Effects Loop Options?

[Jennings]

I’ve got a few Vox AC style builds around, mostly AC15 orientated, and I’m curious to add in an FX loop on one. Only problem is I can’t go valve driven due to not having enough transformer juice to power the heaters. So what sort of solid state circuits would people recommend I look at implementing instead?

[tubenit]

Amazon.com: Mojotone Discrete Hi-Voltage Series Effects Loop : Musical Instruments

[tubenit]

I have two amps where I've used a mosfet cathode follower and then taken the unused triode as the recovery stage for a psuedo active FX loop. All the time signature pedals I own like chorus, phaser,  delay, reverb, etc...... have worked to my satisfaction doing this in both my amps.


Just a thought to consider.  Note how V2b is now the FX recovery stage instead of the cathode follower in this schematic.


with respect, Tubenit

[Jennings]

Thanks Tubenit...really useful info and advice.  Interesting Mojotone module...I'm doing some googling about to have a look at the circuit and seen some other threads.  Looks like it's a got boost and pad type functions for the loop.  I like the simplicity of your approach, freeing up the triode to use as recovery.  How do you like the mostfet driven tone stack?  Does it change the character of the amp much?   

[tubenit]

I can NOT tell any difference in tone using a tube triode or a mosfet in a cathode follower position. They sound the same to me.  I've been very happy with the mosfet CF approach.


geofex.com/Article_Folders/mosfet_folly/mosfetfolly.htm


With respect, Tubenit

[RoadShow]

I bought the Mojotone FX board a couple of weeks ago to try in my JTM45. 

If you want to sit tight I can let you know by the end of the weekend what my thoughts are.

[Jennings]

Thanks guys    I'd never even considered how mosfets could be used in tube amps until now, so it's sparked a few ideas and thoughts of its own for me to try in various places in due course.  It'll be a little while before I get to installing a loop, so definitely report back on how the JTM45 install goes with the Mojotone, please.  I've got no natural followers in my AC type circuit as it's two simple pre amp channels (EF86 pentode based) into either side of the PI, so I'd be looking to mod the input into the PI (bring the channels together with mixing resistors before the PI) and tap in the effects loop there. 

[neskor]

this one is great:
https://store.metropoulos.net/products/zero-loss-fx-loop-board-only?variant=26133128903
same FX loop you can find in Friedman and Headfirst amps.

[RoadShow]

this one is great:
https://store.metropoulos.net/products/zero-loss-fx-loop-board-only?variant=26133128903
same FX loop you can find in Friedman and Headfirst amps.

Yes, I've used that one, works well, but
George shut the business down and has no boards left.  Steve will be producing and selling the boards, but with a price increase.

[Jennings]

I think I've come across a schematic for the Metropoulos loop circuit.  I might have a go at building my own then without a PCB or pre-built module in due course.

[Merlin]

Just posting it as an image rather than a .doc

[pdf64]

It seems like the 1k5 in the recovery stage should be a gate stopper, rather than being in series with the 1M gate reference resistor?

[RoadShow]

I think I've come across a schematic for the Metropoulos loop circuit.  I might have a go at building my own then without a PCB or pre-built module in due course.

That schematic is incomplete.  When I bought 2 of them some time back I compared what I had to the schematic and noted the differences.  I also generated a schematic of the Mojotone and Granger versions.  There's also the KLD and Tristan Collins versions where they provide everything you need to spin your own board.

I really suggest just getting the board and having a clean solution.  All the parts are maybe $15, not much, and buying from him you're installing it with a clean deal for whatever he charges now.  Steve did a lot of work on his version that has become the version that others are judged by and I respect that.   Heck, with what I know and having a spare to copy I could easily get boards made and sell kits for $20 and break even, but nope, not me.

Anyway... do what you want...

[AlNewman]

That schematic is incomplete.  When I bought 2 of them some time back I compared what I had to the schematic and noted the differences.  I also generated a schematic of the Mojotone and Granger versions.  There's also the KLD and Tristan Collins versions where they provide everything you need to spin your own board.

I really suggest just getting the board and having a clean solution.  All the parts are maybe $15, not much, and buying from him you're installing it with a clean deal for whatever he charges now.  Steve did a lot of work on his version that has become the version that others are judged by and I respect that.   Heck, with what I know and having a spare to copy I could easily get boards made and sell kits for $20 and break even, but nope, not me.

Anyway... do what you want...

So what are the differences?

[Jennings]

I’m just gathering thoughts and ideas at the moment, rather than set on one particular path or circuit. My space is confined and some of the boards I’ve seen won’t fit without some head scratching and fettling. Plus I’m in the UK, so factoring in buying from abroad, shipping tax etc…I’m not stumping up more than is sensible given I’m uncertain of fit/format. Seems there aren’t any UK based kit types that I’ve found just yet anyway.

[pdf64]

Just to note that for regular classic non master volume amps, the benefit of fx loops seem negligible, and they have the downside of cluttering up a clean simple signal path.   
Fx loops come into their own with overdrive preamps, especially those with switchable gain.

[Jennings]

I never use effects loops, and never build them into my amps usually. I’m a simple kind of chap, so less is more usually. All my effects have always gone in the front of the amp, and if anything more is needed I do it at the PA or desk. But I’m thinking of potentially thinning the herd, and despite my best efforts to explain otherwise loads of players I know seem dead set on loops. So I fired it wouldn’t hurt to have a play myself.