Hi all,
I have done following modifications on my Willsenton R8 MKI amplifier:
1.) Power supply mods, remove 115V/230 switch - Sonic (no hiss or hum), SQ
2.) Voltage Regulator Mod - Sonic, SQ (removes crosstalk, lesser noise floor, darker background)
3.) Bias Boards Mod - Sonic, SQ (smooths the sound)
4.) Grounding Mods (headphones wires removal and input relay board grounding)- Sonic (no hiss or hum), SQ
5.) Grid stopper resistors 1kx4 on output tubes - Reliability, Safety, SQ (smooths the sound) 6.) Choke replacement - Reliability, Safety
7.) Power supply caps replacement with min. 500V ones - Reliability, Safety
Optional
8.) Replace capacitors with higher grade electrolytic or polypropylene capacitors (Nichicon, Mundorf). - Reliability
9.) Replace all resistors with Vishay PRO metal film resistors - Reliability
10.) KT88 heaters wires rerouting and removing grounding jumper from heaters - Reliability, Safety
11.) Global Negative Feedback - GLNFB - Ongoing... I have tested with 24K resistor and 220 pF MICA cap but it my case that does not work correct. The ringing on sqaure signal is gone but the output power dropped in UL Mode from 38W to 22W.
After all job done I'm pleased to confirm everything that Stephe said or demonstrated in Willsenton R8 series.
Thank You Stephe for posting all these valuebale videos and documentation!!!
Best regards,
Robert
Thanks for the update!!!
Hi again,
I have tried different values and combinations of resistors and MICA capacitors for GNFB:
1.) Resistors - 24k, 27k and 33kOhm
2.) MICA Capacitors - 110pF, 180pF, 220pF and 330 pF
For my setup, I have chosen a 27k resistor and 180 pF MICA capacitor (which measured with a tester are 220 pF actually). This combination gives a noticeable sound difference and removes the ringing on square signals with the tube preamplifier section (CD, AUX1 and AUX2). If the PRE IN is used there are still some signs of ringing but I'm very pleased with the overall sound signature with these values. There is also a slow roll off after the 20kHz frequency region. The overall sound I can describe like mids and highs are smooth, the bass is authoritative and controlled and the S/N ratio is increased which brings more details and resolution to the music compared to the unmodified version of the amplifier. Measured output power in UL mode after all the modification is 38W per channel on 8 Ohms.
I had bad luck with the original Willsenton output tubes, which turned out to be of really bad quality since two of them, V3 and V4, had heater-to-cathode leakage. This resulted in an annoying 50Hz hum from the transformer every time the amplifier was powered on for 2-2.5 minutes. So, I replaced the Willsenton tubes with PSVANE KT88C matched quad tubes, and now the amplifier is totally silent."
I read on some of the forums that PRE IN is strange in terms of interferences and after doing the mods with grounding and input relay board I must say that I prefer this input for streaming. The streamer DAC is directly connected to this port and it works excellently.
For analog reproduction from the turntable I use AUX1 or AUX2 inputs which are using 6SN7 and 6SL7 preamplifier sections.
I hope this helps.
Best regards,
Robert
It will lower the input sensitivity, but it shouldn't kill the power output like that.