Ok it worked a bit better, but it still cuts out..I think I'm goin to throw away that power amp..it's not enough for real bass.
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Show posts MenuQuote from: phatt on October 14, 2016, 11:12:45 PMThis partially answers why it was completely unusable when I initially put a buffer after the master pot (wich actually is 100k indeed).
You could try a simple voltage divider at the output of your preamp.
If the volume control is at the end of your preamp and it's say 100k pot then change it to a 10k pot, that will limit the maximum swing. or just bridge a 10~20k resistor across the existing volume pot.
Phil.
Quote from: Roly on February 15, 2014, 02:15:09 AM
Yeah, well that looks like about a 200VA core to me.
What am I missing here?
Let's go back to the OP. If the amp is "underpowered" then that is a function of the power supply capacity, and changing the power amp to Class-D, Project 27, or anything else, isn't going to make any difference at all; the power supply is delivering what it can into the load (apparently without catching fire).
Changing the power board might make it more reliable (if the basic cause of blowing transistors is original mis-design; possible but unlikely), but things like faulty speaker leads or connectors have to be considered and eliminated first.
Currently it has "two BDW52C/BDW51C couples". These are each 100V/15A/125W transistors and it has 2 pair - so why has it "busted the output section so many time(s)"? At face value these should be more than capable of delivering 100W into 4 ohms (given sufficient heatsink).
Upping the power output would require some major changes, such as a heavier power transformer (but to me that core looks quite sufficient for 100W output); but again I would want to eliminate the possibility it has inefficient speakers and could possibly be improved by changing the speakers for more efficient ones.
Now if it has the original power supply and the original speaker load it can only perform as original, and it seems the problem here is blowing transistors, not blowing the power supply, so the supply must therefore have sufficient capacity to drive the original load.
Until we change the basis of this discussion to "more volts" or "fewer ohms" the power supply won't need changing.
220v * 1A = 220 watts in, about what you would expect for a nominal 100W output amp.
35VDC implies ~25VAC * 2.5A = 62.5 watts. But it has two such secondary fuses and there would seem to be no reason for that with a single winding into a bridge, so (without a circuit) we can guess that it has two fuses because it has two secondary windings to protect, and that the available DC power will be around 125 watts. Fuse blowing isn't the complaint.
So;
- what is the original nominal output power?
- what is the speaker cab impedance? (or simply measure the cab ohmmeter resistance and post that)
Quote from: Superfuzz on October 11, 2013, 08:19:56 AMQuote from: J M Fahey on October 11, 2013, 06:38:14 AMSo you're telling me of, reducing the sensing resistor to 0.1 ohm and then take the signal directly from the node beetwen speaker - and resitor, without any resistor inbeetwen?
Interesting.
Why those values?
Quote from: J M Fahey on October 11, 2013, 06:38:14 AM
Interesting.
Why those values?