18Watt.com

GR, I'm all for it.The layout shown on the gearpage link above
has a parallel/single sw. on V1, I'm not exactly sure what it does?

I don't think I see a cascade , but I have never implemented one,
maybe you can take a look and let me/us know whats going on!

The single/parallel mode either selects one input triode or both in parallel. The single input uses only one triode for the input stage, this sends a pretty low signal to the PI and is usually described as thinner and cleaner. The parallel input uses both triodes paralleled, the input signal goes to both input grids and the combined signal is fed to the PI, it's usually described as thicker with more harmonics and is a bit dirtier. There's twice the signal getting to the PI in the parallel mode, and since the two triodes aren't exactly the same there is a 'swirl' or 'dimensionality' to the tone that you don't get with a single triode.

In cascaded mode the first stage output is usually attenuated about 50% (even at full 'Gain') and then it goes into the second stage so the second stage multiplies the voltage gain of the first stage ... so it's not 2 times the voltage gain of a single stage, it's the voltage gain of one stage times the voltage gain of the second ... which gives a lot higher preamp voltage gain.

The PA-16 uses the LiteIIb preamp, so the preamp is basically clean and the distortion is generated in part by the PI, but mostly it's PA distortion ... which gives a kind of Plexi-like character. With the cascaded preamp you'll have some preamp distortion and then the PI and PA distortion, so it's going to be a higher gain amp than a Plexi-like amp.

So the parallel mode is a cascade mod built in ? so to speak

now that I read again I see the answer is no....I think

It's like having two amps in one, although the Phat Ass 16 is an example of just a selection of either single triode, or parallel triodes without the cascade modification. That might be a good explanation.

The parallel/single looks fairly simple, I would prefer a cascade
switch I'm sure given the MV. Do you do both or just choose one
or the other ?

I do the parallel/cascade, since I really like the tones available ( I only build the parallel / cascaded version, don't build the single / parallel version). The single triode by itself is ok too, but a tad vanilla, when it takes very few extra parts to get a killer amp. There are several others that love that tone too. But to each their own, and that's the great thing about being a builder

all this time, i thought parallel WAS cascade....now i know better. anyone know where a schematic of a cascaded preamp can be found...?
sorry for the hijack

I need a layout for hi/lo input parallel/ cascade arrangement.

I found alot doing google image searches, mostly for the 2-channel

18 watt plexi types.I can't quite work off of schematics.Try the

google image search, lotta stuff pops up !

GR, Can you hook me/us up with your par/cascade circuit ?

Those are the tones I would prefer I'm sure.

basicbill, maybe this is helpful...? i haven't examined it too closely
http://brownnote.net/forum/viewtopic.php?t=808

I saw that one, not sure about the balance pot and the gain pot.

I guess its a start, he seems to have stated he removed the pots, I'll have to look it over......Thanks

Here's a long thread on it
http://www.18watt.com/modules.php?name= ... c&p=182419

I presume you have already built the lite2b, or are you starting from scratch? Here is a link to the schematic I used . Its by Collosal and is a pretty good summary of the mod http://dl.dropbox.com/u/7561678/18W/18W ... %202.2.pdf
I then worked out the layout using the previous thread you posted , although in the end I used a layout that suited my board better...
I used a gain knob but didnt bother with the balance knob.
Also used a 220k trim pot instead of a 200k resistor and a 25k trimpot.
I connected the 33k resistor directly from the gain pot to the switch.

To do the layout I'd start by working out where your plate resistors are going to go, then where the coupling caps connect to the plate resistors. Don't solder any of the components in until you have connected all the necessary wires to the valve socket and the switch.
I used screw in turrets from Ampmaker in the UK , rather than terminal strips.
Hope this helps!
It's definitely worth the effort of doing this mod.

basicbill wrote:I need a layout for hi/lo input parallel/ cascade arrangement.

I found alot doing google image searches, mostly for the 2-channel

18 watt plexi types.I can't quite work off of schematics.Try the

google image search, lotta stuff pops up !

GR, Can you hook me/us up with your par/cascade circuit ?

Those are the tones I would prefer I'm sure.

Bill, I only have a "paint shop" hacked layout that I use, and it certainly isn't worthy of being made public on here because it isn't very clean, but if you want a copy e-mail me and I could send you one. If I had access to a decent program for layouts, I'd redo the one I have.

nyazzip wrote:all this time, i thought parallel WAS cascade....now i know better. anyone know where a schematic of a cascaded preamp can be found...?
sorry for the hijack

I think it's in this thread, although at work I can't look at certain sites. If not, e-mail me at: shaffer_terry@yahoo.com and i'll send you a copy of the PDF file that Colossal drew, which in itself is a work of art.

Bronsboi wrote:I presume you have already built the lite2b, or are you starting from scratch? Here is a link to the schematic I used . Its by Collosal and is a pretty good summary of the mod http://dl.dropbox.com/u/7561678/18W/18W ... %202.2.pdf
I then worked out the layout using the previous thread you posted , although in the end I used a layout that suited my board better...
I used a gain knob but didnt bother with the balance knob.
Also used a 220k trim pot instead of a 200k resistor and a 25k trimpot.
I connected the 33k resistor directly from the gain pot to the switch.

To do the layout I'd start by working out where your plate resistors are going to go, then where the coupling caps connect to the plate resistors. Don't solder any of the components in until you have connected all the necessary wires to the valve socket and the switch.
I used screw in turrets from Ampmaker in the UK , rather than terminal strips.
Hope this helps!
It's definitely worth the effort of doing this mod.

Brons, I'm still awaiting parts and stuff to convert an already assembled 5E3, so I need some time, between colossals document and pc18's layout in the above listed thread I think we're well on our way.I'll do like you did and omit the balance pot and just use a 220k resistor, I have to see how much room I have in the 5E3 chassis to manage this .Thanks for the input.

GR, I think I/we can swing this with the 2 resources above (pc18 layout & colossals doc) colossal has condensed much of the thread into that 1 document.I should have some parts in a few days ! Thanks people !

On cascading inputs on an amp such as the 18 Watt Lite IIb, can I run the input triodes together with the 820 ohm resistor and 47uF capacitor on the cathodes while using separate plate resistors while running one triode input into the other? Or do I have to give them their own cathode resistor and capacitor? Thanks.


Had a slow brain day, figured it out. No.

The two cathodes are out of phase with each other when in cascaded mode, so it's not really recommended. Apart from that, the parallel mode gets more harmonic complexity if you separate the cathodes and put different RC values on them. So this is itself a great mod for a regular Lite IIb or classic 18W.