PCBs available for 1176-flavoured FET compressor w/ opamps - (almost) no wiring

Help Support GroupDIY:

fripholm

Well-known member
Joined
May 26, 2013
Messages
302
Location
DE
EDIT: PCBs are now available!

Only 35 Euros/pc. + shipping. If you're interested in the boards, email me for details to fripholm(AT)gmail(DOT)com - make sure to include your Groupdiy name and your country.

Manual, updated 2021/05/30: TTx OP76 Guide


op76_boards2.jpg


1176-flavoured FET compressor with opamps - PCBs for an easy build without (almost) any wiring

Oh no, not another 1176?! I know there are a lot of 1176 projects out there, but this one is not meant to be a 100% faithful recreation but merely a great sounding tool, that is quick and easy to build. The reason for this thread is to gauge the amount of interest in a run of PCBs for this compressor project. The pictured boards are revision 1. The next version (that I'm about to sell if there's enough demand here) will add a few new features and overall improvements.

Similar to my TG1 Zener Limiter project this one started out as a PCB design for my own use at my studio and for live work. I already had one Mnats 1176 revision D but I wanted more channels of 1176-style compression with a smaller footprint and without the hassle of long-winded and error-prone wiring. Two stacked boards easily fit into Hammond Steel Instrument enclosures (1458 series) or side by side in 1U NRG Cases by frontpanels.de - or even better; two stacked pairs side by side in a 2U case for 4 channels ;)

op76_stack.jpg


I'm a big fan of those Hammond enclosures as I can carry them around in my backpack when going out for live work. And they are half the size of a real 1176 but include two channels! Next picture shows it in use at a live show I was mixing back in April 2018. One channel was used for the saxophone, the other for her lead vocal - awesome :)

op76_live.jpg


The circuit is based on Igor's opamp version of the 1176 with quite a few changes. The signal preamp expands on a mic pre design by Samuel Groner. The noise floor is much lower than on an original 1176, distortion is about the same (after all - it's a FET comp ;) ). Compared to my RevD it definitely has the same character minus transformer colouration. All-buttons-mode is also included using an illuminated switch. Input and output are electronically balanced, gain reduction metering is provided by eight LEDs and a couple of comparators. Personally, I've found the boards very easy to stuff and setup and there are no unusual, expensive or hard-to-come-by components involved. The calibration procedure is basically the same as for an original - the video tutorials for e.g. Mnat's versions also apply here.

The next revision of the boards will have optional pads to connect input and output transformers (and in this case omit active components associated with I/O) and exposed pads for an optional LINK switch and the sidechain HP filter. However, all of those options include additional wiring or even additional components/circuitry. When built as originally intended, there's only one 10-way ribbon cable for I/O and a connection to the PSU board.

The complete PCB is a panelized board that includes the main compressor board, a power supply PCB (which can easily be modified for different AC input sources), metering PCB and two different I/O boards; one with XLRs and one with TRS jacks (both Neutrik) - whatever is preferred. Price for one panelized board (which is one channel) is 35 Euros plus shipping.

If there is enough demand for these boards, I will prepare another guide including BOM, schematics etc. as I did for my TG1 project - in addition to ordering the boards, of course... 8)

So, what do you think? Anyone interested!? ;D

op76_boards1.jpg
 
Last edited:

Jarno

Well-known member
Joined
Nov 5, 2009
Messages
212
Nice work, didn't know about those cases, but they are very nice!
How tall/ wide is the main board?
 

TillM

Well-known member
Joined
May 21, 2016
Messages
587
Location
Berlin - Germany
I'm also interested in two.
As we write via PM.
It would be cool if you could do a fpd for the hammond chassis.
You told me, that I can use 9v to power it up.
I'm a bit confused how it will work, but I'm sure that you can help me with that.
Great project !
What is your idea with the transformer options.
Will it also fit in the hammond chassis and is the wiring also as less as possible ?
 

fripholm

Well-known member
Joined
May 26, 2013
Messages
302
Location
DE
Jarno said:
Nice work, didn't know about those cases, but they are very nice!
How tall/ wide is the main board?

Thanks! The main board is 196 x 75 mm (7.716 x 2.95 in). The height of the assembled board with attached ratio switch board is about 32 mm (1.26 in) without standoffs. I'm using 8mm standoffs on the bottom and 30mm between two boards.

rock soderstrom said:
I am in for both versions!  8)

Thanks Thorsten, will PM you later! 8)

TillM said:
I'm also interested in two.
As we write via PM.
It would be cool if you could do a fpd for the hammond chassis.
You told me, that I can use 9v to power it up.
I'm a bit confused how it will work, but I'm sure that you can help me with that.
Great project !
What is your idea with the transformer options.
Will it also fit in the hammond chassis and is the wiring also as less as possible ?

Yes, I will provide an FPD file for my frontpanel design.

The PSU can be configured for the use with a simple AC (!) wall wart or your usual center tapped power transformer (2x15VAC). In case of the 9VAC wall wart (which I'm using, because that's what I had laying around here) there's a voltage doubler that provides the bipolar +/-17 volts needed to power the circuit. With a couple of simple changes this voltage doubler can be bypassed and you can use an AC wall wart with 12-15 volts. On the other hand, for the use with a center tapped transformer there are other simple changes needed. All this will be documented in the guide. Nothing more than omitting a few parts or putting jumpers in place of a component or two...

The options for input and output transformers are just connector pads on the main board. The idea was to omit the components for the input (and/or output) section and connect your favourite transformer to these pads. Personally, I didn't bother too much for transformer colouration, so these pads are provided 'just-in-case'. Right before the output section is a NE5534 which can easily drive down to 600 ohms. You just have to keep that in mind when choosing the output tranny. For example, a massive step-up wouldn't work too well ;) Depending on your choice of transformers, there should be plenty of space within the enclosure where they can be mounted. You also need to wire the transformers manually, so there's a lot more wiring involved as well  :-X







 

fripholm

Well-known member
Joined
May 26, 2013
Messages
302
Location
DE
Ok then, I've just ordered a batch of these PCBs. Should take 6~10 days until they arrive. I guess, now it's time for me to prepare the build guide.

Will let you guys know when the boards are ready to ship  ;D
 

rock soderstrom

Bee with temporary limited flying abilities
Joined
Oct 14, 2009
Messages
1,118
Location
Berlin
fripholm said:
Ok then, I've just ordered a batch of these PCBs. Should take 6~10 days until they arrive. I guess, now it's time for me to prepare the build guide.

Will let you guys know when the boards are ready to ship  ;D

That's good news!  :)
 

fripholm

Well-known member
Joined
May 26, 2013
Messages
302
Location
DE
op76_boards_new.jpg


Good news! The new boards have arrived and are ready to ship.

First post updated with instructions on how to order and a link to the finished guide. The front panel design file (FPD) will follow within the next couple of days. This thread will also  serve as build thread, if that's ok with the mods.
 

tony hunt

Well-known member
Joined
Mar 13, 2014
Messages
103
Location
Frankfurt 230V / 50Hz
Those build documents look really good and clear.  :)

Money sent out for two boards a minute ago.
My build will take a while because I need to finish others in the hopper first.

Besten dank, tony
 

fripholm

Well-known member
Joined
May 26, 2013
Messages
302
Location
DE
The guide is now a ZIP archive which now includes an FPD file for Front Panel Designer 6.0 which might come in handy when using the Hammond 1458 series enclosure. Also the guide's PDF has been updated with a drilling and silkscreen template. See the updated link in the first post.

tony hunt said:
Money sent out for two boards a minute ago.

Thanks Tony, boards have shipped today.
 

fripholm

Well-known member
Joined
May 26, 2013
Messages
302
Location
DE
Potato Cakes said:
Will a second PSU be needed to power four sets if one wanted to fit that many in a 2U chassis?

Two boards draw about 190mA of current. Depending on your input AC voltage, one PSU board should be able to power four channels but the ripple might go up a bit. You could increase the filter caps to compensate and make sure your power transformer (or wall wart) can handle this.
 

Latest posts

Top