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PPAS Build Thread. - Page 17

post #241 of 254
using the stock parts from the PPAS bom, what is the default gain of a PPAS?
post #242 of 254
hmm good question as I'll be building one sometime too. I looked on the PPAS site & tangent's PPA site and couldn't find it either. This may help? Btw, anyone know if those discrete buffer boards ever got made?
post #243 of 254
Quote:
Originally Posted by el_matt0 View Post
using the stock parts from the PPAS bom, what is the default gain of a PPAS?

Don't quote me on this but I believe it's around 10. Too much for my Grados but you should check it out with Tangent's calculator.
post #244 of 254
Hey guys,

I just wanted to revive this thread. I'm about to build one (got my hands on a board) with AD8066 and AD825 opamps with LMH6321 buffers. I'm not one to optimize the resistors for bipolar opamps. I ordered from DigiKey so no Class-A (no SST502) but they did have MMBFJ310 (SST310 substitute).

I will be running this off 8x AAA in a Hammond 1455C1202 case along with a trickle charger (too bad I couldn't fit it into the C802. If only the board was just a little shorter with the POT facing to the side, it would be possible to put it into the C802 with 8x AAA easily (hint hint for next revision of the board ).

Any suggestions, experience to share about this amp would be appreciated.

Thanks
post #245 of 254
Quote:
Originally Posted by FallenAngel View Post
Hey guys,

I just wanted to revive this thread. I'm about to build one (got my hands on a board) with AD8066 and AD825 opamps with LMH6321 buffers. I'm not one to optimize the resistors for bipolar opamps. I ordered from DigiKey so no Class-A (no SST502) but they did have MMBFJ310 (SST310 substitute).

I will be running this off 8x AAA in a Hammond 1455C1202 case along with a trickle charger (too bad I couldn't fit it into the C802. If only the board was just a little shorter with the POT facing to the side, it would be possible to put it into the C802 with 8x AAA easily (hint hint for next revision of the board ).

Any suggestions, experience to share about this amp would be appreciated.

Thanks
The PPAS is a great performer - you will be well pleased with your build.

My on hand SOIC AD8620/8610 and BUF634 chips dropped into my build along with a SST502 for Class A Op. It uses the basic BOM resistor values since it is uses the baseline 8620/8610. Two 9V rechargeables Batteries really wake this portable Amp up.

For the build - follow the instructions for the order of the parts to be installed. Standard build fare lowest to highest, etc. Be patient with the SMD component installs making sure that you have each properly oriented before soldering. You really don't want to rework these if at all possible. Check your solder job on each SMD component with a Magnifier as you proceed - it will help to eliminate a lot of debug work later by maintaining quality as you build.

Recommend you go to TANGENT's site for his SMD soldering techniques instructional videos unless you have done a lot of SMD work. Even if you have done some experience - he has very good tips (real hands on experience base) that are very useful and worth some review time.

Enjoy....!
post #246 of 254
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post #247 of 254
Quote:
Originally Posted by pinkfloyd4ever View Post
(from the first post of original PPAS build thread)

does this still apply?
Why would it not? You might be asking about the new boards by error401 in which case, I'm not sure
post #248 of 254
Kind of a mini bump..

After 2 years (!?!) I'm FINALLY getting ready to build this thing. I'm putting my BOM from pddjsteve's list (page 12, post 169). There are a couple of parts that seem to be no longer available at Mouser:
JFET, Mouser part #781-SST310-E3
CRD, Mouser part #781-SST502-E3

I'm sure I could plow through the catalog and find something that might work, but I'm not technical enough to know what would work for sure. Can someone point me in the right direction?

Also, Digi-Key is out of the buf634, but mouser did have it in stock -- mouser part #595-BUF634U.

And one final question -- is there someplace I didn't see where the merits of the different gain values of R4L and R4R are explained?

Thanks for any help/guidance.

JCD
post #249 of 254

I'm going to have to dig this one up again... scored a PPA-S board and I'd like to find a replacement for SST502. Are there any viable replacements? or am I SOL at this point?

post #250 of 254

www.trendsetter.com has them.  Budget price of $4.73 each and if I remember correctly they kill you on shipping charges.

post #251 of 254

Oooff... hehe. To run the PPA-S in Class A... that is the question. It looks like I only need two anyways and not a third for the GND channel.

post #252 of 254

Just about to hit the buy button in Mouser. I was able to find 99% of the parts there with the exception of the SST502. I decided to go with the OPA2107/LM6171/LMH6321 config. Is there any reason I should choose the OPA627 instead of the LM6171? I tempted to go with the OPA627. Other than that, I've chosen to lower the R4 value to 2K in order to get a gain of 3. Also as an alt. went with 5.11K for a gain of close to 6. Is there any reason I should be changing my other values? I read up on balancing the values, but in the end Tangent mentions in his parts selection guide for the PPA to change the value for R4 to adjust gain.

 

Finally, I'm considering adding in a PINT type trickle charger -- if I plan on using two 9v NiMH batteries what would be the most ideal AC/DC adapter to get voltage-wise that would let me keep default values for C1 and C2 -- 330uF? Or would I have no choice and have to up the values here in order to add in the charger?

post #253 of 254

I'd go with the AD8620 and AD8610 combo.  I was hesitant to try it with my Pimeta but I really liked it.  It will be hard to get the opa627 to work.  There's no opa2627 that I know of.

post #254 of 254

The reason I'm swaying towards the OPA2107/LM6171 instead of the AD8620/AD8610 is because people have complained that the 8620 combo to be a bit more harsh in the highs. Other than that if the OPA2107/LM6171 combo is for the most part a drop in replacement I'd go with that. The only reason I brought up the OP627 is because a few people mentioned they used it with success and they thought it sounded better than the LM6171 for the GND channel position.

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