The Singing Bush Tips 'n' Tricks

Official Court Jester
Joined 2003
Paid Member
LM 317 pinout is - numbers to you, pins down : most left Adjust, mid out, most right input

all ref to GND:

on input you must see close to your Aux AC*1.41; if you have 15Vac there, DC must be close to -20Vdc

of course, worth repeating, that Aux (15Vac) must be independent/floating of main audio PSU secondary

so, confirm that you have proper Aux AC voltage, then if anything is fishy with LM317 voltages, replace it
Official Court Jester
Joined 2003
Paid Member
see this

think, try and say where you can see difference to yours


  • The Singing Bush THF51_2SK180_2SK182 Gain schm wth voltages.png
    The Singing Bush THF51_2SK180_2SK182 Gain schm wth voltages.png
    104.2 KB · Views: 38
the preliminary checks carried out before assembling the components do not always give us back the truth. I discovered the component responsible for the problem after examining it several times and found it suitable, I set it aside. It was the R8 which, checked again today with another tester, did not return any value: it was the faulty one and also interrupted the circuit in its position. I happily replaced it on the fly and of course was able to bias the buffer to 20mA. Finally the first step is done. Obviously if I had sensed that resistance was about to die I would not have tried frantically to shoot into the pile...and despite the shots no one fell...I was swollen with rage that was the engine to control everything again. I hope I don't have any more problems. Everything went smoothly in the previous construction of the Bush.
I thank ZenMod who generously helped me: I'm leaving again also thanks to your support


  • IMG_20230525_180324.jpg
    411.4 KB · Views: 15
  • Like
Reactions: 1 user
biased the power section. Obtaining it was not easy: I had to change the values of two Resistors.
The first on the MU board R3 increased from 100 to 150 R. The other on the SIT board, R11 increased from 1k5 to 3k3.
So I was able to get the design values: 460mV for Iq and the potential of 37V on the drain of the SIT (2SK180). Good progress. Tomorrow I fight with the other channel


  • bias 1.jpg
    bias 1.jpg
    562.8 KB · Views: 21
Great Zen Mod, the new Bush is playing. Wonderful as always: the magic of this amp repeats itself. Forget the hitches of the initial tests, now the Music and what Music.
A lot of gratitude for the help you have always given to everyone, not only to me, but above all for having given us this incredible amp.


  • IMG_20230529_094800.jpg
    228.7 KB · Views: 23
  • IMG_20230529_094849.jpg
    211.8 KB · Views: 23
  • IMG_20230601_091806.jpg
    118.2 KB · Views: 23
  • Like
Reactions: 2 users