Sooo.... whats the difference between a t.i. opa134pa and t.i. opa134pag4 chip?
Can they be used interchangeably?

TI's datasheet mentions no differences between these variants, so I can only assume they would be entirely interchangeable. Possibly they were made in different chip fabs or one has updated masks or uses somewhat different semiconductor technology node.

Both are old in the tooth opamps from the later 1980's/early 1990's. The OPA164x series is the better replacement. BB still charges a fortune for the 2134 DIP at 4 bucks. The OPA1642 is under $2 each.

Thanks for the replies. Im contemplating changing opamps in some old dbx 163x's i have lying around, mostly to reduce the noisefloor.
I might try out both the OPA134pag4 and some OPA1642's.

Just wanted to make sure I dont fry the board by putting in the wrong type of chips. :-)

The G4 and E4 suffixes were added for ROHS conversion. The
G4 and E4 parts are exactly the same as the original parts
without the G4 or E4 suffix.

OPA164x aren’t available in DIP format, so if you’re planning to retrofit you’ll have to get adapter boards

That's the same story with all new opamps, DIP's are being phased out.

I ordered some NE5532AP's and OPA134pag4's, both 8DIP. Hopefully they'll do the job.

Anyone recapped the power supply section of a 163x? I have looked inside a couple 163x's now, and the capacitors installed seem sort of random for the power supply. The big ones are always 470uF/35V's, but the four smaller ones can be 10uF/35V's or 10uF/50V's, and sometimes two of them are just 1uF/50V's.

Maybe it doesn't matter that much as long as they are good quality?

Do you need single or dual? OPA134 is single, NE5532 is dual, they are not interchangeable.

One is single, the other dual. I follow the recommandations from this thread:

2016 DBX 163X Modifications

Other than that I have no experience with op-amps, complete rookie. So your responses here are much appreciated.

Just modded mine last night and they sound great.
Full run down in here:
2016 DBX 163X Modifications

@rithma: Great stuff! Will be checking this out.

I took notes from this thread and a couple others when I did both of mine. They turned out very nice. I have to watch the VU’s to know they are compressing. I used opa2134’s for the duals and can’t remember if I used 134’s or LME49710’s for singles. Honestly, I can’t even remember if there are singles in the circuit. I replace all 553x’s everytime I see them and I’m always happy with the results. Solder in sockets and draw your own conclusions. I did use the THAT2180a as I do every time I can. My 2180a Symetrix 501’s fully modded the same as my Valley People VCA 501 sound better to my ears.

Now, as someone who has walked your path, get a scope. Learn how to use it. The sooner the better. Don’t wait as long as I did. There’s so much more to modding than swapping parts. I will hopefully be “optimizing” circuits soon and not just swapping. Totally different beast.

Brian

The 163 uses a 5534 output opamp. It runs a little noisy due to a 20k resistor off the non-inverting input to ground. That's to minimize DC offset. The 20k resistor adds thermal noise to the low noise 5534 opamp. I bypass it with a cap to remove the noise while retaining the DC levels.

Same .01uF/250 WIMA like when bypassing an electro? And, should this be done every time I see a resistor hanging off pin 3 to ground?

Brian

Bigger The R/C timing should allow for signals below 20 hz. 47 uf is safe.

Yes sir. Once again giving me a new direction to focus on.

Brian

Little trembling newbie question about modding the 163X:

If I were to install a THAT2180 VCA and remove the two trim resistors,
should I remove the resistors and leave the trace cut, or solder/connect the trace back together afterwards?

Remove and leave out. The THAT 2180a is pretrimed and does not require that part of the circuit. Google “THAT 2180a pinout” and you’ll notice pin 4 is labeled “NC” for no connection. Jim has told me in other posts to just cut pin 4 off. I removed R9 and R10 on both my 163x’s. I cut pin 4 on both my Symetrix 501’s and left the resistors in with no issues.

Brian

Thanks! The answer I was looking for.