Studer 169 EQ in API 500 format

[rmaier]

Finally done! Thanks for everyone's help. I used rotary switches throughout, with 3 frequencies each for high and low, and 7 for the mid. Cut/boost values for the lows and highs were taken from AudioX's mastering version, and I based the mid cut/boost on those numbers as well. The unit works very well, so I think I managed to get pretty close on the math. Thanks for your input, DMP. Unfortunately it came after I had made up all my switches, but I'm sure I'll be able to use it in another project.

As far as the sound goes, I have to agree with the general consensus: this is a lovely sounding EQ. It seems capable of gentle, transparent sculpting and is forgiving enough that its pretty hard to make it sound bad without really working at it. AudioX's incorporation of a midrange was a great addition to the original version - it seems extremely versatile and will see a lot of use in the future, I'm sure. The highs sound particularly sweet to my ears, even on tricky sources like violin. The lows are nice for gentle boosting as well - made a grand piano sound a couple of feet longer, without getting pushy.

 

[rmaier]

A few pics (sorry they're a bit large):

 

[rmaier]

Channel:

 

[rmaier]

Inside:

 

[rmaier]

Open front:

 

[rmaier]

Open view from the back:

 

[rmaier]

A good view of the rotary switches:

 

[rmaier]

Mnats little PSU:

 

[Indecline]

Thanks for putting me on the right track! I dug back into it and worked from U4 through the circuit. Come to find out, there's a huge difference between 680 and 680k!!  

I should be able to get a couple 680k resistors tomorrow, i will let you know!

okay, I'm an idiot, the 680k resistors were correct... i read the meter wrong!!

I swapped the feedback resistor on the output balancing amp to 5k to try and boost the output. It did nothing, so dmp you are correct, the output balancing amp isn't functioning correctly. I followed the power rails with a continuity test and all doa's and ic's are getting power from both + and - voltages. Output from the 5534 also passes through to pin 4 on the card. input can be traced back through the 10k input resistor to the doa's output passing a continuity test. I'm stumped! 

i guess the next thing would be to get a power supply to test voltages for opamps?

the saga continues..... 

 

[dmp]

Wow - looks great! Good job rmaier.

If you sweep the response I'd be curious how well the channels match. (I did this with RMAA and found my channels didn't match very well - probably due to the pots)

 

[rmaier]

Thanks, DMP. I'm humbled by the kind of great work I see around here, so thanks indeed.  Thanks also for pointing out the rmaa software. I'll try to give it a go and see how the eq stacks up.

I can say I was pretty obsessive about matching resistors when I did up the switches, so I have a feeling things are pretty tight. We'll see...

 

[dirtyhanfri]

I just built a pair of this eq's  in a 2u enclosure, something like what rmaier showed some posts ago (Thanks for the info on the rotary switches and everything else)

I have to recheck mi wiring in one channel, it's loosing some db's, even in bypass mode, but the eq looks to work nice.

Well, everybody wants porn

Now I'll design the front pannel, I will silk screen it and wait for some 20mm. knobs wich are slowly coming from China.

Thanks audiox for publishing all this stuff (I built your 2 studer eqs this month), and rmaier for sharing the info and kindly answering all my questions.

EDIT: I've been playing with the eq with a few voices and it's just amazing, a very worth build

 

[iprovlek]

Is there a gerber files for this Studer 169(500 series)?

Thanks!

 

[dirtyhanfri]

I don't think so since Gustav sells the boards on his page (great quality for sure, I 've done a pair of projects with his pcbs, and the boards are just great). But the copper layer is published on the first post, maybe you can get done with that.

 

[iprovlek]

Thanks you a lot....

 

[Dr nEon]

Hey Guys,

I have a question regarding making the mid frequency sweep switchable:-

I intend to replace the dual 100k pot with a dual wafer switch (12 way).  I have measured the pot, and found that at each of the centre frequencies that I want, the needed resistance is always one of the standard values, luckily. This means that I could use my switch to simply select a pair of fixed resistors for a given frequency. ( It would be the same arrangement as the way the capacitors are selected in the HF section of the mastering version, but with a 'branch' of resistors hanging instead).

When we make the gain controls switchable, we have to build a cumulative string of resistors to mimic a pot, because this is when the pot is a potential divider.  This frequency pot is a two ganged variable resistor, and so I believe it probably isn't necessary to build a resistor chain. In my case, it will be more accurate/easier to switch between standard values, than trying to get the increments of a chain where I want them.

In practice, one side of each resistor will go to it's switch terminal, and the other side of all the resistors will be tied together.

So my only doubt/question is: Could this branch of open resistors potentially induce more noise into the circuit, than a closed resistor chain? Or is the difference probably negligible..?

I'm making the thing switchable, to use on my mix buss, of course, so I want to keep it as clean as possible.

I'd appreciate any thoughts on this one.

Cheers

nEon.

 

[druu]

This should explain it well:

http://www.goldpt.com/attenuator_types.html

A lot of the guys usually go for series type with 1% resistors and work fine.

 

[Dr nEon]

Hey druu, thanks...that link is about attenuators though, and I'm not sure if it applies here...

I am asking about the frequency controlling dual ganged "variable resistor" in the Wien bridge portion of the mid band, and whether my suggested(see above) switching arrrangement is likely to be susceptible to, say, RF pickup, or other internal stray noise.

I'm also thinking that switching single resistors rather than chaining them, shouldn't affect impedance, in this part of the circuit, but I could be wrong, and would like to be corrected , if so..

Cheers again!

nEon.

 

[Harpo]

This should explain it well:

http://www.goldpt.com/attenuator_types.html

A lot of the guys usually go for series type with 1% resistors and work fine.

...for attenuators.
None of the pots in this 169EQ circuit is an attenuator.

 

[druu]

Ahh my mistake, carry on!