FX Loop

[EL34]

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Slunkmeat
I am not registered :(
(8/3/03 11:11 pm)
68.0.169.61
Reply | Edit | Del All  FX Loop
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 Adding an FX Loop to 1976 Marshall 2203, anyone know of a good site with an easy to read schematic?

Dax
 
vonderhulls
Junior tube assistant
Posts: 25
(8/4/03 3:34 am)
172.141.47.253
Reply | Edit | Del  re: fx loop
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 i don't know either but i would really like to add an FXloop to the plexi i'm trying to build as my first mod. i've heard that there's a really good one in the book, "The Ultimate Tone" by kevin o'connor. anybody out there with a copy wanna be a copyright infringing rebel and post some of that info somewhere for use rookies?
 
jerrydyer
Junior tube assistant
Posts: 8
(8/4/03 5:33 pm)
64.52.89.117
Reply | Edit | Del  Re: re: fx loop
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 use dougs on his H50 or 100 or just the line off the master to a 1/4" jack, grounded to chassis of course. That becomes your send, go to effects and return it to amp via another jack grounded to chassis of course then send it back to the.022uf that is right in front of the phase inverter(aka 3rd preamp tube). done. sounds great only looses a tiny bit of treble at very high volumes.  
 
EL34  
I got your parts right here.
Posts: 1808
(8/5/03 2:42 pm)
66.82.48.1
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  Re: re: fx loop
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 Click on the library link and go to The H50 layout diagram.

This is your simple/standard/series Marshall effects loop.

You need to free up 1/2 of a 12ax7 to make it work.

Edited by: EL34   at: 8/5/03 2:50 pm
 
jerrydyer
Junior tube assistant
Posts: 9
(8/5/03 2:49 pm)
64.52.89.117
Reply | Edit | Del  Re: re: fx loop
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 Doug, have you ever tried not using the 1/2 tube for the loop. your input on straight line out/line in method?
 
EL34  
I got your parts right here.
Posts: 1809
(8/5/03 2:54 pm)
66.82.48.1
Reply | Edit | Del
  Re: re: fx loop
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 The level needs to be jacked up to it's previous level in order to feed it to the phase inverter.

After it comes out of an effect, the signal is 1 volt or less peak to peak.
 
geoffreyreed
Junior tube assistant
Posts: 97
(8/7/03 11:04 am)
152.163.253.69
Reply | Edit | Del  Re: re: fx loop
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 Some rackmount FX come back at Zero db, or +4db studio level  adjustable, thats +- 2.5 VRMS? Consumer electronics come back at -10db about .75V PtoP. Considering lots of the rack mounts use +- 15 V op amps its annoying they all can't put out 10VRMS, but that would be another thing for people to get confused about. geoff
 
jerrydyer
Junior tube assistant
Posts: 10
(8/7/03 4:42 pm)
64.52.89.117
Reply | Edit | Del  effects loop
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 Doug, I'm looking at the effects loop on the H50 and I dont see why it needs half a tube or where you connect. Am I stupid?  
 
Tiny Daddy
Junior tube assistant
Posts: 78
(8/7/03 6:14 pm)
67.30.35.67
Reply | Edit | Del  Re: effects loop
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 I am looking at:
www.hoffmanamps.com/images/H50pre.gif
and I can't tell either, please help us Doug!
 
geoffreyreed
Senior tube assistant
Posts: 109
(8/8/03 1:21 am)
64.12.97.6
Reply | Edit | Del  Re: effects loop
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 Thanx Tiny D for the many informative posts. Someone finally set me straight on A.C. power distribution. I've always wondered, and now I finally hear from someone who knows their stuff. Your advise is consistantly knowlegable and thoughtful. today I was reading every post and ended up hogging too many so I'm combining this thank you with comments on FX loop:

Dougs layouts are beautiful and easy to build from but a little hard to follow schematicwise. I think the effects send is from Plate (8) second 1/2 of V-2 gets attenuated by Master,& tone network (22k resistor also when not plugged into loop ) and comes back to grid of V-3 (2) the half gain stage. This is a preamp with 8 gain stages, so there is plenty of gain. I think the idea is that he is taking send from V-2 out and everything is attenuated by the tone network and Master vol. and comes back to return and everything gets another 1/2 tube of gain, so its not totally obvious that the return is getting extra gain because even the direct signal is getting attenuated. If that is not it, I guess I'm stumped as well. Anyway he's doing what lots of preamps do in 4-6 stages in 8 stages so there is plenty of gain, if necessary. geoff
 
EL34  
I got your parts right here.
Posts: 1824
(8/10/03 8:21 am)
66.82.48.1
Reply | Edit | Del
  Re: effects loop
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 How many pre amp tubes/stages are in a standard marshall/bassman type circuit?

How many preamp tubes do you see on the drawing?

Compare my stock plexi layout with the H50 layout to see what I mean.
 
 
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