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solid state preamp project

Started by hyperion007, February 17, 2010, 09:08:51 AM

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This is a thread about my preamp project. I have asked Per-Anders for help with designing a complete solution and corresponding PCB to meets my following requirements. He has yet to accept this challenge but it is looking promising, right Per-Anders? ;)

Here are the specs:

input voltage: 230V
case outer dimensions: 420(W)x320(D)x70(H) (mm)
Inputs: 5 (pairs) RCA (No phono input, only analog inputs like CD, PC, TV etc.) Bonus would be a digital input like a optical TOSLINK and DAC but it might be over the top.
Output: 1 (pair) RCA
Lighting: 5 LEDs, indicating which input is selected. Then output for at least 8-10 LEDs for lighting up the ring around the volume knob.
Input selector: This really don't matter as long as there is 5 notches in the selector hardware and a nice "feel" to the rotary selector switch. How it controls the input selection, be it relays or what ever, doesn't matter.
Volume control: Same here as with the input selector. The feel is the most important aspect. Be it ALPS or a stepped attenuator doesn't matter but price is always a factor. Power switch ON/OFF: I want to use this switch, Bulgin vandal proof momentary switch ( ) Model MPI002 dual color LED, Red/Blue.
PCB quality: Doesn't matter but both Per-Anders and I like fancy, good looking PCBs of good quality so it is leaning towards that.

My budget for this build is about 4000kr or $500-$600. That is to include PCB, interconnect cables, components, switches, potentiometer but not the RCA connectors and chassis.

I am not an audiophile and don't have trained ears so I am sure I will be happy with almost whatever I end up building. I am mostly doing this because it is fun to build stuff I can use and to create something esthetically pleasing (and good sounding)

Any and all contributions to this project is greatly appreciated!



I will start thinking at least  :-)
/Per-Anders Sjöström, owner of this forum

Homepage with my DIY hifi stuff


I hope this project will inspire you and your thinking will inspire you even more :)


This is something I want to avoid :) I rather do most of the cables integrated into one PCB.


Yes, this is a night mare. One big pcb is the goal, yes.
/Per-Anders Sjöström, owner of this forum

Homepage with my DIY hifi stuff


I have started to draw up my very first PCB but it is very hard :) it is like playing the game Snake on old Nokia mobile phones, only a thousand times harder :) I always get caught out, having nowhere to draw my lines without crossing paths with other lines :(

Right now I think I have it all worked out except for how to connect to the output. (I have put 6 inputs instead of 5, just in case I might need one more later on)

Since it is my first attempt at PCB design there is obviously room for improvement, wouldn't you say Per-Anders? :)

I have attached a picture of the drawing.

The 8 holes are for a relay but PCB Express did not have one that matched it so I just used the measurements from the component data sheet. 


I had a friend take a look and I also made a version using both top and bottom layers of the PCB, If you decide you have the time and interest, do you think you can use "my" designs at all?

I will attach both versions



A good first shot but lot's of stuff need to be fixed. Give me one week or two and I'll come up with something.
/Per-Anders Sjöström, owner of this forum

Homepage with my DIY hifi stuff



No problem. I am in the process of ordering some stuff for the project and it will take some time to get the parts anyway and I'm in no hurry :)

Thanks again


Hi again,

I have now made a schematic of the complete (I hope) preamp PCB.

I have used Express Schematic and ExpressPCB but they are free programs and the files created are only good to ExpressPCB and I don't want them to manufacture this board for me since they only have green PCBs. I have tried a few other more serious PCB CAD programs but they seem way to hard to learn for me to be able to create this board.

Per-Anders, if you want to take a look at my schematic and tell me what you think, and if you might be able to help with the actual PCB design (gerber files) I sure would appreciate it. Just let me know how much you want for it. I guess you would need the parts list as well to see what components I plan on using to know the hole spacing etc? Just let me know and I'll get the list of components and whatever else you want/need  :-)

Enough talk, here is the schematics :-)


Well it is that time again, updating this thread.

The project has come along nicely but I have hit a snag. I was planning on using Alexw88's design for the actual preamp part of the PCB, and though I had it all figured out. But then I got my OPA1632 IC's and WOW they are TINY! only 3mm wide and 8 pins. I have not found this IC in a DIP-8 version  :-(

Anyway, the problems I have at the moment are:

I need help making this part of the PCB since I am using hole mounted components (except for the OPA1632) and I really would like to find this IC in a DIP version but I'm a novice and can't find it anywhere, and it might not exist at all.

The second problem I have is that I use the free program ExpressPCB which is not able to save as gerber files :( That means that only ExpressPCB (the company) can manufacture this PCB for me and I really don't want to use them as they can't make this PCB in black and that is pretty important to me  :-D.

So if you Per-Anders installs the free ExpressPCB program, maybe you can create it in a more professional program? and make any tweaks you think is needed (I am sure there are many) As I said before, I am willing to pay you for it of course.

I have chosen nearly all the components for this project. I will attach the Microsoft Excel parts list and the .PCB and .SCH files for you to have a look at if you are willing and able :-)

I really hope you want to help me with this.

Best regards,

Daniel Sallros


This is the official schematics I have been using when I did mine.

It is a bit prettier than mine so it might help.