gc design q#1 - buffer

[meta]

Hey...

I'm kick starting my gc amp project again...I want to have 6 inputs (1 bal/5 unbal) selectable via a rotary switch and also a stepped attenuator for vol control. I also understand a buffer would be a good idea...with that in mind I've started laying out a schem. The buffer design is pulled straight out a german magazine article that I got from somewhere a while back - not speaking german tho I'm unsure of a few things related to the design (or if it's even suitable for this application) but I did hear good things about it...

So, is it looking okay atm?

Cheers

[janneman]

Can't see anything wrong with it.
What will you use for the vol controls?

Jan Didden

[meta]

Hey Jan...

What will you use for the vol controls?

A stepped attenuator made from a rotary switch, like shown here: http://www.platenspeler.com/backgrou...enuator_1.html

I've updated the schem with 1 channel of a para LM3886 design for output to a 4ohm speaker - still lookin good?

Thanks again

[lgreen]

Looks ok to me. FYI, I have 2 input GC with one input balanced, and use the INA134s as the buffer. When the SE inputs are selected the negative input on the INA134 is grounded, and it acts as a buffer.

http://home.san.rr.com/john1in2/DIY/GC_1/

[meta]

Hey...

I have 2 input GC with one input balanced, and use the INA134s as the buffer. When the SE inputs are selected the negative input on the INA134 is grounded, and it acts as a buffer.

ah, so I could make things alot simpler by removing the discreet buffer circuit and implementing the INA as you've done....is your's stuffed just as mine is or have u done some further tweakin?

Thanks again

[lgreen]

Mine is similar with the following differences:
1. I don't have a parallel config (only 1 LM3886TF per channel instead of the 2 you have).
2. My inputs are selected via a DPDT switch, so I cannot use both XLR and RCA hooked up simultaneously because one connects to the other (my switch simply grounds the - input on the XLR if RCA is selected so this might not be good if the XLR source is connected while selecting RCA) . You have 4 inputs and a selector switch so you should not have this problem.
3. I am using separate low noise regulated power supply for the INA buffer as you can see on the web page.

Yes you could make it a lot simpler by simply using the INA as buffer. It is adaquate to drive the LM3886.

[meta]

Hi...

I've decided to keep the design much simpler (single LM per chan) based on the non-inverting application schematic. Here's a newer schem (cleaner layout then the 1st):

GIF

I'm just wondering if the P and S gnds are where they should be...and everything else I guess

Thanks

[sek]

Hi,

not speaking german tho I'm unsure of a few things related to the design

It sounds like an interesting project.

Can I help out with a translation or two?

Sebastian.