ESL speaker - Static in Bias Supply

[jazzman53 1,276]

I know just enough about electronics to get myself in trouble, but not enough to fix anything -- and I need some help diagnosing a problem with one of my newly built Jazzman MkIII electrostatic speakers.  I was burning it in, and after about 2 hours playing, I started hearing a low level static, which sounds something like radio static.   I've never had this problem with any of my prior speaker builds.   My schematic is posted below. 

 

I swapped out the electronics interface (HV bias supply & step-up transformer package) from one of my other speakers, and the problem went away.  So; the problem has to be within the bias supply or step-up transformers. 

 

I checked the diodes for one-way conduction and found no faults.  I don't have an ESR meter, and I understand that capacitors should be checked out of circuit with a DVM.  I didn't want to pull those ceramics out of the board because I cut the leads so short, but as best as I could tell checking them in circuit with a DVM; I'm not seeing anything wrong there.  

 

What I don't know how to check are the small transformer feeding the bias supply, and the toroidal step up transformers.  Note that the bias supply has a floating ground connecting to the center tap between the step up transformers.   Aside from the low level static, the speaker plays normally with no distortion, so I'm thinking the step up transformers should be OK (?).  

 

The 115V AC input to the bias supply is switched with the amps.   And when I turn the amps on; I immediately hear static emanating from the ESL panel.  Then; a few seconds later the relays in the amps switch on, bringing the amps into the circuit, and the static decreases but doesn't go away.  

 

I've ordered the parts to replace the entire HV bias supply, including the PC board.  If that doesn't fix the problem, then it has to be within one of the step-up transformers, and I would then replace both transformers.   The step up transformers I have to order from Europe-- they aren't cheap and it takes several weeks to get them. 

 

Anyone got any ideas what's causing the static?

 

 

   

Edited February 19, 2021 by jazzman53

[wrf 4,980]

One easy thing to do is check for leakage between the primary and secondary of you transformers.  Based on the schematic, you should be able to just check it with an ohm meter.  There should be infinite resistance between primary and secondary.

 

What size are the caps?   ESR is often a good clue when tested in circuit, but far from a definitive test due to potential interference from other components.  From the photos, the look like ceramic caps -- very unlikely to cause problems.  Simple resistance measurements across each cap (both polarities) and a comparison with a good board may reveal something.

 

Diodes can be leaky.  It might be useful to look at the drop across each one with you DVM in diode mode, then compared with a good board.

 

Other than that, a through inspection of the board and solder joints would be in order.  I know every time I start thinking I'm good at soldering, I discover a bone head solder joint I'm responsible for.

 

Good luck.

 

[jazzman53 1,276]

Forgot to add:  I've already reflowed all solder joints, to no avail.

[jazzman53 1,276]

Thanks, Wrf

 

The caps are .01uF 

[wrf 4,980]

Is the noise present with no amp connected?

[jazzman53 1,276]

1 hour ago, wrf said:

Is the noise present with no amp connected?

 

I think I can answer yes to that--   That is; I didn't disconnect the speaker cables, but I did turn the amps OFF and powered up the bias supply from a wall outlet, and the static was still there.  

Edited February 19, 2021 by jazzman53

[jazzman53 1,276]

Maybe I should just throw in the towel and wait for the new parts to arrive...

 

I just pulled the step up transformers off the board, and both read open (infinite) resistance between the primaries and secondaries.  Likewise with the small transformer, which I checked in circuit, on the board.  

 

The drop across all the diodes is about 0.61V and the resistance both ways across all the caps reads OL (infinite).  

 

The traces on the board look OK too, so it's either shoot myself in the head or walk away for a while. 

 

Thanks for your help, Wrf  (Wayne?) ! 

 

My senility has no patience... 

[jazzman53 1,276]

Update 2/20/21:

 

Yesterday I didn't know whether the static was coming from the bias supply or the step up transformers.  

So this morning I connected those transformers to a known good bias supply, and the speaker plays with no static.  So; the source of the problem is one of the components in the bias supply, or the board itself.  

 

Since I can't isolate the problem further; I will build a new bias supply, on a new PC board, when the parts arrive from Mouser.  Not sure when that will be because the blizzard has delayed the shipment.  

 

At least I won't have to replace the transformers too 🙂

[BarryG 2,853]

Glad it’s not the transformers, good luck with the rebuild.

[jazzman53 1,276]

Static problem is resolved:  

 

This afternoon a received the parts from Mouser, and built a new bias supply on a new PC board, for the problem speaker.  

 

While I was installing the new bias supply, I found the REAL source of the static-- something I had completely overlooked, and it wasn't in the bias supply, but the connection from the AC receptacle to the bias supply.   When I soldered that connection, I couldn't see it straight on, and had to solder it from an oblique angle.   It's easy to see now; thru the plexiglass cover, but when I soldered it; I had not yet peeled off the protective backing from the plexiglass.  

 

The wire is merely inserted thru the hole in the connector -- the solder bead didn't even wet it --- have a look below.   The second photo is looking thru the plexiglass cover.  

 

I'm feeling like an idiot for the screwup but I now have a spare bias supply if I ever need one (not likely because  I've never had one fail in 13 years building ESL's) 

 

I have the speakers playing a Vanessa Fernandez album while I'm writing this, and it's sounding fabulous.  Both pairs turned out really nice.   

 

 

Edited February 26, 2021 by jazzman53

[RodH 4,866]

Nice find!

 

(I hate it when that happens.. 17 pairs of glasses for me , and yet...)

 

Your work is very meticulous, this is a rare anomaly.

[Balok 1,677]

Glad you found the problem Charlie.  There's always something...........

 

Most excellent project!

[wrf 4,980]

Been there.  Done that.

 

Bet it doesn't happen again.

[BarryG 2,853]

Glad you found the problem!  

[AndrewJohn 10,502]

13 hours ago, jazzman53 said:

now have a spare bias supply if I ever need one (not likely because  I've never had one fail in 13 years building ESL's

 

Glad you found it !  Now..., what to do with the extra bias supply....

 

Could be a sign..., that you have one more pair to build 😉 around the spare bias supply. 

 

Don't they say things come in three's?  you've got two done, now, the third.

 

(Just teasing..., )