This thread is of some interest to me because I've done some of the things mentioned, and am planning some of the things you guys have already done.
I'm currently listening to a pair of monoblocks made from boards out of a NAP140. Each board is powered from a 500VA 35-0-35 Avel Lindstrom transformer. The rectifiers are hexfred diodes, the smoothing caps are NOS Chemicon 4600uF/100V cans in a cap8 style arrangement. There's a Rod Elliott soft start module on each monoblock to keep the inrush current under control.
They're slightly different from that picture because I replaced the wires between the cap terminals with inductors. They have only a few windings just now, but will be 10uH in the final build:
The boards are modified NAPs that incorporate some of the stuff from earlier posts. The first thing to go was the SOA components. After that, I replaced the LTP transistors with matched BC546C that are rated at 60-odd volts and can cope with the 50-0-50 DC supply:
You can see the 22uF/16V Wima MKS2-XL feedback cap to the right. Critical resistors have been replaced with RC55Y 0.1% resistors. From left to right you can see the black RC55Y resistors 24k3, 3k01, 1k02, and 26k7:
The 1k02 feedback resistor legs have been bent to accommodate the size of the Wima cap. The front end power supply is decoupled from the main supply Avondale-style with a 220R/330uF RC filter on the +ve and -ve rails. Here's the +ve one:
The diode orientation on the -ve rail is reversed. The capacitor arrangement isn't ideal at the moment, following the Avondale 0V arrangement of returning the 0V points of the front-end decoupling caps directly to the signal input 0V:
Junk in the power rails will show up at the signal 0V - hardly ideal. But it was an easy mod to make and is, on balance, worth it. In the final build I'll run the front-end 0V line directly back to the PSU 0V and remove it from the signal 0V.
Both monoblocks will be incorporated into a single large Hifi2000 enclosure. Before that happens I'll be revising the PSU/amp/signal 0V scheme but haven't decided on the best approach yet. I think listening tests will be in order.
In a parallel project I'm building another 4 amps (2 monoblocks in each enclosure) for a total of 6 amps to be used in an active 3-way system. The 4 new amps are based on the eBay clones:
They've had quite a few component changes, but I haven't hooked them up to see how they sound yet. I still need to get the output transistors on and some testing done. The changes so far are based on the NCC200 list of parts, although some substitutions have been made. The resistors are a mix of Dale RN55 & RN60, Welwyn RC55Y for feedback and LTP, and generic metal films.
The transistors small transistors are BC546, ZTX653, ZTX753, and 2N5551. The drivers are MJE15030G and MJE15031G. The legs on the ZTX and 2N transistors all had to be bent to accommodate the alternative pin assignments. For example here's the ZTX751 (Q4):
The evil ceramic caps that come with the kit have all been replaced with polystyrenes, and there's a 47pF silver mica decoupling Q4. C5, the bybass of Q5, has been replaced with a 68uF BC128. The front-end decoupling caps are Panasonic NHG 100uF. Input and feedback caps are Wima MKS2-XL 10uF and 22uF, respectively.
The zobel network is a 3W 8R2 + 220nF polyester cap. One thing that really needs to be done here is to separate the zobel 0V track from the signal 0V. Yuck. I'll be cutting the track and running a separate cable for that! The output of the boards has been replaced with an Avondale-style inductor//resistor combination.
The 4 clone boards each have a dedicated 250VA 30-0-30 Avel Lindstrom transformer and will be used via a custom active crossover to drive the treble and midrange units of the 3-way speakers. The 500VA monoblocks will drive the bass units.
It really is a labour of love to try and make all this stuff, so it's taking some time. I'll start a thread when I make some real progress.
For you guys with the Hifi2000 cases: how did you go about drilling your casework?
Cheers,
Carl