|23rd August 2017, 04:31 AM||#1|
Join Date: May 2005
Location: Vancouver BC Canada
Available in September 29 , 2017
TU-8600 is a 300B single-ended tube amp kit. In pursuit of great sound quality of the 300B amp, we have updated and improved the amplification, power, and feedback circuitry. The result is an amp with amazing sound quality, super low noise, and can be used with headphones.
Power circuit enhancements
A high efficiency, low magnetic flux leakage R-core transformer is used. The rectifier consists of a schottsky barrier diode that requires a shorter recovery time. This results in a reduction in even negligible noise spikes. The windings of the power transformer include individual windings for the filament heater (A- Power), high voltage (B-power), and bias to stabilize the Negative Feedback (NFB) circuitry(C-Power). In addition, all power is stabilized to reduce residual noise as much as possible. [U][I]This results in a noise level that is as low as 1/10 of the TU-8300R.
Output stage : 300B Class A single, active automatic bias adjustment
Voltage amplification stage : 1st stage 12AX7(ECC83) + parallel drive 12AU7 (ECC82)
Heater filament power : DC-Power (LDO)
B-Power : MOAFET + BJT ripple filter (for L & R separately)
Stable Negative Feedback (NFB) circuitry for great audio quality
(output transformer with cathode feedback CFB winding)
To make the most of the 300B tubes, the characteristics of the various parts and circuits including the OPT have been improved. NFB is applied to the cathode of the 300B by the third winding of the output transformer as well as to the voltage of the amplifying stage. Overall NFB is minimized as well as the chance for transient response.
Why CFB is important - Cathode Feedback minimizes THD and intermodulation distortions and makes total bandwidth ultra-wide using the lowest overall negative feedback from output to input of your amp. All of it makes sound amazing, detailed and spacious.
New active automatic bias
For 300B tube bias, the power supply is equipped separately and a “new active automatic bias” is used where the amp detects plate current and automatically adjusts the negative voltage to the grid. This design earns the TU-8600 the privileges of both self-bias and fixed bias. Also, the current detecting circuit is moved from the cathode side to the B-power side resulting in even better sound quality.
Driving 300B tubes to full power
A very orthodox design is used for the voltage amplifying stage to bring out the outstanding characteristics of the famed 300B tubes. Of special note is the 12AU7 (ECC82) is used in parallel for the second stage to drive the 300B tubes to full power- resulting in 200Vp-p without clipping.
Warm-up time for directly heated and indirectly heated tubes differ. In most designs, amp power-up starts heating both the directly heated 300B tubes (fast warm-up) as well as the indirectly-heated 12AU7 and 12AX7 (slower warm-up). In the TU-8600, the 300B tubes are heated after the indirectly-heated tubes have warmed up. A very tube-friendly design that will not overload tubes that have not warmed up fully.
Ample space for larger coupling capacitors
Capacitors can have a big effect on sound. The TU-8600 uses high quality conductive polymer hybrid electrolytic caps and polypropylene film caps. For those who wish to use other high quality caps, there is ample space provided on the PCB for mounting larger caps.
Selectable settings to match headphone impedance
4 output settings to match your headphone impedance.
Lundahl LL2770 option
Last edited by vkung; 10th January 2018 at 05:12 AM.
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