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Brief Description of Problem:
Hum in Leslie speaker pedal channel and Space Generator.
No hum in organ at any time.
No hum in the other two Leslie channels (Red/Black and Tibia).
No hum in Leslie pedal channel if the input is disconnected at that channel’s amplifier inside the Leslie.
Description of equipment:
Wurlitzer 4570 Organ
Leslie 212S Speaker
Leslie Console Connector Kit 7773 (which includes 118220 chassis)
Description of Circuitry:
The Leslie consists of three channels with four identical 30-watt amplifiers.
Three of the channels are as follows:
■ rotating drum for Tibia
■ rotating drum for other voices (Red and Black)
■ stationary speaker for pedal (and possibly some other tones).
The fourth channel is for the Space Generator. That channel’s input is the same as for the pedal channel.
Description of problem:
See Console Connector schematic, in two parts, is attached.
This organ and this Leslie were purchased new together in 1974 and have been working well together until recently.
The Console Connector gets its signals from various points in the organ circuitry.
When the three-position Echo/Ensemble/Main switch is set to Main (internal organ speakers), the relay near the left side of the Console Connector schematic is deenergized, allowing the organ’s internal amplifiers and speakers to sound. There is no hum in either the organ or the Leslie when the switch is set in that position.
When the switch is moved to Ensemble (both organ and Leslie) or to Echo (Leslie alone), the hum occurs. The hum is only in the pedal channel and the Space Generator whose input is connected in parallel with the pedal channel of the Leslie.
The pedal signal from the organ, through the Console Connector and through the Leslie pedal channel is present along with the hum.
The other two channels for the rotating drums work properly. The Space Generator channel works properly when connected to either of the other channels.
Drum high speed/low speed controls work properly and do not affect the hum.
Troubleshooting thus far:
Disconnected pedal input directly at the Leslie pedal amplifier inside the Leslie speaker. The hum goes away completely. There is no other hum evident in any channel. This indicates that the circuitry within the Leslie speaker is working satisfactorily.
If the pedal input to the pedal amplifier inside the Leslie is moved to another Leslie channel inside the speaker, the hum follows the pedal input. That is, the hum goes to the other channel to which it has been connected. This indicates that the hum is being introduced before the pedal input to the Leslie.
Rerouting the organ-to-Leslie cable has no effect.
The Leslie is powered through the organ-to-Leslie cable connected to the Console Connector. The Console Connector is powered from a receptacle inside the organ console. There has not previously been any trouble with ground loops.
The Console Connector circuitry is powered from two sources:
■ a small transformer on the Console Connector provides power to a rectifier/capacitor network (shown near the lower right of the combined schematic) to operate the DC relay inside the Console Connector. This relay grounds the signals to the organ amplifiers when the Echo/Ensemble/Main is set to Echo.
■ the 117VAC power provided by the Console Connector through the organ-to-Leslie cable powers the transformer inside the Leslie including a 28 VDC voltage which is sent back through the cable to provide power for the other circuitry in the Console Connector.
When the Echo/Ensemble/Main switch is set to Main or Ensemble, the relay in the Console Connector is deenergized and allows the signals to go to the various amplifiers and speakers in the console. Also, the circuitry near the bottom-center of the combined schematic changes the voltage leading to the gates of the field effect transistors Q1, Q2, and Q3 to turn them on and allow the three signals to reach the conductors for each of the three channels within the organ-to-Leslie cable.
The voltages called out in the table in the upper right of the combined schematic were measured and found to be correct.
Because the hum is being introduced before the Leslie pedal channel amplifier inside the Leslie speaker but after the organ inputs to the Console Connector, the pedal circuitry in the Console Connector is suspect.
The integrated circuits called out as IC 3 and IC 4 are OpAmps, are the same type as the others in the Console Connector, and they are socketed. Swapping IC3 and IC4 with two of the others had no effect on the pedal channel hum.
Replacing electrolytic capacitor C16 had no effect on the hum.
I used a very makeshift signal tracer and I believe the hum may not be present at the left end of R13, and at the left end of C13. There is some hum at pin 2 of IC4. There is significant hum at the left and right ends of C16.
What should be done next?
I have the schematics for the organ and for the Leslie if reference is needed.
Does anyone have an inexpensive Console Connector of this type lying around in an unused organ?
I note that the field effect transistors are type 2N5163 and the OpAmps are type LM307 (or 7323 or SG307M) are no longer readily available for replacement. What are suitable replacements?
Hum in Leslie speaker pedal channel and Space Generator.
No hum in organ at any time.
No hum in the other two Leslie channels (Red/Black and Tibia).
No hum in Leslie pedal channel if the input is disconnected at that channel’s amplifier inside the Leslie.
Description of equipment:
Wurlitzer 4570 Organ
Leslie 212S Speaker
Leslie Console Connector Kit 7773 (which includes 118220 chassis)
Description of Circuitry:
The Leslie consists of three channels with four identical 30-watt amplifiers.
Three of the channels are as follows:
■ rotating drum for Tibia
■ rotating drum for other voices (Red and Black)
■ stationary speaker for pedal (and possibly some other tones).
The fourth channel is for the Space Generator. That channel’s input is the same as for the pedal channel.
Description of problem:
See Console Connector schematic, in two parts, is attached.
This organ and this Leslie were purchased new together in 1974 and have been working well together until recently.
The Console Connector gets its signals from various points in the organ circuitry.
When the three-position Echo/Ensemble/Main switch is set to Main (internal organ speakers), the relay near the left side of the Console Connector schematic is deenergized, allowing the organ’s internal amplifiers and speakers to sound. There is no hum in either the organ or the Leslie when the switch is set in that position.
When the switch is moved to Ensemble (both organ and Leslie) or to Echo (Leslie alone), the hum occurs. The hum is only in the pedal channel and the Space Generator whose input is connected in parallel with the pedal channel of the Leslie.
The pedal signal from the organ, through the Console Connector and through the Leslie pedal channel is present along with the hum.
The other two channels for the rotating drums work properly. The Space Generator channel works properly when connected to either of the other channels.
Drum high speed/low speed controls work properly and do not affect the hum.
Troubleshooting thus far:
Disconnected pedal input directly at the Leslie pedal amplifier inside the Leslie speaker. The hum goes away completely. There is no other hum evident in any channel. This indicates that the circuitry within the Leslie speaker is working satisfactorily.
If the pedal input to the pedal amplifier inside the Leslie is moved to another Leslie channel inside the speaker, the hum follows the pedal input. That is, the hum goes to the other channel to which it has been connected. This indicates that the hum is being introduced before the pedal input to the Leslie.
Rerouting the organ-to-Leslie cable has no effect.
The Leslie is powered through the organ-to-Leslie cable connected to the Console Connector. The Console Connector is powered from a receptacle inside the organ console. There has not previously been any trouble with ground loops.
The Console Connector circuitry is powered from two sources:
■ a small transformer on the Console Connector provides power to a rectifier/capacitor network (shown near the lower right of the combined schematic) to operate the DC relay inside the Console Connector. This relay grounds the signals to the organ amplifiers when the Echo/Ensemble/Main is set to Echo.
■ the 117VAC power provided by the Console Connector through the organ-to-Leslie cable powers the transformer inside the Leslie including a 28 VDC voltage which is sent back through the cable to provide power for the other circuitry in the Console Connector.
When the Echo/Ensemble/Main switch is set to Main or Ensemble, the relay in the Console Connector is deenergized and allows the signals to go to the various amplifiers and speakers in the console. Also, the circuitry near the bottom-center of the combined schematic changes the voltage leading to the gates of the field effect transistors Q1, Q2, and Q3 to turn them on and allow the three signals to reach the conductors for each of the three channels within the organ-to-Leslie cable.
The voltages called out in the table in the upper right of the combined schematic were measured and found to be correct.
Because the hum is being introduced before the Leslie pedal channel amplifier inside the Leslie speaker but after the organ inputs to the Console Connector, the pedal circuitry in the Console Connector is suspect.
The integrated circuits called out as IC 3 and IC 4 are OpAmps, are the same type as the others in the Console Connector, and they are socketed. Swapping IC3 and IC4 with two of the others had no effect on the pedal channel hum.
Replacing electrolytic capacitor C16 had no effect on the hum.
I used a very makeshift signal tracer and I believe the hum may not be present at the left end of R13, and at the left end of C13. There is some hum at pin 2 of IC4. There is significant hum at the left and right ends of C16.
What should be done next?
I have the schematics for the organ and for the Leslie if reference is needed.
Does anyone have an inexpensive Console Connector of this type lying around in an unused organ?
I note that the field effect transistors are type 2N5163 and the OpAmps are type LM307 (or 7323 or SG307M) are no longer readily available for replacement. What are suitable replacements?
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