From Scratch Amp Building Chronicle - 6/13/10 UPDATED!!

[jerrydyer]

if you suspect under the board prob you can just do a duplicate over the top where you suspect a prob. do you have sound like a clean channel but no lead or visa versa, can you get sound or a test signal thru to the output of the loop etc? for me, it took a long time to realize I HAD to do it this way, build amp without switching then add. maybe jumper out all you relays and get one channel to rock.

 

[gbsmusic]

This is awesome I've been following the thread since the start... good luck getting it figured out, it's gotta be frustrating not being able to play it!!! Looks sickkkk as hell dude can't wait to hear it!!!!

Dallas

 

[duesentrieb]

I have a dentists mirror (I guess that you know what I mean) for that "hidden stuff"

(If you get one, just make sure everything is drained - these things are not isolated/insulated)

 

[Anonymous]

if you suspect under the board prob you can just do a duplicate over the top where you suspect a prob. do you have sound like a clean channel but no lead or visa versa, can you get sound or a test signal thru to the output of the loop etc? for me, it took a long time to realize I HAD to do it this way, build amp without switching then add. maybe jumper out all you relays and get one channel to rock.

At this point no signal/sound at the regular outputs or the loop output. It looks like I have a working power section... As Olaf said, I need to see if the loop and the PI work and take it from there... Woulda been nice if everything just worked, but this is kind of fun as well...

Steve

 

[Anonymous]

I have a dentists mirror (I guess that you know what I mean) for that "hidden stuff"

(If you get one, just make sure everything is drained - these things are not isolated/insulated)

Yeah, I have one of those as well - I've already used it once to check something... I'm pretty fanatical about draining the big filter caps at this point...

Steve

 

[cyndicate]

The thing I found to help the most was checking continuity with my multi-meter, thing saved me so much time, no clue how I would have found my problem without, especially for checking areas that are grounded when its not supposed to be.

 

[Anonymous]

Based on Olaf's suggestions, I continued my troubleshooting last night... I tried the guitar into the loop return thing he suggested and as I expected that didn't work. I then decided to just check the voltages on the PI and got:

Pin 1 333.3
Pin 2 280.8
Pin 3 315.7
Pin 6 332.5
Pin 7 281.2
Pin 8 315.8

Obviously something crazy wrong here! I then tracked down two problems:

1.) I missed an under-board connection I was supposed to wire from the PI 10K/.1uF junction to the NFB circuit. I found this by continuity checking as Will mentioned. I just wired this above board. (Good thing I had pictures of the underside of the board as well as a good layout diagram from documenting this! Although my layout diagram needs an update as it has many mistakes now!)
2.) I had not grounded the Presence pot! Fixed that as well...

Re-measured with these fixes in place and got:

Pin 1 206.7
Pin 2 21.99
Pin 3 34.57
Pin 6 200.7
Pin 7 23.21
Pin 8 34.56

That looks much better...

I also think I know what is wrong with the switching. My manual switches are all wired wrong (I found this with continuity checking as well), so I'm going to fix that and try the guitar into loop return thing again (I believe the loop is always off now). If that doesn't work, I'll try wiring a jack into the PI and checking the guitar into it, but I think that will actually work now...

My troubleshooting continues after work tonight - this is fun actually, although I wish it just worked when I turned it on!

Steve

 

[tweed]

Steve,

You don't look so good this morning. I think you should head home.

Randy

 

[Anonymous]

Steve,

You don't look so good this morning. I think you should head home.

Randy

Steve

 

[cyndicate]

Getting close Steve! It's a great feeling when you fix everything and it works, especially when it drives you bat shit crazy

 

[Anonymous]

Getting close Steve! It's a great feeling when you fix everything and it works, especially when it drives you bat shit crazy

Getting "closer", but I hesitate to say close yet...

When you post something like the summary I put in my last post, it looks like that would take about 5 minutes to figure out and fix, but it took me HOURS last night of checking different things, looking at my schematics, checking my layout diagrams, finding mistakes between them, going back to the amp, checking resistance and cap values, checking continuity, etc., etc., etc....

I'm not at the "bat shit crazy" stage... I keep coming up with things that might be wrong to check - not running out of ideas yet. Like I said earlier, it is actually kinda fun and time FLEW by last night. I sat down at my workstation at about 8PM and when I finally finished getting the PI values in line I checked the clock and it was midnight! I was actually ready to continue on to the next step, but I had to get to bed...

Steve

 

[cyndicate]

Getting close Steve! It's a great feeling when you fix everything and it works, especially when it drives you bat shit crazy

Getting "closer", but I hesitate to say close yet...

When you post something like the summary I put in my last post, it looks like that would take about 5 minutes to figure out and fix, but it took me HOURS last night of checking different things, looking at my schematics, checking my layout diagrams, finding mistakes between them, going back to the amp, checking resistance and cap values, checking continuity, etc., etc., etc....

I'm not at the "bat shit crazy" stage... I keep coming up with things that might be wrong to check - not running out of ideas yet. Like I said earlier, it is actually kinda fun and time FLEW by last night. I sat down at my workstation at about 8PM and when I finally finished getting the PI values in line I checked the clock and it was midnight! I was actually ready to continue on to the next step, but I had to get to bed...

Steve

Yep I hear you, a fix that took me a few seconds to fix, took me 5 hours to find

 

[jerrydyer]

welcome to the madness. next thing youll be wearing funny hats with dog ears on them and dressing like a hobo.

 

[Anonymous]

welcome to the madness. next thing youll be wearing funny hats with dog ears on them and dressing like a hobo.

But... I was doing that before I even started playing with the insides of amps...

Steve

 

[Anonymous]

Signs of life...

Last night, I made some manual switching fixes and then tried the guitar into loop return, which did not work...

I then followed Olaf's suggestion of putting a jack in at the PI to ground and that worked. I got a clean guitar sound at the cab that I could adjust the volume of with the PPIMV. Even with the PPIMV up all the way it wasn't as loud as I'd expect a 100W amp to be though, but I got reasonable volume sound.

For the heck of it, I then decided to try just plugging the guitar into the regular inputs again. Now, I get somewhat what I'd expect - a reasonable volume distorted guitar sound at the cab that I can adjust the gain of with the plex gain control and adjust the overall volume with the PPIMV! Sounds like a guitar amp now! Both the high and low inputs work as I'd expect them to.

I can change the plex gain control and go from a completely clean sound to a distorted sound pretty much like I'd expect for the plex mode, however, once again, the amp isn't near as loud as I've experienced cranked plexis when the PPIMV is cranked. Also, none of the tone controls or masters (except the PPIMV, of course) seem to do anything. When I adjust the masters - the volume does not change. When I adjust the tone controls, the sound stays the same. This seems to be the case with the presence and density controls as well, which doesn't make sense to me since everything past the PI seemed to check out.

Troubleshooting continues and there is a long way and probably lots of problems still to tackle, , but I heard a distorted guitar tone out of my cab, last night!

Steve

 

[tweed]

Excellent!!

 

[Anonymous]

Excellent!!

I wept uncontrollably.



Steve

 

[Gainzilla]

This thread reminds of that quote " It takes an entire village to raise a child"

Very cool to follow this project from inception to completion

Kage

 

[Sixtonoize]

So what's the retail on this thing gonna be?
3 years of work, so what...$150,000?

 

[Anonymous]

This thread reminds of that quote " It takes an entire village to raise a child"

Very cool to follow this project from inception to completion

Kage

While others have thrown in with helpful tips and suggestions that I really appreciate, I have gotten so much help from Olaf on this project, it's ridiculous. I could have never gotten this far without his help. I was a complete noob when I started working on this, even with my EE background and the Egnater Seminar under my belt (in many ways, I'm still a total newb really - hell, I'm still struggling with the switching aspects of this project... ). Without his patient explanations, suggestions and corrections I would have abandonded this long ago... Great guy and I so appreciate his taking an interest in this and sharing his knowledge...

Steve