GC Preamp Suggestions

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#781
steenoe said:

Russ, thats a hit😉 Are your designations equal to PMA's? And please, zip up the Eagle files and post them, if you care😉 I would like to etch a board like that🙂 Since not being one, needing the buffer😉 Ohhh, and a BOM please🙂 In that way, everyone can play along🙂 If that is not asking too much. You are rollin'😀 😀

Steen😎


Great, gives you some flexibility🙂
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Thanks Steenoe,

Always glad to share. 🙂

My designations are my own, and the circuit is not really the same as PMAs, though really it has a lot in common with a lot of circuits. 🙂

I will post a BOM in a little while. Work issue to take care of first. 😀.

Here is the eagle file:

pre1.brd
 
#783
steenoe said:
Thanks a lot, Russ🙂 I will try this one😉

Steen😎
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I am honored. 🙂 Though if it blows up, please forget I designed it. 🙂

Here is a cursory BOM(no part numbers):

C1, C2 2.2uf (I will be using 50V metalized polyester) or builders preference 😉
C3, C4 330pf (these are to shunt RF to ground)
C5, C6, C7, C8 .1uf bypass caps
C9, C10, C11, C12 47uf25V low ESR electrolytic caps.

R1, R2 1K metal film 1% (forms low pass RC filter with C3/C4).
R2, R3 100K metal film 1% (along with R1/R2 forms high pass RC filter with C1/C2)
R5, R6 2K metal film 1%
R7, R8 10K metal film 1%
R9, R10 47ohm metal film 1%

I know most of you know this but for those who dont:
Adjust gain as follows:

G = 1+(R7/R5)

So for the values given gain should be 6;

U1 and U2 are OPA627 or can be just about any pin compatable JFET/BiFet input single opamp.

All connectors are standard 2 or 3 pin male headers with .1" spacing.

Cheers!
Russ
 
#784
Russ White said:
Ok one more tweek before I etch this baby. 😀

An externally hosted image should be here but it was not working when we last tested it.


fixed image
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How about one more tweak....swap the positions of the feedback and output resistoes to have a shorter feedback path...
You could actually rotate the feedback resistor 90 degrees and place it under the opamp and solder it on the bottom side of the board, then rotate R5/R6 90degrees and put them directly beside pin 2. If I were Carlos I would certainly complain about the bypassing and indicate that you could certainly move the electrolytics a fraction of an inch closer to the supply pins as well as the non polar caps...Just kidding Carlos 😉 .....And finally you could realize that the design that you have already will sound just fine without any of these changes and go ahead and etch the little guy 😀

Have fun playing with those chemicals

G.
 
#786
steenoe said:

I wouldnt bother too much, about that fraction😉

Steen😎
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I didn't 😉

But did listen to George, and switched the resistors. I also did some other little tweaks, and make pads for slightly larger bypass caps since I have some Wima's that size. (5mm) 🙂

Cheers!

Here is the result:


An externally hosted image should be here but it was not working when we last tested it.


pre1.brd
 
#787
Russ,

I was looking at the .BRD file you attached and I noticed that when moving some of your components that you have not connected them with a signal. I have found that the easy way to do a layour is to place all the parts as they are in the schematic. Make all the necessary connections using the signal tool, then rearrange until you have a nice neat arrangement without crossing too many signals (if you are doing one sided bords at least). Hit the Ratsnest button a few times as you go, it will reroute the signals through the nearest appropriate point making things a little neater for you. Then I use the Route tool to complete all my traces. After that you can tweak until your hear is content.

By the way...I still haven't gotten around to etching those preamp boards and the PCM2906 board for you. :cannotbe: I have an older (but very nice) preamp design done waiting to mail, but the others are still waiting on photo paper to be transfered and etched. I think that I am going to add TTL level convertors to the PCM2906 though. I can send you the .brd files if you want to make them yourself. Otherwise it won't be until I get back from vacation.
 
#789
I would love the BRD files, but I can also wait. I am in no hurry. Thanks!

Thanks for the advice too.

I really did not use signals too much except for ground. I let eagle assign default signal names, some of which I redefined (which you proabably saw).

I placed the compenets and started running wire in such A way that my ground plane would be uninterupted since I knew I wanted a single sided board.

Did you find any problem?

Thanks again so much for your advice. 🙂
 
#790
jleaman said:
Gcollier,

What paper do you use ? Is it blue iron on stuff pressn peel ?Id like to etch a few boards here that i have all i have is the amonium-persalphate... Do you have a link to the paper you use ?


J'
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No need for press and peel or anything fancy. Ordinary inkjet glossy photo paper through a laser printer works great. I have even used non glossy satin coated injet paper and it worked fine as well. I am partial to the Epson paper myself, it peels really easy and leaves very thick resist. Ammonium persulfate will work great, put it in a try and cover the board with the dry powder, boil some water and dump it in. If you can keep it warm all the better.
 
#791
Gcollier said:



No need for press and peel or anything fancy. Ordinary inkjet glossy photo paper through a laser printer works great. I have even used non glossy satin coated injet paper and it worked fine as well. I am partial to the Epson paper myself, it peels really easy and leaves very thick resist. Ammonium persulfate will work great, put it in a try and cover the board with the dry powder, boil some water and dump it in. If you can keep it warm all the better.
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I'll try this.. what tempature do you use your iron at ?
 
#793
jl-

From what I have read, a medium to medium-high temp. Try medium, then work your way up. I'm going to try the glossy paper methid myself. I usually use photo method, but the copper is too expensive.

I did buy this stuff:

http://rocky.digikey.com/scripts/ProductInfo.dll?Site=US&V=182&M=GREENTRF-P

Green Toner foil. It's supposed to be used over the toner left from the toner transfer paper, but I figure I can use it to improve the glossy paper method. It basically adds a think layer on top of the toner to reduce pitting and improve fine lines. Cheap enough for a try, and you get a bunch.

I'll post some results after I give it a whirl. You try this George?
 
#794
BrianDonegan said:
jl-

From what I have read, a medium to medium-high temp. Try medium, then work your way up. I'm going to try the glossy paper methid myself. I usually use photo method, but the copper is too expensive.

I did buy this stuff:

http://rocky.digikey.com/scripts/ProductInfo.dll?Site=US&V=182&M=GREENTRF-P

Green Toner foil. It's supposed to be used over the toner left from the toner transfer paper, but I figure I can use it to improve the glossy paper method. It basically adds a think layer on top of the toner to reduce pitting and improve fine lines. Cheap enough for a try, and you get a bunch.

I'll post some results after I give it a whirl. You try this George?
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Nope never tried it, my results have been very good just with the photo paper, I figured there was no reason to add any additional expense.

As fore iron temperature I set it on high. Make sure your boards are very clean by scrubbing with steel wool or 400 grit sandpaper first, then wipe off and grit. Iron for a long time with lots of pressure. It helps to use light pressure at first just to get the transfer stuck down so it can't slide then press hard.

Well have fun everyone, I'm off to the cottage for a week!
 
#795
Re: Preamp boards

bearddavid said:
Hi Russ,

have you considered a group buy on your preamp boards ?

I'd certainly be interested.



Dave
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I may do a group buy, but first I need to build it and test it. The copper laminate I was expecting at my house yesterday did not appear. But maybe it will be here today and I can etch this thing. 🙂 If it works well I will consider a group buy if there is enough interest. Its a pretty small board (like 3" x 2") and it's one sided so it should be relatively cheap.

🙂

Cheers!
 
#796
Re: Re: Preamp boards

Russ White said:


I may do a group buy, but first I need to build it and test it. The copper laminate I was expecting at my house yesterday did not appear. But maybe it will be here today and I can etch this thing. 🙂 If it works well I will consider a group buy if there is enough interest. Its a pretty small board (like 3" x 2") and it's one sided so it should be relatively cheap.

🙂

Cheers!
Click to expand...

I was thinking about another group buy also because now im setup to do it and now know what it takes.

J
 
#797
Hi J,

I am sure you would do a great job on a group buy, but I will handle the GB for my own boards since I am handling one other right now, and there is a lot of cross interest.

I also have stock of all the parts (including 627s) for a kit once I have tested the design. So If things work ok, I will be offering kits and PCBs.

Thanks for the offer. You may consider one of the other designs.

Cheers,
Russ
 
#799
demogorgon said:
one of the great things about the buf\opa pre vas the fact that it just as easily could be used as a very good headphone driver, now, without the buffer this is no longer possible, or less ideal anyways.

but since your mind is set on this one..
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Never fear! 🙂 I am working on a opa/buf design as well. 🙂

I will offer both designs in seperate group buys, with parts kits. Probably in the next 15 days or so. I just need to do some testing and some design comparisons.

Cheers! 🙂

BTW very few headphones really need more than 10-20ma to drive you deaf. And two OPA627/637 can deliver something like 45ma apiece with 100ma bursts. Way more than enough for all but the most current hungry headphones (though I do acknowlege they do exist thus the need sometimes for buffered amps).

😀
 
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