Ampeg Reverberocket--Changing Input Jacks to Normal and Bright

[wsscott]

I'm working with a buddy on his Ampeg R12R, and it has 3 Input jacks--Instrument, Accordion, and MIC.  Attached is a schematic.

He wants to change the Inputs so that I1 and I2 are "Normal" and I3 is "Bright".  He wants to be able to also jump I2 and I3 for a third tone.  He plays standard guitar and lap steel, so that's what the amp will be used for.

Your suggestions on changes and wiring configurations would be greatly appreciated.  Thanks.

[shooter]

find the section on understanding input Hi-Lo jacks, read, steel, n be happy 

[wsscott]

I've read the article, and I've wired the first 2 of the 3 input jacks like the Fender wiring shown on the attached page from the article.  They are working fine.  A big difference between the two jacks.

Now I want to add the 3rd Input jack to the circuit using just a 470K ohm resistor rather than the 1 Meg.  I have the jack wired like the Hi Jack in the article.  One side of the resistor connects the G and S, and the other end connect to the Tip.

So how do I wire it into the circuit so all 3 work independently, and also if I want to jump 2 of the Input jacks?

I ran a wire from the J3 Tip to the J1 Tip and although I get sound out of J1, both J2 and J3 don't produce any signal.

[wsscott]

Ok, some progress.

If I connect the Tip of J3 with the Tip of J2, I only get sound out of J1.

But if I insert just a plug with no signal into J2 I get sound out of J3 and J1.  And if I move the plug to J3 I get sound out of J2 and J1.

Obviously that's because the switch on the jacks at J2 and J3 send the signal to ground.

So is there a way to make this work without using a plug to break the switch in J2 and J3?

I guess I could use non-switching jacks for both of those 2 positions.  Or maybe just for J3?

[passaloutre]

"Jumping" isn't really a thing with an amp like this, where all inputs go to the same tube. If you look at other amps where it's common to "jump" channels (e.g. 5F6, 5E3, JTM45, Plexi, see snippet below), they have separate channel inputs going to different triodes. Jumping them sends the input signal to two separate tubes whose output gets mixed further down the line. On a single channel amp like this, jumping the channels is impossible because there is no other channel.

Likewise you cannot have "normal" and "bright" inputs (at least in the traditional sense) because there is no bright channel, just the normal one.


In these two-channel amps, each channel has a "high" and "low" input. Plugging into the high (1) input, the low (2) input is shorted, so the signal sees both grid stoppers in parallel (34k) and a 1M grid leak. Plugging into the low (2) input, the high input is shorted, giving you a 68k grid stopper and a 68k grid leak, so the signal is attenuated by ~50%. This appears to be what you've done with your inputs 1 and 2, but none of this is the same as "jumping", where you would send your signal to a whole other channel of the amp to get additional gain in parallel with your first triode. This is not a possibility with the amp you have (unless you do something extreme like adding a tube/transistor or ditching the tremolo and using that tube for the second channel).

[wsscott]

Maybe I should say "HI" and "LO" vs. "Normal" and "Bright".

J1 and J2 are wired just like the Fender Deluxe Reverb's jacks, so that's what I'm getting with a big difference in sound between the two inputs.

I don't know if the input into J2 is just louder or if there are higher frequencies being produced in J2 vs. J1, but there is a major difference.

With J3 added into the circuit as described, the output seems a little lower than the J2 output, and I'd like to know if that's due to a change in the frequency due to the 470K resistor on that jack, vs. the 1M on the J2 pot, or if its something else.

Any suggestions on how to avoid using a separate plug to make all of these 3 switching jacks work?  Change J3 to a Non-switching jack?

Thanks for your input.

[passaloutre]

Can you draw us a diagram of what you've created? And label the jacks 1, 2, and 3

My only suggestion is to leave this one stock and accept its limitations (it's already a wonderful amp). It was designed to mix the inputs equally so you could plug the whole band into it if you had to. If the guy wants a different sound, tell him to buy an EQ pedal.

I'm sorry if that sounds rude. I'm all about modding amps, but I think you're asking a little much of this one. I don't think any workaround with switching jacks and different grid stoppers, etc. is going to provide a satisfying result.

[wsscott]

Here you go.

[passaloutre]

And what's the end goal? Will one guitar be plugged into multiple jacks at the same time? At different times? Will multiple instruments be plugged into different jacks at the same time? At different times? What behavior would you like to get from the different jacks?

[Merlin]

Maybe I should say "HI" and "LO" vs. "Normal" a

It sounds to me like what he actually wants is a Hi and Lo jack, and a switch to add/remove a bright cap across the gain pot.

[SEL49]

He wants to change the Inputs so that I1 and I2 are "Normal" and I3 is "Bright".  He wants to be able to also jump I2 and I3 for a third tone.

This circuit is based on the Sunn Sceptre amp circuit...

     https://el34world.com/charts/Schematics/files/Sunn/Sunn_sceptre.pdf

[wsscott]

SEL49-Thanks. This looks like what I'm trying to do. 

Could I leave the J1 and J2 jacks as is with the current resistors, and just change J3 from a Switched Jack to a normal jack, and wire it into the circuit as shown in the schematic you posted?

Or would the resistors and wiring as I have it now (excluding J3 wiring which I know needs to be changed) not get the desired effect?

[SEL49]

I suggest to wire it exactly as shown using the same component values I've shown. You may prefer to use two jacks and a switch.

Jumping channels on a two channel amp produces a lot of useful tone combinations. But, IMO, jumping two inputs on a single channel amp is just a dumb idea. Having normal and bright inputs is marginally useful. I always use the bright input on my Sceptre.

[wsscott]

SEL49 Thanks.  I decided to do it that way anyway.  I don't have a 150K resistor on hand.  Any suggestions on a different value for that one?

[shooter]

150K

anything +/-20% is well within audio fudge factor

[wsscott]

I've got a 150K but it's 1/4 watt.  I've been using 1/2 watts for this.

Any problem with a 1/4 in the SEL49 schematic?

[SEL49]

Any problem with a 1/4 in the SEL49 schematic?

no

[wsscott]

Got it all wired in and up and running.  Sounds really good.  All 3 Input Jacks working and I can tell differences between their tones.   Minor differences but still some differences.  I haven't tried jumping the channels.  I think the "Normal" J1 Channel seems brighter, but that may just be ear.

We removed the foot pedals, and so the Reverb is On and also the Tremolo is On all the time.

The Reverb can be totally shut off and it's dead quiet.

The Tremolo still has some very low volume ticking even it the Speed and Intensity are all the way Off/CCW. It's always there. The ticking can become noticeably louder if the Speed control is increased CW, and there are some spots where just turning the pot you can find a quiet spot even if its in a faster speed position.  I don't know what to do to keep it quieter.  Maybe it's in the Speed or Intensity Pot?

Thanks for all the help.

[SEL49]

I haven't tried jumping the channels.

What does that mean??? When you plug into the JUMP/BOTH jacks, the Normal and Bright jacks are automatically jumped. You don't need any jumper cables.

[wsscott]

Sorry, I didn’t realize that was how it was setup.  Even better.