JLTi-reengineered EE MiniMax Tube MC/MM Phono Preamplifier

2 years ago 183

Item Condition: Excellent

Shipping Options: Pickup available and you can audition.,Shipping is available at agreed cost.

Suburb or Town: Summer Hill

State: NSW

Payment Method: Cash, PayPal (F&F or Buyer covers fees), EFT

Reason for selling: NLR

Purchased July 2022 from another SNA member. Original ad text below. All photos mine except the internals which are from the previous seller who took those to show some of the upgrades.

This is an amazing phono preamplifier. It was re-engineered by Joe Rasmussen to overcome some limitations in the original design.

The Eastern Electric MiniMax Phono Preamplifier has some exceptional qualities, but required some changes to the design of the MM stage and the power supply to let it reach its potential. Joe Rasmussen reworked the design to spectacularly improve every aspect of its performance.

At first glance, it looks very similar to a standard EE MiniMax, but under the hood, it is a very different beast, thanks to the complete circuit overhaul by Joe Rasmussen.

The stock EE MiniMax uses very high quality permalloy transformers for the MC amplification stage (these alone should cost several hundred dollars), and a well thought out (if slightly flawed) unconventional circuit design. All amplifier wiring is point-to-point! It has a sound which is characterised by drama, realism and superb female vocal rendition. However it had a fairly unimpressive noise floor (now amazingly quiet), and an intermittent grounding hum problem (now completely eliminated).

Joe Rasmussen deconstructed and modified the circuit for me (and has since modified others using the same mods). He split the RIAA between stages, allowing him to replace the first stage 12AX7 by a 12AT7 for far better sonics. At the same time, he was able to remove a capacitor from the output stage, fix the intrinsic grounding problem, use Jantzen Superior Z-caps to replace two audio-critical capacitors (incredible performance for the price), and a few other improvements. I watched him work this magic.

Joe lowered the noise floor by at least 10 dB, making it one of the quietest valve phono preamps you will ever hear. The sound was stunning.

Replacing the original Chinese tubes, trying various combinations, I found that this tube combination offers extraordinarily lifelike timbres and imagery. The effect on the best recordings is truly breathtaking. Thrilling.

For the super-critical first stage 12AT7 tube, I have used a matched-parts NOS Raytheon JAN 12AT7WA
For the 2nd stage amplification tubes, I settled on a matched pair of NOS UK Mullard ECC83 tubes

For the 6X4 rectifier tube, I initially swapped the woeful Chinese 6X4 to a NOS Mullard, but have since gone to a British NOS Brimar 6X4

The original price of the EE Minimax was $1400 (note that the RRP in the UK was £1400)

Joe charged $850 for the mods which was an absolute bargain considering the hours of work involved and the spectacular improvements achieved

The tube rolling cost about $300 and many hours of critical assessment.

Note that
MM has a fixed 47KΩ load resistance
MC High has a 100Ω load resistance

MC Low has a 47Ω load resistance

Stated specs before modification:
Nominal input sensitivity 15 mV/MM and 4mV/MC.

Maximum input 150 mV/MM and 40 mV/MC.

Nominal output is 2000mV and maximum 20V.

Gain (1kHz) is 42dB/MM and 58dB/MC.

Load resistance is 47k Ohms/MM, 100 ohms/MC High and 47 ohms/MC Low.

Signal to noise 90dB/MM and 87dB/MC