Starting a 2204 build

  • Thread starter Thread starter ledvedder
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SpiderWars said:
The first main filter is filtering out the main bulk of the power supply ripple to ground and is the dirtiest ground. It's a term I read Larry use. He likes to keep it separate from all other grounds and close to the earth ground.

But if you have a known good ground scheme then stick to that. I would expect it to be good. I've seen ground schemes like that too.

I rechecked your pics after posting and edited my post. Its crazy how simple these amps are yet we all do them a million different ways.
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So the filter cap on the left, where the OT CT, choke, and wire from the standby switch should have its own dedicated ground? And I should also connect the heater CT and HT CT to that same ground point?

Sorry, I'm still trying to learn all this stuff. This is my 3rd build, but 1st where I'm not specifically following a layout.
 
ledvedder said:
How do you know if the OT leads are wired to the correct power tubes?
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You should know the start of primary and secondary windings. It's quite common mistake to swap OT primary leads, the result is uncontrollable squealing, if NFB is used. Another usual mistake is that the secondary common wire is not connected to the ground. But of course it could be anything else.
 
For the life of me, I can't figure this thing out. Maybe I bit off more than I could chew. I tried to do this "Neil Special" 2in1 1987/1959. All I'm getting in 2 of the inputs is a hum that gets louder as I increase the MV. In the channel II low input, I get some sound, but it's barely there with the hum.
 

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You’ll have to troubleshoot.

Layouts aren’t always reliable which is why it’s important to know how to read a schematic.

Lead dress really matters with this stuff. How much shielded cable did you use?

And remember this is a marathon not a sprint. Take a deep breath. We’ve all fought problems in our builds myself included.

Take an alligator clip and clip it directly to the grid of the first stage. Clip your guitar cable tip to the other end. See if by injecting a signal to the first stage you get anything.

Also sometimes amps squeal if you don’t have them in the chassis. I have a giant sheet of air duct tin from lowes hardware that I use as a cover for my high gain mods. Sometimes without a ground enclosure high gain stuff will squeal on you.

Check all of your solder joints with a chopstick and reflow suspected bad ones.

IMO I’d take out the front end switch stuff and wire the inputs regular for a 1987 or a 1959. Get it working like a normal amp first then add back in that mod. That’s what I’d do at least.
 
glpg80 said:
You’ll have to troubleshoot.

Layouts aren’t always reliable which is why it’s important to know how to read a schematic.

Lead dress really matters with this stuff. How much shielded cable did you use?

And remember this is a marathon not a sprint. Take a deep breath. We’ve all fought problems in our builds myself included.

Take an alligator clip and clip it directly to the grid of the first stage. Clip your guitar cable tip to the other end. See if by injecting a signal to the first stage you get anything.

Also sometimes amps squeal if you don’t have them in the chassis. I have a giant sheet of air duct tin from lowes hardware that I use as a cover for my high gain mods. Sometimes without a ground enclosure high gain stuff will squeal on you.

Check all of your solder joints with a chopstick and reflow suspected bad ones.

IMO I’d take out the front end switch stuff and wire the inputs regular for a 1987 or a 1959. Get it working like a normal amp first then add back in that mod. That’s what I’d do at least.
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I only have shielded cable from the push pull pot to v1a. I didn't install the ppimv. My first thought was to pull out all the input jack stuff and wire up to standard 1987. That's a great idea with the alligator clip to the grid. I didn't know that could be done.
 
The ground scheme in that layout is interesting. The entire preamp is grounded at the Master and Middle pot casings? There are a couple ground loops in that layout. But ultimately it may be ok. Not sure where your hum and oscillation are coming from. You'll have to troubleshoot some more.
 
FourT6and2 said:
The ground scheme in that layout is interesting. The entire preamp is grounded at the Master and Middle pot casings? There are a couple ground loops in that layout. But ultimately it may be ok. Not sure where your hum and oscillation are coming from. You'll have to troubleshoot some more.
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If you're looking at the same one I am, everything except the power cord IEC earth grounds at that bolt near the input jacks. I bought a Tweed Bassman clone with this ground scheme. All grounds go to a ground buss that connects to the chassis at only one point. It is drawn a little weird.
 
Since you've already built a couple I would expect the issue to be that input jack stuff. I do stuff like that a lot. My last one was the JEL mod that was similar to this but the 4 modes are: Plexi/2203 Lo/2203 Hi/JEL. If you turn the Master up and then mess with the Tone controls you should be able to hear the hiss and for it to affected by the tone stack and Presence. That would at least indicate you've got everything else right except for that input jack stuff. You could pull V1 for this test if the noise is bothering you. The noise should likely go away with V1 pulled if you've got everything else right.
 
SpiderWars said:
Since you've already built a couple I would expect the issue to be that input jack stuff. I do stuff like that a lot. My last one was the JEL mod that was similar to this but the 4 modes are: Plexi/2203 Lo/2203 Hi/JEL. If you turn the Master up and then mess with the Tone controls you should be able to hear the hiss and for it to affected by the tone stack and Presence. That would at least indicate you've got everything else right except for that input jack stuff. You could pull V1 for this test if the noise is bothering you. The noise should likely go away with V1 pulled if you've got everything else right.
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Yeah, the hiss noise does change with the tone controls and preamp gain. I've pulled the the input jacks and preamp gain pot once and went over the wiring with a fine tooth comb. Didn't see any issues. Maybe I'll try it once more before I give up and go with a straight up 2204.

Another thing happened last night. Now I'm not sure if this is normal, since I haven't done it before. I hadn't screwed the turret board in yet. So when I was prodding around with a chopstick, the board moved, which made a loud pop through the speakers. I then started lifting the board a bit and was able to make that sound happen over and over. Maybe there's an issue under the board.
 
ledvedder said:
Yeah, the hiss noise does change with the tone controls and preamp gain. I've pulled the the input jacks and preamp gain pot once and went over the wiring with a fine tooth comb. Didn't see any issues. Maybe I'll try it once more before I give up and go with a straight up 2204.

Another thing happened last night. Now I'm not sure if this is normal, since I haven't done it before. I hadn't screwed the turret board in yet. So when I was prodding around with a chopstick, the board moved, which made a loud pop through the speakers. I then started lifting the board a bit and was able to make that sound happen over and over. Maybe there's an issue under the board.
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Check all of your ground points, and reflow
 
ledvedder said:
Yeah, the hiss noise does change with the tone controls and preamp gain. I've pulled the the input jacks and preamp gain pot once and went over the wiring with a fine tooth comb. Didn't see any issues. Maybe I'll try it once more before I give up and go with a straight up 2204.

Another thing happened last night. Now I'm not sure if this is normal, since I haven't done it before. I hadn't screwed the turret board in yet. So when I was prodding around with a chopstick, the board moved, which made a loud pop through the speakers. I then started lifting the board a bit and was able to make that sound happen over and over. Maybe there's an issue under the board.
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You have a cold solder joint somewhere or a loose ground connection. Reflow the joints and when you touch your soldering wand tip to the joint, add just a bit of solder. Each solder joint should be touched for 3 seconds max.

As others have said disconnect all of that stuff up front and wire it as a stock 2204 and get that working first. Once it’s working, then you can add in the switching stuff later.
 
SpiderWars said:
If you're looking at the same one I am, everything except the power cord IEC earth grounds at that bolt near the input jacks. I bought a Tweed Bassman clone with this ground scheme. All grounds go to a ground buss that connects to the chassis at only one point. It is drawn a little weird.
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Look at the layout for MD800 50 Watt Kit. Yeah there's a ground lug at input as well. But everything is also grounded at pot casings as well. Big ground loops.
 
FourT6and2 said:
Look at the layout for MD800 50 Watt Kit. Yeah there's a ground lug at input as well. But everything is also grounded at pot casings as well. Big ground loops.
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Hmm, Michael from Modulus was saying his ground scheme is the one I should follow.
 
ledvedder said:
Hmm, Michael from Modulus was saying his ground scheme is the one I should follow.
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Actually looking at that scheme again, the pot casings aren't grounded to that bus, only lugs 1. So it should be good. My mistake. If you followed that layout for grounding and you've checked all your grounds, then you should have confidence that isn't your problem.
 
How do you feel about the so called "Larry" method? Or Ceriatone's method?
Screenshot_20220826_085930_Gallery.jpg
JCM800_2204Ceriatone.jpg
 
I wouldn't go down the rabbit hole of grounding schemes on a build like this. Get it up and running properly first.
 
FourT6and2 said:
I wouldn't go down the rabbit hole of grounding schemes on a build like this. Get it up and running properly first.
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Totally agree with this. If you've done that grounding scheme as pictured that shouldn't be your problem. With the amp unplugged, you can check all of them for 0 ohms to the chassis. What might not be obvious in the layout is the buss going laterally across the circuit board where the speaker jack ground wire connects to the board.

Lots of different grounding schemes that can work but if you go mixing them there can be issues.
 
Well, it lives! But it has a buzz when I turn up the MV or gain. Still operates fine, but there's definitely something off with grounding. I checked resistance at all grounds, and it's anywhere between 0.5 to 0.9 ohms.
 
The resistance to ground isn’t the cause of the buzz, it’s the loops of currents within the grounds that cause a problem. That’s why myself on the headfirst page and everyone else here has been talking about grounding - it matters a lot not only where grounds are attached but also how you can reduce or at least minimize ground loops of current.

Another source of buzz is wire location. Have you chopsticked each of the preamp tube wires to see what changes the buzz? Is the buzz 60Hz or 120Hz?
 
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