[audiox]

Why? I had some spare time yesterday. And my friend is planning to build an API format console and he likes this eq. I know that he probably never actualises his plans but it was quite fun to do this...

Low shelving filter +/- 15dB. Default frequency is 20 Hz as in the original circuit,
but you can select a new value for C6 from this graph to change it:
http://audioxxx.googlepages.com/EQ_169_STD_frq_selection_lo_filter.pdf

High shelving filter +/- 15dB. Default frequency is 20 kHz as in the original circuit,
but you can select a new value for C4 and C5 from this graph to change it:
http://audioxxx.googlepages.com/EQ_169_STD_frq_selection_hi_filter.pdf

Presence/absence filter +/- 12dB. Frequency adjustable from 150 Hz to 7 kHz.

Schematic (see the layout drawings for the input section component values)
http://docs.google.com/fileview?id=0B_XBYPfmG8pVZGViZTg4YmQtMDM0Yi00M2IzLTkwYTYtOWE4Zjg2YTk0MDE3&hl=en

Layout with components designations
http://docs.google.com/fileview?id=0B_XBYPfmG8pVYTI0MWQ0NTEtYzVmOC00ODU4LTkzODQtZDBhYTFkYTc3N2U0&hl=en

Layout with components values (active balanced input)
http://docs.google.com/fileview?id=0B_XBYPfmG8pVNzM2OGQxMDEtZGM4MS00ZjYwLThlYjEtNWYzNzE1NGQyNTlk&hl=en

Layout with components values (transformer balanced input)
http://docs.google.com/fileview?id=0B_XBYPfmG8pVMmRhZmNkZWEtMjU2ZS00YmI1LWFjNTYtY2ExY2Y4NDFjY2Vh&hl=en

Copper layer for home etchers (the board is single sided)
http://docs.google.com/fileview?id=0B_XBYPfmG8pVM2U5MzM3ODEtN2E1Yy00NTBhLWE5ZTEtZGNlZWU3ZTUzYzJl&hl=en

PCB drill sizes:
Switch and potentiometers 1.3mm
Discrete op-amps 2.3mm
Transformer 1.0mm
Mounting holes 3.2mm
All others 0.8mm

Front panel
http://docs.google.com/fileview?id=0B_XBYPfmG8pVNWZlNzA1ZjktOTA3ZS00Nzg5LWI2NWMtMzEzMjAyNmEyMjkw&hl=en

Front panel supporting hardware
http://docs.google.com/fileview?id=0B_XBYPfmG8pVMjVkMDYzNTEtYzdhMS00ZDlkLWJjNWMtZGZjMGFiODAzYTNl&hl=en

---

Boards are available from Gustav:
http://www.groupdiy.com/index.php?topic=37783.0
http://www.groupdiy.com/index.php?topic=10776.0

Potentiometers are 16mm Omegs (to keep the costs down):
P1 = 2x 22K LIN center detent (order code OM-01-023)
P2, P3 = 2x 10K LIN center detent (order code OM-01-005)
P4 = 2x 100K REV LOG (order code OM-01-059)
http://www.audiomaintenance.com/acatalog/potentiometers_carbon_16mm_diameter_dual_gang.html

Switch is C&K (ITT Schadow), Alps etc.
http://classicapi.com/catalog/product_info.php?cPath=51_52&products_id=88

Transformer Studer 1.022.405.00 = Neutrik NTL1
http://www.neutrik.com/fl/en/audio/210_197961/NTL1_detail.aspx
http://www.canford.co.uk/Products/23-003_NEUTRIK-NTL1-TRANSFORMER-Analogue-audio-PCB-line-input
http://uk.farnell.com/neutrik/ntl1/transformer-1-1/dp/8314659
or ask your local dealer: http://www.neutrik.com/content/contact/worldwideagents.aspx

Discrete op-amp sockets
http://classicapi.com/catalog/product_info.php?cPath=71_77&products_id=122


As usual, I don't sell anything related to this project. All the information is provided "as is".

If you need stepped level and frequency settings but you don't need presence/absence filter, please check this:
http://www.groupdiy.com/index.php?topic=33996.0

**********

My other projects:

Neumann W492 EQ
http://www.groupdiy.com/index.php?topic=28332.0

Studer 169 EQ (stepped gain and frequency selection)
http://www.groupdiy.com/index.php?topic=33996.0

Neumann OA10 discrete op-amp
http://www.groupdiy.com/index.php?topic=34105.0

Balanced 12 input summing amplifier
http://www.groupdiy.com/index.php?topic=29082.0

Balancing/unbalancing amplifier
http://www.groupdiy.com/index.php?topic=29333.0

[okgb]

if you can squeeze the preamp in there i'd be in for two

[[silent:arts]]

cool!
and so much PCB space left  
ever thought of (optional) DOA footprints (your OA10 comes to mind), or some input and / or output transformers?

[Mike D]

Nice! I just finished a pair of your standard 169 and  I'm very happy with them. It's good to see this EQ coming to the 500 format.

[Joechris]

"if you can squeeze the preamp in there i'd be in for two"
rule of the tumb, maximum 4 knobs for a 500 series thing.

:-)

[mylesgm]

very cool...

[Mbira]

How are people doing the metalwork on these 500 series?  Is there a group buy I'm missing, or some inezpensive method?  This eq look really nice!  Thanks for sharing!

[matta]

+1 for the mic pre, makes for a great channel strip... and not much extra to add the pre, there is space on the PCB, panel spac is ata  premium though. Why not move the EQ IN switch to an off board toggle switch? Should clear up some space for a grayhill for the mic pre?

Cheers

Matt

[audiox]

if you can squeeze the preamp in there i'd be in for two

and not much extra to add the pre, there is space on the PCB

rule of the tumb, maximum 4 knobs for a 500 series thing.

I knew this... Joechris already answered, but seemingly not clearly enough.

Yes, there is enough space on PCB for the Studer mic pre. But you should also be able to fit the following controls to the front panel (in addition to the existing 4 pots and a switch)

- rotary switch for the coarce gain
- potentiometer for the fine gain
- phase invert switch
- phantom switch
- high-pass filter switch

Any volunteers to try that?

[mpc3000limited]

I think it is fine as is, no need to complicate a good thing! there are plenty of pre's out there to choose from making a dual purpose eq/pre wasn't what you were after! Nice job as always you make useful PCB layouts for gear otherwise left to the wayside!

[desol]

I think it is fine as is, no need to complicate a good thing! there are plenty of pre's out there to choose from making a dual purpose eq/pre wasn't what you were after! Nice job as always you make useful PCB layouts for gear otherwise left to the wayside!

Yep, looks good to me to. I'm sure adding more in the way of discrete opamps, transformers, etc, would involve more re-design than easily suggested...and probably would make little to no difference...maybe worse. Keeps it affordable as well.

Bunch of board real estate left? Draw a naked girl holding a beer.

I've never had to pleasure to hear these...but i'm probably down for a pair. Cheers.

[mpc3000limited]

Bunch of board real estate left? Draw a naked girl holding a beer.

X2

[ChrioN]

Optional DOAs and input/output transformers and its a sweet unit

If making all those choices up to the builder, it can be either very simple or pretty simple.

[Baltimore]

I think selectable frequencies for the high and low bands would be a better addition than the mic pre. And would make the eq much more versatile.  Either way, I'll probably build a pair.   Looks awesome!

Add transformer I/O and DOA option and I'll build more than a pair!

[2Low]

I think it is fine as is, no need to complicate a good thing!

me too !

[audiox]

ever thought of (optional) DOA footprints (your OA10 comes to mind), or some input and / or output transformers?

Optional DOAs and input/output transformers and its a sweet unit

Add transformer I/O and DOA option and I'll build more than a pair!

The discrete op-amp idea came into my mind too but... In my mastering version prototype of this same circuit I included a socket for plug-in op-amp boards. My friend and his colleagues made comparison between NE5534 and NTP M-100 discrete op-amp but there was no difference. I understand the discrete op-amp concept in high gain applications like mic preamps but in eq circuit like this there is no real benefit.

Adding transformers... The nature of this eq is very neutral and adding quality transformers wouldn't change it much. I actually have a layout version which has a Studer 1.022.405.00 = Neutrik NTL1 (the original Studer 169 line input trafo) at the input and active balanced output. The line input trafo configuration of the 169 is not zero-field like in later Studers, so it adds a little coloration. But the effect is still quite minimal...

I publish the transformer version since there are so many who like the idea. The extra cost for those not assembling the trafo is only two wire links.

[okgb]

the idea to add the mic pre
was just like extending the other thread
about making the studer channel strip
if i was up to speed and smart enough
i'd help with the design
ever use a 550 a or b  , thats small

[matta]

I know front panel real estate is tough, though it can be done... this for me pushes the limits, 10 knobs, 4 push buttons:



It is Dan's new 500 series Harrison Eq, talk about fitting alot into a SMALL space!

Matt

[audiox]

I know front panel real estate is tough, though it can be done... this for me pushes the limits, 10 knobs, 4 push buttons

I never said that it is impossible. I have designed that kind of puzzles too, when I worked as an electronic designer. Doable but takes a lot of time.

But now we are talking about DIY project which must be easy to assemble, contain only minimum of mechanical parts and most importantly components must be cheap and easily available.

Do you remember the whining when I used (small but expensive) Sfernice potentiometers in the Neumann W492 project?

[Brizco]

Thanks for all the infos. Very interesting project!
I'd go for more space for different caps. just a wish