- #1
NavinRJohnson
- 7
- 2
It's been over 20 years since I received an electronics degree I never utilized. Hopefully you guys can help jog my memory a bit as I really want to start getting back up to speed.
I've now taken on a more aggressive project, other than soldering pre-made boards, to help lubricate my old wheels. It's an older Adcom amp that had bad caps on the PSU that were repaired and still has some slight hiss issues that I'm working through. I'm sure I still have a few caps to replace and I need to clean up the rat nest wiring.
In the meantime I had a few questions about the power section and a couple transistors
1: The transformer has 4 output taps and is running the input (preamp?) section at 65Vdc and the power section mosfets at 55Vdc. This seems common among some of the "higher end" amplifiers. What's the advantage of running the front end at a higher voltage? Just lower gain so noise is less of an issue?
2:The +55V and +65V rails are connected just before R905 in the PSU section. A friend of mine suggested suggested this was to keep power to the mosfets on the input section during power down because there is more capacitance on the power section PSU board. That sounded like it fit the bill but, wanted to make sure I wasn't missing something else. Sound correct to you folks?
3:Q633 and Q635 right before the power section followed by the zener diodes. I honestly can't make heads or tails of what's going on there. Any ideas on the purpose of these transistors?
The full res schematic is at the end of the attached PDF if you can make out the image below.
I've now taken on a more aggressive project, other than soldering pre-made boards, to help lubricate my old wheels. It's an older Adcom amp that had bad caps on the PSU that were repaired and still has some slight hiss issues that I'm working through. I'm sure I still have a few caps to replace and I need to clean up the rat nest wiring.
In the meantime I had a few questions about the power section and a couple transistors
1: The transformer has 4 output taps and is running the input (preamp?) section at 65Vdc and the power section mosfets at 55Vdc. This seems common among some of the "higher end" amplifiers. What's the advantage of running the front end at a higher voltage? Just lower gain so noise is less of an issue?
2:The +55V and +65V rails are connected just before R905 in the PSU section. A friend of mine suggested suggested this was to keep power to the mosfets on the input section during power down because there is more capacitance on the power section PSU board. That sounded like it fit the bill but, wanted to make sure I wasn't missing something else. Sound correct to you folks?
3:Q633 and Q635 right before the power section followed by the zener diodes. I honestly can't make heads or tails of what's going on there. Any ideas on the purpose of these transistors?
The full res schematic is at the end of the attached PDF if you can make out the image below.
