Hughes & Kettner - Rotosphere  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
fosnal1950
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Post by fosnal1950 »

I think it's much too complicated to clone imho , just buy a secondhand one. I have one, it's a favourite but what I would like is a better signal to noise ratio. It should have a separate inputlevel and outputlevel.

And changing the tube is a bitch !

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Post by ssmc »

fosnal1950 wrote:I think it's much too complicated to clone imho
It may be,but then it wouldn't be fun if it would be simple :D

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Post by blackbunny »

fosnal1950 wrote:I have one, it's a favourite but what I would like is a better signal to noise ratio. It should have a separate inputlevel and outputlevel.

And changing the tube is a bitch !
Odd, my Mk 1 isn't very noisy at all. I like to put it at the end of my signal chain, right before the amp, and I don't use much input drive on the Rotosphere. Sounds magic with a Timmy, Big Muff or whatever in front and a clean Fender or Ampeg valve (tube) amp bringing up the rear.

I like the JJ Tesla 12AX7 tube best, so far. Changing the tube is a bit fiddly.

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Post by fosnal1950 »

No , it's not very noisy but a bit too much to my liking.

But I do like its sound especially the point where the brake starts to kick in or when it accelerates.

One of my favourite songs to play with it is "rocky mountain way" with a nice grinding distortion that's where it can really shine.

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Post by squatch »

Thanks blackbunny for those schematics, they'll come in handy
I just got my Mk 1 working after 5 years of thinking it was broken
Turns out I was using the wrong supply...not enough grunt
It was lighting up but no signal and the rotor lights were'nt firing

I sure would like to know how to reduce the hiss....low noise valve perhaps?
Maybe I'll put a on/off breaker switch in as well

Cheers, squatch

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Post by blackbunny »

squatch wrote:I sure would like to know how to reduce the hiss....low noise valve perhaps?
That will help. I tried various ECC83 / 12AX7A / 7025 valves and settled on the JJ 12AX7 because I liked the tone best. The Mesa / Baron and Sovtek 12AX7LPS both had slightly lower noise than the JJ, but sounded a tiny bit thinner or "harder", while the JJ sounded "warmer" and more like an old valve Leslie speaker.

The lowest noise of all was a Marshall-branded ECC83 from the late 1990's; these have an unusual plate structure and look like a TAD ECC83 / 12AX7A.
squatch wrote:Turns out I was using the wrong supply...not enough grunt
It was lighting up but no signal and the rotor lights were'nt firing
I use a 1500 ma 12.6VAC supply so that there is no sag. I also replaced the regulator IC's with 7812 and 7912 regulators in TO-220 cases, and added 0.1 poly film capacitors to the regulator outputs in parallel with the 2.2uF tantalum capacitors.

To keep noise down, make sure your gain-staging is optimum. I set the input level switch to the 'low' position and get some nice overdrive when my guitar level is cranked for solo's, and it also seems to result in the lowest noise and hiss.

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Post by squatch »

Thanks again blackbunny, great info
I was fiddling about the other day with the gain settings, trying to balance the output of the Mutron III to the input,
the Mutron's a fairly hot output,but I got it sounding pretty good.
Now I want to put a Blue Boy Deluxe between the two but I worry about blowing the BBD input with the Mutron
With the Mutron peak on 3 and the gain on 6 (in High mode), it worked pretty good into the Rotosphere
I can sort out a better PSU (which might also reduce the hiss), and change the valve, but I'm just a regular guitar
tech, so I'll get my synth tech to do those other mods

Cheers, squatch

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Post by blackbunny »

squatch wrote:Now I want to put a Blue Boy Deluxe between the two but I worry about blowing the BBD input with the Mutron
Yep, that's a risky proposition alright. I have a late 70's EH Electric Mistress and Deluxe Memory Man both sitting in my cupboard waiting for SAD1024 BBD's. Best to put any high output devices after them....but then you amplify all that BBD hiss!
squatch wrote:I can sort out a better PSU (which might also reduce the hiss), and change the valve, but I'm just a regular guitar tech, so I'll get my synth tech to do those other mods
The important thing is to get a strong enough power supply so that the voltage at the effect input never drops below 12VAC under load. The regulators need at least 15VDC inputs to regulate properly. If they don't get enough input voltage, there is little or no regulation so hiss and hum levels will increase in the DC supply to the IC's and transistors.

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Post by squatch »

blackbunny wrote:
squatch wrote:Now I want to put a Blue Boy Deluxe between the two but I worry about blowing the BBD input with the Mutron
Yep, that's a risky proposition alright. I have a late 70's EH Electric Mistress and Deluxe Memory Man both sitting in my cupboard waiting for SAD1024 BBD's. Best to put any high output devices after them....but then you amplify all that BBD hiss!
Sorry about the confusion blackbunny...what I should have said 'I worry about blowing up the MI Blues Boy Deluxe input with the Mutron'
heh...I wasn't even thinking about Bucket Brigade Device LOL

Thanks again
squatch

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Post by blackbunny »

No problemo, sounds interesting. Unlikely that you will blow your MI Blues Boy with a high-level input from your Mutron....more likely that you will overdrive the input stage and experience some extreme phased distortions that will make you seasick! Cheers, bb

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Post by DougH »

Or...

Just get one of these:

Image

These are actual leslie units from home console organs. You can find these for sale pretty reasonably. I bought the one on the right for $40. I've built it into a suitcase-sized leslie for my guitar or organ. It sounds very good- 2 speeds with the speed ramp etc. Has an 8" speaker and I just plug one of my amps into it.
"You have just tubescreamered or fuzzfaced yourself " -polarbearfx

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Post by blackbunny »

I wish! Years ago I used to lug a Leslie 122 cabinet around in my truck for the keyboard player in a band I was in. The little 25 watt valve amp inside was never loud enough to be heard above the band's racket, so he took out the amp chassis and connected a HiWatt 200 valve PA head. It sounded gorgeous, but was a pain to lug around.

Now I'm older I'm happy to settle for "second best" and save my aching back. Thanks to the Rotosphere.

I must say your cut-down rotary speakers look like a cool idea Doug. :thumbsup

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Post by Dirk_Hendrik »

DougH wrote:Or...

Just get one of these:

Image

These are actual leslie units from home console organs. You can find these for sale pretty reasonably. I bought the one on the right for $40. I've built it into a suitcase-sized leslie for my guitar or organ. It sounds very good- 2 speeds with the speed ramp etc. Has an 8" speaker and I just plug one of my amps into it.
I once recorded one of those on a 4 track with 4 mics evenly spaced around it. Playing it back with, guess what, 4 speakers gave.... incredible surround!! Changing position of the speakers was even more fun.
Sorry. Plain out of planes.

http://www.dirk-hendrik.com

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Post by DougH »

blackbunny wrote:I wish! Years ago I used to lug a Leslie 122 cabinet around in my truck for the keyboard player in a band I was in. The little 25 watt valve amp inside was never loud enough to be heard above the band's racket, so he took out the amp chassis and connected a HiWatt 200 valve PA head. It sounded gorgeous, but was a pain to lug around.

Now I'm older I'm happy to settle for "second best" and save my aching back. Thanks to the Rotosphere.

I must say your cut-down rotary speakers look like a cool idea Doug. :thumbsup
I just finished the wood-finishing last night and I'll post some pics in another thread. This is fairly light- no power amp. I just use it as a cabinet with one of my guitar amps. I don't know what the power capacity of the speaker is but I've been using a 10W amp with it and it sounds good. Would need to be mic'd in the p.a. for live band use. I'm just using it at home for recording etc. Next project is to do some repairs to a Korg CX3 drawbar organ, which will get used with this leslie. It's a fantastic sounding combination.
"You have just tubescreamered or fuzzfaced yourself " -polarbearfx

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Post by ssmc »

I think I have almost finished layout for this thing :D

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Post by blackbunny »

ssmc wrote:I think I have almost finished layout for this thing :D
Great news! Post it here as soon as you can and we can help verify and de-bug it. :thumbsup

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Post by ssmc »

OK.I've uploaded .bmp export on my photobucket account, and Sprint layout file in zip.

Image

Image

Image

Image

I still haven't finished control board yet.
Attachments
Rotosphere.zip
Sprint layout file, for those with the Sprint layout program.
Control board (board 2) is not finish.
(243.52 KiB) Downloaded 203 times

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Post by ssmc »

Since I can't edit....

Can somebody confirm if I made the correct spacing for tube socket?

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Post by ssmc »

Fredenando wrote:Original PCB dimmensions

http://picasaweb.google.com/fredenando/ ... Rotosphere
Thank you oh so much :thumbsup

I'll finish controls sooner then.

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