FX Loop in Ceriatone TW Clone

[BasementJames]

Hi,

Although potentially offensive, I'm adding a MojoTone series effects loop (Version 3) to a Ceriatone Trainwreck Expression clone.

The problem I am encountering is that everything works when I am in bypass, but engaging the loop kills the signal.
I attached a picture of the amp as well as a layout drawing with some scribble showing where in the circuit I added the loop.

The instructions provided by MojoTone say to connect the "out" pad to the "coupling capacitor just before the input of the amplifier's phase inverter circuit."
I believe that is the .01uF capacitor.
For the "in" pad, the instructions say to "connect to the preamp side of the circuit where the signal path was broken."
That would be the turret with the 100k resistor.

As seen in the layout drawing, I moved the V2 Pin 1 plate wire to the turret that the 100K resistor attaches to, as well as broke the connection between the 100K turret and the .1uF turret.
The MojoTone instructions say that "The loop features its own input coupling capacitor, so no additional capacitor is necessary for installation."

I have just over 200 volts of B+ going to the loop as well.

Any ideas as to why I lose the signal when engaging the loop would be greatly appreciated.
I'm stumped.

Thanks,
James

[Guy77]

Hi,

Although potentially offensive, I'm adding a MojoTone series effects loop (Version 3) to a Ceriatone Trainwreck Expression clone.

The problem I am encountering is that everything works when I am in bypass, but engaging the loop kills the signal.
I attached a picture of the amp as well as a layout drawing with some scribble showing where in the circuit I added the loop.

The instructions provided by MojoTone say to connect the "out" pad to the "coupling capacitor just before the input of the amplifier's phase inverter circuit."
I believe that is the .01uF capacitor.
For the "in" pad, the instructions say to "connect to the preamp side of the circuit where the signal path was broken."
That would be the turret with the 100k resistor.

As seen in the layout drawing, I moved the V2 Pin 1 plate wire to the turret that the 100K resistor attaches to, as well as broke the connection between the 100K turret and the .1uF turret.
The MojoTone instructions say that "The loop features its own input coupling capacitor, so no additional capacitor is necessary for installation."

I have just over 200 volts of B+ going to the loop as well.

Any ideas as to why I lose the signal when engaging the loop would be greatly appreciated.
I'm stumped.

Thanks,
James

Hi, if you are getting signal when the loop is not engaged usually means the issue is not the wiring from where you have grabbed the loop from the preamp.
I would check the small trimmer pot on the board of the effets loop. They are blue if I remember correctly. Make sure that pot is turned fully in cranked position. Try turning it the other way and see if you can get signal. Also make sure you have turned up your external pot. Also make sure your external pot is wired correctly.
You can run these loops into the 300v range without issues. They get a little louder sounding as you increase the voltage but not a huge amount louder.
I usually grab the B+ for these from the phase inverter area.

Cheers
Guy

[BasementJames]

Thanks Guy.

I did check the blue pot, tried it both ways, also in the middle.
Same with the external pot, even removing it.

Same thing every time. As soon as I engage the loop, I get complete silence.

[Guy77]

Thanks Guy.

I did check the blue pot, tried it both ways, also in the middle.
Same with the external pot, even removing it.

Same thing every time. As soon as I engage the loop, I get complete silence.

Check what the voltage is on the other side of the large resistor that connects to your B+ wire on the effects loop board. Make sure its good and dropping some voltages usually about 50v. I usually run the voltages at 320v when it hits the entrance to the resistor and that gives me about 275 on the other side of the dropping resistor.

[sluckey]

What is plugged into the send and return jacks?

[BasementJames]

Thanks Guy.

I did check the blue pot, tried it both ways, also in the middle.
Same with the external pot, even removing it.

Same thing every time. As soon as I engage the loop, I get complete silence.

Check what the voltage is on the other side of the large resistor that connects to your B+ wire on the effects loop board. Make sure its good and dropping some voltages usually about 50v. I usually run the voltages at 320v when it hits the entrance to the resistor and that gives me about 275 on the other side of the dropping resistor.

Tapping into the B+4 location (from the layout drawing), I was getting about 230 volts before the resister and just under 200 volts after the resistor.
The instructions talk about dropping below 200 volts, so I used alligator clips and tapped into the B+3 location. This is about 260 volts and got me over 200 volts after the resistor but didn't make a difference as far as performance.
Same symptoms.

[BasementJames]

What is plugged into the send and return jacks?

I threw a jumper cable in there, just to try.
No difference.

[Stevem]

Try plugging a cable into the send jack and then into another amp do you get signal?
If you do not have another amp then use your meter set for ac volts across the end of the cable .

I would expect at least 1 volt.

On the flip side of this if you plug a cable into the return jack and touch its tip do you hear a low level buzz out of the speaker which is as it should be.

[BasementJames]

Great idea, thanks!

I tried that and did get a signal from the send. I got about a volt from the send using a jumper.
Plugging into the return and touching the tip generated no noise at all, though.

I guess we narrowed it down.

Maybe the loop is just bad?

[Thomas_H]

The output stage seems to be the culprit. You could debug it with an audio probe and see if it’s the transistor or just a cold joint somewhere. Be careful, and be sure that your audio probe (basically a capacitor) can handle the high voltages.

[BasementJames]

Thanks!

I went back and looked over the solder joints again to make sure I didn't short something out.
I don't see it.

I did notice that it says Version 4. The most current instructions are Version 3. They look the same except for that trim pot.

I'll wait and see what MojoTone says.
I should probably try the audio probe.

I appreciate all the help.

Maybe I should take it as a sign.

[Guy77]

Thanks!

I went back and looked over the solder joints again to make sure I didn't short something out.
I don't see it.

I did notice that it says Version 4. The most current instructions are Version 3. They look the same except for that trim pot.

I'll wait and see what MojoTone says.
I should probably try the audio probe.

I appreciate all the help.

Maybe I should take it as a sign.

I installed several Ver 3 and none have had issues except that they had soldered the In and Out points were the board connects to the preamp in some of them and I had to remove the solder to install my wire connections.
This is probably because its not the same person soldering these all the time.

I am sure they will get it fixed. Otherwise they are great boards.
I am sure they will replace it for you at no cost.

Let us know how it goes with your replacement board.

If you get a chance can you attach a pic showing all the components on yours. Maybe we can spot some differences compared to the pic of my ver 3.

Thanks
Guy

20260209_110222.jpg

[BasementJames]

MojoTone and Nik at Ceriatone (as if this is his problem) have been really helpful.
I'm exchanging emails with MojoTone now.

As far as the placement of the loop, they both said I should have cut the signal between the .1uF cap and 1M resistor on the phase inverter, rather than where I did, before the .1uF cap.
I tried that new location this morning, but it didn't make a difference.

I'll keep everyone posted and grab a better shot of the loop.

[BasementJames]

I have an update of sorts, but definitely a resolution.

I took the loop out and got better shots of the front and back. Not sure where it is going to end up.

After speaking with MojoTone further, they recommended that I place the loop in a new location.
They recommended that I take the signal out of the center lug of the treble control, into the send (in) of the loop, out of the return (out) of the loop, then to the right solder lug of the volume control.
This is a common spot for some non-master amps, they say.

Where I had placed the loop before, sent about 200 volts into the IN of the loop. This may have damaged it, I really don't know. Apparently, the loop is only designed to work with signal voltage.
I am a bit confused because the instructions say that the loop has its own input coupling capacitor. If it had its own input coupling capacitor, wouldn't the DC voltage have been blocked?

It also seems like where they are recommending I place the loop is pretty early in the signal and probably not worth having in the first place.

In any event, I don't think the juice is worth the squeeze to even try, considering I'm not even sure the loop works anymore. It's not that important to me.

I used Pacific Transformers on this build and am very ecstatic about the overall tone of the amp.
It has been a very fun and interesting build...and doesn't need a loop.
Serves me right for trying.

[Guy77]

I have an update of sorts, but definitely a resolution.

I took the loop out and got better shots of the front and back. Not sure where it is going to end up.

After speaking with MojoTone further, they recommended that I place the loop in a new location.
They recommended that I take the signal out of the center lug of the treble control, into the send (in) of the loop, out of the return (out) of the loop, then to the right solder lug of the volume control.
This is a common spot for some non-master amps, they say.

Where I had placed the loop before, sent about 200 volts into the IN of the loop. This may have damaged it, I really don't know. Apparently, the loop is only designed to work with signal voltage.
I am a bit confused because the instructions say that the loop has its own input coupling capacitor. If it had its own input coupling capacitor, wouldn't the DC voltage have been blocked?

It also seems like where they are recommending I place the loop is pretty early in the signal and probably not worth having in the first place.

In any event, I don't think the juice is worth the squeeze to even try, considering I'm not even sure the loop works anymore. It's not that important to me.

I used Pacific Transformers on this build and am very ecstatic about the overall tone of the amp.
It has been a very fun and interesting build...and doesn't need a loop.
Serves me right for trying.

Hi, thanks for the update. Yes the 200v should not go to the Input of the loop, only the signal from the preamp should go there which is less than 1v, much less than the 200 v. This may have damaged something like you mentioned.

The 200v connection should go to the B+ connector where you have your red wire connected. The connection where the red wire is can handle up to just below 400v.

Cheers
Guy