rotosphere problem- noise from high rotor

[imaradiostar]

I bought a used H&K rotosphere mkII and it has a crackling noise only from the "high frequency" rotor. Does anyone out there have a copy of the service manual that they could send me?

thanks!

jamie

[imaradiostar]

Nevermind- found a bad MN3102. Is there anyone nearby that has one they'd want to sell?

jamie

[seaward_son]

Hello Jaimie,

I think I'm having the same issue with my Rotosphere MK II. Same symptoms at least. Were you able to source a MN3102 and fix yours? Do you have a schematic for this thing? Where was that chip located? I have experience working on tube amps, but not too many PCB tube pedals. This thing seems pretty complicated.

Thanks for your help!

-Chris

[vintagekiki]

https://elektrotanya.com/hughes_and_kettner_rotosphere_sch.pdf/download.html

https://schems.com/bmampscom/hughes_ketner/hk_rotosphere_sch.pdf

https://en.audiofanzine.com/rotary-speaker-simulator/hughes-kettner/tube-rotosphere/medias/other/

https://en.audiofanzine.com/rotary-speaker-simulator/hughes-kettner/tube-rotosphere-mkii/medias/other/

https://www.schematicsunlimited.com/h/hughes-kettner
rotosphere mkii service manual; rotosphere mkii service bulletin

https://www.freestompboxes.org/viewtopic.php?t=11817
Hughes & Kettner - Rotosphere
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... Here's some schematics for the original Rotosphere. The Mk2 is almost identical, plus 2 extra trimpots beside the Rotor Balance control to fine tune the low and high rotor speeds ...

[seaward_son]

Thank you for the resources vintagekiki! I have some learning to do!! I found that thread on the Freestompboxes site. Seems to be a lot of info there.

[seaward_son]

I was able to fix my pedal by replacing the MN3102 and MN3207 chips. I’m thinking only one of the MN3207s was causing the noise however. It was still noisy with e new MN3102s and the original MN3207s. I purchased new chips in a set of 4 on eBay.