Krakauer Bros. PR3-PO3 Schematic

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Product Information:
Manufacturer:Krakauer Bros.

Schematics Content:

Page 1:

NDDEL PR3 - P03 Super Electone Piano
Wiring Assembly. Delay Switches Details
Polarizing Switch and Power Stage Circuits

Page 3:

Phasing - Tone & Volume Control Circuits.

Page 4:

SETTING UP OF CONTROLS: Due to variations in the case design of pianos, the components trill be located in different positions in different instruments; however, sech of the controls which comes to the attention of the serviceman will be plainly marked. The controls will be positioned either directly under the top cover of the piano or in back of the lower section under neath the key board. If in the latter position, the lower front board of the piano can be removed by releasing a simple spring catch at the center of its top edge.

Turn on the 701290 and set the left and push-button of the tone control switch. This connects the three phasing control potentiometers and the two (bass and treble) tone control potentiometers. Following the accompanying diagram and the customer's general desire as to who ler a basically thick or thin tone is rented, try various settings of the five controls mentioned above until the customer is satisfied. Select the button which this tone jato be set up on permanently. Take the corresponding color coded wire at each of the resistance banks opposite each of the five potentiometers and connect each wire to the resistor numbered the same as the nearest merl: to the pointer of its potentiometer. Then making these set-ups, the polarizing: stitch circuits should be set to that one of the three positions (piano, organ or banjo) which the customer expects to use most with this particular tone. Do not set-up the basio " regular " piano tono at this time. Do not set the volume control on the push buttons until later.

When all tones other than the regular plane tong are set up, this tone quality can then be set following was Phelsing control No. 1 at 10, Phasing control No. 2 at 3 (which is the balanced or " no response " position), Phasing control No. 3 at B, Treble cut tone control at 1000, and Bees out tone control between 3,000 and 10,000 - as the customer's our diotocos. The corr19 TG loft in this position so that the left-hand button is always " Regular Piano Tone ".

The pre-set volume control may now be adjusted. The two red wires (left hand button) should be placed on the sixth connection of each of the volume control.banks. Press the other buttons in order and set the pairs of wires corresponding to these buttons so that the volume of each setting is equal to the volume of button 1o. l. As this is a constant impedance type Level control it is necessary to get both the wires of a pair to the same resistor in the respective banks. That is, with one wire of a button set to, say resistor No.5, then the other wire from this button must also be set to resistor No. 5 on its bank.

GROUNDING AND BONDING: If oscillation is present in the amplifiers it is probably due to defective grounding of the components or bonding of the shields. Another cause is an open rid connection ALL SUI LDS, CHASSIS, TRANSFORMER CORES, SPEAKER FRAME, AND OTHER ELECTRICAL COMPONENTS MUST BE FIRMLY GROUNDED. Oscillation above audio frequencies is often the result of apparent speaker rattios, This can be cheeked by using the head-phones to determine if the rettle is in the speaker or the amplifier. In case of oscillation the condensers across the secondary of the driver transformar (which is in the pre-amplifier) ray be at feult.
Rattles occurring when the pedals are used or on mechanical disturbances, such as prssing on the piano top, pressing dom (not striking) the keys, slapping the side of the instrument, eto, are usually caused by bad bonding between any two touching conducting objects in the instrument. This is not confined to the electrical circuits alone but may be, for example, between one of the piano action brackets and its supporting bolt. Per severance is the only way to find the trouble and bonding is the cure.

POLARIZING CIRCUIT TROUBLES:. Terrific clicks when a key is pressed or struok is usually due to an open ground on its delay filter condensers. If the trouble is on ell keys, it is probably an open ground wire to the common bus at the Found end of those condensers.

A short of a piano string to ground my be tested with a 1000 - ohm per volt Voltmeter which should read 0.2 volt on the in - volt scale or 0.3 Toit on the 15 volt scale, when connected between the string and ground, the string being positive, Low voltage indicates a short, providing the corresponding delay switch is not open and the polarizing switch is on " banjo ". The delay switch should normally lay against the rear bus.

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