Factory bulletins on the Fender Princeton 112+? Nope but here are some mods I did

[Jayz]

Thanks. I ordered the same tank model 8EB2C1B that was in there. I didn't notice any "toasting" but I'll look again. And unless Daren Riley shipped me the wrong part, his order confirmation says "50K". (Although I don't recall actually confirming before I installed it). Time to open it up again!

[g1]

While you are in there checking that it is the right part, also check that it is working. Measure from wiper to ground leg and wiper to hot leg at various settings.
Just because a part is new does not mean it is good (unfortunately). Usually they are, but you can be sure no one tests them before they ship them to you. A defective new part can be a technicians nightmare, in this case it is easy enough to check, but when it's a semi-conductor or transformer or something it can really mess you up.

[Jayz]

Certainly worth a try - thanks for the suggestions!
(Canada, somewhere north of Buffalo)

[Jayz]

On a related topic I used an A-B pedal to alternate between the P112+ and an original '65 Deluxe Reverb I have. I was surprised that the P112+ was "noisier" than the DLR. Is there something I should look at or a mod to reduce the noise?

[R.G.]

First time I looked at these amps.

That is one ugly power amp design. At one time using a flying opamp might have made sense, but today's transistors are so good and so cheap that I can't understand why you'd do it.

[Jayz]

Thanks R.G. Do you have any suggestions to quiet it down and make it "less ugly"?

[JoeM]

"Ugly" maybe from an engineers viewpoint, but these amps actually have a pretty decent clean sound.

[R.G.]

"Ugly" maybe from an engineers viewpoint, but these amps actually have a pretty decent clean sound.

I'm sure they do. The "ugly" comment is based on my expectations that good designs should be reliable and durable as well as sounding good. I didn't mean to imply anything at all about the sound.

I used to love driving British sports cars with side draft carburetors because the cars as a whole were great fun. But the problems with needing to tune/synchronize the old SU or Bosch side drafts was enough to drive you crazy.

It is even better if you can get "love the way it sounds" at the same time as "tough and reliable".

Do you have any suggestions to quiet it down and make it "less ugly"?

Oh, sure, make the guy who just spouted off some techie stuff put up or shut up!

I'd have to look at it for a while. For the power amp, I ...think... you could add on a baby board with everything except the output power devices and just neuter the onboard opamp driving them now.

And on the low voltage power, I actually did a scribbled replacement of the power resistors and zeners with something I thought was better. I'll go try to look it up.

The problem with this is that I don't have one of these to try the surgical procedures on, so it requires someone willing to do the surgery to a schematic to see if what I think works really does.

[Jayz]

Thanks RG. No expectations. The "noise" doesn't make it unusable - still quiet enough for rock 'n roll. Just thot I'd ask. No need to spend any time on it.

[Jayz]

Help please! The 112 Plus has been a great little amp for rehearsals. I haven't made any mods yet but last evening during band rehearsal it started making intermittent "popping" sounds. I unplugged the guitar at the amp input jack and the popping continued (about 1 "pop" per second). I turned the amp off and back on again and the popping continued. I only know enough electronics to be dangerous and so am hoping you can advise me where to begin looking for the problem. This was on the clean setting, no reverb, bass--mid-treble set to 5 - I haven't tried the dirty setting.
Any suggestions would be greatly appreciated.
Thanks.

[Jayz]

Finally got around to opening up the P112+ to start the MODS you all have been helpful to suggest. Of course I wanted to check out my reverb problem again. I found the problem. When I initially removed the PCB a few months ago I intentionally cut the the reverb send-rec cable to make it easier to remove the PCB. When I soldered back together I assumed (I know- never assume) that the "grounds" were common. I checked the schem today and nope - they are not common! Voila! Reverb working!

[Jayz]

Quote: > > > Replaced R47(470k) with a 500kB pot as a Master Volume

Does anyone know whether the 3rd connection on the pot should be wired to ground or left open?

I'm an electronics neophyte.

Thanks.

[g1]

Leave it open or connect it to the middle lug.

[Jayz]

Thank you! Also, Steve A also recommends: Quote"Comparing the schematics of the P112+ to its replacement, the Princeton 65, I see that a 0.1uF/250v cap was added between the "hot" PT secondary leads which I think will reduce the pop on shutdown considerably".

I can't tell for sure from the P65 schem but would you know whether the 0.1uF/250 cap is polarized or non-polarized? (C64 on the P65 schem)

[Steve A.]

Thank you! Also, Steve A also recommends: Quote"Comparing the schematics of the P112+ to its replacement, the Princeton 65, I see that a 0.1uF/250v cap was added between the "hot" PT secondary leads which I think will reduce the pop on shutdown considerably".

I can't tell for sure from the P65 schem but would you know whether the 0.1uF/250 cap is polarized or non-polarized? (C64 on the P65 schem)

I used a polyester cap which has no polarity. The cap reduced the pop to some extent but I usually turn the MV all of the way down before turning off the amp.

Steve

BTW after installing the MV you may notice that it doesn't do much between 1 and 3 or 4. If you want to eliminate that dead spot measure the resistance when you have the pot set to the lowest volume you want. You can then add a fixed resistor with a value close to the measured resistance in series with the pot as that will set a minimum value.

Also if you want more total volume when you have the gain set low you can put in a larger MV pot. If you use a 1M pot and put a 1.5M resistor between the two terminals being used it will reduce the net value of that pot to 600K. Since 1.5M resistors can be hard to find you can wire a 470K or 510K resistor in series with the 1M resistor. Once again you can find the optimum value for yourself by installing the 1M pot and then figuring out the maximum volume you want. Measure its resistance and use the following formula to determine the value of the resistor to add between the two active terminals:

1/R(added) = 1/R(desired value) - 1/R(value of pot)

I can compute that with the Windows Calculator in about 2 seconds since it has a 1/x key. (You can use any calculator that has a 1/x key.) If you get a negative number just ignore the minus sign.