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PPAS Build Thread.

post #1 of 254
Thread Starter 
I'll start this thread since Daniel's shipped off all the boards.. and some of you have already gotten them ( Filbuuurrrttt)

This thread is for any and all troubleshooting of PPAS, and to document compatibility with different parts and opamps.

All standard SMD build procedures apply.. opamps and buffers first, then resistors, then build higher.

Also, the PPAS is VERY unfriendly to sloppy soldering.. DieInAFire's prototype failed twice because of sloppy soldering.. be careful and you should be fine..

Parts Availability
BUF634U - this part is ALWAYS out of stock, but I have 23 or so left, ask me.

LMH6321 - This part is stocked at digikey.

TLE Railsplitter - There are no alternate parts for this.

SST310 - Ive just been told the SST310 is out of stock.. Currently reccomended subtitute is the BSR-57 from mouser electronics. If you know of any better substitutes, please PM me.

Build Warnings.
PLEASE make sure you buy the SST 310.. the SST309 was marked in the old revisions of the BoM. The SST309 may be unable to supply enough current..

Silkscreen may be missing at parts.. due to gerber issues our manufactuerer may have left out sections of the silkscreen.. NB that you should use http://apuresound.com/ATAT/PPAS/PPAS...%20Artwork.htm as reference during the build.

NB The tantalum capacitor direction.. the Tantalum cap is polarized.. it is marked on the board artwork link, but NOT on the board (see warning above).

NB Opamp and buffer direction.. Opamp and buffer pin 1 is indicated by the strip on the artwork above.. just for reference here's the directions.. Looking from the top down onto the board, OPA L/R pin 1 is left top, BUFL is right bottom, BUFR is left top.. on the bottom, looking down onto teh bottom of the board, both OPAG and BUFG have their pin 1s on the left top.. (the picture is mirrored)

Configurations/changes that *should* work
Using a larger ELNA sized cap on the rails (capacitor bending) should still fit in MINT tin.

LM6172 / LM6171 / LMH6321.

Warning for those using LMH6321 - The LMH6321 is a great buffer, can output nearly .7A of current and its ridiculously fast.. one problem. Pin 2 is used as current control. Before you solder the LMH6321, cut off Pin #2 (or bend it upwards). Pin 2 is connected to output on the schematic (so that opamps can be used as buffers) but this will prevent sane operation of the LMH6321.

Warning for those using OPA551 or other Opamps. - The PPAS can accomedate using running opamps in closed loop mode as buffer.. There's two things to watch out for. First, bandwith, make sure your opamp is fast, as well as being high power.. if a fast opamp feeds a slow buffer, you'll have some serious issues with the feedback loops (also stability) if using the OPA551, use a slow opamp like the OPA2227. Also, even though the L/R buffers wont have an issue running closed loop, the ground buffer is *finicky* and I'd suggest using the BUF634 or LMH6321 unless you're really feeling lucky.

Currently Tested Configurations -
(by ATAT)
AD8620 / AD8610 / BUF634 (both bandwiths) (lots of detail on this one)
AD8620 / THS4631 / BUF634 (both bandwiths) (similar to the above, but seems fater, and eats more battery)
AD8066 / LM6171 / BUF634 <-- See above
AD8066 / OPA132 / BUF634 (bass beast.. nearly overpowering..)
OPA2701 / LM6171 / LMH6321 (Amazing detail and midrange.. my rec, but KILLS battery)

(by quicksilver )

AD8610 / AD8620 / LMH6321 <-- LMH confirmed working.

(by ozshadow)

OPA2701 / OP627 / BUF634 <-- OPA627 confirmed

A List of Problems encountered

9v Offset on Channel

(fixed)Prototype 1 - Routing problems

(solved)Final Board (Proto 2) - Soldering issues(happened twice)

One Channel dead

(solved)Proto 1 - Ground Mistakenly swapped with Left channel (whoops)

Current draw absurd

(solved)Proto 1 - Case shorted SST310.

Amp clips at all audible volumes

(fixed)Proto 1 - SST309 Used instead of SST310.

post #2 of 254
I'll start off the build discussion with this: Mouser's SST310 is out of stock, both RoHS and the good old stuff (actually 2 in stock of the leaded version- not enough for one amp).

Any suggestions for alternatives? Maybe SST-109? That is 40ma, which kind a bit high, but I always thought the PPA ccs was mainly for noisy wall PSU's. Since this is battery powered (and should be very low noise power), does it really help?

Edit: Digikey alternate would be fine....
post #3 of 254
The schematic on the web site is a bit small- would it be possible to get a higher res version? My tired old eyes would appreciate it!
post #4 of 254
Thread Starter 
NeilR - Ill try to get a higher res version, but the size is limited by photobucket I believe..

Hmm the lack of SSTs are a problem.. I'll have to find alternatives..

Possible altenratives -

to be honest, the SST212 will likely work for most current conservative opamp setups.. since its designed as a N channel amp, its got a lower distortion figure than the others (*might* matter) while the others are N channel swtiches.. to be honest, it probably wont matter, so just pick the SST4392 if you dont know any better. (26 in stock) when that runs out, use the SST212 it should work for 90% of the people.. ´╝łEDIT- comment about SST109 removed. Was incorrect.. what was I thinking anyway? )

*edit* found the BSR57, in stock for about 2000 units at mouser, and it looks like its about as good as the SST310 (maybe better)

From Vishay Siliconix - (from most desireable to least)

SST4392 - 25mA Idss, N Channel switch.
SST212 - 15 mA Idss, N Channel amp
SST109 - 40mA Idss, N Channel switch

Fairchild Semiconductors -

BSR57 (might be better than SST310) - 20mA Idss, N channel low noise amp
MMBFJ310 - 24mA Idss N channel amp (same as SST310)
MMBF4392 - 25mA Idss, N Channel switch.
MMBFJ111 - 20mA Idss N channel switch.
post #5 of 254
Atat- I was looking at the schematic on the top of the build notes page. The schematic on it's own link is fine. Thanks anyway- don't worry about it.

Regarding the SST310... It appears you are running them in parallel, not as per the PPA schematic. Is that correct? What is the idea behind that?

My understanding is that if I use an excessively high Idss jfets, it will not draw any additional current, it will just act like a constant current source that is configured for more current than will be drawn. It can't "push on the string" so to speak (won't draw more than the load demands). Is that not correct?

Edit: Nevermind... I was thinking this was some sort of cascode setup, but after reading PPA V1, I'm not sure why you and Tangent used two in parallel (as opposed to PPA V2) but I see clearly they are in parallel and can deal with it.

post #6 of 254
Wow, really glad I put in an order in the beginning of the week - maybe I got the last ones

All I've got left to order is the buffers, and C3/C4. I found the dimensions for C1/C2 in the other thread, but I'm not sure the size for C3/C4 was. 5mm? 6mm?

Edit: I can donate space for a high res version of the schematic if you need it.
post #7 of 254
Thread Starter 
I didnt write down the dimentions for C1/2 C3/4? sorry! the originally spec'd part is 5x11mm. Voltage rating needs to be at least 9 volts.

The idea behind running the SSTs in parallel was to increase the max IDss, this way you could use some of the lower IDss chips.. the

NeilR- you're absolutely right must be all that biology work clouding me.. a higher IDss will not affect battery draw.. but it will decrease the isolation between the two rails.. Tangent describes this in detail, but the closer you run your JFEts to max IDss, the better the isolation.. so you *could* use the SST309 in a conservative setup to ensure maximum isolation..

Its entirely possible to get the SST309 working just make sure to use less than 8 mA / channel for each opamp.
post #8 of 254
double post - mod please delete
post #9 of 254
Originally Posted by ATAT
I didnt write down the dimentions for C1/2 C3/4? sorry! the originally spec'd part is 5x11mm. Voltage rating needs to be at least 9 volts.
Well, you mentioned C1/C2 were 8x10 25v but I couldn't find anything specific about C3/C4 (granted, it was a big thread).

Looks like I can use a 10v 100uF Panasonic FM (digikey part number P12919-ND) and it will drop right in. I also accidentaly ordered a 470uF 25v FM that was 8x20 instead of 10x16, one number off from the part number for something meant for another project (P12389-ND), that turns out to fit for C1/C2 (the height isn't an issue as I plan to have mine on its side in a hammond J1201 case).

Digikey shows the following (it says 3 because that was how many I added to my cart):

Product Lead Time Estimates

Part Number: BUF634U-ND
Description: IC 250MA BUFFER 8-SOIC

Ship dates are approximate and subject to change.

Quantity ExpectedShip Date Estimate
So it looks like everyone jonesing for the buffer might get a shot in a day or so. I'm going to try ordering it, I've also got some lm6321 on order from National Semi.
post #10 of 254
dont you mean LMH6321?
post #11 of 254
Thread Starter 
absolutely right.. corrected in main post.

Edit - You could also just not use JFETS altogether, shorting the pins will make for a unified rail. Your pick.
post #12 of 254
One more question about the JFETs. You indicate that the SST309 was insufficient and resulted in clipping. That part has an Idss of 12ma. Assuming you used them in parallel, that would provide 24ma to the 3 opamps, or 8ma each channel. If you tested this with AD86x0, that is 2.5ma per channel, plus 0.5ma for the SST502 class A bias. It seems to me that that should have provided far more current than required for that particular Opamp.

(I built a PPA V2 using 13ma JFETS per channel and successfully ran it with OPA627/OPA637 with 1ma Class A bias, for about 8.5ma per channel. It works very well. I used 2n5486 hand picked for 13ma Idss).

I just want to make sure I'm not missing something here as I pick my JFETs. At this point I will also probably use AD86x0.
post #13 of 254
Thread Starter 
NeilR - you're correct, and that is the reason I originally reccomended the SST309 for the stock build of the PPAS, however I had issues with the prototype #1 which were resolved as soon as the SST309 was replaced with 310s. Although I havent the time to check again with the 309s, I felt the need to reccomend a configuration which is known to be working...

In other words, it should work on paper, it didnt work once, so I'm suggesting a config that works. I'm hoping it was a defective SST309 and so each channel had 4mA =/... it'd be interesting if someone got it working with a 309 configuration.
post #14 of 254
Atat- did you use the SST309 with a THS4631 in the ground channel? Your post#1 indicates you used that part and an AD8610 in the ground. That amp sucks up to 14ma, which would put the total draw on the opamp rails at 20.5ma, which is a little tight. Maybe that was the problem?

(The JFET isolation is an interesting and tricky idea since, as you discovered, it is easy to totally hose the performance while chasing the last 1% performance )
post #15 of 254
Thread Starter 
SST309 was with the first prototype which used a AD8620 and 10 on ground.
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