Mesa Boogie Rocket 440 Reverb issue

[Platefire]

This will take laying a little background to understand so here goes---When I bought this amp around 2007 the mini reverb tank that mounts to the bottom of chassis was non-working with a broke spring. I latter decided rather than replacing the original tank, I would attempt to install a full size tank and mount it in the bottom of cab like big grown up amps have!

I even coordinated this with a tech a Accutronics in 2009 and gave them the measured Ohms resistance on the input and output of the old tank as shown in the attached picture. The company was then labled as MORLEY.accutronics EBTECH in Cary IL. They sold me a tank supposedly to match my old tank input and output Ohms. 

So I did the installation borrowing the old connectors from the old tank's input and output wires that connects to the PCB board and wired them to RCA jacks on the back of the amp. So in turn built a tank cover bag, and purchased RCA connectors to connect the tank in my cab to the rear chassis connectors I installed in the back of amp chassis.

The end result is the installation looks real pretty and the reverb works but with very little depth. That is with the reverb knob a 100%. That was in 2009 and I have left it at that up until now.

I'm thinking surely there is a resistor or something I can tweak to increase the depth!!! I am attaching a schematic of the reverb. There is a 10K resistor on the output to ground--wondering if changing that might effect it? Anyway I'm appealing to you guys that are way smarter than me on this for help. I would like to finally see this reverb mod finally working as intended. Thanks in advance! Platefire

[shooter]

here's a link for a gain calculator, might help;

https://www.allaboutcircuits.com/tools/op-amp-voltage-and-gain-calculator/

It seems like the 10k should be on the "right" side of the cap, but my AC brain theory is full of holes

[2deaf]

The 10K load on the output of the tank forms a low-pass filter with the output coil.  The cut-off frequency is proportional to the load resistance, so 10K will shear some highs off of your reverb.  100K or more puts the cut-off frequency way higher than what would dull the reverb.  The 10K load will affect the brightness, but not the overall output of the tank.  The output is what I think you mean by "depth".

What is the code on the Accutronics tank?  What is the Op Amp driving that tank?

The Belton code:

B = Belton
S = Small
3 = 3 Springs
B = 190 Ohm input impedance
B = 2575 Ohm output impedance
3 = Long decay
E = Input isolated, Output isolated, no outer channel

[92Volts]

How did you measure the input and output "Ohms" of the original tank? The input impedance is likely different at AC (audio) frequency than the simple resistance you can measure with a voltmeter. The output impedance describes its ability drive a signal into some load, which depends on the coils producing that signal. MUCH more complicated than any resistance you can directly measure.

Lowering the 220k resistor leading up to the left-side opamp "should" increase the gain it's providing, and therefore increase input to the tank (but only if the op-amp can drive a larger signal without problems).

[Platefire]

The op amp is a 5532 on the input and output. The number of the new reverb tank is
009-BB2A1B-000 Type 9 Reverb---that is off the sales reciept from Accutronics.

I scanned the general block diagram that is a pretty poor scan but you can make out some
of it. That's where it shows the op amp numbers. Platefire

[PRR]

Change the 220K on the recovery amp to 470K, even 1Meg.

I assume you got the IN and OUT the right way around?

[shooter]

fwiw, here's the reverb from the Nomad, might add (confusion ) to the mix

[Platefire]

Thanks!

At this point I haven't tore the Boogie Down, just trying to get an attack plan. There is no schematic of this Rocket 4Fourty(440) with the 4-10 cab like I have. Believe me I researched it full course way back when when I worked on this reverb the first time. Boogie did make a Rocket 44 with the same identical amp only in a smaller cab. So that's what I have, the 44 schematic. So----the hard part at this point is the schematic don't have part numbers(like fender or layout) that I can see on the schematic and no parts list to reference to. So referring to PRR's 250K resistor and the two op amps, driver and recovery, I'm having a hard time locating those on the board?? I do have some pixs of the pcb in three separate shots. I also made a shot of the reverb schematic with a little better resolution I'm attaching. Maybe you can help me locate these circuit parts on the board?? Maybe you can make sense out of it. Platefire

BTW-The reverb level pot is the 7th pot from the input jack. I looked around there where the pot wires go into the PCB but couldn't see any familiar parts related to the reverb circuit?

[PRR]

> I'm having a hard time locating those on the board

The reverb recovery chip takes the tank signal, feeds the reverb pot. Both of these should be clear. We expect an 8-pin chip there.

[2deaf]

I feel for you, man, with that damn two-sided PCB.  At least you can see the traces on top and you can shine a light through the board to see the traces on the bottom.  I have seen completely opaque PCB's with at least two sides that would about take low-level X-Rays to see the traces on either side or in the middle.

I can see the three Op Amps right there in a line.  You would think the 220K NFB resistor would be right around there since it connects between two pins on the reverb Op Amp, but it's not necessarily the case with these guys.

[Platefire]

Well I was really hoping one of you guys would come over
to the house and fix this for me


Yeah, I've studied the pics and having a hard time marrying up
what I see with the schematic. No doubt I will have to pull
the chassis to locate it and when I do, planning on cheating by
using the old resistor leads to scab in a new resistor. Platefire

[Platefire]

OK, I finally figured out the location on the PCB for the reverb input/output connections shown in the attached view. You can clearly read the 5532(well i can on my higher resolution pix) on the op amps and the two pin connector marked H2 and the other two pin connector right on the outside corner of the board with a 8K marking by it. I think the H2 connection is the sent to tank and the connector in the corner is return--I think? The recovery op amp with the 220K resistor should be red/red/yellow but I don't see the color code for that resistor in the vicinity? Platefire

BTW- I don't seen any traces going from the pin connectors to anything? so how can you tell what they are connected to?

[sluckey]

BTW- I don't seen any traces going from the pin connectors to anything? so how can you tell what they are connected to?

You must look on the other side of the board. Really need a board layout for this stuff.

[Platefire]

It's a big mess-of-boog-eeeee is what I say

No complete layouts like old Fenders on any of their amps I can tell? only schematics! so the only real way would be to open the amp up and chase continuity from point to point to find a point of origin or destination.

I'm starting to ask my self the question! Even when I have an amp with fully functional reverb,
I set it very lightly 2 or 3 at the most. I've presently got light reverb pretty close to what I would use, even though the setting is wide open to get there. So why am I chasing this rabbit when for my purposes I'm already there. That was exactly the reason I didn't pursue it when I installed it the first time in 2009. The only answer I can come up with, is it bugs me to know something isn't working the way it should or as I originally intended. Platefire
 

[sluckey]

Perhaps everything is working correctly and the replacement reverb tank isn't performing like the original tank. Or maybe the amp was never meant to give Dick Dale surf reverb.

Before you button it up, put a note inside to remind you that you've already been down this rabbit hole.   

[Platefire]

This rabbit is officially dead!!!

[DummyLoad]

[Platefire]

Har!! Yeah, just dare that wabbit to stick his head out again