New Hybrid JOYO Mini Amp issue. Clean Channel blending into Overdrive Channel

[Anthonyx82x]

Hi all, from Illinois here.

So I recently bought the JOYO Bantamp Zombie 1 & Zombie 2. Both JOYO Amps have a 12ax7 Preamp Tube in them.
The Zombie 1 has two channels with no foot switch to change them unless you mod it.
The Zombie 2 comes with independent clean and overdrive channels with a foot switch.
I included a picture of what the Amp looks like with the top off showing the tube.

Both amps sound great, the Zombie 1 and 2 are modeled after the Mesa Dual Rectifier.

So my main question here and I can't seen to find it anywhere and it's making me go crazy. My new Zombie 2 with the foot switch is giving me this weird bleeding or blending issue.

I'm going to try to explain this as best as I can here, so when I go to plug in and switch from the clean channel to the overdrive channel and I turn up the volume just a little, I get what sounds like the clean channel mixing in with a little bit of the overdrive channel at the same time, it gets worse if I turn down the volume on the overdrive channel. Now this is where it gets really weird, if I turn the GAIN, TONE, VOLUME all the way down on that overdrive channel I can still hear clean volume coming in, but only on the overdrive channel, if I switch back to the clean channel it's fine, not overdrive blending into that signal, also if I turn everything down it stays silent.

Now what in the world could this be? I noticed if I turn up the volume on the overdrive channel it seems to not be as noticeable.

Some troubleshooting I have tried.

1. Try different guitars, most of my main guitars use Active EMG Pickups. So I tried my Les Paul Deluxe with passive pickups and I was still getting the same results.

2. Tried a different cab. I built myself one 2x12" Cab with two Celestion vintage 30's in it. Recently built another cab with two Celestion 15 8" Speakers in it wired in series to get 8ohms. This is the main cab for this little amp. I seemed to be getting the same results from both cabs.

3. Tried pushing the Preamp tube down or wiggling it to see if that might be an issue?

4. Tried different power supply from the Zombie 1 amp.

5. This is the weird one, I tried using headphones on the headphone jack in back and noticed it worked fine this way, no bleeding of the channels.

I do not have this problem with the Zombie 1 amp, so I'm at a loss here, I have no clue what this issue could be? Bad Preamp tube or faulty amp?

I recently ordered a new Mesa Preamp tube to see if that is the issue? Maybe a faulty tube?

If anybody out there knows what this could be, some input/help would be greatly appreciated.

Thanks.

[Jazz P Bass]

Without a schematic ?????
Have you contacted the company to see if this is a known issue?
It may be inherent to the design.

[Anthonyx82x]

Without a schematic ?????
Have you contacted the company to see if this is a known issue?
It may be inherent to the design.

It's still pretty new, like a few months new, I haven't been able to find one online, only for the original Zombie 1 model.

I have contacted the company, I haven't heard anything back yet, based in China, so who knows when or if I'll hear back. Got my money back on the unit but was able to keep it, so If I could get it fixed somehow I would be willing to, if it's a faulty unit. I just don't know what the problem is? I was thinking of taking it to a local music store I've been going to, maybe they can diagnose the issue. Or maybe once this new preamp tube comes in that might solve the problem? I guess will see. Thanks.

[J M Fahey]

It's still pretty new, like a few months new, I haven't been able to find one online, only for the original Zombie 1 model.

Post it here, maybe itīs "two of that" plus some switching which we could analyze.
Also post gut closeups from both, so we compare them side by side.
Show the boards and pots/jacks/etc.

was thinking of taking it to a local music store I've been going to, maybe they can diagnose the issue.

Good joke, know others as funny?
Typical store tech quality is low, with exceptions.
And 95% of the job is diagnosing, actually replacing the bad part is the easy one.

Or maybe once this new preamp tube comes in that might solve the problem?

Doubt itīs a tube problem, more probably a switching or layout problem.
But letīs have a look under the hood.

[Anthonyx82x]

Post it here, maybe itīs "two of that" plus some switching which we could analyze.
Also post gut closeups from both, so we compare them side by side.
Show the boards and pots/jacks/etc.


Good joke, know others as funny?
Typical store tech quality is low, with exceptions.
And 95% of the job is diagnosing, actually replacing the bad part is the easy one.


Doubt itīs a tube problem, more probably a switching or layout problem.
But letīs have a look under the hood.

So I found a few out there on the internet. This first link is the teardown of the original Zombie 1 which I own and that one works perfectly fine, minus having a channel foot switch (which I plan on using the MOD I seen someone do on YouTube, which I may need to ask some advice on here for that one)

https://khronscave.blogspot.com/2019...rdown.html?m=0

https://www.diystompboxes.com/smffor...topic=124100.0

https://fccid.io/2AIN7BANTAMP/Intern...Photos-3736791

[mhuss]

Yikes, might be fun reverse engineering that 'flea'-infested main board.

I don't think the section of schematic posted in the link above will be helpful.

[Anthonyx82x]

Yikes, might be fun reverse engineering that 'flea'-infested main board.

I don't think the section of schematic posted in the link above will be helpful.

So I disassembled both amps last night, took out the preamp tube from the Zombie 1 which works fine, put it in the Zombie 2, just testing to see if the tube was bad. Well, it's still the same result. I also took some close up pictures of the inside of the Zombie 2 board.

I would upload the pictures on here, but for some reason it keeps giving me an error saying "Upload failed. You have exceeded your usergroup's upload quota of 976.6 kb by 937.3 KB" which makes no sense because the last image I uploaded was over the upload quota, it was in MB not in KB, weird.

I also tested out the amp again last night on a different cab, I tested it out on the 4 12" Marshall JCM 2000 and it sounded pretty powerful for a little 20 watt amp, but I was getting the same result, a bit of clean channel mixed into the overdrive, more I turned it up the more it masked it a bit, but you could tell it was still there when you hit single string notes.

So I guess I'll be using this amp just as a power amp on the clean channel with my digitech multi effects pedal going into it, and I'm gonna have to try to mod the Zombie 1 to take the foot switch so I can change channels with the zombie 2's foot switch. Not much else I can really do with trying to fix it when I have no clue what the issue could be.

[christarak]

Or maybe once this new preamp tube comes in that might solve the problem? I guess will see. Thanks.

I have worked on several of the Bantamps, of which the Zombie is one. I have not come across the Zombie 2 in Australia. The preamp, DSP and power stage are all on SMD boards. I am not set up to repair these boards, and they are so cheap (to the manufacturer) its most effective to swap the boards. Find the importer in the USA and ask them. Forget asking Joyo in China directly.
The harsh reality is that its cheaper to scrap the entire amp than it is to send you individual PCBs.
It won't be the 12AX7, so don't throw good money after bad. I have found earthing to be a problem in these cheaper Joyo amps, eg earth connections screwed to a painted chassis. Make sure that all your earthing points have good contacts. In one case I ran a separate earth wire. I don't have any schematics to share, but they won't help unless you have the equipment and expertise to repair very cheap SMD PCB's.