The diary of a very very complex audio build - Studer 169

[Luke Emrose]

Hi everyone!

I am currently undertaking another rather insane audio build, but this time I want to share the entire shebang with the list.

I've put every other build on hold for the moment as this one has shown itself to be the most important thing in my studio at the moment, as I'm suffering from a few recording issues that this is intended to solve.

I currently have been having issues recording my analog gear into my computer - and the issue is a combination of the level coming out of my analog synths being too low, or just not quite sounding right.

So I've decided to build a front-end line amp and equalizer, which I've decided to base off of the Studer 169 mixer:

Because it's got a nice warm sound to it, and has an excellent line amplifier and very very music equalizer on it.

I recently sold an old Yamaha mixer, and this will replace it for recording duties - keeping in line with my current 5-10 year plan of an entirely DIY studio from the ground up.

I managed to find the schematics from the Studer website: ftp://ftp.studer.ch/public/products/Mixing_Analog, and have now gone through the extremely complex process of refactoring the design to my purposes.

My modifications include the user of 12 position rotary switches for the boost/cut selections, and 6 position rotaries for the frequency selections on the EQ.

I've also made some feature additions including multiple selections for the low frequency HP filter, including the choice between 6dB per octave and 12dB per octave slope selection.

Using rotaries rather than pots has one main advantage - perfect recall.  I can write down the settings I use and then simply recreate them at any point, which I couldn't with a pot.

Recall is quite important for me.

The next modification is modern transistor replacements, since the original circuit uses BC239C, BC560B, BC309B's.  I'm going to likely have to go with whatever element14 has in stock, which means something like this set of substitutions:

BC560C for BC560B (with the amount of negative feedback in these amps this substitution shouldn't make too much difference)

2N5089G for BC239C

BC109 for BC309B

Also I managed to find the original Neutrik input transformers here:

• http://www.canford.co.uk/Products/23-003_NEUTRIK-NTL1-TRANSFORMER-Analogue-audio-PCB-line-input
• http://www.canford.co.uk/Products/23-002_NEUTRIK-NTM4-TRANSFORMER-Analogue-audio-PCB-microphone-input

Which I've bought 4 each of, since I'm recreating the entire input stage for both the line and mic stages for 4 channels (2 x stereo), as I have 2 main synths I use.

I bought a 2u rack case from Altronics.

So, I'm gonna post the entire schematic and all the engineering drawing here for anyone interested within the next few days, including all the spice files.

It'll be fun ;-) but it'll take a while.

regards, hope someone finds this crazy journey useful also!

P.S. I just purchased the full 4m x 4m professional version of Eagle PCB so I can properly design the PCB's, which I've quite excited about.

--
Luke Emrose
aka evolutionary theory
www.evolutionarytheory.com
www.soundcloud.com/evolutionarytheory
www.reverbnation.com/evolutionarytheory
http://www.facebook.com/pages/evolutionary-theory/110717958952413

[Gav]

Nice writeup, Luke!

I'm pondering how much stuff I could fit on a 4m x 4m PCB...

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[Luke Emrose]

A LOT.

Actually tbho, what I'm wondering more about is why you would limit it to 4m x 4m and who would need more than that....

[Luke Emrose]

And here is v5.1.0 of the schematic - I'm almost done designing!

The PCB layout however will be EPIC....

On this LTSpice schematic is the balancing transformer stage, the preamp stage, the high-pass filter, then a fader, then a fader buffer, then an eq, then an output driver.

[Nanik]

Awesome mate !

[Charles Horn]

Hi Luke,

Thanks for sharing, it's good seeing clear schematics along with knowing the design considerations that led to them -- it is educational :)

I was wondering how important are the tolerances on the resistors off the rotary switches? Obviously whatever they are they are the control will be repeatable, but do you need them to be super close in value to each other so each position is a very accurate increment? Unfortunately on the image I can't see the actual values due to the res, but I presume most (all?) are log scale values.

I have often thought that if really accurate tolerances were required you could just measure the specific resistance of each individual resistor and discard those outside your own tolerance... assuming, as I am, (never needed to or bothered to check for myself) that a 5% tolerance resistor could just happen to be within say 0.1%  of its stated value. Anyway, speculation aside, I'd be interested to know how you factor the component tolerances into your designs of differing high-endedness :)

Cheers,
Charles.

[kris]

oOOO
I'd always assumed that every resistor is made the same way and then measured and those close to what they were supposed to be get painted and sold as high tolerance and those that are out by up to 5% are painted low tolerance.

[Luke Emrose]

Heya!

I'll post a super high res reveal-all version as soon as I can ;-) i only screen grabbed this so sorry it's missing details.

Currently I've only adjusted values by simulation but i will calculate their exact values as a logarithmic scale in the next version of the schematic.

I use Vishay-Dale 0.1% tolerance metal film low noise audio resistors for faders/attenuators etc. but you should also remember that standard 1% metal film resistors are still 1% accurate in a serial configuration both individually and as a whole since probabilities scale proportionally and not additively .

1% accurate is probably enough but since i require stereo tracking the closer the better.

Glad to see it's useful to some people!

I'll post the "fully working" spice files too as a learning exercise since you can probably gain a lot by checking it out - it contains a lot of helper script for analysis that I've developed over time.

cheers

[Luke Emrose]

This assumption is correct.

On Jun 3, 2012 10:13 AM, "kris" <kr...@sleepingplanet.com> wrote:

[Luke Emrose]

I've attached a schematic that should be easier to read (it's ginormous!), any questions just lemme know.

I'll post the LTSpice files once I get my act together - we have people over for lunch today so the chicken in the oven takes priority!

L

[Luke Emrose]

Another quick post....

Here is the missing schematic for the "Neumann OA10" discrete operational amplifiers (note the triangle OA10 labels present 3 times around the EQ) that I am using throughout the design (except for the NE5534 fader buffer stage) - these puppies run off of +-22V rails (the original Studer ran off of  +-15V rails, but I've found that raising those to 22V increases the headroom MASSIVELY and also won't make anything explode since everything remains within tolerance) - so in a way it's an improvement over the original.

The original Studer actually used LM301 opamps, which are known for being pretty average for audio.  What's impressive about the original design is the way in which they complemented the poor performance of the LM301 by CORRECT design practices (correct rail decoupling and compensation techniques) and buffering with low-noise BJT's, resulting in a design that people LOVED the sound of, but that uses cheap and relatively "poor" performance parts.  Good design done well!

This Neumann OA10 is the precise opposite - buttery warm sound that is regarded as amongst one of the nicest sounding opamps ever invented, so that's of course what I'll be using as a replacement ;-)

[Charles Horn]

Ok, so my assumption was wrong :) I just found this link which shows the actual value distribution of 10% resistors:
http://dangerousprototypes.com/2010/07/01/actual-values-of-10-tolerance-resistors/

It makes sense from a manufacturing cost cutting point of view, but it still strikes me as odd that say a 5% tolerance resistor is _guaranteed_ to be at least 2% (since that is the next possible tolerance level(?))
off the stated value, no one seems to advertise that fact. Semantically just saying 'within 5%' doesn't imply there'd be that notch of missing values.
 Also, surely at some point for higher tolerances they would have different manufacturing processes
to be more reliable rather that testing and binning for every single one. At some point might it not be more cost effective to just make them better than the lower tolerance ones?
-- a comment from the link above mentions a laser trimming method for high accuracy...

I don't why I woke up today so interested in resistor tolerances :) 'Tolerance' makes sense statistically for designing large scale runs of something, but for one-off designs
'tolerance' as I understand it just isn't a physical property of any individual resistor.... statistics are tricksy!

One day I might do my own investigations into a batch of resistor values. I'd be interested to know if anyone on the list has looked into this before, or knows of any good articles that
give more info on the manufacturing process and what values to expect.

Charles.

 On 3 June 2012 10:43, Luke Emrose <evolution...@gmail.com> wrote:

[kris]

I guess they always strive to make the best resistor they can, and if one manufacturer manages it more than the other, they can sell their premium resisters at a lower price (beating the competition) or sell more at the higher price (thus increasing profit/share price against the competition).

I was amazed to find that CPU's are grown not made and the difference between a 1.8ghz and 2.4 ghz processor is simply that it grew better.

it is a bit of a bugger that if you buy a 5% resistor it will be at least 2% out but i guess it depends on your project.
If you've got a pot down one end of the process you can iron out all the issues i guess (maybe? I'm just guessing) thus you can swap cost of material for cost of labor (since you would need to spend time fiddling with the pot after making each circuit).

hmmm i apologies for how many times i used the words guess in that.

[kris]

Hi all,
Does anyone have a Makerbot Cupcake CNC?

I have a Cupcake Ultimate
http://wiki.makerbot.com/cupcake-cnc-10:ultimate-build-instructions

and it has never ever worked, i won't bore you with the details*, but according to makerbot the latest fix is to put a Makerbot StepStruder Mk6 on it.
Now I have Gen3 electronics which means the upgrade is not very simple.
Since it's never worked I'm reluctant to spend a further $370 on Gen4 electronics.

To that end, i found this
http://www.thingiverse.com/thing:11837
which allows me to hack a gen3 board to work with a stepper extruder.
scroll right to the bottom and you will find "ugly cable hack" which is what i want to do.

When i got the upgrade i was told i also needed to get a type-K thermocouple.
Which i have done, but:
do i simply connect it to where the old thermister was or do i keep with with thermister since i'm using gen3 electronics?

I've made a rudimentary search in the intertubes but not made a proper effort as yet. I was wondering if someone on the list already know the answer.

kind regards,
Kris


*alright since you asked (and I'm English and therefore racially required to complain at any given opportunity)
it was purchased as a present for me by my then fiance in February 2010
i started the build in august 2010 only to find they had sent the wrong screws
they then sent the wrong screws again
they then sent the right screws
then i discovered the power supply they had sent had no 12v rail (to which they explained they wouldn't be sending me a replacement)
When the build was finished the makerbot did many odd things, but never finished a print.
the build instrucitons offer no advice on calibration and i spent many months changing the values only to find a bug in repG wans't saving it
I then built an entirely new computer running linux (not my os of choice but many people had more joy with the driver than using win7) trying to chase why it would not build properly
I then decided it was the ftdi cable buggering things up so i bought a max32 ttl voltage stepper so i could use native serial port from the computer. Just before i connected that up i was told to check the motor on the extruder.
Apparently there was a large batch of faulty motors which cause feedback into the circuits and bugger everything.
then the gears jammed.
so they nice people at makerbot advised me to spent another 25% of total cost of the machine on a upgrade in order to fix my problem.
so here we are. it sits on my desk next to me and makes me angry just to look at it.
it is as if they started out with the best of intentions (the build instructions are really, really good at the start) and then at some point just went "fuck it, I'm bored" (the build instructions end with "add details here" http://wiki.makerbot.com/cupcake-cnc-10:cupcake-calibration)

[Ada Lim]

There is an unloved makerbot cupcake in the corner next to the Up!.  It will print calibration cubes but I haven't attempted anything more complex.

You could try bringing it in and comparing the notworking to R&D's notworking.

-A

[Kris]

Cool, will do, what days during the week evenings are you open?
Apparently Wednesdays are a bit busy at the moment because the robots have a expo coming up?
--
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[Max Nippard]

Should be open Tuesday evening.

Robodino members can come on Wednesdays but please let the Robot Workshop people have the workbenches and priority access to the tools.

[Luke Emrose]

It all depends on what you are making.

If you are talking digital, a lot of the time tolerance is irrelevant, stuff is either on or off, generally with quite a distinct difference, and quite a simple way to ensure, even within impressively bad tolerances, that the on and off is on and off when you expect.

Analog audio is a WHOLE other ball-game, and, significantly more difficult.

However the main rule is that you should ALWAYS strive to make circuits that can operate with the +-20% or +-10% tolerance of capacitors, the +-1% tolerance of resistors and the VERY broad, approx 500% variance in transistor Hfe (into which you must include temperature changes, which rather drastically effect transistors parameters).  Generally choosing A, B, or C series transistors (C is the highest Hfe), is all the grading you are allowed to assume.

This means designing for tolerance and resistance to temperature etc. etc. etc. This is why it's totally OK to manufacture resistors using the "binning" technique to grade the most expensive 0.1% resistors down to the 10% ones, since designing for 5% tolerance is, as you can see, actually designing for resistors that are very likely all more than 1% out in the first place.

Some of the best designs I've ever seen have amazingly tolerant configurations, and can withstand a lot of situations by self-biasing and self-regulating techniques and properties.

Having to match transistors is a chore (such as in long-tailed pair configurations), hence pre-matched transistor pairs on one-die, etc. etc. but should be the exception and not the rule.  I'm yet to have to do this as I purposely choose circuits that continue to operate well with little trimming.

However, if you identify at the design stage that stuff might be a touch picky, then there are always trim pots or even trimmer capacitors - but from a manufacturing perspective this isn't good, since the calibration of that pot costs money.

[Madox]

I might come in, should I bring in the ARDrone2 Max?

Should I bring in sensors for Ada?

Anyone need 3D printed bits and pieces done?

Bearings?

Motors?

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[Max Nippard]

I'm not sure if i'll be in on tuesday.

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[Luke Emrose]

OK, so I now have a tentative front-panel design that I'm happy with.

But it's also helped me to understand where I have to rearrange stuff to make it fit, so it'll be a bit of an ongoing process - it's a good start however:

It is a lot of switches however, so I'm slightly worried about ergonomics....

Hoping to take delivery of all of the Lorlin switches shortly.... but my mill-max pins to hold all the amps in place just left Digikey in the US.

more soon....

L

[Luke Emrose]

Since the front panel is simply black-anodized aluminium - I'm planning to just CNC the entire front text, and also try and cut the holes also, which might take a while ;-) but should give me a VERY accurate result.

[tALSit de CoD]

Given how much time, effort and money you're going to spend on the thing, I would suggest you look at getting the panel done by a professional.

Just sayin! 
// talsit.org

[Luke Emrose]

Normally I would say yes, but in order to try and cut costs, the Altronics 2U rack that I got is far from ideal - I doubt any metal place would take it - it's not a flat piece of metal - it has these "revolutionary" rivets and channels on it.  Personally I think it's a stupid design and I'm totally regretting getting it, but I think I have to eat my mistake now and just make it myself.

You are right, it's gonna still be relatively costly, but I have to cut corners wherever I can - the case was like about 40 bucks, and all the custom case places I know of charge about 120-150.

L

[Max Nippard]

Black anodizing lasers really nicely. You could use the beehive laser to engrave the text and cross hairs marking the drill holes then centre punch and drill on the drill press. 

You have probably already thought about this method but I just had to mention it since lasers are cool and all. :-)

--

[Luke Emrose]

Actually I was kind of discounting that idea due to the manual drilling, but it does bring up a very valid point.

I might investigate a combination.

1.) Laser the surface

2.) CNC the holes

Because if I was to centre punch and drill via the laser markings, I'm still at the whim of my ability to drill in the right spot.

The reason this might get difficult, is that I'm mounting all of the front panel switches and rotaries on a PCB that supports them - hence there can be not much play between

the locations of the parts on the pcb, and the front panel hole that they occupy - hence I wanna rely mostly on machine precision than manual precision.

I'm gonna do a test first by lasering the rear of the front panel, and adjusting everything based on that.

thanks again, it's a great suggestion and will definitely save me time.

L

[Kris]

I'll be bringing a spare rpi if your still interested.

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[Max Nippard]

The other suggestion I thought of after posting was adding white (or other colour) enamel paint in the cnc cut labels. Not sure of the best method of getting the paint in there though. 

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Luke Emrose
aka evolutionary theory
www.evolutionarytheory.com
www.soundcloud.com/evolutionarytheory
www.reverbnation.com/evolutionarytheory
http://www.facebook.com/pages/evolutionary-theory/110717958952413

[tALSit de CoD]

If the pots and switches are panel mounted, and you have a knob on them, you can always drill oversize, to allow some play and use the washer to make sure it fits snug against the panel. To a test run on a piece of sacrificial acrylic for hole dimensions. 
// talsit.org

[Luke Emrose]

That's a really good point - I thought about that too today and yeah, I think that's definitely the go.

[Luke Emrose]

As per another thread that I started about the LM301A operational amplifier, please find a growing number of LTSpice files I've started to share online that I use for all of my simulation:

http://www.evolutionarytheory.com/downloads/LTSpice/

Of special note are the rotary switches and potentiometer LTSpice files, that are incredibly useful for simulating stuff, and took me AGES to figure out how to do nicely.

enjoy!

[Luke Emrose]

It's all coming along now - aside from finding the right substitute transistors (I might just go for the more expensive but guaranteed to work but hard-to-obtain NOS options....), which is an interesting exercise considering there are no modern through-hole PNP parts anymore with as low a noise response as parts from the 70's.... (thanks Apple for ruining through-hole production by making iPads/Pods/Poops).

Just ordered the rotaries from element14, and just took a bulk delivery of 300 mill-max gold terminals and sockets for the discrete amps from Digikey - they are of amazing quality, and considering the quantity I ordered, rather cheap:

[Luke Emrose]

WOOO!

Almost all of the switches are here!

(these aren't ALL for the this Studer 169 build - these also fill up my "evolutionary recordings" stock - back-orders for clients also).

[Luke Emrose]

talsit wanted to see the top of the switches, so:

[Luke Emrose]

The input line and mic transformers arrived today - which is huge as they are key components for the sound of this thing!

Weirdly they are TINY little things.
I'm much more used to big transformers.

[Luke Emrose]

The album I am working on, as it draws to an end (slowly!), is taking up ALL of my time, and therefore until a few months time, DIY has to take a back seat.

However, today, there is a tiny bit of progress, as I had a delivery of 400 VERY rare and new-old stock Fairchild BC212B transistors that I bought from ebay,

of which there are enough + spares, to make the 12 discrete operational amplifiers that I will need for the 4 x Studer input channels I'll be building first.

cheers,

L

[giovanni spinotti]

hi etheory, i found this thread as for my first ever electronic project i'm trying to build a 169 preamp - but just the preamp and bass cut though, not the whole channel as you.
really great schematics you've done, and they're more true to the original project than anything i have found.
how is the build coming along? did you finish it?

since my knowledge of electronics is really really basic, i'd love to ask you a couple of questions:

- first of all, in your schematics you often add 2 resistences on the output of the block, for instance, in the bass cut out R50 to ground and R51 to out. these were not present on the original studer schematics and i wonder if you included them for some kind of stabilization

- secondly, the replacement of transistor. i do find original pieces quite easily on online distributors, except maybe the bc309b that pops up in ebay though, so i wonder if the substitutions are made with quality in mind

thanks a lot!

On Sunday, June 3, 2012 2:59:25 AM UTC+2, etheory wrote:

I've attached a schematic that should be easier to read (it's ginormous!), any questions just lemme know.

I'll post the LTSpice files once I get my act together - we have people over for lunch today so the chicken in the oven takes priority!

L

On 3 June 2012 10:43, Luke Emrose <evolution...@gmail.com> wrote:

This assumption is correct.

On Jun 3, 2012 10:13 AM, "kris" <kr...@sleepingplanet.com> wrote:

oOOO
I'd always assumed that every resistor is made the same way and then measured and those close to what they were supposed to be get painted and sold as high tolerance and those that are out by up to 5% are painted low tolerance.

On 3/06/2012 10:08 AM, Charles Horn wrote:

Hi Luke,

Thanks for sharing, it's good seeing clear schematics along with knowing the design considerations that led to them -- it is educational :)

I was wondering how important are the tolerances on the resistors off the rotary switches? Obviously whatever they are they are the control will be repeatable, but do you need them to be super close in value to each other so each position is a very accurate increment? Unfortunately on the image I can't see the actual values due to the res, but I presume most (all?) are log scale values.

I have often thought that if really accurate tolerances were required you could just measure the specific resistance of each individual resistor and discard those outside your own tolerance... assuming, as I am, (never needed to or bothered to check for myself) that a 5% tolerance resistor could just happen to be within say 0.1%  of its stated value. Anyway, speculation aside, I'd be interested to know how you factor the component tolerances into your designs of differing high-endedness :)

Cheers,
Charles.

On 2 June 2012 12:27, Luke Emrose <evolution...@gmail.com> wrote:

And here is v5.1.0 of the schematic - I'm almost done designing!

The PCB layout however will be EPIC....

On this LTSpice schematic is the balancing transformer stage, the preamp stage, the high-pass filter, then a fader, then a fader buffer, then an eq, then an output driver.

On 2 June 2012 11:34, Luke Emrose <evolution...@gmail.com> wrote:

A LOT.

Actually tbho, what I'm wondering more about is why you would limit it to 4m x 4m and who would need more than that....

On 2 June 2012 11:25, Gav <the.mechat...@gmail.com> wrote:

Nice writeup, Luke!

I'm pondering how much stuff I could fit on a 4m x 4m PCB...

On Fri, Jun 1, 2012 at 12:50 PM, Luke Emrose <evolution...@gmail.com> wrote:

Hi everyone!

I am currently undertaking another rather insane audio build, but this time I want to share the entire shebang with the list.

I've put every other build on hold for the moment as this one has shown itself to be the most important thing in my studio at the moment, as I'm suffering from a few recording issues that this is intended to solve.

I currently have been having issues recording my analog gear into my computer - and the issue is a combination of the level coming out of my analog synths being too low, or just not quite sounding right.

So I've decided to build a front-end line amp and equalizer, which I've decided to base off of the Studer 169 mixer:

Because it's got a nice warm sound to it, and has an excellent line amplifier and very very music equalizer on it.

I recently sold an old Yamaha mixer, and this will replace it for recording duties - keeping in line with my current 5-10 year plan of an entirely DIY studio from the ground up.

I managed to find the schematics from the Studer website: ftp://ftp.studer.ch/public/products/Mixing_Analog, and have now gone through the extremely complex process of refactoring the design to my purposes.

My modifications include the user of 12 position rotary switches for the boost/cut selections, and 6 position rotaries for the frequency selections on the EQ.

I've also made some feature additions including multiple selections for the low frequency HP filter, including the choice between 6dB per octave and 12dB per octave slope selection.

Using rotaries rather than pots has one main advantage - perfect recall.  I can write down the settings I use and then simply recreate them at any point, which I couldn't with a pot.

Recall is quite important for me.

The next modification is modern transistor replacements, since the original circuit uses BC239C, BC560B, BC309B's.  I'm going to likely have to go with whatever element14 has in stock, which means something like this set of substitutions:

BC560C for BC560B (with the amount of negative feedback in these amps this substitution shouldn't make too much difference)

2N5089G for BC239C

BC109 for BC309B

Also I managed to find the original Neutrik input transformers here:

• http://www.canford.co.uk/Products/23-003_NEUTRIK-NTL1-TRANSFORMER-Analogue-audio-PCB-line-input
• http://www.canford.co.uk/Products/23-002_NEUTRIK-NTM4-TRANSFORMER-Analogue-audio-PCB-microphone-input

Which I've bought 4 each of, since I'm recreating the entire input stage for both the line and mic stages for 4 channels (2 x stereo), as I have 2 main synths I use.

I bought a 2u rack case from Altronics.

So, I'm gonna post the entire schematic and all the engineering drawing here for anyone interested within the next few days, including all the spice files.

It'll be fun ;-) but it'll take a while.

regards, hope someone finds this crazy journey useful also!

P.S. I just purchased the full 4m x 4m professional version of Eagle PCB so I can properly design the PCB's, which I've quite excited about.

--
Luke Emrose
aka evolutionary theory
www.evolutionarytheory.com
www.soundcloud.com/evolutionarytheory
www.reverbnation.com/evolutionarytheory
http://www.facebook.com/pages/evolutionary-theory/110717958952413

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Luke Emrose
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www.evolutionarytheory.com
www.soundcloud.com/evolutionarytheory
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Luke Emrose
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www.evolutionarytheory.com
www.soundcloud.com/evolutionarytheory
www.reverbnation.com/evolutionarytheory
http://www.facebook.com/pages/evolutionary-theory/110717958952413

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