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Old 28th September 2012, 05:07 PM   #1
tonepub is offline tonepub  United States
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Default new 1+1 has developed a distortion, ideas?

Well, I've been enjoying my 1+1's for a couple of weeks now and finally have the room taken care of, but I just noticed a distortion in the left speaker that sounds like a blown tweeter almost in a cone speaker. I've also noticed that the last few days, even with my power amplifier off, that the left speaker also has a random static-y kind of noise now and then, much like a noisy volume control makes.

Any suggestions?

Thank you all in advance...
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Old 28th September 2012, 05:52 PM   #2
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Switch the interface boxes from one speaker to the other ad see if the problem follows the interface then let up know what happened. Do you have a high voltage probe and a multi meter? Are you able to replace caps and or diodes on the HT supply if necessary? If no can you find a bud who could help you if necessary? Waiting to hear your results. Best regards Moray James.

PS one other question do these Acoustat's have the stock blue 47uf NP input caps in them still? If so you want to replace both of them with a good cap personally I would go for multiple plastics in parallel to get your value.
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Old 28th September 2012, 05:56 PM   #3
tonepub is offline tonepub  United States
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Thanks for the help James.... I do have a multimeter and was actually thinking about rebuilding the interfaces anyway, so this will force my hand! Getting ready for RMAF, so it might be a little while, but I'll get back to these!
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Old 28th September 2012, 06:02 PM   #4
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Find yourself a high voltage probe which will plug directly into your meter and will let you measure the HT supply without blowing up your meter. I would suggest that you buy the parts to rebuild your HT supply and get enough extra parts to add on a few extra stages. I am sure that you will find that the stock supply is only putting out around 3Kv and bumping it up to about 5 Kv or so will make a huge improvement for a few dollars worth of parts and an hour of your time. Enjoy the show and the weather in Denver. Best regards Moray James.
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Old 28th September 2012, 07:14 PM   #5
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First of all, I think you may have two unrelated problems. The occassional 'crackling' or 'static' noise you hear from the panel indicates that your panels probably need a thorough vacuuming. Yes, the grill sock must be pulled down to do this, which can be a real pain-in-the-***. Once you have the panels exposed, be sure the panels are fully discharged before vacuuming or (carefully) blowing out with compressed air. I recommend compressed air first, and then vacuuming. Do both sides of the panel. This process may have to be repeated several times to be effective, so don't re-attach the grille socks until you've got the problem solved.

This distortion you hear is most likely a problem in the interface, and unless you find obviously bad resistors or capacitors, then the problem could be in one of the audio transformers (probably the larger LF transformer).

I disagree with previous comments about the bias voltage. When using a high voltage probe, it is normal to read only about 3-kV, but the actual voltage will be closer to 5-kV. Although the typical high-voltage probe is very high-impedance, the bias supply has an even higher output impedance, so the probe significantly loads the supply, giving you a reading lower than actual. At the Acoustat factory, a measured voltage of 3-kV was considered normal, even though the circuit was theoretically putting out 5-kV.

As you might surmise, I am not a great fan of the idea of adding more stages to the voltage multiplier. The factory set-up of 5 stages yields the best compromise between efficiency and problems with high-voltage leakage under high-humidity conditions.

Changing out the electrolytic capacitor(s) in the audio input is a good idea, and will yield a noticeable improvement. But I would suggest you get the real problem fixed before complicating matters by making changes to part types or circuitry.

Last edited by AcoustatAnswerMan; 28th September 2012 at 07:16 PM.
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Old 28th September 2012, 07:16 PM   #6
tonepub is offline tonepub  United States
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That sounds like great advice. Thank you. In the event I need a new transformer, and seeing these are the older, non Medallion interfaces, is there anyone you'd suggest that I could just send both interfaces to to have rebuilt? Might as well do em both. I'm guessing if one is failing, the other will too.

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Old 28th September 2012, 07:20 PM   #7
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Quote:
Originally Posted by AcoustatAnswerMan View Post
When using a high voltage probe, it is normal to read only about 3-kV, but the actual voltage will be closer to 5-kV. Although the typical high-voltage probe is very high-impedance, the bias supply has an even higher output impedance, so the probe significantly loads the supply, giving you a reading lower than actual.
Do you happen to remember where you were connecting the HV probe when you were getting the 3kV readings?
ie. was it before or after the 500Mohm series resisitor?

If it was after, that would make perfect sense as most HV probes have 1000Mohm input impedance.
5kV x (1000/1500) = 3.3kV

Last edited by bolserst; 28th September 2012 at 07:22 PM.
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Old 28th September 2012, 08:49 PM   #8
tyu is offline tyu  United States
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My My...how could a over 30year old ESl bais in a metel box 1 " away from the HV mixer ever be off it bias.....When every time a big base note hits the Transfourmer mixer setup.... the what ever 3k...5k... bias get pulled down ......Nothing was made to last for ever not with high V....but most who own these great speakers just think thay should.....
Man out do your self an spend $50ea. US... an put some new diodes an caps in.... Acoustats are worth it.....Long live Acoustat panels...bias not so much...thay all need a littel lov by now...goodluck
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Old 29th September 2012, 08:02 AM   #9
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You can use your multi meter to check the output of the high voltage transformer going into the ladder. Check them both. I think from memory it should be 750 volts but I am sure that you will hear if I am off. It is likely ok, I have had one go south but they are well made and seem to last. The caps (mostly) and diodes are the first things to check. If you swap the interfaces you can establish it the problem lies with a panel or not. one step at a time and you are sure to find the problem. There is plenty you can do later if you want including reading about building new panels which you will need some time. Best regards Moray James.





Quote:
Originally Posted by tonepub View Post
That sounds like great advice. Thank you. In the event I need a new transformer, and seeing these are the older, non Medallion interfaces, is there anyone you'd suggest that I could just send both interfaces to to have rebuilt? Might as well do em both. I'm guessing if one is failing, the other will too.

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Old 29th September 2012, 11:50 AM   #10
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Quote:
Originally Posted by bolserst View Post
Do you happen to remember where you were connecting the HV probe when you were getting the 3kV readings?
ie. was it before or after the 500Mohm series resisitor?

If it was after, that would make perfect sense as most HV probes have 1000Mohm input impedance.
5kV x (1000/1500) = 3.3kV
The 3-kV is measured after the 5-Mohm resistor. If measured directly at the output of the multiplier, you will measure around 4.5-kV. Again, less than the actual 5-kV due to loading effects.

If you determine you need transformer repair, try contacting Sounds Like New. Contact info can be found at www.audiocircuit.com in the Acoustat section.
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