DCAudioDIY.com

For cutting holes in heavy gauge Aluminum I would suggest at rotabroach if you can afford one -

https://www.amazon.com/Blair-11090-Roto ... deae8f9840

I have the item shown in the link. If 3/4" is large enough I would be glad to loan it out (I live in Wheaton, MD)

You can find larger cutters on Amazon.

Thanks for the offer but I already finished the job. I used 3/4", 1 1/8", 1 1/4", 1 5/16" and 1 5/8" hole saws. BTW, I'm now living just outside Philadelphia. I'm enclosing a photo of the template I made to locate the components.

Tom

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Walt

5MM thick panel is way too thick for Greenlee punches. Also in that size they are very expensive for one time use. The 1 5/8" alone is $138 on Amazon. Similar prices for Rotabroaches in the same sizes.

New Preamp - Broskie Aikido using 12SN7

Grover suggested that the Musician Amplifiers I built a few weeks ago really benefits an active preamp with some voltage drive over a passive preamp. He uses a Tubes4HiFi PS14, a 6SN7 based Aikido topology and really likes it. Since I had an Octal Stereo Aikido board (from 2008) from Broskie that I never used, and already had TubeCAD PS-1 and LV regulated power supplies built but not housed, I only needed a suitable toroidal transformer from Antek. I started building a linestage since all my extant preamps are either passive or buffers. One thing that Grover suggested (which is implemented in the SP14 design) is a resistive ladder attenuator consisting of a coarse step gain control, which sets overall level, and a fine control for zeroing in on level and balance. I bought the TubeCAD ladder attenuator kit, which uses very nice Grayhill switches and populated them with 1W Takman REY metal film resistors (being lower noise and better suited for attenuator duty than the popular Takman REX carbon films). The attenuator as designed has 1dB steps over a 65dB range.

I did onboard rewiring of the Broskie Aikido board to permit independent heater supplies for R and L channels. Didn't have to cut any traces, just added a couple of bridging wires to create H- buses for each channel, using the on-board H- and H+ inputs as H+ for each channel. Broskie provided enough pads to repurpose for the wiring, new connection points, a electrolytic reservoir caps.

Decided to go with 12SN7s, since I have a bunch, they are still pretty cheap compared with 6SN7s, and they don’t compete for tubes with my amps using 6SN7s.

Used HV(SiC) and LV Schottkys for rectification for low noise. The Broskie kits use ultra-fast rectifiers with a reverse recovery spike filter across each diode. Figured it would be better to just use diodes without any reverse recovery spike for the lowest noise.

Also beefed up the power supply PP bypass caps on the HV power supply and the board with 20uF PP DC Link capacitors, still retaining the large (100uF) electrolytics as reservoir.

Starting off with the CDE 942C 1uF/1000DC caps for output caps, will start my search for better caps in that position. VH Audio has a sale on their discontinued V-Cap TFTF, and the 0.47uF/600V looks very tempting.

Chassis size was constrained by the size of the aluminum top plate (a spare from my previous amp project), fabricated a chassis from 3"x1" 6062 Aluminum channel. I have a perf panel the same size for the bottom for ventilation.

Almost ready to start testing -