Questions on implementing a star ground

[markmalin]

Hey guys!
In hopes to quiet down my AC30 build, I’m going to try a “star” ground and would like your input on whether this makes sense.  Doug’s layout separates things nicely, so here’s what I’m thinking:


1. Isolated input jacks, with the ring connection tied directly to the pre-amp “buss” area (white line in drawing is ground buss, green arrow shows single wire from input jacks to that buss)
2. I have a buss wire to the volume/tone control grounds (white). I’ll use a single wire from there to the “star” point (green wire in drawing)
3. The “preamp bus” (D and E on supply – white line in drawing) will have a single wire back to the star.
4. The power amp and PI bus (white line) will have a single wire back to the star
5. The filter caps are separated so A will have a single ground wire to the star (green line), B and C will be tied together at ground and a single wire to the star (green wire) and the same with D and E
6. The Star will have the PT center taps (heater center and power center).
7. The safety ground will be tied from the mains jack to a nut next to the jack

Some things I’m not sure about:

1. The output jacks are not isolated, I have the ground side of the OT running to the ring terminal on these, do I need to run a wire from there all the way back to the star??
2. The way the chassis is laid out, there are terminals to the right where A and B supplies come in.  There is a choke between A and B, and A has the OT center tap tied to it.  Physically what I did was run the choke wires to these terminals (blue circles in drawing) and ran the OT center tap to the A terminal here.  Would it have been better to run the choke and the CT wire all the way back to the power supply filter board and attach them directly to the caps’ eyelets??  Does that really make any difference?

Thanks guys!
humbly,

Mark.

[Willabe]

Doug’s layout separates things nicely,

Did you use Doug's layout or did you change it?

[markmalin]

Doug’s layout separates things nicely,

Did you use Doug's layout or did you change it?

It's Doug's layout pretty much, but it's changed somewhat.  There were some things that were not clear and I may have made some bad choices due to not understanding.  For example:

(this is long...sorry... )

- he uses a ground buss, it's not clear whether it's soldered to the back of the pots.  Reading, I found that's a no-no and used a ground wire to the ground connections of the volume/tone controls which I've done before, ran that to the shield of the non-isolated input jacks, then to a ground point.  Then, for the pre-amp buss I ran a wire to that same point.  But now that's modified because I'm going to isolated jacks to see if it will help with hiss, so I separated that wire on the pots and need to tie to a good ground point.
- Doug uses a single ground buss for the PI and cathode bias resistor(s).  I added a half power switch which grounds the inputs to 2 EL84's and originally tied it to that bus, but in another thread it was suggested to separate that, connect part of it to the buss on the pots, and the other half (with the cathode resistor) to the star and tie the EL84 inputs to that ground when the 2 tubes are turned off.
- Dough had all 5 filter caps on a buss, and tied to the power supply ground point.  I've just separated it into three segments, A, B-C, and D-E, and would run individual wires to the star.

Basically I'm trying to use Doug's original setup, but with isolated input jacks, then run each buss section separately back to one ground point.

I did some reading and thought I understood it was best to separate these out.  I'm probably in over my head, but this hiss problem is kicking my back-side.  Here was my thought process:

I'll try isolated input jacks to see if that helped the hiss, but what do I do with the wire on the pots' grounds?  Tie that to the chassis by itself?  Where do I run the common side of the input jacks??  Reading I find I should run them right to the ground buss section for the pre-amp...but then how do I tie that buss to ground?  Do I run a wire all the way to a single lug and make this a star ground?  And then...why not run the ground for the pots to that same single star point?  And if I'm doing that, why not separate out the filter caps so that the first one (A) is tied directly to the star?...

Much reading, cursing, pulling of hair, breathing solder flux ensued and this is where I'm at.

So basically it's now like Doug's, but with isolated jacks which gives me a dangling wire across the pots and I'm not sure where to attach that.  And being at this point, it seems straight forward to make a star ground out of this.  So I drew some things out on that picture and am wondering if I'm heading in the right direction.   

[PRR]

> hiss problem is kicking my

Hiss is not a grounding problem.

[markmalin]

> hiss problem is kicking my

Hiss is not a grounding problem.

I guess that's good to know, but I'm running out of ideas on the hiss.  Here's a link to the thread, PRR. 
http://el34world.com/Forum/index.php?topic=18898.msg194412#msg194412
The thing I wanted to try with this exercise was to use isolated input jacks.  With a listening amp I can hear the hiss right at the plate of the first gain stage in channel 2 (the one with the tone stack).  It increases in gain with gain stages from there.  I just want to rule out isolating the input jacks, and it's not a bad thing to do anyway from what I can tell.

[John]

You've already replaced the plate resistors I think? And checked the solder joints on them too.


The hiss is getting amplified at each gain stage of course....


And I think you already swapped out tubes with known good ones.


Isolating the jacks is a "hum fix" thing, I believe. But, won't hurt anything.


Just remind yourself that it's good getting lots of practice on desoldering! It's kept me sane a few times. 

[shooter]

output jacks are not isolated, I have the ground side of the OT running to the ring terminal on these

I have never run a ground to my output jack(spkr).  I DO ohm it to chassis ground and make sure it's zero.  I run my OT output common directly to the main star point.  not sure this is best practice, it's just one less wire

[Fresh_Start]

Sounds like the original layout had the input jacks grounded directly to the chassis and to a ground wire. That may not be causing hiss, but it is a ground loop.

Please read Merlin's essay which drgonzohm linked to. Several times. That galactic grounding scheme works.

So does Hoffman's. Here are two links from his Library that might help:

http://el34world.com/charts/currentflow.htm

http://el34world.com/charts/grounds.htm


If you study Doug's grounding approach carefully, you'll see that it's close to a "galactic star" except that the big currents from the speaker jacks and power amp are grounded away from the preamp ground. 


Hope this helps,
Chip

[markmalin]

You've already replaced the plate resistors I think? And checked the solder joints on them too.

Right.  In fact, replaced all the carbon comps with Vishay/Dale metal film. I've re-soldered just about every joint as I'm swapping parts in and out.  I can check to see if I've missed anything

The hiss is getting amplified at each gain stage of course....

right.  I can hear it faintly with my listening amp at the plate of V1.  By the time it exits the cathode follower it's wonderful white noise ;)

And I think you already swapped out tubes with known good ones.

Yes, I swapped the pre-amp tubes with several other sets, one out of a quiet amp.

Isolating the jacks is a "hum fix" thing, I believe. But, won't hurt anything.
Just remind yourself that it's good getting lots of practice on desoldering! It's kept me sane a few times. 

lol.  Yah, I think I finally wore out my solder sucker.  I've had that thing for 10 years!

[markmalin]

Hi Chip!  Nice to hear from you :)
I printed out Merlin's essay.  I'll pick through that this weekend.


In the mean time I did go forward and do more of a star ground like I was describing above.  The amp hums about like it used to so nothing gained nothing lost.  May be a little more hummy, but then again it's quiet here tonight.  My main concern is really this his (see the other thread).  I can live with the mild hum, but that his is just not acceptable.  I'm beginning to wonder if I've done something really stupid and obvious that I can't see because I've been staring at it too much.  But I'll leave that for my other thread post rather than get this one off track.
Mark.

Sounds like the original layout had the input jacks grounded directly to the chassis and to a ground wire. That may not be causing hiss, but it is a ground loop.

Please read Merlin's essay which drgonzohm linked to. Several times. That galactic grounding scheme works.

So does Hoffman's. Here are two links from his Library that might help:

http://el34world.com/charts/currentflow.htm

http://el34world.com/charts/grounds.htm

If you study Doug's grounding approach carefully, you'll see that it's close to a "galactic star" except that the big currents from the speaker jacks and power amp are grounded away from the preamp ground. 

Hope this helps,
Chip

[John]

Mark, just occurred to me. Re-check your input jack. Make sure you've got ~33K ohms between the tip and the grid of V1 (or whatever value that resistor is), that you've got 1 meg between the tip and ground with a cable plugged in, and that you've got zero ohms between the tip and ground with no cable plugged in.


Not that I've ever wired them wrong, or anything. 

[markmalin]

Mark, just occurred to me. Re-check your input jack. Make sure you've got ~33K ohms between the tip and the grid of V1 (or whatever value that resistor is), that you've got 1 meg between the tip and ground with a cable plugged in, and that you've got zero ohms between the tip and ground with no cable plugged in.


Not that I've ever wired them wrong, or anything. 

Sure.  I'll check that out.  I'm open to anything :)  Something isn't right and the fact that I've done all these mods w/out any results makes me wonder if it's something simple that I overlooked.


Mark.

[markmalin]

Update: Actually I'm pretty sure it hums slightly louder now than it did before.  I suspect it's the isolated input jacks?  Luckily I can play around with things as they are without much trouble (i.e. remove one star lug and place it somewhere else to see if things change, etc.) but I may switch back to non-isolated jacks to see if it goes back to the way it was.  I think it's Aiken who suggested a cap from the input tip to ground to deal with RF noise when you have isolated jacks - that's easy enough to try as well.


A time-lapsed picture of this chassis would be a laugh.  I think it has morphed over time into a completely different amp.   

[Fresh_Start]

Did you use shielded wire anywhere?  Input jacks to first stage plus to and from tone stack might help.

Are there grid stoppers on each preamp stage?

And a warning about "re-soldering".  Remove all old solder first and start over.  Don't try to melt and reapply existing solder. Use little heat sink clamps to protect components, especially caps.

Cheers,
Chip

[markmalin]

Did you use shielded wire anywhere?  Input jacks to first stage plus to and from tone stack might help.

Are there grid stoppers on each preamp stage?

Yes, both pre-amp inputs have 33k grid stoppers.  I have shielded cable on the input jacks to the first stage, and added them in parts of the tone stack, but not all the too-from connections.  Just for grins last night I tried a larger value treble cap and attached it directly to the pot to see if that would do anything.  Not really.

[jojokeo]

Mark,

You are sort of stuck with your existing layout & design as related to trying to create a star system from a bus system. Despite your best efforts you simply cannot reap all the benefits of a star system unfortunately the way your components are physically laid out. This is partly why you're not seeing any real benefits to all of your changes and also backs up what PRR is also saying.

Always use isolating jacks when possible, it doesn't hurt and can only help the situation. This goes especially for the output jack. Yes, you always run a ground wire from this negative jack terminal directly to the star ground point. The output tranny wiring has very large currents which will be connected directly to the chassis if not isolated, especially the more the amp's power is turned up.

The OT's primary wiring needs to be checked regarding it's placement. This should be ran away as practically possible from any preamp wiring and away from the power tube's grid wiring, especially on high gain situations or noise is easily picked up/generated/ coupled by this if not done.

You mention earlier about the input jack's shielding & output jack's negative using the ring terminal to go back to ground buss - no, don't do this! This goes directly to the ground non-switched terminal. If you're doing what you're describing, then it's possible they are being switched OUT of circuit and why you're now worse off than you were prior to your wiring changes.

You should always put your heater wiring's center tap to the positive side of the cathode resistor & bypass cap to assist with applying DC voltage to your heater's CT. This is free hum insurance as they say. The other thing that helps is raising DC voltage by a voltage divider (& cap) off of B+.

More on heater wiring: despite what some will say, keep your phasing correct, especially on your power tubes. ie - the same wire going to pin 4's and the other going to pin 5's. I HAVE see this cause hum before on a 5E3 because the owner didn't know what he was doing. I asked later why he was selling it so cheaply and after receiving it I noticed this had happened. I only corrected this one thing and immediately the amp quieted up. No I didn't re-sell it back to him :)
 
On your choke wiring - it is always best to put the wires directly between nodes A & B right at the caps' + wiring -  again this should be easy to do with proper planning beforehand. But it may not do anything about your hiss you are experiencing currently? But couldn't hurt to do it properly.

Without seeing your tranny placements or anything else under the board, your design schem, etc. it pretty difficult to guess anything else you may or may not have done?

[markmalin]

You mention earlier about the input jack's shielding & output jack's negative using the ring terminal to go back to ground buss - no, don't do this! This goes directly to the ground non-switched terminal. If you're doing what you're describing, then it's possible they are being switched OUT of circuit and why you're now worse off than you were prior to your wiring changes.

Thanks.  I'm confused about what you said above, though.  Check out this picture.  The tip of the guitar cable contacts the tip terminal of the isolated jack, "A" in the picture.  I connected the conductor wire of my shielded cable here, and that runs to the grid stopper resistor which is connected to grid pin of one half of the V1.  The 1M resistor is across points A and B (which is effectively the tip and sleeve of the input jack).  The B point in the pic, the sleeve of the input jack, has the shield from the V1 input shielded cable attached to it, as well as a wire going from B down to the pre-amp ground buss at point C.  (I've shown a red arrow and the letter "D" to indicate I have run a wire from this point to the star ground terminal to ground this buss.
 
The "Normal" channel is wired up exactly the same way as the Top Boost channel.  At this time I do not have isolated jacks on the output (speaker jacks are just Switchcraft non-isolated jacks)

Are you saying this is incorrect?

[Willabe]

Look in this link for pictures on how to wire up input jacks. It's in Doug's library, pics from Sluckey.

Scroll down to the bottom for pics.

http://el34world.com/charts/CommonHookups.htm

[markmalin]

Look in this link for pictures on how to wire up input jacks. It's in Doug's library, pics from Sluckey.

Scroll down to the bottom for pics.

http://el34world.com/charts/CommonHookups.htm

Ok - that's the diagram I used.  The difference being I have only one input (not a HI and LOW).  Here's a pic.  If this is incorrect, I need to fix this, but it looks OK to me, yes?

[jojokeo]

You mention earlier about the input jack's shielding & output jack's negative using the ring terminal to go back to ground buss - no, don't do this! This goes directly to the ground non-switched terminal. If you're doing what you're describing, then it's possible they are being switched OUT of circuit and why you're now worse off than you were prior to your wiring changes.

Thanks.  I'm confused about what you said above, though.  Check out this picture.  The tip of the guitar cable contacts the tip terminal of the isolated jack, "A" in the picture.  I connected THE CONDUCTOR WIRE OF my shielded wire CABLE here, and that runs to the grid stopper resistor which is connected to grid pin of one half of the V1.  The 1M resistor is across points A and B (which is effectively the tip and ring SLEEVE of the input jack).  The B point in the pic, the ring SLEEVE of the input jack, has the shield from the V1 input SHIELDED cable attached to it, as well as a wire going from B down to the pre-amp ground buss at point C.  (I've shown a red arrow and the letter "D" to indicate I have run a wire from this point to the star ground terminal to ground this buss.
 
The "Normal" channel is wired up exactly the same way as the Top Boost channel.  At this time I do not have isolated jacks on the output (speaker jacks are just Switchcraft non-isolated jacks)

Are you saying this is incorrect? No, it's fine. The terminology was incorrect therefor confusing things unnecessarily is all.

[markmalin]

Roger that.  I went back and edited my post to make it less confusing.
Thanks

[markmalin]

So does Hoffman's. Here are two links from his Library that might help:

http://el34world.com/charts/grounds.htm

If you study Doug's grounding approach carefully, you'll see that it's close to a "galactic star" except that the big currents from the speaker jacks and power amp are grounded away from the preamp ground. 

I've got a question on Doug's ground layout.  He has the pre-amp grounds to the bus on the pots, then to the (-) side of the pre-amp filter caps.  Does it tie to the chassis through the non-isolated input jack, then??  With isolated jacks, this would totally float from the chassis...so with isolated jacks you'd need a wire from the sleeve to the chassis near the input jack, right?

[sluckey]

You're missing something about Doug's pot buss. That buss is soldered to the back of every pot. It's not just floating over the pots. This means that the body of every pot provides a ground connection to the chassis. So, the pot buss is not solely grounded at the input jack.

[HommeMarrBuckley]

No expert here but just went through bout with grounding.
If you have it wired just like the diagram, I would think that your preamp ground signal would be floating/looping considering that you're using an isolated jack.  I think you're correct that it would need ground somewhere near that input.
Did Doug/others use an isolated jack?


side note---always dug the 2002 sharknose

[jojokeo]

I've got a question on Doug's ground layout.  He has the pre-amp grounds to the bus on the pots, then to the (-) side of the pre-amp filter caps.  Does it tie to the chassis through the non-isolated input jack, then??  With isolated jacks, this would totally float from the chassis...so with isolated jacks you'd need a wire from the sleeve to the chassis near the input jack, right?

The bus may be soldered to each pot but IMHO it should be floating not soldered and physically attached to the pots. But the picture doesn't actually show this.

Yes, it would "tie to the chassis through a switchcraft type of input jack's ground at that point of the chassis. With a Cliff jack you would run the Sleeve to the ground buss near the jack. But on a Star system such as Merlin & Aiken describe you would have the preamp filter cap nearby it's local components and therefore all of those local grounds, including the input jack's sleeve be tied directly to their filter cap's negative wire point. In a star ground system there is one and only one grounding point connected to the chassis. In the photo shown, there are 3 chassis contact points - provided the bus bar is floated behind the pots and not to the pots. You may get away with using the chassis as one large big ground but there would be numerous points of ground loops created in doing so and is not recommended. If you do have an issue that's created - and there's a high possibility - good luck on remedying the situation. What people don't understand sometimes is that the signal ground is a signal return path. Therefore things can be picked up and injected back into the actual signal as a result. Chassis ground is different from signal ground and should be treated as such.

[sluckey]

The bus may be soldered to each pot but IMHO it should be floating not soldered and physically attached to the pots. But the picture doesn't actually show this.

There's a note on the pic that states "soldered buss wire". But that could be misinterpreted. However the text that is on the page that pic came from clearly states "This is a bare wire that is soldered to the back of every pot and is connected to the input jacks ground lugs." No way to misinterpret that. Doug even goes on to tell you how to get a good solder joint on those pots.

I don't like soldering the buss to the pots but not because I don't think it's a good system. It complicates a pot replacement.

[jojokeo]

The bus may be soldered to each pot but IMHO it should be floating not soldered and physically attached to the pots. But the picture doesn't actually show this.

There's a note on the pic that states "soldered buss wire". But that could be misinterpreted. However the text that is on the page that pic came from clearly states "This is a bare wire that is soldered to the back of every pot and is connected to the input jacks ground lugs." No way to misinterpret that. Doug even goes on to tell you how to get a good solder joint on those pots.

I don't like soldering the buss to the pots but not because I don't think it's a good system. It complicates a pot replacement.

I haven't read Doug's actual page - at least in a long time. And not trying to diss anything regarding his grounding scheme but rather explaining a different approach and comparison to a star system w/ differences between them since markmalin seems betwixed and between them? I don't recommend using pots as ground points simply because they come loose and cause intermittent issues aside from multiple ground loops created. Good techniques are developed over time and subsequent builds get better as a result for most people so why not develop good habits as early as possible? I'm sure that last part is controversial, like religion or politics, grounding can be a hot button issue and people have their own beliefs & experiences. BUT, it's when they suffer negative consequences with one of their builds that causes them to question themselves and this aspect.

[markmalin]

It does seem like a black art with lots of differing opinions.  Aiken and O'Conner say to use a star ground, while Doug says to NOT use a star ground.  Doug's scheme looks more like a galactic ground, and Aiken says galactic is better. Doug says to solder the ground bus wire to the pots, while Aiken says don't do that.

My original question was, given Doug's ground layout drawing combined with isolated input jacks, does there need to be a wire connecting the sleeve of the jack to the chassis.  The answer is, it depends on whether the pots are soldered to their ground bus or not, as Doug's design intends.  If they are not (which is contrary to Doug's instructions for this drawing), then a wire is needed from the input jack sleeve to the chassis otherwise the pre-amp ground is floating.  In that situation (and that situation alone), the only connection between the pre-amp section ground and the chassis would be through that wire.

Things to factor in:  (thing 1) Sluckey (and myself included) doesn't like soldering the buss to the pots because he and I both have had to remove/swap pots from builds when they're soldered to a bus.  Nothing against it design wise and not the slightest disregard to Doug, it just makes for painful pot extraction.  (thing 2) Doug's original design assumed non-isolated jacks and grounding the bus through the pots, so it is not intended to float with respect to the chassis.  (thing 3) probably better to stick to a known design from tip to tip.  Even though the ground structure in the layout of the AC30 doesn't seem to match Doug's ground drawing, probably better to stick to the AC30 layout diagram.

[sluckey]

I float the buss bar above the pots with no connection to the pot bodies. The buss is terminated at the non-isolated input jack sleeve lug. I also use a dedicated chassis ground lug near the input jack with a short wire connected to the buss bar near the input jack. The preamp ground wire from the board also connects to this dedicated ground lug.

You can see all this in the linked pic...

    http://home.comcast.net/~seluckey/amps/6v6plexi/P-6V6_05_big.jpg

There are plenty of successful variations of grounding schemes. There is no 'one and only' perfect scheme that stands tall above the others.

And nothing you do to your ground scheme will fix your hiss problem.

[Willabe]

It does seem like a black art with lots of differing opinions.  Aiken and O'Conner say to use a star ground, while Doug says to NOT use a star ground.  Doug's scheme looks more like a galactic ground, and Aiken says galactic is better. Doug says to solder the ground bus wire to the pots, while Aiken says don't do that.

There's a difference in a 'star' ground and a 'galactic' ground scheme.

A star ground ties all the circuits grounds, K resistor/K bypass cap, grid return R/volume pot, input jack ground together, then they tie 1 single wire to that ground and run it over to the single 'star' ground chassis point. All B+ filter caps grounds tie together and run a single ground wire to the single chassis 'star' ground connection.

Look at this link for a good drawing on a star ground by R.G. Keen, scroll to the bottom; http://www.geofex.com/Article_Folders/stargnd/stargnd.htm#what_causes_hum

Kevin O'Connor uses a 'galactic' ground scheme. He ties all the grounds for a circuit that are fed by a single B+ filter cap to that caps ground, this makes a single ground star, BUT, then he runs a single ground wire from that ground star to the next ground star. So you end up connecting/stringing the single ground stars together (these are the stars in the galaxy) 1 by 1 and terminate the string at a single chassis point.  And he uses isolated jacks, so no extra chassis ground point connections.

What all these grounding schemes have in common are;

1. Getting away from using the chassis as a ground wire, ie, randomly grounding to the chassis for convenience instead of a 'wired' ground scheme. The less chassis ground points the less chances you have for a ground loop. (Less ground chassis connections all the way to only 1 circuit chassis ground connection. The safety ground wire connection from the power cords 3rd wire usually has it's own separate chassis connection, although some connect it to the main star/galactic chassis ground.) 

2. Separating the power amp ground (which has the most current) from the preamp/PI grounds which can be modulated by the heavy power amp ground currents.

3. Shorting the length of the ground loop of the circuit the B+ filter cap is feeding (R.G. Keen's star ground doesn't do this) ie, placing the circuits B+ filter cap close to the circuit it's feeding. Current for the circuits tube can be pulled up from the B+ filter caps ground connection, go up the tubes K, go to the tubes plate through it's plate R, then back to the filter caps B+ connection, that's the loop. This loop can go round and round all it want's to without messing with anything else.

Look at this link for more info and drawings drawings;   http://el34world.com/Forum/index.php?topic=18828.msg193010#msg193010   

[markmalin]

And nothing you do to your ground scheme will fix your hiss problem.

Right.  I'm aware of that - that's why I started a new thread

Thanks for all the help by the way!

[Fresh_Start]

For the record, Keen's "star ground" on that page is another variant of "galactic grounding".  Earth ground from power cord should always have a dedicated ground point though.

A pure start ground has a wire from EVERY ground point in the circuit to a single ground point. I've seen builds done that way, and even simple circuits look ugly as all get out. To say nothing of confusing with bundles of wire going to the star.

Like you and Steve, I don't like soldering to the back of pots. However, it's easy to put the bus wire on the edge of your board, isolate input and output jacks, ground preamp bus close to inputs, ground output jack with power amp from a Hoffman layout.

The difficulty here is that you've already built the amp with Hoffman's grounding scheme. Changing to a different approach post-build seems like asking for trouble, especially when we know that Hoffman's scheme works when done correctly.


Cheers,
Chip