"Improved "my PS by adding massive amounts of 120Hz Buzz! [resolved]

[galyons]

 I may have gotten a wee bit overly tweakish. Looking to “improve” the power supply with some additional filtering. But what I got was massive amounts of 120Hz buzz in both channels. 

I decided to try adding filter chokes to the power supply and replace the electrolytic caps with film caps.   Looking to do a CLCLC filter.  (C1: 62uF 250v => L1:10H 90mA => C2: 62uF 250v => L2: 1H 240mA => C3: 10uF 250V)   Rectified with a Cree CSD01060A bridge built on a Parts Connexion board.

Took some rerouting of PS wires and building a platform for the chokes and final PS  Cap, (Russian MBGO) that hangs below the power tranny secured with 8/32 machine screws.  The 62uf caps went where the electrolytics were.  Simple, solid and I thought “clean”.    I changed nothing but the PS.  The chokes are at 90 degrees from each other.  I must have screwed up a ground somewhere. But I can’t find it.

The voltage tests were spot on with 120VAC line giving 200V to the PS reg boards of the Smashup. The only somewhat off voltage is OB, (45-75V) and I got 78.5V on both channels. “Good to go!”, I thought, and into the system.  But instead of cleaner B+, I got massive amounts of 120Hz buzz, completely drowning out the music. Volume control had no effect. Back out of the system, re ran voltage checks, ran continuity checks on all the PS wiring, re-flowed all of the joints. Everything tested to spec, again. Back into the system….same problem. Repeat a couple more times, than raise the “white flag”!

Was going to take some pics, but camera battery is dead. Charging and I will shoot some tomorrow.  In the mean time…any thoughts?

Cheers,
Geary

[kgoss]

Did you tie the choke frames to ground?

[mcandmar]

If i'm not mistaken the Smashup replaces the voltage regulator tube with Bottleheads shunt regulator design which should filter out a huge amount of power supply noise/ripple.  Certainly that's been my experience using SS shunt regulators.

If you are getting hum that badly i would suspect either as Grainer says the chokes are picking up the mains transformer (or interacting with the output iron if it had any), or something is wrong with your grounding scheme.  At what point do you have the negative side of the power supply tied to ground?      It may also be worth double checking the choke bodies are grounded, chuck a few test leads on them and see if it changes anything.

[Doc B.]

Inductors couple 60Hz, not 120, and it wouldn't swamp out the music. Geary has a lifted ground somewhere.

[galyons]

Inductors couple 60Hz, not 120, and it wouldn't swamp out the music. Geary has a lifted ground somewhere.

I agree, just cannot find the ground problem.  Everything measures to spec, except for the 120Hz on the outputs!!!  I spent last night and much of today taking apart, checking, re-flowing & testing. Still no love!     I tried with the choke frames grounded, choke frames and metal cap body grounded....no difference.  Switched out the Russian final cap, no  difference. 

It is not a complicated PS scheme, but I have screwed up something.  Any thoughts or observations gladly welcomed. (I am on "thin ice" here. Today is my 45th Wedding Anniversary and someone ELSE is not feeling the love, either.  So, I am done for today....Better take her to dinner!   )

Here are some pics.
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FZxWTNn7.jpg&hash=518354147efbc8ec2f3711603aefa1cfcc08f7f1)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FcPwpU2J.jpg&hash=dcaf4eb0719f56842660bba7e04f25699a959485)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FM11NTtV.jpg&hash=87ffd2a166cf96ffe5824cc982079c8972fabe98)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FwOU3XX0.jpg&hash=564dbc255f03bbd0b48debc678c9974ae06f0015)

[Strikkflypilot]

But isn't that a ground wire touching the hex standoff top left in the first picture before it is soldered to the strip? Happy anniversary!

[mcandmar]

The big silver box cap, i assume thats the 10uf at the end of your power supply has two small wires coming off it, do those go to each of the constant current boards?   If so i dont see any connection from the negative side of the power supply to ground.  If there isn't one i would run a ground wire the negative terminal of the second 62uf capacitor and connect it to the chassis.  The bottom left transformer mount in the first pic looks ideal where the mains earth is connected.

[galyons]

But isn't that a ground wire touching the hex standoff top left in the first picture before it is soldered to the strip? Happy anniversary!

Thanks Geir,
That is a drain wire for the shield to ground.  The other end, at the IEC receptacle is open.

Cheers,
Geary.

[galyons]

The big silver box cap, i assume thats the 10uf at the end of your power supply has two small wires coming off it, do those go to each of the constant current boards?   If so i dont see any connection from the negative side of the power supply to ground.  If there isn't one i would run a ground wire the negative terminal of the second 62uf capacitor and connect it to the chassis.  The bottom left transformer mount in the first pic looks ideal where the mains earth is connected.

Thanks Mark,
Yes, the big silver box cap is the PS final.  The big black wire comes from 28L to the ground side of the silver box cap.   The two small wires go to grounds at 6L & 7L.   Then a ground buss is formed with wires from 6L to  2L then to A5 on the tube and 7L to 11L to C5.  Ground wires go to the boards from 2U & 11U.  In the original grounding scheme the wires to 6L & 7L originate at the 2nd , (final), 220uF electrolytic at 28L.  So I put them on the final cap, big silver box cap,  in my scheme.   

I have tried putting my meter on Hz connected to the output RCA and running a jumper from the  ground tab in the top plate, near the IEC plug, to the various ground connections at the PS caps and the ground buss at the preamp tubes. No change, still a solid 1V+ of 120Hz at the outputs.

I am going to keep testing and probing today.  I might have shorted something to ground in rerouting wires.  I wish finding where the issue occurs were as easy as determining what the issue is!

Cheers,
Geary

[galyons]

DONE Done & done!  Sadly it took over a month and a tremendous amount of effort to find the cure for what was a self-inflicted wound.     I had to  put fly leads on the filament supply cap to make room for the the PS film caps.   Must have nicked the fly lead wire when I stripped it.  It broke when I was moving the cap into position.  So no filtering of the filament supply.  I couldn't see it because I put shrink tubing on the joints. 

So a BIG thanks to PB and Doc for  their help and patience in sorting this out.  Not simple....took out the filament regulator and the 4 LM431's on the PS reg/C4S boards.

So how does it sound?  Damn fine!  But the sad reality is not having all of the AC at the outputs sounds heavenly, regardless of any improvement from the chokes.  My aural recall of the pre-choke configuration is pretty much none existent, now a month later.  I will listen to some of my reference recordings and then "pass judgement".

Cheers,
Geary