#1
I've been modifying my 30 watt solid state amp, and after i modded 2 clipping stages, with 2 germanium diodes on one side and red leds on the other sides, the amp got hot and apparently blew a fuse.
So i'm going to stick to it's stock configuration but with 4 diodes in place of 2, it shouldnt be as bad on the voltages or whatever the problem may be.
I didn't expect this to happen, so i got a fuse to replace it.
The problem is, the stock fuse is 250V 1A.
The fuse i got is 250V 5A.
Should i expect much of a problem with the A differences? the voltages are the same...
Cusp of Magic
#2
Yeah, it won't blow and your amp will be fried.
It's supposed to open at 1A (which is a lot for your amp) but if you run it with that fuse then you could have up to 5A coursing through the circuit, ****ing shit up in there.

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#3
Don't replace a fuse with a higher amperage fuse, that's not smart. Fuses are for safety and are rated for a reason. You're letting the possibility of 5A into a circuit that was rated for 1A. I wouldn't be surprised if it goes up in flames if you modded it without changing the rest of the parts to handle it!

Having a fuse continually blow is a sheer indicator of a fault in the circuit.
#4
Okay, so what resistors or caps would i have to change in order to handle this fuse? I take that it would only be a minor modification to a few components?
Cusp of Magic
#6
Quote by Chaos-Serenade
Okay, so what resistors or caps would i have to change in order to handle this fuse? I take that it would only be a minor modification to a few components?

It's not a matter of being able to "handle" a fuse. You COULD stick that fuse in there right now and it wouldn't be the cause of the failure (it's just a wire bro.)
It's for protection, the current will open the fuse before hitting a more valuable/harder to replace component in your amp.

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#7
I do not. it's a 30 watt solid state amplifier. It's from 1987.
Uhm, maybe something to throw out some values, the bass section i guess has 2 very large 3300 uF capacitors, and when the fuse blew the first time theres 1 very large resistor that was hot, but it's not burned or anything.
Cusp of Magic
#8
It's impossible to tell without the schematic or at least the amplifier topology. Is it a chip amp (one integrated circuit with a bunch of leads) or discreet transistor (a bunch of 3 leaded devices)?
#10
Those are most likely op-amps. Like this?:

http://www.reuk.co.uk/shopImages/lm741.jpg

Those are used as pre-amps.

The easy way to tell is to try to find the model number on the transformer. The max rated current on the transformer will give you a good indication. Amplifiers are designed with transformers that are rated to supply a specific amount of current without getting too hot. If you exceed that, you need to replace it as well as every component that is not rated to handle the new current draw.
#11
it should not have blown from changing the clipping diodes. are you sure those were actually the clippers you changed.
Prs se Holcomb is the answer
#12
I believe germanium diodes have a smaller forward voltage drop than silicon. Germanium diodes have an average drop of around .25V, rather than the .7V drop on the more common silicon. You'd need 3 of these in series for each silicon diode you're replacing to maintain the circuit's rating. The voltage drop across an LED is much higher, around 1.4 for red LEDs. I wouldn't suggest replacing standard diodes with LEDs because they need to be current-limited with a series resistor, which could end up changing the entire circuit's properties. They can't handle much current compared to rectification diodes.
#13
Yes, op-amps. There are 3 that say 4558DD JRC 7005.
All the transformer says on it is:
SE-6628 UC
N Y 86 I
And i'm positive i only modified the diodes in the clipping section, the overdrive is actually a small seperate board, with the pre gain volume and overdrive controls mounted on it, and the LEDs lit up only when i had the overdrive maxed, also noted, after i modded the diodes, there was a hissing sound with the overdrive on 10 and pre gain volume on 10.
Cusp of Magic
#14
Common diodes are 1N400X, where X can be a different number depending on it's voltage rating.

If you took a 1N400X diode from your circuit, you'll need to do this:

Replace this 1N400X:

(+) --|>|-- (-)

With This (3 series dioides if Vdrop = .3V):

(+) --|>|----|>|----|>|-- (-)

Remember, the current rating on each of the 3 new diodes must equal or exceed the rated current on the original diode. Not all germanium diodes have a voltage drop of .3V, so make sure you look at the data sheet so that you know how many you need in series to equal the original diode's voltage drop.
#17
The orignal diodes where 2 sets of orange banded germanium diodes (4).
I took them out, put 2 of the diodes together on one side with a red LED on the other side. i did this for both sets of clipping diodes.
I imagine that the LEDs were too much and it overloaded it somehow, which would describe the hissing sound, and also they lit up when playing and on full overdrive.
that's when i noticed a burning smell, and unplugged it, turned it off and let it cool. thankfully nothing was burned the fuse blew.
So now, i want to try 2 orange germanium diodes together on one side and 2 blue germanium diodes on the other, for both sets in the overdrive section, which equals 8 diodes all together.
problem is, i'm worried about using this 5A fuse in place of the 1A.
Cusp of Magic
#19
It's hard to tell without model numbers of the diodes. One germanium could be 1Vdrop, another could be .25Vdrop!
#20
if the doubled diodes on each side are different voltage drop, then that means i would acheive asymmetrical clipping, which, i kind of wanted in the first place for a more natural sound.
All i'm doing is modifying the amp stock to achieve more distortion.
I upgraded the old scratchy 10k pre gain volume pot with a working 100k pot, and took out the overdrive pot and put a simple on/on toggle to kick into clean or distortion mode.
Surprisingly, those mods worked great, but it's the diodes im having trouble with.
I may just have to resort back to the simple 2 pairs of 2 germanium diodes.
Is there any trick i can do with the 5A fuse to prevent it from overloading my amp?
Like, aluminum foil or anything some of you may know?
Cusp of Magic
#21
Definitely use the 1A fuse. The transformer is only rated at what the amp was originally designed for, which apparently was a max of 1A. If you use anything higher than 1A, you're playing with fire.
#22
I tried the 5A fuse.
It appears to work okay, but I haven't had it on long or used full overdrive, i'm going to play it safe and wait till i get the proper fuse.
I changed it back to 2 pairs of germanium diodes, and the only mods I have done are taking out the overdrive pot, putting in a toggle switch in it's place, and i changed the old scratchy 10K pre gain volume pot to a 100k pot.
What does changing the value on the pre gain pot like this do exactly?
Cusp of Magic
#23
A pot is a resistor that can be wired to vary the resistance when the knob is turned. Using a 100k pot instead of a 10k will likely make the audible change a bit different. It's a matter of preference when it comes to those kind of things. Just make sure it's a logarithmic taper pot. Linear pots don't work well for audio.
#25
Are you certain you didn't have any excess solder shorting something? That would result in less resistance and more current at a given voltage, triggering the fuse.
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#26
Quote by BasementCat
Are you certain you didn't have any excess solder shorting something? That would result in less resistance and more current at a given voltage, triggering the fuse.


While that is true, the temperature variation of the circuit would have a much higher effect deeming that unlikely.
#27
Quote by NakedInTheRain
Yeah for fuck's sake don't replace the fuse with one rated at a higher amperage. Fuses blow for a reason - to protect your amp from killing itself.


I work for an auto company as a technical field rep-

I saw a guy stick a 30a fuse in a 5a socket. Lets just say it was easy to find the short... just follow the smoked wires...

Can't fix stupid.