27-11-2016, 10:33 AM
Honestly, I wouldn't try to unwind the secondary windings. It's perhaps feasible if there is only one secondary to reduce, but when there are 2, it's another game. Leave the transformers alone.
Given that you're using it to play music in a domestic environment, I reckon it'll be absolutely fine. While 96V seems a bit close to the 100V rating of the capacitors, I've seen much worse in practice (like, 75V across 63V capacitors! They worked reliably for over a decade, but I wouldn't have done that myself!). Likewise the ratings of the transistors might seem a bit close, but they only see the total voltage at clipping, when the rails will have sagged anyway. There are so many pairs in parallel that I doubt you'll run into SOA issues.
The only potential issue might be the LT supplies, but as I said yesterday, see how hot the regulators run. I'd be a lot more comfortable retro-fitting small heat sinks than unwinding a transformer!
If you wish to reduce those rails, putting resistors in parallel with the smoothing capacitors would be a bad idea. Something in series is what you need. However, see if you can improve the heat sinking arrangements first. That's the best "engineering" solution.
Alternatively, you could add some windings to the mains transformer. If these gave between 5 and 10 volts, you could then wire these in antiphase with the existing 24-0-24 secondary winding to subtract some of the output. What some people call "bucking". You'd need 2 separate windings - each goes on the end of the 24V outputs. Just check with a DVM before hooking it up, as you don't want the phases to add. Cover the new windings with suitable tape. It works well (but I'd go down the improved heat sinking route first).
I have a bit of a thing about heat sinking! I'll quite often add heat sinks to devices on a PCB that don't have them, or upgrade the ones fitted. It goes back to my days of servicing domestic gear where sometimes you'd see a TO220 regulator standing up on a PCB with no heat sinking, but also no PCB material! The thing was supported by just the PCB traces!
I'm not surprised it sounds good. Most amplifiers clip far too easily because of the wide dynamic range of music - which is why so few domestic amplifiers have clipping indicators, and why designers work so hard at optimising the clipping behaviour. But there's no substitute for raw watts
Good luck,
Mark
Given that you're using it to play music in a domestic environment, I reckon it'll be absolutely fine. While 96V seems a bit close to the 100V rating of the capacitors, I've seen much worse in practice (like, 75V across 63V capacitors! They worked reliably for over a decade, but I wouldn't have done that myself!). Likewise the ratings of the transistors might seem a bit close, but they only see the total voltage at clipping, when the rails will have sagged anyway. There are so many pairs in parallel that I doubt you'll run into SOA issues.
The only potential issue might be the LT supplies, but as I said yesterday, see how hot the regulators run. I'd be a lot more comfortable retro-fitting small heat sinks than unwinding a transformer!
If you wish to reduce those rails, putting resistors in parallel with the smoothing capacitors would be a bad idea. Something in series is what you need. However, see if you can improve the heat sinking arrangements first. That's the best "engineering" solution.
Alternatively, you could add some windings to the mains transformer. If these gave between 5 and 10 volts, you could then wire these in antiphase with the existing 24-0-24 secondary winding to subtract some of the output. What some people call "bucking". You'd need 2 separate windings - each goes on the end of the 24V outputs. Just check with a DVM before hooking it up, as you don't want the phases to add. Cover the new windings with suitable tape. It works well (but I'd go down the improved heat sinking route first).
I have a bit of a thing about heat sinking! I'll quite often add heat sinks to devices on a PCB that don't have them, or upgrade the ones fitted. It goes back to my days of servicing domestic gear where sometimes you'd see a TO220 regulator standing up on a PCB with no heat sinking, but also no PCB material! The thing was supported by just the PCB traces!
I'm not surprised it sounds good. Most amplifiers clip far too easily because of the wide dynamic range of music - which is why so few domestic amplifiers have clipping indicators, and why designers work so hard at optimising the clipping behaviour. But there's no substitute for raw watts
Good luck,
Mark
