microcontrolled pre for a GC power amp

[demogorgon]

Hey guys!

I have a bit of a dilemma here.
I'v made the descition to have an active pre for my GC and need the input selector to be controlled my a micro controller.
this because the amps are my term-asignment and i have to include cerain things.

It would altso be preferable if i could get away with using transistors to controll the line-ins, relays are so damn expensive, and my budgette is already blown with aboute 70 euro.

If anyone has some tips, links or other thing i might find usefull i would be eternally gratefull!

regards
marius

 

[demogorgon]

her is the atempt i made, thinking i was sooo clever, tehn all of a sudden it struck me as lightning from the sky, those things wont let AC through!

and here i am again, back to square zero, but it show the sort of layout i planed, and still hope to use thoug.

regards

edit: and again the picture does not appear, mystical..
well, clic in at www.home.no/demogorgon/ and you should come to a apache server index and there se a picture named scetch.JPG.

 

[nuppe]

Maybe an analog mux would work for input selection like a 4051 or 4351? I know they are not exactly Hifi but they are cheap and easy to use. An SSM2404 is higher quality but might be harder to find. For the microcontrol i can't give you any clues as i have no experience with this yet, but i can give you a couple of links:

Mark Hennessy's preamp and Devil_H@cks preamp

I got some great inspiration from these two sites for an integrated amp i'm planning, but haven't had the time to get started yet.

Edit: i saw your second post after i posted mine. I'm a complete dummy when it comes to analog transistor level stuff, but won't the transistors in your sketch need to be biased to pass AC?

Good luck with your project!

/Andreas

 

[demogorgon]

mux? would this be short for what at least i know as a multiplexer?

if it is i have thought of it, but i do have to use a microcontroller =<
(or something containing assembler code anyways )

 

[nuppe]

Yep, a multiplexer was what i was suggesting. You could still use a mux controlled by a microcontroller, it's a bit over the top, but it would work. Or do you need the microcontroller to control the inputs directly?

/Andreas

 

[squadra]

edit: and again the picture does not appear, mystical..
well, clic in at www.home.no/demogorgon/ and you should come to a apache server index and there se a picture named scetch.JPG.

To solve at least one of your mysteries...
you need to prefix the image with http:// otherwise your url will be appended to the current location ( http://www.diyaudio.com/forums/ )

Regards,

Pj

 

[demogorgon]

well, to have the microcontroller controlling the "gate medium" in lack of a better term, was the original plan, and would have saved me a lot of truble, but if that should prove to be an impossibillity, then i have to offcource consider other options.

I really dont know that mutch about multiplexers to judge if it is a actual choise or not, making this thing as easy as possible and having as few components in the signalpath as possible are high priorities.
the gainclone certainly sounds bad enough allready, so decreasing the sound quality further would ultimatly mean i would have to go solid state!

I'l have to google a litle on the subject and consider the pros and cons of the mux. But if it turns out that the mux is not suited for the task at hand, any other tips?

regards
marius


Squadra: Thanks! I'l keep that in mind the nexttime i post image links!

 

[squadra]

Hey guys!
It would altso be preferable if i could get away with using transistors to controll the line-ins, relays are so damn expensive, and my budgette is already blown with aboute 70 euro.

regards
marius

There used to be an IC DG212 that contains 4 switches.
If you only require 2 inputs you can use the attached schedule.
Or you might create 4 inputs with 1 IC like that, so only 2 IC's for stereo.

Maybe that IC can still be found, it was pretty cheap.
Otherwise look for a replacement.
No transistors, but close enough, I hope

regards,

Peter

 

[squadra]

The IC is still available, and this is the datasheet:
http://pdfserv.maxim-ic.com/en/ds/DG202-DG212.pdf

 

[demogorgon]

well, I'l have a look at it then..

dont quite grasp how to controll them with a microcontroller yet, but i'v got all weekend.

regards
marius

 

[mcs]

You can also look at the 4066 which is a quad analog switch. The 4051, 52 or 53 may be easier to use however, as they can pass ground-referenced signals (on a +/-5V supply). All these chips are very cheap and easy to get.

Best regards,

Mikkel C. Simonsen

 

[demogorgon]

Is a DG4066? considering that you didn't nemtion the letters in front of the numbers it probably has been nemptioned before?

I'l do a couple of googles.

thanks!
-marius

 

[mcs]

They are standard 4000 series CMOS logic chips. So they can be called CD4066, HEF4066, MC14066, TC4066 etc. I have never seen a DG4066 though.

Best regards,

Mikkel C. Simonsen

 

[demogorgon]

Mikkel, this a bit of an embarrasing question that i should have known the answer to myself, but i have the tendency to forget things i dont use activly so here it goes:

will the original consept i worked on work, and if not, why?
as there will be input resistors on the amp and on the opamps in teh pre that will lead to ground so the damn thing will work at all, and dont there exist transistors (wierd kinds of darlingtons?)who will do the work of boath NPN's and PNP's?

sorry for the stupid questions, but as they say, "those who are afraid to ask, are afraid to learn".

regards
marius

 

[demogorgon]

and one more thing, i didn't see the need to open up another thread for this: do you know of a volt regulator somewhat simelar to the lm317T but bigger?
i need one that can tackle about 3-4 amps.. bigger is better..
I need it for a 5.1 amp with 5 tda 2050 and two bridged or paralelled lm 4700. I fugure i still ned to paralell a few of them..

acouple goes into the GC ad well i suppose,when i find the time for it..

regards
marius

 

[djQUAN]

LM338K. it can handle 5A. though it is a to-3 device.

 

[demogorgon]

I see national got'em as TO-220 devices too, so it sholdn't be a problem. guess i'l have to find some place that sell them.. elfa.se shurley don't got'em, and that's where i usally do my shopping.

edit: how do i use this to get negative voltage regulation as well?
Or do i have to use another chip for that? (sort of the difference between complementary NPN and PNP transistors?)

regards
marius

 

[djQUAN]

you could search national for the one used for negative voltages.

 

[Kermit]

Use a dual secondary transformer, build one regulator pr winding, and reference the positive off one to ground. Search for 338 regulator and I'm shure you'l find a schematic.
A cheaper soulution would be to use 317 together with a pas transistor to increas curent.

 

[demogorgon]

well, found what i was looking for, or rather figured out.

im buing a shitload of lm137HV's and paralelling them. four per rail gives me the ability to reatch 6amps continous per rail, and up to +-47V to boot, so im content with that for the time being.

I really hope going regulated helps the sound, and maby in time changing capacitators to black gate.

edit:
Sven, I didn't quite follow you completly there, think you could outline a litle about the transistor idea?