Parallel/cascaded inputs on a tweed Deluxe

[ChopSauce]

EDIT: I was searching for a way to achieve the serial/parallel feature of the input triodes - see picture below - without resorting to several pluging/switching operations. In vain:

- I ended to the conclusion that it would require physically breaking the connection of the tip switch, in the jack itself.
(for the cascading to take care of all the switching/"work" even when plugged on the Channel2/Mic input jack)

I kept the original message - below - for the record, though.

____________________________________________________


This mod has already been documented by Rob Robinette and reported here https://ampgarage.com/forum/viewtopic.php?t=32027 and there https://ampgarage.com/forum/viewtopic.php?f=4&t=33301 (in the Dumble discussion section).

Here is a schematic for it (thanks to Fred and Martin)



However, despite my interest for the mod, it seems to me that it has some flaws and I need help to fix these - possibly.

First, one detail. According to my semantics, the mod does not really do, neither cascading, nor paralleling. What it does it serialize the entries or leave them side by side. Cascading sounds too much like http://www.valvewizard.co.uk/cascode.html and paralleling - what is often refered to as "bridging" - does not seem easy to make co-exist with this mod, wich is the second point.

Paralleling/bridging the entries is usually done using at least 3 input jacks, but the serial/side-by-side mod only works with two jacks. The "serializing" feature is disabled when one jack is inserted in the Mic/Bright entry & I can't figure myself how to wire this if there were two entries there?

Any idea to achieve a safe/full serial/parallel inputs feature for a 5C3...

[ChopSauce]

(no answer... )
Maybe should I have written something less provocative/more informative - out of frustration - above, but my intuition is that:

- it should be possible to avoid canceling the cascading feature when a jack is plugged into the Channel2/Mic input, of the above schematic, and instead rely on the cascading switch to also do that...



IMHO, that would be a plus to be able to use and A/B(/Y) box in input and still be able to use cascading.

I have a 4PDT switch and with it I feel it ought to be possible to also switch on/off the Channel2/Mic input, so no current flows back to the guitar when cascading - for that is the concern, right?

Unfortunatelly, I see no mean to simply add that to the above schematic. Anything I could think of implies further modifications to the suggested wiring & I'm (still) lost there, so far...

At least could you recommend me some reading about the relevant methodology - if any such thing exists?

I searched the internet for "method designing switching logical" but that leaded me somewhat farther than expected ...

[pdf64]

Cascade in this context just means to arrange the output of one stage to feed into the input of another, eg such that the the output of A feeds into the input of B, so the output of B = A x B. Contrast to parallel mode, where their outputs would be summed, A +B.
Cascode is a different thing again.

[ChopSauce]

Yes. I shouldn't have mentionned this on my first post, for it is not relevant to my main concern, that is:

- how to achieve all that with a single switch (& an A/B/Y box)...

[fred.violleau]

Hey @ChopSauce, this is something I want to achieve as well. I have exchanged my Tweedle Dee for 2 impeccable 10'EVM L that sound glorious. I now have to build another Tweedle Dee with that mod and I want to put it on relays as well.

So here are my thougths :

We could break the two inputs and keep just one. A relay could switch the signal into either the normal channel or the bright channel.
on the build I did, these two channels were voiced differently, which allows the cascading while filtering som extra lows on the normal channel.

We could then break the interactivity between the two Vol knobs (in case of this build, the interaction does not bring much value, but I don't know what the impact on the sound would be...).

So technically we could have a second relay that cascade input 1 into channel 2.

What's your take on that scenario?

Fred.

[ChopSauce]

Well, loose take I must admit.

I was feeling a bit lonely on this one, and thought "no answer" to this post stood for "no obvious answer", which is not encouraging at all when considering the sum of expertise available here...

Plus, reading again Marcus' reports about his build influenced me towards building the thing as a (sort of) Tweed Deluxe combo, which lets very little room for mods.

Marcus also agreed that channel switching looks a lot like a must have, especially for a gigging amp, but I could find no common way to achieve both the serial and parallel feature in a manageable way.

Didn't I wrote that my last attempt to design - from scratch - a common way to do that ended up to the point where the tip switch of the jack itself would had to be broken - which I consider not feasible?

Maybe I'll try something else/one more time, under your encouragements...

Oh, and yes: I noticed... you lucky one, having found these EV, does it seem...

EDIT/Post Scriptum:

Marcus suggested that the parallel feature be achieved with an A/B/Y box and Alexander already removed the interaction between channels, does it (also) seem.

[fred.violleau]

@ChopSauce, nope interaction between the two channels is still here.
If you keep having the output of the vol2 control bleeding into vol1, they do interact.

Fred.

[fred.violleau]

Here is one way to do it :

use one input jack that feeds both V1A and V1B.
Then disconnect bright channel VOL out and vol NORMAL channel
and add an A B Y type of relay setup that allows to use either NORMAL Channel or BRIGHT Channel or both channel parralleled, with a variable resistor in order to adjust the level output into V2A

here is a quick layout of the relay setup.

Capture d’écran 2021-02-08 à 11.17.00.png

Let me know what you think.

Fred.

[fred.violleau]

If you cannot feed the two channels with the single input jack then you can add another relay that would be synchronized with the other A / B relay :

Capture d’écran 2021-02-08 à 13.25.04.png

Fred.

[norburybrook]

the simple answer is to just have 2 tweedle dee's you have redundancy then as well on a gig in case one amp goes down



M

[fred.violleau]

Of course Marcus !

Fred.

[ChopSauce]

If you cannot feed the two channels with the single input jack ...

Why wouldn't that work?

I'll manage to pause and think about your suggestions...
(well Fred's one, firstly)

[fred.violleau]

If you cannot feed the two channels with the single input jack ...

Why wouldn't that work?

@ChopSauce, it works, I have done it on a previous build.
I was wondering though if it had electrical consequences that I did not foresee. I am not an electronic engineer.. I don't know much, but I am willing to test and learn !

Fred.

[ChopSauce]

Of course. Same for me...

So, your suggestion to use only one input jack, which directly feeds both halves of V1 (& to make the connection after the volume pots) seems fine...

but then the 1M/680k no more inserts before V1 - or am I missing something...

In extenso: I understand how to do parallel (A/B/Y) but still not how to achieve both that and serializing without resorting to (un)plugging at least once.

[fred.violleau]

but then the 1M/680k no more inserts before V1 - or am I missing something...

It seems to be the tricky part of the way Rob Robinette wired the switch.
My understanding is that when the switch is out, shunt from the BRIGHT input is grounded and signal comes from V1A coupling cap into pin 2 of the NORMAL vol knob and then out via pin 3 onto the next stage : V2A.

But when the switch is engaged, signal coming from V1A coupling cap enters the NORMAL vol knob into pin 3 and then out via Pin 2, into the 680k resistor, and then feeds V1B via the shunt of the BRIGHT input jack that connects to the tip. So V1A is cascading into V1B.

Maybe I got this wrong, and somebody else can shine some light on how the switch operates.

So if you want to be able to switch between cascade and parallel, on the Y position, use DPDT switch on the front of the amp that allows you to choose between paralleled and serialized, like this :

Capture d’écran 2021-02-08 à 22.25.17.png

Since I haven't played with the parallel option, you will have to tweak how much of the NORMAL channel signal you want to keep without overloading the next stage, but that is an easy tweak

Fred.