Marshall ish build issues

[Captain chunkulus]

Hey guys, can't seem to figure out what I've done wrong with this build. It's based loosely on a marshall jvm topology. I have been over every resister, capacitor, every wire, every pinout many many times and still cannot figure out what's wrong with the amp. I'm posting a link to a video of the issues. Any help would be great.

[Ritchie200]

Reverse the wires on your output transformer.

Jim

[Captain chunkulus]

Just tried that. No difference.

[Ritchie200]

Hard to see on the video, what configuration are your input jacks?  I thought I saw some holes.  Are they mounted up? Sorry I did not have the volume up enough on the first listen.  Almost sounds like a jack needs to be retentioned on the shorting lug.  Easy stuff first.  Could also be lead dress.  Is this a proven design?  Layout?

Jim

[Captain chunkulus]

Well, I had previously built this circuit and couldn't ever get rid of the hum so I rebuilt the preamp circuit and now it's doing what it's doing. When I get a chance, I will draw a schematic for the circuit and post it. I have tried several  different input options. It sounds somewhay like grounding issues but I haven't been able to find anything wrong. I have used a continuity meter and traced Eveything from point to point and Eveything is wired to the places they should be. Minus a few circuit tweets, this is pretty much a copy of the high gain marshall jvm circuit if that helps. I have tried using chop sticks while the amp is on to move signal wires around to see if something changed but little to no difference. 

[Ritchie200]

How many input jacks do you have?

Jim

[Captain chunkulus]

Just one. One Meg to ground, 1k, .047uf, 100pf to ground, 1 Meg to ground, 1k to input.

[Ritchie200]

FX loop?

Jim

[Captain chunkulus]

Input picture

[Captain chunkulus]

No effects loop yet. I wonder if the fact that I built the input circuit on a daughter board and ran wires to the fist stage has any bearing on this. I used shielded  guitat wire first but it doesn't seem to make any difference.

[Ritchie200]

Shouldn't be a problem.  I'm sure you checked your wiring on that board?  No bridges when you cut the board?  Are you going to a good ground?  I'm hoping someone else will jump in here!

Jim

[Ritchie200]

Sorry, I thought that was a strip board.

Jim

[Captain chunkulus]

No worries.lol. I'm sure my lead dress could be better but, this seems so much worse that just a lead dress problem. Like I said, I'll try to draw up a schematic for the circuit and post it in the next day or two.

[SILVERGUN]

Input picture

Just one. One Meg to ground, 1k, .047uf, 100pf to ground, 1 Meg to ground, 1k to input.

So, you brought the cathode resistor, cap, grid stopper(s)? from the preamp gain stage(s) over to that little board where your input jack is??
If so, where did you come up with that idea?

Ok, I found this in the schematics library....now I get it

[Captain chunkulus]

Yeah, that's the one.

[Captain chunkulus]

Like I said, I had it working before but could never completely  get rid of the hum so, I rebuilt the preamp. The power amp is exactly the same as it has always been since I first built it.

[Captain chunkulus]

Here's a little more info. I'm using a non center tapped tsl100 power transformer, a mercury magnetics super stack output transformer. The bias circuit is from a jcm900 amp. Using 22uf500v caps and 10k 2 watt resister on the power rail from the preamp except for the phase inverter which is tapped separately from the power supply with a 2 watt 22k resister and a 500v 47uf cap on its power rail. Pretty much just like the jvm. Since I'm only using 4 preamp tubes and not 5 like the jvm, there is one less cap and resister on the preamp power rail that the jvm has. The guitar input, preamp are grounded to a ground buss that connects to the speaker ground then to the ground lug on the power jack. The power supply is grounded via the center lug where  the 2 100ohm resister on the heater circuit goes to ground. Don't know if any of this helps or not.

[shooter]

The guitar input, preamp are grounded to a ground buss that connects to the speaker ground

take the speaker outta the loop, ground the preamp buss to the input jack ground tab, which should be chassis ground also, just further away than HT ground

[SILVERGUN]

The guitar input, preamp are grounded to a ground buss that connects to the speaker ground then to the ground lug on the power jack.

This sounds squirl'y. Try to isolate the preamp ground.

The power jack ground should only be connected to the chassis at a point that is very close to where it enters the chassis with it's own separate connection. (in theory)
It is a safety ground only and should not be confused with the circuit ground.

Take a look at the library for some grounding schemes and listen to shooter

[SILVERGUN]

It looks like you've got some serious wiring faux pas going on there

Whats happening with all of those green wires coming off of the cliff jacks?

[Captain chunkulus]

The green wire from the board is the -feedback wire going to the 16 ohm tap. The other great wires are going back to the output transformer 4 8 and 16 ohm taps. I just chose green for those runs because I had a lot of green wire laying around.

[SILVERGUN]

Some good old hi rez pics all around the inside of the chassis will be very helpful to anyone who is playing along,,,,even Jim

[Captain chunkulus]

Currently it looks like a rats nest because I've been rewiring stuff. However, I used shielding guitar cable from the input grounded on one end and the high pitched oscillation stoped.

[Captain chunkulus]

Okay here are some pics. One thing, the sound fades back in when you hit a chord. In other words sounds right but when you stop the hum fades back in almost like a compressor sound.

[Captain chunkulus]

More pics.

[Captain chunkulus]

Pics cont.

[Captain chunkulus]

More.

[Captain chunkulus]

Last note, all controls work as they should. Resonance, presence, eq. However, the gain pot seems strange,  it should completely mute the sound if turned all the way down but it allows a completely clean guitar sound through when turned off.

[SILVERGUN]

That sounds like a wiring error but without a working schematic we can't tell for sure. There are different ways to make gain controls.

[Captain chunkulus]

This is how it's wired.

[Captain chunkulus]

Okay, so comming off the 2.2 Meg it goes into the gain circuit then comes back in at the 2nd tube stage.tried to make connections on my phone in red..

[Captain chunkulus]

That sounds like a wiring error but without a working schematic we can't tell for sure. There are different ways to make gain controls.

I'm certain that I have stuff wrong.lol. any help from you amazing knowledgeable amp gurus is greatly  appreciated.

[SILVERGUN]

Take some time, edit the schematic so it accurately reflects what you have in front of you, and if you can't stay away, just continue looking for wiring errors.

[shooter]

Is this your basis for your amp;
http://el34world.com/charts/Schematics/files/marshall/Marshall_jvm410%20sch.pdf

have you pulled tubes 1 at a time starting with V1, then 2 then 3 till you only have PA tubes in?

and move the speaker ground out of the preamp

[Captain chunkulus]

Already moved the speaker ground. Lol. I was using a jcm800 2204 schematic for the grounding schem originally. My original video post however is no longer relevant because I figured out the main issues. #1 shielded guitar cable to the1st stage grounded at 1 end. 2nd had to reverse the two wires on the output transformer.  Now I'm left with just some sort of ground hum and the weird gain pot thing. Yes it's the jvm 410 or jvm210 schematic. I will try to get a modified schematic up over the weekend for what I changed. Haven't tried pulling tubes since after I found the other issues but will give it a try this evening.

[shooter]

it's the jvm 410

the schematic looks more like a EE grads final project trying to impress the teacher than a tube amp

[Captain chunkulus]

it's the jvm 410

the schematic looks more like a EE grads final project trying to impress the teacher than a tube amp

Right, lol. That's why I'm doing some things different.

[Ritchie200]

Some good old hi rez pics all around the inside of the chassis will be very helpful to anyone who is playing along,,,,even Jim

Hey Mr. Latetotheparty....  We were deep into it before you came waltzing along...  Real techs don't need no hi-rez pics!

Jim

[Ritchie200]

it's the jvm 410

the schematic looks more like a EE grads final project trying to impress the teacher than a tube amp

Man, I was thinking the same thing!  Although connectors and other details relevant to the layout is kind of nice - but does get cluttered.

Jim

[Ritchie200]

Captain

Just for giggles, try lifting your feedback.

Jim

[Captain chunkulus]

Captain

Just for giggles, try lifting your feedback.

Jim

I will when I get home this evening. Btw Jim, thanks so much for being patient with me. I love learning about this stuff and building stuff. The first build I did was with my Dad. We built a delux reverb with a full eq. This is my first real serious  build by myself. I taught myself how to read schematics and have been reading lots of books. I have a copy of the tube amp book ( that's where I started) mullard circuits for tube amps and several others. Haven't been doing this very long. I just love it! Tube technology fascinates me. 

[Ritchie200]

Hey I learn something new every time I come here!  This is a cool hobby and this forum is the best place on the planet to learn.  Other than Silvergun and Jojo, and... we are all nice people!

The first modification I ever did was with my dad converting a mono hi-fi tube amp for guitar back in the 60's.  Great memories.  Don't forget to thank Pops for your current obsession!

Jim

[Captain chunkulus]

Indeed! My dad got me into electronics  when I was about 9 or 10 years old. He used to work for a company called Valley People here in nashville tn. I helped him populate the pc boards as a sub contractor. They didn't know it was a kid building the stuff at home, my dad would pay me like .25 a board. Gain brains, kepex's etc.

[shooter]

My dad got me into electronics 

Same here, my dad was a recovering alcoholic , he was working with/for Goodwill fixing broke TV's n radios.
he taught me to solder, then shag tubes to the local shop to test, pretty soon I was running test patterns n tweaking color guns
Guess what you HAVE to do in the future

[Captain chunkulus]

Captain

Just for giggles, try lifting your feedback.

Jim

Tried the feedback wire, not that. It's really weird, I can turn the gain all the way down and the channel volune as well but I'm still getting signal at the phase inverter.

[Ritchie200]

I think at this point we need you to draw up a schematic of exactly what you have.  You mentioned that you checked and double checked your wiring and components. We need to see your design.

Jim

[Captain chunkulus]

I think at this point we need you to draw up a schematic of exactly what you have.  You mentioned that you checked and double checked your wiring and components. We need to see your design.

Jim

Well, it's not really my design. I'm working off of a jvm 410 schematic. Only real changes are plate resister values. Cathode bypass caps, bias voltage circuit and the addition of a dc heater circuit for the first two tubes. This is a one channel amp, no switching or reverb or effects loop as of yet. I can upload a schematic of the jvm with what values I changed and the bias circuit as well as the DC heater circuit.

[Captain chunkulus]

Don't know if this helps or not. 

[Captain chunkulus]

Pics

[Captain chunkulus]

Pics