Building Purple MC76 - troubles and solutions

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Purusha

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1. I can't figure out how to solder the round input transformer and if I need to connect any wires to the 6,8 place next to it.

altran.jpg




2. Is this the right way to jump the connectors to get 230V?

VAC.jpg




3. I can't find the place for the 22nF cap anywhere on the board. It's marked as C27 on the paper ... anyone.
 
C27 is point to point, fixed to the back of the Attack Pot in parallel with a 470R
 
Regarding the Input transformer, looks to me like the board will accept both PCB pin type, and also a trafo with coloured leads. It would be interesting to see the back of the board at that point.. and the relationship between points 1, 5 7 & 8 any chance of a pic? ;)
 
Cool, looks like you just solder in straight in, the traces on the back act as the wires from the T-attenuator +/- (point 1-5) in and out of the trafo to point 6 and 8

Also..Is the orientation of the trafo marked in any way?
 
Mmmm.. That might be Trafo Pin 7 that goes to the Mu Metal Can..

The Black dot near the 'Altran logo' should indicate Pin 1, how does that figure?
 
From another thread:

Q: I'm building a pair of mc77s with Altran c-3837-1 input transformers provided in the kit from Purple Audio. I have two questions:

1. I installed the transformer so the black dot on the label is above pin 1 on the pcb. Is this correct orientation?

A: yes the black dot indicates pin 1.

sorted! :)
 
hey Ed!

I read here that the original input transformer UTC 0-12 was wired 500:200 stepdown.
http://www.groupdiy.com/FORUM/viewtopic.php?t=5581&highlight=mc76&sid=fe7cd14e1855d956b9e22f866a458d62

When I measured my Altran c-3837 for resistances I found it to be marked pin one with the dot, a step up transformer copy of the UTC 0-12. If we put the Altran in with pin one matching pin one with the MC77 board numbering, matching #1 to #1, then wouldn't it then be a step up input (200:500) rather than a step down input?
 
[quote author="Purusha"]OK, now I need to solve only the second dilemma

VAC.jpg
[/quote]
Take a look at the traces on the back. In one position (115V) they should make the primary wiondings parallel. In the other (230V) they should make them series.

Your red-line assumptions are probably correct, but it's a simple matter for you to confirm them yourself by following the traces on the other side of the board.

Keith
 
Could that be 115v setting!!?? and the top blue link makes the series connection for 230v??? (Red lines the opposite way)
 
Could that be 115v setting!!??
It would appear so... -unless there's been some confusion when inverting the board to have a look!

Hmmm..

Well you know what I did?

I just wired mine in parallel (115V) and never took the AC to the PCB.

I suggest you just wire yours in series and don't take it to the PCB. -I mean there's no benefit to it anyway, since you plainly don't intend to wire up the 115/230 switch, -right?

Keith
 
The suggested part number is: Digikey CKC3001 maybe look at the data sheet, but my vibe is: make the Red links from center to top for 230v operation.

Maybe also make a pic of the back section of the Board at this point, just to double check.

I'm planning to skip this switch also :) so eager for conformation.
 
Follow the schematic with reference to your pic, looks as if your photo is wired 115v.
 
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!
 
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