Installing Mojotone's effects loop in a weber 6O100

[csjoyner]

We are having problems adding Mojotone's effects loop to a Weber 6O100. When the loop is off it bypasses fine but when it is on it kills the sound almost entirely (if you turn everything up you can barely hear it). Contacted Mojotone but they just sent a new one that had the same problem so I am assuming we did something wrong. The connections are simple but I just wanted to check the collective to see if I chose the right access points. I've included the links to the loop directions and amp schematic and layout. We took the power from the point marked "C" on the bottom right of the layout. It measured about 320V. We split the signal after the 100k resistor on the drive switch. Any input would be great. Thanks.

https://tedweber.com/media/kits/6o100_layout.jpg
https://tedweber.com/media/kits/6o100_schem.jpg
https://www.mojotone.com/manuals/mojoto ... oop-v2.pdf

Here is a list of more info of things we tried just for more info:
We did jumper the trim and left the send (switch) unjumpered (basically, the loop is hooked up correctly according to the directions)
We used a patch cable to eliminate any outside variables
We checked the connections (solder points) on and to the loop

[jajoyner]

Here's a pic of our amp for reference. Scottie didn't have a good one. I tried to get an "overview" pic. If you need a close-up, let me know.

tempImageG4IP3h.gif

[Stevem]

I find monotones labling of the jacks in the least unintuitive if not backwards!

Send should also be called out, and return should be called in, not the way they have It labeled on there schematic!

Are you just maybe due to this labling just plugging things in backwards since it works in bypass?
Is it working as if it where in bypass by just jumping it with a cable?

[csjoyner]

We thought of that and switch the in and the out on the loop. Same results, worked in bypass but not when on. Also, we used a patch cable when testing to make sure we were not doing something stupid like leaving a pedal unplugged.

[ViperDoc]

Is your FX board ground attached to chassis?

[FUCHSAUDIO]

do you own a scope and can you trace it out ?

[csjoyner]

Q: Is your FX board ground attached to chassis?
A: Yes.

Q: do you own a scope and can you trace it out?
A: No

[Stevem]

You can signal trace thru it without a scope, use your ohmmeter set for low AC volts.
Just be sure to only tap into the down stream side of the coupling caps, not the plate side!

Do you have a way to pump a test tone into the amp?

[csjoyner]

I’m sure we can do a test tone. What frequency? What would we look for on a multimeter? Also, scopes are not that expensive. I know very little about them other than they send out a wave then measure a wave in do you can see the difference. We live building amps, should we just buy one? If so, is there anything specific to look for. We would use it to bias, diagnosis, and signal tracing and anything else I don’t yet know about.

[Stevem]

Here’s a example of signal tracing thru with just a voltmeter set for AC from this 1968 Fender bandmaster I
Have on the bench that I just retubed and caped.

Into the vibrato channel input number 1 I amp pumping in .118 volts ( about -10 dB) at a 1k frequency.
You can see this on the photo of my meter set for Ac volts.
This goes into pin 2/ the first gain stage.
It comes out of pin 1 and on the other side of the coupling cap there is then 77 volts of signal.

It then goes thru the tone stack and then due to the losses comes out with a maximum( if the volume is wide open ) of .580 volts and then goes into pin 7 where it’s reamplified again and then goes out pin 6.

[pompeiisneaks]

I made a video on how you can test this with a multimeter:

https://www.youtube.com/watch?v=f1uc62xqJsQ

~Phil

[sluckey]

Here’s a example of signal tracing thru with just a voltmeter set for AC from this 1968 Fender bandmaster I
Have on the bench that I just retubed and caped.

Into the vibrato channel input number 1 I amp pumping in .118 volts ( about -10 dB) at a 1k frequency.
You can see this on the photo of my meter set for Ac volts.
This goes into pin 2/ the first gain stage.
It comes out of pin 1 and on the other side of the coupling cap there is then 77 volts of signal.

Incredible! That's a gain of 652.

[Stevem]

Lol, sorry I got a decimal point misplaced!
Anyway it’s a valid way to surf through a circuit other then a PI section where you need to measure across the outputs.

[csjoyner]

So this is embarrassing. We got an oscilloscope and were ready to trace the signal. Before we started I wanted to make sure that the power was running correctly to the rest of the amp. It was but while doing this I noticed something ridiculously obvious. One of the caps on the loop board was actually touching the chassis. We moved it and of course it worked. I feel like this would have been something we would have noticed if we built the board ourselves but it didn’t even cross our mind. I apologize for wasting your time but we now have an oscilloscope and kinda know how to use it. I’ve included a pic so you all can laugh at us righteously. Thank you all for you time.

[Stevem]

Well, All’s well that ends well!

If that would have been the DC hot end of the cap you would have known right away, lol!

So you got a scope, so now get two 50 watt 8 ohm heat sinked load resistors and a double pole double throw HD switch and your set with a 4 and 8 ohm set up to test with.