Melcor AML-27 Preamp questions

[tony dB]

i have that album

 

[zmix]

[quote author="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.[/quote]


Thanks for the offer Paul!

PM me. I'm in Manhattan.

-Chuck

 

[gar381]

I have 2 AML-27 cards and have good schematics of them. I can e mail
to any one who needs them. .bmp or .sch

Gary

 

[CJ]

Any iron in these 27's?
Or did I miss something?
:?:

Pat who? :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted:

Oh. Mor-turd. That's cool. :grin:

 

[MikoKensington]

You can send them to me at the address below. It would be most appreciated. I can host them for the group as well.

 

[MikoKensington]

Yeah CJ, there is iron.

 

[franklinh]

Hello all,

I figured I'd add that I have a Melcor CL-20 that I'm sluggishly rebuilding piece by piece. One of the 1731s was responsible for crackling and popping sounds, so it was switched with a Hardy 990C. I had tried a 2520 and the results were similarly noisy, with less money in pocket. That fixed the popping but the circut was still pretty noisy when engaged. Figured to replace the electrolytic capacitors (hey, they look old and I need the soldering practice) and then go hunting for another bad 1731, or some other issue. Maybe change the resistors to 1% metal film.

Any other Melcor CL-20 owners out there?

 

[gar381]

Has anyone had a chance to play with these melcor pre's and have anything new to add sence the last post?

Gary

 

[okgb]

i have the schematic of it around here somewhere

regards Greg

 

[soundguy]

franklin, do you (or anyone else for that matter) have a a schem for a CL-20?

dave

 

[franklinh]

Dave,

The only two relevant schematics I have are:
One that I drew out in pencil on two pieces of paper taped together of my CL-20 (messy!), which has a few blanks to fill in because of older nomenclature on 'lytic caps. The other is a jpeg of an API 525C which seems to share some fundamentals with the melcor, but it has refinements like LED metering and transformers.

Can't host anything from here, but I could send the jpeg to you if you PM me.

Franklinh

 

[pmroz]

HI, i've been doing some Bauman boards and opamps (first project) that are similar to these, and have managed to accumulate some other stuff:

2x Melcor 400-17-2 out trafo
1x Map 5002 opamp
1x black box, 8-pin opamp style pinout, '2351B' white stamp, any ideas?

Also a mic/line card labelled 'Audio Acoustics' with Beyer in trafo, 7pin for DOA (but no opamp), and Melcor 400-17 out. The card is 24pin double-sided, so maybe not much use in this thread, not official MAP. But old.
i've done the schem, it's similar to Fabio's 'rel3*1*2' schematic... also rafafredd has done a revised version. If it helps anyone i can send or post .ckt, .wmf, or scan pencil schem.

CJ , have some 4804s here too like in your great dissection... 400-17s are practically identical, a kick for how old they are. If i find a bad one, you want it for science?

 

[gar381]

Hi All

I want to build a gain switch for my aml-27 cards.
Has anyone had any luck using the am-27 gain ris.
http://img.photobucket.com/albums/v357/plushmore/QE712/am_27.jpg
on the aml-27.

Also..
I want to recap mine..What is a good brand/model of axial
caps that I can buy at digikey or mouser with low esr?
Something as good as panasonic fc radials.

Thanks

GARY

 

[pmroz]

.

anyone have more info on the Melcor 400-17-x trafo?

 

[gang of elk]

..speaking of melcor. i just got some melcor eq-20's that i'm firing up for the first time this week i hope. does anybody here know anything about these? not much info out there i guess. upon popping them open i was surprised to find non-potted amps (i counted 5 transistors), and transformers! wasn't expecting those. anyway, will report if when get them going.

 

[gang of elk]

got the eqs going and they sound great. just may have to get a melcor preamp project going soon.

 

[pmroz]

.

gang of elk...
i can recommend the bauman/peter c./etc. melcor/a.p.i. project.
sounding great here.

did you do a schemo of those eqs? I'm interested in a couple 2-band eqs for 2ch bass pre. How do you like them on the low freqs?

 

[gar381]

Hi all

Finally had a chance to play with my AML-27 cards.
I recaped them with BC radials. I built a shunt gain switch using the am-27 values (see.. http://img.photobucket.com/albums/v357/plushmore/QE712/am_27.jpg ) I fired them up with a +-15 volt supply. My early
tests reveal that the they are unstable with gain resistors smaller than 330R..they start to osc somewhere around 300Khz. Therefore mine don't seem to like gains above 55db. At lower gains they seem clean and flat from 15Hz to 30Khz on my scope up to 27 volts out where they start to clip. WOW 30+db!! Wish I had a distortion analyzer. Has any one else
had a chance to play with theirs? Would like to know your findings!

GARY

 

[jho-audio]

Ive got some par-metal chassis coming in this week and I am hoping to get these preamps racked up soon.

My plan is to have the following functionality available:
- 20db pad
- Phase
- 48v phantom (using cool JLM power supply with 48v feed)
- shunt attenuator (as per Gary's note, 55db max)

I've got this all figured out and have experience with everything except the attenuator. Im thinking that I need a 1pole 6pos switch (have spare 2pole 6pos switches available for this).

Can someone please confirm or help me to understand better the shunt resister network. Am I correct in thinking I only need to use one pole? As well, is the grounding scheme right? Where does this ground to, chassis?

Anyhow, came up with the following using the AM-27 values:

Good/Bad? Thanks for any help as I am feeling very lost with stepped attenuators!

 

[clintrubber]

from Gary:

Finally had a chance to play with my AML-27 cards.
I recaped them with BC radials. I built a shunt gain switch using the am-27 values (see.. http://img.photobucket.com/albums/v357/plushmore/QE712/am_27.jpg ) I fired them up with a +-15 volt supply. My early
tests reveal that the they are unstable with gain resistors smaller than 330R..they start to osc somewhere around 300Khz. Therefore mine don't seem to like gains above 55db. At lower gains they seem clean and flat from 15Hz to 30Khz on my scope up to 27 volts out where they start to clip. WOW 30+db!! Wish I had a distortion analyzer. Has any one else
had a chance to play with theirs? Would like to know your findings!

Do your cards have an 1731 opamp ? Recently, there's been some threads about the stability of cloned 1731-opamps, but now it looks like the original situation isn't stable either. But... AML-27 card with a small resistor gives the more gain, right ? Very strange you get stablity problems at higher gains, unless the layout is not good.

If it's fully related to the design one would expect more problems w.r.t. stability at lower gains (higher valued gain setting resistor).

Well, likely we have two different instabilities here.

Regards,

Peter