New to this, not to soldering, need help

[hyperion007]

Hi,

I'm a total beginner when it comes to making my own HiFi gear and hence I need some help from you guys.

I want to build my own preamp and after searching the web for at least 50hours this week I decided to ask for help.

I want to build a preamp with 4 analogue inputs and 1 analogue output. I really would like to have an SPDIF input as well but it is not a necessity, it would just be a fun thing to build and might prove useful for connecting the digital output from the computer.

From what I have gathered, it would be very easy to build a passive preamp if I skip the digital input. The hard part being to "impedance match" it to the rest of my system as I have no idea of what that entails.

So that leaves me with a transformer based preamp right? I should point out that I do not want to build a tube based preamp.

The reason for building my own is that my Proton AP-1000 is acting up and I want to build something.

My budget is not that large so I think DACT and other very pricey attenuators are out of my price range. The ALPS pot in the AP-1000 is a 40 step one and I only ever needed to use the first 4-8 steps before it got way to loud using my B&K ST-140.

I first contemplated using DACT products and even made some drawings of a system based on their modules but that was before I saw what they were charging for them


So what to do now? I was looking at the First Watt B1 buffer but it has only 2 inputs and seems to require some knowledge about impedance matching. I have really been looking for a kit with PCB and most of the components but have yet to find anything that fit the bill of price and features.

I have great soldering skills (having worked with manual surface mount soldering under a microscope for a living) so I do want to build it all by my self, including chassis etc. but rather not wish to hunt for PCB components from all over the place (I do like to hunt for rca connectors and knobs etc)

Oh and it should be single ended and not balanced.

I really like this one: http://www.shine7.com/audio/bpre.htm
But as I said, I don't want balanced in-/outputs and DACT etc are too expensive

I really hope you guys can help me in this quest of mine

[Steerpike]

Generally, for all modern audio, impedance matching is nothing you need to worry about.
The source impedance of all new analogue sources like CD players, DVD players, tuners, etc. is low - in the tens or hundreds of ohms. (I class CD players as analogue sources because thats what you are getting out of them, if you aren't using SPDIF).
As long as you keep the input impedance of the pre-amp substantially higher - a few hundred times higher - you don't need to worry about the numbers.

If you go passive, a pot with a resistance of 10k to 20k or higher will work.

Valve (tube) sources will have a problem with that, but not transistorised sources.
An active buffer preceding the level control will provide the source with a very high impedance, (the value depends on the design) but that is necessary if you have any tube sources.

There are a number of single-IC spdif D/A converters. It would be trivial to install one in your preamp as an additional source. SPDIF IS sensitive to impedance, so if you follow the IC application notes and ensure a 75R loading resistor is present, all will be well.

[hyperion007]

I found this:
Ultimate Remote Volume Control/Selector System | Diy HiFi Supply

but as I want to solder my self I don't really fancy this product.

If someone can help me by pointing me in the direction of kit suppliers that make kits for volume control, input selection (with LED indication preferably) and PSU to drive these modules I would be very great full. The suppliers don't need to have all these kits, I can shop from different places.

I have attached two pictures of two designs I'm working on.

Thanks in advance,

/Dan

[hyperion007]

Well, here we go again, more questions.

I have made some progress but need some help figuring out some stuff.

I have now decided that I will have 4 single ended inputs and one balanced input. 1 single ended output and 1 balanced output.

Now, is there ANY way to combine a 5way rotary selector switch AND a remote control for the input selection? I really want to use a rotary switch for that manual feeling but still want a remote for comfort.

If you guys have any good ideas for a balanced volume control that doesn't cost me my entire budget then I would be glad to hear them. I have found some pots and stepped attenuators but in my price range ($50-$150) I really only find ebay "bargains" and I am a little worried after reading about the hatred for ebay junk here on this forum.

Sure I would love to get my hands on a DACT or a GoldPoint attenuator but their price is way to much for me.

So if you guys would grace me with your answers, I sure would appreciate it!

Thanks
/Daniel

[fastbike1]

Rod Elliott's pages. High Quality Audio Preamp

Project 88, 06, 05B will get you everything you want. Buy the PCBs from Rod, follow the parts list and build instructions and you'll be all set.

Omit project 6 if you don't need phono input.

[hyperion007]

Thanks fastbike1!


I have done some schematics and pcb designs for this project now. This IS my first time doing this and I know I have borrowed ideas from others designs but I really hope this is ok as I don't have any thoughts about selling anything hence not making money off of someones designs.

I'll attach a gif of where my schematics are at the moment. I have yet to put the power supply stuff in there but if someone spots a problem with the schematic, please let me know

Best regards,

Daniel