Raven Labs PHA-1 schematic?

[metron]

So I plugged the power supply into the wrong jack on the back on my Raven Labs PHA-1 headphone amp. Now there is no right output. I think one or more of the op amps is toast but the surface has been scratched off all 4 in the unit so I can't identify the devices. I think there are 2 dual and 2 singles but I don't really want to guess.

I searched high and low on the web for a schematic but came up with nothing. Anyone have a copy?

[metron]

Anyone? I called/emailed the place that supposedly handled the service for raven labs when they stopped production but i dont think they are around anymore either.

[fdeck]

I might be able to help if you take careful close-up pics of the top and bottom of the board. The reason is that singles and duals have different power supply pinouts. Singles are 7+ and 4-, while duals are 8+ and 4-. You might even be able to beep this out with an ohmmeter. Next, you can probably replace the op amps with any decent modern JFET type. If you install sockets, then you get more than one try. Sockets also let you power up the board without the chips to verify that the supply voltages are up and running, before you commit the chips.

[metron]

Originally Posted by fdeck

I might be able to help if you take careful close-up pics of the top and bottom of the board. The reason is that singles and duals have different power supply pinouts. Singles are 7+ and 4-, while duals are 8+ and 4-. You might even be able to beep this out with an ohmmeter. Next, you can probably replace the op amps with any decent modern JFET type. If you install sockets, then you get more than one try. Sockets also let you power up the board without the chips to verify that the supply voltages are up and running, before you commit the chips.

Hey thanks for taking the time to post! Good news is all the op amps are socketed. I did test the supply pins which is how I figured there are dual and singles in there. The power supply appears to be in working order. I found some old parts I've had sitting around forever and I actually found a few burr brown op amps, one dual one single. Not sure if they are good or not though. I might have a chance to take it completely apart and snap pics tonight.

[gregbackstrom]

Originally Posted by metron

Hey thanks for taking the time to post! Good news is all the op amps are socketed. I did test the supply pins which is how I figured there are dual and singles in there. The power supply appears to be in working order. I found some old parts I've had sitting around forever and I actually found a few burr brown op amps, one dual one single. Not sure if they are good or not though. I might have a chance to take it completely apart and snap pics tonight.

I'm glad to hear that some other folks have these, and that repairing them may be an option. I'll have to unbox my non-working PHA-1 and remind myself why I stopped using it. I believe that the Aux input--or output-- stopped working. IIRC, the other functions worked fine.

[daveman50]

I love my PHA-1. Too bad Steve retired.

[fdeck]

Originally Posted by metron

Hey thanks for taking the time to post! Good news is all the op amps are socketed. I did test the supply pins which is how I figured there are dual and singles in there. The power supply appears to be in working order. I found some old parts I've had sitting around forever and I actually found a few burr brown op amps, one dual one single. Not sure if they are good or not though. I might have a chance to take it completely apart and snap pics tonight.

Burr-Brown (now TI) OPA134 (single) and OPA2134 (dual) would be a good choice. Mouser has them in plastic DIP, with quite a few in stock, suggesting that they are a widely used part. You should poke around the socket for the single, because they might be using pins 1, 5, and 8 for compensation. If you're unsure, you could lift those pins on the replacement chip when you insert it.

@greg, the OP's problems notwithstanding, most gear problems are mechanical at the root cause level. Maybe the solder joints broke between the jacks and the circuit board. This could just require re-melting the solder. It's worth inspecting the entire board with a magnifying glass and bright flashlight for cracks or other damage.

I am guessing that the circuit is a straightforward design, not exotic, but just good solid engineering and a high quality build.

[chucko58]

Francis's post gave me an idea: If all the chips are socketed, maybe the socket contacts have gotten dirty. At the very least, see what happens when you remove and re-insert each chip. That may be all it needs.

[fdeck]

Originally Posted by chucko58

Francis's post gave me an idea: If all the chips are socketed, maybe the socket contacts have gotten dirty. At the very least, see what happens when you remove and re-insert each chip. That may be all it needs.

Worth a try. That's how most repairs went when I worked at a place that serviced Apple computers in the 80s.

[gregbackstrom]

Originally Posted by fdeck

Burr-Brown (now TI) OPA134 (single) and OPA2134 (dual) would be a good choice. Mouser has them in plastic DIP, with quite a few in stock, suggesting that they are a widely used part. You should poke around the socket for the single, because they might be using pins 1, 5, and 8 for compensation. If you're unsure, you could lift those pins on the replacement chip when you insert it.

@greg, the OP's problems notwithstanding, most gear problems are mechanical at the root cause level. Maybe the solder joints broke between the jacks and the circuit board. This could just require re-melting the solder. It's worth inspecting the entire board with a magnifying glass and bright flashlight for cracks or other damage.

I am guessing that the circuit is a straightforward design, not exotic, but just good solid engineering and a high quality build.

Thanks Francis! I'm still digging my HPF-3, BTW. It has become my favorite "instant lousy room rumble-remover"!