Hello,
Yes I am learning a little diy electronics the hard way, trial and error :-(
I have attempted the first phase of a two phase plan to remove the transformers, rectifiers and smoothing caps to a separate dedicated psu box for my stereo power amp.
Reason being, to see if I can do it, and, to see if there is any sound improvement.
1st phase is to site the transformers in the planned psu enclosure and run wires to the cct board just as original but naturally the transformer tails are now much longer, I have fitted in higher spec caps (same uF, same V, higher temp) in place of the original caps. Plan was to go one little step at a time to see if it works and not go too long without music ;-)
There are 4 pairs of wires off the two transformers, 2 pairs measuring at 37.5Vac and 2 at 42.8Vac.
The 42.8V are for control and safety circuits I guess as they have tiny smoothing caps and tiny diodes in the rectifiers.
The 37.5V have much larger 3x4700uF each and much larger diodes, so I guess these are the rails for the power amp audio part of the board + 0 - ?
If all transformer tails are connected to the circuit board apart from one 37.5V supply neither of the 2 internal fuses blow, when this 37.5 supply is connected the fuse associated to this supply blows instantly on power up.
I would assume as the amp worked fine before I removed the transformers and changed the large smoothing caps, that it is something that I have done, but a few soldered joints and extending a couple of wires that I have checked over and over again, I don't see how they can be the problem?
The original caps are approximately half the physical size of the new ones, but all basic specs are the same, I would guess that they may pull more current at start up as they are physically bigger? However, I don't understand how one side does not blow, and the other always blows, and yes I did jiggle the 6 caps, to get two sets of 3, each set approx equal in capacitance.
I did however have to use a screwdriver to gently persuade the transistors off of their silicone sheet (heat sink joiner sheet) so I could remove the amplifier cct board from the case, they look undamaged, but I guess they may be a good place to start testing - out of circuit testing I guess?
From what I have read the other common thing to check are the diodes in the bridge.
Would you think I am along the right lines thinking of testing the transistors and then the diodes?
Many thanks for any thoughts or comments, I am a beginner so very simple technical talk much appreciated
Cheers
DC
Yes I am learning a little diy electronics the hard way, trial and error :-(
I have attempted the first phase of a two phase plan to remove the transformers, rectifiers and smoothing caps to a separate dedicated psu box for my stereo power amp.
Reason being, to see if I can do it, and, to see if there is any sound improvement.
1st phase is to site the transformers in the planned psu enclosure and run wires to the cct board just as original but naturally the transformer tails are now much longer, I have fitted in higher spec caps (same uF, same V, higher temp) in place of the original caps. Plan was to go one little step at a time to see if it works and not go too long without music ;-)
There are 4 pairs of wires off the two transformers, 2 pairs measuring at 37.5Vac and 2 at 42.8Vac.
The 42.8V are for control and safety circuits I guess as they have tiny smoothing caps and tiny diodes in the rectifiers.
The 37.5V have much larger 3x4700uF each and much larger diodes, so I guess these are the rails for the power amp audio part of the board + 0 - ?
If all transformer tails are connected to the circuit board apart from one 37.5V supply neither of the 2 internal fuses blow, when this 37.5 supply is connected the fuse associated to this supply blows instantly on power up.
I would assume as the amp worked fine before I removed the transformers and changed the large smoothing caps, that it is something that I have done, but a few soldered joints and extending a couple of wires that I have checked over and over again, I don't see how they can be the problem?
The original caps are approximately half the physical size of the new ones, but all basic specs are the same, I would guess that they may pull more current at start up as they are physically bigger? However, I don't understand how one side does not blow, and the other always blows, and yes I did jiggle the 6 caps, to get two sets of 3, each set approx equal in capacitance.
I did however have to use a screwdriver to gently persuade the transistors off of their silicone sheet (heat sink joiner sheet) so I could remove the amplifier cct board from the case, they look undamaged, but I guess they may be a good place to start testing - out of circuit testing I guess?
From what I have read the other common thing to check are the diodes in the bridge.
Would you think I am along the right lines thinking of testing the transistors and then the diodes?
Many thanks for any thoughts or comments, I am a beginner so very simple technical talk much appreciated
Cheers
DC
Build and use a Mains Bulb Tester for EVERY power ON, after EVERY modification.
Even if you just resoldered a wire.
Always use it.
But it does not work well with a Power Amplifier that is biased to pass a high output stage current. It works best when the output stage is NOT biased.
Once you have the prototype powered up via the bulb tester, you can check measurements around the amplifier to find faults or just to check that currents and voltages are at the design values.
But the bulb tester does not prevent damage if a probe slips and shorts together two leads !!!!!!!!!!!!
You must still be very careful. Clip on test leads are a big help. Even just one to the Power Ground, so that you can concentrate on accurately positioning the other measurement probe.
Now back to your fuse blowing problem.
Can you draw a sketch of your new wiring setup.
Post a pic of the sketch and a pic, or two, of the amplifier.
Even if you just resoldered a wire.
Always use it.
But it does not work well with a Power Amplifier that is biased to pass a high output stage current. It works best when the output stage is NOT biased.
Once you have the prototype powered up via the bulb tester, you can check measurements around the amplifier to find faults or just to check that currents and voltages are at the design values.
But the bulb tester does not prevent damage if a probe slips and shorts together two leads !!!!!!!!!!!!
You must still be very careful. Clip on test leads are a big help. Even just one to the Power Ground, so that you can concentrate on accurately positioning the other measurement probe.
Now back to your fuse blowing problem.
Can you draw a sketch of your new wiring setup.
Post a pic of the sketch and a pic, or two, of the amplifier.
The higher voltage is for the low power stages of the amplifier, the lower voltage is for the output stage only. Doing it this way allows the output to be run close to saturation so is slightly more efficient on heat dissipation.
As the fuse blows when you connect the power output stage then I suspect the output stage has gone short circuit.
I'm afraid what you are trying to do will only make things worse as far as performance and electromagnetic emissions goes. The only way to gain with this kind of arrangement is by adding a bigger PSU remotely.
As the fuse blows when you connect the power output stage then I suspect the output stage has gone short circuit.
I'm afraid what you are trying to do will only make things worse as far as performance and electromagnetic emissions goes. The only way to gain with this kind of arrangement is by adding a bigger PSU remotely.
Andrew - Ah I am afraid I would not know where or how to use a build tester :-( not yet any way
I do have bias values written on the inside of the case lid, I guess the last time it was serviced, and yes it is a power amplifier.
I will see if I can get the scanner, camera/phone and pc working together! ha! better luck with the amp I think ;-)
It is basically the same circuit as original but the transformers are on extension wires and so are the new caps, I know loop area silly at the moment, until phase2.
Basically I shall try to describe :-o
two transformers
one with two wires 37.5V
other with 6 wires 37.5, 42.8, 42.8
each pair wired to circuit board,
where each pair are wired too, a small cap bridges between the two wires of each pair,
then each pair goes to a set of 4 diodes
after the diodes are 4 sets of smoothing caps
I have not worked out exactly what goes where from there as of yet, as it seems rather complex (to me) but there are 4 transistors next to the smoothing caps, two pairs I think as two have 2SC2922 as their part numbers and the other two are 2SA1216's
Don't know if this description helps...
Richie - interesting to know why the main power part runs on the lower voltage, makes sense, thanks,
Output stage.., oh dear, I would guess most of the bits on the circuit board are the output stage? could I have messed something up by soldering or keep flipping the board over?
I took some measurements of the transistors (in circuit) I need to learn more about these things, all I know is that the results look sort of mirrored, that means all must be well... if testing in circuit is okay!
Multimeter on diode test mode:
.................black on base.........red on base
pt.no.16
emit............0.05v...................0.05v
collect.........0.5v.....................O.L.
pt.no.22
emit............0.04v...................0.05v
collect.........O.L......................0.5v
pt.no.16
emit............0.05v...................0.05v
collect.........0.5v....................O.L.
pt.no.22
emit............0.05v...................0.05v
collect.........O.L......................0.5v
Phase2 of the project is to have the transformers, diodes and smoothing caps remote...
Thanks for the comments
cheers
dc
I do have bias values written on the inside of the case lid, I guess the last time it was serviced, and yes it is a power amplifier.
I will see if I can get the scanner, camera/phone and pc working together! ha! better luck with the amp I think ;-)
It is basically the same circuit as original but the transformers are on extension wires and so are the new caps, I know loop area silly at the moment, until phase2.
Basically I shall try to describe :-o
two transformers
one with two wires 37.5V
other with 6 wires 37.5, 42.8, 42.8
each pair wired to circuit board,
where each pair are wired too, a small cap bridges between the two wires of each pair,
then each pair goes to a set of 4 diodes
after the diodes are 4 sets of smoothing caps
I have not worked out exactly what goes where from there as of yet, as it seems rather complex (to me) but there are 4 transistors next to the smoothing caps, two pairs I think as two have 2SC2922 as their part numbers and the other two are 2SA1216's
Don't know if this description helps...
Richie - interesting to know why the main power part runs on the lower voltage, makes sense, thanks,
Output stage.., oh dear, I would guess most of the bits on the circuit board are the output stage? could I have messed something up by soldering or keep flipping the board over?
I took some measurements of the transistors (in circuit) I need to learn more about these things, all I know is that the results look sort of mirrored, that means all must be well... if testing in circuit is okay!
Multimeter on diode test mode:
.................black on base.........red on base
pt.no.16
emit............0.05v...................0.05v
collect.........0.5v.....................O.L.
pt.no.22
emit............0.04v...................0.05v
collect.........O.L......................0.5v
pt.no.16
emit............0.05v...................0.05v
collect.........0.5v....................O.L.
pt.no.22
emit............0.05v...................0.05v
collect.........O.L......................0.5v
Phase2 of the project is to have the transformers, diodes and smoothing caps remote...
Thanks for the comments
cheers
dc
Last edited:
I'm having trouble getting things to talk and work since upgrading to windows8...
this is why I said I shall try, in the mean time I tried to describe...
sorry not ignored, just a delay,
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