PARALLEL-CASCADE SWITCH

[ViperDoc]

Is this a "set and forget" type of mod or is it useful to have it on a foot switch? I can't seem to find any sound examples online. Much appreciated.

[dbharris]

I haven't implemented it myself, but would imagine it is a large volume jump. Not like switching between channels with balanced volume but more dirt. I think you would need to tweak other controls with the amp to get the sound you want switching between the two modes.

-Dan

[JMPGuitars]

I like the switch and use one on my main amp. It's a switch and a gain knob, and not something you want run outside of the chassis.

[ViperDoc]

I like the switch and use one on my main amp. It's a switch and a gain knob, and not something you want run outside of the chassis.

Thanks, guys. I'm referring to the ZP Parallel-Cascade mod on this site. When you say gain knob, do you mean Gain control off the V1A triode, or the 20KB trimmer off of the cascade? I wondered if the 20KB trimmer was on the board or whether it's useful to have the control on a pot? It could also be switched with a relay to keep it inside the box.

files/Zaphod_Phils_18W_Cascade_Mod.pdf

[JMPGuitars]

I like the switch and use one on my main amp. It's a switch and a gain knob, and not something you want run outside of the chassis.

Thanks, guys. I'm referring to the ZP Parallel-Cascade mod on this site. When you say gain knob, do you mean Gain control off the V1A triode, or the 20KB trimmer off of the cascade? I wondered if the 20KB trimmer was on the board or whether it's useful to have the control on a pot? It could also be switched with a relay to keep it inside the box.

files/Zaphod_Phils_18W_Cascade_Mod.pdf

Yes, that's basically the one I used. There's an A1M Gain knob labeled VR1 on that schematic. I didn't use the 20k trimmer. I used a 205K resistor for R7 instead. I modified the circuit a little bit besides that, but that example is fine.

[ViperDoc]

I like the switch and use one on my main amp. It's a switch and a gain knob, and not something you want run outside of the chassis.

Thanks, guys. I'm referring to the ZP Parallel-Cascade mod on this site. When you say gain knob, do you mean Gain control off the V1A triode, or the 20KB trimmer off of the cascade? I wondered if the 20KB trimmer was on the board or whether it's useful to have the control on a pot? It could also be switched with a relay to keep it inside the box.

files/Zaphod_Phils_18W_Cascade_Mod.pdf

Yes, that's basically the one I used. There's an A1M Gain knob labeled VR1 on that schematic. I didn't use the 20k trimmer. I used a 205K resistor for R7 instead. I modified the circuit a little bit besides that, but that example is fine.

That's what I was wondering, so you don't find any need to adjust the trim, you just set it where you like it. Might be better on the board, then.

[JMPGuitars]

That's what I was wondering, so you don't find any need to adjust the trim, you just set it where you like it. Might be better on the board, then.

I read that a couple people wound up around 205K, and I started there. It sounded great, so I didn't bother testing other values. Both of these amps have (basically) this mod in them: https://youtu.be/GZPsdjDZd58

You don't need the trimmer off the board (or at all). The gain pot is separate, and needed, and can't be on board. In my demo linked above, you can see there's two gain knobs, one for when cascade is active.

[ViperDoc]

Ok, I think I’m seeing this a bit more clearly. I wasn’t paying attention to the standard volume control later in the ZP schematic. Is that your other gain control, or did you add another after V1B?

[JMPGuitars]

Ok, I think I’m seeing this a bit more clearly. I wasn’t paying attention to the standard volume control later in the ZP schematic. Is that your other gain control, or did you add another after V1B?

The amps in that video are my own circuit design, and not relevant beyond the cascade mod.

[pummpy]

Hi all
Thanks for your time .
I have a Mojotone 18w TMB that i just finished populating the board . I see these gain mods and would like to do this to my TMB .
My issue is i am not sure where to tie it in to my amp . All the layouts i see are for different 18w amps . Any input would be appreciated .
Thanks

[Bieworm]

I cascaded the normal channel after the tremolo channel in my modern classic. With a switch to choose between the regular tremolo channel and the cascaded.. works like a charm! Well.. I only added the extra double triode , not the tone stack of the normal channel.. so I don't have the normal channel anymore actually.

20210131_175950.jpg

And I finally am building a head shell for this amp.

20210131_175919.jpg

[pummpy]

Nice .
This is my issue . Mainly what input jack do i use and remove . Where to start basically . the rest looks pretty cut and dry .
Thanks

[Bieworm]

What are you trying to achieve? Do you want to separate the parallel 2nd stage of the TMB channel and cascade that one instead? Or do uou want to cascade the normal channel into the TMB channel? How much gain do you need? That's kinda crazy...

[JMPGuitars]

Nice .
This is my issue . Mainly what input jack do i use and remove . Where to start basically . the rest looks pretty cut and dry .
Thanks

Are you trying to add a parallel/cascade switch as per the topic, or are you trying to cascade the channels? If the switch, then follow the doc in the thread. If you're trying to cascade the channels, start a new thread instead. That's a different topic.

[pummpy]

Thanks , yes . Would like to do the Parallel-Cascade switch .
Main question i have is Do i mod the TMB input or The Low Hi input jacks as there are two there and TMB has one input jack .
I see the the Modded input jack goes to Pin2 V1 where my Hi Low input goes to that pin on V1 that has two input jacks . Do i eliminate both jacks if using that input and replace with one input jack as shown in mod ?
Hope i am making sence .

[JMPGuitars]

Thanks , yes . Would like to do the Parallel-Cascade switch .
Main question i have is Do i mod the TMB input or The Low Hi input jacks as there are two there and TMB has one input jack .
I see the the Modded input jack goes to Pin2 V1 where my Hi Low input goes to that pin on V1 that has two input jacks . Do i eliminate both jacks if using that input and replace with one input jack as shown in mod ?
Hope i am making sence .

It won't work the way you want. A parallel / cascade switch means it changes the way the input V1 works, when V1 is used for only 1 channel.

Your build is using V1 for both channels, and the TMB channel already uses V2 as a cascaded gain stage.

If you look at a different circuit like a Lite 2b, you can see that V1 uses both halves for the same input(s). In that case, V1 can be used either as a parallel tube (V1a and V1b connected in parallel together), or it can be cascaded with one half of the tube being fed to the other.

If on the other hand, you wanted to modify the TMB channel so that the cascaded V2 could be switched to parallel instead, you could do that.

Another option would be to remove the TMB channel input from V1 and insert it on the first half of V2, and change the wiring for V2. This way the non-TMB channel could have a cascade/parallel switch. But this is probably more work than it's worth.

Take a look at a few different schematics (including the switch schematic in this thread) so you can see what parallel or cascaded tubes look like in the circuit.

Thanks,
Josh

[Bieworm]

Maybe the world is waiting for the tremolo TMB with an extra gain stage (cascade.. cathode follower,...) for the high gain guys

[JMPGuitars]

Maybe the world is waiting for the tremolo TMB with an extra gain stage (cascade.. cathode follower,...) for the high gain guys

nope.gif

[pummpy]

Thanks again . I understand . Like to ask questions when not sure .

[geoff 1965]

check out this plexi mk2 schematic, cascades normal channel into TMB channel.

18WattPlexiMkIISchematic5 (1).pdf