Hello! I'm not building a guitar amplifier yet, but I've built a few guitar pedals before and would like to get started with some of the theory behind amplifiers. Since I've only worked with unipolar DC power where you only have to worry about 2 poles (where chassis and signal ground are combined), I have a question regarding 3 pole power from an IEC jack.
From what I've understood, the earth/ground connection on the IEC jack is mainly used for chassis grounding. Does that mean the neutral connection (on the secondary side of the transformer) acts as the signal/power ground? This is how I've understood it, but when I check continuity between the ground connections on the 1/4" jacks and the earth pin on the IEC jack, it turns out they're actually connected while the jack ground isn't connected to neutral. This seems like such a simple thing to grasp, but I'm really having trouble finding any information on it. Please help!
Thank you!
IEC jack signal/chassis ground
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ajaxlepinski
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Re: IEC jack signal/chassis ground
Welcome to the fold brother! This is the best guitar/amp forum on the interwebznet!!! 
There are a few guys on the forum who are very knowledgeable about amp design and repair.
I'm sure they will chime in, over the next day or so.
I started studying amp repair about 2 years ago and I've yet to grasp the ins-and-outs of grounding schemes.
Grounding design is strange alchemy.
There are a few guys on the forum who are very knowledgeable about amp design and repair.
I'm sure they will chime in, over the next day or so.
I started studying amp repair about 2 years ago and I've yet to grasp the ins-and-outs of grounding schemes.
Grounding design is strange alchemy.
1969 Sunn Solarus ● 2x 1980's Randall RG-80 ● 2013 Hi-Tone HT103-DG (Best Rig 2014) ● 2015 Mortatone 12/15 Cab w/EV SRO's ● 2017 Jubilee ● 2019 Ceriatone Model Tee ● 2019 Randall Diavlo ● 2020 VHT D50 Dumble Clone
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Re: IEC jack signal/chassis ground
This explains pretty much everything you'd want to know about grounding: http://valvewizard.co.uk/Grounding.pdf
The outlet ground is safety ground. This should be made securely on the chassis as close to the IEC socket as possible on it's own screw, and not as part of some other assembly, i.e., the transformer bolt as seen on some old amps. This is there to act as ground path in the event of a catastrophic failure, such as the B+ or an AC winding shorting on the chassis, stopping the chassis from becoming live. Fun fact; before anyone gave a shit it was perfectly legal to sell radios and the such with a hot chassis and shocks were common.
The neutral is part of the AC along with the live. The important thing to grasp is that the AC goes through a transformer to step the voltage up and then by means of diodes or a tube, is then rectified to DC. This DC voltage is then referenced to some other DC voltage. Usually 0V though another ground connection, usually close to the signal input.
The pdf I linked to above does a much better job of explaining this and there are many ways of doing it. I follow the ground plan outlined here and usually end up with pretty quiet and safe builds.
The outlet ground is safety ground. This should be made securely on the chassis as close to the IEC socket as possible on it's own screw, and not as part of some other assembly, i.e., the transformer bolt as seen on some old amps. This is there to act as ground path in the event of a catastrophic failure, such as the B+ or an AC winding shorting on the chassis, stopping the chassis from becoming live. Fun fact; before anyone gave a shit it was perfectly legal to sell radios and the such with a hot chassis and shocks were common.
The neutral is part of the AC along with the live. The important thing to grasp is that the AC goes through a transformer to step the voltage up and then by means of diodes or a tube, is then rectified to DC. This DC voltage is then referenced to some other DC voltage. Usually 0V though another ground connection, usually close to the signal input.
The pdf I linked to above does a much better job of explaining this and there are many ways of doing it. I follow the ground plan outlined here and usually end up with pretty quiet and safe builds.
Loop wrote:I’m currently shopping for a 1996 Red Dodge Viper with yellow wheels. Who gives a shit about taste?!
Re: IEC jack signal/chassis ground
ajaxlepinski wrote:Welcome to the fold brother! This is the best guitar/amp forum on the interwebznet!!!
There are a few guys on the forum who are very knowledgeable about amp design and repair.
I'm sure they will chime in, over the next day or so.
I started studying amp repair about 2 years ago and I've yet to grasp the ins-and-outs of grounding schemes.
Grounding design is strange alchemy.
Thank you!
You're right. Grounding is an artform in its own right.Zozobra wrote:This explains pretty much everything you'd want to know about grounding: http://valvewizard.co.uk/Grounding.pdf
etc
Thank you for the link and explanation. I've read parts of that pdf before, but I'll take a look at it again.
I continued checking the continuity in one of my amplifiers and the image below showcases how the ground seems to be connected. Sorry for the rough sketch. I don't have access to a computer atm.
As you can see, the earth pin on the IEC jack and the neutral on the secondary side of the transformer are both connected to the chassis and circuit ground. Is this a good way to do it? The amp is a discontinued, but still pretty modern transistor amplifier.
Re: IEC jack signal/chassis ground
Ok, so to simplify the question a little bit, do you use the neutral connection from the transformer secondary as the circuit ground?
Re: IEC jack signal/chassis ground
No. It's not especially useful to think of the secondary as having a live and neutral. You need to ground the DC reference, which then acts as the ground reference for the amp.
You may find this better for your needs as it's specifically about solid state amps:
http://www.thatraymond.com/downloads/so ... a_v1.0.pdf
It's a bit slow moving but this is a good forum on SS design/repair:
https://www.ssguitar.com/index.php
You may find this better for your needs as it's specifically about solid state amps:
http://www.thatraymond.com/downloads/so ... a_v1.0.pdf
It's a bit slow moving but this is a good forum on SS design/repair:
https://www.ssguitar.com/index.php
Loop wrote:I’m currently shopping for a 1996 Red Dodge Viper with yellow wheels. Who gives a shit about taste?!
Re: IEC jack signal/chassis ground
Zozobra wrote:No. It's not especially useful to think of the secondary as having a live and neutral. You need to ground the DC reference, which then acts as the ground reference for the amp.
You may find this better for your needs as it's specifically about solid state amps:
http://www.thatraymond.com/downloads/so ... a_v1.0.pdf
It's a bit slow moving but this is a good forum on SS design/repair:
https://www.ssguitar.com/index.php
Thank you for the links! I'm not entirely sure what you mean by DC reference, but I'll read at least the power supply chapter of the PDF soon and see if I can figure it out. Unfortunately I'm in the middle of a move right now, so I don't really have time for it now.