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And Princeton 112+ ~ Princeton 65 ~ Frontman 212R (but not as closely)
I picked up a Princeton 112+ a few years ago because I thought that the Normal channel was top-notch. I finally got around to doing some mods to it (MV, Mid control for the Normal channel, smooth out Drive channel, improve reverb.) I had thought that the Princeton 112+ and the Princeton 65 were some of the last 100% solid state amps from Fender since they morphed into DSP models. Same with the Champion 110 and Champion 30 twins which I am also modding.
However I was wrong- Fender continued those Princeton and Champion solid state designs in the Frontman series with the 25R and 15R having the same preamp as the Champion 110 & 30. The 100 watt Frontman 212R adds a Mid control for the Normal channel which is practically identical to the Normal channels on the 65 watt Princeton 112+ & 65. The Drive channel looks like a combination of both of those models, with a switch to select between the Contour control of the P112+ and the Mid control of the P65. I am studying the circuits of all of those amps to give me idea for further mods.
The good news is that the mods I am developing for these Princeton and Champion amps should also work on the Frontman amps which are still being made. I don't know if the chassises, cabinets and reverb tanks in the Frontman line are as heavy duty as their predecessors which were built like tanks but I'd have to give the Frontman amps two thumbs up for staying true to their analog roots.
Steve Ahola
Here is the text from Princeton 112+ mods.txt which is still a work in progress.
I finally got around to modding my Princeton 112+ that I bought a year or two ago for $99.99 from the GC site- with tax and shipping from across the country it came out to about $120. I bought it because I was really impressed with the clean sounds from the Normal channel. It got way too loud way too fast so I had been thinking of wiring something like a 100k pot in a box that I would plug into the FX loop. Not exactly the most elegant solution. And as several people have mentioned the Normal channel would have been more versatile with a mid control.
I just put a master volume and adjustable mid control for the Normal channel in mine- fairly easy to do. I also did some mods to the Drive channel to make it more usable for me (I hate fizzy buzzy distortion!)
For the MV replace the NFB resistor R47(470K) for U3A with a 500k linear pot wired as a variable resistor.
Normal Channel:
To add a mid control replace R10(470R) with a 5k linear pot wired as a variable resistor in series with a 470k resistor so that you have the stock mid sound with the control set to 0. After doing that the upper range of the control wasn't very usable for me so I wired up a 2k7 resistor across the two terminals used for the variable resistor. That allows the mid resistor value to be adjusted from 470 to roughly 2k2. (For reference the next generation Princeton 65 used a fixed 1k8 resistor.)
I thought that the treble cap C3(1000pF) was too thin so I first wired a 1200pF cap across it bringing the net capacitance up to 2200pF. To make that more versatile I wired up a center off DPDT full-sized toggle switch to select between 1000pF, 1750pF and 2200pF. It might not be a bad idea to wire this to a 6 position rotary switch to access more values.
Drive Channel:
R22/C15 act as a bright cap. I replaced R22(3.3k) with 6.8k to smooth out the sound a bit.
The Gain control R23(100k) is wired to the NFB loop of U2A. To lower the gain I wired a 68k resistor across C14(470pF) which brought down the net resistance of R23 down to 40k.
With those two mods I thought that the Drive channel was still too bright so I added a 820pF cap the treble bleed cap C22(1500pF). Surprise, surprise- the Drive channel actually sounds pretty good now! With the Gain set low (as I prefer) the overall volume of the Drive channel was lower than the Normal channel so to bring the volume back up I replaced the R25(470k) with a 1M resistor [R25 is the NFB resistor for gain stage U2B.]
One more mod- I thought that the amp had a very loud pop when you turned it off. I checked the schematics and saw that the amp that replaced it- the Princeton 65- has a 0.1/250v across the leads from the PT secondary. It was tricky fitting in the capacitor on the board- I mounted it between the "front" lead of CR22 to the "back" lead of R73. (It would have been easier if I had a smaller 0.1uF/250vdc capacitor.)
I'll post a link to some drawings once I get them done.
Enjoy!
Steve Ahola
P.S. I did all of the experimenting without having to remove the PCB- adding components in parallel with existing resistors and capacitors whenever possible which would lower the net resistance and raise the net capacitance. However to raise the resistance or lower the capacitance I had wired up the added component in series with the existing component which involved the blind soldering of the added component to one of the copper pads. I ohmed the joints out to make sure that there was a continuity however when I eventually pulled the board to make sure that everything was okay most of those blind solder joints were pretty flaky; I could see how vibrations might have broken some of those connections later. So I would advise not doing any blind soldering through the board to a copper pad.
The component leads on the PCB are generally pretty short so if you cut out the resistor or capacitor leaving just the leads in most cases there would not be enough lead left to make a decent connection. However I think that if the component was snipped in half you might have enough lead to make the a good connection.
In many cases I was able to trace through the circuit so that after removing a component I was able to wire up the new component to the leads of other parts so that I did not have to make a blind solder joint. You do need to ohm out the copper pads to determine how to best wire all of this up as there is no indication of copper traces on the factory layout drawing.
I picked up a Princeton 112+ a few years ago because I thought that the Normal channel was top-notch. I finally got around to doing some mods to it (MV, Mid control for the Normal channel, smooth out Drive channel, improve reverb.) I had thought that the Princeton 112+ and the Princeton 65 were some of the last 100% solid state amps from Fender since they morphed into DSP models. Same with the Champion 110 and Champion 30 twins which I am also modding.
However I was wrong- Fender continued those Princeton and Champion solid state designs in the Frontman series with the 25R and 15R having the same preamp as the Champion 110 & 30. The 100 watt Frontman 212R adds a Mid control for the Normal channel which is practically identical to the Normal channels on the 65 watt Princeton 112+ & 65. The Drive channel looks like a combination of both of those models, with a switch to select between the Contour control of the P112+ and the Mid control of the P65. I am studying the circuits of all of those amps to give me idea for further mods.
The good news is that the mods I am developing for these Princeton and Champion amps should also work on the Frontman amps which are still being made. I don't know if the chassises, cabinets and reverb tanks in the Frontman line are as heavy duty as their predecessors which were built like tanks but I'd have to give the Frontman amps two thumbs up for staying true to their analog roots.
Steve Ahola
Here is the text from Princeton 112+ mods.txt which is still a work in progress.
I finally got around to modding my Princeton 112+ that I bought a year or two ago for $99.99 from the GC site- with tax and shipping from across the country it came out to about $120. I bought it because I was really impressed with the clean sounds from the Normal channel. It got way too loud way too fast so I had been thinking of wiring something like a 100k pot in a box that I would plug into the FX loop. Not exactly the most elegant solution. And as several people have mentioned the Normal channel would have been more versatile with a mid control.
I just put a master volume and adjustable mid control for the Normal channel in mine- fairly easy to do. I also did some mods to the Drive channel to make it more usable for me (I hate fizzy buzzy distortion!)
For the MV replace the NFB resistor R47(470K) for U3A with a 500k linear pot wired as a variable resistor.
Normal Channel:
To add a mid control replace R10(470R) with a 5k linear pot wired as a variable resistor in series with a 470k resistor so that you have the stock mid sound with the control set to 0. After doing that the upper range of the control wasn't very usable for me so I wired up a 2k7 resistor across the two terminals used for the variable resistor. That allows the mid resistor value to be adjusted from 470 to roughly 2k2. (For reference the next generation Princeton 65 used a fixed 1k8 resistor.)
I thought that the treble cap C3(1000pF) was too thin so I first wired a 1200pF cap across it bringing the net capacitance up to 2200pF. To make that more versatile I wired up a center off DPDT full-sized toggle switch to select between 1000pF, 1750pF and 2200pF. It might not be a bad idea to wire this to a 6 position rotary switch to access more values.
Drive Channel:
R22/C15 act as a bright cap. I replaced R22(3.3k) with 6.8k to smooth out the sound a bit.
The Gain control R23(100k) is wired to the NFB loop of U2A. To lower the gain I wired a 68k resistor across C14(470pF) which brought down the net resistance of R23 down to 40k.
With those two mods I thought that the Drive channel was still too bright so I added a 820pF cap the treble bleed cap C22(1500pF). Surprise, surprise- the Drive channel actually sounds pretty good now! With the Gain set low (as I prefer) the overall volume of the Drive channel was lower than the Normal channel so to bring the volume back up I replaced the R25(470k) with a 1M resistor [R25 is the NFB resistor for gain stage U2B.]
One more mod- I thought that the amp had a very loud pop when you turned it off. I checked the schematics and saw that the amp that replaced it- the Princeton 65- has a 0.1/250v across the leads from the PT secondary. It was tricky fitting in the capacitor on the board- I mounted it between the "front" lead of CR22 to the "back" lead of R73. (It would have been easier if I had a smaller 0.1uF/250vdc capacitor.)
I'll post a link to some drawings once I get them done.
Enjoy!
Steve Ahola
P.S. I did all of the experimenting without having to remove the PCB- adding components in parallel with existing resistors and capacitors whenever possible which would lower the net resistance and raise the net capacitance. However to raise the resistance or lower the capacitance I had wired up the added component in series with the existing component which involved the blind soldering of the added component to one of the copper pads. I ohmed the joints out to make sure that there was a continuity however when I eventually pulled the board to make sure that everything was okay most of those blind solder joints were pretty flaky; I could see how vibrations might have broken some of those connections later. So I would advise not doing any blind soldering through the board to a copper pad.
The component leads on the PCB are generally pretty short so if you cut out the resistor or capacitor leaving just the leads in most cases there would not be enough lead left to make a decent connection. However I think that if the component was snipped in half you might have enough lead to make the a good connection.
In many cases I was able to trace through the circuit so that after removing a component I was able to wire up the new component to the leads of other parts so that I did not have to make a blind solder joint. You do need to ohm out the copper pads to determine how to best wire all of this up as there is no indication of copper traces on the factory layout drawing.
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