For repair and upgrading of Acoustat interfaces, try contacting Roy Esposito, a former Acoustat employee. His contact info can be found on www.audiocircuit.com in the Acoustat section. I'm not sure of Roy's opinion about changes to the bias circuit - you'll have to ask him. But if your high voltage multiplier has gotten 'tired' after all these years, merely rebuilding it with new parts may gain the improvement you are looking for.
According to Jim Strickland (Acoustat's chief engineer), the bias voltage for Acoustat was chosen after much experimentation as the best compromise between efficiency and any tendency to arc in high humidity conditions. If you live in an area of high humidity, increasing the bias may run you into trouble. In low humidity conditions, increasing the bias voltage 10-20% is probably okay. For me, I have never tried it, and have no desire to do so: my Acoustat Spectra 4400's are still thrilling me on a daily basis.
According to Jim Strickland (Acoustat's chief engineer), the bias voltage for Acoustat was chosen after much experimentation as the best compromise between efficiency and any tendency to arc in high humidity conditions. If you live in an area of high humidity, increasing the bias may run you into trouble. In low humidity conditions, increasing the bias voltage 10-20% is probably okay. For me, I have never tried it, and have no desire to do so: my Acoustat Spectra 4400's are still thrilling me on a daily basis.
Thanks...................
I took a good look at them along with the diagram and it doesn't look as complicated as I thought.
Sliding resister looks easy to measure my settings and change.
The three bypass caps in the high frequency section look easy to replace with same values.
I just upgraded the speaker binding posts on my power amp so should be easy on the speakers too.
I think I only have a couple of questions on the bias circuit if anyone can answer.
The five 3300 pf caps would be a very simple to replace rather than adding another section (cap and diode(which I don't feel confident in doing)) can the voltage be increased any by using a different value on the five caps? Or better to just replace with same?
Another question is the 500 m ohm resistor. Would lowering this value increase voltage to the panel or is this resistor's purpose only to limit current surge's to protect the panels?
Thanks, Mark
I took a good look at them along with the diagram and it doesn't look as complicated as I thought.
Sliding resister looks easy to measure my settings and change.
The three bypass caps in the high frequency section look easy to replace with same values.
I just upgraded the speaker binding posts on my power amp so should be easy on the speakers too.
I think I only have a couple of questions on the bias circuit if anyone can answer.
The five 3300 pf caps would be a very simple to replace rather than adding another section (cap and diode(which I don't feel confident in doing)) can the voltage be increased any by using a different value on the five caps? Or better to just replace with same?
Another question is the 500 m ohm resistor. Would lowering this value increase voltage to the panel or is this resistor's purpose only to limit current surge's to protect the panels?
Thanks, Mark
Yes i pulled the 50m out 5years a go....i now have a 10m 1w there, an the sound is much better....Faster...louder....better in ever way...here the deal these are all old, an i love Acoustats now an as long as i live.. i well have some of them.....but this is HV the bias...30years old thing chang...most like them the way that thay are....but for me i wont the most i can get.... An for jim an the bias he set them at 5k.....i have had 4pr....1+1,2+2.M3s,M4,......all there bias was Off...at about 35-3800...jim set at 5k...
at 3500 you over drive All the Tranfourmers..T1 an T2...that how i found this out i lost a T1...so say what you well ...A fullrang as all ESL is only as good as it Bias!
I well not just have the Great Acoustats just seting here, looking good...thay still can sound to me are As good as ESL can get...An for the $$$ NOW....NOT MUCH CAN EVEN GET CLOSE....goodluck an Hohoho
at 3500 you over drive All the Tranfourmers..T1 an T2...that how i found this out i lost a T1...so say what you well ...A fullrang as all ESL is only as good as it Bias!
I well not just have the Great Acoustats just seting here, looking good...thay still can sound to me are As good as ESL can get...An for the $$$ NOW....NOT MUCH CAN EVEN GET CLOSE....goodluck an Hohoho
Quote;
I think I only have a couple of questions on the bias circuit if anyone can answer.
The five 3300 pf caps would be a very simple to replace rather than adding another section (cap and diode(which I don't feel confident in doing)) can the voltage be increased any by using a different value on the five caps? Or better to just replace with same?
Another question is the 500 m ohm resistor. Would lowering this value increase voltage to the panel or is this resistor's purpose only to limit current surge's to protect the panels?
Thanks, Mark[/QUOTE]
The multiplier ladder increases the voltage with the number of stages or steps. That's the only way to increase the voltage at the output. Adding a stage or two is very simple as you are simply extending what is there to begin with. DO NOT use larger value capacitors in the multiplier this will increase the current at the output which is not what you want and can be dangerous to the speaker and to your life. The cap values that are stock can deliver a tremendous wallop if you get across them and are well grounded at the time (as in knock you down) larger values could be dangerous and it does not make things any better. Your speaker needs only voltage on the diaphragm not current. With clean diaphragms I have not noticed any difference with lower value load resistors. For that matter the high voltage 500 meg ohm resistor Jim used is one of the very best sounding resistors I have ever used and betters most all you might substitute. Age does not have any impact on that resistor. The caps do age though age and you would do well to put in new ones of equal quality and the same value as was stock. Remember the load resistor limits not only current to the diaphragms so they don't burst into flames when there is an arc but to you should you touch where you should not. By now you must know this happens too often. Legal safety limits for current are 10 mili amps maximum. Best regards Moray James.
I think I only have a couple of questions on the bias circuit if anyone can answer.
The five 3300 pf caps would be a very simple to replace rather than adding another section (cap and diode(which I don't feel confident in doing)) can the voltage be increased any by using a different value on the five caps? Or better to just replace with same?
Another question is the 500 m ohm resistor. Would lowering this value increase voltage to the panel or is this resistor's purpose only to limit current surge's to protect the panels?
Thanks, Mark[/QUOTE]
The multiplier ladder increases the voltage with the number of stages or steps. That's the only way to increase the voltage at the output. Adding a stage or two is very simple as you are simply extending what is there to begin with. DO NOT use larger value capacitors in the multiplier this will increase the current at the output which is not what you want and can be dangerous to the speaker and to your life. The cap values that are stock can deliver a tremendous wallop if you get across them and are well grounded at the time (as in knock you down) larger values could be dangerous and it does not make things any better. Your speaker needs only voltage on the diaphragm not current. With clean diaphragms I have not noticed any difference with lower value load resistors. For that matter the high voltage 500 meg ohm resistor Jim used is one of the very best sounding resistors I have ever used and betters most all you might substitute. Age does not have any impact on that resistor. The caps do age though age and you would do well to put in new ones of equal quality and the same value as was stock. Remember the load resistor limits not only current to the diaphragms so they don't burst into flames when there is an arc but to you should you touch where you should not. By now you must know this happens too often. Legal safety limits for current are 10 mili amps maximum. Best regards Moray James.
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