Auditronics 501 Schematic request

I am working on a console with boards screened Auditronics 501-1M-1-B, I believe the metal work is screened 501 or 501B. Is this a "son of grand" desk? At any rate, I could really use a schematic for these if anyone has one. I cant tell if these channels were sloppily made or fucked with by an overzealous tech in the past, Im guessing the later. Did these ship standard with 5534 ICs?

Any help on this one is greatly appreciated.

dave

Auditronics 501, "Son of 36 Grand". I used to have one of these! And I am sorry that I sold it. As I remember the channels were originally populated with LM301s. There was a NE5534 in the mic pre circuit. Most of them had Jensen transformers too. The inductor eq was very musical in these beasties. A popular upgrade was to replace the faders that were made inhouse by Auditronics with faders made by P&G. Auditronics built 150 of them from 1972 thru 1978. As of 5 years ago (according to a factory tech) nearly half of the 501 desks built are still in service all over the world.

Kev (here on the board) has one. Perhaps he has a schematic that he can scan and send you.

I wonder what a 24 ch 501 is worth, Im not really up on these things at all. I told a friend I help him out, hes got one in a shed that he needs to bring in his studio to get working, trying to suss out what needs to happen to this thing to make it work. He mentioned jensen inputs, but the transformers on the channels I have looked at seem a little small (narrow) for jensens for what Im familiar with. A large part of what I need to do is figure out what is stock and what is mod, lots of boards have cut traces and screwing around... Was the main output transformer balanced or electronically balanced?

dave

i NEVER thought this would happen, but...

i've been working on joel hamilton's 501 at his "studio g" in williamsburg. it has been extensively modded by a number of techs prior to me, and has rev A, B, and C channel cards in it. i have pretty much a full book on it, and a decent amount of experience working with the channels cards.

i don't think the mic input transformers are jensen either; not sure where that rumor started. i've seen an unpotted one and it doesn't have any of the normal jensen/reichenbach codes on the inside. not a bad transformer, but small.

the mix buss output, both the quad and stereo mix busses, were transformer balanced out, using triad hs-66s, wired 1:1 at 600ohms, off the top of my head. the channel amps go to the buss routing modules, through a 4.7k dropping resistor into the summing amp and out through the master section.

everything was originally 301 and 709 opamps, but at some point they switched over to 5534s, which requires a 150pf compensation cap and some other mods to be stable. the original sockets are crap, also. little metal fingers for each leg with no plastic body... prone to shorts.

any questions just ask. if you need docs, i can get them for you next week when i am back in the shop.

ed

Thanks for the info guys. My first thought on the transformer was utc oncer, the can even has indentations where the screw sockets are on the top of an oucner. They look too small to be any stock jensen that I have ever seen, but there are no markings on the can, so who knows. I dont have the thing powered up so I cant comment on how they sound.

Ed, if you have schematics, would be awesome if you could shoot me a copy. Only need the schem for the 501-b EQ right now.

thanks!

dave

Auditronics quit making large format consoles sometime in the the late 80's. Only their broadcast console business remained. They made a few consoles that had full blown parametric eq sections that looked strikingly similar to the 501. Sometime in the early 90's wheatstone bought them (what little remained of them) and shutdown the Memphis factory. Auditronics had sheds full of vintage parts that just disappeared during the move. I remember seeing boxes and boxes of knobs and inductors!

The eq in the 501 was really pretty simple. They were switched LCR circuits in the feedback path of an op amp. Usually they failed when one of the fragile wires into an inductor broke. The inductors were wound on small 'donuts', stood on edge and held on to the PCB with plastic tie straps. You could easily break an inductor wire just by bumping it.

Anybody know who makes a suitable replacement inductor part??

dave-

the schem is of the whole channel module. i've been working on redrawing just the eq and makeup amp. when i get back in town on monday i'll scan it and get it to you. i'll also scan the factory 301 and 709 to 5534 mods so you can see what should have been changed from stock.

carl-

wilco makes a line of toroidal inductors that look like they'd probably work; they don't make the exact values as stock parts but say that they will make intermediate values. you might even be able to get a few as samples. look at the ITM and HFT series toroidal inductors at:

http://www.wilcocorp.com

auditronics used two different core types; the 1.2hy coil is smaller than the others even though it is a higher value, so it must be wound on a higher perm core. if you're really adventurous, you could get some toroid core samples from fair-rite and wind your own!

Ed,

Thanks for the tip on Wilco Corp. I'll check them out. I once took a shot at winding my own inductors but quickly realized that my fingers were too big and my patience too small! I've recently placed an order for inductors from OpAmp Labs. I am going to experiment with those and see what kind of eq magic that I can come up with. http://www.opamplabs.com/

ed, that would fully rule, thanks!
dave

I`ve got a module with a jensen 110K transformer and ne5534s in it so their must have been some variation over the years in components.

i'm glad people are discussing the inductor section. i need as much help as anyone, and i need soundguy's hairless cat. a number of my inductor coils were chewed up by a mouse that was trying to eat the parafin wax that these things are dipped in. any help would be a godsend.

otherwise, here is the information that i have:

my input modules are im as opposed to the later ime. they are marked 501-im-2-(d on one side and e on the other.) the mic input trannies are marked je-6110k-a...PC. the inductor values are 20mh, 100mh, 400mh, and 1.2h top to bottom. the ime module pictures show different values for the top two inductors with appropriate changes to the adjacent capacitor values. the output transformers littering the underside of the board are unmarked. this console version originally had 4 vca modules ganged to a single fader pot but these have been bypassed in favor of a stereo p&g fader for the front l/r with a separate arrangement that controls the rear busses and rear monitors concurrently with a single pot. kind of wierd, but it works. i still have the vca's. it's all 5534 with the exception of one of the echo returns which was never converted from the 709 for some reason. the group muting is flawless, and quad monitoring sure is fun.

-js

[quote author="edanderson"]i don't think the mic input transformers are jensen either; not sure where that rumor started. [/quote]

My Auditronics 110b modules have Jensen's on them.

marked je-6110k-a...PC.

Click to expand...

I have 6 of these transformers. They are small than UTC ouncers. The data sheet says they are for IC based mic preamps.

here's a photo of the auditronics mic input (left mounted on the pcb), je-6110k-a pc (center), and a utc ouncer (right) for size comparison.



i wouldn't say that the je-6110k-a is smaller than an ouncer, just shorter. i would even guess that the core size is the same, just horizontal instead of vertical.

i've seen a taller can version of the same mic input, also painted yellow, but the core inside was the same size. they probably changed over to jensens later in production, but i don't think that's what these little yellow guys are. they don't look like any utcs i've seen either.

for inductors, i don't know of anyone who makes off the shelf exactly equivalent replacements. you can get some samples in similar values from wilco, the HFT series of toroid inductors:

http://wilcocorp.com/catalog/series.cfm?series=HFT

if you're willing to order enough they'll probably make them in the exact values for you. you might also ask at mcemagnetics.com, but they'll probably be too expensive.

for the 20mh and 75mh (or in your case 100mh), you could try the toko or fastron inductors. they aren't the same thing, but they might work okay. the bigger values are really hard to find in off the shelf inductors. consider winding your own if you only need a few.

if anyone has any more questions, i'll try to answer them.

ed

ps- dave and anyone else, i stopped working on redrawing the eq section of the 501 by itself. if i ever go back to it, i'll post it here for all to see.

If my notes are still accurate ....

This is what the EQ section of an Auditronics 501 'Son of 36 Grand' console input module looks like.

http://s1.simpload.com/110843711d163187b.jpg

ed-

do you have any idea what that yellow transformer is?

the console my friend has is split between those yellow things and jensens.

dave

Sorry Dave !!!
:shock:

I was supposed to be doing something about this ... wasn't I ? !

I have two PC and set up to do this Saturday but if I get past that I'll try to find time to dig out some of my stuff for you.

I think the yellow trafo is the basic Auditronics trafo. I have no records as to who made their OEM stuff.
Both my desks also have a mixture of Jensen and Yellow.
....
and modded transformerless mic-pres
my guess is that some trafos failed and this was a solution.

hey kev-

no worries, no rush, its not my console, Im just helping a friend out with his when I get some time, its sort of our backburner project when we both have time, the console is just sitting in his garage waiting for some attention. Would be great to get docs but the world wont stop in the meantime.

thanks!

dave

.
Kev, if you are digging through a certain box already...
I'm looking for 501 SM , MEM , and CM module schematics.

Like Soundguy, far back burner. Timing seemed right to ask...

BTW all NE5534s w/ 150pf bypass mods
CM has Jensen 6110... for test osc? or super-smooth talkback?

email skunkdoggy at hotmail dot com ... or if you'd have to copy and mail, I'm happy to trade for your trouble. Send a PM.

Thanks, Paul

dave-

i don't know what the yellow one is. the windings are taken directly to the board, not soldered to PCB pins or leads, which makes them fragile. i've been able to dig through the potting on a few and solder a resistor leg to the winding end to "repair" a few, but it is very dicey. i doubt jensen/reichenbach would ever make anything this delicately built.

carl-

what you've posted is at least the general idea of the auditronics son of grand eq. there are a few non-essentials missing (the output follower after the opamp) and some of the resistor values don't match up with the schematic i have, but it is the right idea.

ed