and optimise the bass amp to produce the best compromises for bass quality.
If the passive crossover split is Bass/Mid and Treble, then there is less to gain, because you don't want to lose the Mid performance you currently have.
The Treble amp could go all film/foil caps for increased fidelity. It would not need any electrolytics.
If the passive crossover split is Bass/Mid and Treble, then there is less to gain, because you don't want to lose the Mid performance you currently have.
The Treble amp could go all film/foil caps for increased fidelity. It would not need any electrolytics.
Problem with fuses blowing
I've just got to the stage of checking my power supply/rectifier board, but I'm hitting problems with the fuse in the IEC blowing, and also not getting anywhere near the DC voltage I should have (35V). I suspect the latter is because the fuse is blowing.
Decibel Dungeon suggests a 1.6A time delay fuse is adequate for Gainclones running at 230V, which mine is.
So I have a 1.6AT fuse in the switch, a 300VA primary with 2*25V secondaries, but the fuse is blowing all the time.
I've got DC measurements of 11.2V the first time (both 11.2V, and both positive), and 1.2V the second time I tried measuring (and to check it wasn't a dud fuse the first time). The 1.2V was positive for both measurements.
Now I'm pretty sure all of my problems are because the fuse keeps blowing, but if DD suggests a 1.6AT fuse to be adequate then what's going on with mine to keep blowing the fuses?
I've checked the joints - everything seems fine - blue to live and brown to neutral, plus earth to ground.
On the secondaries the black and red wires are to one AC input (black 0V, red 25V) and yellow and orange to the second AC input (yellow 25V, orange 0V).
I'm wondering if I've damaged the switch - I soldered the primary wires to the switch contacts, so perhaps I've done something to the switch with the heat?
Each secondary is rated at 6 amps.
I've just got to the stage of checking my power supply/rectifier board, but I'm hitting problems with the fuse in the IEC blowing, and also not getting anywhere near the DC voltage I should have (35V). I suspect the latter is because the fuse is blowing.
Decibel Dungeon suggests a 1.6A time delay fuse is adequate for Gainclones running at 230V, which mine is.
So I have a 1.6AT fuse in the switch, a 300VA primary with 2*25V secondaries, but the fuse is blowing all the time.
I've got DC measurements of 11.2V the first time (both 11.2V, and both positive), and 1.2V the second time I tried measuring (and to check it wasn't a dud fuse the first time). The 1.2V was positive for both measurements.
Now I'm pretty sure all of my problems are because the fuse keeps blowing, but if DD suggests a 1.6AT fuse to be adequate then what's going on with mine to keep blowing the fuses?
I've checked the joints - everything seems fine - blue to live and brown to neutral, plus earth to ground.
On the secondaries the black and red wires are to one AC input (black 0V, red 25V) and yellow and orange to the second AC input (yellow 25V, orange 0V).
I'm wondering if I've damaged the switch - I soldered the primary wires to the switch contacts, so perhaps I've done something to the switch with the heat?
Each secondary is rated at 6 amps.
fuse rating
Wattage times 3 for an inductive load divide by voltage to find the start up fuse rating.
This applies to motors and transformers.
300VA * 3 / 240 = 3.75A. Use an T4A fuse.
But, this will pass 4A for days even though something has blown inside.
It is far safer to close rate the fuse as Nuuk has suggested. This requires you to fit a soft start circuit. Again Nuuk gives all the details.
Why did you start up without using a mains light bulb tester?
This would save the fuse and prevents other damage if you have wired up something wrongly.
Build the tester and use it! Nuuk has given you all the details for this as well.
Wattage times 3 for an inductive load divide by voltage to find the start up fuse rating.
This applies to motors and transformers.
300VA * 3 / 240 = 3.75A. Use an T4A fuse.
But, this will pass 4A for days even though something has blown inside.
It is far safer to close rate the fuse as Nuuk has suggested. This requires you to fit a soft start circuit. Again Nuuk gives all the details.
Why did you start up without using a mains light bulb tester?
This would save the fuse and prevents other damage if you have wired up something wrongly.
Build the tester and use it! Nuuk has given you all the details for this as well.
Peter,Peter Daniel said:
he just told you the T1.6A blows at switch on.
On the UK 240Vac mains, this fuse is large enough for 384VA.
The fuse is big enough, the start up current is too high, so the fuse blows.
Westers,
Don't fit a bigger fuse, instead fit a soft start, the fuse and transformer combination needs it.
After doing the soft start you may find that a T1.2A or T1A will suffice.
Not wanting to start an argument/heated debate, I can see where you are both coming from.
Peter, you're right that in theory my 300VA primary shouldn't need a soft start, but I'm getting through fuses like there's no tomorrow.
A bigger fuse could be the answer as you say, but, as Andrew points out, this could cause other issues elsewhere in the circuit.
Andrew, a question for you. Having thought about it I can see how the light bulb tester acts as a soft start for the transformer, but once the testing is completed and I remove the bulb, then surely I face the same problem everytime I switch on the amp - the fuse blows because there is nothing to throttle back the current?
Peter, you're right that in theory my 300VA primary shouldn't need a soft start, but I'm getting through fuses like there's no tomorrow.
A bigger fuse could be the answer as you say, but, as Andrew points out, this could cause other issues elsewhere in the circuit.
Andrew, a question for you. Having thought about it I can see how the light bulb tester acts as a soft start for the transformer, but once the testing is completed and I remove the bulb, then surely I face the same problem everytime I switch on the amp - the fuse blows because there is nothing to throttle back the current?
Yes, the bulb tester is only for safe start up. It is a Positive Temperature Coefficient (PTC) soft start. works but is designed to NOT tolerate any big load. That's why it lights up and reduces the supply voltage to the equipment.
You need a Negative NTC soft start or constant resistance soft start to allow sensible and safer fuse use, once you know the amp is wired correctly.
You need a Negative NTC soft start or constant resistance soft start to allow sensible and safer fuse use, once you know the amp is wired correctly.
Yes - IEC earth to the case, although I've got everything mounted on square bit of MDF so there's no real case to earth. To be safe I've drilled a hole and attached the IEC earth lead to a bolt through the board (using a crimp on circle connector to go over the bolt). That way there's an earth if something happens.
I'm guessing that there's no real need for an earth as there's no casing, but I thought it good practice to get into the habbit of creating an earth.
As for getting time to get readings, good question. The first time I switched on I got an 11.2V reading on both + and - rails. That caused me to scratch my head and think there was a problem, which lead me to look at the fuse. The glass fuse had clearly blown (it was black inside), so I replaced it, but this time the reading was about 1V (+/-) and when I looked at the fuse it was even blacker than before.
I've pulled all the connections apart so I can do the soft start light bulb test to check the switch, but also make sure I get secondary voltages that are correct (35V). However, looking at the connections (both primary and secondary to the Bridge) they're all connected up correctly and nothing is shorting out.
I even pulled the switch apart to see if something had gone wrong there (I couldn't think what would have gone wrong as it's just a method of making and breaking contacts) and that was fine.
So, it must be the sudden rush of mains current is very high and the fuses don't like this.
Assuming the above is correct then it possibly doesn't surprise me. The house is prone to blowing light bulbs, especially if one blows and is not replaced straight away then often we get a number of other bulbs blowing. I know it's a totally different circuit, but I think the house was a 1980's Friday afternoon job, judging by some of the other workmanship I've had to fix.
I'm guessing that there's no real need for an earth as there's no casing, but I thought it good practice to get into the habbit of creating an earth.
As for getting time to get readings, good question. The first time I switched on I got an 11.2V reading on both + and - rails. That caused me to scratch my head and think there was a problem, which lead me to look at the fuse. The glass fuse had clearly blown (it was black inside), so I replaced it, but this time the reading was about 1V (+/-) and when I looked at the fuse it was even blacker than before.
I've pulled all the connections apart so I can do the soft start light bulb test to check the switch, but also make sure I get secondary voltages that are correct (35V). However, looking at the connections (both primary and secondary to the Bridge) they're all connected up correctly and nothing is shorting out.
I even pulled the switch apart to see if something had gone wrong there (I couldn't think what would have gone wrong as it's just a method of making and breaking contacts) and that was fine.
So, it must be the sudden rush of mains current is very high and the fuses don't like this.
Assuming the above is correct then it possibly doesn't surprise me. The house is prone to blowing light bulbs, especially if one blows and is not replaced straight away then often we get a number of other bulbs blowing. I know it's a totally different circuit, but I think the house was a 1980's Friday afternoon job, judging by some of the other workmanship I've had to fix.
No, I haven't checked my mains voltage - I wouldn't know how to, although I'll google it to see how to.
No caps on the bridge - I'm using Peter's kit and haven't installed the optional caps included for the bridge - I wanted to hear what it sounded like before adding those.
All will be revealed when I build the light bulb tester tonight.
No caps on the bridge - I'm using Peter's kit and haven't installed the optional caps included for the bridge - I wanted to hear what it sounded like before adding those.
All will be revealed when I build the light bulb tester tonight.