1176LN mnats board - wiring up step by step

Hi all,
as a newbye there are a lot of things I'd like to know.
First of all, thanks to all people that give so many contributes to realize good limiters with their precious indication.

Before starting up with this project, I've red a lot of topics. It seems that there is not a "common way" for all, it depends on what type of board you use, what kinda transistors you mount on that, what type of signal transformer you choose - and so on and on.
I'm coming from a little experience of LF electronic (I realized little mixers, little amplifiers, easy projects BTW).

Anyway, this topic's going not only to help me if you wanna, but I believe it will contain some useful informations for ALL people that intends starting this wonderful project... so I'm going to post little pictures about my increasing work.

I bought three chassis from www.proelgroup.com: its name, if you like this box, is SCA2ARACK. (please note my ultra-satisfied face )






I received from mnats a couple of his wonderful boards rev J. I ordered from Mouser and Digikey using his BOM and... go!
(mnats parts list: http://www.geocities.com/m_natsume/1176_bom.html)
After half an hour I damaged the boards. I used to handle a 40W soldier (really too much) and did a disaster.

Mnats sent me a couple of previous boards, rev H. I try again with a little soldier of 15W. All appears to be ok.
In mnats rev H board, the input transformer doesn't fit at all with the place of resistor R*. I had to solder this resistor UNDER the board. See this image:



Now, PANIC. I'd like to know what else I have to do.
- In this project I used both input and output transformer, as you can see, and i used for R* and R*1 a value of 12K. ("as lundahl suggests"). Is it right?

- I didn't put: C*1, C*2, C*3, C* and all the optional components of 'input balanced' option (IC2, C30, C31, C32, C33, C34, C35, C100, C101, R1A, R1B, R1C, R1D, R1E, R3, R4). Is it right?

- I measured the voltage. The board returns me not +30 and -10, but +34.7 and -11. Is something going wrong?

- Trim pots R55 and R81 are 2K2 instead of 2K. It's the same?

- The condenser C16 of 33pF is considered "legacy item". I put it on the board for an error. Have I to remove it?

For now I stop with this questions... is this project ready for wiring up?
I'll update, for all, the pictures showing this work step-by-step.

Thanks to all that can help :wink:


maalexx

[quote author="maalexx"]In this project I used both input and output transformer, as you can see, and i used for R* and R*1 a value of 12K. ("as lundahl suggests"). Is it right?[/quote]

I think so

[quote author="maalexx"]I didn't put: C*1, C*2, C*3, C* and all the optional components of 'input balanced' option (IC2, C30, C31, C32, C33, C34, C35, C100, C101, R1A, R1B, R1C, R1D, R1E, R3, R4). Is it right?[/quote]

Yes

[quote author="maalexx"]I measured the voltage. The board returns me not +30 and -10, but +34.7 and -11. Is something going wrong?[/quote]

You shouldn't be out much more than less than one volt. +4.7 sounds very high. Suggest you check over the psu section of the board very carefully before firing it up and make sure it is spot on. Have you checked the voltages on the transistors? This could be a useful cross-reference to do, to check whether your voltages are ok. (the long G1176 build thread has details on what transistor voltages you should be getting)

[quote author="maalexx"]Trim pots R55 and R81 are 2K2 instead of 2K. It's the same?[/quote]

I've used 2k2 and it works fine.

[quote author="maalexx"]The condenser C16 of 33pF is considered "legacy item". I put it on the board for an error. Have I to remove it?[/quote]

Don't think so - from memory it doesn't do anything in or out.

FYI - next time post in the long G1176 build thread - better way to help create the knowledge base. You'll also find your questions have probably been answered there before :wink:

Thank you very much. +4.7 ... really too much.
My board, as you can see from the picture, is entirely stuffed with all components... is it dangerous now feed the circuit to measure the single voltages on the transistors?

In the while, I drilled the basement of the rack box. I put in it the toroidal transformer and the pcb. Look at this.

Hi maalexx!

I got your PM about high voltages on PS outputs. I though it best to post my reply in this thread in case someone else may be having the same problem.

Positive power supply consists of the IC 7824, which is a three-pin 24V regulator, and resistors R87 and R89 (used to set the output voltage to 30V). If you are getting 34V at the output, the problem may be incorrect R87 and R89 values, which should be 1100 and 220 ohms, respectively. So, you may wish to check the values of these two resistors first.

Next, try shorting the R89 with a tiny piece of wire to see if the IC 7824 is OK. If the output voltage decreases to 24V, the IC 7824 is fine. Make sure that no part of the heatsink comes in contact with any part of the PCB because the heatsink should be on a positive potential.

Negative power supply is determined by the series resistors R85 and R86 and the Zener diode 1N4740 (10V). If the voltage on the diode is -11V, this may indicate that the diode is not working properly or that the values of R85 and R86 are less than 1kohm. If the latter is the case, the diode will heat too much. However, even with -11V on the diode the compressor should work just fine, IMO.

Regards,
Milan

I just checked.

R87 is 1K1 (1W 5%), R89 220ohms, R85 and R86 are 1K. If I short R89i HAVE 24V...

In the transformer, from CENTER TAP to either LEFT TAP or RIGHT TAP the voltage is 27.7 / 28VAC, with the transformer disconnected from the board. From LEFT TAP to RIGHT TAP the voltage is 56.2VAC...

What do i do? Am I going to connect the pcb as well?

Transformer ratings are OK.

Could you please check voltages on R89 and R87?

Moamps,
do you mean "connect the transformer to the board"? My worry is to damage some components if there's something wrong.

But if you say me that i can connect... I'm going to do this just now


maalexx

Sooner or later you'll have to connect the transformer to the board. In my experience, 34V (or -11V for that matter) can do nothing to damage the compressor. Besides, all parts of the compressor except the audio transformers (which cannot be blown up), are dirt cheap so no worries there.

Do it tomorrow, though. It's way too late in this part of the world to be messin' with that sort of thing right now. :wink:

Regards,
Milan