[wew01]

Edited. Thanks, Reima, for pointing out.

 

[Reima]

^ That's a V1.
RC

 

[H22]

Well, I finally got one board finished

.
 
Didn't take too long, and went fairly smoothly. Tangent, that is a very high qualty board, much better than the ones i get from express PCB.
 
I did have to substitute the C3 & C5 with some kemmet gold, these were X7R rate rather than those specified. Had them left over from a mini3 build. ( do have the right type on the way)
 
I ordered a set of 637 opamps to use as L&R (on a brown dog) and a 627 for opaG. however I could not get them to work. when testing I got 1.17ish volt DC offset between IG and OR, the OL test was fine.  SO I swapped the 637's on the brown dog to see if it would follow the opamp, but instead it made both channels read 1.17v on the DC offset

.
 
So I put some 843's in all the chanells and got no DC offset at all.
 
So I  listened to it for awhile, sounds very good, looking forward to analizing it more as the built progresses ( case etc. )
 
I am curious why the ($$$) 637's did not work though, are they a finiky op amp? Would love to test them, not only did i spend a small fortune on them, but i really want to kno how they sound.
 
Also, Tangent, you just sent me a couple of SOIC to DIP adapters with the brown dogs, but they do not apear to be pin for pin.  I soldiered couple 8610's t the 2 you sent and tested the DC offset, over 2 volts! once i took a closer look, it apears they are not pin to pin?  So i will be needing to order a couple more 8610's and the proper adapters.
 
Will post pics and more impressions later.
 
so far sound like an awesome amp so far.
 
 
hope i can get the 637's to work.......
 
 
Joe

 

[H22]

 

[H22]

 

[MisterX]

 
Quote:

 I am curious why the ($$$) 637's did not work though, are they a finiky op amp?

 The default gain is a little low for those op-amps but your DC offset numbers suggest another problem.
Try soldering both sides of your R7 resistors and see if it helps.  

 

[tangent]

Quote:

Tangent, that is a very high qualty board, much better than the ones i get from express PCB.

Thanks!  The PIMTEA v2 boards are indeed made by another board house.
 
 
Quote:

I soldiered couple 8610's t the 2 you sent and tested the DC offset, over 2 volts! once i took a closer look, it apears they are not pin to pin?

 
Check the bottom side of the adapter: if there's a second SO-8 footprint down there, it's the dual op-amp adapter, not the SO-8 to DIP-8 adapter. That's what you want for AD8610s in OPALR.  You want the other SO-8 adapter -- the straight one -- for OPAG.  Better to use an AD8620 in OPALR, though.
 
If you got the wrong parts, email me.
 
Quote:

Try soldering both sides of your R7 resistors and see if it helps.  

A plan so crazy it might just work.

 

[H22]

 
Quote:

The default gain is a little low for those op-amps but your DC offset numbers suggest another problem. Try soldering both sides of your R7 resistors and see if it helps.

Good Eye MisterX ! lol
 
yea, I took that pick before I was done soldering everything . that was all done two days ago, ( and i did get R7 tacked down on both sides, just dawned on me i should take a pick of the assembly )
 
 
Quote:

Check the bottom side of the adapter: if there's a second SO-8 footprint down there, it's the dual op-amp adapter, not the SO-8 to DIP-8 adapter. That's what you want for AD8610s in OPALR.  You want the other SO-8 adapter -- the straight one -- for OPAG.  Better to use an AD8620 in OPALR, though.

Yea, I saw the bottom side (after I installed the opamp's on the top and it tested out bad.......) and indeed there is another SOIC8 pad there, so I asummed that was the case ( that i got a dual adapter...) I was running out of time to mess with it today, but if I understand you correctly, the adapters you sent me allow 2 single SOIC8 to be installed and mimic a DIP8 dual opamp ( ie, use 2 8610's to create an 8620?) . If so i will try to remove one of the 8610.s and install it on the bottom of the adapter. Only reason I ordered 3 8610's instead of an 8620&8610  is I wanted to play with op amps to decide what i liked the best. 
 
 
 
Still not sure why the 637's were giving me trouble, I can asure you it was not the R7 . But I will keep working with it.
 
Thanks for the help guys.
 
Joe

 

[H22]

 
Quote:

A plan so crazy it might just work.

..........I knew i should'nt have posted that pic..., that just happened to be the one that came out the best......
 
 
In any case, The only divergence I have taken from the specs is the use of X7R rated "kemet-goldenmax" caps in C3&5, Could that cause an instabillity issue? My instincts tell me not, but I am no expert.
 
just turned it on again, and now it has distortion and clipping, ??. might be the batteries going dead, but i doubt it. they were just charged (for testing using two 300ma 9v batteries in series) and only been on for an hour or so, tested the current draw back at the shop while running LOUD on my M50's and it waqs averaging 75ma, so i doubt it is low voltage. If I touch the board right between R1/2lL and R1/2R the distortion and clipping goes away. not sure what is going on here, it was just sounding great.
 
I have re-flowed everything at least once, most likelly twice ( usualy standard procedure for me when doind SMT, makes it look much nicer ) so I highly doubt it is a cold joint.
 
OH well, sure it will pan out!
 
HAPPY NEW YEAR !!!!!
 
Thanks Tangent for all you work!
 
I have a hang over to look forwad to!!!!!!!

 

[H22]

 
Quote:

just turned it on again, and now it has distortion and clipping, ??just turned it on again, and now it has distortion and clipping, ??
 

OK, well no volt meter handy, but the tounge test tells me the batteries are running low. guess I will have to test the current draw again.
 
What is the "idle" (on with no headphone load) current for a "schem" PIMETA with an 8620+8610 and three buffes, even with the max ~3ma opamp biasing?
 
without the 2-3ma bias, and 643'sin L&R, and an 8610 for opaG, MY M50's ( granted not a hungry can at all ) up to the pain level i saw ~75ma. So a little suspicious why mt spanking new 300ma batteries are dead after less that a couple hours of moderate listening with the same cans...
 
more testing!

 

[tangent]

Quote:

The only divergence I have taken from the specs is the use of X7R rated "kemet-goldenmax" caps in C3&5, Could that cause an instabillity issue?

No.
 
Quote:

tested the current draw...averaging 75ma

 
 
That's a bit high, but not unreachable. Minimum likely current draw is about 50 mA, but you'd have to change several things about your configuration to achieve it:
 

1. two AD8610s draw about 8 mA less than two OPA637s (OPALR)
2. 3 mA bias is probably too high. I doubt you can hear a difference relative to a much lower level, 1 mA or less.
3. Your ~18 V supply voltage causes the buffer current draw to go up. You can probably get away with a single 9 V battery, which will reduce current draw.

 
Quote:

Originally Posted by H22 /img/forum/go_quote.gif
 
637's did not work...i spent a small fortune on them...no volt meter handy

I think your sense of priorities needs adjustment.

 

[H22]

 
Quote:

I think your sense of priorities needs adjustment.

Just meant i did not have the multimeter with me, I am an electronic tech by trade, so my bag of tools is fairly well stocked
 
 
Quote:

 
That's a bit high, but not unreachable. Minimum likely current draw is about 50 mA, but you'd have to change several things about your configuration to achieve it:

The ~75ma reading i obtained when it was far from idle, had a set of M50's blairing away.

.

 

[H22]

Ok, now for the good news.
 
I removed one of the 8610's from the top side of the DIP adapter it was soldered to and put it on the bottom of the other DIP adapter, works great now, DC offset is neglagible, and idle current draw is ~40ma Sounds very good.
 
As for the 637's, I suspected the issues i was having were due to the DIP socket > brown dog adapter > two more DIP sockets > opamps.......
 
So I removed the DIP sockets from the brown dog and soldered the 637's right to the brown dog. Resulted in an idle current of just over 60ma, and DC offsets of ~3.5mv R and ~5mv L . Sound is aslo very good.
 
For now both combo's are using an 8610 on the ground as I put it on the board.
 
Also wired up the 4 cell Li-PO pack and controll board, its 16.8+v fully charged, and should cut out at about 12v, and using 500mah cells should give 10+ hours on the 8610's, and hopefully 7-8 hours with the 637's. So so far so good.
 
Still have to get it mounted in the case, but trial fit looks like there should be no issues. I did play around with the opamp biasing with both set-ups, and if there is a benifit to the biasing it will take some real in depth listening. sometines it seemed like i could tell a very, very subtle differance with the biasing in, but hard to tell for sure.
 
Thanks Tangent

 

[tangent]

Yes, many contacts make for many parasitic Cs and Ls, which can cause a problem with a fast chip like the OPA637, particularly when you're running it so close to its minimum stable gain.
 
Glad you got it worked out.

 

[H22]

Quote:

Yes, many contacts make for many parasitic Cs and Ls, which can cause a problem with a fast chip like the OPA637, particularly when you're running it so close to its minimum stable gain.
 
Glad you got it worked out.

Well. sorta....... just realized last night that i grabbed the two 843's and hard soldiered them to the brown dog, not the 637's. my eye sight is not what it used to be. So I ordered a couple more brown dogs from you, as well as a PPA board to start playing with . 
 
So, for now i will listen with the 3 8610's in place, and play with op-amps as time permits. Here are c few shots of me getting it cased up :

 
side shot showing the big MUSE caps, 2x470uf, I may change these out at some point to make more room.
 
also shows how tall the 4 cell Li-PO pack is, the 14.8v cell protection PCB is on end in front of the cells, wrapped in white electrical tape to protect from shorts.
 

 
one from the top, charging the batteries from a benchtop power supply. Full charge is ~17volts, I need to build a small regulator for my charger to keep the voltage to ~17.5-18volts, and under 500ma charging current, but with those figures it should charge in about an hour.
 
The battery pack is a tight fit, had to cut the  9v holder out of the case, but it does fit. with the current op-amps and no biasing, should be able to get well over 10 hours of playback.
I am going to try and implement a PPA style bass boost, but it will be a serious effort to make room for it.
 
Joe