princeton reverb grounding Hoffman layout

[wetdog]

I have a question regarding the grounding for my second amp build, a Princeton Reverb using the Hoffman board. I've soldered a  buss bar across the back of the potentimeters and was going to connect the end of the buss bar to the input side of the chassis on the bolt shown in the picture. Grounding the input on a dedicated bolt follows the previous PR Hoffman layout.
 
My questions: do I need to use a dedicated grounding bolt as my input ground or can I just connect the input stage and my shielded input wire ground to the buss bar? Also, does the reverb inputs and outputs need a dedicated ground if my RCA jack are not isolated? Some layouts seem to show a dedicated reverb ground.

[EL34]

The library page has links to my build
http://el34world.com/Hoffman/Princeton_Reverb_Board_Build.htm

And it has a grounding scheme
http://el34world.com/charts/grounds.htm

[hesamadman]

You want to be careful with having too many ground connections. There are many different methods and everyone has their own way. Some will argue the potential of ground loops when soldering the bus directly to the back of the pots. However, anyone who has built one of Dougs builds will tell you that soldering to the pots did not give them any trouble or noise. I've done it about any way you can do it. But to answer your question, you should be able to ground from input Jack directly to pot bus without a problem. However I have not built this amp exactly but I've done it this way on similar ones without an issue. It's an easy change though if you were to have issues.

[rhodco]

I did mine exactly like Doug's photos and I have no noise issues at all.

[p2pAmps]

I did mine exactly like Doug's photos and I have no noise issues at all.

I did Doug's ground scheme as well, complete silence...

[wetdog]

Thanks for the replies!My understanding is the pots and jack must be grounded, but I do not need to ground the buss bar to the a dedicated ground bolt. Since the pots and jacks are in securely in contact with the chassis, the green line shown in the picture is the olny ground connection the input needs. please correct me if I'm wrong;)

[EL34]

Did you look at my build page?
I posted the link for you up above

You can clearly see how I did it.

[Willabe]

Umm, it looks like the white wire from the power cord is heat shrink-ed off and not connected to anything?

[HotBluePlates]

Umm, it looks like the white wire from the power cord is heat shrink-ed off and not connected to anything?

It's connected to a black wire from the PT primary, which is barely visible and laying alongside the white wire. The two ends are soldered together, with heatshrink over them. Kinda the same orientation you'd have if there was a wire-nut instead of heatshrink on the ends.

[Willabe]

Thanks. 

[EL34]

Umm, it looks like the white wire from the power cord is heat shrink-ed off and not connected to anything?

Oh crap, the amp must not work!!!! 

[Willabe]

I know you wouldn't leave a wire not hooked up, I couldn't see what you did. 

[EL34]

It's magic wire slight of hand stuff 

[Willabe]

    Yeah, that's it!

[wetdog]

I really appreciate all the information on the Hoffman Amps website and have read everything pertaining to the Princeton Reverb layout. My initial question about buss bar grounding relates the this older version showing a separate ground bolt on the chassis next to the input. I put a bolt there on my chassis but am assuming based on other pictures and layout examples that the bolt will not be necessary.


Kind Regards,
Andy

[HotBluePlates]

The layout doesn't imply the use of plastic Cliff jacks, but I wonder if the author was thinking about that when drafting the layout. I'm pretty sure either Sluckey or Bnwitt, not Doug, drew that layout way back when we first discussed a Hoffman-style layout for the PR on this forum (maybe in the 2005-2007 timeframe?).

[EL34]

I really appreciate all the information on the Hoffman Amps website and have read everything pertaining to the Princeton Reverb layout. My initial question about buss bar grounding relates the this older version showing a separate ground bolt on the chassis next to the input. I put a bolt there on my chassis but am assuming based on other pictures and layout examples that the bolt will not be necessary.


Kind Regards,
Andy

I don't know what that drawing is
It is not one of mine

If you are doing one of my boards, why would you be consulting someone else's documents

I am just asking

[Fresh_Start]

The layout doesn't imply the use of plastic Cliff jacks, but I wonder if the author was thinking about that when drafting the layout. I'm pretty sure either Sluckey or Bnwitt, not Doug, drew that layout way back when we first discussed a Hoffman-style layout for the PR on this forum (maybe in the 2005-2007 timeframe?).

I think you are correct about the time frame and you may be right about the Cliff jacks. But that's not Bnwitt's layout.(Yes, he got help from Sluckey, Tubenit and HBP if I remember right.) Looks like someone else started with his Visio file and tweaked a few things - including the grounding.

I built a couple of Princton Reverbs starting with Bnwitt's layout and it followed Hoffman's grounding scheme very closely. I don't like the physical separation between the grounds for the volume and tone controls vs. the ground for rest of the preamp as shown in that layout. However, I know that it worked just fine for several forum members.

Respectfully
Chip


P.S.  There's nothing wrong with looking at other layouts, however, the first law on the AX84 forum is DONT BUGGER UP THE LAYOUT. In other words, Doug has a known-good layout. If you're going to change it (like I did), have a really good rationale (I didn't know any better 8 years ago)

[drew]

I don't know what that drawing is
It is not one of mine

If you are doing one of my boards, why would you be consulting someone else's documents

I am just asking

In your write-up of the Princeton build, you might want to add a sentence or two explaining that the Princeton board you're selling is not the same as the one that was initially laid out some years ago by forum members without your direct involvement, and that current builders should only be referring to the layout diagrams that you have linked to, not older ones that they might run across in doing forum searches.  It could prevent confusion on the part of guys like Andy who may not have been hanging around here for years and don't know the back story of this particular circuit board.

[sluckey]

That file was created by Barry N. Witt on 12/13/2006. There were several forum members working on that layout. Version 1 was a long board that covered up the cap can. Soon afterward a short board version (the one in the pic above) was created by Barry.

IIRC, HBP actually modified an old style Hoffman AB763 drawing to create the PR layout. Then Barry took that and made one of his nice Visio drawings. I think Fresh_Start was the first to actually use that layout to build an amp.

I still have all those drawings including HBP's PR layout. At the time I was busy with the ax84.com November amp and by the time I was done, you guys had the PR hammered out. I never actually worked on that project.

You can probably still find the original discussion thread but I'd be surprised if the attached files have survived.

[Fresh_Start]

 Sluckey is absolutely right - that layout was the original "short board" Princeton Reverb drawing Bnwitt developed.  The earlier version had the circuit board actually covering up part or all of the cap can.  The original layout was based on a Hoffman AB763 schema-out with bias vary tremolo drawing.  (Don't know what else to call those hybrid drawings.)

I was not the first to use that layout.  At least one person built the long-board version (physconoodler?) and several more built the short board version before I dove in for my first PR build.  I made a few changes to the layout, the grounding in particular.  However, it wasn't until my third Blackface Fender build that I achieved a layout and grounding scheme that I was really happy with.  Funny enough, it's actually closer to Hoffman's standard grounding approach in concept than the earlier versions.

I repeat:  Don't booger up the layout!

Respectfully,

Chip

P.S.  While I strongly recommend using Hoffman's current layout, the original layout discussion (l-o-n-g) from the 2006-2008 period is in the "Schematics" sub-section of the forum.  However, all of the file links are dead except Barry's last schematic PDF.  I have some of the files on my computer but don't want to add to any confusion.  This did prompt me to visit PhotoBucket and discover that many of my old build documentation is still there and accessible - including a couple of amp build slide shows. 

Note that it looks like Doug was already selling populated Princeton Reverb boards at that time.  IOW he already had a "known good" layout back then.

[EL34]

This is my princeton reverb layout PDF file
http://el34world.com/Hoffman/files/Hoffman_PrincetonReverb.pdf

Use the document above and the other ones shown here
http://el34world.com/schematics.htm#Hoffman_Princeton_Reverb_

[bnwitt]

Yep that's my short board layout.  I have built (6) amps with that exact layout.  The last one is in my studio.  Typical Hoffman separate preamp and power section grounds.  Dead quiet on idle.
Barry