My take on a 2nd Gen ODS

[Matt J]

Pictures of how it currently sits.

[Matt J]

I'm going to take a look at it tomorrow with a fresh set of eyes. My suspect is that it is a missed/accidental ground issue.

Any feedback is always appreciated!
Matt J.

[GAStan]

What's the value of the resistor on your input jack? Check it with a meter. Best I can tell (small phone screen) color code is Brn-Blk-Red.

[Matt J]

What's the value of the resistor on your input jack? Check it with a meter. Best I can tell (small phone screen) color code is Brn-Blk-Red.

Good eye! I put a 1K in there on accident.

Replaced it with a 1Meg. Still not passing signal but it is certainly something in the preamp. Plugging into the FX return jack you do get sound, but it is not affected by any of the front controls.

Matt J.

[GAStan]

Thanks!

Looks like V1 pin 5 (heater) has no solder. Not sure this is enough to cause no signal. Still looking....

[GAStan]

I'm not real familiar with 2nd Gen. Is it supposed to have an OD entrance trim pot? Unable to see under the board but something seems off to me in that area. Where does the green wire land?

[Matt J]

I'm not real familiar with 2nd Gen. Is it supposed to have an OD entrance trim pot? Unable to see under the board but something seems off to me in that area. Where does the green wire land?

Reflowed the solder on V1's heater to make sure that's connected.

No trim pot with the OD entrance on the 2nd/3rd gen circuits, though some here have added them as a mod to fine tune the OD.
Green wire leading to V2a leads to a small jumper from the eyelet to the 1.2M/33K junction at the bottom.

I didn't get any pictures of the underside before I installed it. I did some desoldering this morning to free up the board to I could check things and grabbed some pictures of the board's underside the best I that could. Note that I run a shielded wire from the FX return to the 5nf PI input cap.

I used Martin's board design with 2nd/3rd Gen values and components for an OD Ratio control. Like this but with the 2nd/3rd Gen OD and 180k to ground from 150k that feeds to the Ratio control.
Basically, something like this. Note the PI plates are 51k and 47k and the grid leaks are 100k instead of 220k. And Martin I apologize for butchering one of your board designs in Microsoft Paint!

MM Board - Partial 2nd Gen hybrid.jpg

Matt J.

[dbharris]

Matt, do you have a scope? If not, a meter set to measure AC might help, black probe to bus bar bar and clip the red probe to trace the signal at input jack and then after the coupling cap for each stage in the preamp.

You can use a phone or tablet as a signal generator to send a sine wave in.

Good luck!

-Dan

[Matt J]

Matt, do you have a scope? If not, a meter set to measure AC might help, black probe to bus bar bar and clip the red probe to trace the signal at input jack and then after the coupling cap for each stage in the preamp.

You can use a phone or tablet as a signal generator to send a sine wave in.

Good luck!

-Dan

Sadly, I do not have a scope, but that is something I've been thinking about investing in. I was planning on using my phone as a signal generator later when setting the PI balance trim pot. Instead of running my phone directly into the amp, would it be better to record the signal on a looper pedal and just run it from there? I have a nice one by MXR I can adjust the levels on easily.

I'm going to redo some of the preamp wiring today after work then give this a go. Thanks!
Matt J.

[dbharris]

Matt, do you have a scope? If not, a meter set to measure AC might help, black probe to bus bar bar and clip the red probe to trace the signal at input jack and then after the coupling cap for each stage in the preamp.

You can use a phone or tablet as a signal generator to send a sine wave in.

Good luck!

-Dan

Sadly, I do not have a scope, but that is something I've been thinking about investing in. I was planning on using my phone as a signal generator later when setting the PI balance trim pot. Instead of running my phone directly into the amp, would it be better to record the signal on a looper pedal and just run it from there? I have a nice one by MXR I can adjust the levels on easily.

I'm going to redo some of the preamp wiring today after work then give this a go. Thanks!
Matt J.

Yes, the looper pedal will work. Maybe strike the open G string once have that looping? I would try to trace out the circuit to find the problem location before making more changes, may complicate things later.

If nothing else, you could alligator clip from your input jack with the looper on to before the grid resistor of each preamp stage to see where signal starts passing to the power amp. Then you would know the problem is in a preceding stage.

-Dan

[ijedouglas]

I don't see any issues under the board, it all looks good to me. You should be able to use your DMM to trace back from known good point (PI) if you don't have a scope (exactly as Dan describes above).

[GAStan]

Typically when I check voltages I have a dummy load connected to the output. Recently I had a speaker connected and when I checked plate voltages on the preamp I noticed a POP sound as I touched the probe to the point I was checking. Maybe you can use this as a method to narrow down where the signal is being lost, only requires a speaker and meter.

[martin manning]

I apologize for butchering one of your board designs in Microsoft Paint!

No worries, but it's best to clearly mark the modifications.

I was planning on using my phone as a signal generator later when setting the PI balance trim pot. Instead of running my phone directly into the amp, would it be better to record the signal on a looper pedal and just run it from there? I have a nice one by MXR I can adjust the levels on easily.

I'm a fan of using a Bluetooth adapter to run signal from a phone app into the amp as described here: https://ampgarage.com/forum/viewtopic.p ... 89#p416389 Sine, square, and triangle waveforms, with frequency sweep and burst are available in some app's.
Raoul Duke's recent experience revealed that some Bluetooth adapters have higher output than others, and the adapter may not have enough output to directly drive the power amp to set the PI trimmer. Raoul used a mixer to boost the signal, but a clean boost pedal would work as well.

[Matt J]

Typically when I check voltages I have a dummy load connected to the output. Recently I had a speaker connected and when I checked plate voltages on the preamp I noticed a POP sound as I touched the probe to the point I was checking. Maybe you can use this as a method to narrow down where the signal is being lost, only requires a speaker and meter.

I normally do my first fire up procedures with a dummy load too, but did poke around with a proper speaker attached later. I certainly got a nice *POP* from the plates and grids in the PI, but nothing before that in the signal chain.
Gonna keep digging more with what all has been mentioned this afternoon!
Matt J.

[Matt J]

I apologize for butchering one of your board designs in Microsoft Paint!

No worries, but it's best to clearly mark the modifications.

I was planning on using my phone as a signal generator later when setting the PI balance trim pot. Instead of running my phone directly into the amp, would it be better to record the signal on a looper pedal and just run it from there? I have a nice one by MXR I can adjust the levels on easily.

I'm a fan of using a Bluetooth adapter to run signal from a phone app into the amp as described here: https://ampgarage.com/forum/viewtopic.p ... 89#p416389 Sine, square, and triangle waveforms, with frequency sweep and burst are available in some app's.
Raoul Duke's recent experience revealed that some Bluetooth adapters have higher output than others, and the adapter may not have enough output to directly drive the power amp to set the PI trimmer. Raoul used a mixer to boost the signal, but a clean boost pedal would work as well.

I'm certainly going to try the method you discussed, Martin! That's how I planned on setting the PI balance and your post does a great job explaining things. I have a bluetooth adapter around here somewhere I can try hooking up. If not that, I can use an audio cable with an 1/8 to 1/4 plug adapter.

BTW - What program do you use to draw your circuit board layouts? Corel Draw?
Matt J.