clean switch

[goodtone77]

i was wondering if any one had installed a switch to remove the third gain stage kind of a fendery/wreck switch?

i am still waiting on the rest of my parts and tring to have the layout finished by the time they arrive?

i have a chassis from ron
and transformers from moose

so far looks awsome

[toddyjoe]

It would be an interesting idea if you could implement it. I am not sure how much the interstage RC networks that Fischer used for the Liverpool/Express circuits would mess with the basic Fender topology underlying the Trainwreck preamp. The British-flavored output sections of the Liverpool/Express design might also take away from the Fender sound. I believe the Bruno Underground uses a Fender blackface preamp and a British output stage (Vox), so maybe the Bruno would be a good reference point for what you are describing?

[erigm]

You could use the unused half of the 12AX7 for a new/clean second stage, and then leave the existing second and third stage in tact so as not to mess with the lead dress ... then possibly switch between the two. You think that would work?

[markd]

An easier way might be to implement the switch shown in Mark Abbott's mods schematic in the Files here:

http://maximoaudio.com/download/schemat ... iation.jpg

This will lower the gain of the preamp and allow for more clean headroom.
markd

[908ssp]

Is that something that could be done with a relay so that it could be foot switchable?

How much volume would you lose doing it?

[electric]

An easier way might be to implement the switch shown in Mark Abbott's mods schematic in the Files here:

http://maximoaudio.com/download/schemat ... iation.jpg

This will lower the gain of the preamp and allow for more clean headroom.
markd

i think that's komet's preamp...

[erigm]

Yeah,

That's the Komet preamp, and the switch is called "touch response" switch. You could use a relay for either idea. The thing about my idea is you could have a seperate volume control for each preamp, which in my opinion would be better for channel switching. You could also use a relay to disengage one or more of the cathode bypass caps. Let us know what you try!

[Funkalicousgroove]

Why on earth couldn't you just put your switch right after the plate load resistor so that it switches between the .002/3rd gain stage and say a .022 or .047 straight into the PI?

[erigm]

yeah, that oughta work too, but you don't have seperate volume control over it.

[Funkalicousgroove]

if you're wanting to make it footswitchable for like stage use I'd say build it like a BF fender with 2 distinct channels and use an A/B box.

[slajeune]

Hi All,

Why on earth couldn't you just put your switch right after the plate load resistor so that it switches between the .002/3rd gain stage and say a .022 or .047 straight into the PI?

This is exactly what I intend to do in my trainwreck. Actually, it's a Jones Amp derailment (single ended ~5W) trainwreck. It's not my design, I am simply adding a few modifications to it.

Here is the schematic (with the switch):

http://www.sopht.ca/schematics/derail1-modif.jpg

And this is where I am with it currently:

http://www.sopht.ca/index.php?s=41

Once evertyhing is wired up and working, I'll you all know how it works!

Cheers,
Stephane.

[slajeune]

All right,

I was able to fire up the amp yesterday. The 'clean switch' works fine. Basically, it bypasses the 'cut' stage.

Please see my previous post for the links to the schematic.

Thanks!
Stephane.

[doctord02]

Stephanie, can you explain your switch a bit? I dont understand your connections to the cathode resistor (and added 3.3k resistor) on the second stage...

(edit)

nevermind, I found your post at ax84 and it makes sense now. Can you switch this while hot?

[slajeune]

Stephanie, can you explain your switch a bit? I dont understand your connections to the cathode resistor (and added 3.3k resistor) on the second stage...

Just to calrify the switch. Basically, it bypasses the cut stage (the typical 10k stage). Furthermore, in my implementation, it also adds a 3.3k resistor in parallel with the 2.7k resistor to make it closer to a typical 1.5k fender gain stage.

Yes, you can switch the mode live. You could use a relay and make it footswitchable also.

Thanks,
Stephane.