“Mimic - Classic and Pro”

 

I required for my own use another MM RIAA phono preamp. I had these two compact enclosures on hand and most of the parts. I only had to purchase a subminiature power switch, cheap RCAs and two metal 9V battery holders. All the passives and chips (OPA2134) I had on hand. "Pro" uses 1/4W carbon film Rs and "Classic" all 1/2W metal film. There is a mix of better and standard caps in "Pro" and just polyester caps in "Classic". 

Both run on a couple of 9V batteries which use a resistive network and a couple of low ESR caps to provide +/-9V and a virtual earth. the entire cct. including the PS section is built on a tiny bit of strip board smaller than a matchbox. Inexpensive gold RCAs were purchased as I wanted to keep cost down. Having so many parts on hand made these builds easy and cheap. Hookup wire is silver plated fine copper wire. 

How do they sound. Good in a word. Bass is solid and the overall sound clear to transparent. No hum or buzz due to battery operation which should give me about 50 hours of play on fresh batteries. There is a battery test point at the front and battery replacement takes only a few minutes. The chip can be changed to any equivalent.  

“MC - Loader”

 

I had a request to build a loading box for MC cartridges. Happy to have this cast Al enclosure on hand and it worked out to be a perfect fit. Not much inside other than six resistors and some fine copper silver plated wire. Solder was WBT silver solder and heavy duty gold RCAs on back. 

The switch is center off and in this position, loading is 330 ohms. Switch to the left, according to the name plate on top, provides 100 ohms and to the right 50 ohms. All Rs were metal film and the Al box is double bitumanised heavy Al foil lined adding weight and resonance control.