GC Preamp Suggestions - Page 11

Gcollier · 17th March 2005, 02:38 PM

As promised here are the eagle board files for the the PMA preamp I have been working on. I have also included the voltage regulator boards. I haven't yet had a chance to label everyting on these boards, feel free to do it and psot them again. You will notice that I made a few changes here and there. Mostly I moved the output so the traces were shorter, added pads for larger capacitors near the OPA's and also added pads for some caps near the input. I also removed the GND input near the DS1802...it was unnecessary and could have caused a ground loop.

I would like it if somone could help me modify the PSU boards to add a discrete regulator as Steeno suggested. I was looking at some designs last night for this...Pedja Rogic has a nice one on his web site...Alcaids is also very nice.

Anyway Enjoy!

Gcollier · 17th March 2005, 04:32 PM

Ok, how about this for a supply regulator. The LM3XX's provide 20V to the discrete regulator which uses 15V zeners and MG3055/2955 transistors to bring the voltage down to +/-15V.

Should I put some caps on the output????

Alcaid · 17th March 2005, 04:38 PM

Quote:

Originally posted by Gcollier
Ok, how about this for a supply regulator. The LM3XX's provide 20V to the discrete regulator which uses 15V zeners and MG3055/2955 transistors to bring the voltage down to +/-15V.

Should I put some caps on the output????

Could you post the schemtic?
If it's a zener + emitter follower the output impedance decrease with increasing value of output capacitance, so yes you need a output cap.

jleaman · 18th March 2005, 05:48 AM

Quote:

Originally posted by Gcollier
Here is the basic schematic that I followed (this came from another post...and is not my design). I added a DS1802 on the input...the circut for this is very simple and should be obvious from the PCB. If you would like I can post the Eagle files.

This schematic is wrong : O ) The buf 634 sybol is wrong leading it with the pin's wrong also.

Gcollier · 18th March 2005, 03:28 PM

Quote:

Originally posted by jleaman

This schematic is wrong : O ) The buf 634 sybol is wrong leading it with the pin's wrong also.

You are absolutely correct...well sort of.

The schematic is correct if you are using the TO220 package...not the dip. Looks like i screwed it up on the PCB. I will re-route it with the proper pinout for the DIP8 package. Thanks for paying attention jleaman you saved me from making a big mistake.

I'm working now on finishing up soldering some LM4780 boards so I likely won't be correcting this today...but likely tomorrow.

jleaman · 18th March 2005, 05:03 PM

send me the sch file ill fix it for ya : O ) I was extreamly confused when i was looking at your board and then yuor schematic : O ) then i got it Its de wrong one HEHE. Just wanted to help that's all..

J'

Fat Dave · 18th March 2005, 06:18 PM

Not sure if it's important to you or not, but I think the TO220 version of the BUF634 has better heat dissipation than the DIP-8 version, plus you could throw a heatsink on for better cooling if you like.

Fat Dave · 18th March 2005, 06:26 PM

I can't find a datasheet for the mg2955/3055 - can someone pls provide a link?

Do these differ from MJE2955/3055?

Thx! I'm intrigued by this PS design...

edit - never mind! The board pic lists MJE2955/3055....

motherone · 18th March 2005, 07:19 PM

No dual discrete bridge rectifiers?! I mean, c'mon. Everyone does those nowadays

I mean, how audiophile can you get if you're not forced to get a transformer with dual secondaries?! Huh?!

Just kidding.

It might be smaller/spiffier if you could make each +/- voltage on a smaller, separate board. That way you have a flexible design (like the digi01 boards) that can be used for more stuff! (I'm being selfish here, 'cause I'm thinking about a way to replace my +/- 15v and +5v PSUs on my DAC)

motherone · 18th March 2005, 07:21 PM

Quote:

Originally posted by Fat Dave
Not sure if it's important to you or not, but I think the TO220 version of the BUF634 has better heat dissipation than the DIP-8 version, plus you could throw a heatsink on for better cooling if you like.

For a preamp, I don't think you'll ever be hitting the 250ma output capability of the BUF634. I use a ton of them to drive various different types of headphones and mine don't get warm to the touch in the SOIC or DIP8 packaging, let alone something that would require a heatsink

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18th March 2005, 05:03 PM	#106
jleaman Banned Join Date: Apr 2002	send me the sch file ill fix it for ya : O ) I was extreamly confused when i was looking at your board and then yuor schematic : O ) then i got it Its de wrong one HEHE. Just wanted to help that's all.. J'

18th March 2005, 06:18 PM	#107
Fat Dave diyAudio Member Join Date: Aug 2004 Location: Calgary, Canada	Not sure if it's important to you or not, but I think the TO220 version of the BUF634 has better heat dissipation than the DIP-8 version, plus you could throw a heatsink on for better cooling if you like.

18th March 2005, 06:26 PM	#108
Fat Dave diyAudio Member Join Date: Aug 2004 Location: Calgary, Canada	I can't find a datasheet for the mg2955/3055 - can someone pls provide a link? Do these differ from MJE2955/3055? Thx! I'm intrigued by this PS design... edit - never mind! The board pic lists MJE2955/3055....

18th March 2005, 07:19 PM	#109
motherone diyAudio Member Join Date: Apr 2003 Location: Seattle	No dual discrete bridge rectifiers?! I mean, c'mon. Everyone does those nowadays I mean, how audiophile can you get if you're not forced to get a transformer with dual secondaries?! Huh?! Just kidding. It might be smaller/spiffier if you could make each +/- voltage on a smaller, separate board. That way you have a flexible design (like the digi01 boards) that can be used for more stuff! (I'm being selfish here, 'cause I'm thinking about a way to replace my +/- 15v and +5v PSUs on my DAC)

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