If interested check my thread on the Goldmund Telos 2500 monoblock pcb kit...
https://www.diyaudio.com/forums/sol...500-monoblocks-clone-pcb-set.html#post6663395
SB
https://www.diyaudio.com/forums/sol...500-monoblocks-clone-pcb-set.html#post6663395
SB
Did you solve the oscillation problem?HOW TO INCREASE QUIESCENT CURRENT OUTPUT STAGE
Hi all, I built these 2 original boards with the attached schematic. The amplifiers are working but they show 2 problems:
1. some high frequency oscillation shown just at the top of output sine wave at 1 KHz, 25 W RMS output over 8 Ohms resistive.
2. some visible crossover distortion.
I used exactly the values shown at the schematic. The MOSFETs are BUZ901 and BUZ906 (not paired, just what it came in the box). I didn't populate the protection circuit components, just the amp.
Output offset voltage no load with shorted input is 2 mV adjusting R8.
The oscillation was reduced greatly by increasing gate resistors from 100 Ohms to 820 Ohms, but output power also decreased to a maximum of 95 W RMS with 56 V rails before clipping. The indicated optional capacitors are in place
Raise time is 1us for the audio frequencies to 300 KHz and it responds flat.
I was about to measure quiescent current replacing the fuses with a 0.1 Ohm resistors and check voltage drop there. It seems that R22 330 Ohms could be adjusted to increase up to 180 mA (I guess this stage was designed for 100 mA or less)
I think that T5 is reversed, but I placed as the original schematic showed. Works fine for LTSpice simulation.
Could you please give me some help ?
Thank you !
I bought the Motorola 2N5566 / 600 pieces in the original packaging as in the photo above from a German dealer in 1984. At that time, counterfeit semiconductors were not on the market.