Studer 169 EQ in API 500 format

[OneRoomStudio]

Yeah, to echo Ricardus, your tech is wrong. R1 isn't anywhere near either of the DOA's.

Ref this schematic: https://drive.google.com/file/d/0B_...M0Yi00M2IzLTkwYTYtOWE4Zjg2YTk0MDE3/view?hl=en

R1 is on the inverting input of U1. When using a transformer, that should be disconnected (open), and the path to the non-inverting input to U1 should be shorted (usually R2, but a wire-short with a transformer). In any case, R1 has nothing to do with either DOA (which replace U2 and U3), and yes, it really should be disconnected (not shorted).

Based on your earlier comments, I'm assuming you're only using a DOA in the DOA1/U2 position. If the DOA really was fried, the only real possibilities are a bad DOA to begin with or a short or wrong resistor somewhere around DOA1/U2.

 

[Ricardus]

Weird, so tech says I blew the transistors on the DOA because R1 wasn't in and it overheated. But on the transformer pdf it says no R1should be in, plus the other unit works perfectly, or so it seemed? Confusing. Think I'll revert to 100% 5534's on both for now. Does it need R1?

Have you uploaded any hi-res photos of both sides of the board yet?

 

[karloff70]

I've built 6 of them according to the "With Transformer" PDF, and they all work fine without R1. I've tried them all with DOAs and 5534s, so the tech is wrong. There is something else going on.

No R1 means nothing though. No jumper, no nothing. Is that what you did?

Yup, had nothing. And yes, tech is wrong, as it didn't come back working either........lap 2 next......

 

[karloff70]

Lap 2 complete. Turns out I had managed to burn loose a track when soldering one of the caps around the output 5534 in without noticing. Sorted. What lovely EQ's!! Going to put some sort of DOA in for the mids as well, and add shelf freq choice switches, but have to move house first.

 

[OneRoomStudio]

PSA - while building one of these up, I ended up finding a Neutrik NTL-1 with an open secondary. Mouser was nice enough to replace it (since it's a $55 part), but it had me scratching my head for a little bit while debugging the circuit - you wouldn't expect a part like that to be bad. Just a heads-up for anyone with one of these that won't pass signal - check the transformer!

 

[Ricardus]

PSA - while building one of these up, I ended up finding a Neutrik NTL-1 with an open secondary. Mouser was nice enough to replace it (since it's a $55 part), but it had me scratching my head for a little bit while debugging the circuit - you wouldn't expect a part like that to be bad. Just a heads-up for anyone with one of these that won't pass signal - check the transformer!

I got a bad transformer once, too. I forget whether it was the primary or secondary. I still have it here. But yeah, the thing was deader than a doornail so I checked the trafo first.

 

[Blondino]

So I finished a couple of this EQ, they sound really nice.
I’m just experiencing, when engaging the on/off button, I got a little white noise coming out. It’s happening on both eq, more or less with the same intensity. I don’t know if are both switches or what could be. Usually my build are super clear I doubt is something dirty. Anyone else experienced the same? How did you solve it?

 

[Ricardus]

So I finished a couple of this EQ, they sound really nice.
I’m just experiencing, when engaging the on/off button, I got a little white noise coming out. It’s happening on both eq, more or less with the same intensity. I don’t know if are both switches or what could be. Usually my build are super clear I doubt is something dirty. Anyone else experienced the same? How did you solve it?

There's going to be a little scratchy clicking. As long as it's not really loud you're OK.

 

[Blondino]

There's going to be a little scratchy clicking. As long as it's not really loud you're OK.

So is a “default” thing. No way to know where it comes from?

 

[Ricardus]

So is a “default” thing. No way to know where it comes from?

It's probably a little DC offset being created somewhere in the circuit.

 

[Richard James]

I’ve tried to go with the knobs I got for a while because the look is such a trivial thing, but they just bother me.
Those of you using the AML pots…
What knobs did you use and where did you get them?

 

[Ricardus]

I’ve tried to go with the knobs I got for a while because the look is such a trivial thing, but they just bother me.
Those of you using the AML pots…
What knobs did you use and where did you get them?

You can use just about any knobs you want. You might need to get some pot-shaft-adapters, though.

I used knobs that take 1/4 inch shafts, with adapters.

 

[wreutz]

Can someone please upload the files (schematic, boards, etc) as the google doc links don't work or at least I can't get access?
Would love to build it.

 

[dmp]

this is what I have

 

[wreutz]

Thank you! more or less what I already found in this thread and on pcbgrinder but thank you! For other people a good starting point too.

I was hoping that someone has access to the google docs from the original post and can upload these as a zip ...

 

[dmp]

Thank you! more or less what I already found in this thread and on pcbgrinder but thank you! For other people a good starting point too.

I was hoping that someone has access to the google docs from the original post and can upload these as a zip ...

Here are a few more with the curves and all the info for the STD version.

 

[MonoCutter]

But the curves are not for the 500 version.

 

[dmp]

These are the same files as 1st post that Audiox is referencing. I think they are the same curves, but as Audiox noted, C6 and C4/C5 in the 500 version

 

[wreutz]

Hi everyone,

I finally built my first 169 EQ and started some measurements. So far so good, eq curves look good and everything seems to work.
BUT I have a question / problem?

Connecting the EQ to my Apollo 8 interface shows a level of about -18dB but this is incorrect as Console software and Pro Tools don't show that level but Izotope Insight shows about -100dB at 45 Hz. (reported that strange behaviour at the UAD forum ...)
Checked this with my NTI Acoustilizer AL-1 measurement device and it reads -90dBu at 50.2 Hz.

So does anyone else has a noise at 50 Hz?
I built the version with stock LF and HF frequencies (no switches) and the Neutrik transformer. Everything else seems to work and sounds as a EQ should sound I guess
Swapped both the API enclosure (Midas L10 and Bento 6S) and the slots and the interfaces (Apollo 8 Duo and Apollo 16 Quad) - no change whatsoever.
If I bypass the EQ with the switch the level disappears as expected. So it has to do with the circuit I guess.

Any thoughts on this or any help please?

 

[wreutz]

Had time to connect a oscilloscope to the output and my suspicion got confirmed: I have a DC offset of about +5.8V.
My test setup was: Studer Module in Midas L10 API rack connected to symmetrical patchbay -> adapter from TRS jack to XLR -> converter from XLR to BNC (Pin 2 -> BNC signal, Pin 3 -> shield of BNC) -> connected to oscilloscope
I checked this with a oscilloscope probe and got pin 1-2 +5.8V, pin 1-3 -5.8V and pin 2-3 +5.8V.

If I press the on/off button it goes to 0V, turning on back to +5.8V.

Anyone an idea what causes this DC offset? If the EQ gets a signal and I turn the knobs it seems to work but the DC offset is something I don't like and suspect that there is an error.

Any advice?