Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Mike_J on August 17, 2014, 02:04:27 pm
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I have attached the reconfigured layout of the preamp section for the Sluckey inspired Plexi/800 amp with OD & FX that also has two separate tone stacks. The help I need from forum members is concerning the mixing circuit to tie the two preamps together. The Plexi preamp exits through the wiper of the treble cap and the 800 preamp exits through the wiper of the Master pot. They both must enter the bottom left corner of the relay board.
What I need is a mixer circuit to send the two preamps to the relay board. I have noticed Fender used 220K and 220K in their mixer circuits while Marshall usually used 470K. Does it make any difference what size resistors I use to do the mixing? Any suggestions would be very much appreciated.
Thanks
Mike
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What I need is a mixer circuit to send the two preamps to the relay board. I have noticed Fender used 220K and 220K in their mixer circuits while Marshall usually used 470K. Does it make any difference what size resistors I use to do the mixing? Any suggestions would be very much appreciated.
Size is probably not very important. But, since you are mixing two Marshall inspired preamps together, I'd use the Marshall values for the mixing resistors.
This is really an ambitious project. I'm guessing that your thread about relay switching also relates to this project? Do you have a schematic for this project? A schematic is very useful for understanding a circuit. It makes answering questions about specific circuit details much easier. It will be invaluable if you ever need to troubleshoot, especially over the internet.
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What I need is a mixer circuit to send the two preamps to the relay board. I have noticed Fender used 220K and 220K in their mixer circuits while Marshall usually used 470K. Does it make any difference what size resistors I use to do the mixing? Any suggestions would be very much appreciated.
Size is probably not very important. But, since you are mixing two Marshall inspired preamps together, I'd use the Marshall values for the mixing resistors.
This is really an ambitious project. I'm guessing that your thread about relay switching also relates to this project? Do you have a schematic for this project? A schematic is very useful for understanding a circuit. It makes answering questions about specific circuit details much easier. It will be invaluable if you ever need to troubleshoot, especially over the internet.
Sluckey
Tubenit was nice enough to create a schematic of the amp before I added the second tone stack. I will probably PM him asking for his assistance in updating the schematic once I am confident the layout is complete and correct.
You are correct about the relay switching thread being related to this project. I have made a few amps with two or three relays but never a single relay amp and never with the Hoffman relay power supply. Trying to make it as simple as possible.
I think 470K mixing resistors probably make the most sense for a Marshall amp.
I went back in forth in an earlier thread about using cap cans versus individual electrolytics for V1 through 4. Space limitations make the cap cans a necessity. They will be placed under the tone stack circuitry.
Thanks
Mike