Hughes & Kettner - Rotosphere  [schematic]

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

I will test stereo mode, the problem right now is that the output levels on both channels are very different. There is probably a wrong resistor somewhere, but i havent searched for it yet. There are also 6 trimmers, two of them conntected to the MN's dont do anything apparently, while the other four change the intensity of the low- and high tremolo-like effects. Maybe its a problem with the MN-circuits, i've got very cheap ones, but i dont know if and how that affects the sound quality. Has somebody experience with this kind of flanger circuits?

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Post by puntxo »

Hello, where do you think is the most suitable place to connect a power on led indicator? I own a MK I and I'd like to add an UV led, like in the MK II model. I was thinking of using a 12V led and connect it to the +12v and -12v pins in the plug 2 connector. Do you think it might cause any problem?

If you have any question or need any picture from the MK I I could post them, just tell me.

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Post by puntxo »

puntxo wrote:I was thinking of using a 12V led and connect it to the +12v and -12v pins in the plug 2 connector.
Ops, I wanted to say +12v or -12v, that is, one pin to 12v and the other to ground for example.

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Post by blackbunny »

You can power an LED from either the + or - DC supply, as long as (1) you connect it with correct polarity, and (2) you wire a current limiting resistor in series with one of the LED 'legs'. Some tips here http://www.freestompboxes.org/viewtopic.php?f=53&t=4523

Let's say you use the +12vDC supply rail; start with a 4k7 resistor in series with the anode (long leg) of the LED and the +12v rail, connect the LED cathode (-) to a nearby ground and power up. If the UV is not bright enough, replace the 4k7 resistor with a 2k7 or 2k2, and power up again.
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Post by puntxo »

Thank you very much, blackbunny.

I've bought some 12v leds that come prewired with a resistor. I still haven't received them but I'll check the resistor value first. My worries were about damaging anything or wheter the led could cause any interference that affect the pedal sound. As you may have noticed, I'm not an expert in electronics :oops:

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Post by krueppel-keile »

Hope that helps:
"12V-Diode" just means that the prewired resistor is already set for a 12 Volt supply, so you should be good to go. Just make sure to get the polarity right :D
Otherwise: Resistance = (E-U)/I,
where E is the supply voltage, U is the voltage drop across the diode, and I is the diode current. U and I comes with the diodes description, a typical value could be U=2V, I=20mA, for example.

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Post by blackbunny »

A better place to insert the LED(s) would be across the filtered -18v supply, close to the 2200 uF filter capacitors C110 & C111.
This is before the regulator, and will minimize the chances of affecting other parts of the circuit.
You could also connect LED(s) to either the + or -12v supply rails, but they feed all the op amps and placing LED(s) there could increase the chances of audible interference.

The UV-purple LEDs I looked at had around 3.2v forward voltage drop, and come with 470 ohm resistors for 12v operation, which would allow approx. 19mA current through the LED.

This seems a bit high to me, and these LEDs are advertised as high efficiency / high output types, so I'd start off with a higher resistor value such as 1k5 (10mA), 2k2 (6.7mA) or 2k7 (5.5mA) on the -18v rail.

The lower the series resistor, the brighter the LED will be, but running the LED at very high currents will increase the chance of early death (of the LED, not you or the pedal). :hmmm:
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Post by puntxo »

Thank you very much again.

Today I've received the leds but finally I've decided not to do the mod. I think is not worth it, specially if it might cause interferences. I thought it would be easier.

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Post by krueppel-keile »

Hello,

After some time i got in a certain mood and went back to this project, and made some progress. I did some audio probing, and it turned out that one of the MN3207 BBDs didnt work (no output signal). I replaced it, that solved the problem with the two channels having different output levels. Also, there was an odd error in the oscillator circuit: One of the ICs (IC8) that produce the modulation signal for the MNs wasnt connected to ground. I disconnected it because my transformer had a different pin-layout than the original one, and needed new holes to be drilled on the board. So, to prevent an accident with the transformer secondary side touching ground, i cut off the connection of that piece of layer and didnt remember to reconnect the IC. So, it could only produce a garbage-like signal (or none at all). The best thing is, i remember double-checking the supply and ground connection of EVERY opamp, but i just looked at this one and thought "well it looks alright". :slap: :slap: :slap: :slap: :slap: :slap: :slap:
Now, it sounds much more like what you'd expect from a leslie emulator, and not like a speaker that gets switched on and off periodically :D .
Also, there were some other minor errors, like loose connections that seemed to make the modulation circuit work or not depending on the lunar cycle, but i think i fixed all of them. Also rewired everything, and the tube board is finally connected to the main board.
I removed the filter circuit that supplied the tube heaters, mainly because i wanted to to have some more space for the tube board, the 5W-resistors were slowly cooking the capacitors right next to them, and i wasnt able to get the heating voltage right by changing the resistor values (again im using tubes that need 6.3 Volts, not 12.6 like in the original design). The solution was an LM337 negative voltage regulator, where the output voltage can be controlled with a trimmer pot (datasheet has some example cirquits). It gets REALLY hot. I will need a bigger heatsink, and i will try to put a small 5W Resistor in series to the heater, so that the regulator's voltage drop is smaller and it doesn't have to radiate so much heat by itself.
Also, a friend of mine who works at a small machine factory will make a steel case for me in his spare time, but it can take a while.
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Post by andresbianco »

Hi all,

I'm new in this foro (from Uruguay =) ) and I love the Rotosphere but it's quite expensive.
I want to congratulate the people who took this and made his own DIY pedal :applause:

I'm drawing the schematic (provided over here) using Eagle in order to have it linked with the corresponding layout (board).
Anyone else uses Eagle for Schematics? Maybe we could collaborate on that.

I'll keep you posted!

Andrés

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Post by atreidesheir »

krueppel-keile wrote:Hello,

After some time i got in a certain mood and went back to this project, and made some progress. I did some audio probing, and it turned out that one of the MN3207 BBDs didnt work (no output signal). I replaced it, that solved the problem with the two channels having different output levels. Also, there was an odd error in the oscillator circuit: One of the ICs (IC8) that produce the modulation signal for the MNs wasnt connected to ground. I disconnected it because my transformer had a different pin-layout than the original one, and needed new holes to be drilled on the board. So, to prevent an accident with the transformer secondary side touching ground, i cut off the connection of that piece of layer and didnt remember to reconnect the IC. So, it could only produce a garbage-like signal (or none at all). The best thing is, i remember double-checking the supply and ground connection of EVERY opamp, but i just looked at this one and thought "well it looks alright". :slap: :slap: :slap: :slap: :slap: :slap: :slap:
Now, it sounds much more like what you'd expect from a leslie emulator, and not like a speaker that gets switched on and off periodically :D .
Also, there were some other minor errors, like loose connections that seemed to make the modulation circuit work or not depending on the lunar cycle, but i think i fixed all of them. Also rewired everything, and the tube board is finally connected to the main board.
I removed the filter circuit that supplied the tube heaters, mainly because i wanted to to have some more space for the tube board, the 5W-resistors were slowly cooking the capacitors right next to them, and i wasnt able to get the heating voltage right by changing the resistor values (again im using tubes that need 6.3 Volts, not 12.6 like in the original design). The solution was an LM337 negative voltage regulator, where the output voltage can be controlled with a trimmer pot (datasheet has some example cirquits). It gets REALLY hot. I will need a bigger heatsink, and i will try to put a small 5W Resistor in series to the heater, so that the regulator's voltage drop is smaller and it doesn't have to radiate so much heat by itself.
Also, a friend of mine who works at a small machine factory will make a steel case for me in his spare time, but it can take a while.
very impressive, but it looks like it weighs 5 kilos :applause:
"Contemplate it - on the tree of woe." :Thulsa Doom

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Post by andresbianco »

I have the Schematic ready in Eagle.
I have to double check with the schematic posted here (BTW how reliable is that schematic? I hope very much...) and then move to the board layout and trace it.
I'm planning to use 33-each to make the PCB but the minimum is 4 units. (so 132 dollars).

Saludos,
Andrés

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Post by krueppel-keile »

It is nice that you want to make your own layout. The schematics are correct, at least as far as i can tell (and that is not too much, but at least it sounds nice and does all the things it should do).
I would never have the nerves to sit down and make a layout of that size myself, instead i used the layout first posted here by ssmc (for the program called sprint-layout(you can get a free demo version to view the layout), i have no experience in eagle but maybe it can import the files).
I compared it to the schematics very thoroughly, and found one or two errors. I think i posted a corrected version a looong time ago, but i will attach it here again. It seems to be identical to the layout of the original rotosphere, it is structured very nicely and size-effective (well it is big, but it could not be much smaller with so many components). In other words, it is very professional.

But dont get me wrong, i dont want to talk you out of making your own layout. The one i used has two big problems: It is double-sided, and the tube is on a separate board. Both made it really difficult to build it. So, i would suggest to make it single-sided so it would not take so much time and effort to build. The board would probably be cheaper too if it is one-sided. On the other hand, the "pedal" would end up being the size of two shoeboxes instead being the size of one shoebox. Could be worse, right? :D

You can get the circuit board cheaper if you try to make one yourself. 130$ is way too much in my opinion, considering all the other parts you probably have to buy. Making a pcb is not too difficult, mine cost me around 20$ for the raw board and the chemical (sodium persulfate), and a few uses of a laser printer. (I had to buy a small drill for the holes too, but it cost only around 20$ and can still be used for other projects.)

Keep up the good work! I wish you much sucess in completing this project. I would be glad to offer my advice if you need any. :thumbsup

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Post by thoro73 »

Important Notice to anyone who can help me:
I am looking for the list of components for electronic effects pedal, brand "Hughes & Kettner", model: "Tube Rotosphere MKII (Leslie effect)."

P.S.: Please forward this message, I hope there is someone who can help me to find it.

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Post by Fredenando »

Sorry,

Here are the part list that I have:


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Post by guylavoie »

Hi all.

I was reading through this thread and was looking to find the spot in the schematic of the Rotosphere Mk I where you would put in the trim pot to allow adjusting the rotor speeds like the Mk II. Does anyone have an idea which resistors and/or capacitors control the two speeds?

Thanks!

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Post by Karsten21 »

[quote="andresbianco"]I have the Schematic ready in Eagle.

Hello andresbianco,

It´s possible to share the eagle schematic and board files please? It would me prevent to do the same work again :D

Thanks a lot
Karsten

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Post by squatch »

Congrats krueppel for persisting with that project...well done!

I was gonna start using my old Mk1 again, but the supply I have with it is buzzing
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?
Thanks in advance if anyone knows

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