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Discussion in 'Marshall Amps' started by Dealmaker, May 5, 2013.
I can't overly read that.
Wondered though if Jubilee uses non LED diodes at all in lead channel. If only using V1, how does it have so much more gain than an 800 with the same tube compliment?
Coles notes, please.
Okay the LED's for the lead channel are in the area right next to V1B. They are labelled LED 2 & 3. LED 1 is the channel indicator. It does have regular James Bond (part number 007) silicon diodes on the lead channel but what they are doing, it looks to me, is making sure that the LEDs clip only one side of the sinewave-insuring an asymmetrical clip. Diodes only allow electrons to flow in one direction, so they are handy in directing the direction of signal flow.
Technically, a diode is any device that has two elements; a cathode and anode. A rectifier tube is a diode. A preamp tube is a triode because in addition to a cathode and anode it has a control grid. A tetrode introduces an additional grid and so forth.
A James Bond diode and an LED are two different types of beasts. They are both only called diodes because they have two elements. In an LED, electrons flow from across a gap negative to positive (or the way??) much like in a tube, but when the electron is received by the other element it emits a photon.
Another thing about LEDs is the forward voltage. This means there must be a minimum voltage presented at the input side in order for it to start passing signal across to the other side. This is why the Jubilee lead channel responds to picking dynamics so well.
V1A is Cascaded into V1B (one is biased colder than the other) this can be rather high gain depending on the value of the resistors involved. This likely sets the tone of the overdrive early in the lead channel signal chain. The LED network is like having an extra preamp tube.
Diodes 1 and 2 are the James Bond diodes used for the pull rhythm clip. You can see them on the schematic next to the switch labeled pull rhythm clip.
That makes some sense. Soooo... in even moee layman's terms, LED s are indeed part of Lead channel circuit in terms of half the waveform.
Not that tt really matters to me , I love my Jubes regardless if iy has a hamster on the wheel.
My understanding was that Steve designed the Jubilee with LEDs partly necause of the lack of good preamp tubes at the time and adding another tube gain stage would mean 1 more tube required for each unit.
Not quite, the Jubilee uses tubes for ALL phases of operation. The Rhythm clipping LED diodes are only used when you pull the Gain Pot out, when pushed in it's all tube distortion, when pulled out it uses the diodes to add a bit more gain.
Where the schematic trips people up is the fact that these LED diodes can be switched on and off via the gain pot. Yes while they may be in the signal path, the path can and does split like a train track taking a detour through the diodes when they are in use and diverting around them when not in use, meaning their contribution to the signal is only present when they are switched on.
Lastly the rhythm clip works on both channels (when their operation is desired via pulling out the gain knob) on both lead and rhythm channel, it's not as obvious on the lead channel but it's still there. If you desire a clean channel it's best not to use them, if all you want is all gain then do use them
As stated earlier, if you really want to know if the LED diodes are contributing to your tone, pull the amp chassis out and have a look while it's on, you can see them quite plainly in the area of the gain pot, they only light up when you pull the rhythm clip on the Gain knob. Be safe and don't stick your hands in it while its on or severe injury could occur.
I've done this before, they go out when the gain knob is pushed in. The only LED Diode it uses by default is the one that lights up to indicate the lead channel, and that one doesn't contribute to the signal path.
So the LED is activated on Lead channel when clip is pulled out on clean channel? It does get quieter but I hear no difference whatsoever in the gain structure on lead channel when that switch pot is pulled out. Only on channel one. There is very little tube distortion on channel one even with full gain if clip is off. I realize the tubes work in all modes.
It's there I promise it's there on the Lead Channel. Its subtle on the Lead Channel, but more obvious the more you crank the volume on the amp. When I first got my 2555x Jubilee I was certain it didn't work on the Lead Channel, however when I removed all my pedals and finally got my 2551AV and 2551BV cabs from sweetwater and was trying it out dry, I could finally tell the difference. The right speakers can help you hear the right things. Also I would make sure your amps tubes are in good shape, even new tubes can be dead on arrival, you should be able to get some good dirt even on the Rhythm channel without the Rhythm Clip pulled.
In fact even on the amp sim program Amplitube for computer, they did a great job of mimicking the rhythm clip sound of the Lead Channel of the real Jubilee. Think of the Rhythm clip as a small OD pedal that gives just a small juicy compression push to the lead channel and a bigger one to the Rhythm Channel, mostly because distortion is more obvious on what's supposed to be a clean channel.
I will try it on the Lead Channel. Yeah, gain full up on clean it gets some dirt. Lately when I dont need cleanish, which I rarely do, I have been using clip on channel 1and using Lead channel for solos. I guess the LED clip is applying a touch more saturation to lead channel then at that point.
Good to know. I assumed since 1987 the clip (unkown to be LED at the time to me) affected only the clean channel.
But kill the clip amd it is a tube path both channels.
It is interesting that control is labeled as "Rhythm Clip". not Clip
I think its because that was the intention to be a Rhythm channel clip, but it also added an extra little push for the lead as a result. It's like what happened back in the 60s and early 70s Gain wasn't marketed, however when the amps were turned up all the way that became an unintended design feature, as with that I believe the LED diodes and many features of this amp basically made it a test of concept amplifier. Testing future technology on a limited run platform.
We can listen to people on forums all day debate what does what, whats a pure tube path and what's not, but the nice thing is that we can visually see for ourselves when the LED diodes are on if we look inside the amp with it opened up. Each LED has 2 leads and signal only goes one way through them, so if they're not glowing, they're not in use.
Like another had said on the forum here that I completely agree with, it's not verbatim, but it went along the lines of "I don't care if it's a hamster spinning a wheel inside the amp, it sounds amazing!" And this I completely agree with! I love all of the versatility of the jubilee and I use the Rhythm Clip a lot as well as every feature of the amplifier, and someday I'll run two of them.
I believe that was myself!! Cheers
If they jubilee are made in england they are all handwired. Imo and from watchng them handwire amps when i visited Marshall factory
I had to open up my mini to look. The LEDs inside never light! Doesn't matter what mode or what channel. Weird.
It appears to me that the 007 diodes are tied to the clip mode, not the LEDs. The LEDs appear to be associated with the lead channel only. Not one to read schematics overy but I see nothjng going from clean channel clip mode to LEDs but there is to 4 diodes.?
Also, again, how does the Lead channel get so saturated with clip off if not using diodes for an extra gain stage? V2 is not used in the gain stages so where does the extra gain come from? Has to be diodes. The singe channel 800s are fairly low gain by comparison. The split channel 800s use diodes for the extra gain stage as they only have 3 tubes. Same with Jubilee. Unless it had an extra gain stage tube, something is required for that extra gain.
Would like to hear @santiall weigh in. Or find a video of the LEDs inside cause mine never lit up.
Take away the Top Hat & carton of Marlboros and they're the same amp.
I'm sorry, but I might have said things a bit unclear. Or I don't understand your point.
There's two separate diode clipping circuits in the Jubilee:
1. two 1N4007 diodes for the "pull Rhythm clip" feature
2. the above mentioned 5-diode network using two LEDs and three 1N4007 diodes. It is engaged for the lead circuit.
For circuit one, it is engaged by the push/pull switch in Input gain. It connects the two anti-parallel diodes to ground, and therefore basically clamping the sine wave peaks to ground, resulting in a heavily compressed sine wave. Thus, it sounds distorted and has quite a lot of sustain already. We're in the clean channel still, by the way!
For circuit two, in clean mode, the signal coming out of V1b is shunted to ground for clean mode by relay RL1. No signal goes into that part of the preamp consisting of the 5-diode-network and the lead master pot. Plus, by doing so, it ENgages the feedback loop around V1B consisting of R6 and R7. This reduces signal level and distortion/overdrive in conjunction wth the surrounding parts of the pramp (very cleverly done!).
Btw., the relay is engaged in clean mode (!) by pulling the master knob.
Pushing it back to its normal position, the lead mode is engaged, relay RL1 is DISengaged, and thus opens the connection (shunt) of the V1B signal to ground, letting it through to the 5-diode network. It also DISengages the feedback loop by connecting the junction R6 and R7 to ground, resulting in a rather "normal" guitar amp tube triode stage, increasing gain that is now fed into the 5-diode network (again: so clever!).
So I have to disagree: diode clipping is present in rhythm clip mode for the clean channel, as well as in the lead channel, but not for the clean mode in clean channel.
Both my 2554 1x12" combo I had back in the 90s and my DIY Jubilee clone I have today, had or have their LEDs emitting light when playing in the lead channel.
Furry Patato: Do you have any links to sources where Grindrod or others stated, that the Jubilee amp only diode clipping in rhythm clip mode?
Thanks for this. That was my understanding, the basic controls operation part. 5 diode including LEDs are active only when Lead Channel is selected.
When Clip knob is pulled in Clean channel, 2 additional 007 diodes come into play to clip the clean channel signal. But this does NOT affect the lead channels 5 diode array.
Rhythm clip pullout on the gain pot affects both channels. You have to use your ears.
This guy even demos it!
When you're looking at the schematic it can look like the signal is going through all 5 diodes all the time and technically it should if you're looking at it from the diode point of view....but what you're looking at is the alternate road parallel to the one that the all tube signal takes in the lead channel, when rhythm clip is pulled these two different roads/signal paths become one.
I just feel like you're only looking at the one signal path in the schematic and forgetting all about where the divergence in signal is and starts. You have to look at and account for the gain stages prior to getting into the diode network.
That dude does run it on the Lead channel I hear very little if any difference on the video. Guess I'll try at home and listen. It is something I have essentially never used in 30 years with the amp so have to give it a good test
The term Rhythm Clip throws me off too. Why call it that?
I will dig out my 1987 at some point for fun. It doesnt really matter but the original manual refers to the clip mode as used on the rhythm or normal channel. It keeps referring to the Rhythm amd Lead channels. I will listen to it amd see. Perhaps they even made a change on the circuit of the newer version.
The line that stands out most is the "It must be remembered that both pull switches are NOT independent and one will override the other depending on switch position. " There are only 2 pull switches on a Jubilee - clip amd Lead channel activation.
I have never noticed any difference in Lead channel sounds when the clip is engaged other than a minor drop in level with my original Jubillee.
In any case, they do not mention using clip with the lead channel at all.
Referring to using Normal channel.