“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.

“Retro-EAR834p” - an EAR834p tube MM phono stage

This is the third of these MM phono stages I have built and all for commission jobs. As an addition here a MC step-up stage was also built. The MC stage is the La Pacific single FET, battery driven stage and is seperate from the MM stage. The PS is external and uses a Hammond tranni. The EAR kits come with a PS board with HT and filament DC rectification and filtering. The HT is smoothed by a high voltage power FET. Works well. 

Looks smart on the stippled Hammond wood cheek chassis. With Tung-Sol and LinLai tubes sounds detailed and transparent and the new owner reports excellent bass. We are both happy with the result.

“ZeroOne-A” - 100 year old globe DHT tubes preamp.

 

Inspired by my 71a tube amp I thought I would try another DHT preamp but with a 01a tube. Again Cunningham tubes used as with the 71a but with the 71a I also have RCA tubes. These globes are from the mid 1920s. Where the 71a preamp - “MWH” - has mainly carbon film resistors in the signal path and a Russian PIO output cap this build has all metal film resistors and a Mundorf EVO oil output cap. 

To enhance the performance of both preamps I built a new much beefier external PS on a repurposed cast AL chassis which already had a RFI/EMI power filter added. The 5V DC on the heaters is regulated and balanced. The 01a preamp has a remote Alps volume control and two inputs. Hookup wiring is via fine silver plated copper wire and high quality heavy duty RCAs ate  used. Not a lot of gain but a very revealing, detailed sound with extended reverb. Love the colour - Iron Stone.

A 6N7 preamp with remote

The now converted 01a preamp is now a RCA - NOS NIB - 6N7. The tube is metal (No!) so not much of a glow and is a dual triode with single cathode. The tubes are wired as a single triode with grids and plates paralleled. 
 

This preamp was designed for me many years back and was originally built into a timber box as “Heavy Metal”. It had heat issues. In the better and classier chassis looks retro and business like. With Alps Blue Velvet remote pot. 
 

I required 0.68uf output caps but had none of that value. But did have four 0.33uf Sprague orange drops. Doubled them up for a near enough 0.66uf. Had them for decades, as the tubes, so time to use them. Most 1W carbon film resistors and some metal film and wire wound. Double Pi HT filtration - 300uf total. 
 

DC on heaters, 260V HT and 2.55V bias. All on point. Gain should be 20db with Rk un-bypassed. 

 

Tubes are run in but the rest new so some complete burn in time required. Sounding relaxed and midrangy with voice a standout from the sound stage. Dead quiet operation with retro-Zen EL34 amp but hummed with my latest EL34 amp. Very happy so far. 

“Perspective” - EL34 Single End Ultra-linear power amp

 

This amp is based on a pair of new Mullard reissue matched EL34s with a universal driver tube. Any 12A*7 can be used as a driver. OPTs are Asian 3.5K 10W with 4 and 8 ohm taps. I have used the 5W 5K versions in other amps with outstanding results. The OPTs and power trannies are shock mounted on split rubber grommets to reduce resonance.  The PS is external with over specced Hammond power tranni. A Sylvania 5U4GB handles rectification. 357uf of filter caps smooth and store 366V of HT. Further filtering feeds the driver tube with a 4uf PIO cap and 2.5K 2W resistor. The amp is very, very quiet. 

Filament current is rectified with a 10A bridge and single Pi filtering - 9400uf of filtration. HT and filament caps are snubbed with 0.1uf polies to reduce noise. The chassis is a Hammond wood cheek and is made of steel for strength. The finish is black stipple. The chassis for the PS is cast Al with a black epoxy enamel finish. The PS is fused and earthed. 

RCAs are Paladium plated and speaker posts solid brass with gold plate. Audio path wiring is fine silver plated copper wire. All wiring is point-2-point, no cct. brds. and no shielded wire. Not required. Sockets are ceramic and power is brought to the amp via three pin large XLR connection. The driver tube being used here is a Tung-Sol ECC803S gold pin. 6L6 and KT88 can be rolled here and any 12AX7 equiv. can also be rolled. 

Amp presents full bass and a complex warm soundstage with smooth highs. It is a pure Class A amp. Not only good looking but excellent sounding and definitely worth the weeks of work. The EL34s I’ve had for twenty years so now they get to entertain as they are designed to do. 

“retro-Zen” Decware inspired 6BQ5/EL84 triode strapped amp

 

A Decware inspired 6BQ5/EL84 (Zen) triode strapped amp with attenuator. Driver is 6N1P. And of course chicken beak knob with AWV 6BQ5.

OPTs are 5W Asian sourced which I and others have used and find excellent. They are shock mounted on split rubber grommets for HF/resonance suppression. Sockets are ceramic and gold plated with Visheys MKP interstage caps. Hookup wire is Cat5 solid core. 

External PS has a Sylvania 5U4GB and works with two other power amps saving me $400 each amp. But if I sell one ill have to make another PS. Power tranni is Hammond. Chassis is a cast Al with Epoxy Enamel paint. This is meant to be a fun amp, single input and just 2.5W. Good den amp or desktop amp. For good level music listening you need speakers with better the 90db sensitivity.