Dual Mid 1084 Clone Project

[bruno2000]

I’ve always wanted a rack of 1084s, but they are really expensive!  So I decided to build my own.  Since I was building my own, I wanted more EQ control, and some more frequencies, especially in the bottom end region, so there are two mid band sections.  On the lower mid band selector, I added a Carnhill HPF inductor and the appropriate caps to enable peaking at some additional lower frequencies.  I left out the LPF entirely since in practice, I hardly ever used it.  

A am also a big fan of the 1073, so I  made the “Hi Q” switch position to match the “Q” of the 1073 (a little sharper than the 1084), getting the best of both worlds.

The rack is a Dumpster Prize (green, huh?), and the faceplates are custom 2"x7" from FPE.  The transformers, inductors, and switches came from Colin at Audio Maintenance.
Best,
Bruno2000

 

[okgb]

nice work all around
but it's not greener than me [ envy ! ]

 

[briomusic]

great project and kudos for seeing this through all on your own!
at first I thought "how does he fit all the switches in" but then I saw it's not actually 500/51x format. :
i am not sure if you are planning to release pcb files, or indeed do a run of pcbs (I am sure interest would be there, especially as a mic pre seems to be included as well), but one thing I would really like to know is the value of the "Q resistor" that you used to achieve a 1073-like bandwidth. I believe it's R51 (7k5) in the original schematic, on the PPEQN it's R17 with a choice of 2k7 or 6k8 (or anything in between).

that's quite a lot of iron colin had to send over the atlantic!

 

[Ptownkid]

wowsers....things like this are starting to motivate me to get on it this winter...but I also have a huge boat restoration project in the works so I may only get a handful of unit finished. Where the time goes I don't know.

Really, really, nice work bruno!

 

[mitsos]

that is real nice man! wish I had a couple of those!

 

[desol]

omg. That's a gorgeous frontend.

Good for you!

 

[mylesgm]

very sweet...

 

[bruno2000]

great project and kudos for seeing this through all on your own!
at first I thought "how does he fit all the switches in" but then I saw it's not actually 500/51x format. :
i am not sure if you are planning to release pcb files, or indeed do a run of pcbs (I am sure interest would be there, especially as a mic pre seems to be included as well), but one thing I would really like to know is the value of the "Q resistor" that you used to achieve a 1073-like bandwidth. I believe it's R51 (7k5) in the original schematic, on the PPEQN it's R17 with a choice of 2k7 or 6k8 (or anything in between).

that's quite a lot of iron colin had to send over the atlantic!

And quite a lot of shipping money going to FedEx!!!!
In the BA211 board circuit used in the 1073 (with no "P" terminal) the resistor setting the "Q" (from the coil "starts" to terminal E) is 2k7 ohms.  In the BA211a board circuit used in the 1084 (with the P terminal), that resistor is 6k8 (6k81).  In the 1084 the resistor switched in parallel with the 6k8 resistor when you select "Hi Q" is 7k5 ohms.  What I did was change the 7k5 ohm resistor to a 4k42 so that the resulting resistance was about 2k7 (2k68) ohms.  I checked all of the curves with "real" 1073s and 1084s and they were spot on.
Hope this answers the question!!!
Best,
Bruno2000

 

[ultra-alex]

awesome!

 

[baadc0de]

Ummm... speechless! You nailed exactly what I wanted (only with an extra mid section no less). A small format 1084 with a micpre and phantom power. Wow!

 

[grantlack]

so this just happened out loud when i saw these pics... i'll do my best to translate into stylized type:

ho-leeeeeeeee SHIT.

no joke.  pardon my "french."

 

[Soeren_DK]

Waoooooouuuuuwwww

Holy macaroni

and the crowed goes: "P-C-B", "P-C-B", "P-C-B", "P-C-B", "P-C-P", "P-C-P", "P-C-P"

Cheers
Søren

 

[Joechris]

Outstanding!!
1000 of hours must have been spend on this project.

 

[California Road]

That is a serious front end!  I would love to hear these in action. 

 

[deuc224]

Since no one has the balls to just come out and ask, i will. Are you gonna do a run for us primative people :'( look at my tears

 

[darnell]

Since no one has the balls to just come out and ask, i will. Are you gonna do a run for us primative people :'( look at my tears

Seriously, this project looks too clean to not put to the presses!!!!!

d.

 

[bpucekov]

WooooooW

 

[evilcat]

Me too ! me too ! me too !!! I want one, no, two, no, eight !!!!

 

[SIXTYNINER]

  compliments !!!
really nice "porn" eq project !
8)

 

[zayance]

Ouch.... heart my eyes