Bose 901 series I active equalizer DIY

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#21
Could not find a saved Active EQ curve

Rather than spend time on two graduate classes 🙂 I took a few minutes and searched for a REW or MiniDSP EQ data for the "stock" Bose 901 II Active EQ. I could not find one. It occured to me, that I had never tried to equal the stock curve (why? I could have just used the EQ unit itself.) Nevertheless, you can find the curve for free on the Internet and/or download the manual(s) from the Bose mother ship 🙂

Interesting you find the active EQ has more impact or "punch." In theory, you can match anything with enough EQ. For everything else I want test evidence or I will just blame it on our notoriously unreliable brains -- subjectivity and all that. And that is the truth because I believe it to be so !!! [sarcastic]

As someone said above, the original EQ was just two boosts (?). My EQ-ing, whether with DEQ2496 or MiniDSP, is usually based on doing a huge broad cut in the mid-range first.

Ideas about DIY: I find it amazing that some, like OP, would even consider building a clone of the original EQ. Why? For the sheer challenge? Go for it! I wish I had those skills. Whether it's a waste of time is another matter. (And I know how to fritter away my time!) Love or hate 901's, one good thing is that you can buy, sell them for cheap and hardly lose any money. I challenge you to ever make a profit re-selling stuff (at least on Ebay). But hey, it's a hobby. If your audio system isn't a rat's nest of wires and (for example) your subwoofer is a twelve-foot cardboard tube with a quality subwoofer epoxied to one end, then you are not a real DIY-er!

Please share with us what curve(s) you find most pleasing for yourself.
 
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#25
They sell everything you need for etching a board at Radio Shack. You need boards (single or double sided), acid, and a stencil kit (which they sell) and/or a pcb drawing pen, which is really just glorified fingernail enamel. In fact, you could swipe your SO's fingernail enamel and use that! (Or even a sharpie.) You must supply a plastic tray large enough to immerse the board in acid. A large tupperware storage bin with a sealed cover is ideal and probably safest.

The acid is dangerous. It will eat right through your clothes and it will etch any metal it gets on. Of course it will burn your skin. Use common sense and store properly.

You've got to leave the board in the acid long enough but not too long. You have to agitate the acid every so often. Double sided boards will require turning the board around a couple of times. Some kind of plastic standoff for the board helps.

You can buy turnkey kits with pump, electric agitator, and everything. For simple boards you don't need it, but if you're making 0.5 mm traces separated by 0.25 mm (like for surface mount chips; you can buy stencils from Digikey etc) you sure will.
 
#26
Someone might mention making PC boards with a computer program. You can draw your PC board on the computer, print it on photosensitive paper, and transfer it onto the board. I have never done this, but it sounds very cool. I described how you made PC boards back in the day. I was making PC boards decades before Al Gore invented the internet. I think I was 12 when I made my first board.
 
#28
rayma said:
The circuit is simple enough that you can build it on a breadboard.
Don't try to etch a board, those are nasty chemicals.
There are several PCB mfr sites with the software to design a pcb if you want to try it.
Click to expand...

They are nasty chemicals. Nowadays if you let your pre-teen play with acid they'd probably take him away from you. Back then it was considered A-OK.

I was working on tube circuits too. I guess it is scary to let your kid work on stuff like that but I never even burned the house down. 😀

I forgot about the PCB services. It would be nice if a PCB manufacturer could make PCBs for me at a reasonable price. At this stage of the game (It's getting a lot harder for me to do this stuff) I might give them a shot. Any recommendations? Thanks.

Edit- thanks for the link.
 
#29
Fast Eddie D said:
It would be nice if a PCB manufacturer could make PCBs for me at a reasonable price.
Click to expand...

There are lots of free software for pcbs. Kicad is popular and well supported.
Eagle (free version, for small pcbs) is ok if you are comfortable with it.
Pcb mfrs can use Gerber files from any program. I'd recommend Osh Park highly,
check it out. Advanced Circuits is especially good for students.
 
#31
Fast Eddie D said:
<snip>
I forgot about the PCB services. It would be nice if a PCB manufacturer could make PCBs for me at a reasonable price. At this stage of the game (It's getting a lot harder for me to do this stuff) I might give them a shot. Any recommendations? Thanks.

Edit- thanks for the link.
Click to expand...

I've used pcbcart and was very pleased with the results.

PCBCART - Professional PCB Manufacturer from China
 
#32
I have the 901 eq for my other 901. I even recapped it last year. I could run it out of tape monitor loop and just run 4 901's. Only need the second eq if I am selling 1 set LOL.
In any case - Is it easier to etch the board from a circuit or a board ???

Thanks.
Srinath.
 
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