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Old Analog desk modification Utility Plugins
Old 29th March 2010
  #1
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Old Analog desk modification

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Hi everybody, this is my first post.

I’m trying to mod the HF and LF EQ section of my mixing console. After research I reckon I can put two extra Caps. in parallel with C12 by using an ON-OFF-ON toggle switch in order to get 12, 8 and 5 KHz instead of the fixed 10KHz. The LF seems to be a bit more tricky, based on a “gyrator” circuit similar to the one shown on the Forsell Technologies site. As stated on the sheet left of the diagram, removing or shorting Cap. “CS” will turn the circuit into a LF shelf filter, which seems to be the case in MY desk’s diagram. Should I put two different Caps. in parallel with C13, via a switch to select three different Low frequencies or put a variable resistance (1M potentiometer) in series with R28 or R29 (don’t know which) to get fully variable choice of Low Frequencies, as shown on the “Gyrator explained” sheet .First is that possible or have I misunderstood the “Gyrator explained”.

Can any one help Please. I would appreciate any help.
Attached Files
File Type: pdf EQ .pdf (150.0 KB, 300 views) File Type: pdf Forsell.pdf (98.0 KB, 234 views) File Type: pdf Gyrator .pdf (106.4 KB, 368 views)
Old 30th March 2010
  #2
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Hmm, interesting challenge here...
I never saw ICs having "Z" as a reference designator. But that's beside the point. First of all I don't understand how the Low Frequency opamp works, it's like there is no output. Oh bother, I just re-read your post, OK I get it, yeah the whole opamp thing with Z3a is a simulated inductor. I think ti would be simpler to insert a pot between R28 and R29. But I'm having difficulty understanding the similarity between the two topologies: your mixer and the gyrator-based LF filter.

I am almost certain that you could change the C13 (680nF) and expect to have the cutoff frequency change. You would have to verify your results on an oscilloscope to be certain it works.


good luck!
2N
Old 31st March 2010
  #3
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Gyrator vs My desk's Circuit

Finally someone with balls,

ooopsss sorry with brains...Well in us, men's case, I can only guess the centre of intellingence really is in the first area mentionned.Back to serious stuff.Fom what I can gather the LF on my desk is a modified version of the gyrator seen on the Forsell paper.Where it says at the begining of the third paragraph:"Eliminating CS (shorting it) will result in a low frequency shelving circuit." Which matches my desk circuit, no cap after the two resistors, just another resistor( for Q factor maybe?).So cap. after resist. = Peak type of EQ, where no cap. after resist.= Shelving Eq.I guess that's how some EQ's can go from Peak/Shelving by pressing or flicking a switch that would bring that cap(CS) in or out the signal path. But that's me guessing.

Thanks for your contribution, every bit of help is needed and welcome.
Attached Files
File Type: pdf Similarities Gyrator:My circuit.pdf (267.1 KB, 234 views)
Old 31st March 2010
  #4
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Making progress

Just want to share,

I found this very handy tool on http://www.whatcircuits.com/lc-reson...cy-calculator/
This will help if you want to change the frequency of your HF from, let's say,12KHz if you are not happy with it, to 10 KHz.
But you need to make sure you enter at least two values with the correct Hz or KHz, uF or pF after, otherwise the result will make no sense.
Example: I entered 10KHz on the F box, 4.7 nF on the C (capacitance)box, clicked calculate and gave me 0.05 H in L box(Inductance).Knowing now what L is in my circuit, I can find what capacitor value I will need to change to, in order to get an HF with a corner frequency of 3,or 5, or 8, or 10,or 12,or 16 etc KHz.In my case i might go for a double pole rotary switch with 6 positions and clickety-click my way from a choice of six different frequencies for my HF.

Still dunno what to do with LF though, fully variable via Potentiometer or fixed frequencies via Capacitors? Any help welcome.
Old 31st March 2010
  #5
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2N1305's Avatar
 

Quote:
Originally Posted by Migs View Post
Finally someone with balls,

ooopsss sorry with brains...Well in us, men's case, I can only guess the centre of intellingence really is in the first area mentionned.
...
"Eliminating CS (shorting it) will result in a low frequency shelving circuit." Which matches my desk circuit, no cap after the two resistors, just another resistor( for Q factor maybe?).So cap. after resist. = Peak type of EQ, where no cap. after resist.= Shelving Eq.I guess that's how some EQ's can go from Peak/Shelving by pressing or flicking a switch that would bring that cap(CS) in or out the signal path. But that's me guessing.

Thanks for your contribution, every bit of help is needed and welcome.
Ha! thanks, actually I'd prefer to have more brains than balls, since I work in a technical area...

I was surprised no other electronics guru (I won't name anyone, you know who) decided to contribute (yet). Anyway. I see that indeed if the CS cap is omitted you end up with a LF eq. I think you should try out both methods and hear which gives you a better result. Because frankly, both are just as easy to implement, either a pot or a switch.

So what is your board, I really want to know, although judging by the writing on the top of the scan, I'd say it's European (French, German?)

take care

2N1305
Old 31st March 2010
  #6
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Ah, one more thing, I just checked out your "equivalent circuit" drawing (thank you). The similarities are now very obvious. Where you mention pins 2 and 1 tied together and say ground, I don't know what you mean. This is simply the configuration of a voltage follower, that's the way it's always been implemented: tie the output to the inverting input.
Old 1st April 2010
  #7
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Any idea waht sort of value the pot?

Thanks to 2N 1305,

I really appreciate your input Sir, specially comming from a fellow Cannuck.
Also thanks for correcting my mistake by pointing out at the voltage follower(first time i hear that word). I have NO electronics background, just a musician wanting to learn.Concerning the board, it's English with lots of "Belclere" transformers in the inputs.Some small broadcast brand,payed about 200$CND for it 10yrs ago was at my dad's place unused for years.When I know more, I let you know.On a previous post you mentionned something about putting a Pot. between Res. 28 and 28.The two res. are 2K2 and the cap. before that is 680nF, which gives me 100Hz fixed frequency at the momment.Any ruff idea what sort of value and type I shoud look into for the Pot between resistors?And how do I wire that????

Thanks again.
Old 1st April 2010
  #8
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Wavebourn's Avatar
 

Hi Migs;

your EQ is already shelving. It has one simulated coil, no capacitor in series for resonance. I.e. no peak at all.
Old 1st April 2010
  #9
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Clarification

Thanks Wavebourn,

I was aware of the shelving on both the HF and LF.What we were discussing with 2N was the comparaison between my desk and a diagram on the Forsell Technologies website and the resemblance to a "Gyrator" circuit.But always good to clarify.

So far I know that changing C12 would alter the HF freq.Now what I'm trying to find out is: Should I simply put 2 caps in parallel with C13 via a toggle switch,giving me a choice of 3 Freq. for the LF. or put a Pot. between R28 & R29 and if yes what value should that pot be and how to wire it???

After this I will look at the transformers(there's quite a few of them), some Belclere in the input and the pre-amp section(Not bad pre-amps actually)As my priority is good recorded sound from the start.

Any sugestions are welcome.
Old 1st April 2010
  #10
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yes, but your board is still a mystery!

Sorry, you've got me really curious now...

Last edited by 2N1305; 1st April 2010 at 07:02 PM.. Reason: added sentance
Old 5th April 2010
  #11
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The Belclere Transformers

When I know more about my desk myself I will tell you, I promise.
For now,I found that the transformers used in the mic/line input of my desk are Belclere EN 8219 a company now called OEM (I think)
Apparently some of the 70's Neve(for a short time) and many other English desks modules used to have Belclere transfos.But let's be honnest that means nothing at all, since Focusrite,Neve and many more brands use 5534 chips yes it's true, but so does Crappomatic, Berhr****ter and probably Tandy.
But I would like to know if anybody has any info,specs sheets etc on these
EN 8219, because I could'nt find any at all on the Net.

Thanks. Happy Easter
Old 6th April 2010
  #12
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2N1305's Avatar
 

Quote:
Originally Posted by Migs View Post
Thanks to 2N 1305,

I really appreciate your input Sir, specially comming from a fellow Cannuck.
Also thanks for correcting my mistake by pointing out at the voltage follower(first time i hear that word). I have NO electronics background, just a musician wanting to learn.Concerning the board, it's English with lots of "Belclere" transformers in the inputs.Some small broadcast brand,payed about 200$CND for it 10yrs ago was at my dad's place unused for years.When I know more, I let you know.On a previous post you mentionned something about putting a Pot. between Res. 28 and 28.The two res. are 2K2 and the cap. before that is 680nF, which gives me 100Hz fixed frequency at the momment.Any ruff idea what sort of value and type I shoud look into for the Pot between resistors?And how do I wire that????

Thanks again.
You're quite welcome!
Well I'm no electronics genius myself, but it is my profession. As for your potentiometer situation (and forgive the lateness of the reply) Iwill have to check that later on today...
Need to work now! (gotta go hook up wires for a test setup)

FUN!

take care,

2N
ps: Juste au cas, je parle français. Sorry if this means nothing to you.
Old 6th April 2010
  #13
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Desk mods galore

Hey Thanks 2N,

I'm a Canadian expat living in London,I work in the UK in the music production field.I'm currently mixing some tracks recorded during the Easter Week-End.Once finished I'm really gonna get cracking on the mods of my desk. Quite a few little features that would make my life easier when mixing or tracking, like an "insert" on or off switch, like I've seen on bigger studio consoles.I would appreciate if you or anybody has any idea on that Pot value for full "sweepable" LF frequencies.
By the way 2N, I speak French too, should we start the Gearslutz francophone franchise???? What would the name be???
Les salopes d'équipement??? No...sounds too dirty....

I've started looking for good audio Cap. brands in order to recap my baby and also replacement IC's (marked as Z on the diagram attached below).I see quite a lot of TLO72 and 2 Sanken 5534A on the pre-amp and output of the desk. Any suggestions on replacements or improvements please people feel free to chip in.Right let's go back to work now.
Attached Thumbnails
Old Analog desk modification-desk-full-diagram-1.jpg  
Old 6th April 2010
  #14
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2N1305's Avatar
 

Quote:
Originally Posted by Migs View Post
Hey Thanks 2N,

should we start the Gearslutz francophone franchise???? What would the name be???
Les salopes d'équipement??? No...sounds too dirty....

.
PFFFHAHAHAHAAAA!!!

I spit all over my screen... that's a good one, yes I'd definiteley go for that!

OR

BORDELECTRONIQUE (needs no explanation)

EQUIPEMENTAL (equipement-mental)

Putains de Studio (studio slutz)

oh man, I am so perverted... But nobody quote me on that!

2N
Old 6th April 2010
  #15
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To finally answer your question about the pot, I would suggest keeping it as close as possible to what is in circuit right now. You see we have 2,2K on each side of the capacitor C13. So I would replace these resistors with say, 1Kohms each, and add a 2K potentiometer in between those two resistors.
The wiper (centre contact) of the pot would be connected to C13. The pot would need to be linear, not audio or "LOG".

But I am still not sure as to what effect that will have. I don't have time at the moment to go through the papers you so kindly posted, but I will later on.

The selectable capacitor solution would be more easy to implement and test.

Do you have an oscilloscope? And a signal generator? It would greatly help to test your results.

2N
Old 15th April 2010
  #16
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Not sure anymore

I'm getting a bit tired of all of this,it's a bit too hard.
So I decided to get rid of this old piece of junk.
Some of the colour caps on knobs are missing, channels need to be pushed in to work sometimes.One channel on the right not working at all(one with tape)I will gladly give it to anybody willing to come and pick it.Only problem is that I live in Timbouctou South, go to google map.If you are willing to get here, it's yours.What do you think???
Attached Thumbnails
Old Analog desk modification-desk-1.jpg   Old Analog desk modification-desk-2.jpg   Old Analog desk modification-desk-3.jpg  
Old 15th April 2010
  #17
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I hate to say it but this forum isnt the best for in depth mod questions

I suggest you re ask the question here Prodigy Professional

please dont ban me for posting that but its the only place i know for in depth modding help

but I can say this finding a replacment for the tl072 is tough it only draws 3ma a chip modern chips draw about 5 to 7ma a chip if you redid the desk you might over tax the psu if it's running to hot on the rails so I advise against changing it unless you know how to beef up your power supply to accept the higher current draw ,also if I were you I'd breadboard the section your interested in and play around with the diffrent methods it's a very simple circuit to do that with then you could plug in difffrent caps and pots till you got what you wanted without damaging your board maybe even make a small run of circuit boards to tap the new eq functions in with minimal work around?
Old 15th April 2010
  #18
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2N1305's Avatar
 

What? You don't want to just try the potentiometer idea?!

It kind of looks like a NEVE!
Old 16th April 2010
  #19
A2D
Gear Head
 

Quote:
Originally Posted by 2N1305 View Post
What? You don't want to just try the potentiometer idea?!

It kind of looks like a NEVE!

thats cuz it is a neve
Old 19th April 2010
  #20
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Dunno really

Thanks Doulos for your advice,


The breadboard idea sounds like good advice.But what do you think people, is it true what he says about this site not being the right place for in depth mods???Certainly there must people somewhere who know bout this stuff?Should I go to Prodigy professional instead???Or should I forget about all this crazy stuff?

Is anyone up for the challenge?
Old 19th April 2010
  #21
Send a channel off to someone that modifies/upgrades recording equipment for a living, look at what he/she did, and do it yourself to the other channels. I'm sure Jim Williams could figure it out.
Old 20th April 2010
  #22
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Quote:
Originally Posted by Sean Sullivan View Post
Send a channel off to someone that modifies/upgrades recording equipment for a living, look at what he/she did, and do it yourself to the other channels. I'm sure Jim Williams could figure it out.
Fur Sure. If anyone here can, it's him. Plus, I'd be up to the challenge, as I am sure many others here could be. They're just not looking at the thread.
Old 23rd April 2010
  #23
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Bread board working

Thanks to 2N,Doulos,Wavebourn and other people for their advices.
I have put together a small breadboard with three capacitors and a DPDT on-off-on switch.Removed cap 12 on a channel's PCB and wired the board.It works fine.I don't have an oscilloscope or signal generator but I have reasonably good ears.I spaced the three frequencies selected by the switch quite far apart (12KHz,8KHz and 5KHz) so I could hear a clear difference between the three of them.And it worked. I played back a voice track first, not much difference, then some keyboards, a bit better, then played back a Hi-Hat track which has obviously a greater hi- frequency content. And you could clearly hear the difference when I go from one position to another on the switch.I'm in the middle of a mix so it was a bold step to do this,quite risky if I messed up something, but so far so good.When I have some time I'll try a double pole, six pos. rotary switch for more choice of frequencies on the HF.But still my biggest challenge is the Low Frequencies.I'm still looking, I might have to do what one of the last posts said, but quite frankly the bank account is low at the momment, i got the parts from Maplin (sort of UK Radio Shack) for about 5 Pounds(roughly 7.50 US dollars).My small project is progressing, next, Low Frequencies and faulty chips etc.on channels.

Feel free to chip in, advices allways welcomed.Thanks my fellow Slutz.
Old 23rd April 2010
  #24
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Pics of my bread board

Pics of Mod.
Attached Thumbnails
Old Analog desk modification-dpdt-w-board.jpg   Old Analog desk modification-dpdt-pcb.jpg  
Old 23rd April 2010
  #25
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Nicely Done! So are those polypropylene caps or Mica caps? I wouldn'T even know which one to choose, but apparently both are quite stable and MICA caps are extremely durable, although expensive. I think any cap will do, other than regular ceramic. That will work too, but generally the poly-materials and mica are better. Wikipedia has good information, in a nicely laid-out manner about the different types of capacitor dielectrics. Types of capacitor - Wikipedia, the free encyclopedia

If you want to do this to every channel, it's going to be a lot of soldering little wires to switch pins and cap leads... You should consider designing some pcbs... This software is easy to use, it was my favorite layout softwarre for many years: ExpressPCB - Free PCB layout software - Low cost circuit boards - Top quality PCB manufacturing

Cheers!

2N
Old 24th April 2010
  #26
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Yeah those caps

Hi,

I think these are metalized polyester film caps. I think that's what it's called.Those were the caps originally on the circuit, I just went to Maplin and got the same but in different values, according to the desired Frequencies.At the place of C12, which was removed, I soldered the two leads and voila.If any of you has any wise advice about the types of caps. versus sound produced by the EQ, warmer, colder, sweeter etc etc please share with us, I'm even greener than green in that field.I will consider the PCB idea, specially if doing HF and LF on each channel.I tried to download that PCB express software but it is on PC platform only, I'm on Mac.Thanks anyway.Shame but hey...i'm sure I'll come across a Mac version sooner or later.Seen bellow:Detail of bread board being swallowed by roll of solder as captured in the wild,very rare picture.Not my best soldering ,in my defence my Iron is dead and I had to use a stumpy "too hot for PCB, 5 million watts, cheap" iron.
Any ideas about those fully variable LF frequencies anyone?
Attached Thumbnails
Old Analog desk modification-board-detail.jpg  
Old 25th April 2010
  #27
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Quote:
Originally Posted by Migs View Post
I'm getting a bit tired of all of this,it's a bit too hard.
So I decided to get rid of this old piece of junk.
Some of the colour caps on knobs are missing, channels need to be pushed in to work sometimes.One channel on the right not working at all(one with tape)I will gladly give it to anybody willing to come and pick it.Only problem is that I live in Timbouctou South, go to google map.If you are willing to get here, it's yours.What do you think???
You do realize you have a Neve console right?
Old 26th April 2010
  #28
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Well it's Timbouctou south

Quote:
Dualflip:"You do realize you have a Neve console right?"
But you do realize that is in Timbouctou South, right? Spell it Timbuktu ot Timboktoo, whatever.
Going back to mods on MY desk, I'm trying the LF with three caps and a DPDT switch on.I found these strange red caps. written WIMA on it.One 1uf, and two 0.33uf.I dunno if they are suitable for this application but they were the only ones with those sort of values I could find at my local store.

Any suggestions always welcome.
Attached Thumbnails
Old Analog desk modification-lf-breadboard.jpg  
Old 26th April 2010
  #29
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Don't take this advice Migs, that guys will kill you for only thinking about modifying of this console! They are mostly fanatics of legendary gear there, and very few of them are real engineers.


Quote:
Originally Posted by doulos24 View Post
I hate to say it but this forum isnt the best for in depth mod questions

I suggest you re ask the question here Prodigy Professional

please dont ban me for posting that but its the only place i know for in depth modding help
Old 26th April 2010
  #30
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Gear holly war

Wow,I love equipment ,but not to the point of becoming a fanatic.

Thanks Wavebourn.I wonder what Rupert, a devout Christian, son of missionaries and a missionary worker himself for a certain time, would say of his gear becoming an object of worship.Not sure he would agree.But anyway.
My project is going well, HF and LF have been fitted with bread boards,with switch and three caps. I dont have a scope but my ears tell me it works.How precise is the choice of frequencies I dunno yet, but the usability of the circuit is right on.I managed to "tune in" just right to remove all the undesired bottom of a snare track with the modified LF in a way I could not have done before, well not with that EQ.I'm still wondering, are those WIMA red caps any good for audio low frequencies or is there better choices?
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