The used Fender Frontman I bought looks like suffering the known overheating problems of several pieces of that series.
I have unmounted the circuit board and suppose there are some signs of overheating around some soldering points, likely from the power amp section.
I would like to isolate the preamp section and practically create a rackmount fender preamp (which could hopefully work with low DC current) to connect it to an external power amplifier (i.e. a QSC PA power amplifier) and a guitar cabinet (2x12 or 4x12).
I don't know much about electronics, but am able to change or remove components if needed. Can somebody help?
The photos of this particular circuit board are attached to this post. The schematic of the Fender Frontman 212R is very easy to find online. I am not posting it here not to risk to see it removed for some reason.
Thank you in advance
0360
I have unmounted the circuit board and suppose there are some signs of overheating around some soldering points, likely from the power amp section.
I would like to isolate the preamp section and practically create a rackmount fender preamp (which could hopefully work with low DC current) to connect it to an external power amplifier (i.e. a QSC PA power amplifier) and a guitar cabinet (2x12 or 4x12).
I don't know much about electronics, but am able to change or remove components if needed. Can somebody help?
The photos of this particular circuit board are attached to this post. The schematic of the Fender Frontman 212R is very easy to find online. I am not posting it here not to risk to see it removed for some reason.
Thank you in advance
0360
Attachments
Looks like you can just use the preamp out jack. Disconnect the +/- 42V to the power amp
by cutting those traces from the supply. Leave the low voltage supply traces intact.
This belongs down in the instrument amp section.
Not sure about overheating, but your pictures show joints that have been resoldered. On the power transistors, most likely reason was they were replaced at some point. Probably the output section was blown at some time.
You have outlines the basic power amp part, the main rail power supply, and the 15v power supplies part.
Look at the schematic, the 15v supplies derive from the main rails, so you need those supplies too.
DO NOT run the amp with the board off the chassis, it NEEDS that heat sinking. For the power amp, if you remove the power amp, this no longer applies.
Some folks have an amp that overheats, most do not.
Good etiquette is to provide the schematic:
http://bmamps.com/Schematics/fender/FM212R,_100H_Schematics.pdf
Not sure about overheating, but your pictures show joints that have been resoldered. On the power transistors, most likely reason was they were replaced at some point. Probably the output section was blown at some time.
You have outlines the basic power amp part, the main rail power supply, and the 15v power supplies part.
Look at the schematic, the 15v supplies derive from the main rails, so you need those supplies too.
DO NOT run the amp with the board off the chassis, it NEEDS that heat sinking. For the power amp, if you remove the power amp, this no longer applies.
Some folks have an amp that overheats, most do not.
Good etiquette is to provide the schematic:
http://bmamps.com/Schematics/fender/FM212R,_100H_Schematics.pdf
Thank you all for the fast response.
If I got your advices right, I then just need to keep disconnected the power supply going from the 220v outlet to to the transformer and then supply the circuit board with the 15v current in order to provide current just to the preamp section.
Can it be done with a "common" DC adapter?
If yes, how many amperes should it need to support? Where exactly should I connect the + and - ?
Please consider that I can barely read the schematic, so a coule of marks added to the picture I took from the top of the board would help a lot.
Best regards
If I got your advices right, I then just need to keep disconnected the power supply going from the 220v outlet to to the transformer and then supply the circuit board with the 15v current in order to provide current just to the preamp section.
Can it be done with a "common" DC adapter?
If yes, how many amperes should it need to support? Where exactly should I connect the + and - ?
Please consider that I can barely read the schematic, so a coule of marks added to the picture I took from the top of the board would help a lot.
Best regards
I tried to connect a 9v battery to the points highlighted in the pictures attached to this reply (please check them).
Regardless to the low tension (9v instead of 15v), the red led of the Fender Frontman 212R front panel slightly turned on.
In order to do a quick raw audio test without soldering anything, I connected a standard audio guitar cable (1/4") to one of the two jack inputs of the front panel and connected the preamp out ("pre out" of the front panel) to the line input of my computer audio interface with another guitar cable.
I then shortened the mono plug at the other end of the guitar cable I connected to the front panel input and the preamp seemed to send the audio board the expected crackle.
Is it now safe to try connect an universal power adapter (15v 1A) to those circuit board joints I highlighted in the photos? Can I remove the capacitors at the position C75 and C76 to make some room for the adapter wires (i.e. the wires that lead to the jack of the adapter plug)?
Thank you in advance for your answer
Best regards
Regardless to the low tension (9v instead of 15v), the red led of the Fender Frontman 212R front panel slightly turned on.
In order to do a quick raw audio test without soldering anything, I connected a standard audio guitar cable (1/4") to one of the two jack inputs of the front panel and connected the preamp out ("pre out" of the front panel) to the line input of my computer audio interface with another guitar cable.
I then shortened the mono plug at the other end of the guitar cable I connected to the front panel input and the preamp seemed to send the audio board the expected crackle.
Is it now safe to try connect an universal power adapter (15v 1A) to those circuit board joints I highlighted in the photos? Can I remove the capacitors at the position C75 and C76 to make some room for the adapter wires (i.e. the wires that lead to the jack of the adapter plug)?
Thank you in advance for your answer
Best regards
Such adaptors (please see attached photo) do have two wires, a - and a +, right?
Why shouldn't such an adaptor provide the needed power supply when the 9v battery seemed to do the job?
Why shouldn't such an adaptor provide the needed power supply when the 9v battery seemed to do the job?
Attachments
Last edited:
You should be able to use the original, internal power supply, and just disconnect
the output stage connections from the supply. Do you have to use an external
power supply for some reason?
A battery has two terminals, a + and a -, but you wouldn't think of it as two voltage sources. A circuit designed to run on a single 9v suply is one thing. A circuit designed to run on +15 and -15 is a different thing. That doesn't mean one 15v supply with + and - ends, It means a +15 supply with the negative end grounded, and a -15v supply with the positive end grounded. You could do it with TWO 15v adaptors, but that gets clumsy fast.
When you see +15 and -15 in a circuit like that, it means there is 30v between the two points. Imagine you have a salt shaker in front of you, and a pepper shaker 15 inches to the right. And a sugar dispenser 15 inches to your left. How far is it from the pepper to the sugar? 30 inches.
The circuit supplies are zener diode derived, so you would have to put higher voltage in for them to work, say 25v plus and minus.
You pointed out the +15 and -15 points in the circuit, but you are ignoring the ground connection for those supplies. it might light the LED a little or even make some sort of sound, but it won't actually function as an amplifer, not very well.
When you see +15 and -15 in a circuit like that, it means there is 30v between the two points. Imagine you have a salt shaker in front of you, and a pepper shaker 15 inches to the right. And a sugar dispenser 15 inches to your left. How far is it from the pepper to the sugar? 30 inches.
The circuit supplies are zener diode derived, so you would have to put higher voltage in for them to work, say 25v plus and minus.
You pointed out the +15 and -15 points in the circuit, but you are ignoring the ground connection for those supplies. it might light the LED a little or even make some sort of sound, but it won't actually function as an amplifer, not very well.
Using only one adapter would cut off half the waveform. In this particular circuit (like most),
you would need one adapter for the top half of the waveform, and another adapter for the bottom half.
This is called a bipolar power supply.
Thank you Rayma for your answer.
I noticed (and learned from the experience of others) that this amplifier tends to overheat and has maybe some major design problems about the heat dissipation.
As I unfortunately don't know much about electronics, I would like to be 100 percent sure there isn't any 200v current going around for any reason, even at the first stages of the circuit board.
Connecting a 9v battery to the capacitor connectors (the minus of one and the plus of the other, like shown in the pictures of the post above) it looked like the preamp was working. The next step would be mounting it in a portable unit, similar to a 19" rackmount (actually wider because of the wider circuit board) and avoid the big 220v adapter which is now part of the original Fender Frontman 212R chassis.
Would the 15v external adapter solution somehow wrong for safety reasons?
As chassis, I am thinking about using the base of the current one, which is metallic, and cover the rest with some mdf plates.
Thank you again for your help!
Last edited:
Ok! Now I understand.
The problem is, that another common issue is the power led going sometimes off and on, likely due to some poor.connectors, socket or switches at the very first part of the circuit. If I used the origimal socket, swirch, adapter and first part of the circuit, I would then have to solve that problem too.
Could I instead use the 15v adapter (mybe bigger, capable of more amperes) to provide the current to both section of the preamp circuit?
Would I, in this last scenario, need to connect the 15v adapter to each of the solder joints where the capacitors C75 and C76 are (or were, if I can remove them keeping the rest of the circuit intact)?
The most likely reason for this amplifier overheating is that WOEFUL heat sink!! I would try the amp with a MUCH larger, finned heatsink---then it might just work fine for you. Looks like there is enough room in the chassis. If you ARE going to use an alternative power amplifier, do as suggested to cut the power amplifier rail traces. You might even be able to fit an IcePower Class-D amplifier inside the existing chassis.
Thank you all for the exhaustive explanation.
I'll rather use the rest of the Fender Frontman 212R as a100W/4 Ohms cabinet. And maybe go hit the seller in the head using the circuit board, as he sold this piece of garbage stating it worked just fine, "it just has a couple of broken EQ knobs..." 🙂
I'll rather use the rest of the Fender Frontman 212R as a100W/4 Ohms cabinet. And maybe go hit the seller in the head using the circuit board, as he sold this piece of garbage stating it worked just fine, "it just has a couple of broken EQ knobs..." 🙂
You still need TWO 15v supplies, one of each polarity. One larger 15v supply won't make a difference. Like a motorcycle needs two wheels. One wheel won;t work. Putting a larger one wheel on it won;t solve the two-wheel problem.
The chassis IS the heatsink, the aluminum bar is there to transfer heat to it. You could bolt fins on the outer side of the chassis, up under. Plenty of room for that.
The chassis IS the heatsink, the aluminum bar is there to transfer heat to it. You could bolt fins on the outer side of the chassis, up under. Plenty of room for that.
Definitely. Connect one 15V supply across the +15V and ground.
Connect the other 15V supply across the -15V and ground.
Carefully observe the correct polarity for each supply connection.
The correct polarity is the same as the polarity of the capacitor
connected to each supply line. One polarity will be positive,
and the other will be negative.
Thank you again for the even more detailed instruction.
I have however one more doubt: how can I connect to ground the two polarities you mentioned, considering that the two DC power suppliers (each providing 15 Volts/1 Ampere to the board) don't have ground connection at the wall 220V outlet?
Could the two polarities be connected to the chassis (just as like the circuit board ground will be connected to the chassis) without causing a short circuit?
Note: I am considering of using two "universal" power adapters like the one shown in the photo in one of the previous posts here in this thread.
Best regards
I have however one more doubt: how can I connect to ground the two polarities you mentioned, considering that the two DC power suppliers (each providing 15 Volts/1 Ampere to the board) don't have ground connection at the wall 220V outlet?
Could the two polarities be connected to the chassis (just as like the circuit board ground will be connected to the chassis) without causing a short circuit?
Note: I am considering of using two "universal" power adapters like the one shown in the photo in one of the previous posts here in this thread.
Best regards
Last edited:
- Status
- Not open for further replies.