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.
User avatar
Resistor Ronker
Posts: 379
Joined: 07 Jan 2011, 08:41
Location: the garage
Has thanked: 251 times
Have thanks: 110 times

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
User avatar
Posts: 29
Joined: 27 May 2011, 18:30
Location: Sydney, Australia
Has thanked: 13 times
Have thanks: 3 times

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?
Posts: 49
Joined: 27 Apr 2008, 12:35
Has thanked: 2 times
Have thanks: 7 times

Re: Hughes & Kettner - Rotosphere

Postby Yazoo55 » Yesterday, 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.
You do not have the required permissions to view the files attached to this post.

For this message the author Yazoo55 has received thanks:
ozzy666 (Yesterday, 17:18)
Posts: 49
Joined: 27 Apr 2008, 12:35
Has thanked: 2 times
Have thanks: 7 times


Return to Modern Stompbox Effects (1975 - ...)

Who is online

Users browsing this forum: ambusch, efe, Google Feedfetcher, kingplank, marcelomd, michaelballard and 4 guests