SpeakerTalk

anatech · Introductory Contributor Joined: 14 Jul 2021 Posts: 2

Hi all,
I am in need of a schematic for the Kube 104/2 electronic EQ unit. IT has a strange fault, and I have been an audio electronic service technician for over 45 years now. I have a very complete and modern bench.

The problem is that the op amps on both channels rise to one or the other supply voltages slowly over time running. Probably 2 to 4 minutes. Then the sound is cut off. A schematic is what I am desperate for so I can get this back in the hands of the owner. His speakers work fine otherwise.

I have contacted KEF and they have no records beyond a parts list. I used to do warranty service for KEF, but sold my shop in 1998, and I don't think I ever had this information. I really hope an engineer or KEF technician can help out.

So far I have checked the grounds, and replaced a couple op amps that were drifting. These seemed to set the DC point on all the other op amps. The DC supply voltages are spot on. Nothing is oscillating.

Thanks in advance for any help you can give, Chris
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speakerguru · Posted: Thu Jul 15, 2021 5:20 pm Post subject:

Sorry, I don't remember which type of KUBE that was and I don't have a schematic. However...

The small KUBEs in plastic boxes has +/-15 V supplies and TL072 opamps. The larger KUBES in Metal cases had +/-24 V supplies and used NE5532 opamps. All were d.c. coupled throughout so I would guess the fault is in the psu or 1st stages.

I have schematics of some KUBES, so if you tell me what the supply voltages and opamps yours uses I can send you something similar (which will have the same circuit topology but a different frequency response)