I just built a WHAMMY and was able to compare it to my build of a PIMETAv2 . I had a PPAv2 and smoked it (my fault) and don't intend to repair. I built the WHAMMY as a junk-box build of whatever I had laying around, which turned out to be real nice components. I compared the two amps using...

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...

I feel like the Pimeta and PPA are really excellent designs. Hats off to Tangent for offering PCB source files! Has anyone tried to organize a group order?

Hey Everyone! It took me nearly a decade, but I finally got my PIMETA v2 working. I think the core issue from the past were no-so-great jacks that we're making weird connections. I replaced all the buffers and blew up a few opamps in the process of troubleshooting. Using a TREAD for a nice...

WAT?  looks at datasheet.  :palmface:   Ok.  I do realize I'm one of the knuckleheads often referred to in the instructions.  :)  Popped in an OPA27GP.  Because I have some.   @tangent nice.

Heh. I put the opa37 (not 637) in backwards. Perfect now.

Got it working, and it sounds really good. So happy. The OPA37 opamp for the ground channel is crazy hot though so I'll need to tinker with that. Running about 0.60 mA for the class A bias. I really like having the option to do SMT or through hole. Photos: (my soldering is not super)

I've had a board laying around too and I'm just waiting on four resistor values to show up.  Accidentally ordered 0402 package sized resistors.  Ha!  So small.   But yeah, hoping to brown dog some OPA637 as well.

I finally broke down and bought a Zhalou 2.5c DAC.  No mods other than some opamp rolling.  I put in a pair of browndogged OPA602's on the analog board and OPA2107's on the headphone amp since my other headphone amps (PPA2) are in for repairs.  The Zhalou headphone amp seems to do better now...

I didn't find any shorts, so I figure I'll put a 1k sine in and test the signal path with an oscilloscope.

Quote: Absolutely.  I don't care for bass boost.

I have a 10k resistor for R4.  My guess is gain would be 10k/1k = 10?  Or is my math wrong?  Left channel is a happy camper.  I could drop in OPA27's for testing.   A few parts are barely warm.  Nothing hot.  The capacitors all check out so nothing weird there.  The silicon parts are...

So I've had some issues with one of my channels with an OPA637 getting cranky. If you look at post #748 you'll see that I used cheap electrolytics and ceramic caps for power smoothing near the opamps.  So I reclaimed four Elna Certifines and some 4uf film capacitors and replaced the cheap stuff...

You're right. I didn't measure the input. Resistance is below 1ohm from the input ground to output. That would be a problem as you suggest.

Just measured the SMPS. All the outputs read in the kiliohms. Seems isolated to me. I'm tempted to swipe some nice Elna Certifines and film caps from other projects to see if that will stablize the OPA637's at higher voltages. Stay tuned...

I've not tried to open the case on the SMPS to determine if it is isolated. In any case it appears to cause the amp to go crazy so it goes back to where it came from. My bad. Wasn't thinking. Ohms law.

I found a SMPS I had laying about that puts out what appears to be 28v regulated. I wired it up to and set off to adjust the buffer bias. I'm doubting my measurement now. Do I measure vdc or vac? Measure at the output or before the output?

For what it's worth, despite the scary look of it, I did use high quality parts overall. The weakest links are the capacitors used near the opamp. The C1 layer of capacitance is from Nichicon KZ's and Panasonic FM's with a lone Elna that I had nothing else to do with. The C2 set are ceramics...

Biased the OPA637's a bit over 1ma. I'm in the happy place.

Up and running. My first solid state amp... that works. First try too! *pat self on back* I haven't set the opamp bias for class A yet. Running at 17.5v with OPA602's. Driving Beyerdynamic DT880's. All is safe so I'm going to break out the OPA637's.

Almost done with my PPA2. I've used whatever I already had where possible, and a lot of surplus parts. There are even a few SMT chip resistors in there.

Quote: Originally Posted by Spacehead What is very important, is to check that any wires aren't bare and everything is well insulated. And no short circuits on the amplifier or the fuse will burn. You don't really learn electrical safety by trial and error. When you have 470uF...

I think by experience, it would mean you know what not to do. In a nutshell, being shocked by a high voltage amplifier is easy and very painful if not deadly. This is a good read to get you started: Electrical Safety

Quote: Originally Posted by tangent A quick look suggests you can probably save enough on parts to cover shipping from Mouser. Allied's prices and selection for semiconductors is poor. If there were just one distributor that had it all, we'd all be using them. You see people...

I'm stuck. I didn't order any 2N5484's. I'd like to get all my parts from Allied Electronics, so I'm thinking that an NTE457 may serve as an alternate. Idss=1-5ma, Crss about 1.5pf, Ciss about 4.5-7.0pf. Looks good enough. Looks like I'll be getting the trim pots after all.