bxt403
Well-known member
Greetings,
I stumbled upon some Modular Audio Products AM-27 modules on ebay in October of last year. The ordeal took one week of my time (over the holidays in December), plus around $1000 CND for the three MAP AM-27 cards, three Melcor 1731 modules, a Five Fish Studios power supply and one of FF's pre amp kits (since there was a bulk discount with the power supply), one aluminum 1RU case (that was originally all black but I decided to sand the faceplate down so it would match another case's colour), and a lengthy Digi-key order. I decided that panel mount connectors for the power and XLR would be a bitch to drill through metal and decided to just use grommets for holes big enough to fit the cable through and break-it-out. It took me three days to drill all the holes using a hand drill (I ended up burning out my Dremel while drilling the sixth hole on the front panel :'(). All the wires were soldered to the modules directly since the idea of using an edge connector didn't cross my mind (I was worried about all the drilling I had to do). I haven't had any issues; aside from noise from issues with grounding (that was sorted through over the aforementioned holiday of assemblage). Here is the finished product:
Partially completed, the holes at the top of the front were misaligned so I decided to not install a pad switch/cct:
At my old job I would just have to mark the holes and hand it to a machinist- but I did like to watch and pick-up on a few orders of procedure (like the use of cutting oil). Notice that I put one of the stock 5004's to good use as a neat-o decal.
top view:
I'm a technician (not a machinist) so the internals are much nicer to look at than the exterior. I recapped all the AM-27s with Panasonic FC-series (and Kemet ceramics, since they change values for a discrete op-amp vs the original 5004 hybrid) and installed metal film resistors. The casing for two of the mic trafo's fell off so I had to secure them with electrical tape. Milton (aka: mkp27 over at ebay- the person responsible for the 500 series Eisen/MAP modules) sold me the Melcor 1731's (and also provided help and schematics for the AM-27 modules for the discrete op-amp version of the circuit) so that I could take out the hybrid MAP 5004 op-amp and install discrete ones. I don't think I overpaid for the opamps, since I also got the documentation. I bought three but one crapped out during initial power up. I had some Millennia Media MM-99's that I didn't end up needing for another pre-amp. Honestly, the MM-99 AM-27 is currently my personal favorite. The clean Five Fish Studios' SC-1mk2 kit bridges the extreme coloration of the 1731 AM-27s and coloured clarity of the MM99 AM-27 quite nicely. I had the Cinemag trafo option installed on the SC-1 at first, and I have to say that it sounded eerily similar to the MM-99 AM-27. I decided to remove the transformer, since I needed more channels of clean sounding pre-amp in my set-up.
installed:
My label-maker was spitting out stickers for a while.
rear view:
The phase reverse for the AM-27 is from the center-tap of the output transformer plus I was using star-quad cable; hence the phase switch is at the back of the unit.
Overall, I'm happy with the end product.
;D
I stumbled upon some Modular Audio Products AM-27 modules on ebay in October of last year. The ordeal took one week of my time (over the holidays in December), plus around $1000 CND for the three MAP AM-27 cards, three Melcor 1731 modules, a Five Fish Studios power supply and one of FF's pre amp kits (since there was a bulk discount with the power supply), one aluminum 1RU case (that was originally all black but I decided to sand the faceplate down so it would match another case's colour), and a lengthy Digi-key order. I decided that panel mount connectors for the power and XLR would be a bitch to drill through metal and decided to just use grommets for holes big enough to fit the cable through and break-it-out. It took me three days to drill all the holes using a hand drill (I ended up burning out my Dremel while drilling the sixth hole on the front panel :'(). All the wires were soldered to the modules directly since the idea of using an edge connector didn't cross my mind (I was worried about all the drilling I had to do). I haven't had any issues; aside from noise from issues with grounding (that was sorted through over the aforementioned holiday of assemblage). Here is the finished product:
Partially completed, the holes at the top of the front were misaligned so I decided to not install a pad switch/cct:
At my old job I would just have to mark the holes and hand it to a machinist- but I did like to watch and pick-up on a few orders of procedure (like the use of cutting oil). Notice that I put one of the stock 5004's to good use as a neat-o decal.
top view:
I'm a technician (not a machinist) so the internals are much nicer to look at than the exterior. I recapped all the AM-27s with Panasonic FC-series (and Kemet ceramics, since they change values for a discrete op-amp vs the original 5004 hybrid) and installed metal film resistors. The casing for two of the mic trafo's fell off so I had to secure them with electrical tape. Milton (aka: mkp27 over at ebay- the person responsible for the 500 series Eisen/MAP modules) sold me the Melcor 1731's (and also provided help and schematics for the AM-27 modules for the discrete op-amp version of the circuit) so that I could take out the hybrid MAP 5004 op-amp and install discrete ones. I don't think I overpaid for the opamps, since I also got the documentation. I bought three but one crapped out during initial power up. I had some Millennia Media MM-99's that I didn't end up needing for another pre-amp. Honestly, the MM-99 AM-27 is currently my personal favorite. The clean Five Fish Studios' SC-1mk2 kit bridges the extreme coloration of the 1731 AM-27s and coloured clarity of the MM99 AM-27 quite nicely. I had the Cinemag trafo option installed on the SC-1 at first, and I have to say that it sounded eerily similar to the MM-99 AM-27. I decided to remove the transformer, since I needed more channels of clean sounding pre-amp in my set-up.
installed:
My label-maker was spitting out stickers for a while.
rear view:
The phase reverse for the AM-27 is from the center-tap of the output transformer plus I was using star-quad cable; hence the phase switch is at the back of the unit.
Overall, I'm happy with the end product.
;D
The power supply is giving +/- 16 volts to all the modules in the case. The limiting factor for me was the 1731's supposed +/-15 volt operation but I was able to get 2/3 of the op-amps running at +/- 16 volts. The MM-99 also runs fine at 16 volts, although I can get away with operating it at +/-24 VDC. The SC-1 can handle a maximum of +/- 18VDC, if I'm not mistaken, but +/- 16VDC hasn't caused a hiccup. 
