Tweedle-D

[Rockwell666]

Hey Folks, I am tinkering around with ideas for the amp. I love the sound and dynamic feel of the tweedle D. Both channels sound pretty identical to me so I was looking at the ever so popular cascade mod BUT there are no mixing resistors on a stock 5e3 or Tweedle D. Do any of you have experience with adding mixing resistors to this circuit? I do expect it to refine the sound abit by removing some of that raw sound. But I am hoping it would make the amp even more versatile.

[pompeiisneaks]

It depends on how you'd set the channels up. Would you only have one volume pot? If you're using two volume post but just jumpering the inputs, then it wouldn't need a mixing resistor setup, because the two pots act as the mixing resistors.

OTOH if you are planning on only doing one volume, then yes you'd need some. Fender typically did 220k to 270 I think, it will diminish the circuit a bit, yes, and I'd almost think having separate volumes may make more sense anyway as you'd be able to balance them. All three inputs are slightly different impedances, due to one being just 33k with the 1M to ground and the other two the typical fender style that does it's weird thing. I can clearly hear three different tones and levels on all three inputs, so you will also possibly lose a little of something sticking with just one. Your call though.

~Phil

[Rockwell666]

Hi Phil, I wired mine up as 68K's one channel 1 and 33K's on channel 2's inputs. (4 inputs total-used a 5e3 chassis). I was thinking 2 volume controls but now that you mention it your right, the way the volume controls are wired they all ready act as mixing resistors...... and the stock tone control is dependent on this dang... doing the 1 wire mod on a marshall is so easy with the mixing resistors. too much work haha

[mojotom]

I didn't build that one but the good old 5E3 was supposed to be used with an A/B box of some kind running one volume dimed and the other lowered to use the advantage of the coupling (pots without mixer resistors) ?
(Fuller mids on the dimed channel and more scooped mids on the other due to channel interaction).

At least I thought that was the purpose of Neil Young motorized pots.

[Bear]

The isolated cathodes on the two input channels of the Tweedle should mean that you won't really get that 5E3 interactive volumes stuff. I figure the 5E3's spongier compression would also help with the fact that the lead input isn't much louder than the clean with that trick.

Given that the Tweedle cathodes are the same values, you could just go to a shared resistor and cathode if you really want it.

[mojotom]

The isolated cathodes on the two input channels of the Tweedle should mean that you won't really get that 5E3 interactive volumes stuff. I figure the 5E3's spongier compression would also help with the fact that the lead input isn't much louder than the clean with that trick.

Given that the Tweedle cathodes are the same values, you could just go to a shared resistor and cathode if you really want it.

You got me interested on that one.
How do you think the shared cathode helped the interaction ?

I was thinking the other channel volume position would load down the other channel as well as the load the next triode.
But I may have read too much Weber stuff back in the days


On another note that thread might give you some ideas, not really making each channel different but scooping mids on both channels to have a different sound available. That sounded interesting when I wrote it.

http://ampgarage.com/forum/viewtopic.ph ... ee#p347060

[Bear]

Honestly, my best recollection of the phenomenon is from Weber stuff and standard folklore for tweeds and very early Marshalls. I forget the tech explanation except that isolating cathodes is the top mod to kill the interaction. The Tweedle is a modernized/improved 5E3, so more predictable behavior for each channel is a piece of that.

[nworbetan]

I stole this image from somewhere else on the net, I apologize that I don't know who to give credit to for it.



The 5E3 tone control gives the normal channel audio signal an extra pair of paths to ground (in yellow), one of which is additionally affected by the bright channel volume control. This is the biggest cause of interactivity.

The shared cathode resistor can cause some interaction if you overdrive one of the channels so hard that the bias changes, but that's not the interactivity that the 5E3 is (in)famous for.

[Rockwell666]

I stole this image from somewhere else on the net, I apologize that I don't know who to give credit to for it.



The 5E3 tone control gives the normal channel audio signal an extra pair of paths to ground (in yellow), one of which is additionally affected by the bright channel volume control. This is the biggest cause of interactivity.

The shared cathode resistor can cause some interaction if you overdrive one of the channels so hard that the bias changes, but that's not the interactivity that the 5E3 is (in)famous for.

I like that explanation of two ground paths and how they interact. shared cathodes, to me, have a different feel. sep cathodes forsure give a more modern feel/sound. but in cascade mods I prefer the shared cathode as it seems to add more feel. I could also be off my rocker and on the hookah too much
I forgot about using an A/B pedal to go from clean to raunchy!!

[nworbetan]

Doing a little bit of googling led me to another post on the el34world.com forums: http://el34world.com/Forum/index.php?PH ... #msg101896

It looks like that's the kind of shared cathode interaction that can happen to a 5E3 modified into a Tweedle D style amp, and definitely not something that anyone wants.