Fender SS amp - heatsink failed - now blowing fuses - I've got details.....

[J M Fahey]

Agree and add: can you please post the schematic of what you are adding?
As we say here: "4 eyes see more than two".
Maybe there's some tiny detail you are missing.
Happens to me all the time.
Thanks.

[AllAmpedUp]

L-PAD: Its a longish story...but the solid-state install is a dry run for a tube amp...

Originally this Amp, the Fender Princeton 112 plus, had a reverse audio (Type C) potentiometers for the NORMAL VOLUME, GAIN and DRIVE VOLUME.
- For those asking "So What?".... Well, the Type C pot (reverse audio) means that the volume is front loaded and the amp decibels are ridiculously loud at low volume (stupidly loud)

I have already switched the NORMAL VOLUME with a Type A normal audio pot (from a spare amp) and now the volume between "zero- & 10" is nice and smooth...but now, my spare-parts amp, a Champion 110, is stupidly loud at Volume 2....LOL....its Ok, the 110 is for parts and experiments anyway.
Unfortunately, I don't have spare Type-A pots for the 112 plus' other 2 controls.....But again, its OK I really don't care....as the 112 plus' Drive/Gain channel has a poor tone and I really didn't plan to use it anyway because my Ibanez TS9DX does the trick with Normal channel.

So, I will install a 100w 8ohm L-PAD on this solid state amp to achieve 3 goals:
1) Make sure that I know what I am doing before I install on my tube amp (hahaha....like not mounting it uninsulated to the chassis)
2) Help manage the Solid-state's drive channel volume which is still stupidly-loud on Volume 2
3) Increase the likelihood I can re-sell this amp because I have solved all the problems

The 1/4 inch jack:
The chrome jack looks pretty neat....and I was curious...
I know it has no real value except....now, I can connect this amp's 12" speaker (which now has a longer cable with 1/4" plug) to another amp....like a small tube amp (assuming it is 8 ohms)...

Now...to my tube amp.
I have a SuperChamp-XD (which as you know is a 15 watts), but to push the tubes to a "happy" sound, I have to crank it up past 5 (which is too dang loud when kids are sleeping or just noodling around/practicing)......For this compo amp, the amp/speaker must match impedance (8 ohms) or you can mess it up....If the warnings from Fender are true....

So, after researching, I noticed that an L-PAD is an impedance matched attenuator (sometimes called a power soaker) thou i am sure a real $300 power soaker is not just an L-PAD....of course it could be just that and then it might be considered a attenuator for stupid people, but I doubt that is the case.
Either way, the L-PAD basically manages the output-volume much like a master volume would without internal pc-board modifications while maintaining impedance matching.
So, I should be able to drive the amp's tubes and limit the output volume......in theory and per some research....
Interestingly enough, the XD's L-PAD (which is an 8ohm 50 watt) will be mounted on the back wood panel not the metal chassis....so my "screw-up" on the 112 was a good learning experience regarding that issue.

So, please....tell me..... Is my understanding about the L-PAD's use on a tube amp valid...or... am I just hacking my way around my amps?

Thanks

Next question: If you have a nice tube amp, why bother with the solid states?
Answer: Because I can.... I already owned the solid-states...and learning about this stuff is helping me deal with my mid-life crisis.

[AllAmpedUp]

Agree and add: can you please post the schematic of what you are adding?
As we say here: "4 eyes see more than two".
Maybe there's some tiny detail you are missing.
Happens to me all the time.
Thanks.

I will sketch it out on my white board and try to post it soon....
If I can load a pic, I will also take pics of the actual install
The install did work good (unmounted)...I think.. but I am not 100% sure as the speaker was face down and the head out of cab was laying over the back of it.

[AllAmpedUp]

attachments
PIC1: Schematic of: AMP >> Speaker on-off (SPST)>> LPAD >> jack >> Speaker
Pic2: Potentiometer types (A, B, C)

[AllAmpedUp]

and parts on the back of the amp

Pic1: on-off (spst) witch for speaker
pic2: Lpad with 1/4 jack under

[JoeM]

What kind of jack did you use for the speaker out? Is it isolated from the chassis?

[AllAmpedUp]

What kind of jack did you use for the speaker out? Is it isolated from the chassis?

It is a mono-n/o and No it wasn't isolated.... nor was the L-PAD.....we surmised that "it" is the likely cause of the latest issue....
Is my schematic correct?

[JoeM]

Your schematic is correct, but the negative side should not be grounded to the chassis - not like a tube amp. I'm not sure what effect the L-pad has on the output on these SS amps either. Some of other members here understand this stuff one heck of a lot better than I do.

[52 Bill]

Your schematic is ok I guess, but I can't tell which part of the 1/4" jack goes to the + and which part goes to the - side of the output. In either case the jack must be isolated from the chassis.

As long as the L-pad's case is not connected to any of the 3 resistance terminals, the case does not need to be isolated.

[Jag]

I'm having a little trouble understanding your need for the L-Pad.

I've used this exact amp, at a friends, during jams and never had an issue balancing the clean and drive channels. I just set the clean channel where I want it, switch to the drive channel and get the grind I want with the gain control and balance the volume to that of the clean channel using the drive channel volume control.

If replacing the volume control on the clean channel to an "A" type resolved the issue on that channel, why wouldn't you just order another "A" pot for the drive channel and replace it too? Actually, if it were me and I only had one "A" pot to install, I'd have installed the "A" pot to the drive channel first and wait until I could order in a second one for the clean channel.

Unlike with tube amps, using an attenuator to reduce the overall output SPL so you can push the amp harder doesn't really do much. I understand that that may not be your reason for the L-Pad but just putting it out there. Using the L_Pad to tame the output level when using the drive channel, is also is going to attenuate the output signal when you switch to clean. You might end up pushing the clean channel into "ugly territory" to get it loud enough to hang with the drive channel.

[J M Fahey]

Thanks for posting the pictures.
The schematic is reasonable.
*There is* some justification for using an attenuator after a SS Power amp, but the effect is somewhat subtle and can be emulated easily for a couple dollars, that's why it's not a popular mod.

[AllAmpedUp]

Thanks Bill, Joe, Jag, JM and Enzo.

I understand that a L-Pad on the Solid State amp is totally unnecessary, and that a few bucks on replacement Type-A pots would be a better solution.
- This solution is still on the table as a solution, I just haven't researched where to buy those pots...if I do, I'll take the L-PAD out and plug-up the hole.

Again, the primary reason for adding it to the Princeton 112+ was to make sure I knew how to wire a L-Pad correctly for when I finally add one to my tube amp. (haha....Fail....)
the secondary reason was to help manage the volume.

I will also replace the current jack with an isolated one (just so I am not messing around with washers and such to isolate the one I have).
I tested that the l-pad is actually isolated (once i disconnected the offending jack)...

My local parts store didn't carry the 5W .22 ohm resistor I needed so I will have to order everything online, probably this week.

Lessons learned (at low cost, fortunately...I hope)