Might have made an oops

[tomp]

Jeff:

I'm retired so weekdays are generally open but weekends can get busy. Next month is particularly crazy as I am away every weekend. Early August could work for a weekend. As far as a transformer, let's build the main circuit first. I'll check my transformers but I think I maight have one that works. The problem with buying parts is that the freight can cost more than the parts. When we get through you can order a bunch at one time and save freight. You can replace whatever I have supplied or get something else. We will build not only a line section but an RIAA phono pre. BTW if others are interested I can accommodate up to three more people in my work area at the same time who can watch the process.

Tom

[JDCrae]

Tom,

August sounds fine to me. Gives me time to finish up the main console itself, and I just got the shipment from PE, some I am hoping to get the drivers installed, and crossovers installed this weekend.

Sounds good as far as the transformer. Will wait. Would it be difficult or expensive to add a sub pre out? Down the road I may want to add one, and I thought that would be on the preamp.

Thank you again for the offer. Very excited to learn and build a preamp!

[tomp]

As the old saying goes, it depends. If you just want another output for the sub which will have its own crossover then it is just adding a connector. The OP Amps have a lot of output drive capability. If you are going to want crossover functionality it would be more complicated. It is probably better to do the crossover function externally as you would then have lots more control. Check out these links:

https://www.amazon.com/Behringer-CX2310 ... B0002Z82LM

https://www.amazon.com/DBX-223XL-Stereo ... +crossover

Tom

[JDCrae]

Every subwoofer I have ever had had its own crossover built in to the plate amp. Not really sure what the sub pre out actually does on my Marantz Receiver at home. That is yet another thing I hope to learn about this process. Hate that I own things that I don't understand how they work.

[tomp]

Some of the receivers have the crossover for the line out or even a separate amplifier channel with crossover for a speaker out connection to an unamplified sub.

Tom

[SoundMods]

And I thought I had a nasty equipment "bone yard."

I am beginning to think that all audio DIY wonks have a lot of crap in their basements.

[tomp]

Tom,

August sounds fine to me. Gives me time to finish up the main console itself, and I just got the shipment from PE, some I am hoping to get the drivers installed, and crossovers installed this weekend.

Sounds good as far as the transformer. Will wait. Would it be difficult or expensive to add a sub pre out? Down the road I may want to add one, and I thought that would be on the preamp.

Thank you again for the offer. Very excited to learn and build a preamp!

I got to thinking and I have never built a passive RIAA phono stage. All of mine have been active. So I decided to layout a board that would have both a pasive RIAA phono and a line stage for two channels. I'm including an image of the board. The top traces are shwon in red, the bottom in green and the component outlines in yellow. There are ground planes on bothsides but they are not shwon for clarity of the traces. The boards will be here in time for our construction project. We will still build the power supply and switch boards using perf board so you can get experience with both construction methods.

Tom

Attachments

Preamp.rtf

(825.14 KiB) Downloaded 620 times

[JDCrae]

Thanks Tom. We are out town for the weekend and that file will not open up on my phone. Will check it out when I get home and can pull it up on my pc

[JDCrae]

Just was able to take a look at the diagram and wow is that impressive. So many connections and components! Have no clue as to what is going on there, but very excited about the fact that I soon will! Cannot tell you how much this means to me, to finally be able to understand whats going on inside these components!

Thank you again

Jeff

[tomp]

Jeff:

Here is the final schematic for the circuit with changes I made that generated the PCB diagram you saw. This is for your archive and I will explain it all when we work on the board. If you are interested in the free program that is used for the schematic and to link it to the board layout here is a link.

https://www.expresspcb.com/free-cad-software


Tom

Attachments

Preamp schematic.rtf

(1.85 MiB) Downloaded 635 times