Steffen

ugly green summing box - but nice fat IRON
« on: August 25, 2004, 07:37:23 AM »
summing boxes seem to be hip these days, so a friend asked me
build one for him...

direct coupled IC buffers --> passive mixing into BA283 amp---> siemens o/p xformer (M core, lams to same direction for 1mm gap)

sounds absolutely sweeeet :green:

steff






larger pix here:

http://home.t-online.de/home/micro.wave/forum/summingboxgreen.jpg
http://home.t-online.de/home/micro.wave/forum/summingbox.jpg
http://home.t-online.de/home/micro.wave/forum/summingguts.jpg


ugly green summing box - but nice fat IRON
« Reply #1 on: August 25, 2004, 08:02:58 AM »
Very neat indeed Steffen! The quality is such that you could build a few and sell them on I think - ebay title:  "Dc-coupled mixer with Neve output stages".

Justin
Prepare yourself. You are about to become the voice of Interplanetary Parliament.

Michael Krusch

ugly green summing box - but nice fat IRON
« Reply #2 on: August 25, 2004, 08:38:22 AM »
:thumb:  Good looking like all of your boxes.

Passive summing looks like a stupid marketing hyped nonsens to me.  But as long as you get paid for it.  :green:

Kev

ugly green summing box - but nice fat IRON
« Reply #3 on: August 25, 2004, 09:06:51 AM »
:green:  :green:  :green:

... is Steff
... is good

 :thumb:
Kev
DIY Factory

Re: ugly green summing box - but nice fat IRON
« Reply #4 on: August 25, 2004, 06:40:00 PM »
Quote from: "Steffen"
siemens o/p xformer (M core, lams to same direction for 1mm gap)


Why you use lams in the some direction?
You use single ended A class output coupled to the transformer
without caps ?
Other you improve LF distortion veryvery.

or to use Tesla transformer as output ?
                                  xvlk

Steffen

Re: ugly green summing box - but nice fat IRON
« Reply #5 on: August 25, 2004, 07:06:34 PM »
Quote from: "xvlk"
Quote from: "Steffen"
siemens o/p xformer (M core, lams to same direction for 1mm gap)


Why you use lams in the some direction?
You use single ended A class output coupled to the transformer
without caps ?
Other you improve LF distortion veryvery.

or to use Tesla transformer as output ?
                                  xvlk


the transformer must eat up to 70mA dc current. without the airgap the trafo saturates to quick and the darn circuit starts oscillation.
even the "gapped" version has plenty primary inductance and great LF response. HF-wise there´s a broad peak of 5 dB @50kHz
sounds reallyBIG

steff

Re: ugly green summing box - but nice fat IRON
« Reply #6 on: August 25, 2004, 07:30:48 PM »
[the transformer must eat up to 70mA dc current. without the airgap the trafo saturates to quick and the darn circuit starts oscillation.
even the "gapped" version has plenty primary inductance and great LF response. HF-wise there´s a broad peak of 5 dB @50kHz
sounds reallyBIG

steff[/quote]

Yes, it is single ended. O.K. Nice work :-)
Single end  is unusual with transistors.
I know it with triodes.
With transistor wou must use feedback to lower its output impedance
for trafo taste.
Some schematics of this?
                                         
                                             xvlk

radiance

ugly green summing box - but nice fat IRON
« Reply #7 on: August 25, 2004, 07:31:26 PM »
This is a very nice summing box.
Looks like a lot of work to build.
"Knowing that you are dreaming, however, does not automatically guarantee full rationality.
Then again, being awake doesn't ensure good thinking, either." -  Lynne Levitan

ijr

ugly green summing box - but nice fat IRON
« Reply #8 on: August 25, 2004, 08:03:14 PM »
Hi Steffen!
GREAT!
Must sound very impressive!

(Just screw some Neumann 1k faders and 5-10 k pan.pot's-
it's serious mixer :-))
What is the core square inside the bobine and how much turns?
Did you used p-s-p-s like .... sectioning or different?
What is approx. pri. ind. (w/no DC) ?
Never tried Siemens cores in SE. But sure, you have no problems with
highs even hard loaded :-)))
(these cores CAN play highs!!!!)
edit:
maybe, I missing something,
 but where is input trafos on summing's amp's kinda 10468,
 this is Neve'ish thing of summing, no? ;-)
Or you did it transformrless at this point?
BTW, Siemens cores sounds very nice if impregnated with hot wax,
this removes light discomfortness on midrange
(in trafos I experimented).

(hehe...now I understood...beware, I'll tell your mom what you did instead of homework on Nevecomp :-)))))
Absolutely COOL!
"The ear is the only judge of tonal balance."
Radio Designer's Handbook, 1953, p.632.

Steffen

ugly green summing box - but nice fat IRON
« Reply #9 on: August 26, 2004, 03:40:02 AM »
Quote
What is the core square inside the bobine and how much turns?


core square is 20mm. gap is 0.5mm (not 1mm as mentioned above)
really dunno the the turns, used the factory winding reverse. the trafos can be configured for 600:300, 600:150 and 600:75 ohm. I used the 600:300 config reverse.

Quote
What is approx. pri. ind. (w/no DC) ?


around 4.5 H. the sowter 9160 measures 500mH pri inductance :-)

Quote
maybe, I missing something,
but where is input trafos on summing's amp's kinda 10468


that´s because they are definately not there :-) 20 input trafos was too
expensive for my friend so I made direct coupled IC based  bal/unbal convesion and buffering.



Quote
(hehe...now I understood...beware, I'll tell your mom what you did instead of homework on Nevecomp :-)))))
Absolutely COOL!


hehe :-) .....the good thing is that the 1272 eurocard from this summingbox can be used for makeup gain in your 33609 (ok, some extra wirering need, but  I dont have a original BA283 card available) and I have 6 siemens biggies left...good for 2 stereo 33609 and another dual micpre :-)
will try to roll my own input and interstage for the comp.....

steff


Steffen

Re: ugly green summing box - but nice fat IRON
« Reply #10 on: August 26, 2004, 03:46:48 AM »
Quote from: "xvlk"
[the transformer must eat up to 70mA dc current. without the airgap the trafo saturates to quick and the darn circuit starts oscillation.
even the "gapped" version has plenty primary inductance and great LF response. HF-wise there´s a broad peak of 5 dB @50kHz
sounds reallyBIG

steff


Yes, it is single ended. O.K. Nice work :-)
Single end  is unusual with transistors.
I know it with triodes.
With transistor wou must use feedback to lower its output impedance
for trafo taste.
Some schematics of this?
                                         
                                             xvlk[/quote]


it´s the classic Neve 1272:

http://members.nuvox.net/~zt.robgrow/circuits/neve/neveba283.html

http://recording.org/users/kev/Project1.htm

greetz, steff

ijr

ugly green summing box - but nice fat IRON
« Reply #11 on: August 26, 2004, 09:15:24 PM »
HI Steffen!
Quote

that´s because they are definately not there :-) 20 input trafos was too
expensive for my friend so I made direct coupled IC based bal/unbal convesion and buffering.

I did not mentioned 'em at all inputs; a great advantage from trafo here is right at summing amp's input(i. e. resistors->trafo->283)

btw, makin' ba283 orig. layout is not a big deal; I've see pdf elsewhere at net. Gold electroplating kits are also cheap and only 3-10 minutes you need to make goldfingers on pcb.

Another question:
Your output looks great; but... 4.5H pri for 1:1.5 trafo...
With 600 Ohm loaded sec, what is the saturation level/freq.????
('xcuse me for too much questions) :-))) I luv Siemens cores too:-)))
I tested Siemens iron for inputs and interstages: I have some 0.78 cm^2 cores and they matches for mic/line_inputs (great, if good wounded:-)
"The ear is the only judge of tonal balance."
Radio Designer's Handbook, 1953, p.632.

Ian MacGregor

    Echo Park, Los Angeles, CA, USA
  • Posts: 280
ugly green summing box - but nice fat IRON
« Reply #12 on: August 27, 2004, 01:45:23 AM »
Steffen,
That box looks fantastic!!! Something I've wanted to try for a while now. Couple of quick questions:

Are the opamp stages unity gain buffer/unbalancers?

Does the output of the op amp go directly to a cap and then the summing node resistor??

Where does the other side of the summing resistor nodes go? I'm assuming to pin U of the BA283s??

Also, how is the output gain taken care of? Is it a stereo pot between the two BA283 stages??

Sorry for the questions, but I'd love to put something similar together!!

Ian
www.blackwatchsound.com
www.standard-audio.com
 ------------------------------

rafafredd

ugly green summing box - but nice fat IRON
« Reply #13 on: August 27, 2004, 11:34:21 PM »
Quote from: "ijr"
I did not mentioned 'em at all inputs; a great advantage from trafo here is right at summing amp's input(i. e. resistors->trafo->283)


Igor, can you elaborate a little more on this? What trannie and why would you use it here?

A 1:2 step up, maybe, so that we can use little value R´s in the summing section for lowest noise and still have some "free gain" from the trafo to match the 283 input?

Am I thinking right about it?

ijr

ugly green summing box - but nice fat IRON
« Reply #14 on: August 28, 2004, 03:36:09 AM »
There was a topic describing Neve's summing bus.
"The ear is the only judge of tonal balance."
Radio Designer's Handbook, 1953, p.632.

rascalseven

ugly green summing box - but nice fat IRON
« Reply #15 on: August 28, 2004, 01:06:22 PM »
I built mine completely passive based on NYDave's design and then fed the balanced busses into 31267's wired in reverse (per Joe Malone's info) at 1:2 feeding the output stage only of a pair of 183 cards.  I also used the T1310 inductor trick and took the actual outputs (api's wired 1:2) from the pin F output.  It's quite a lot of gain setup that way... way more than needed even with no resistor to set gain on the output stage (gain at minimum).

I think I'm gonna wire the 31267 1:1 to drop the level a bit and allow for more level to the amp circuit.  The api at 1:2 is just a little more than the LO1166 intended for this circuit (which is like 1:1.7 I believe), though I may try wiring it 1:1 too and see which I prefer.

BTW, even with all the unnecessary gain, this thing sounds fantastic!

Peace,

JC
"If you dig the gig, do it. -But listen to the signal, not the person talking."  -Keef


 

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