Auditronics 501 Schematic request

[quote author="edanderson"] ... the windings are taken directly to the board, not soldered to PCB pins or leads, which makes them fragile.... [/quote]
yep
that's what happens

I didn't bother to try to fix as I was never short of an external mic-pre
BUT
if it is fixable , then one should try

I will get those schems up ... at least all that I do have
even if/when I do get rid of the desks, I'll still post the info.

[quote author="edanderson"]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[/quote]I realize this an old post, but wanted to provide this info for the better good of mankind, sorta. My Dad worked at Auditronics/Spectrasonics starting in 1970 and several of my friends worked there over the years. The transformer in question was not originally designed/built as a mic transformer, nor was it manufactured by Jensen, Triad or anybody else from the audio field. It was a $1.25 transformer for some sort of door buzzer and if hooked up differently in some bizarre way it functioned as a mic tranny. I also believe that there was a patent applied for something to do with this. The reason the wires are breaking I that the early potting material used had a high acid content which corrodes the wires. There was one console that went to South America where due to the higher humidity they failed within just a few months and all had to be replaced. That type of potting material was replaced after this.

My Dad actually got a lot of these transformers and repaired them by digging out the potting material and replacing the wires. He built a 110 console for our studio using these and PC boards that failed QC (due to bad traces that he added jumpers to repair), face plates that had faded or smeared lettering, but the dang thing worked after about a year and a half he took to build it. I remember the QC guys from Auditronics eating dinner at my house a lot when I was 16.

jcraft,

that is pretty cool. i think it is awesome when engineers find novel uses for inexpensive parts. i like the recycling also. i'm not 100% sure, because i don't have the schem at hand, but i don't think the yellow input transformer was hooked up in any special way, at least not in the 501. auditronics did get a patent on some interesting output transformer feedback hookup ideas, which may be what you are remembering.

thanks for sharing that info. the 501 EQ was what got me started on my design for my own "swinging inputs" EQ.

ed

I think one of the reasons for potting these xfmrs was to hide what they were doing. I know one of the principles in Auditronics was "Tighter Than Bark On A Tree", so anything to make an extra nickel appealed to him. You might be right about that patent as I recall it did have something to do with a feedback circuit. Geezzz, were talking 30+ years ago.

I have had a couple of Auditronics consoles over the years, the last being a 32 input 501 with Allison Reaserch VCA based automation. The first one I got was a Auditronics branded Spectrasonics 1020 in 1980, which by the way I just "Rescued" from a date with the Nashville landfill about 3 weeks ago. It's in pretty sad shape as a whole, but the input, routing and fader modules appear to be in very good to excellent condition. A couple of ex-Auditronics employees are going to help me restore it, just tracking down documentation on it and figuring what all we have here at this time.

Does anyone have a scan on the schematics for the 501 pre/eq?

Thanks,
Adam

Good luck getting inductors....Wilco has a minimum 100 per item order, Gowandas is more likely but expect to pay $25 each or more... I do think there is something to the torroids, and have had some luck finding them surplus
Every 101 / 501 I have seen had Jensens in it, but I guess I'm just lucky! I am currently modding a 26x16 in 501, putting a DOA mic preamp in, balanced line (aka insert return)/ tape ins, changing the audio path FETs to relays, balance 2 track monitor ins, and using the back of the quad buss to bring the monitor path into the mix (who ever came up with this monitor scheme, anyway?)
I am experimenting with moving the feedback point on the output driver "back" to the op amp to get rid of timing errors
the cool thing about these boards is that the components are very high quality, and there is room (and edge pins) for mods

Hey niels - hows your 501 coming. I installed a 2520 in one preamp so far in my 110 and im pleased - im looking to do 7 more with DOAs. I also installed direct outs on 11 channels using surplus output cards with the jenens - though now im thinking i could have elimated the driver/buffer stage by just installing a switch that would send the signal either to the output transformer or the normal signal path. I could just monitor off my converters. then it would look just like a 312 when the direct out switch was flipped. for now, with the 2520, it looks like a 312 with a buffer stage before the output transformer made of a 5534 and 2 transistors. these are definately fun boards to mod. I "re-knobed" mine because im just that vain :grin: If you need any 501 info ive got a boatload. the dealer manual, full-size, fold-out schematics, and the original documentation on retrofitting modules with 5534's when they came out (which they sold a kit for) and retrofitting with jensens (which they also sold, for $35)
-Ben

I am getting a proto board made for a DOA/PRE card, I came up with the idea for this project, but as it is a kind of "band aid" approach, I may offer some up on the ol' black market. As soon as the proto is tested, I will make a run of them. I reversed a current version of the oh so desireable DOA (and it is different than any posted so far, and has none of the problems) and layed it out with room to work, with jumpers and associated circuits so it can be a mic preamp, a balanced line input, or an output line driver. I am sick of building these tiny boards that take lots of troubleshooting, when I could care less if they are in a certian footprint.
There is room on the 501 input, and it has a 14 pin footprint for the mic pre op amp, so I am using a header there to go to the new board, and mounting a new mic out tranny on the board (now the insert send / mic pre direct on the patch).
I'll post a pic once I have the proto up and running in the module.

niels - are you mounting the output transformer to your new boards? and when you use the insert/direct out patch, does it divert the signal or spit it? (meaning can you tap the micpre and send the signal to mixbuss simultaneously?) if so, how is it buffered? that board sounds like a good idea, though i do like the idea of being able to switch out different DOAs.
-ben

If you need any 501 info ive got a boatload.

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Could you send me a large schematic for the 501-IM input module for serial numbers 113 and above?

Adam

Hello All,

Can anyone please provide me with the 501 input module schematics?

Best Regards,

Raffaele

Go to > [email protected]

edanderson said:

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

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Hi Ed,
I know this is a really old thread by now, but I had a couple of questions related to your post that I may as well ask here.
I was asking Joel H. some questions about the various revisions of the Auditronics 501 input channels and he mentioned that he prefers the earlier "IM" version, compared with the later "IME".
I wondered if you know what are the differences and how they contribute to the sound and performance of the modules?
When you refer to Rev A, B, & C channel cards, does that relate just to the earlier "IM" revisions, or a combination of "IM" and "IME"?
It sounds like, from your description (circa 2005), that maybe none of the earlier "IM" revisions came stock with the Jensen input transformers, but rather some older variations?  (It would be cool to know what character you have noticed being imparted from the different transformer versions).
From what I've seen, all the later 501 "IME" versions (like what I have), and also the later versions of the 110 series channels, came standard with the Jensen 6110K input transformer.I did see reference in a few places that the earlier transformers were sourced from some kind of door bell transformer stock? (!!)