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PPAS Build Thread. - Page 12

post #166 of 254
Thread Starter 
Looks good at least on back of the napkin check... (R6 does look tad high though.. are you sure that one's right?)

I think my values were
R1 - 1k
R2 - 100k
R3 - 1k
R4 - 10k
R5 - 220
R6 - 6.2k
post #167 of 254
Ok, so I'm on the right track with the calculations. I'm going to play with this and see if I can come up with some good values for a range of gains, and then find part numbers.
post #168 of 254
Yeah, my R6 above way way out of wack. I just reduced it based on what I had on hand. Bad idea.

My goal is to keep my gain around 4 and minimize my DC offset. I'm not sure, but I am going to choose either AD8058 or LM6172 for OPALR. I haven't selected OPAG yet. I'll be using LMH6321 as my buffer.

How do these look?

R1 = 3.8K
R2 = 100K
R3 = 400
R4 = 2.43K
R5 = 3.32K
R6 = 35K

The cap I picked out for doing the additional power supply bypassing:

CBypass: 80-C0603C104J3R (0603 .1uF 25V 5% X7R)

I could try going .01 and a COG/NPO


Here is a work-in-progress BOM based on the original, with R4 values for various gains, a start on a bipolar version (pending me playing some more with the numbers) and a very little section on the opamps and buffers.

Excel Spreadsheet
Zipped Excel Spreadsheet
post #169 of 254
So I picked up a couple of the AD8058 and AD9631 from digikey, and I was too impatient to wait to figure out proper resistor values, so I put one of each on a browndog and threw them in my Pimeta (ran off a single 9V to better match what I'll be running my PPAS off). I'd previously gotten LMH6321 on browndogs for my Pimeta with good results.

Holy crap. Blows everything else I've tried out of the water. I can't decide if I like the AD8058/AD9631/LMH6321 or the AD8058/LM6171/LMH6321 combinations better, but right now I'm running the 9631 in ground.

DC offset is managable (4mV to 18mV at the volume range I was listening at, mid 30's when cranked to full volume) even without bypassing or resistor optimizing. I'm optimistic about what it will give with the right treatment.

This just sounds amazing. Detail, punch, not lacking but not overpowering in bass, highs are not harsh.

I think I've settled on these values:

R1 4.32K
R2 100K
R3 3.32K
R4 14K
R5 698
R6 42.2K
Cbypass = .1uF X7R (or would .01uF NPO be better?)
New version of the BOM is done... I made the opalr/opag/buf selectable from among the list of what people have confirmed working. I think I'm going to do the same for the gain resistor R4 for the normal config. End-of-year boredom was getting to me at work, and playing with exeel makes it look like I'm busy :-p

Excel Spreadsheet
Zipped Excel Spreadsheet
post #170 of 254
I have a few questions regarding parts for the PPAS

1. Mouser is currently out of 647-UPW1A101MDD, but they have UPW1A101MDH and the only difference I can see is that the MDH caps aren't RoHS compliant. The MDH caps will replace the MDD caps without any problems correct?

2. Mouser and Digikey both don't stock the TLE railsplitter. Does anyone have a spare one they could sell me?

3. I'm going to use the OPA2107 / some ground opamp / BUF634 combo on my PPAS. First of all, what ground opamp do you guys recommend that is currently available at digikey? Do I need to change any resistor values or is what is in the original BOM fine?
post #171 of 254
Thread Starter 
1. RoHS is irrelavent for the functionality

2. Sorry, I'm beginning to run low too, but if you're running 18 volts, you can leave TLE not populated and put the midway point of the 18 volts soldered to the VGND pad

3. BoM is fine for that config. I would suggest something easy to handle like the OPA132? I'm not familiar with easy to work with single channels... I'd go with the AD6171, but that's a bit cranky to work with.
post #172 of 254

opa2134 L/R, opa134 G, BUF634 all around.
Sounds nice.
post #173 of 254
Qsilver2001 has asked me what is pin #1 on the IC.
I agree it is a bit unclear.
Here is a modified picture that should clear it up

Pink dot is pin #1.
post #174 of 254
Hi blueworm,

Thanks for the pics. Hope other new builders will benefit from this clearer diagrams like myself.
post #175 of 254
Nice amp! I like your connectors in the picture above. They seem like plastic body, meaning isolated GND from chassis. Old parts or still available? I've just spent 1-1/2hours digging through Digikey Newark and Mouser with no joy finding something similar.

I may use miniQ XLR instead.


Anyone have one or two PPAS boards they'd consider selling? Puhleez?

Else, count me in for the NEXT round! Hehehehe.
post #176 of 254
Originally Posted by OtterMarc View Post
Nice amp! I like your connectors in the picture above. They seem like plastic body, meaning isolated GND from chassis.
Those are Kobiconn 161-7300-EX from Mouser.
post #177 of 254
Originally Posted by Qsilver2001 View Post
Those are Kobiconn 161-7300-EX from Mouser.
post #178 of 254
Thanks QSilver1. Noted and added to my list.

Now if only I could tempt someone with an extra PPAS PCB (hint hint) to part with theirs. Chocolate? Beer? Magic head-phone mojo juice? Hopefully progress will bring about a Ver.2! You guys have made a nice little and rather desirable project amp a reality. Nice going.


Seeking PPAS PCB...
post #179 of 254
I'm going to do more investigation myself on this, but I'm just wondering if anyone had any good pointers for where to look first:

My PPAS has been pretty darn cranky from the start. First, I had a huge DC offset issue which I found out was somehow related to the fact that I'd lifted one of its pins.
Now that got fixed for the night, but a couple of days later I started getting something like 100-200mV on both channels. I was debugging everything with the meter, and managed to short out two pins of the TLE for a moment (I think it's ground and one of the rails) Guess what? The offset disappeared, and it suddenly started working again. I suspected it was some bad solder joint, so I reflowed everything. Still working a couple of days after that.

I haven't been using the amp for a while, and today, just to retest it, I discovered that there was about 40something/30somethingmV offset on both channels. Actually, now that I check again, it's at 38mV/28mV. It's just within the range in which I'd call the offset unreasonably dangerous for 64ohm headphones. I'm most worried that this might be some weird intermittent/drifting problem. Any ideas on where this problem might be? I've already un-glue-gunned this thing and desoldered the jacks like ten times, and I'd rather not do it again unless I have a good idea of what to look out for.

My configuration is the one recommended in the first post, LMH6321 buffers, OPA2107 OPAR/L, and LM6171 in the ground channel. The isolation JFETs are in there, the CRDs are installed; pretty much everything's maxed out. The main nonstandard features in my PPAS are a homemade SOIC->DIP adapter, since I don't have any SOIC OPA2107's on hand, 12V TREAD power supply (no batteries), trimpots for volume adjustment, RCA outputs + 1/8" inputs. Weird, I know, but these are just a couple of needed modifications for a little project I'm working on.

this is really weird now. I just plugged it in and tested again, and it measures 11mv/22mv offset. Bad component? weird solder joint? I'm really not sure what kind of problem this might be.

I just remembered, I bumped the voltage of my TREAD to 13V from 12.5V. Maybe the opamps just need voltage? I heard the OPA2107 likes lots of voltage. But then again, this looks a lot like something weird going on with the ground channel, and the OPA2107 is in L/R. I'll play around with the supply voltage a bit more. . .

--> It seems that it is a LR channel problem; all the offset in the L/R channels also appears as offset from input to output. Is this just a problem with the OPA2107 wanting more voltage, or is it a more serious problem? Anyone with experience with this confgiuration?
post #180 of 254
Threepoint one,

Any progress? Answers to your questions have been slower than usual.

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