Purusha

Building Purple MC76 - troubles and solutions
« Reply #20 on: December 01, 2006, 09:17:52 PM »
OK, thanks. Will try like you said.
Regards as always, Purusha


Family Hoof

Building Purple MC76 - troubles and solutions
« Reply #21 on: December 03, 2006, 02:50:40 AM »
RE: input transformer

Yes, it's 500:200 ohms. That was accounted for.

Pin 7 is tied to the can externally, as you can see, and the silk screen shows that pin 7 belongs in the row of holes on the right side. Pin 1, indicated by a dot on the label, then ends up in the upper left, just like the silk screen shows. Trust the silkscreen!

hitchhiker

Building Purple MC76 - troubles and solutions
« Reply #22 on: December 03, 2006, 01:14:44 PM »
Thanks Hoof!   So right you are.  I must have got things flipped around when I was measuring the transformer.

sintech

Building Purple MC76 - troubles and solutions
« Reply #23 on: December 06, 2006, 06:18:33 PM »
Bump! regarding the bridging of jumpers for 240v operation, I don't even have my kits yet.. but I still want to know the answer!! hehehe Maybe Ed can confirm this finally. :thumb:

Purusha

Building Purple MC76 - troubles and solutions
« Reply #24 on: January 21, 2007, 07:42:53 PM »
I am still wondering how to connect the torroid to 220VDC without going to
the board and using one of those



Can someone tell me how they work? I couldn't find any schematics of the
switch. Can someone make a simple drawing of how the switch works? The
 rest I can figure out on my own.
Regards as always, Purusha

Purusha

Building Purple MC76 - troubles and solutions
« Reply #25 on: January 21, 2007, 07:46:33 PM »
Quote from: "hitchhiker"
Purusha!  I did the same as Keith, and didn't take the ac to the pcb.  

For 220v primary I figure the split primary is wired in series. I think the primary hook up would be the orange and yellow wires tied and the white and black to the 220v ac . Hook the transformer up that way and measure the secondary voltage.  Mock up a switch affair to confirm the pcb makes the same result . If all checks out you are good to go!


I also think this is the way to go but would be nice to see how the switch works.
Regards as always, Purusha

sintech

Building Purple MC76 - troubles and solutions
« Reply #26 on: January 22, 2007, 04:33:48 AM »
Quote
   
hitchhiker wrote:
Purusha! I did the same as Keith, and didn't take the ac to the pcb.

For 220v primary I figure the split primary is wired in series. I think the primary hook up would be the orange and yellow wires tied and the white and black to the 220v ac . Hook the transformer up that way and measure the secondary voltage. Mock up a switch affair to confirm the pcb makes the same result . If all checks out you are good to go!


I also think this is the way to go but would be nice to see how the switch works


To tie Orange and Yellow wires, the center pads must link to the top pads.

I'm thinking..would this be safer to feed 120v AC (from my 240->115v converter) into the unit firstly just to be sure? and what damage could be done feeding 220-30v in the 115v switch setting?

Building Purple MC76 - troubles and solutions
« Reply #27 on: January 22, 2007, 05:50:17 AM »
Well if you feed 230V into both of the 115V windings seperatly (means that every single 115V winding is seeing 230V) then the transformer should blow up. Some years ago i worked on a project at 3 am and was really tired so i wired up the transformer that way and the result was that i had to buy a new transformer as the old one was totally destroyed.

Flo

Purusha

Building Purple MC76 - troubles and solutions
« Reply #28 on: January 22, 2007, 05:58:21 AM »
:shock:  :shock:  :shock:  

OK, I don't want to be the one who will try this first  :green:
Regards as always, Purusha

sintech

Building Purple MC76 - troubles and solutions
« Reply #29 on: January 23, 2007, 09:16:38 AM »


Ok. I was able to feed the unit firstly 115v via an adapter and test both options:
 
Jumpers up gave 20-0-20v AC Jumpers down gave 39-0-39v AC

Therefore Jumpers up as suspected gives 39-0-39v AC under 230v mains


Purusha

Building Purple MC76 - troubles and solutions
« Reply #30 on: January 28, 2007, 04:17:52 AM »
I have one question for the experts here  :thumb:

I couldn't get the 1N4936 fast rectifiers for the Purples but I got ultra fast ones UF5404
which have same specs but they are ultra fast. Can I use these instead?
They come in the PSU section.
Regards as always, Purusha

Purusha

Building Purple MC76 - troubles and solutions
« Reply #31 on: February 12, 2007, 07:38:29 PM »
OK, next question regarding the MC76 DIY  :roll:

Does anyone know how to hook up the T-pad attenuator (input) to the PCB?



This is the last thing I need to wire and I am done   :thumb:
Regards as always, Purusha

Purusha

Building Purple MC76 - troubles and solutions
« Reply #32 on: February 13, 2007, 06:10:04 PM »
OK, the T-pad wiring is solved.

BTW, anyone remembers the value of drop voltage resistor used for wiring the 12V meter bulb?  :green:
Regards as always, Purusha

khstudio

Building Purple MC76 - troubles and solutions
« Reply #33 on: April 14, 2007, 03:07:24 PM »
What is the deal with R44 :?:

It says (T&C) ~1k on the schematic but calls for a 2k trimmer on the PCB :roll:

In the "Calibration instructions" it says to disconect for one of the measurments.

I have already installed the 2k trimmer but there are not enough detailed instructions about the 2k trimmer.

Please Help! :sad:
Kevin ~ KHStudio

JdJ

Building Purple MC76 - troubles and solutions
« Reply #34 on: April 14, 2007, 04:05:19 PM »
R44 in the rev D Mnats schematic is a 2K trimmer used to tweak the meter tracking.  In Mako's notes for the Rev D he says to leave R44 off the board until you have calibrated the meter circuit according to the 1176 service manual on the JBL site.

Hope it helps-

Josh

edanderson

Building Purple MC76 - troubles and solutions
« Reply #35 on: April 14, 2007, 04:18:23 PM »
on the MC77 PCB R44 is both a 2k trimmer and a 100ohm resistor.  read the calibration instructions - you are supposed to make R44 be some value around 1k.  you've already put in the trimmer.  you can connect or disconnect the trimmer by installing or removing the 100ohm resistor.

read the calibration instructions, look at the PCB, look at the schematic, and most importantly... think about it.  i'm sure you can work it out.

i'm not going to answer any questions about it.

ed

khstudio

Building Purple MC76 - troubles and solutions
« Reply #36 on: April 14, 2007, 08:14:04 PM »
Quote from: "JdJ"
R44 in the rev D Mnats schematic is a 2K trimmer used to tweak the meter tracking.  In Mako's notes for the Rev D he says to leave R44 off the board until you have calibrated the meter circuit according to the 1176 service manual on the JBL site.

Hope it helps-

Josh


Thanks man :thumb:
Kevin ~ KHStudio

khstudio

Building Purple MC76 - troubles and solutions
« Reply #37 on: April 14, 2007, 08:18:43 PM »
Could one of you guys tell me if your 600 ohm T-Attn (3 Deck) feels smooth.

Mine is not right :sad:

From about 8:00 to 12:00 it feels stuck and not smooth at all!

I tried to contact Andrew but it's the weekend... I hope he will replace it. It's a very important & expensive part of the KIT.
Kevin ~ KHStudio

sintech

Building Purple MC76 - troubles and solutions
« Reply #38 on: April 15, 2007, 04:14:23 AM »
I also have the newer style 3 deck T-Pads, they all feel like silk with a very smooth rotation and very little resistance.

dissonantstring

Building Purple MC76 - troubles and solutions
« Reply #39 on: September 25, 2007, 03:21:04 PM »
hi everyone,
i've hooked up my PSU section on my MC76 kit and i've taken measurements and everything seems o.k. as far as voltages (-10.71VDC and +30.43VDC), but a strange things occurs after a few minutes of the unit being on.  the positive voltage measured off the zener stud diode starts to creep up slowly.
after about 5 minutes or so it went up to about 33VDC.  negative rail is stable.

is this normal?  is this a bad thing?
as I have no experience with this type of zener, i'm really sorry for this  newb question

i didn't really want to leave the unit on for too long thinking it was going to continue to creep up.  any insight to this would be greatly appreciated.
-grant


 

Related Topics

  Subject / Started by Replies Last post
2 Replies
1888 Views
Last post September 23, 2005, 11:14:20 AM
by edanderson
5 Replies
2922 Views
Last post January 19, 2006, 09:25:13 PM
by edanderson
73 Replies
31267 Views
Last post October 22, 2006, 12:41:09 PM
by hitchhiker
17 Replies
5746 Views
Last post December 16, 2006, 11:11:32 AM
by TomWaterman