8, Low supply voltage

Read more on the Acoustat 8 in our home audio section

Fitzroy Wellington2008-11-04 19:09

hello Andy thank you for your response to my query regarding a very unusual problem with my speakers. i am in the process of removing and inspecting the panels since the interface checks out ok.I will be checking each panel individually,if theere is no physical fault in either one or in the wiring then please let me know what resistance or capacitance I should expect from each. i greatly appreciate your advice and assistance since i know of no other reference in the caribbean where i live; i agree with you, a better speaker is yet to be built. with thanks, fitzroy wellington trinidad


Andy Szabo2008-11-04 20:29

Before you do any measurements of the panels, please make sure they are completely discharged. Otherwise, you may damage you meter, or at least get an erroneous reading. For an individual panel, you should measure infinite resistance (i.e. no conductivity)between the red wire (diaphragm) and either of the blue or white wires (stators). You should also measure infinite resistance between the white and blue wires. Be sure to use the highest ohms-range on your meter. Any finite resistance (i.e. some conductivity) measured between these wires would indicate some sort of conductive path inside the panel, most likely caused by foreign matter lodged between the stator and the diaphragm. If you have the ability to measure capacitance, the capacitance between the blue and white wires should measure about 200 picofarads (pF). However, resistance measurements will be more telling of a problem, so I don\'t think a capacitance measurement will be much of a troubleshooting tool. You should also inspect the wires leading up to the panels. Look for any signs of arcing (black marks are a tell-tale sign)or for pinched wires. It is possible, though not likely, that a defect in the original assembly of the speaker took all these years to manifest itself. So far we have been looking for a short circuit that could be pulling down the bias voltage. This is the most likely scenario since the entire set of panels connected to that interface is not playing loud enough. One bad panel (or bad wire) with a short circuit would affect the whole set of four panels. The other possibility is an open circuit that is not letting the bias voltage get to a panel. However, this would affect only that panel, so unless you have four bad panels in one set, this would not be the case. Just in case, I will tell you how to check the bias feed to the panel. The red wire is connected to a small metal-foil tab, that is laid on top of an extension of the diaphragm\'s conductive coating. Measure the resistance between the red wire and the conductive coating near where it connects to the foil tab. Be careful not to puncture the diaphragm with the meter probe (probably best to use a blunt tip), and make sure you are measuring on the side of the diaphragm with the conductive coating. I can\'t give you an exact reading to look for, but if you get infinite resistance, then you have a problem. A normal measurement would probably be in the range of a few thousand or ten-thousand ohms. The measurement will depend on how far from the tab you are measuring (closer will yield a lower resistance). Fixing a bad bias tab is nearly impossible, as the panels are permanently glued together. I don\'t think I\'ve ever run into that problem, and I have no experience in trying to fix one. So let\'s hope that\'s not the problem. If all else fails, you can send me a plane ticket and I will come and fix them for you. I could use a vacation in the Caribbean! Just kidding of course, but do write again if you need further help. We need to keep those Model Eights running for a long time!

Fitzroy Wellington2010-09-29 20:59

hello andy
it's been a long time since i contacted you last, but i finally took my speaker apart and found that some of the wires were corroded and broken. i did a repair job but the solder joints all seem to corrode again and cause the same problem; i do not know if this is a problem consistent with the tropics. can you advise me as to how to join these high voltage wires so that they do not go green and separate. also can you recommend alternate diodes that i can use in the power supply since i cannot find the originals.

Andy Szabo2010-10-26 02:17

The original diodes have been discontinued for some time. Replacement diodes are avilable from: http://www.deantechnology.com/pg_home/home.aspx. Search for part number G10FS, which is rated at 25 milliamps and 10,000 volts. You should be able to buy directly from them, but there may be a minimum order.

Corrosion could certainly be a significant factor in your humid salty air, and is probably made worse by the high-voltage attraction of salt particles. First, make sure you are using a high grade solder intended for electronic connections. Never use an acid flux solder like you would use for plumbing. Clean all the corrosion off the connections with emery cloth or a fiberglas bristle brush, and then coat the troublesome areas with Glyptol, which is a thick, dull red enamel designed for protecting electrical connections. It should be available from any well stocked electronics supplier. The down side is that it makes later repairs more difficult, as the coating has to be scraped or dissolved off prior to re-soldering. The same Glyptol can be used to coat the first inch or two of the wires, in an effort to prevent further 'greening', or oxidation of the copper conductor.

Good luck, and do write again if I can help further. The offer still stands for that plane ticket...

Fitzroy Wellington2010-12-28 01:20

Hi Andy
Again I must thank you for your very useful advice. I certainly have benefited, since I have the eights running at close to 'full steam' now. I got the G10FS diodes and upgraded the power supplies but those high voltage capacitors are hard to find, even in the US.I would appreciate any advice on this since efforts on my part through suppliers recommended by other contributors on the website proved unsuccessful. Apart from the diodes and capacitors (.0033/1500V are all I can find, bias voltage slightly low 4.5kv supply volts 2.8kv) in the voltage multiplier, everything else is original equipment and needs upgrading so I guess what we have so far is a work in progress, sweet however.
I extend fond wishes to you for the new year. As a professional pilot myself, who knows, maybe I will fly up to the US and bring you to Trinidad... think I"ll need an airplane though.
PS: what is the minimum supply voltage to the panels for proper operation?

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