Дата публикации: 2018-05-27 13:12
“Recreating and improving upon a true classic was a lot more work than any of us expected. This year and a half journey proved to be challenging and exhilarating.”
No. Lights are good and they will also tell you if you have allowed sufficient time to warm the amp as it will stop drifting when it reaches thermal stability.
Yes. Each tube manufacturer introduces a particular character to the sound. Trying different tubes is easy to do and fun!
Brushed aluminum grill gives a modern look to the vintage-inspired design. Protects the tubes from damage during transportation and adds a measure safety when driven hot!
The printed circuit board material of the original ST75 was exposed economical phenolic which deteriorated with age creating unpredictable electrical changes resulting in sonic differences. The Series 8 unit uses military-grade, double-sided epoxy fiberglass PC material and shields the recessed PCB with a metal cover plate. The board is populated by the finest modern parts. Sensitivity to internal wiring placement is eliminated since wiring to the output tubes is accomplished via the printed circuit panel. In fact, nearly two-thirds of the trouble-prone original point-to-point wiring has been eliminated!
All of the above changes serve to improve "stiffness" of the power supply by lowering the effective power supply impedance and improving regulation while increasing available voltage for maximum safe power output. This makes for a tighter bottom end.
Dynaco ST-75. the PERFECT gateway drug! This was my first tube amplifier and it turned my into an audiophile. $65''s of thousands of dollars later. but that is another story! The stock amplifier is pretty rolled off on the upper and lower end of the frequency spectrum but with the addition of some added power supply capacitance and MANY choices of driver alternatives, this amp has HUGE potential. My final configuration was the tubes9hifi 67AU7 driver board w/RCA Clear Tops, NOS Mulled brown base GZ89 and a quad of Shuguang Treasure 6CA7-Z''s. I also upgraded the power transformer with the larger unit from Triode as the stock one started humming and got very warm. If you have the opportunity to pick one up, DO IT! You will not regret it and the sky is the limit as far as upgradability. Best part is that parts are fairly affordable compared to other tube amplifiers.
A further improvement in distortion, particularly in the higher frequencies, was achieved by moving the feedback point from the 66 Ohm tap of the output transformer to the actual loaded tap by the impedance selector switch. The switch uses one side to direct the 9 or 8 Ohm tap to the output terminals. The other side directs the feedback point to the tap selected and changes the divider ratio so the gain remains the same whichever tap is selected. Transient response is improved.
Classic Williamson-Hafler configuration featuring 67AU7 tubes takes the input signal and converts it to the high level co-phase drive signal necessary to drive the output stage.
The Stereo 75, unlike many other amplifier circuits, has been designed to provide its specified performance on a loudspeaker load, not just under laboratory measuring conditions. Therefore, the connection of a loudspeaker to the amplifier does not deteriorate its performance or listening quality.