5 Slightly Different FX Loops. Need Help Deciding.

[Papa Jim]

Attached are 5 FX Loops that are all very similar. The slight differences on #1 thru #4 are shown in red. The difference of #5 is that it only has 1 control pot. I have never used a FX Loop so I don't know if that is good for my application. The FX loop chosen will go into a  2 Watt 4-4-0 Studio  (Trainwreck) Clone amp. All suggestions are welcomed and appreciated along with any explanations of differences known.
Thanks to all.

[Glennjeff]

An opinion,

No 5 could be a problem depending on the gain structure of the effects you are using. It might overload some FX units or fail to drive them hard enough.

No 5  It also does not have TRUE BYPASS which the DPDT switches provide in the other circuits, if you like the sound that those two triodes add to your sound then that is an advantage, the others could be modified to this IN/OUT scheme.

No 1 is the most flexible if you've got room for three pots, although No 4 should get the job done just as well with 2 pots, but  MAY need a little tweak of the 220k resistor in red box. (unlikely)

No 2 and No 3 may need some tweaking of those resistors in red boxes to match your effects units and then they will work fine, until you get a new effect unit with different gain structure and then they MAY need tweaking again.

Depends on how many pots you can fit in your amp, and how much you enjoy adjusting them.

The 10M resistor and 0.22uF capacitor could be placed into any one of those systems, it is a negative feedback circuit to reduce gain,  give flatter frequency response and reduce any reactive imbalances that may occur due to long cables from effect units to amp. You may or may not be able to notice the difference in tone. If you need to cut the return level gain down a bit this may be useful.

There are also some slight differences in the valve biasing which you could tweak to taste although it is doubtful I could hear the difference, others might think it is a major issue.

Have fun.

[Papa Jim]

That sounds great because I have room for the 3 pots. Also I have all the components and values to start with for #1.
Thank you.

[tubenit]

I've tried just about all of those.  I personally do NOT like the local negative feedback loop. And so, I won't recommend that.  I originally did several that were switchable between the loop engaged and not and quickly gravitated towards not using the local negative feedback loop. IF you use the LNFB,  I would suggest putting it on a simple toggle switch.

In light of that,  I would probably use #1 without the LNFB loop.

OR #2 or #3.  I do not currently have an FX return pot on my Tweed BluezMeister and have played it that way for several yrs and like it.

I would NOT use #4 with a resistor for the FX level control.  I think that would be a mistake.  Same thing for #5.

Attached is what I currently have in my Carolina BluezMeister amp and my Tweed BluezMeister amp.  I have become partial to the paralleled FX, but also like the series FX. 

With respect, Tubenit

[Papa Jim]

This may be a dumb question but being a newbie at this, gonna ask anyway. When you mention the LNFB Loop on circuit #1 are you referring to the .22uF cap & 1M Resistor connected to tube's pin 6?

[tubenit]

Not a dumb question at all & yes that is what I was referring to.   

Yes, and it was not drawn correctly (error may have been on the original schematic).  Should have been .22, 10 M & .22.


With respect, Tubenit

[Papa Jim]

Cool.  Thanks.  Gonna go that route.

[Papa Jim]

Please take a look at the attached it's the circuit #1 with the LNFB Loop removed and what how I plan to get the FX Loops 2 voltages. My amps (B+5) voltage is good for the 262v needed. I will need to create a (B+6) of 196v for the FX Loop also. Is it ok to just add another dropping resistor and filter cap to get this, as long as the existing tranny can supply the current?