Hi all!
Last year my Technics SA-GX505 receiver's output stage fizzled. Since then I have been without the luxury of hi fidelity. I've been reduced to listening to computer speakers! Oh the humanity!
Necessity breeds invention...or in this case, construction. What I plan to do is rip the large proprietary amp chip out of my receiver, throw it away, and wire RCA jacks from the original chip's inputs effectively making it a pre-amp with a huge power transformer, and build a gainclone to act as the power amp.
Unfortunately, the large transformer in the receiver has too high a voltage rating to use with the LM3875. Too bad. I ordered a Plitron 25V-0-25V, 300VA toroidal tranny a while ago and it arrived last week. Now I'm scrounging up the rest of the parts.
Since this is my first amp project, I will resist the temptation to buy the most expensive parts. For the power cord, I will use a standard computer power cord with Molex connector. To interface it to my enclosure I will raid a Molex jack from a computer power supply. I have a spare panel-mount fuse holder in my parts bin, and a number of power switches to choose from.
I'm going to order my bridge rectifiers from Digi-Key, along with the Panasonic FC caps for the power supply, and mounting pads to attach the hot parts to the heatsink(s). I'll order some metal film resistors and reasonable RCA jacks and speaker terminals.
I will probably use the wire from the computer power supply for the internal power wiring. That is handy because there are three colours which will correspond to +V, -V and Ground. For internal signal wiring, I can probably raid some shielded signal wires from an old VCR. (I can see some people shaking their heads right now!)
As for heatsink(s), I've been looking on eBay. There seem to be a lot of CPU coolers on the eBay market. I would be interrested in hearing other peoples' experience in using CPU heatsinks without fans. Would a basic Pentium II sink be large enough without a fan?
Actually in the computer power supply I'm gutting, there are two identical aluminum sinks 2.25" x 2.25" with 7/16" fins on the upper portion. There are a couple of TO-220 devices currently mounted to each one. I wonder if they would be sufficient using one per LM3875 near the high end of its supply voltage? Possibly not without a fan...Perhaps I'll try them and see.
I have some VCR chassis to raid for enclosures. That should do for now until I make something more styley. Here's an idea -- motorized door on front to open the controls!
Maybe not. 
Anyway, I'll post my progress...and will also be documenting my progress on my website:
http://www.colp.ca/projects_gainclone.html
http://www.colp.ca/projects_technicspreamp.html
Hey, I understand there are a couple of you guys from Winnipeg...Elizard and Spind. Let me know how your projects worked out!
Cheers folks!
Last year my Technics SA-GX505 receiver's output stage fizzled. Since then I have been without the luxury of hi fidelity. I've been reduced to listening to computer speakers! Oh the humanity!

Necessity breeds invention...or in this case, construction. What I plan to do is rip the large proprietary amp chip out of my receiver, throw it away, and wire RCA jacks from the original chip's inputs effectively making it a pre-amp with a huge power transformer, and build a gainclone to act as the power amp.
Unfortunately, the large transformer in the receiver has too high a voltage rating to use with the LM3875. Too bad. I ordered a Plitron 25V-0-25V, 300VA toroidal tranny a while ago and it arrived last week. Now I'm scrounging up the rest of the parts.
Since this is my first amp project, I will resist the temptation to buy the most expensive parts. For the power cord, I will use a standard computer power cord with Molex connector. To interface it to my enclosure I will raid a Molex jack from a computer power supply. I have a spare panel-mount fuse holder in my parts bin, and a number of power switches to choose from.
I'm going to order my bridge rectifiers from Digi-Key, along with the Panasonic FC caps for the power supply, and mounting pads to attach the hot parts to the heatsink(s). I'll order some metal film resistors and reasonable RCA jacks and speaker terminals.
I will probably use the wire from the computer power supply for the internal power wiring. That is handy because there are three colours which will correspond to +V, -V and Ground. For internal signal wiring, I can probably raid some shielded signal wires from an old VCR. (I can see some people shaking their heads right now!)
As for heatsink(s), I've been looking on eBay. There seem to be a lot of CPU coolers on the eBay market. I would be interrested in hearing other peoples' experience in using CPU heatsinks without fans. Would a basic Pentium II sink be large enough without a fan?
Actually in the computer power supply I'm gutting, there are two identical aluminum sinks 2.25" x 2.25" with 7/16" fins on the upper portion. There are a couple of TO-220 devices currently mounted to each one. I wonder if they would be sufficient using one per LM3875 near the high end of its supply voltage? Possibly not without a fan...Perhaps I'll try them and see.
I have some VCR chassis to raid for enclosures. That should do for now until I make something more styley. Here's an idea -- motorized door on front to open the controls!
Anyway, I'll post my progress...and will also be documenting my progress on my website:
http://www.colp.ca/projects_gainclone.html
http://www.colp.ca/projects_technicspreamp.html
Hey, I understand there are a couple of you guys from Winnipeg...Elizard and Spind. Let me know how your projects worked out!
Cheers folks!