So you decide to repair amps. You have a multimeter and a soldering iron.
A workbench and empty ice cream containers for screws and the like.
Full of ambition you start by removing the pcb if present. You read all these stories of ugrading caps and resistors to a "better sounding" replacement that cost as much as all the rest of the components together.
You start to swap all these caps, resistors, transistors, chips and tubes. All because it's been said...
Well let me tell you; it's sad.
First, You have to find your way in the amp. Even if it takes a whole day to grasp the way it's build.
Then, Find a schematic. So you have a reference at hand and you can allways come back to the original.
Third, Check if there are any changes made and record them.
Then, have your bench power supply ready. If you do not have one, buy one.
This is a life saver. Here is an example: PSU Assembly kit H-Tronic ATT.FX.INPUT_VOLTAGE: 30 V AC (max.) ATT.FX.OUTPUT_VOLTAGE: 1 - 30 Vdc from Conrad.com
Voltage and current can be adjusted. Build two of those, place them in a nice box with bannana connectors, add two volt and amp meters and you are ready.
In the event of a short, nothing will burn, the psu will go in protection. After some time you will have saved quite some money on burned components.
So, you're settled to open up your amp, heat up your iron and have pen and paper ready.
But hold on!
My teacher, long time ago, allways told me to be safe. One hand away from the unit and the ground (massa). Remove the ac power cord from the unit or the socket. Only then put your fingers in the unit.
You can check the low voltage parts by feeding them with your newly build psu. Connect them acros the rectifier. Remove the connection to the transformer first.
Preamp or whatever is working?
OK, connect the psu in the same manner to the power amp.
In most cases 30V is ok to find the problem and repair it.
Only then reconnect the original psu via a bulb circuit that's been described in a multitude of ways here in this forum.
Again, I firmly believe that a decent psu is worth having if you are serious about working on amps and the like. If you can find a proffesional one for sale, and it's within your budget, do not hesitate.
A double 60V/3Amps would be heaven.
Maybe after all, it would be great to start a thread with advise to the next generation of technicians with what they need to start with and how to distinguish real and false hints and recomendations scattered over the internet.
After fifty five years of service in the audio and telecom business, at the end of this year slowly but steady it will be over. And then, it's a repair when time permits and I feel the need to do it.
It's sunday now. I go for a good coffee and a cherry cake baked by mother the wife.
A workbench and empty ice cream containers for screws and the like.
Full of ambition you start by removing the pcb if present. You read all these stories of ugrading caps and resistors to a "better sounding" replacement that cost as much as all the rest of the components together.
You start to swap all these caps, resistors, transistors, chips and tubes. All because it's been said...
Well let me tell you; it's sad.
First, You have to find your way in the amp. Even if it takes a whole day to grasp the way it's build.
Then, Find a schematic. So you have a reference at hand and you can allways come back to the original.
Third, Check if there are any changes made and record them.
Then, have your bench power supply ready. If you do not have one, buy one.
This is a life saver. Here is an example: PSU Assembly kit H-Tronic ATT.FX.INPUT_VOLTAGE: 30 V AC (max.) ATT.FX.OUTPUT_VOLTAGE: 1 - 30 Vdc from Conrad.com
Voltage and current can be adjusted. Build two of those, place them in a nice box with bannana connectors, add two volt and amp meters and you are ready.
In the event of a short, nothing will burn, the psu will go in protection. After some time you will have saved quite some money on burned components.
So, you're settled to open up your amp, heat up your iron and have pen and paper ready.
But hold on!
My teacher, long time ago, allways told me to be safe. One hand away from the unit and the ground (massa). Remove the ac power cord from the unit or the socket. Only then put your fingers in the unit.
You can check the low voltage parts by feeding them with your newly build psu. Connect them acros the rectifier. Remove the connection to the transformer first.
Preamp or whatever is working?
OK, connect the psu in the same manner to the power amp.
In most cases 30V is ok to find the problem and repair it.
Only then reconnect the original psu via a bulb circuit that's been described in a multitude of ways here in this forum.
Again, I firmly believe that a decent psu is worth having if you are serious about working on amps and the like. If you can find a proffesional one for sale, and it's within your budget, do not hesitate.
A double 60V/3Amps would be heaven.
Maybe after all, it would be great to start a thread with advise to the next generation of technicians with what they need to start with and how to distinguish real and false hints and recomendations scattered over the internet.
After fifty five years of service in the audio and telecom business, at the end of this year slowly but steady it will be over. And then, it's a repair when time permits and I feel the need to do it.
It's sunday now. I go for a good coffee and a cherry cake baked by mother the wife.
I find amps fail in one of two modes.
1/ Amp has blown up and cant be powered up.
2/ Amp has blown but not fatally.
You can remove output transistors if they are blown and still power up the amp usually.
Voltage measurements then give an indication of the area of the fault.
I had a nasty fault on an amp once. All transistors diode checked ok and all resistors were correct. On power up it always pointed to same transistor at fault. The number had been worn off so I couldn't read it. It diode checked ok but then I realised it was an NPN and not a PNP ! Someone had attempted a repair but fitted wrong transistor.
1/ Amp has blown up and cant be powered up.
2/ Amp has blown but not fatally.
You can remove output transistors if they are blown and still power up the amp usually.
Voltage measurements then give an indication of the area of the fault.
I had a nasty fault on an amp once. All transistors diode checked ok and all resistors were correct. On power up it always pointed to same transistor at fault. The number had been worn off so I couldn't read it. It diode checked ok but then I realised it was an NPN and not a PNP ! Someone had attempted a repair but fitted wrong transistor.
No no, We in Belgium say to our wife and especially when she makes good food, "Mother, the wife". It's a friendly way of mentioning her, again when she makes delicious food.
And the other times aswell...
btw, the coffee is gone now as is a big shunk of that cake. I stil have some for this evening...
And the other times aswell...
btw, the coffee is gone now as is a big shunk of that cake. I stil have some for this evening...
As there are many varieties of amps on the market, it is really difficult to give general advice. In case of the one I repaired today, your hints would not be very beneficial to the beginner. It was a peavey classic 30 (tube amplifier) with a blown 10 amp fuse securing the filament circuit.
In this specific case a simple mains power meter told me 5-6W of power consumption. So I once guessed this was the primary loss of the unloaded mains transformer - which quickly led to the blown secondary fuse.
So my recommendation is always insert a power meter between ac-outlet and the unit to be repaired. This can save you lots of time...
In this specific case a simple mains power meter told me 5-6W of power consumption. So I once guessed this was the primary loss of the unloaded mains transformer - which quickly led to the blown secondary fuse.
So my recommendation is always insert a power meter between ac-outlet and the unit to be repaired. This can save you lots of time...
Last edited:
For stuff that eats 30V "too well", and you have verified that the 30V happens when the amp is disconnected, I like a couple LARGE 100 Ohm resistors. When the amp just pulls infinite current, 100r on 30V rails limits it to 0.3A or a couple Watts. At this point you can probably let it sit there while you verify junction voltages.
i'm posting to subscribe to updates...
tho when my wife and I are talking to the dogs that live with us in our house, we refer to each other as 'ma and 'pa to them, i think parents refer like this to their children too, in a 'normal' family environment;
" ...
But hold on!
My teacher, long time ago, allways told me to be safe. One hand away from the unit and the ground (massa). Remove the ac power cord from the unit or the socket.
Properly discharge capacitors in the unit
Only then put your fingers in the unit. ..."
You may need to repeat the cap discharging, potentially after each power-applied cycle, between each powered test point survey. At a minimum treat every power cycle / undischarged condition as still under power when touching the Device Under Test (DUT).
But hold on!
My teacher, long time ago, allways told me to be safe. One hand away from the unit and the ground (massa). Remove the ac power cord from the unit or the socket.
Properly discharge capacitors in the unit
Only then put your fingers in the unit. ..."
You may need to repeat the cap discharging, potentially after each power-applied cycle, between each powered test point survey. At a minimum treat every power cycle / undischarged condition as still under power when touching the Device Under Test (DUT).
Last edited:
When that is the only reason, you can instead use the Subscribe function, drop-down at top of thread:
Attachments
Interestingly, the kit cited in the OP is sold by Conrad in the EU.
Conrad ships to "more than 210 countries across the globe", which is an unusually large number ... the list of countries with actual functioning governments is less than that (38 fail that requirement) and even if you include them, the number is still generally held to be 195 worldwide, even including the Holy See and the State of Palestine.
Why the preamble? Because Conrad does NOT ship to two countries ... the US and Canada.
Conrad ships to "more than 210 countries across the globe", which is an unusually large number ... the list of countries with actual functioning governments is less than that (38 fail that requirement) and even if you include them, the number is still generally held to be 195 worldwide, even including the Holy See and the State of Palestine.
Why the preamble? Because Conrad does NOT ship to two countries ... the US and Canada.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.