Advice needed...

[TriodeLuvr]

No, that's not what he means. Only the cap(s) for the power amp section go to the main star ground (a shared lead is fine if they're going to the same place). The other cap(s) go where they're filtering. For example, it looks like two of the caps are filtering the power amplifier, and one is filtering the preamp. That preamp filter cap should be grounded in the preamp section, along with the preamp, pots, and input jack.

Thanks,
Josh

That's a little confusing. All those caps must somehow have their negative terminals connected to the negative output of the power supply. That's the return path for the DC differential. A ground loop can be created if the caps share the same conductor, whether it's a single wire or the chassis. However, running a separate wire from each cap's negative terminal back to the star prevents that. Once that's done, the negative terminal of the preamp bypass cap serves as a local ground. All grounds within the preamp circuit should be connected there. I think the OP has done this correctly and it won't be a problem.

Jack

[JMPGuitars]

That's a little confusing. All those caps must somehow have their negative terminals connected to the negative output of the power supply. That's the return path for the DC differential. A ground loop can be created if the caps share the same conductor, whether it's a single wire or the chassis. However, running a separate wire from each cap's negative terminal back to the star prevents that. Once that's done, the negative terminal of the preamp bypass cap serves as a local ground. All grounds within the preamp circuit should be connected there. I think the OP has done this correctly and it won't be a problem.

Jack

Yeah, it can be confusing discussing it in text, that's why I have the diagram linked in the grounding thread.

[The4thWatcher13]

\Each cap get's it's own lead to the "star" ground.

No, that's not what he means. Only the cap(s) for the power amp section go to the main star ground (a shared lead is fine if they're going to the same place). The other cap(s) go where they're filtering. For example, it looks like two of the caps are filtering the power amplifier, and one is filtering the preamp. That preamp filter cap should be grounded in the preamp section, along with the preamp, pots, and input jack. Thanks, Josh

[My page loaded slowly so I missed Jack's replay to Josh.
Below is my reply to Josh's correction of my interpretation.]

I think I get what you're saying. I've got three caps;
C3-A is a smoothing cap and only connects to the next two caps, C3-B goes to the power amp section (Plate winding CT, Screens & filament CT for ground elevation)
C3-C is both preamp tubes plate supply. So C3-C gets grounded with the pre tubes and input on a separate ground "up front".
C3-B (power amp)goes to the main star ground so would the smoothing cap also go to the main star ground or can it be strapped to C3-B?

That's a little confusing. All those caps must somehow have their negative terminals connected to the negative output of the power supply. That's the return path for the DC differential. A ground loop can be created if the caps share the same conductor, whether it's a single wire or the chassis. However, running a separate wire from each cap's negative terminal back to the star prevents that. Once that's done, the negative terminal of the preamp bypass cap serves as a local ground. All grounds within the preamp circuit should be connected there. I think the OP has done this correctly and it won't be a problem. Jack

The way Jack describes it is how I actually reconfigured the PS ground scheme last night. All three caps have a separate lead to the star ground and the input jack is to be grounded at a separate point. But Apparently, from Josh's viewpoint, I made a mistake in my interpretation, and therefore now I'm rather confused. So I defer to my reply and question, to Josh, about what he was describing in his post above. [The schematic below hasn't been changed: it's just there for your convenience]

[JMPGuitars]

But Apparently, from Josh's viewpoint, I made a mistake in my interpretation, and therefore now I'm rather confused. So I defer to my reply and question, to Josh, about what he was describing in his post above. [The schematic below hasn't been changed: it's just there for your convenience]

The schematic doesn't need to change, it's simply the location of the preamp filter cap ground that moves, which is a layout change only.

As Zaphod_Phil mentioned previously, look at my grounding scheme thread (link in my signature).

Jack mentioned the grounds all returning to the OT negative terminal (which connects to the star ground). But this only applies to the power amp section. Since the preamp filter cap is filtering the preamp, and the preamp is grounded elsewhere, you're creating a potential ground potential by not grounding that filter cap with the preamp. This means that you put your amp at risk for parasitic oscillations and unwanted noise. Sometimes you can get away with the star ground as you have it, but it's not a good idea. A PTP build like this, you need to take precautions to avoid noise, as PTP can be much harder to deal with than using a circuit board.

This is the layout referenced in my ground thread: files/JMPGuitars_18_Watt_Lite_2b_Layout.pdf

You can see how the preamp grounds all go to the input jack ground terminal, which is then connected to it's own grounding point.

Thanks,
Josh

[TriodeLuvr]

Since the preamp filter cap is filtering the preamp, and the preamp is grounded elsewhere...

Grounded elsewhere? It shouldn't be. All the preamp circuitry, including the sleeve of the input jack, should be grounded only to the preamp bypass cap negative terminal. Grounding in more than one location is practically the definition of a ground loop.

Jack

[The4thWatcher13]

The schematic doesn't need to change, it's simply the location of the preamp filter cap ground that moves, which is a layout change only.
As Zaphod_Phil mentioned previously, look at my grounding scheme thread (link in my signature).
Jack mentioned the grounds all returning to the OT negative terminal (which connects to the star ground). But this only applies to the power amp section. Since the preamp filter cap is filtering the preamp, and the preamp is grounded elsewhere, you're creating a potential ground potential by not grounding that filter cap with the preamp. This means that you put your amp at risk for parasitic oscillations and unwanted noise. Sometimes you can get away with the star ground as you have it, but it's not a good idea. A PTP build like this, you need to take precautions to avoid noise, as PTP can be much harder to deal with than using a circuit board.
This is the layout referenced in my ground thread: files/JMPGuitars_18_Watt_Lite_2b_Layout.pdf
You can see how the preamp grounds all go to the input jack ground terminal, which is then connected to it's own grounding point.
Thanks, Josh

Thank you, Josh, I think we're on the same page. And thanks for taking the time to explain a little better what you...eh..explained before! I've sent the C3-C cap (far left) ground to a common preamp/jack ground point. Although I did have to physically elevate it a little to evade heater wires and an excessively long run. Now all of the preamp circuit has it's own ground point and the power supply/ power amp has it's own. Although it looks a bit funny I've changed the schematic to reflect this. Hopefully this will be OK.

[TriodeLuvr]

This is all you need to do. Not sure what you've changed, but I think it was correct, except for maybe the ground to the input jack.



Jack

[JMPGuitars]

Since the preamp filter cap is filtering the preamp, and the preamp is grounded elsewhere...

Grounded elsewhere? It shouldn't be. All the preamp circuitry, including the sleeve of the input jack, should be grounded only to the preamp bypass cap negative terminal. Grounding in more than one location is practically the definition of a ground loop.

Jack

Elsewhere compared to the power amp star ground. Look at my layout for reference: files/JMPGuitars_18_Watt_Lite_2b_Layout.pdf

Pictures and words and whatnot.

Thanks,
Josh

[JMPGuitars]

This is all you need to do. Not sure what you've changed, but I think it was correct, except for maybe the ground to the input jack.



Jack

No. Absolutely not. That preamp filter cap should NOT be touching the power amp star ground.

Thanks,
Josh

[JMPGuitars]

Thank you, Josh, I think we're on the same page. And thanks for taking the time to explain a little better what you...eh..explained before! I've sent the C3-C cap (far left) ground to a common preamp/jack ground point. Although I did have to physically elevate it a little to evade heater wires and an excessively long run. Now all of the preamp circuit has it's own ground point and the power supply/ power amp has it's own. Although it looks a bit funny I've changed the schematic to reflect this. Hopefully this will be OK.

There was no need to change the schematic, it was fine. It's really only a layout change. I can understand wanting it to reflect the location of the ground, but schematics don't tell much for location regardless.

The only question now is if your ground lead is too long due to its location. It might be fine considering how small the whole amp is, but if it turns into an antenna, then you may want to relocate that cap closer to where it should be. Ideally, the filter cap should be next to the cathode cap for the stage it's filtering.

Thanks,
Josh

[TriodeLuvr]

This is all you need to do. Not sure what you've changed, but I think it was correct, except for maybe the ground to the input jack.



Jack

No. Absolutely not. That preamp filter cap should NOT be touching the power amp star ground.

Thanks,
Josh

If the negative terminal wasn't connected to ground, the preamp wouldn't have power. And if the various stages aren't connected to the common point, it wouldn't be a star ground. Just to be clear, the "GND" label in the preamp box is just a label. The preamp is grounded only at the star, and only the star is connected to the chassis.

Anyway, this is how you eliminate the possibility of a ground loop. The ground current of each stage is separate from the ground current to the power stage. You can wire as many stages as you want using this method without worry. The guitar amp I posted here used this method for four sections. No hum, no oscillations.

Jack

[JMPGuitars]

If the negative terminal wasn't connected to ground, the preamp wouldn't have power. And if the various stages aren't connected to the common point, it wouldn't be a star ground. Just to be clear, the "GND" label in the preamp box is just a label. The preamp is grounded only at the star, and only the star is connected to the chassis.

Anyway, this is how you eliminate the possibility of a ground loop. The ground current of each stage is separate from the ground current to the power stage. You can wire as many stages as you want using this method without worry. The guitar amp I posted here used this method for four sections. No hum, no oscillations.

Jack

What you're saying is not best practice for guitar amps. Review the layout I linked. That's best practice. files/JMPGuitars_18_Watt_Lite_2b_Layout.pdf

That layout is based on my and Zaphod_Phil's grounding schemes.

You can also read Aiken go into more depth about it: https://www.aikenamps.com/index.php/grounding

And here's Merlin's thoughts on the subject: http://www.valvewizard.co.uk/Grounding.html

Thanks,
Josh

[TriodeLuvr]

Josh, I just want to be sure there's no mistake about what I'm saying. The diagram below is somewhat more definitive than my previous hand sketch. Wiring in this way can not create a ground loop. I'll just add that I've read your treatise on this subject, but I found it confusing. I'm only weighing in here in an effort to simply it for the OP. If you think there's something wrong with this technique, you'll need to tell me what and why. I've used it in wiring countless amps and preamps, as have many other builders.



Jack

[TriodeLuvr]

Josh, just as background, I recently retired from my engineering job of more than 15 years designing and testing low noise amplifiers, filters, mixers, etc. The work involved high gain circuitry from audio to tens of GHz. Audio circuitry involved input-referred noise levels of less than 1nV/√Hz, and RF products approaching noise levels of -180 dBC. This is several orders of magnitude better than anything that can be achieved with tubes. Please believe I understand grounding. You don't need to refer me to online references on this topic.

Jack

[JMPGuitars]

Josh, I just want to be sure there's no mistake about what I'm saying. The diagram below is somewhat more definitive than my previous hand sketch. Wiring in this way can not create a ground loop. I'll just add that I've read your treatise on this subject, but I found it confusing. I'm only weighing in here in an effort to simply it for the OP. If you think there's something wrong with this technique, you'll need to tell me what and why. I've used it in wiring countless amps and preamps, as have many other builders.

Jack

the links I provided above, Aiken goes into more depth about it.

One of the reasons I personally have always separated the preamp from the power amp grounds is because if you try to use a single star ground, and you turn up the master and preamp gain/volume knobs, you will most likely get loud/high pitched squeals. Separating the stage grounds eliminates that. I've experienced this on multiple amps that I repaired by applying similar ground schemes to my thread.

Obviously that's not as relevant in a HiFi amp. I know you have a background related to this, but it's actually holding you back in this regard. You should be more open to reading other opinions about it. Zaphod_Phil, Aiken, valvewizard etc... have extensive EE backgrounds as well, but also far more relevant guitar amp experience, as ZP mentioned, the rules are different here. I'm just sharing what I've learned from them, both in theory and practice.

Thanks,
Josh

[TriodeLuvr]

One of the reasons I personally have always separated the preamp from the power amp grounds is because if you try to use a single star ground, and you turn up the master and preamp gain/volume knobs, you will most likely get loud/high pitched squeals.

The diagram I posted separates the preamp ground from the power amp.

I also want to point out that this has nothing to do with hi-fi vs guitar. Constantly falling back on that refrain whenever there's a disagreement is disrespectful, and it's a disservice to other readers. I make a concerted effort to provide data and reasoning to make my points. It would be appreciated if you would do the same. Also, if experts you respect have published theories that contradict my position, please quote the specifics. I don't have time to read an entire paper for the purpose of guessing which part you consider relevant.

I'll add here that I do value your experience in this genre of electronics. Your wisdom regarding tone, distortion, speakers, etc. etc. is substantial and very welcome. I only ask that you not assume the areas of expertise I bring to the table are any less important or correct.

Jack

[The4thWatcher13]

Wow, I love listening to you guys! Your experience in all associated fields is a benefit to us all. As this pertains to my current project the difference seems to come down to one wire, the pre section filter cap ground. The question: whether it goes to the star or to a separate input/preamp ground. I had it Jack's way at first with all PS caps grounded to the star and then I changed it to Josh's. For me, it's an easy enough fix if, for some reason, it should go back to the star.
So, I got some slow blow 1.6A & 2A fuses from the HW store yesterday and I'll try them with the power tubes removed per Jacks suggestion and we'll see what we get. I'll be back in a couple. Gotta do some quick yard work in 87deg heat. Michigan switches from spring to summer instantly, usually, and it's always a pain.
Oh, and thanks again, you guys, for your input. I really appreciate it.

[JMPGuitars]

The diagram I posted separates the preamp ground from the power amp.

I also want to point out that this has nothing to do with hi-fi vs guitar. Constantly falling back on that refrain whenever there's a disagreement is disrespectful, and it's a disservice to other readers. I make a concerted effort to provide data and reasoning to make my points. It would be appreciated if you would do the same. Also, if experts you respect have published theories that contradict my position, please quote the specifics. I don't have time to read an entire paper for the purpose of guessing which part you consider relevant.

I'll add here that I do value your experience in this genre of electronics. Your wisdom regarding tone, distortion, speakers, etc. etc. is substantial and very welcome. I only ask that you not assume the areas of expertise I bring to the table are any less important or correct.

Jack

The diagram you supplied shows the filter cap for the preamp going to the star ground, and that's the problem. That filter cap should be grounded with the preamp ground, and only at that point.

My referencing your HiFi experience isn't intended as a slight, so don't take it as such. I only mentioned that at all because it would be highly unlikely that you would recreate the issue I mentioned previously with a HiFi amp. Guitars go for dirt, HiFi doesn't, so HiFi amps aren't going to push the amp to a point where that situation would arise. As I mentioned previously, I will be picking your brain in the future when I'm ready to build a HiFi project. Though I do understand how reading text on the web makes it hard to discern whether something has a "tone" or not, and please understand that was never my intention, as I do very much respect you.

the Aiken link. It's not that long, shorter than this conversation so far, and he covers the details well. Otherwise, I would just be copying the page and pasting it here, which isn't appropriate. He's a well respected guru, and deserves the internet traffic. Given your background, I know you will understand his article better than I do anyway.

Thanks,
Josh

[The4thWatcher13]

I've come across the Aiken site too in my collecting of credible practice references. As I progress with my amp I found one last 1.25A slow blow fuse (and I have actually been using Littlefuse slow blow fuses from the start (apologies)..and I started the amp up without the two power amp tubes. I'm using a Kil-A-Watt meter to measure current. The current went quickly up to 2.35A and I shut it off. I tried it again 30 seconds later and the 1.25A fuse blew. I also have some 1.6A and 2A slo-blow fuses. I've been going over the schematic and build looking for mistakes and such but haven't found any as of yet.

[TriodeLuvr]

The diagram you supplied shows the filter cap for the preamp going to the star ground, and that's the problem. That filter cap should be grounded with the preamp ground, and only at that point.

OK, let's work on that. Unless the point within the preamp that's designated "ground" is connected to the negative output of the power supply - in this case, the star ground - the preamp can't draw the DC current it needs to function. Do you agree or disagree with this?

Jack