Friday, October 7, 2011

Aikido Pre-Amp Project - part 9

My brother came with a home-made chassis; Something my brother designed some years ago. 18"x12"x 4" high.
This is the chassis after a quick clean up.

This will be a great time saver since I've already spent nearly 60hrs on the project & any quick solution put things back into prospective.

This is the new amendment to the layout.
Ample real estate available.
As I'll not use a separate base plate for mounting the irons, it will be difficult to mount the previously selected irons. So I've change the 2 transformers to vertical mount type EI laminate tranny.
Since he don't require source selection, so the selector switch is obmitted.
Now, I need to find suitable IRC sockets that will fiit the opening already on the chassis.
I'll fill in the common mode filter & other switches & socket when I can find more time for it.

Sunday, October 2, 2011

Aikido Pre-amp Project - Part 8

It is easy to get carried away & fall pray to unnessary desires & unrealistic wants.

Time to put on my contractor hat & give the whole PSU a final round of scrutiny.


Virtual capacitor
I have never suffer premature valve failure other than applying brute force with a blunt object on them... I've yet to see any valve died of voltage stress... Seriously, what can 30ma current surge do??? or even 300ma??? Tubes are built to take brutality like fish in water!!! So it will reduce the valve life from 200,000 hours to 180,000hour... so what!?
Aikido were born with PS ripples cancellation. Let them do what they do best!
This is a class A1 amp, the load behaviour is almost a constant current and the signal source will most likely be solely fed from a CD player or a DAC with 2Vrms signal, it will never come close to clipping! Moreover, since it is not a power buffer stage with transformer coupling, high power supply Zo is not a real issue.

Why bother with the extra works when one can get away with it???

Another visit to PSU2 & came up with these component numbers, the damping is sightly over 1 which is where my preference lies.

and the following is what I'll build.

Final check,

A costumed RFI/EMI common-mode filter,
All important last line of defence, 0.1A fuse,
The indispensable power rocker switch,
Obviously essential IEC power socket,
A spikes treated rectifier bridge,
A snubber treated choke,
A CLC network which gives a well damped & quiet B+,
A floated AC filament supply with twisted solid core leads.

This should put everything back in prospective & an end to the PSU design...


Another look at the chassis...

Saturday, October 1, 2011

Aikido Pre-amp Project - Part 7


My bad..... Made a blunder with the capacitor multiplier schematic in the last post...

This is the correct schematic.

I forgot about the potential divider for biasing the MOSFET. My bad.

In doing so, we will reduce the B+ by 5% & also provide a short term regulation of +/-10%. Hence, smooth out sudden mains voltage fluctuation within to 5%.

In the long term sense, the B+ will track the mains voltage fluctuation.

Under New Management

In this new arrangement, the gyrator is after the CLC network filter, just like how everyone else arrange their voltage regulator.
Since we happened to have a gyrator in the circuit. Might as well let them do what they do best i.e. reduce Zo to single digit & excellent ripple reduction.
Now I can reshuffle the component values of the CLC to achieve the damping factor which I am looking for, highest B+ possible & lessen capacitance further.
Added a 220R 5W resistor in series to the choke, this was not an option earlier as it will add on the PSU Zo, with this, I can reduce 120uf to 47uf.
I could had use 10uf at the last cap, but the gyrator only mimic a huge capacitor without actually storing any real energy, so using a 47uf as reservoir seems reasonable.
Also, 3 more snubber capacitors for the rectifier, now, there is a snubber cap for every diode in the bridge rectifier. This will work better yet still not too much work...

We loss about 15V on the B+ with the gyrator & CLC amendments, but I consider that a bargain with the added slow-ramp, cleaner, stable B+, better damping pattern & reduced Zo significantly.

..........PREVIEW Part 8..........