Melcor 1731 PCBs.. Where we left off....

[fum]

Just a post to ask how many people have them up an running? I'm just starting to test a couple of mine, and am not getting signal through yet ( built two of them, they're both doing the same thing at present)

am going back over the parts layout at present, making sure I stuffed correctly.

regards

ju

 

[Tekay]

The pcb sockets works fine for Neve BA boards to, I use the knurled gold version for my pcb's that takes original BA boards!
The catalogue says 1,8mm and a 2mm drillbit works fine!

I'll ask Farnell for a for a sample of the pins!

 

[tony dB]

concerning the pins, i wouldn't mind sharing an order with any of you...
the minimum quantity at my local electronicstore was 500 and a long time before delivery...

Tony

 

[Flatpicker]

[quote author="fum"]Just a post to ask how many people have them up an running? I'm just starting to test a couple of mine, and am not getting signal through...[/quote]No, but I'm real curious as to why yours isn't working. Check all DC voltages and then try tracing the signal from input to output. Keep us posted!

 

[fum]

Well, let's start with my test setup, to make sure I'm not doin something dumb =).

So I built a pair of 325(thanks Peter P!) cards:

http://www.shinybox.com/diy/325.jpg

I wired up an edge connector so that I've a 25K pot across pins 7&8 ( gain trim, I believe it should be a reverse taper, but for testing, I can remember to turn it the other way =) ), and a balanced signal feeding pins 4 (-) and 5(+). I'm using a +/- 18V supply.

Since I don't have a great balanced source on my test bench, I'm using a bass plugged into a passive DI box ( which is a 50K: 600 ohm transformer). Not an optimal setup, but should at least get a signal through.

output is going to the balanced in of a mixer, hooked up to some speakers so I can hear the noise. =)

So the 325 card should be running in differential mode. Presently, it's running in silent mode =)

Will start checkin voltages, and will post results as I go. If anyone sees anything glaring in what I've stated above, give a shout =)

Regards

ju

 

[peter purpose]

Ju.. Have you tied pin 4 to pin 3 ground?

 

[fum]

Ok, well that works. Thank ya Peter.

But why does that work? :? Or why doesn't just hooking up to - work, like I've seen in regular opamp designs?

take a look at something like:

http://myweb.tiscali.co.uk/crowley/mattweb/balmicpre/balanced_preamp_v35_schematic.pdf

ju

 

[fum]

Oh, wait a tick. Looking at the 325 schematic, (-) is actually connected to gain trim, so the - of the input would need to tie to ground. makes sense.


another side note. Originally I had Q7 and Q8 in backwards. I now have one opamp with them backwards, and one with them correct. Both opamps pass audio. I'm gonna have to look at the datasheet and schematic to figure out which one is correct. =)

 

[Flatpicker]

[quote author="fum"]Or why doesn't just hooking up to - work, like I've seen in regular opamp designs?[/quote]I wouldn't call the INA103 a "regular" op-amp - it's more like an instrumentation amp. You have to wire up the gain resistors and input transformers to a 312 card just like it shows on the 312 schematic (links to that are in the META thread).

 

[fum]

ah, this is a 325 card, tho. First, build the testbed for the opamps ( 325 card), then use them in the 312 cards, and then use the 325 cards for something else =)

ju

 

[Flatpicker]

[quote author="fum"]ah, this is a 325 card, tho...[/quote]If I only had a brain, then maybe I could read...

 

[fum]

that's ok, If I would have read the schematic, I would have seen that the (-) on the opamp was connected to ground, thereby preventing this whole sequence of posts =).

I will have a followup pic in a bit, as I'm gettin crazy with the soldering iron :green:

ju

 

[fum]

Bench before this evening:

http://www.shinybox.com/diy/Melcor-before.jpg

My bench now:

http://www.shinybox.com/diy/Melcor-after.jpg

 

[Bauman]

Ha, very nice.
I see a SSL compressor with some 202 VCAs, any word on that ?

cheers!
Fabio

 

[fum]

shhhhh! you'll scare them away, and plus they go in a different thread :grin:

 

[tony dB]

do we need poly caps somewhere on the melcorboard?

remember having asked some at my suppliestore, but i don't see any in the box with goodies what returned :?

In other words, are the ceramic a real equivalent to the poly's?

 

[tony dB]

since i find it handy to have a list with parts numbered as in the schematic, i've updated Soundguy's list a little bit.

Solid State
-----------

Q1, Q2, Q5, Q6 = BC550
Q3, Q4 = BC560
Q7 = BD135/237
Q8 = BD136/238

D1, D2, D3 = 1N4148

Resistors
---------

R1 = 130K
R2 = 91
R3, R4 = 39K2
R5 = 2K
R6 = 5K6
R7, R10 = 120
R8 = 360
R9 = 18K
R11, R12 = 8.2
R13, R14 = 10

Capacitors
----------

C1 = 1000 pf polystrene or ceramic
C2, C3 = 10 pf ceramic COG or NPO
C4, C5 = .1 uf ceramic COG or NPO

 

[dukasound]

Hi
Last days I worked on pcb for Peter C´s Melcor circuits.
I exchange position of Q1 and Q2 and now they have place: face to face with flat sides.

Moby suggest me, this would be good for this pair of transistors. Also I will put some paste between and involve with ring or with a pieces of cooper solid wire.
We discuss about this because original opamps are in plastic-acril
Any comments?.
Duka

 

[Kev]

If Q1 abd Q2 benefit from being thermally coupled then it looks like a good move.

Let us know if you can find any differences in performance to the old layout and if you can measure a difference ... even better.

 

[dukasound]

[quote author="Kev"]If Q1 abd Q2 benefit from being thermally coupled then it looks like a good move.

Let us know if you can find any differences in performance to the old layout and if you can measure a difference ... even better.[/quote]

I didnt finish main circuit but this would be good theme for discussion.
Duka