Hughes & Kettner - Rotosphere  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.

Re: Hughes & Kettner - Rotosphere

Postby blackbunny » 25 Mar 2014, 12:22

squatch wrote:Just wondering if it's safe to plug in a 15VAC adaptor? (but I'd check the output first) How much voltage do you think a MK1 would handle safely?

I wouldn't use a 15VAC supply on this pedal, 13VAC (loaded) @ 700mA - 1Amp would be the maximum. Why? All internal voltages will be be raised by about 25% if you plug in 15VAC.
The positive & negative 12VDC IC supply rails would be OK as they're regulated, the HT supply on the valve anodes will go up from 280VDC to 350VDC, which will probably be OK, but the heater supply for the valve will go from 12.6VDC to 15.75VDC, which is way too high.

Study the power supply circuit diagram I posted on the 15 May 2013 (a few posts back, on this page). You would have to replace the 2 x 1 watt 4.7 ohm resistors R209 & R210 with 18 ohm 2 watt resistors to drop the heater voltage back to 12.6VDC.
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Re: Hughes & Kettner - Rotosphere

Postby squatch » 25 Mar 2014, 14:05

Thanks blackbunny, I'll just stick to 12VAC...I've got another here
The one I was using was getting hot and buzzing so I thought I needed more than a 1 amp supply
I've got another newish 12VAC 1 amp so I'll try that, maybe the old one's kaput
Cheers, squatch
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Re: Hughes & Kettner - Rotosphere

Postby Yazoo55 » 08 Aug 2018, 18:48

OK, I've now got the full-on hots to build this. I always get this way when I got interested in a new project. I decided to use Kicad to do new layouts and get them fabricated since it is a double-sided board beyond my capabilities.

The photos have been invaluable. I've got the control board set up in Kicad and being able to see the track layout has made it a lot easier.

Any advice on wiring up the sockets/pins P01 - P06 would be greatly appreciated. I can see they relate to the Slow/Fast footswitch and the Bypass footswitch. What kind of footswitches are they?
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Re: Hughes & Kettner - Rotosphere

Postby Yazoo55 » 23 Sep 2018, 12:52

I went ahead and built my version of the Rotosphere, definitely following in your footsteps. I got the board fabricated for me and I have almost completed it. I have built a base out of plywood and I am going to use two pieces of aluminium sheet, one for the back and another for the cover. It should be easier to fit with two separate pieces. It works out cheaper than trying to buy an enclosure and it's always difficult to find a suitably shaped one any way.

I just need to set the trimmers. Is this just by ear? If you can offer any advice, it would be very welcome.

Here is a picture.
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Re: Hughes & Kettner - Rotosphere

Postby joseluisrio@ono.com » 27 Dec 2018, 11:36

Hey guys,

fantastic work, the hughes and kettner people would be stunned if they knew the forum, they know it surely

I have followed all the works and in the end I see that it is a work of months of individual people, someone has thought of making some pcbs already working and passing them, it would save a lot of time and mistakes to the rest is a matter of agreeing on the cost and Shipping.

On the other hand, this pedal is a megamonstruo can be reduced enough in its basic components to make a simpler version, for example, eliminating the stage of the tube would reduce it a lot, I will work on this and publish a scheme if I have time, I have experience with CI BBDs although following this scheme is a bit complicated.

a greeting

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