hans a

+- 16v Virtual Earth summing ideas.
« on: March 29, 2021, 07:12:26 AM »
Im trying to setup my custom 16ch console for a recording session.
The board was bought unfinished with most of its funcionality (i would guess 😋). Its a 16ch board with two stereo subgroups and 2 stereo master strips where The master sections are missing (and with them The two echo send/returen masters).
All The infrastruktur is there, output connections, lundahl output trafos. But The Electronic are not. Also wiring is setup on what i would believe is a dB connector.

I have a female connector in my stash and also basic components.

Even an untouched ready lade channelstrip PCB. But im uncertain what to build. Firat thought of 2520 or equivalent. But im in a bit of hurry and IF there is a schematic People use often with basic parts i would settle for that.

Any ideas maybe?
I can research The xfo.
Br Hans


hans a

Re: +- 16v Virtual Earth summing ideas.
« Reply #1 on: March 29, 2021, 07:17:57 AM »
Yeah also, thought about The possibility to make near 30v glass a. The xfo i believe is not "DC-Rated" or cant be an active part in The circuitry like most Lundahls as ive read.

But that would be East enough maybe? Passive summing, a buffer and an output stage with four transistors? It would be Nice with AT least one of The four master strips to be sonically apart.

abbey road d enfer

Re: +- 16v Virtual Earth summing ideas.
« Reply #2 on: March 29, 2021, 10:17:25 AM »
We miss some vital information there.
Are the bus balanced or unbalanced?
What is the value of the bus injection resistors?
What is the operating level before the bus?
What are the specs of the output xfmrs?
I suppose there are faders between the summing amps and the outputs...
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

hans a

Re: +- 16v Virtual Earth summing ideas.
« Reply #3 on: March 29, 2021, 03:42:19 PM »
Ok i Will try to find out these things👍

hans a

Re: +- 16v Virtual Earth summing ideas.
« Reply #4 on: March 31, 2021, 10:11:05 AM »
Ok i went trough The documents i have. I Will photograph them and post. Im quite certain that The console is based solely on Steven Doves console design ideas from The studio sound article. Im missing The technical documents on The channelstrip and The master. But i have The subs and The limiter part of The preamp.
The preamp design is straight of The mic-pre tied to vactrol (dual rectifying detector) limiter design he proposed. The transformer balanced version with ll1538. NO line input as I can see.

The documents drawings show an input to The subs containing one bead to ground and a coil 150mh to an opamp, also passes trough a 10k attenuator first of. But i Will post...

JohnRoberts

Re: +- 16v Virtual Earth summing ideas.
« Reply #5 on: March 31, 2021, 10:26:36 AM »
You could do worse than copying Steve Dove... Last time I spoke with him (last century) he was living in PA, and had moved on to working with DSP instead of analog audio.

Look for schematics of respected designs and reverse engineer why the designers did what they did.

JR
Cancel the "cancel culture", do not participate in mob hatred.

hans a

Re: +- 16v Virtual Earth summing ideas.
« Reply #6 on: March 31, 2021, 10:39:08 AM »
Lol. Thanks Mr. Roberts. I guess that is called retirement then? 😊

Ive read that studio sound article a lot. This console has gotten me interested in op-amp design (by nescessity mostly. Right know theres NO time to fully invest in this hobby) so right know im looking at Dobkin's Op-Amp Circuit Collection. I actually found a PDF of your article too that i Will read. Theres a lot of stuff i've noticed that you can find if looking trough technical archives.

Im thinking of posting The documents i have in The technical documents section. It is a one of console but it Maybe someone else made a singular design? Br Alex
« Last Edit: March 31, 2021, 10:58:31 AM by hans a »

JohnRoberts

Re: +- 16v Virtual Earth summing ideas.
« Reply #7 on: March 31, 2021, 11:29:32 AM »
Lol. Thanks Mr. Roberts. I guess that is called retirement then? 😊
That was called consulting... by now a couple decades later I hope he is retired.
Quote
Ive read that studio sound article a lot. This console has gotten me interested in op-amp design (by nescessity mostly. Right know theres NO time to fully invest in this hobby) so right know im looking at Dobkin's Op-Amp Circuit Collection. I actually found a PDF of your article too that i Will read. Theres a lot of stuff i've noticed that you can find if looking trough technical archives.

Im thinking of posting The documents i have in The technical documents section. It is a one of console but it Maybe someone else made a singular design? Br Alex
There is a ton of reference designs out there, some are obviously better than others, but many are more than adequate.

JR
Cancel the "cancel culture", do not participate in mob hatred.

hans a

Re: +- 16v Virtual Earth summing ideas.
« Reply #8 on: March 31, 2021, 01:31:15 PM »
It seems there is. Just glad to have a console that i may (😋) be able to record on an learn from. It's also very Well crafted, and that makes it a Joy to use.
What i Will try to fix/continue where he left of:

> Dir Out is tapped at the Insert point before EQ section. I want The signal after fader to be able to adjust The signal when recording from externa pres. And also to be able to use The console for mixing to an interface.

> The limiter was, as read in Studio Sound, designed for more of a protection duty and it is not usable when recording and mixing right now. I'm reading up on this and atleast gonna try to make it more usable. It's hitting to hard and has too a long release. It seems the (home made) foto cell either is like that inherently, or maybe a timing cap that i can take away.

> Two stereo channels are missing

> Master section is missing

> Echo master (summing and send and return)

Br

hans a

Re: +- 16v Virtual Earth summing ideas.
« Reply #9 on: March 31, 2021, 01:34:06 PM »


































jacomart

Re: +- 16v Virtual Earth summing ideas.
« Reply #10 on: March 31, 2021, 07:12:10 PM »
If you are interested I have just posted the link to an Acrobat Pdf document containing the entire series of 14 articles "Steve Dove: Designing a professional mixing console", published on "Studio Sound and Broadcast Engineering" from September 1980 to January 1982, in the Technical Documents section of the forum.

Cheers
J.

hans a

Re: +- 16v Virtual Earth summing ideas.
« Reply #11 on: March 31, 2021, 08:03:35 PM »
Hey jacomarth. Thanks for letting me know😊

This is what i've got for the console if anyone is interested. I also posted it in the technical documents section.

Löhman LE 84 Mixing Console (Steve Dove design i mostly certain of) https://imgur.com/gallery/PbzyL3l

abbey road d enfer

Re: +- 16v Virtual Earth summing ideas.
« Reply #12 on: April 01, 2021, 02:35:07 AM »
Seems to be inspired by Steve Dove, however significant departure using discrete mic pre instead of 5534.
TL071's in summing amps? I didn't remember Steve Dove advocating that, but yes, he did. 5534 was expensive at the time...
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

JohnRoberts

Re: +- 16v Virtual Earth summing ideas.
« Reply #13 on: April 01, 2021, 09:43:49 AM »
Seems to be inspired by Steve Dove, however significant departure using discrete mic pre instead of 5534.
TL071's in summing amps? I didn't remember Steve Dove advocating that, but yes, he did. 5534 was expensive at the time...
A TL07x is not an obvious choice for a summing amp due to relatively high ein (3uV) and modest open loop gain @ 20kHz...  That said I resolved a bus rectification (radio station interference) issue inside a small Peavey mixer I inherited by using a JFET opamp. Not sure why the bus inside a steel chassis was acting like an antenna but swapping out the bipolar summing opamp for a JFET opamp cleared up the radio interference issue relatively simply.

I recall speaking with Steve at a trade show back in the 80s and he shared that he did some consulting work on broadcast mixers/consoles operating in high RF environments where a JFET opamp might make sense.

JR

PS: JFET opamps can tolerate a couple volts of RF superimposed on inputs before rectifying, bipolar opamps start playing radio tunes at roughly 1/2V of RF
Cancel the "cancel culture", do not participate in mob hatred.

hans a

Re: +- 16v Virtual Earth summing ideas.
« Reply #14 on: April 01, 2021, 09:52:49 AM »
Im there is two pictures of SR HB66 that slipped by when i uploaded. They are the discrete stuff.
The mic pre is a ne5534.
Br Alex

hans a

Re: +- 16v Virtual Earth summing ideas.
« Reply #15 on: April 01, 2021, 09:55:44 AM »
All master outputs have ll5519 on the output. Br Alex

Edit: 1529
« Last Edit: April 01, 2021, 02:24:25 PM by hans a »

abbey road d enfer

Re: +- 16v Virtual Earth summing ideas.
« Reply #16 on: April 01, 2021, 12:53:06 PM »
I recall speaking with Steve at a trade show back in the 80s and he shared that he did some consulting work on broadcast mixers/consoles operating in high RF environments where a JFET opamp might make sense.
That's correct. I remember having solved a similar problem in a FET compressor of mine located right under a 1kW FM rig, by replacing the 5534 make-up amp with a TL071.
Trading RF immunity for increased hiss.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

hans a

Re: +- 16v Virtual Earth summing ideas.
« Reply #17 on: April 01, 2021, 02:12:43 PM »
The first time we recorded thru this console we used the master out to be able to use the eq and the hiss was really loud. The sound was rather nice tho. A couple of years later i tried it with a band using dir outs and i got bad distortion.
Maybe try to find a less noisy equivalent or replacement then.
Or try to put something more modern in the empty master sections.
There is a post eq tap that i did use on a few channels. But i think there is oscillation since the led level meter is stuck on overload. It might explain the distortion on the session. It sounded like a touch of high frequency modulation.
When i have a day of i will restore these channels and try to find a more decent place to tap if possible. Maybe the fader buffer?

hans a

Re: +- 16v Virtual Earth summing ideas.
« Reply #18 on: April 01, 2021, 02:15:56 PM »


 

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