Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Rp3703 on April 13, 2016, 10:01:30 am
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I’m looking into building a rack mount guitar preamp that can switch between a Marshall 1959 circuit and a 2203 circuit. I’ve attached a schematic of how I think it should work. I have a few questions though. First, will what I’ve drawn work? Second, My goal was to eliminate any connection to the second tube stage while the 1959 circuit is engaged. Is that necessary? Could I have eliminated any of the switch positions with no ill affects? Third, I changed the value of the coupling cap on the first tube stage from .0022(1959) to .022(2203). Will that affect the sound significantly? Fourth, This may be a confusing question but how important is it to have the Lo input on the 1959 to gang with the Hi input? I built a 1959 preamp that only has the three tube stages for the Hi input and does not have the Lo stage. It sounds good but sounds way better with an overdrive in front of it. Would ganging it with the Lo input make it sound better? How often is this done?
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Ok, So After doing a little more searching, I see now that Sluckey has already designed a plexi/2203 amp http://sluckeyamps.com/misc/Marshall_Dual_50.pdf. (http://sluckeyamps.com/misc/Marshall_Dual_50.pdf.) Has anyone built it yet? It looks as though even he has not built it yet. On his schematic, the plexi circuit is built ganged. Just wondering how that sounds. I guess the only way to find out is build it.
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Hi, I've build it an it sounds great.
Another possibility is this. If you don't use the normal channel of the 1959 preamp, you can change it into the second gain stage of the 2203 preamp. The first gain stage of both preamps are equal.
With regards,
Auke
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See that’s pretty much what I was trying to do with my design. Looking at Sluckey’s design though, it looks like the bright channel follows the normal channel. Can the amp be played just through the bright channel by turning the normal volume down and vice versa? If so, do you prefer the sound of both bright and normal combined or just bright?
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I think the bright channel of any stock Plexi is too bright, almost brittle. And the normal (dark) channel is too muddy. But when combined you can use the volume controls to blend the channels together for a very nice sound. If I was gonna build a single channel Plexi I would definitely modify it.
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... Looking at Sluckey’s design though, it looks like the bright channel follows the normal channel. Can the amp be played just through the bright channel by turning the normal volume down and vice versa? If so, do you prefer the sound of both bright and normal combined or just bright?
You could just play the bright channel of the 1959 circuit by turning the volume down of the normal channel. But...
I think the bright channel of any stock Plexi is too bright, almost brittle. And the normal (dark) channel is too muddy. But when combined you can use the volume controls to blend the channels together for a very nice sound. ...
+1.
I used to own a '73 50w Marshall. The channels should be called "Screech" & "Mud". Neither one was useful to me by themselves, so I jumped the inputs to play through both channels & blend the treble & bass to get a useable sound. The volume controls are actually more (and more effective) tone control than the tone controls themselves.
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Haha! That's why you put a treble booster on the mud side. The voice of many a 70's album.
Jim