- Dec 10, 2019
- James Island, SC
There are many things that we have learned from this iteration of my pair of APT/Holman Preamps. The overload margin as it is does not meet original spec, the opamps are an idea that we have been thinking about (we have been unsure of which ones to use). But I am pretty sure that the TLE2071's will happen in my next collaboration with Peter Williams at Quirk Audio, as he is willing to make more changes & adjustments than some others. These Preamps are, for me, a constant work in progress. At the next update, a few years hence, these and other things that we have found through this generous allowing of the testing of my units by Amir, will be addressed. It is my intent to keep the original circuitry design and take it as far as I can with the best of what is available that I can afford to have done. Therefore, every few years, there will be updates to these Preamps, based on the science of the issues that we have found. Thank you so much Amir for allowing me to have this reviewed.No, it does not even meet the requirements set forward by the main consumer media in 1979 - that of the phonograph record. The overload margin of phono input above 5 kHz - where almost ALL of the action is ( due to the RIAA curve ) - is way too low . Too low even for normal better recorded musical material, let alone for ticks/pops - not to mention an occasional scratch that is sadly unavoidable in records. It is the typical limitation for the circuits operating with standard +'- 15 V DC power supply rails using op amps.
The review itself is good, but clearly displays that the reviewer is not at home with phono gear. There is no mention of the phono input gain adjustment that can be set for each channel independently ( to cater for the compensation of phono cartridge output voltage imbalance - allowing for the correct balance rec out levels ) - which has been unheard of at the time. Nor is there any mention of the circuit having - as one of the first if not actually the first to do so - a buffer stage at the input that isolates further circuitry from the interaction with phono cartridge inductance, an old and known problem affecting RIAA accuracy when using real world source and not lab measurement gear.
This preamp is a large collection of TL071 ( family.... ) opamps. Therefore nowadays it can be considerably improved by the use of direct replacement modern version of this op amp - TLE2071 ( family ). Lower noise, lower distortion, triple slew rate ... - it yields both measurable and audible improvement.