Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: SLW on September 07, 2012, 02:44:17 pm
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I did a quick search but didn't find the information I was looking for. I have a Laney that is a copy of a Marshall 2204. It looks like the best place is after the master vol pot. Where would you tie in an effects loop?
I think I am going to suggest a simple passive loop as a start. I don't know anything about the transformers in the amp so I don't know if it could handle another tube.
Has anybody out there ever put a passive loop in a 2204?
Thanks
SLW
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Did you check ARCHIVES?
http://www.el34world.com/Forum/index.php?topic=10208.0 (http://www.el34world.com/Forum/index.php?topic=10208.0)
For examples of a passive effects loop, just check out the HoSo56, Tweed Overdrive Special, Tweed BluezMeister or D'Mars Overdrive Special.
Or do a search on "passive effects loop".
with respect, Tubenit
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Doug has a nice buffered fx loop in his h50 pre, which is a souped up 2204 'oid.
(http://www.el34world.com/Hoffman/images/H50pre.gif)
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Thanks TopBrent. This is the sort of thing I was looking for. It appears that Doug splices it in where the signal goes from the treb pot to the master pot. That makes sense. It looks like a simple voltage divider to knock the signal down on its way to the send jack. I am not sure what the cap and resistor on the return leg are doing. I do like how simple it is. Three resistors, a cap and two switching jacks and perhaps a small tag board would get it done.
SLW
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I do like how simple it is. Three resistors, a cap and two switching jacks and perhaps a small tag board would get it done.
There's more to it than that. V3 is a recovery amp, rather than the typical LTP PI.
Here's a totally passive loop that works well with some effects. It also works well for sending the output of one amplifier's preamp to the power amp of another amplifier. (Kinda mix and match several amps) Tubenit used this in a lot of his builds. All you need is two jacks stuck in line just before the PI input cap. Take a look...
http://home.comcast.net/~seluckey/amps/november/november.pdf (http://home.comcast.net/~seluckey/amps/november/november.pdf)
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Thanks for pointing that out. I saw the wiper of the master pot connected to V32 and just assumed it was the PI. Dumb me for being in a hurry and not studying it a little harder. I was trying to go from memory of the 2204 schematic to the layout posted. I should have looked closer. I would have noticed that only 1/2 of V3 is being used. Oh well. :rolleyes:
I knew I would get proper advice here. This Laney has an extra hole in the chassis for another preamp tube. It has a few extra holes actually. I do not know if the PT will handle another tube so I am hesitant to mount a socket and give it a try.
I have seen the simple two jacks before the PI here (most of Tubenit's stuff). That would be the easiest thing.
SLW
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Adding one extra 12AX7 is such a small additional load that I would not think twice about doing it. I do believe tubenit has used a Dumble inspired active loop also. Should be easy to find those schematics also.
Just a thought... You're gonna need two jacks regardless of which type loop you use. Why not try the simplest passive circuit first. If it gives satisfactory results, you're done. If not, then add the active components.
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I use the passive loop too, the one Sluckey and Tubenit use a lot. He's right, dead simple, and reverb, delay/echo and chorus sound just fine through it. :smiley:
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i like the lee jackson buffered efx loop in the 2203 and 2204 marshall's. it gives a lot of control over your effects level as well as adding gain if desired. it just seems to make the amps sound a little fatter to me.
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Thanks again for the input everybody. I spoke with the owner of the amp and laid out options for him. I suggested a strictly passive loop would be the most simple and cheap way to start (two jacks and wire). I told him that adding a tube was also an option and gave him a few example schematics with different degrees of complexity. He had sent me a link to a loop kit from Metro amps that he found and I think installing it would be pretty simple so I told him that.
He came back and told me that he was going to order the kit from Metro amps and bring it to me when it comes in. I will post here how it goes. Perhaps somebody here will find it useful.
You guys can critique my work. :)
SLW
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The metro amp loop is good one but if you use rack effects some times it can be overdriven its very good for pedels one of the first ones I ever used. I dont use it now only because I cant build it from scratch and I haven't exhausted all the tube driven ones yet. (LOL)
Thanks Bill
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I did put the loop in the amp. I just finished actually. It was simple to install. I think it works great. It came with a bypass switch that I installed. I could not tell any audible difference with the loop bypassed or not. It worked will with the stomp boxes that I tried. The circuit looked pretty simple. I will start another thread about it in the solid state section.
SLW