 50uF ASC oil cap, followed by Electra-Print's 20H choke, and then a dual combo of 100uF Solen aluminium can and a 47uF Solen PPE capacitor. There is scope to change the last 47uF to a 50uF ASC Oil. Wanted to avoid electrolytics not just for the rumoured acoustic difference, but also for reliability. The power supply transformer is 410-0-410V, which is an odd rating, but I am sure that Jack (Electra-Print) is able to wind one that is suitable.
Thursday, 11 October 2007
Here is another nifty calculator for determining the frequency response of a LC filter circuit. This could also be useful for PSU design calculations. I used this to aid in the understanding of the determination of the 'Ultrapath' capacitor. Using an example Plitron PAT-3035-SE, with a primary inductance of 28H and an Ultrapath cap of 51uF, the frequency cutoff (not sute if it is f-3dB) is 4.2 Hz. My understanding from this, is that any audio signals above 4.2 Hz will be returned back to the cathode to ground, rather then through the PSU capacitors to ground. Doubling the capacitance to 100uF, results in a frequency cut-off of 3 Hz.
Monday, 8 October 2007
After some weeks of research, dialogue and thinking, the 300B amp has been put on hold for the moment, to make way for a 45 DRD monoblocks. The main reasons behind this change is; lower operating B+ voltage and availability of quality new and NOS tubes (there are no NOS 300B easily available). To this effect, I have ordered the chokes and reactors from Electra-Print, and they arrived within a few weeks. In addition, I have started to place the other components on order. In the signal section, I am using Caddock MK132 resistors, Mills high wattage resistors, Ohmite adjustable rheostats, Blackgate NH driver cathode bypass, and Solen PPE Ultrapath. Tube sockets will be teflon type. In the PSU section, I will basically using the same design as Electra-print design. The diodes will be changed to hyper-fast diodes, the filter caps will change in value. At this moment, I am considering filter values in the range of 500uF to 1100uF. Apart from some minor changes in component specification, it is very similar to the schematic as provided by Electra-print. The irons will all be Electra-Print, except for the Power transformer, which may be sourced from another supplier. Though the change from a 300B to 45 reduces power significantly, from around 8W to 1.5W, I believe that tandem with a 95dB+ speaker, and given my listening room is a small room, I shouldn't be too concerned. Full schematic, photos and progress will be available shortly. About half the components have already arrived, so looking forward to completing all parts, ready for construction and audition!