6 Channel Preamp Project

[DC Dave]

I'd like to use this thread to document my 6 channel pre project.

After building a few chipamps I decided its time to build a preamp. There are a few features I want to incorporate into the design.

First it must be an active design. I'm thinking maybe going with a AD815 or OPA2132 design for the gain stage. I don't have 6 OPA627s, otherwise I might use those.

I need a headphone amplifier, must likely a 2132/BUF634 combo. I built one with that combo and am happy with it.

It needs to be able to switch between three sources.

I'm thinking about having a subwoofer crossover and output built into the main channels.

The basis for this project is a Yamaha MVS-1 Master Volume Control I bought from the local Goodwill store for $15. It has a nice 6 channel pot and three input selector. It will switch between two 2 channel sources and one 6 channel source, and also has Tape inputs and outputs. It is a purely passive device with lots of room in the case. I figure I will reverse engineer it to make it an active pre and add the headphone amp and sub crossover. I might also add a NOS DAC and USB input.

I don't really need 6 channels, but I don't want to waste the 6 channel Alps pot, and I might get into multi channel audio later.

 

[Russ White]

Sound like a fun project!

If you liked the 2132 and the BUF634, I wonder if you might like the 627/634 combo even better for the headphone amp.

 

[DC Dave]

Here is a pic of the insides. I have one of the PE $5 buyout toroidal trannys that will fit in the corner easily. I might get rid of the stock PCB and just keep the selector switch part of the board. The RCA connectors are crap and will be replaced. Seems like it should be pretty straight forward.

 

[DC Dave]

Sound like a fun project!

If you liked the 2132 and the BUF634, I wonder if you might like the 627/634 combo even better for the headphone amp.

I have a couple of the 627s in my parts box and will most likely try them out.

 

[cowanrg]

wow, its crowded in there!

 

[DC Dave]

This is the sub crossover I want to incorporate. I want it to be part of the 2 channel inputs. Should it be placed after the gain stage (after the OPA2132 with gain of 3) or should I place a buffer after the input, then feed the crossover network, then a gain stage?

 

[DC Dave]

This pic explains my crossover integration question better. Which way should it be done, Top design or Bottom?

 

[Russ White]

I would go with the top design. You may not need the buffer, but it is a nice touch.