Phono amp top slot board for O2 amplfier in B3 case - diyAudio
Go Back   Home > Forums > Amplifiers > Headphone Systems

Headphone Systems Everything to do with Headphones

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 21st June 2013, 06:10 AM   #1
agdr is offline agdr  United States
diyAudio Member
 
agdr's Avatar
 
Join Date: Sep 2010
Default Phono amp top slot board for O2 amplfier in B3 case

Here is a revised version of a phono amp board I posted yesterday in the main O2 amp thread that would fit in the top slot of an O2 headphone amp in a B3 case. This version uses stacked film caps in the feedback path instead of 1206 COG/NPO MLCC ceramics. This is just the simple single stage phono amp from the LT1028 data sheet.

If RCA jacks are mounted on the O2 front panel they should not be grounded to the B3 chassis, even through it is grounded to the O2 PCB. Instead the jacks should be the type that are insulated from the chasis. The two signal wires from the RCA jacks (left and right) should be twisted together with the RCA jack's common ground and all 3 soldered onto this board's inputs. I've added a ground PCB hole to attach the RCA jack ground wire to.

Then the 3 wire PCB holes for power and ground go to the O2. There is a hole in the O2 PCB that allows V+, V-, and ground wires to go under the board and solder to the output of the O2 mosfets.

I haven't fabricated or built this one and I'm not going to since I don't have a turntable. So builder beware, there may be an error somewhere I've missed, so you might want to do your own layout and just use this as a guide. The board goes upside down, with parts down and solder joints up. The circuitry area is placed over the (low noise) signal input section of the O2. The BOM has both Mouser and Digikey part numbers. Mouser doesn't have the LT chips.
Attached Images
File Type: png LT1028 phono circuit.png (20.8 KB, 94 views)
File Type: png LT1028 phono layout.png (40.7 KB, 90 views)
Attached Files
File Type: pdf LT1028 phono preamp BOM 5.pdf (72.3 KB, 5 views)
File Type: zip 80x100mm 2 layer 1.6mm green HASL.zip (19.8 KB, 2 views)

Last edited by agdr; 21st June 2013 at 06:18 AM.
  Reply With Quote
Old 21st June 2013, 08:06 PM   #2
qusp is offline qusp  Australia
diyAudio Member
 
qusp's Avatar
 
Join Date: Oct 2009
Location: Brisbane, Australia
I would be surprised if pps are lower noise/distortion than high quality np0

you REALLY hate ground planes dont you mate?
  Reply With Quote
Old 22nd June 2013, 03:10 AM   #3
agdr is offline agdr  United States
diyAudio Member
 
agdr's Avatar
 
Join Date: Sep 2010
qusp - I was wondering about that (COG/NPO)! On the initial version I seemed to recall that COG/NPO solved the ceramic capacitance change vs. voltage issue along with temperature stability, but when I went looking to verify that I couldn't find anything. So hence version 2 where I made the change to film. Lol - you are exactly the one I figured would barbeque me (and rightly so) for putting ceramics in the feedback path on the first version.

What are some better phono amp circuits that are in the public domain? I see the one on the LT1115 data sheet which looks like it may be a bit more precise. Seems like the OPA1641 / OPA1642 would be a good modern chip for this kind of thing with the JFET inputs.

Yep, I'm not feeling the love with ground planes for "lumped" elements where the wavelengths involved are vastly longer than the size of the parts. I did some microwave stripline / transmission line research work a long time ago with GaAs MMIC's (microwave integrated circuits we designed) where ground planes were part of the transmission line. At high frequencies the wavelengths involved are comparable to the size of the parts and everything is treated as a distributed transmission line. But at audio frequencies I don't get it. I can see some value for electrostatic shielding but I am more concerned about magnetic field cancellation. That is why I have the power supply rail traces sitting right on top of each other on the Amplifier Previously Known As An ODAC Version. The few milliohms that may be saved by the large ground plane vs. a properly sized ground trace seem pointless to me for an audio amp. As for trace inductance, at lower audio frequencies it won't matter and at higher (audio) frequencies and oscillation frequencies of the op amps, that is what bypassing and decoupling capacitors are for at the end of the various power line segments.

I would however be concerned about ground return currents flying all over the place on a solid ground plane that is carrying currents, running by and through parts I don't want such currents near. For example, on the ODAC thing, follow the current loops from the input. The high frequencies trace a short route from the input jack through the EMI X2Y cap back to the ground on the input jack. The lower RF current trace a slightly longer route through the 220pF and 274R filter, but all still very near the input jack. Those RF ground return currents never leave the premises, so to speak. Then with the RF removed the audio currents trace a slightly larger loop through the 10K ground return resistors in front of the gain stage op amps, etc, etc. Finally the output of the gain stage op amp traces the full loop back through the ground star point. The heavy output stage return currents never get anywhere near the gain stage parts.

But... I'm probably just out of date. Everyone seems to be using ground planes with the audio. I've bought all of Doug Self's and Cordell's amp books recently and I see reference to the Henry Ott EMI PCB stuff. As time permits I'll do some reading and maybe I'll have an epiphany.

Last edited by agdr; 22nd June 2013 at 03:33 AM.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
LM4562 Phono Pre Amp Circuit Board eldarvanyar Parts 2 3rd April 2013 02:40 PM
Red board add-on phono/RIAA pre-amp rsumperl Tubes / Valves 5 14th May 2011 04:40 PM
HI-END Phono Amp - QSXM3 RIAA board rclourenco Analogue Source 0 8th June 2009 04:57 PM
WTB - Top loading CD Case / Broken Transport stellavox Swap Meet 0 24th February 2007 01:35 PM
Circuit board for phono pre-amp peterb Analogue Source 1 4th February 2004 04:56 PM


New To Site? Need Help?

All times are GMT. The time now is 01:02 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2