PPA v2 construction discussion

[tangent]

In case it isn't clear from the above, you should be measuring 1V across R10 if it's 1k to achieve 1mA through the resistor, not 1mV.

 

[fc911c]

Thanks for clearing that up. I was running the amp at around 250mv that's why it didn't sound right. Every thing else checks out in the troubleshooting guide. Also I had the power supply set at 24v not 29v.

Supply 23.88v
S1+ to S1- 23.08v
DC offset input to output gnd .02v
V+ to V- = 21.8v on L R and gnd
V+ to input gnd = 10.8v
V- to input gnd = 10.9v
Amp is drawing 100 - 125ma depending on opamp 8610, 637 627
Dc offset R output to out gnd .2 mv Left .9mv.

 

[tsaavik]

I thought I had resolved my 'ground' issues at my new location (my Aliendac failed chip gets REALLY hot, but no audio output). Ha no ground problem at all!

I got feed up with no PPA at work, so I brought it back in and plugged it into the built in sound on my MB.
I didn't have my STEPS with me so I used a 16V laptop power supply (sucky, but better than nothing, SOO MUCH BETTER).

The next day I brought the 24V Steps in and hooked it up. I got horrible white noise and muffled-weird-phased music.
When I touched the (grounded) case of the STEPS the white noise changed! I made sure the steps and ppa were not touching chassis or anything.

I'm happily back on the laptop power, but any ideas what is wrong? Could my work have a poor ground? The power DOES run through a cubicle tray system.
I checked the STEPS, I get continuity between chassis and AC ground pin, and no continuity between +- DC or either phase of AC.

** Update **
Update, after an hour of bliss I walked away and came back to some hiss (not like before though, the audio was not muffled or out-of-phase sounding). The hiss does not increase/decrease in volume in relation to input volume (pc volume) or analog volume on the amp. For kicks I pulled the gnd opamp and hiss went away. I swapped chips (no change), then I got crazy and shorted pins 3 to 5 of the gnd opamp together (+ in to output), NO HISS! I've since pulled the ground opamp out and shorted from pin 3 to pin 5 (R1G to R10G), the socket holds the wire well.

No parts were too hot to touch and opamps were cold as ice. Maybe I have some instability? Can that sound like constant hiss? Or maybe it is just an artifact of running the PPA without an (presumply) isolated power supply.

AD8610 in all 3 locations. Should I buy/try a different model GND opamp, or add some resistance/capacitance between pins 3/5?

4 years later, here is an update!

After 4 years of running off a 16v switch-mode power supply and bypassing the ground channel, I finally decided to fix my amp, darnit!
I recently got a smart load, so hooked my STEPS (at 24v) up and confirmed everything was good with a 120ma draw. I lowered voltage to 16v to match my SMPS at work and rule out the 24v causing the issue.

I confidently brought it into work, swapped out my SMPS with the STEPS and powered it on. Everything seemed normal until I touched the STEPS and PPA at the same time, massive white-noise! WHAAA?!
I took a page from 1950s style troubleshooting and thumped the STEPS a good one and BAM no more right channel!

Upon closer examination of the case, it appears my heatsink was making contact with the side when the lid was installed AND the back screwed on, but not when the screws were removed!
I've now insulated this area with a long piece of hot glued lego axle (don't judge, it fit perfect in the hammond case's rails).

The PPA suffered 3 dead 2n5486 power rail isolation jfets. 1 in the right channel and 2 in the ground. I'm assuming I blew the ground channel ones 4 years ago
I still had spares, so I swapped them out and will be bringing the amp back into work on monday, wish me luck!!

** UPDATE ** I'm at work, listening to Orbital's 'The Box' and it sounds so beautiful...I can't even **

 

[whitelabrat]

Hey everyone! Sorry for the necro-thread revival, but after a decade+ I've finally got my PPAv2 working! When I started the project I was broke af so I used a lot of parts that I already had, even though they didn't fit perfect. I apparently ran out of 10ohm resistors and janked in a SMT resistor for R33. I suspect this caused a problem with the Right channel, but I can't confirm that. A few years ago I ordered new transistors and 10ohm resistors, but I still didn't have time or patience to troubleshoot.

November was the month of DIY victories for me. I first got my PIMETAv2 working for the first time, and emboldened I got a busted pmillet HA-2 clone working. I learned how to test transistors for functionality and did a bit of tracing on the PPAv2 with a signal gen and oscilloscope with nothing standing out as a problem. So I pulled out all the buffer active components, and disabled the CCS. I got new 10ohm resistors and I replaced the one for the Right channel, and then replaced all the active components. That appeared to work! I re-enabled the CCS, and added optional components like opamp power supply caps and such. All good!!!

So it's still a bit jank, but works great. For example, I have fistfulls (no joke) of ceramic capacitors, so heck, they're in the C2 and C5 positions and seem to do the job. They just won't support super-high frequencies, but I feel it's good enough for audio power supply use. I'm using some Nichicon FP for C4. They're low ESR and typically used for computer applications. LOL. Also got OPA827 in L/R channels with an OPA27 for ground channel. Cheap 10K pot is also in use which is not-awesome. I made a mistake of soldering two OPA637s to a browndog directly, and there's no chance I'll get those unsoldered for use on this amp.

On order I've got a RK27 pot on the way, a bunch of 220uf caps for C1, and chassis bits. Also some browndog soic-8 to pdip adapters, so I can use some OPA1641 that have become my favs. I don't have three so I may steal the OPA1641 that's in my PIMETAv2 and give it a set of opa827's. I've also tested a TREADS ps at 26v which I plan to use for power. I bought a few 24v 40va doorbell ringer transformers a _long_ time ago that are perfect for the job, but it also seems to run great on the LiFePO4 batteries I've got too.

Cheers!