Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bnwitt on May 13, 2012, 08:02:33 pm
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Steve,
Do you still have your dual preamp 2204 amp? Are you happy with it's tone? I'm thinking about building one.
Barry
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Hi Barry. I never built this. I think plexi50 built the full dual amp. Maybe a couple others built it also, but I can't recall. Be sure to give us a report if you build it. If you need any of the files for the preamp or full amp just let me know.
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If it can help you, I can add that I have built a 2204 according to the schem found in Doug's library and it sounds VERY good , a lot better than any pc board Marshall amp.
Colas
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I built one. I opened up a Fargen ole 800 and copied it. Great amp with beautiful cleans, but it one loud beast. Of course the thing is at home playing hard rock. Not sure what you mean about the dual preamp.
I'm listening.
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Fargen olde 800 you built ? If you'd post a schem here, lots of people would be happy ( me first ) !
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I had a friends and just copied it. No schematic, but I am learning to draw schematics. I will next time I take it apart. I am planning a loop for it, that would be a good time to draw it.
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ok cool, thanks anyway :sad2:
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This is what Barry is interested in...
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This is what Barry is interested in...
Very nice idea, a switch from 70's to 80's.
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I have build about 4 of them so far. I love them. You get the cleans you would like in a plexi and the growl using either a panel switch or A/B box. The November build as well is really sweet. I just finished another November. This latest one uses 4 EL84 1958 Bugle Boys. I did something weird different as well in the EQ. I made a fixed bass (no bass pot) allowing the mid pot to fatten or tighten the bass and mids. Sounds strange but i had little front panel space and i had to have a master for this amp. I calculated the resistor value of 150K for the bass level. You have to build the November or Dual preamp amps. Either one of them is killer
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Hmm, I may have to try the November amp too. I've still got 6 or 7 sets of 18Watt trannies from my 18 watt days so I can do several different topologies. I really want a great sounding Marshall style amp with a couple different gain settings like the DSL 401 and maybe a reverb too.
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Steve,
Actually the document I'm working off of is the one you did with the complete amp layout.
Plexi50,
What layout did you use on the dual preamp 2204's you built?
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Barry, I did the dual preamp with a slightly different board layout. Main difference is the 2204 section is now all the way to the right end of the board. Here's the pdf so you can compare. If you want the .vsd file send me a pm with your email addy. I seem to have lost it.
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Steve,
Actually the document I'm working off of is the one you did with the complete amp layout.
Plexi50,
What layout did you use on the dual preamp 2204's you built?
I used the the Marshall Dual Preamp. Using a 470k between the channels. Two inputs to A/B switch between the two channels
I think it is a brilliant design and layout
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What are the voltages? If I were to build a stand alone preamp what should my PT be?
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What are the voltages? If I were to build a stand alone preamp what should my PT be?
http://mhuss.com/MyJCM/JCM800_2204.pdf (http://mhuss.com/MyJCM/JCM800_2204.pdf)
mark huss was kind enough to record the voltages of a plexi build for us. click link above to see .pdf.
looks like you'll need around 350V. you'll probably want to add some sort of buffered output. this has been discussed here before but i'm too lazy to chase down the thread for you.
rule of thumb - DC to ACrms = DCV/.707 so PT with somewhere around 250VACrms at around 25-50mA
respectfully,
--DL
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Thanks, I look for that buffered output thread. I know very little about why that's necessary. I realize that a preamp like this will output a larges signal than a guitar but could you just use a resistor and a pot to simulate a pot turned down real low?(1M + 1K pot is amost like a 1M pot that you can't turn up much)
What does the buffer do? More than just reducing signal? With out getting to into it, what is the porpuse of a buffer?
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That preamp was designed (by Marshall) to drive a very high impedance LTP. It's very capable of driving most any power amp that has a hi-Z input. I don't think you need a buffer (cathode follower) unless you will be connecting thru a looooong cable or using a LO-Z input power amp such as a solid state amp.
This was never meant to connect into another full blown guitar amp. Some people (including me) like to put a pair of phone jacks between the preamp and power amp of a build. Some use the jacks for a passive effects loop. And some use them to mix and match different preamps and power amps.