My 2nd gen 50w hybrid, trouble shooting the switches.

[Matt J]

Hey everyone,

I have not posted here on a while but I wanted to share with everyone a build I've been working on. I've built a 2nd generation 50w hybrid using JBoarders' circuit boards and the layout posted below. I finished up everything today, tubed it, fired it up, and biased it. Everything started up fine, no sparks, red plates, or blown fuses. Trying it with a guitar everything sounds ok, it still needs to burn in, I did discover that the volume pot is a little scratchy and will need to be replaced.

I am having problems with the switching system though. Everything was wired up according to the layout. The OD switch on the footswitch seems to work, but the overdrive seems a little weak. The PAB footswitch causes no audible change. When the FET switch is engaged it lights up correctly but the volume suddenly drops, the volume increases as you turn up the FET knob on the faceplate but there does not seem to be any over all gain in the signal as compared to when it's turned off.

The bright and mid boost switches on the faceplate work, the Rock/Jazz switch acts funny. Rock position seems fine, putting it in PAB or Jazz only causes a volume drop.

Some more info on the build: I was originally going to use a Natchanis silverface chassis, after getting one I was not happy with the build quality. Too many bolt holes were either too large or too small and it seemed too weak to be able to hold up the transformers without bending. I ended up using a CE chassis that's great. The resistors are Pihers from ebay and metal films from Markoparts.

I have to send out a big thank you to Taylor at Amplified Nation! He provided a lot of advice and help when sourcing the parts and built a gorgeous black suede with vox cloth 1x12 combo cab this amp's going in when I'm done fine tuning it.

I've attached some photos. They show the how the switches are wired both inside the amp and in the footswitch. Any feedback and critique would be welcomed to help me trouble shoot this problem!

Thanks,
- Matt J.

[Matt J]

More pictures:

[Structo]

Nice clean build.

Usually when something is wrong on a new build it is a simple wiring or connection mistake.

I think I would bypass the FET (disconnect it) and see if things work correctly.

I looked over the relays and switches and it looks ok at first glance.

If you have been obsessed with finding the mistake, take a break and walk away for a day or two, then come back fresh and look it over.
I'm sure it is something simple.

[amplifiednation]

Matt,
I'm glad it finally came together! Does your tone stack work when in "rock"? I just figured out that my build was tripping PAB when in rock mode...which was given no audible change when selecting PAB, since it was already selected. I haven't had time to review the layout to further investigate, but I used the sane layout for my .build

I would do what Tom suggested and disconnect the FET, then work on the amp, its totally independent, so get the amp working first and then fix your FET issue.

[Matt J]

I switched the leads coming from the R/J switch to the relay board I can get PAB now but I noticed the same thing Taylor that PAB engages when I put it in the Rock position - a noticeable volume boost and the tone controls became inactive. In fact, only the Treble and Mid controls seem to work when PAB is off, the Bass pot does not work at all. The Presence control is really weak to so I'll try changing the resistor out. I'm going to disconnect the FET and work from there. I'll probably redo the entire tone control and relay system wiring. I'll just have a footswitch for OD and PAB and have the FET as input only. I'm looking at something similar to the wiring in this 102 hybrid layout I'm posting below, but keeping the 2nd gen values.

It's going to look killer when it's all finished and in the cabinet you made Taylor. I'm still using the silver face style round knobs and they made the black chassis very well.

[Structo]

The Rock position is quite a bit louder than the Jazz setting.

But if it seems that PAB is on and the tone controls don't seem to work properly then I would look at the PAB circuit.

Maybe pull the relays and see what that does for the tone controls.

[steve_p]

Its not on the layout, but you are missing the 10k tail to ground on the bass pot.
Take a look at the 2nd gen layout in the files section for reference.
Hopefully that will clear up that issue.

I just started my pab and rock jazz writing on my 100 watt version of this.
I'm going to be away on business next week, so i won't get to work on it. Hopefully you guys can figure out the problem.

Good luck,
Steve

[amplifiednation]

I switched the leads coming from the R/J switch to the relay board I can get PAB now but I noticed the same thing Taylor that PAB engages when I put it in the Rock position - a noticeable volume boost and the tone controls became inactive. In fact, only the Treble and Mid controls seem to work when PAB is off, the Bass pot does not work at all. The Presence control is really weak to so I'll try changing the resistor out. I'm going to disconnect the FET and work from there. I'll probably redo the entire tone control and relay system wiring. I'll just have a footswitch for OD and PAB and have the FET as input only. I'm looking at something similar to the wiring in this 102 hybrid layout I'm posting below, but keeping the 2nd gen values.

It's going to look killer when it's all finished and in the cabinet you made Taylor. I'm still using the silver face style round knobs and they made the black chassis very well.

This is exactly what is happening in my amp. I think the r/j switch needs to be wired differently, more like 183. I have no rock-or I have no rock without PAB. If I switch PAB when in jazz, I get the same thing as 'Rock'. If you get no tone controls in Rock, then its gotta be going to PAB...we gotta look at that layout.

Darin had a similar issue with PAB but I think his was different than this one. I don't know if anyone else has built that layout.

I'll take a look at the amp and see what's going on.

I had a scratchy pot too, it wasn't getting any connection to pin 1.

You may find the OD comes alive with more 'clean' volume. Did you keep the dual masters?

You are damn right, that cab is gonna look great!

[steve_p]

So i was just comparing the hybrid layout with the 124 layout. I have built a 124 and know that the PAB and rock jazz switches work correctly.

If you look at the 124: The left common terminal of the R/J switch goes to the common terminal of the relay, then the n/c goes to the treble pot. the right common terminal of r/j goes to common, then the n/c goes to the bass pot.

On the hybrid layout, the left common terminal of r/j goes to common, then to the bass pot. the right common terminal of r/j goes to common then to the treble pot.

Maybe try switching the wires on the n/c terminals of the PAB relay?

Also, did you try adding the bass pot tail resistor?

Let us know if this makes a difference.

Steve

[amplifiednation]

Steve/Matt,
I did some work on my 2nd gen this morning to try to sort out the PAB/Rock thing.

I realized I should probably try to finish my build before you guys do, since I started it 9 months ago!

I'm attaching a drawing I got from Structo, which shows the difference between the Dumble wiring and the wiring on the JBorders relay boards.

I have mine wired the way this drawing shows. I do have an extra 22M resistor, I have them coming from both common terminals. I'm going to pull the 22M on the left most common to match the drawing.

[amplifiednation]

Here's how my PAB is currently wired...just like the diagram.

It's still switching with Rock/Jazz

Maybe I have the switch wired incorrectly?

[Structo]

Hi Taylor,

The reason that layout only shows one 22M resistor is because the other one is on the Rock/ Jazz switch to the Treble pot.

Just a different way of wiring it and it is still in keeping with the ODS amp designs.

[steve_p]

Taylor,
If you look at the 124 layout, it does indeed have both 22m resistors in the circuit, however only 1 of them is located on the PAB relay board.
The 2nd one goes straight from the treble pot to the R/J switch. However, schemtically, both ways are the same.

Definitely try swapping the leads going to the treble and bass pots on the relay board.

Steve

EDIT: beaten by tom.... that's what I get for starting a post, going off to have a conversation, them coming back to finish up.

[amplifiednation]

it was like open heart surgery to put that 22M back on the relay.

Steve, why would I switch the bass and treble wires?

[steve_p]

it was like open heart surgery to put that 22M back on the relay.

Steve, why would I switch the bass and treble wires?

Take a look at 124 wiring of the r/j switch and PAB relay and compare it to the hybrid wiring.
On the 124 wiring, the left side common terminal of the rock jazz switch goes thru the common terminal of the relay, then to the treble pot.

On the hybrid, the left side common on the r/j goes thru the common on the relay, then to the bass pot.

It appears that the hybrid layout has these connections reversed from the known-good 124 layout. I am not certain that this matters at all (I haven't drawn it out schematically yet to see the differences visually...i can't wrap my brain around it totally by looking at just the layout). However, it is a difference and could be something to do with the problem.

Worst case, it is an easy thing to try.

Steve