sontec 1 RU build thread

Hi people, I updated second post of this thread, in case of whatever:

HERE YOU CAN FIND ALL DOCS:

http://twin-x.com/groupdiy/thumbnails.php?album=399

awesome! thanks igor 

MrZpliff
Best way of running the Calrec EQ unbalanced ?
« on: March 07, 2008, 06:02:56 pm » Quote  
--------------------------------------------------------------------------------
Hi !
What's the best way to run Gyraf's DIY version of the Calrec EQ unbalanced. Me think's disconnect pin 3 on both input and output and just connect pin 2(+) and ground.  :?
--------------------------------------------------------------------------------
gyraf Reply
Ground -input, leave -output floating..

Click to expand...

Sontec seems to be the opposite of this, correct?
Which is to say the sontec8 is built to be unbalanced out...

Exactly. Instead of adding balanced line driver running at +/-18V max, I left it unbalanced.
This EQ runs on +/-24V, and there's a plenty of headroom.

From the other side, I personally prefer gear with high power supply rails, balanced input and
"balanced-ground-compensated" output, like here.
You can add output transformer to Sontec to make output balanced, it is easy.
JT-11 (IIRC) should work fine here as well as any other 1:1 or 11...2) ratio trunny.

Thanks Igor for the feedback!

Dear diyer,

i would like to know if i could use this DAO http://www.audiophonics.fr/burson-audio-opamp-aop-simple-p-3715.html for the output and input stage or which other DAO could i use?

thank you

You mean, DOA (Dead On Arrival or Discrete-Op-Amp), right?

Can't read french, but this opamp seems have different pinout than 990* etc.
I like OPA604 at input stage and fast Fred Forssel's opamp (993) at summing circuit.

Isn't this Burson a DIP8 pin compatible?

compatible in DIL8 configuration for some chips maybe, but dimensions 48 x 22 x 24 mm ?
At least you'll have to cut some windows in your 1HE case lid to make them fit thru. Not reliable, but might look funny with the DOA ends sticking out like a tube amp ... : 
(Why can't they give some chip data, at least say being bipolar or fet type DOAs)

Harpo said:

might look funny with the DOA ends sticking out like a tube amp ... : 

Click to expand...

;D ;D ;D

I'd stay out of company selling gold-plated USB cables.
/just kidding/

Nice looking op-amp, but useless here.

is it posible to get the boost/cut to 5db? i know the values for 6db but im not sure if the best way is to decrease r18-r21 or rf1c aso.. + rf18 aso..

It is possible to increase R18...R22 to 47k, r21 to 22k (closer standard values).

A new EQ was born today...

Aside from a few bad solder joints in a couple of bands and a ground problem to fix with the freq pots, everything works on paper:

(shouldn't the overall gain remain at the baseline when a band is raised or lowered?)




But it sounds terrible...when the gain goes above +9 it suddenly sounds like a ring modulator...both channels, every band. In this pic, the green is just before distortion and the others just after. Weird.

Edit: It sounds great. I changed the source and lowered the input levels and now the unit is behaving...I was apparently overdriving something when I raised band gain levels... not sure where since the output levels always seemed fine. ???  End Edit.

I used OPA604s for input & summing and OPA2604s elsewhere.
Anyone else have this happen? I may try limiting the gain to +6 to avoid this if cleaning up the ground problems doesn't fix it.

Otherwise, this was a lot of fun to build and play with...  

Just wondering, what would be the ideal DOA's for this sontec?
I already have one running with opa's but i'm going to build another one now with stepped switches and DOA's.
So... what (DIY prefered) DOA's are the best to use?

i think igor likes the forssell 993...

Igor said:

(me is a big fan of Forssell newer fast (993) opamps,
I think they UNBEATABLE by any other amplifier in this Sontec).
They are ideal opamps with very nice color.

Click to expand...

Hi Bobine, the graphs looks a bit strange for me. The overall gain should not change when boosting/cuting. And, seems like an oscillation at >15k? Let me know which soft was used to take these graphs,  and maybe it is good to put it on scope. I don't trust to soundcard-based analyzers Let us know if everything works fine after the fix.

Ultimate op-amp. Forssell's 993 is a cherry at summing circuit, IMHO.

Yep, forsell 993's it will be
OK.. now trying to find some decent 24 steps switches, elma's will be a 'bit' expensive maybe, i need 20. 

I bought 20 chinese stepped attenuator on ebay for my Sontec the dealers name is hampton if i remember correctly, got me a good price for them, they are Vishay i believe.
Seems like we will be building same sontec, i went for forsell also ;-)

My third:





I can really recommend this EQ. Jump on this as long as Igor stocks it...