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Rocktron Rampage R80 - No Sound problem

Started by paolone, January 16, 2021, 01:43:50 PM

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Hi dmeek

You say "...if the overdrive channel is OK..." but I haven't test it. I have tested only the clear channel with the oscilloscope, following your note.

Can you please explain me how i have to test with the oscilloscope the overdrive channel, as you have explained me how to test the clear channel?

Then i'll test the R44, Q4, R41 desoldering them




If the overdrive channel sounds like it should with a guitar you don't need the check it with the oscilloscope.
Leave the amp switched to the clean channel and remove Q4. See if there is a difference with or without Q4



I have some time now so i have made the test with the oscilloscope without the Q4 transistor
1- check tone on the input jack and set to 1 division amplitude
    (Photo 2)
2- IC6 pin 1 must have 5 division amplitude
    Now is correct (Photo 3)
3- clear pot full up, check central pin, must have 5 division amplitude
    Now is correct (Photo 4)
4- IC6 pin7 must have more than 5 division amplitude
    NO - only 3, the same with or without Q4 (Photo 5)

5- photo 6 is the test 3 with overdrive mode on
6- photo 7 is the test 4 with overdrive mode on

What is the SVR1 of 100k in the Photo 8?



SVR1 is to set FET bias for the compressor. Don't touch it. I don't know how to set it.

I guess Q4 is not the problem. I'm running out of ideas. Are you sure there is something wrong with this amp? It's normal for the overdrive channel to be louder.



I have played a little now without the Q4 but is the same than with Q4...
I have resoldered the Q4. Nothing has changed. 
The problem is not that the clear mode is lower than overdrive...
The problem is that the clear mode of a 80watt amp at max master volume plays lower than a Fender mustang 2 amp that is a 40watt amp, set to half master volume pot...
This is the real problem... I have an 80watt amp that sounds like a 20watt amp...

I have forgot to tell you that sometimes before start this tests and also this night, the overdrive starts by itself and the red light switches on while i am using the clear mode. Then it switches off.

When the reverb is more than half pot you can hear a noise that disappears under half pot


The 40 Watt Fender might have a High SPL speaker while the Rockton maybe much lower.

This is measured in SPL (Sound Pressure Level)
So a speaker that is rated at 102 Db SPL will be twice as loud as one that claims 98 db SPL.
All these things can be very confusing as there is no straight line in these numbers,, i.e. 1+1 =5  :duh
A lot of electronic equations are log curves.
Just like Earthquakes where an 8.2 on the richter scale is x10 more powerful than a 7.5

Maybe connect the Fender speaker to the rockton and hear if there is much difference?

Number 3/
The Rockton circuit may not have the same preamp gain and so is not as loud. Also the Input sensitivity of the power amp section may not be as high as the Fender power stage.
        The power supply voltages may be higher in the fender which will give it more output power.

It's likely the Rockton is ok except for the switching,
Re switching Amps in general;

Keep this in mind when buying multi channel amps.
I've repaired quite a few amps over the years and I can tell you this,,, more often than not the Audio path is actually working fine,, it's the switching crap that breaks. 8|


Ok thanks
Fortunately i have paid this amp quite nothing...

To fix the autoswitch on overdrive channel what i can do, please?
Which component do i have to control?

To lower the noise on reverb mode what can i do please?

@phatt Here is the spec of Rocktron R80:


Hi Paolone,

Sadly without a schematic of the switching setup it's impossible to tell what is wrong.

I should ask,
If the channel switch changes as per normal and it's only the led not lighting then maybe leave it.
Some amps have a front panel channel switch as well as a foot switch, so be aware that the pedal might be causing faults.

So Q.  With pedal disconnected, Does the channel switch work normally?

IF not,, then the front panel Switch maybe faulty.
Some of those push button switches are prone to not making proper contact due to the poor cheap design.
Many times I have replaced Push switches with Toggle switches which are less prone to poor contact.
Either way as I mentioned those switching circuits are often the first thing to fail.

Regards to Reverb adding noise to the signal.
If you have checked that all the RCA leads are making good connection then you have a well know problem of poor design. The biggest issue is the DRIVE circuit is poorly designed and does not have enough Drive to excite the Springs. So to compensate they turn up the Pickup circuit gain which makes the reverb PU very prone to picking up any stray hum from the mains.

Also Check how close the PU end of the tank is to the mains transformer. Some times just by repositioning the tank to keep the PU end away from mains can help reduce the noise.

Re the Rockton Manual;
Look at the last page, it states 80 Watts.
Sadly without stating what load that amp is driving it's meaningless number.
Could mean 80watts of bananas :duh

Here is a rule of thumb for power.
it's likely that 80Watts is based on a 4 Ohm load which is 40Watts into 8 Ohm
and 20Watts into 16 Ohm.

When looking for Meaningful specs for wattage look for something like this;
     *80Watts RMS into 8 Ohms*

Remember the power output the circuit is capable of producing is governed by the Power supply NOT how many watts the transistors are capable of producing.


Thanks to dmeek and phatt for all your help

When the amp has the drive mode selected, it works fine, I cannot go over 1/2 master pot and over 1/2 drive pot or there is too much volume.
When the amp has the drive mode deselected (clear mode on), it works bad, sometimes it switch by itself on drive mode for 1 or two seconds and the re-switch by itself on clear mode. There is NO footswitch inserted.
But the real problem is not the auto switch, is that if you're playing in clear mode, you have to set full up the master pot and the clear pot to hear quite well and if you switch on drive mode you have to reset to half master pot or less... it's quite impossible while you're playing...

I have re-check with the oscilloscope the amplitude on IC6 pin 1. With Q4 is 4 division, without Q4 there is 5 division (right division, as you shows = 5).
On the center pin of clear pot with Q4 there is 4 division, without Q4 there is 5 division (right division = 5).
On IC6 pin 7 with a Q4 there is 2 division, without Q4 there is 3 division (right division = 5)

- With Q4 there is a loss of 1 division, maybe there is a bad component between the Q4 and ground.
- the amplitude on IC6 pin 7 is still under the right division, maybe there is a bad component between the clear pot and the circle circuit of IC6 between pin 7 and pin 6.

- How does it work IC6? There is pin 5 on ground and pin 6 from center pin of clear pot. The other circuit of IC6 pin 1 don't have any pin 2 - 3 on ground... From the datasheet of IC6 https://www.mouser.com/datasheet/2/294/njr_njm072_njm072b_njm082_njm082b_e-547738.pdf i can see that the pin 6 is the negative input and pin 5 is positive input...

- dmeek can you please deepen the wiring schema of this point of the circuit (the clear pot and the circle circuit of IC6 between pin 7 and pin 6) to expose all the components, so i can test them one by one with the oscilloscope or with the multimeter after desoldering them, to find where the right amplitude decreases? I have try to do it but i find some different from yours... maybe my is wrong...

Thanks for all your help



While i was testing the amp, in the clear mode it start to schratch.
I've put a registration here.

Dmeek i think there is something other to find... can you help me?

Some other test with the oscilloscope?

The scratch noise i think is a cap broken... right?