New TMB w/reverb Build

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Re: New TMB w/reverb Build

Post by JMPGuitars »

To set the probe settings, click the channel button the probe is connected to. Then you should see the option you need on the screen.

Turn off the reverb. Look at the schematic. Follow the signal path from the input jack through different parts of the circuit. As you move further through the amp, the signal will be hotter, and the scope will need to be adjusted. You can adjust the vertical knob, or hit auto again.

If you make it through the whole circuit to the output speaker jack without anything jumping out at you, you can try turning up the reverb. Keep in mind though, that reverb will, by its own nature, make the scope look a little goofy. You want to see if anything like a parasitic oscillation pops up.

With the reverb on, you can go through the circuit again and see at what point it gets weird, if that's indeed the issue.

You may find that adjusting other knobs is related to an issue, if you find one.
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Re: New TMB w/reverb Build

Post by foreverstrung »

I need some help setting this scope properly.
I’m able to get the signal from the audio generator to the scope and I get the sine waves like in this pic

When I set up my calibrated probe to 10x
Hit auto and get this
https://youtu.be/k8-rKcc6tLw
That’s with the probe at the input jack shown in the video. I know I don’t have the mV set to 200mV or their abouts, but I’m confused on how to do this and where exactly to do this. I’ve set it to 200 in the course adj, but I don’t think that’s right. When I do, it doesn’t stay at 200mV.
I really wish I’d taken more electrical engineering courses in school another lifetime ago, but alas, I’m an old carpenter fuddling about. Appreciate the help
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Re: New TMB w/reverb Build

Post by JMPGuitars »

You set the signal amplitude at the signal generator. It might already be set if it remembers my last setting used. What's on the screen of the signal generator?

If you look at the screen on your scope, it says 50mV/div. That means each division (box on the screen) covers 50mV. You have the signal spanning 4 divisions, so you're pretty close to 200mV already.

If you want to see more information (including what the scope sees for your signal amplitude) click on the measure button, and choose some fun options like averages and/or peaks.

For sharing your scope screen with us, you can plug a USB stick into the front port on the scope, and it will screen capture and save to the USB stick. Or, you can actually connect to your scope over your home network if you connect the scope to the network. You can completely run the scope from your computer, and save screen captures directly to your computer as well. You can see more about it on my review of that scope: https://youtu.be/HI7DGjgl2tw?t=346

Thanks,
Josh
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Re: New TMB w/reverb Build

Post by foreverstrung »

Ok. With all that being said, how about what I was picking up at the input jack? Did I have the probe hooked up correctly? The sine wave reading on the scope was nothing even close to the AG plugged directly into the scope. What should it look like? Should I expect it to be similar as the AG directly.
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Re: New TMB w/reverb Build

Post by JMPGuitars »

foreverstrung wrote:
Sat 12/31/22 8:56 pm
Ok. With all that being said, how about what I was picking up at the input jack? Did I have the probe hooked up correctly? The sine wave reading on the scope was nothing even close to the AG plugged directly into the scope. What should it look like? Should I expect it to be similar as the AG directly.
If you have the signal generator plugged directly into the scope (without a probe), you need to either use a 50 ohm terminator, or change the input settings to account for it. Don't worry so much about that right now.

Just follow the logic: amplitude is set on the signal generator; now what do you see on the scope? Then leave the signal generator doing its job, and continue using the scope to test the signal path in the amp.
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Re: New TMB w/reverb Build

Post by foreverstrung »

Turn off the reverb. Look at the schematic. Follow the signal path from the input jack through different parts of the circuit. As you move further through the amp, the signal will be hotter, and the scope will need to be adjusted. You can adjust the vertical knob, or hit auto again.

If you make it through the whole circuit to the output speaker jack without anything jumping out at you, you can try turning up the reverb. Keep in mind though, that reverb will, by its own nature, make the scope look a little goofy. You want to see if anything like a parasitic oscillation pops up.

With the reverb on, you can go through the circuit again and see at what point it gets weird, if that's indeed the issue.
OK, I've been going thru this now the last couple days maybe an hour each time with about 7-8 times. I'm def get more comfortable using these tools.
It appears to be good all the way thru the tone stack, then it gets weird. So maybe it's more than just the reverb. With the reverb off and I run thru the amp from the input jack, after the "high" pot, it gets weird and never totally recovers.
When I hit the right lug on the volume pot with the probe, were golden, but when I increase the volume, there's minimal rise in my peeks, but when I add gain, it moves the peeks as I'd expect the volume pot to do normally. When I hit the center lug of the volume pot with the probe, it's fragmented. As I work my way backwards from this position of the volume pot onto the PCB board, the problem persists. Still trying to find the sweat (bad) spot.
So, IDK what all this is just yes. Still checking all my joints. Repositioning some wires. I've completely replaced the V3 socket (3 times) and rewired everything connected to V3.
So IDK if anyone sees something thru these words that I'm putting down.
Appreciate all thoughts
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Re: New TMB w/reverb Build

Post by JMPGuitars »

foreverstrung wrote:
Sun 01/01/23 4:44 pm
OK, I've been going thru this now the last couple days maybe an hour each time with about 7-8 times. I'm def get more comfortable using these tools.
It appears to be good all the way thru the tone stack, then it gets weird. So maybe it's more than just the reverb. With the reverb off and I run thru the amp from the input jack, after the "high" pot, it gets weird and never totally recovers.
When I hit the right lug on the volume pot with the probe, were golden, but when I increase the volume, there's minimal rise in my peeks, but when I add gain, it moves the peeks as I'd expect the volume pot to do normally. When I hit the center lug of the volume pot with the probe, it's fragmented. As I work my way backwards from this position of the volume pot onto the PCB board, the problem persists. Still trying to find the sweat (bad) spot.
So, IDK what all this is just yes. Still checking all my joints. Repositioning some wires. I've completely replaced the V3 socket (3 times) and rewired everything connected to V3.
So IDK if anyone sees something thru these words that I'm putting down.
Appreciate all thoughts
We can't really guess from your descriptions. You should do each thing you're referring to, and hit the print button on the scope to save screenshots. Then post the screenshots here with your descriptions so we're on the same page. It would help if you take notes while testing, and write the file number that pops up on the screen when you hit the print button. Then your notes shared here will match the screenshots. You'll be able to communicate much more clearly that way.

Thanks,
Josh
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Re: New TMB w/reverb Build

Post by foreverstrung »

Just curious. How do you guys bleed the amp before working on it? I use a resistor on all the caps n then check with my MM.
You guys got a quicker way?
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Re: New TMB w/reverb Build

Post by JMPGuitars »

foreverstrung wrote:
Wed 01/04/23 7:03 am
Just curious. How do you guys bleed the amp before working on it? I use a resistor on all the caps n then check with my MM.
You guys got a quicker way?
The 221K resistor on the cap can is a bleeder resistor. If you soldered it in correctly, there's nothing for you to do but wait a few minutes...and test to be safe anyway.
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Re: New TMB w/reverb Build

Post by Bieworm »

I let the 220k bleeder resistor on the 1st filter cap do its job for half a minute…
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Re: New TMB w/reverb Build

Post by foreverstrung »

We can't really guess from your descriptions. You should do each thing you're referring to, and hit the print button on the scope to save screenshots. Then post the screenshots here with your descriptions so we're on the same page. It would help if you take notes while testing, and write the file number that pops up on the screen when you hit the print button. Then your notes shared here will match the screenshots. You'll be able to communicate much more clearly that way.
So here are 6 points (#004-#009), I probed with the scope. (Siglent 1104x-e) using a audio generator, (UNI-T UTG 932E) set at 50ohms and 1 kHz
IMG_0757.jpg
Right out of the gate I'm getting this fragmented wave at my first point from the input jack.
SDS00004.png
Each of these scope screen shots are numbered and the last 3 digits correspond to the point I've marked and highlighted on the schematic.
This is a place to start. Hopefully we can find the spot(s) causing the problems.
Josh suggested I redo the entire input jack and assembly which I have, but still with no change.
All knobs are at 0
Anyways, attached. Questions? Thoughts and suggestions encouraged.
Thx
SDS00005.png
SDS00006.png
SDS00007.png
Volume pot center lug
SDS00008.png
Volume pot right lug
SDS00009.png
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Re: New TMB w/reverb Build

Post by foreverstrung »

Chasing this down, the center lug of the volume, gain and reverb are all grounded. IDK where. I'm looking. I don't believe the center lugs are supposed to be directly grounded as the left lug of all 3 of these pots have a designated ground. I've determined this "grounding" with the continuity setting on my MM.
The TMB is not hitting ground, (except as it's supposed to), this is why I'm getting a good wave reading there.
It makes sense that I'm grounded as the neg readings on the scope appear near exactly the same as if I just intentionally put the probe to ground
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Re: New TMB w/reverb Build

Post by JMPGuitars »

All your knobs are at 0. Do you see how 004, 006, and 008 look almost the same?

You can't test a sweeper on the volume pot at 0, for the same reason you can't scope 006. You're scoping ground. You have to pay attention to where the signal is coming from, and where it's going to.

Your signal at 004 and 006 look similar, which means you're likely still testing ground at the input jack, or having a related issue. Try moving your ground lug for the probe to the output ground and see what that looks like.

Put all your knobs at 50% and test again. Make sure the input plug is pushed into the jack firmly. Once your probe is connected, and before you turn the amp on, test the input jack tip for resistance to ground.

EDIT: you should turn off the channels on the scope you're not using. Double click the channel button that you're not using, and it will shut off. Also, set your bandwidth limit on the channel you are using to 20M.
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Re: New TMB w/reverb Build

Post by JMPGuitars »

foreverstrung wrote:
Fri 01/06/23 12:24 pm
Chasing this down, the center lug of the volume, gain and reverb are all grounded. IDK where. I'm looking. I don't believe the center lugs are supposed to be directly grounded as the left lug of all 3 of these pots have a designated ground. I've determined this "grounding" with the continuity setting on my MM.
The TMB is not hitting ground, (except as it's supposed to), this is why I'm getting a good wave reading there.
It makes sense that I'm grounded as the neg readings on the scope appear near exactly the same as if I just intentionally put the probe to ground
A volume pot typically works by bleeding signal to ground. at 0, you're bleeding 100% signal to ground. At Max, you're bleeding 0% signal to ground. See my post above how to test correctly.

Thanks,
Josh
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Re: New TMB w/reverb Build

Post by foreverstrung »

Also, set your bandwidth limit on the channel you are using to 20M.
How do I do this?
Thx
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