WOPL 700B A/C hum ?

mattoe

New Around These Parts
Joined
Oct 2, 2016
Messages
38
Location
Hamilton Ont Canada
Tagline
Don't let any smoke out !
#1
Gentleman,

I just noticed that my 700 has a hum. I noticed this when working on speakers without any crossovers....
Connect the amp to the speakers , with no inputs to the amp and we get a low but obvious hum.
Connect The amp back to my system speakers ( paradigm signature s8"s ) and the hum is just about gone..
I suppose the crossovers take care of this ...
I have never noticed the hum because its always been running my paradigms ! till now...

All the ac wiring is relatively isolated to the top of the case and the dc and signal wiring along the bottom.
New 50 amp reg with .01 caps as snubbers... all good....
I did however remove the input potentiometers and connect directly to the board...
Do I have a floating input issue ??? I have heard some say to solder a 100K resistor from sig to ground at
the rca's ... also read to try a 220pf cap to ground ? Any of this sound familiar to anyone ?

Cheers !

Mattoe
 

NavLinear

Veteran and General Yakker
Joined
Apr 12, 2012
Messages
5,639
Location
SoCal
Tagline
Survived the Thomas fire
#2
Here's a section from the Phase Linear 700 700B service manual that may help. I've had a similar problem where tightening the transformer bolts corrected the issue.
 

Attachments

laatsch55

Administrator,
Staff member
Joined
Jan 14, 2011
Messages
54,975
Location
Gillette, Wyo.
Tagline
Halfbiass...Electron Herder and Backass Woof
#3
Second what the Navo said. Also, is the wiring from the inputs to the board shielded?? What iteration of amp and control board do you have? No need for a resistor or cap.
 

laatsch55

Administrator,
Staff member
Joined
Jan 14, 2011
Messages
54,975
Location
Gillette, Wyo.
Tagline
Halfbiass...Electron Herder and Backass Woof
#4
Here's a section from the Phase Linear 700 700B service manual that may help. I've had a similar problem where tightening the transformer bolts corrected the issue.
What manual do you have Dennis, mine doesn't even mention hum>??
 

mattoe

New Around These Parts
Joined
Oct 2, 2016
Messages
38
Location
Hamilton Ont Canada
Tagline
Don't let any smoke out !
#5
Second what the Navo said. Also, is the wiring from the inputs to the board shielded?? What iteration of amp and control board do you have? No need for a resistor or cap.
Thanks for the reply,

The transformer bolts are tight, and yes... The input cabling is coaxial shielded... full WOPL rev "E" I believe....
When I connect the pre amp and bring up the volume the "hum " is negated.... The amp plays beautifully....
I never knew there was an issue until I used a speaker without any crossover ....

Mattoe
 

mattoe

New Around These Parts
Joined
Oct 2, 2016
Messages
38
Location
Hamilton Ont Canada
Tagline
Don't let any smoke out !
#6
Thanks for the reply,

The transformer bolts are tight, and yes... The input cabling is coaxial shielded... full WOPL rev "E" I believe....
When I connect the pre amp and bring up the volume the "hum " is negated.... The amp plays beautifully....
I never knew there was an issue until I used a speaker without any crossover ....

Mattoe

Any suggestions ?
 

marcok

Chief Journeyman
Joined
Jun 9, 2014
Messages
592
Location
Milan Italy
Tagline
I'm very curious about any tech item
#7
Reverse the AC plug and check .
Short the inputs of PL using two shorted RCA plugs and check .
Replace the speakers with 2 other ones and check .
In this way you could find the issue and after the solution .
In other words first the diagnosis and after the therapy .
Ciao
Marco
 

laatsch55

Administrator,
Staff member
Joined
Jan 14, 2011
Messages
54,975
Location
Gillette, Wyo.
Tagline
Halfbiass...Electron Herder and Backass Woof
#8
Matt, are you running the White Oak back planes and Wattsabundant DC protect board?
 

Northwinds

Veteran and General Yakker
Joined
Mar 18, 2013
Messages
7,276
Location
Coventry, CT
Tagline
Fondler errrr... fan of all Nav's avatars
#10
Matt, are you using a power conditioner or plugged straight into the wall? Might be dirty power supply and you getting a ceiling fan hum or something similar. Also, I had a problem with an outlet that was part of a circuit with a dimmer rotary control making a hum which controlled living room ceiling fan and light. Once I used the power conditioner, hum gone
 

WOPL Sniffer

Veteran and General Yakker
Joined
Aug 10, 2015
Messages
3,519
Location
Arizona
Tagline
Screw it
#11
Ground loop??? Did you stick to Joe's Star-Ground scheme??? Maybe a pic of the build as it went along? Did you keep the power and signal wires at their respective sides of the chassis?
 

WOPL Sniffer

Veteran and General Yakker
Joined
Aug 10, 2015
Messages
3,519
Location
Arizona
Tagline
Screw it
#12
As Ron was saying, maybe trying a different outlet on a different circuit in the house? Did you use an IEC plug and ground it inside the amp? (I hope not).
 

jbeckva

Admin/Server Dude
Staff member
Joined
Jun 11, 2010
Messages
6,373
Location
Powhatan, Virginia, United States
Tagline
Errm... Ey Vatos!!!!
#13
Ground loop??? Did you stick to Joe's Star-Ground scheme??? Maybe a pic of the build as it went along? Did you keep the power and signal wires at their respective sides of the chassis?
I tell ya.. when I was doing a 700 (and you know who you are, person I built it for :toothy8:), I missed the one single wire that should go from star ground at the caps to the chassis. But with my setup I could NOT hear the hum.. Unfortunately he could and we went back and forth for a bit.. even had a woofer shipped over to see if I could hear it then. Felt like an ass haha.. One of the first builds.. hey.. what can I say?

But anyway... basically what I learned from all that is that there should be only *one* connection to the chassis and direct from the star ground. On the inputs, both shields together at the RCA's and with the RCA's *isolated* from the chassis.. with a copper shield laying on top of the fiber swag washer installed on the inside Re-use a shield from a 400 .. works good.. or make your own.. or if you use different RCA jacks solder the two ground tabs together and run the combined shields L/R to the same point. Then back to each channels input on the Rev "E". I take the pots out of the circuit as well - maybe overkill but less wire, clutter, etc etc.
 

grapplesaw

Chief Journeyman
Joined
Aug 13, 2014
Messages
1,287
Location
Vancouver
Tagline
---
#15
If I can add my five cense worth. The problem may lay more with that set of speakers. There may be inductance from the voice coil causing the hum when connect to that amp. Try putting a .1uf or .01uf cap across each channel’s Leeds. One per channel. Try it at not to high a power first.
 

mattoe

New Around These Parts
Joined
Oct 2, 2016
Messages
38
Location
Hamilton Ont Canada
Tagline
Don't let any smoke out !
#16
If I can add my five cense worth. The problem may lay more with that set of speakers. There may be inductance from the voice coil causing the hum when connect to that amp. Try putting a .1uf or .01uf cap across each channel’s Leeds. One per channel. Try it at not to high a power first.
Thanks for all the suggestions !

I'll try to touch on all these points...

My 700 build followed the White oaks instructions and yes I do have the single point ground scheme ... 2 prong plug not the IEC 3 ! The input rca's are insulated from the chassis with a copper strip and single point ground and directly to the board ,pots are eliminated.

The ac wiring is all along the top and dc and signal wiring along the bottom of the chassis

Monster power conditioner doesn't seem to make any difference.


I will try a cap across the speaker leads and post the result
Maybe flip off house breakers and move the amp to another house circuit just to see....

Matt

Thanks again for the input !
 

WOPL Sniffer

Veteran and General Yakker
Joined
Aug 10, 2015
Messages
3,519
Location
Arizona
Tagline
Screw it
#17
Insulated with a copper strip??? I hope you mean the one with the black insulators. Did you try the drinking straw trick on the transformer bolts? I never had to do it but some did.
 

mattoe

New Around These Parts
Joined
Oct 2, 2016
Messages
38
Location
Hamilton Ont Canada
Tagline
Don't let any smoke out !
#18
Insulated with a copper strip??? I hope you mean the one with the black insulators. Did you try the drinking straw trick on the transformer bolts? I never had to do it but some did.
Yes Sir,

the RCA's ground via a copper strip between and common to both ... Not directly to the chassis....
The drinking straw trick ??? That's new .... I can only assume insulating the bolts as they run the length of the
laminated stack ?

Matt
 

WOPL Sniffer

Veteran and General Yakker
Joined
Aug 10, 2015
Messages
3,519
Location
Arizona
Tagline
Screw it
#19
Yes Sir,

the RCA's ground via a copper strip between and common to both ... Not directly to the chassis....
The drinking straw trick ??? That's new .... I can only assume insulating the bolts as they run the length of the
laminated stack ?

Matt
Yeah, I think our guru's read that it can eliminate the eddy currents if you have any. Make sure you get the bolts nice and tight after. Are you sure it's the amp? And not another piece of equipment? I usually try just the amp, and a ipod with a set of speakers. The Ipod has enough juice to drive the amp. It does'n't sound the best but it helps track down noise.
 
Top