melcor schematics

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enthalpystudios

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Joined
Sep 15, 2005
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539
Location
kent, oh
anyone have any melcor schematics? I'm having a hard time finding much info about anything but the 1731. With all these 1731's floating around, it could be cool to see how they were used originally. gme20(?) eq, or a c20(?) comp... i'm sure they had a mic pre circuit....

just a thought, maybe someone has some info.

billy
 
Sent you an email.

Here are some things in the meantime.


http://smg.photobucket.com/albums/v473/MikoKensington/?action=view&current=AM27Schematic.jpg&refPage=&imgAnch=imgAnch10
This is a MAP preamp which is pretty much the same as the Melcor preamp. It just has phantom feed resistors at the front.


http://img.photobucket.com/albums/v473/MikoKensington/gme20sch.jpg
A small GME-20 Schematic.

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I have an old eight channel SSI premap built with Beyer input transformers, Melcor 1731's, and Melcor output transformers. It's very close to the API 312 circuit, with an output coupling cap like the MAP circuit linked above. I'll draw the circuit with values and post some photos when I get a little time. Who'd like to see it?

I also have a pair of Melcor GME-20's racked up, but I don't have any schematics on those.
 
hey thanks! no worries, whenever you get around... I was just thinking it would be nice to see how they used them.....

basically, i really like my 312 fabio boards with cinemags and 1731's..... but for some reason i have a feeling that the 312 circuit might just not be optimal for the 1731.... got to finish these fabio 2520bc's and test em out.

but yeah, i thought, why not see how melcor used em'

looks like slightly different input R, input cap (C3/C4) looks real similar, feedback R is a bit diff, and it's cap probably is just adjusted to match Freq response. zobel and what not, but thats dependant on the input tranny.....

then there's something between the opamp and the output tx to look at.....

so, if looking at the first schem miko just linked to, would it possibly be wise to change R4, R5, R6, C4, C5, and C6?

i guess thats one of those 'try it and see' questions.... so i guess thats my first task today.....

better question.... If I change those values, should my gain trim be something along the lines of a 15k rev log rather than a 22k rev log? or will a 22k rev log still work?

or, in my case, a rotary switch approximation of such.

thanks for the stuff.... can't read that eq schem very well, but i bet it'd be a cool project... probably switches will be the tripping point.

billy
 
ultrasonic, how do you like your gme20's? found a couple pics on ebay, looks like all the frequencys are fairly musical, octaves of A

if the switches weren't dual concentric, and just split into 4 for rackmounting, it could be a real cool 'thing'
 
what are R6 and C6 doing anyway, on the melcor am27 schem that is.

I imagine C6 is there to keep dc off of the output of the opamp, and R6? just a termination to give consistent performance into different loads?

are these important when using the 1731 i wonder?
 
[quote author="enthalpystudios"]ultrasonic, how do you like your gme20's? found a couple pics on ebay, looks like all the frequencys are fairly musical, octaves of A[/quote]

I like 'em well enough. I thought it was interesting to see the freq. centers in A, too. Mine seems to have been modified, the highest freq. on the top band is now 10k-ish. I've never measured it, but sounds higher than 7k, and the guy who sold them to me claimed it 10k. There is a bunch of overall gain, though. Might have been useful when these were in a console, but I'd rather have them at unity.

Most recently though I've mostly been working out of a studio that has an API Legacy, so I don't patch in the Melcors very often as I have 48 550's in front of me. Really, the Melcors are quite similar to the API's, very solid and pleasant. You just don't have the range with them like you do with the API. Not as many bands, not as many frequencies, and not as much boost/cut.
 
[quote author="enthalpystudios"]what are R6 and C6 doing anyway, on the melcor am27 schem that is.

I imagine C6 is there to keep dc off of the output of the opamp, and R6? just a termination to give consistent performance into different loads?

are these important when using the 1731 i wonder?[/quote]

http://www.groupdiy.com/index.php?topic=3808&postdays=0&postorder=asc&highlight=am27&start=45

Also in the Melcors the output transformer is a 90:600 transformer. Not sure if that has much of an effect.
 
[quote author="ultrasonic"]I have an old eight channel SSI premap built with Beyer input transformers, Melcor 1731's, and Melcor output transformers. It's very close to the API 312 circuit, with an output coupling cap like the MAP circuit linked above. I'll draw the circuit with values and post some photos when I get a little time. Who'd like to see it?

I also have a pair of Melcor GME-20's racked up, but I don't have any schematics on those.[/quote]

Thread from the dead.

Photos of the SSI w/ Melcor guts:

SSI_preamp_f.jpg


SSI_preamp.jpg


Photos are a bit old. I'm now running 2520's in all eight channels, and have replaced the power connectors with a 6 pin xlr.
 
hello, I'd like to know the dimensions of the 2520 pcb. I have a first pcb and I'm not sure the size is correct.
Thank you
:thumb:
 
[quote author="Baltimore"]damn, that thing looks awesome! Do you know what model beyer that is on the input? I have two marked "melcor 400-16", and I don't know what they are exactly or what to use for a zobel.[/quote]

I don't have the numbers from the Beyer right now, they're difficult to see inside the chassis. I will be taking the whole thing apart soon to perform some mods and restoration. It is an awesome piece. Anything sporting that color green is a piece of gear to contend with. I have many hours sitting behind an API Legacy and the SSI certainly has a similar characteristic to the Legacy and 512 preamps. I can't answer to the zobel question, but I'll either find my old drawing of the SSI circuit, or make a new one when I have it apart.

With the new power supply and better external wiring it my simply stay in the rack for a while. It sounds great.
 
ultrasonic said:
I have an old eight channel SSI premap built with Beyer input transformers, Melcor 1731's, and Melcor output transformers. It's very close to the API 312 circuit, with an output coupling cap like the MAP circuit linked above. I'll draw the circuit with values and post some photos when I get a little time. Who'd like to see it?

I also have a pair of Melcor GME-20's racked up, but I don't have any schematics on those.
What Beyers are in your preamps? If you have send me schematic.
Thanks
Duka
 
dukasound said:
What Beyers are in your preamps? If you have send me schematic.
Thanks
Duka

This is a really old thread!

I don't know exactly what Beyer transformer it is. As far as the schematic is concerned... look up an API 312. This looks nearly identical. A couple values may be a little different, and the only major difference is that there is a coupling cap between the opamp output and the primary of the output transformer. That part of the circuit looks more like an API 325. I did have an schematic of this at one time, but I lost the file. Seriously, it's the same as the API circuit with different iron.
 

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