Rivera problem

[myopicmusician]

When the gain channel (channel 1) on my Rivera Knucklehead is engaged, there is a fizz type of sound along with the note that will decay.
This is not your typical fizz with having the gain set high and master low but something different. It happens with gain set relatively low and present until master on or above 4 (which is very loud on this 100 watt amp). It very much sounds like the preamp is being overdriven as it seems to be sensitive to transients. When playing very, very softly it is not audible, but when playing normally it is heard and increases more relative to digging in. The noise is not present at all on the clean channel (channel 2).

Here is the strange part. When unplugging the DIN Rivera footswitch and using the push/pull function to engage channel 1, it is not present--only when the footswitch is connected. Even when the footswitch is connected, pulling the potentiometer out to engage channel 1 does not resolve it. The footswitch must be physically not connected to the amp.

I am using the Rivera FS-7 footswitch which is the correct one for the amp. I have another Rivera amp (Suprema) and have connected the FS-7 footswitch from it to the knucklehead but the issue remains, so the problem is not with the FS-7 or cabling. I have cleaned the DIN jack on the back of the amp but did not change anything.

Can anyone put me on the track to troubleshooting? It would make sense to me if the noise was present in channel 1 no matter HOW it was engaged, but this seems strange to me. I'm trying to include a schematic attachment. Thanks for any help.

[nevetslab]

While I've never worked on any of Rivera's amps, what you're describing suggests that the local push-pull pot is engaging the same device that switches the function, like either a relay or an analog switch, FET switch, or the like. And, the pedal also engages that same switching device, only there's bad connections inside on the PCB, perhaps on the DIN connector itself. I've had 7-pin rt angle DIN connectors with fractured solder joints cause problems, while the local switching doesn't.

Not sure how tedious it is to get at that connector inside the amp, but that's where I would start. Do you have a schematic for this amp? Perhaps one of our members does, so we can look closer.

[myopicmusician]

Thank you very much for the reply and help. I do have the schematic and tried to upload but was not successful, probably because I was attempting at work behind a VPN. I will try from home in a bit.

I’ve had the chassis pulled and remember the DIN jack on its own separate PCB along with the effects loop. You raise a good point with a possible solder issue. Maybe I should chopstick when I get home?

Edit: I can't seem to upload anything on this site. At home on a Mac, it doesn't give me the options to upload attachments using either Safari or Chrome. Maybe because I'm a new user? Anyway, I found an old post here on the forums that contains the schematic. It would be page one for the Knucklehead.

https://music-electronics-forum.com/...cklehead+rt101


Update: I think I may have found the problem. I pulled the chassis and chopsticked the plugin connectors between the effects loop PCB where the DIN jack is to the main PCB and the noise is now gone. There are seven wires on that harness since it is a 7 pin DIN and I'm not sure which one is the problem but I can track it down from here. I'm tempted to leave as is since it's working, but there's no doubt in my mind it will return if I don't have it properly fixed.
Thanks for your help nevetslab, you put me on the right track in understanding the problem had to lie somewhere close to that DIN.

[nevetslab]

OK, I got that knucklehead schematic downloaded and took a look at it. They're using VacTEC's to do the switching functions, driven by turning a transistor on, either locally or by way of the pedal. When you use the pedal, and the panel switches are NOT engaged, I assume the pedal's LED and the panel's LED would both light. I haven't yet figured out their switching logic, so I'll refrain from asking a dumb question, like if the panel switch is engaged, does it light up the pedal LED?

[myopicmusician]

Yes. See my update in the previous thread. Seems like the issue is a 7 wire cable harness between fx loop PCB and main PCB. To answer your question though, yes—when engaging Footswitch, both pedal and chassis LED lights. With pedal connected and activating channel with push/pull on chassis—both the pedal and chassis LED lights as well.

[g1]

schematic:

[myopicmusician]

I posted a response here yesterday but it never published.

Nevetslab, please see my update in my earlier post.

To answer your question, yes—both panel and Footswitch LEDs illuminate simultaneously regardless of how the channel is engaged, whether by Footswitch or push/pull on chassis.