Pro Reverb mod

[firemedic]

Someone here must have tried this before.
I'm going to build a Pro Reverb AA165 and keep the Vibrato channel unmodified, or minimally modified.
I'd like to turn the Normal channel into a footswitched tube overdrive, feeding the Vibrato channel. Does anyone have an existing schematic of such a mod, so I'm not reinventing the wheel?

[jim]

hey firemedic--Early in my amp tinkering days I modified a DR Hoffman board in this way using mod kits from London Power.  You will need the pre-amp mod itself and also another kit to handle channel footswitching--either relay or JFET.  These kits are designed for moding a Fender layout.   Don't start until you have read Kevin O'conner's "The Ultimate Tone-Modifying and Custom Building Guitar Amplifiers" The book is expensive but worth every penny.   The LP cascaded triode overdrive sound is richer than any commercial production OD style amp on the market and the clean is unmolested Fender.  I do not believe the Fender chassis (two identical sounding channels + reverb + vibrato) lends itself easily to this type of mod.  You will spend many hours trying to resolve the noise and parasitics that occur in high gain designs.  Do yourself a favor and build it amp head style in an 11 X 17 Hammond box so you can spread it out.  Don't get me wrong--my DR mod is my #1 gigging amp and is now quiet -- but it was painful getting there.  Here is a pic of my mod before I started troubleshooting it.  The routing of all those shielded signal runs is super critical and I was mistaken in running wires under the board.  You can see the little JFET driver board I built and screwed to the back of the chassis.  The JFETS are hung right on the volume and drive pots. 

[jim]

Here are pics:

[jim]

Here is a schematic:

[firemedic]

That's what I'm talkin' about. I knew I would need some kind of relay. I'll check out the London Power mod.
Here's the deal, I converted what looks like a super reverb blackface cabinet that I rescued from my local guitar shop, into a 2/12 cab for my homebrew head. Man it was in bad shape, tolex painted silver etc.
But my Marshall style chassis head has a lot of OT hum on the reverb, even with the short tank, all the way over to the other side. So I don't want to make a pro reverb head since hum will always be a problem with the tank being so close to the OT.
Also I have the cabinet. I figured I could experiment with the normal channel. I was thinking about the D_mble distorto?   

[jim]

The PT is usually the big noise maker.  Keep the tank input away from it.  I'm not sure about D_mble but I have a FUCHS head, supposedly a D_mble clone--The LP overdrive sounds broader and less fizzy to me.  Anyway, you have homework--don't rush it.   The LP kits come with a hand-drawn diagram and not much hand-holding to get you through so do as much reading as you can.  Jim

[firemedic]

I did mean PT, had a senior moment.
This will be my 2nd build and I don't even have the chassis yet. I do know I'll be getting most of my stuff from Hoffman this time- I learned that from the 1st build.
How much PCB will I be putting into this thing? I see the channel switch has a little one which is okay but if the Fender mod is only some resistors & caps I can get those myself & figure it out. Is the schematic you put on this thread the LP or is that yours?
One thing i saw on the d--ble distorto is the shunting caps which should help w/ oscillation. Also, is it absolutely necessary to have a filter cap for each stage? I know I'll need to add one or two but come on.

[jim]

Alright, Build your Pro-Reverb Fender style into your chassis.  Build you own Hoffman board or use one built by the good techs here.
Get the basic Pro-Reverb working first and then modify it. Everything you need is here:   http://www.el34world.com/schematics.htm
The schematic I showed you is out of one of O'Conner's books but you can keep all the filter caps in the doghouse as Leo intended
and the mod will work just fine.  I do not have the mod instructions--you will need to buy the kit or at least read the book.  Jim

[firemedic]

Thanks for humoring me Jim, I'm just floating ideas around.
It seemed like a good idea since I hate using pedals but I almost never use overdrive anyway. I'll just use the normal channel to experiment. I'd like to try the parallel triode, with a single tone control maybe the insertion loss will be low enough to drive the PI.