Since I started over (finished and same problem) FIXED BUT WITH A TAD FEEDBACK

[hesamadman]

EDIT::: Amp is working. Thanks SILVERGUN and EVERYONE ELSE. Now we have a bit of feedback but progress is there!!!! 




 

Here we are. Finished rebuilding it.....aaaaand.....you guessed it.

Same problem. Only differences in this time compared to last is a little bit more volume.

Issues-
Only one input makes any sound
Volume knob doesn't seem to do anything at all. Any guesses without me taking all my voltage readings and such? Ill get to that eventually. Just wondering what the hell it could be. 2 builds in a row.

This build I have. Whole new board. New tube sockets. New output tubes.

Here's a video
http://youtu.be/Y30EV5zXZLU

[Willabe]

Sorry to hear it's not fixed.

It can be frustrating. But if you are going to fix it you can't let it fog your head.

Something's got to be wired wrong. You have to find it.

The other thing is you might have melted the insulation on the inner wire in a shielded cable causing it to short out the signal? It has happened more than a few times here.

You can check for shorts in the shielded cable with your meter set to resistance. The inner wire should have infinite resistance to ground.


                   Brad       

[sluckey]

The inner wire should have infinite resistance to ground.

Probably not since they are connected to stuff in the circuit.

It's very easy to wire the input jacks wrong on that amp. The input jacks on a JCM800 2204 use a unique circuit to switch in the high gain channel. See pic...

[Ed_Chambley]

I do not think it would be the same problem, but it is making sound.  There are too many things that can cause this, but you can be assured you have some wiring errors on your input jacks.  Rework those and see where you are.

Getting voltages for you are difficult and I do understand, but you never really do not want a build without voltage readings recorded.  The reason is for troubleshooting now and in the future.  You are close to having it where it will be running.  You have been working hard and you are doing just fine.

Even if i have a new build working well, I still record the voltages.  There is really no way around it if you want help troubleshooting.  Other than that, you can keep on checking your wiring, but if you post voltages we can tell you locations of interest.  Without them, it is just guessing.

I promise when it will play louder than you really want, you will be pleased and all the frustration will turn into happy.  I will give you credit for perseverance.  

[Willabe]

The inner wire should have infinite resistance to ground.

Probably not since they are connected to stuff in the circuit.

Then the meter should be set to continuity to check for a short in shielded cable?


                 Brad    

[sluckey]

Then the meter should be set to continuity to check for a short in shielded cable?

I think the continuity function on a meter has very little value inside an amp. Why not just measure the actual resistance and compare to the schematic. May require some analysis in the case of parallel paths.

[Willabe]

Use the rubber boot alligator clip or like IIRC 11 teen said use a piece of wire insulation over the + meter probe. All you need is a small amount of the probes tip still exposed to take a reading.

Try it on the 1st preamp tube as it has the lowest voltages 1st to see what length of probe still exposed you feel comfortable with.


               Brad        

[Willabe]

I think the continuity function on a meter has very little value inside an amp. Why not just measure the actual resistance and compare to the schematic. May require some analysis in the case of parallel paths.

Ok, thanks, makes sense.


             Brad      

[labb]

build yourself a signal generator and start injecting signal from the pre amp to the power tubes. find out where you are losing the signal. You can build a signal generator using a walk man or radio. Put a 630 volt rated cap in the hot wire of the input jack to the walkman. Play a cd in the walkman and use to opposite lead of the cap to inject the signal where you want to.( you will have to ground the lead shield to the amp chassis) it is a take off on the listening amp design. Be careful don't let the amp voltage bite you.

"There's a really cool way to debug your circuit besides the look and guess/measure with voltmeter technique. This gift was given to me by my friend Craig Ochikubo. (from "uncle Jimmy")

You take a plain old amp cord, cut off the 1/4" connector. Put a .1uF non polarized capacitor on the hot lead, put the shield/ground to the ground of your circuit. (If you use alligator clips, then the shield clip goes to ground) Now plug the other end into an amp and turn the volume low. News Flash - New Improved Audio Probe from R.G. Keen!

Now you can use the tip of the capacitor to probe around the circuit. You can hear how the circuit works by touching different places in the circuit. Start from the input of your stompbox and work your way through the circuit. Follow the signal path to see where your problem lies.

You can plug your guitar into the circuit and have someone else strum it while you probe OR you can use a signal generator or a keyboard or a CD player etc.... to send signal into the circuit. You can hear the effect change the tone of the input signal."

[Slimtim]

Hell yeah you're making progress,CONGRATS.So close to having you a jcm 800 clone i bet you can taste it,lol.I'm so glad i found these forums.nice folks here.

[alerich]

It could a dozen different things causing your symptoms. Voltages would be helpful, sure. Schematic and highlighter. Start at the input and confirm every connection and every component value. It's tedious but you must confirm that the circuit is wired correctly with the correct value of every component. That's why I use the schematic and highlighter when building. Much easier to confirm as you wire rather than sort it out in a built amp. I wish I had a quick fix to offer but sometimes you just have to bite the bullet and do the legwork.

You'll find the problem(s) - it just takes patience. It's most likely a wiring error. My money is on one or more of the tube sockets being miswired. It's easy to do since they are a mirror image from the wiring side that they are from the tube side. That's the odd thing about tube amps sometimes. You can miswire them and they will sorta work.

[eleventeen]

"That's why I use the schematic and highlighter when building. Much easier to confirm as you wire rather than sort it out in a built amp."

 

[spacelabstudio]

Can you post some big close up photos of your amp's guts?

[SILVERGUN]

It's very easy to wire the input jacks wrong on that amp.

  but you can be assured you have some wiring errors on your input jacks.

There is a 92% chance that you have at least one wire wrong in those input jacks.
The jacks themselves also act as switches, so every wire on every tab is critical....each tab performs a different function in the switching system that automatically happens when you plug into one jack or the other....... not a guess
The fact that one input is working and the other one isn't, is pretty conclusive evidence that we may be onto something

If nothing else,,, please provide a close up, well lit, high resolution pic of that area
I amended the schematic to represent how simple it could look with just one input (high)......it's the one most guys use to get that JCM800 sound....
If you'd like,,,I can amend your layout to reflect these changes, and you can try one input and see if the "high" vol. is there

[hesamadman]

The only possible way my input jack wiring can be wrong is if there are more than one kind of cliff jacks out there. Meaning, the ones I have switch opposite from the ones on my layout. Ive stared and traced my input jacks. Wiring is identical to any single layout I look at online. I dont understand the schematic that was posted so I cant check it with that.

Once again, and I know something is obviously wrong but, once again......

Ive checked EVERY component. Resistors are all correct values. Capacitors all correct.

I thought maybe since the presence knob was part of the power amp....i thought maybe I should check that. Its fine. Filter caps are fine. Im going to post voltages later but I have a feeling one of my pre amp tubes voltages will be too low like last time.

[SILVERGUN]

1)There is a black dotted line (and a red one) in the layout that is meant to be an under the board connection....is it there?

2)If you'd like to try to bypass the input jacks I can adjust your layout to show you how....just say the word

3)How about a pic of that area?

4) http://www.cliffuk.co.uk/products/jacksockets/index.htm

Just tryin' to help 

[sluckey]

Not all cliff jacks are created equal.

Show us some sharp, hi rez, close up pics of the input jacks. We need to see the jacks, every wire connected to them, and where the other end of those wires connect. Multiple pics from various angles would be very helpful.

[hesamadman]

1)There is a black dotted line (and a red one) in the layout that is meant to be an under the board connection....is it there?

2)If you'd like to try to bypass the input jacks I can adjust your layout to show you how....just say the word

3)How about a pic of that area?

4) http://www.cliffuk.co.uk/products/jacksockets/index.htm

Just tryin' to help 

WHERE...... DO...... YOU.... LIVE!!!!! I NEED TO HUG YOU. IT WORKS!!! WAS MISSING THE RED LINE. I CANT SEE IT BECAUSE IT BLENDS IN WITH MY LAYOUT>>>> GEEZE!!!!!!!!!!!!!!! Im about to really jam it and test it!!!

[SILVERGUN]

WHERE...... DO...... YOU.... LIVE!!!!! I NEED TO HUG YOU. IT WORKS!!! WAS MISSING THE RED LINE. I CANT SEE IT BECAUSE IT BLENDS IN WITH MY LAYOUT>>>> GEEZE!!!!!!!!!!!!!!! Im about to really jam it and test it!!!

I'm in Philly...and I'd take a handshake   

I'm very happy that I was able to help you, and you should be very proud of your own persistence!

Let us know if all else is OK....everyone who has posted will be happy to hear your results 

 

[hesamadman]

Thanks to you all and (SILVERGUN for pointing out my problem), I now have a working amp. HOLY COW!!

However...some minor tweeks needed. Im using a single coil telecaster on it. In my hi gain input at larger volumes i get a high pitch squeal when not playing a note. Now the problem was my jumper from my .022 cap to the 500pf cap/470k resistor. I have not fixed this permanently. I just put alligator clips from one lead to the other to temp it and see how it works. Any possibility when I do a final repair, it may take the noise out?

I love you guys!!!!!!

 

[Willabe]

WAS MISSING THE RED LINE. I CANT SEE IT BECAUSE IT BLENDS IN WITH MY LAYOUT

Was that same wire also missing in your 1st build of that amp? Red wire under a red board in the layout drawing, no wonder you couldn't see it.

Glad you got it running.

Good call SG. Good eyes.


              Brad      

[Willabe]

Any possibility when I do a final repair, it may take the noise out?

Yes, maybe. You'll find out soon enough.


                   Brad     

[Glennjeff]

That was a good catch by SILVERGUN. Those sort of problems can follow you till the end of time.

Im using a single coil telecaster on it. In my hi gain input at larger volumes i get a high pitch squeal when not playing a note.

I think that may be normal amp/pickup behaviour.

Glad it's going and all the best.

[Willabe]

I think that may be normal amp/pickup behaviour.

That's a very good point. Some Tele bridge PUP's are notorious for feedback squeals because of loose coil winds.

Modern vintage PUP winders talk of this and that there's a balance (and differing opinions, of course) between "should the PUP be potted or not and if so how much potting so as not to kill the vibe/tone?"

All part of the magic of some of the old Tele PUP's. Some want/need a Tele PUP that's free from it and others want/need it to have some but not uncontrollable squeal to it.

To each their own.

Me, well, I want 1 of these;    


                  Brad         

[hesamadman]

WAS MISSING THE RED LINE. I CANT SEE IT BECAUSE IT BLENDS IN WITH MY LAYOUT

Was that same wire also missing in your 1st build of that amp? Red wire under a red board in the layout drawing, no wonder you couldn't see it.

Glad you got it running.

Good call SG. Good eyes.

 


              Brad      

  YES!!! ha ha but its about the knowledge just as much as the sweet tone. So.....I learned to solder better. and tons of other goodies since I re did it.

[hesamadman]

That was a good catch by SILVERGUN. Those sort of problems can follow you till the end of time.

Im using a single coil telecaster on it. In my hi gain input at larger volumes i get a high pitch squeal when not playing a note.

I think that may be normal amp/pickup behaviour.

Glad it's going and all the best.

Thought that could be too but havent had the issue with any other amps. Its like when you put a microphone close to a speaker. So it makes sense.

[eleventeen]

Fun thread. We got to hammer you, and it worked, LOL. Happy ending. As Larry David once said.

[SILVERGUN]

Hey HAMM (Hes A Mad Man),,,,congratulations again, and if you get a chance we'd all love to hear a clip...

At one time or another during the last couple weeks we have all mentioned the word schematic
There is one thing that I know we would all like you to take away from this....the value of that word
98% of the "regulars" here wouldn't start a new build without one....and we don't always understand everything we see either 

If you're planning on continuing this as a hobby it is a must that you'll be able to follow along with your schematic, right next to your layout....in this case, it would have led you right to your problem...

And now that you have a successful build under your belt, I would suggest taking the schematic and highlighting the circuit as you follow along on your layout, going back through this circuit slowly and meticulously, using a yellow highlighter marker to follow all of the paths,,,,and that will help you learn to read a schematic

Don't look at it as some type of way-too-complicated over-scientific map of the galaxy that you might never understand.......look at it for what it is, a simple cave-drawing of this connected to that, connected to that and so-on,,,,once that clicks, you'll never want to build from just a layout again

Rock on Sir,,,,I'm officially done hammering you about it......you did good

[eleventeen]

I will echo SILVER but I would suggest using a colored pencil....which you can erase if you go too far (meaning....extend a valid connection past the point where you have actually MADE it [during construction] or TRACED it [post-const] because you can't erase a highlighter...and you can make a colored pencil really, really light and of course erase it.

Same theory, though. 

Most of the veterans here, would NEVER use layout dwgs TO THE EXCLUSION OF schematics UNLESS they have a pre-made turret (or similar) board on which they are planning to build. Don't misinterpret what I am saying by thinking I'm saying "real men don't use layout dwgs". But there is a different mindset when it comes to working from a schem vs a layout. For example, take a res and a cap in series with nothing connected in the middle. On the schematic, this is a "nothing" connection. On the layout, it is two separate connections (2 turrets). On a terminal strip or point-to-point, one would just slam the parts in and move on. On the layout, the signal path take a back-and-forth path, and the parts occupy two "part spaces" unless you are piggybacking them. If you did not allow for the side-by-side "part spaces" (on a generic, non-specific-to-that circuit model) mental anguish results.

My only point is that a layout does not make it easy to "see" the circuit..it is more of a "paint by numbers" deal. You'll understand what you're building much more working from the schem, IMHO.