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RE: bobwire and the Acoustat Spectra 11

Posted by john65b (A) on January 17, 2015 at 12:14:36

In Reply to: RE: bobwire and the Acoustat Spectra 11 posted by bobwire on January 17, 2015 at 10:56:57:

Your standard 10 Meg Ohm DMM cannot read past 1000V (likely), but you can still use a standard DMM - it will "load" the high voltage / low current of the bias circuit, so typicality 75v on a normal DMM will be around 5kv.

I forgot you do not have that standard Ultrasonic power supply the Spectra came with - you stripped it out in favor of a standard power supply. You now have no way to dial in your bias voltage... You replaced it with a tranny and voltage multiplier. But you can add another cap/diode "rung" on the voltage multiplier ladder to get around another 1kv bias.

Below is the BIas Adjustment of Ultrasonic power supply
ULTRASONIC BIAS POWER SUPPLY - ADJUSTMENT

Measurement and adjustment of the high voltage bias power supply is vital to the proper operation of the speaker. If an imbalance in playing volume is noted, or any modifications or repairs have been made, the bias power supply should be measured and adjusted if required. Two methods of measurement are provided.

• This procedure requires specialized equipment and electronic skills. DO NOT attempt this procedure if you are unfamiliar with safe operating practices around high voltage (+5000-volts DC).

• Do not be concerned about the exact voltage measurements. Due to variable loading effects of different meters, it is impossible to accurately measure the output of the supply. What is important is that both speakers are adjusted to read the same voltage using the same meter.

• This procedure requires that the interface be disconnected from both the speaker and amplifier. Do not plug in the wall transformer until told to do so.

• Location '5KV' is the point (used for method #1 only) for measurement of the 5000 volt power supply. Location '5KV' is the circuit pad next to the "+5 KV" label located at the center of the large printed circuit board.

METHOD #1: (Preferred) Using a high impedance, 1000:1 high voltage probe, and digital voltmeter, connect the ground lead of the probe to chassis ground (at the solder lug attaching the white wire to the chassis). Apply power via the appropriate wall transformer, and allow the system to stabilize for several minutes. Connect the hot lead of the probe to location '5KV'. Adjust the trimmer potentiometer on the PC board until the probe reads approximately 4.3 volts DC.

METHOD #2: (Alternate) Using a 10 megohm input impedance digital voltmeter, connect the ground (black) lead of the meter to chassis ground (at the solder lug attaching the white wire to the chassis). Apply power via the appropriate wall transformer, and allow the system to stabilize for several minutes. Connect the hot (red) lead of the meter to the red pin-plug terminal (where the panel connections are normally made). DO NOT CONNECT THIS TYPE OF METER TO LOCATION ‘5KV’. Adjust the trimmer potentiometer on the PC board until the probe reads approximately 75 volts DC. This reading will correspond to an actual 5000 volts, but the measurement is greatly reduced due to the voltage divider effect of the power supply and voltmeter.

I VOID WARRANTIES

Edits: 01/17/15

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