GC Preamp Suggestions

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#442
jleaman said:
I havent tested any of these yet : O ( i need to buy parts..
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BrianDonegan had etched a couple of my boards up and they can be seen further back in this thread.

I have not however heard back from him, to see if he has any comment on the quality or not 😉 of my design.

If you are out there Brain, what do you think, is it any good?
 
#447
Since I have only really been reading lately, I was looking at these as well:

http://rocky.digikey.com/WebLib/Quantum Research/Webdata/QT113, QT113H (QProx).pdf (fixed)

($1.98US each) I was thinking of using the DS1802 volume controls I have for my preamp, but was stuck on what to use for buttons. With these (as cheap as buttons really), I could make a glass front plate for my pre, with touch spots for volume up and down, mute, and balance. The non-H version of the 110 chip has a logic-low output, which seems like it would easily trigger the DS. Also, if you ground the option pins, it goes into toggle mode (instant soft-touch power switch - add transitor, diode, and relay). Seems pretty neat. Just like a B&O.

They also make a chips for slider and dial touch control, though they have serial out which would require a lot more work.
 
#451
Originally posted by Russ White
I would defer to noober since he did so much work, but if OK with him I would really like them.
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Brian its ok with me if you send Russ the boards.
I am also tied up with doing work to my house at the moment in preperation for the summer, so I would rather see some results than me hanging onto them.

Iam also working on a headphone amplifer and a SMD gainclone (hopefuly) so i may just panelize them all onto one board and get them made that way, but we will see, when I have more time maybe.

Enjoy the build russ, and let us see some results and let us know how they sound.


Cheers

n00b
 
#454
BrianDonegan said:
Since I have only really been reading lately, I was looking at these as well:

http://rocky.digikey.com/WebLib/Quantum Research/Webdata/QT113, QT113H (QProx).pdf (fixed)

($1.98US each) I was thinking of using the DS1802 volume controls I have for my preamp, but was stuck on what to use for buttons. With these (as cheap as buttons really), I could make a glass front plate for my pre, with touch spots for volume up and down, mute, and balance.
Click to expand...

Toooo cooool! :bigeyes: I MUST get some of these for my preamp since I already have the DS1802 onboard. Time to put in an order to digikey.

One of the best ideas I've seen yet!

G. 😀
 
#455
Brian, Good work on those boards. I got them this afternoon safe and sound. I am organizing my parts right now. Lucky I had .1 uf wimas in stock, as well as some 10uf 16V tants I will use in place of the ELs. I am still waiting for the polarized connectors I ordered to get here, but they should come by Friday. I might just have a working preamp by the end of the weekend (fingers crossed).

I finished a 12V reglulated supply for this preamp yesterday.

Thanks so much n00ber and Brian.
 
#457
Thanks Carlos.

Ok, I can ditch the tants, but I only have 2.2uf 4.7uf and 47uf electrolytics that will fit, which would you recommend?

The only transformer I have right now is a center tapped 25.5V 2A piece. My current 627/634 pre(on protoboard) sounds great with it. maybe later I will get a 40V trafo so I can build a regulated 18V supply.

Or.... would you suggest I use a voltage doubler?
 
#458
Russ White said:
Ok, I can ditch the tants, but I only have 2.2uf 4.7uf and 47uf electrolytics that will fit, which would you recommend?
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47uf.

Russ White said:
maybe later I will get a 40V trafo so I can build a regulated 18V supply.

Or.... would you suggest I use a voltage doubler?
Click to expand...

You can regulate to something close to +/-18V (16~18V), and for that you can use a (minimum) 2x15V trafo, easy to get and cheap.
No voltage doublers, please...
 
#459
Ok, I have a few more questions about n00bers final design. It looks like there is a resistor and a capacitor in parallel(E$2 and E$38 on the eagle layout). I expected the cap, but what is the purpose of the resistor in parallel with this cap?

Also can someone tell me what values to use there?

I was going to use a 1uf cap.

Also, there is a diode between V- and out on the opamp. Is this for input protection or for biasing? Can someone tell me what part to use there? Is it a zener, or a small signal diode?

Thanks,
Russ
 
#460
Russ White said:
Ok, I have a few more questions about n00bers final design. It looks like there is a resistor and a capacitor in parallel(E$2 and E$38 on the eagle layout). I expected the cap, but what is the purpose of the resistor in parallel with this cap?

Also can someone tell me what values to use there?

I was going to use a 1uf cap.


Also, there is a diode between V- and out on the opamp. Is this for input protection or for biasing? Can someone tell me what part to use there? Is it a zener, or a small signal diode?

Thanks,
Russ
Click to expand...

Russ, I used a 0.47 uf Cap on the input of my pre, seems to work fine. I suspect the 1uf would be fine but I wouldn't go much bigger. In fact some "purists" would suggest just jumpering this and forgetting the cap altogether.

As for the diode, yes it is definately for biasing the OPA627 into class A, and is optional, I'd leave it out, Carlos mentioned something regarding this earlier in the thread...I believe something about biasing the biased 😉

Good luck...let us know how it turns out!
 
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