FX loop for Matchless Lightning build?

[chuckb]

Hey guys, I have my Matchless lightning build finished and I was wondering if anyone here can give me some direction on installing an FX loop? A schematic would be great. Thanks in advance.

Chuck.

[Chuck H]

You should know that most of the OD in this circuit is from the PI and power tubes. Many effects won't work well in an effects loop if you run it distorted much.

That said, most loops are placed right behind the PI. For a circuit like the Lightning you'll need another triode to do it well. You could steal it from the parallel triode input circuit and I'll bet you won't hear any difference. That way you won't need to punch a new hole. You may need to rewire all the preamp tube sockets to place the loop recovery triode in a good place layout wise. That way V1 won't be both the first and last gain stage for the preamp and you won't have leads dragging from near the PI toward the input. No matter if you rewire as a single triode input or add a tube it's a pretty ambitious venture to put an effects loop in that amp.

Chuck

[chuckb]

hey Chuck, Well I guess I'll justl leave it for now. I really don't want to bother rewiring the tube sockets and the like right now. I'm just beginning to enjoy t the amp. The reason I wanted the Fx loop was for my "G System" which sounds much better through the loop then in front. I may tackle it in the future though. Thanks for you input.

Chuck.

[GibsonLover]

Oh Charles....

I think there's a wrong turn here.
"... most loops are placed right behind the PI." No sir, most loops are before the PI. (After all, which phase would you put the loop on?) Maybe that's what you meant, but you seem to back it up by saying the loop won't sound good with a distorted signal. That true, but still on the wrong side.

If you feed the EQ into a cathode follower with a re-wired first tube, then to two normalled jacks (send/return) thru a cap, then into your PI, the mod is almost easy and also very similar to many amps with simple effects loops. I did exactly the same on mine and it works well. I've found a loop recovery triode is really not necessary since your FX output is usually low impedance. Ideal, but not necessary. Use shielded cable to and from the Send/Return jacks, and to the rewired follower stage. You add one resistor, one cap, and move a few wires. If you find the signal to your effects is a little strong, add one more resistor for a simple voltage divider at the output of the cathode follower.

You might even find that you like the sound of your amp more because you are buffering the output of the EQ before it feeds the PI. It's subtle, but it's there. With an effect plugged in, you basically have the same thing a buffer offers; high input impedance, low output impedance.

PM me if you'd like, and I'll take the time to draw you a schematic.

[GibsonLover]

Attached are two pages. The first is the Lightning schematic, and the second is just the preamp with the FX loop added. The only values that are labeled are the components added, for clarity. You will see there are very few changes from the original schematic. You will break a connection after the EQ stage, rewire the second triode, and add two jacks. I would recommend adding the Level control to give you a range of input to your effects to avoid overloading them. Since the FX send is after the volume control, there is less chance of overload unless you like your volume near "10" most of the time. You decide, it can always be added later.

For full disclosure, I do not have a Lightning, I have a Chieftain, but I did this mod to a Gibson amp that I built. Both designs have two gain stages and EQ before the loop, and both returns go straight into the PI as in this design. The 100K resistor added can be any value between 56K and 100K. I would mount the FX send level control on the back of the chassis near the Send/Return jacks. With the level all the way up, and no effects in the loop, it will act the same as the stock circuit. If you replace the 50K pot (audio taper) and 47K resistor with a 100K audio taper pot, you will have a send level control that also acts as a Master Volume. Try shorting the 47K resistor just to see if you like it as a Master Volume first.

Use either shielded cable or short lengths of wire for the added connections. You can risk using unshielded wire if you feel the connection is short, but be aware that if you have noise problems shielded wire will be required. A shield only needs to connect to ground on one end.

[chuckb]

Hey, thanks so much for the schematics, I really appreciate it. I have a Matchless Clubman 35R as well and the G System works excellent through the FX loop. I'll rewire the Lightning now as soon as I'm finished putting the tolex on the cab.I'll probably be emailing you for some guidance along the way with this mod. This only goes to show that this forum is the best place to go for help of any kind.you guys are the best. I have a small amount knowledge when it comes to amp building but I'm learning alot through this forum with the help from you guys.Thanks so much again.


Chuck.

[jighead81]

[QUOTE=GibsonLover;152601]Attached are two pages. The first is the Lightning schematic, and the second is just the preamp with the FX loop added. The only values that are labeled are the components added, for clarity. You will see there are very few changes from the original schematic. You will break a connection after the EQ stage, rewire the second triode, and add two jacks. I would recommend adding the Level control to give you a range of input to your effects to avoid overloading them. Since the FX send is after the volume control, there is less chance of overload unless you like your volume near "10" most of the time. You decide, it can always be added later.

Do you still have the schematic for this? I couldn't get it to open. I was wanting to do the same thing, but add a tube buffer with send/return pots, kind of like webers buffered effects loop schem. Any help would be appreciated,

Thanks

[Tubenit]

There is a considerable amount of info along with schematics and layout on effects loops here:

tube effects loop on board - Hoffman Ampifiers Guitar Tube amp forum

With respect, Tubenit