ground loop issues

[ang3lus]

so with some magnifiers i.traced the.gnd connection.here and.this.what ive found

that is suppoaed to be a gnd right ? its corroded and doesnt read back to the black wire gnd, should ijust run a wire and thats it or.bad things will happen?

[ang3lus]

ok so i connected a trace

everything works now !!!!  :banana-jazz-smiley-emoticon: :banana-jazz-smiley-emoticon: :banana-jazz-smiley-emoticon: :banana-jazz-smiley-emoticon: :whoohoo!: :whoohoo!: :whoohoo!: :whoohoo!: :whoohoo!: :headbanger: :headbanger: :headbanger: :headbanger: :headbanger: :headbanger: :headbanger: :headbanger:

thank you guys so much for the tips, i would have never found it.

funny thing about PCBs, if this was a turret or tag board tube amp the first thing i would have checked with no output is the jack and GND connections from that jack, i trust PCBs so much that i would never have thought of that... go figure

[Rusty]

Could be a dry joint.

Have you tested for continuity


Check all the tracks too, meter them from point to point per component as per schem.


F,    nice to hear the good news and hopefully I gave you a hand on the way,

Keep her lit sir, and enjoy the new ADA experience,     :thumb-up:

[rnolan]

 :whoohoo!: :thumb-up:

[ang3lus]

Rusty, that's the thing, i did test for all joints, right up to the jack and also the input jack TIP, when that worked i think i figured (probably and mistakenly) that the GND jack works too... lesson learned

[Rusty]

Could be a dry joint.

Have you tested for continuity


Check all the tracks too, meter them from point to point per component as per schem.


F,    nice to hear the good news and hopefully I gave you a hand on the way,

Keep her lit sir, and enjoy the new ADA experience,     :thumb-up:

Great news,

Give us the ADA gossip, we need new blood, kinda gets slow sometimes ?   ;D

[MarshallJMP]

Well done! Must say never encountered this problem before, so good to know.

[Rusty]

the wiring harness i have has the red wire cut, and i searched on the forum and saw this is a factory upgrade, probably to prevent loops ?

so i jumpered it to GND and BAAAAM, sound, clear and beautiful and POT works beautifully.

but if i don't need to have gnd refrence from the cut wire, where should i be getting the GND refrence ? is there another component bad somewhere ? or a trace that lost its gnd ?

Hey ang3lus

I would just like to say,

In many digital audio digital pieces of equipment, quite often ground is whats called a floating ground, hence; not directly connected to mainsground/earth.

Even though the schematic provides you with a ground symbol sign on the diagram.

The reasons; to cut down back round noise.

Very often this so called ground/earth is lifted up by a 10 ohm resistor in the circuit.

Why ?   well,  Im not a circuit design engineer,  but MJMP is,  so I cannot go any further on that one,  I would love some education on that if MJMP would share those reasons why that is the way some audio equipment is like that.

Please MJMP, light us up ?   ;)



ang3lus, I'm delighted you got that sorted out.

You obviously have good skills in your mind and hands. Please stay in touch and give us all of the new ADA news,   :bow:

[ang3lus]

thanks rusty, im educated electronically, as a technichan though,.beinv fasicinated with guitars i started building amps, usually high gain stuff, the ada intrigued me immensly, so i boughttgis unit in unworking condition for 70 bucks... just had the time now to see whata going on.

im so glad this is working, as i have big plans for this unit,.it looks fun and convinient

[MarshallJMP]

Well the V2 (hardware version) MP-1 has a 10 ohm resistor between circuit ground and earth, the V1 the earth and ground are connected through the starground. You can see on a V1 that the earth wire is directly connected to the starground and the 15V regulator (7815) is not isolated from the chassis. On the V2 the 7815 is isolated from the chassis and the earth wire is directly connected to the chassis. On the midi board is a earth wire (green) connected to one of the chassis screws that holds the midi board in place and the other side goes to the pcb, there it is connected with a 10 ohm resistor to the signal ground. You will also see that the red wire is connected to the red connector near the front vol pot. On the V1 this wire is cut (although on some very old V1's it's connected). The Mp-2 has a 4.7 ohm resistor. The classic has a 4.7 ohm resistor with a 0.1µF cap in parallel. MB-1 has a 10 ohm. I took a few pics and made a quick PDF file of the differences.

What the 10 ohm resistor does is reducing ground loop currents when a ground loop is created. In modern designs you will also see a cap in parallel with the this resistor, this ensures that ground has a low impedance pad to earth for high frequencies. Next you will sometimes also see 2 diodes in anti parallel over this cap and resistor. This is to bypass more high amp fault currents (which could burn the resistor open). These will only kick in if the voltage over the resistor is bigger than 0.6V so small hum voltages will still be blocked.

A floating ground can not be done anymore (CE), they do allow the 10 (4.7) ohm thing with the cap and diodes.

So the chassis is STILL directly connected to the earth so don't put a resistor between the earth line and the chassis, or even worse cut the earth connection!!! Safety first.
And of course make sure you have a decent earth connection in your house with a resistance lower than 25 ohms. An earth leakage circuit breaker also helps too keep everything safe. My work space and rehearsal room each have a 30mA type.

[Rusty]

To MJMP,

Thank you so much for that powerful in-depth detailed information about the ground loop circuit technique thing.

Very, very well explained MJMP I must say.

Thank you so much for that sir.   :thumb-up:

[MarshallJMP]

No problem  :thumb-up: