Melcor AML-27 Preamp questions

[jho-audio]

I second that request. I would really like to see your mods zmix as well as any info gold is offering. Im itching to get these cards going now after such great response to this thread.

Cheers, Jason

 

[MikoKensington]

I third that. Turd that? :green:

 

[Gold]

Here is the data sheet
http://img.photobucket.com/albums/v357/plushmore/QE712/am_27.jpg

 

[Jeff Goodman]

Thanks, Gold. Very nice.

I wonder if there's any difference between the model on the data sheet, and mine which are AML-27's?

Jeff

 

[zmix]

Thanks for the datasheet, Paul!!

The modules I purchased on e-bay were the "AML-27" which are a slightly different layout, and included a 7.5k feedback resistor and a 330 ohm divider resistor, giving a fixed 55dB of gain. I came up with a set of values to give between 23 and 70 db of gain. As you can see from the datasheet, the 1731 amplifier does not behave predictably within standard opamp gain setting parameters.

I have some rack chassis, but I need to know where I can find someone to punch the usual holes for XL connectors and IEC power. Can anyone help?
Preferably in the NYC metro area....

 

[Jeff Goodman]

unfortunately, this datasheet is not what we're looking for. The pinout is completely different that what I have notated earlier in this thread, and the board layout is different as well. Maybe the gain resistance might be useful though.

Thanks anyway, Gold.

zmix, back to you, what gain resistors have you been using?

Jeff

 

[jho-audio]

Thanks Paul. I have the MAP (Modular Audio Products) AM-27 but this is an entirely different preamp then the AML-27 made by Melcor.

Jeff, can you post a copy (or PM) of the schematic that Glenford sent you? I recieved a corrupted one from them and no reply since then.

Zmix, definitely interested in your resistor values. And for that, a beer :guinness:

Cheers guys, Jason

 

[zmix]

[quote author="jho-audio"]Thanks Paul. I have the MAP (Modular Audio Products) AM-27 but this is an entirely different preamp then the AML-27 made by Melcor.

Jeff, can you post a copy (or PM) of the schematic that Glenford sent you? I recieved a corrupted one from them and no reply since then.

Zmix, definitely interested in your resistor values. And for that, a beer :guinness:

Cheers guys, Jason[/quote]

The MAP and Melcor circuits are the same, except for the fixed resistors I mentioned...

 

[Jeff Goodman]

jho-audio,

no problem on the schematic, I will pm it to you when I get home, I don't have a way to post it myself, so maybe you can?

Also remember that it is something that they, Glenford, drew up themselves, not anything originally published by Melcor, and so should be taken with a grain of salt.

zmix,

obvious clues like the similarity of model numbers aside, how do you know it is the same circuit? I'm not trying to be snotty, just curious, because if it is the same circuit, it is certainly laid out differently, and definitely has a different pinout.

Jeff

 

[zmix]

OK kids, here we go!

On my AML-27 boards, the pinout is thus:
15=V+
14=gnd
13=V-
12=1731 out
11=nc
10=1731 inverting in
09=gnd
08=I xfmr br
07=I xfmr r
06=I xfmr or
05=I xfmr y
04=gnd
03=Oxfmr y (ct)
02=O xfmr or
01=O xfmr g


The active circuit has THREE resistors.. 3k trim to B+, 7.5k feedback and 330 ohm from the inverting input to ground..

The input transformer has a 2k7 in series with 470pf damping.



So... who can help me with the mechanical mounting and hole punching???

 

[MikoKensington]

I just use Frontpanel designer and send my material to front panel express.

http://img.photobucket.com/albums/v473/MikoKensington/kensingtonEQs.jpg

When it comes to back panel holes, I use a 50 year old Bridgeport. Hole saws work too.

 

[jho-audio]

Great, thanks!

I am going to work on a front panel using frontpaneldesigner. When I complete that I will post the .fpd in case anyone else is interested. Might be a little while before I get this done as I need to learn front panel designer besides the fact that each day of this season gets far more busy than the last.

Zmix, I have tried to punch some rear panels with poor results. I'm sure that someone on the group will be able to either provide valuable input on the how-to's or even help you out with the task itself. Look at chrissugars recent posting on chassis! They are works of art.

As for the melcor vs. map issue, I was wrong, my MAP preamps are model #4004 - same layout and pinout as the AM-27 in the link above. My MAP 4004 preamps have the same output transformers as the Melcor AML-27 down to the model numbers (400-17-1) but the MAP ones are branded "QUALITY TRANSF., INC." and the Melcors transformers are branded "MELCOR"

The MAP AM-27 seem to be quite a bit different from the Melcor AML-27 though.

I was reading up on MAP and found a post on google groups by Paul Wolff (ex-owner of API) http://groups.google.ca/groups?hl=en&[email protected] that lends some more insight into the MAP/Melcor/API ties.

 

[MikoKensington]

Cool link!

 

[zmix]

[quote author="Jeff Goodman"]jho-audio,


zmix,

obvious clues like the similarity of model numbers aside, how do you know it is the same circuit? I'm not trying to be snotty, just curious, because if it is the same circuit, it is certainly laid out differently, and definitely has a different pinout.

Jeff[/quote]

Jeff,
I say the circuits are the same because the gain table and resistor values correspond exactly to my own AML-27 measurements, so It's a safe bet that the input and output transformers are largely identical in turns ratio. They use the same 1731 opamp, too. There isn't anything left to the circuit!

My cards use the "MELCOR 400-20" input transformer and the "400-17-1 497019" output transformer...

 

[Jeff Goodman]

well alrighty then. now we have something. :thumb:

I guess I'll be using the AM-27 gain table for mine. :grin:

Jeff

 

[MikoKensington]

Has anyone had any success with either MAP or Melcors? After I finish my Langevins and API, I want to start on these again.

 

[Jeff Goodman]

unfortunately, I haven't had any time for anything lately. we moved over the holidays and after I started setting up my workspace in our new garage, found out that the whole garage leaks like a sieve (sp?) when the rain started here a few weeks back. So everything is under tarps until the roof gets fixed, which should be soon, I hope.

Jeff

 

[Gold]

So... who can help me with the mechanical mounting and hole punching???

I have a 15/16" greenlee punch for Neutrik universal XLR's. I'm in Brooklyn and you are welcome to borrow it or use it here. They don't cost too much on ebay and are about $35 new. If you do this with any kind of regularity you should buy one. For the IEC I would drill a bunch of small holes then use tin snips to finnish the job.

 

[tony dB]

[quote author="soundguy"][quote author="Jeff Goodman"]
what record was that?[/quote]

uncle meat.

dave[/quote]


Can anyone point me too that plz? Or other information...
would like to hear some of it before going to 1731 all the way

The only Uncle Meat i know of is a band from Belgium from the early 90's
featuring world idols 2004 3rd place ended singer Peter Ev.
That album was done with mainly digital equipment for mixing.

 

[Tungstengruvsten]

'Uncle Meat' is a Frank Zappa/Mothers of Invention Album from the late 60's....some killer tunes, lotsa musique concrete.

I have a handful of MAP AM27 docs including schematics and layouts for both the mic pre and the bridging line amp. I sold a bunch over the last 6 months to pay off racking up the 8 I kept. A friend and I racked up 2 as a prototype, they sound great, and we modded a pair of cards with Hardy 990's that sound stellar. Also there is a post on here somewhere from 'B3groover' on how he racked up a pair he purchased from me....if anyone needs the docs I can send em out!