[BUILD] 1176LN Rev D DIY

[PeterL]

In76d, Hank, thanks for taking the time out to help me. I'm going to take new measurements this afternoon after work. The way I had it hooked up when it worked a couple months ago is the way it is in the picture I posted, with red and orange tied together for center tap with black and yellow on either side. But it stopped working and has not worked since, with questionable voltage readings from the secondaries. I'll post in a few hours what I find.

 

[ln76d]

In76d, Hank, thanks for taking the time out to help me. I'm going to take new measurements this afternoon after work. The way I had it hooked up when it worked a couple months ago is the way it is in the picture I posted, with red and orange tied together for center tap with black and yellow on either side. But it stopped working and has not worked since, with questionable voltage readings from the secondaries. I'll post in a few hours what I find.

If you have same markings on transformer like those from the photo - you really connected it bad.
Maybe this could work, but it's really weird connection. It's parallel connection with center tap, so i truly don't know how this could work, but in usual parallel connection without center tap you should get only one 25V but with higher current. With center tap? I don't know...
You should have double 25V with center tap, to correct working.
Center tap means - zero with zero.
First  measure secondary windings as i described - it will tell you what's the condition of transformer.

 

[Hank Dussen]

If you have same markings on transformer like those from the photo - you really connected it bad.
Maybe this could work, but it's really weird connection. It's parallel connection with center tap, so i truly don't know how this could work, but in usual parallel connection without center tap you should get only one 25V but with higher current. With center tap? I don't know...
You should have double 25V with center tap, to correct working.
Center tap means - zero with zero.
First  measure secondary windings as i described - it will tell you what's the condition of transformer.

I really don't think centre tap means you have to connect 'zero to zero'. In fact this is AC, so there is no 0 and 25V. There is just 25V between them. You should connect the 2 secondaries so they become '1 big secondary' with a centre tap in the middle. So you should connect the ending of the first secondary (= no dot = red) to the beginning of the next secondary (= dot = orange).
This is the way I've done it with all of my PSU's and I've never had a problem with them...

 

[ln76d]

Maybe you have right...
I've asked once manufacturer of toroids, where i've always ordered transformers, about center tap connection. Does it not matter which wires will be put together for center tap. He told me that it should be connection only on windings marked as zero.

 

[ln76d]

Or maybe you're wrong... again  ;D

I found an article, where's described as i thinking earlier.

"If the transformer is a 110V input with two 12V outputs, you can connect the two secondary coils in series to get 24 volts out, or you can connect them in parallel to get 12V out.  You have to be careful to connect the right ends of the two secondary coils in both the series and in the parallel connections.  If you reverse the connections, you will get 0 volts out because the two voltages will cancel each other out."

http://jacobs-online.biz/understanding_transformers.htm

This is from mnats site:

"Identify the two "0V (centre tap)" wires coming from the power transformer secondary. Twist them lightly together and secure them in the middle terminal of the terminal strip. Now take the two remaining secondary wires and attach them to either end of the terminal strip. The order of the top and bottom wires is unimportant. Just make absolutely sure you have tied the two "0V (centre tap)" wires together as indicated in Mr. Burnley's illustration"

 

[Harpo]

ln76d, get rid of the idea, each transformer winding comes with a 0V wire end.
A transformer transforms an applied AC voltage in to an AC voltage out at a specific ratio. The dots at the transformers schematic symbol indicate, which wire is the in-phase/hot end of a primary and secondary windings end in respect to its other side for the same snapshot moment in time. This 0V or 25VRMS at the transformer drawing is only another way of indicating where the in- or out-of-phase winding end is located. Its a point of reference for measuring the floating voltage across this winding for the moment when the amplitude of AC mains is at maxRMS in respect to the other windings end. This will be different or just the other way round again, depending on the snapshot moment of your local 50 or 60Hz AC cycle. When both of your secondary windings (2*25V) have the same primary:secondary ratio (115V+115V:25V+25V or 1+1:0.2174+0.2174 turns ratio) and you connect these secondary windings in series in their correct orientation, this will make these combined windings behave as a single secondary winding (115V+115V:50V or 1+1:0.4348 turns ratio) with a single in-phase/hot end at one side, an out-of-phase/cold end at the opposite combined winding side and a center tap in the middle of both combined windings.
For the Avel Lindberg transformer in question you would either have red+orange joined for the secondary center tap, as shown on the manufacturers site,  or yellow+black joined for the secondary center tap. Always assume transformers of other manufacturers might come with a different colour coding.

 

[PeterL]

Hey guys, I had a few things to take care I at home yeaterday so I did not get to test any voltages but I heard from a nice guy not far away who is willing to try to fix these for me. I don't know as much as you guys do, so I'm goin to hand them of to him. I can post what he finds if you are interested.

Thank you everyone who took the time to try to help me fix this problem.

 

[ln76d]

I think your only problem with compressor is bad connection of secondary windings You should try as i described this it's simple.

 

[ln76d]

For the Avel Lindberg transformer in question you would either have red+orange joined for the secondary center tap, as shown on the manufacturers site,  or yellow+black joined for the secondary center tap.

Yeah, ok, fine. So if we have in phase and out phase windings, it will be no problem join "0V" with "25V" to make center tap?

I understand, that we can make center tap from joined two "0V" windings and from joined two "25V" with phase changed.

Always assume transformers of other manufacturers might come with a different colour coding.

Yes it's obvious, but we writing about Avel Lindberg Y236106.
I base on the photo from forum, where the colour of the individual windings are specified.

 

[PeterL]

I just tried to measure voltage a moment ago, just to see.

With no load and black and orange 0v from secondary in the middle tied together, I read 85vAC and the same for yellow and red.

With no load and orange and red tied together in the middle, I read 85vAC across all three like above.

 

[number2]

Q13 is a problem: I read -1.7 VDC on the top pin. (board oriented with mnats logo in bottom left corner)

[these are  npn's so I guess that is the emitter because the typical voltage schematic reads -1.63vdc and it's the arrow pointing away?]

I get +11.11 vdc on the center pin. (is that the base?)

and on the bottom pin I get -0.9 vdc (or is this the base b/c the schematic says the base is -1.04 vdc and the collector should be +9.75 vdc?)
I'm also getting the same +11 vdc on both ends of R74 which I was told was no good.

what do I do?

 

[Echo North]

Q13 is a problem: I read -1.7 VDC on the top pin. (board oriented with mnats logo in bottom left corner)

[these are  npn's so I guess that is the emitter because the typical voltage schematic reads -1.63vdc and it's the arrow pointing away?]

I get +11.11 vdc on the center pin. (is that the base?)

and on the bottom pin I get -0.9 vdc (or is this the base b/c the schematic says the base is -1.04 vdc and the collector should be +9.75 vdc?)
I'm also getting the same +11 vdc on both ends of R74 which I was told was no good.

what do I do?

Start by downloading the datasheet for the transistor and confirm the pin configuration:
http://www.centralsemi.com/PDFs/products/2n3707-3711.pdf

Seems like your voltages may be ok.  Look at the schematic with V added:
http://mnats.net/files/1176REVD_VOLTS.pdf

See R74? Voltage is simular on both sides.  In fact the EBC of Q12 and Q 13 should be similar.

Mike

 

[mitsos]

hey guys,

got one little thing bothering me on mine.  It's the same dual channel unit I posted about a couple weeks ago, using rotary switches, with ratios 2,4,12,20, ALL.  Both calibrate fine.  The left channel apparently works in all ratios, and the right channel works OK in 2:1, 4:1, 12:1,  but on 20:1 and ALL the meter stops working.  I'm not using the mnats rotary meter PCB, I wired the meter like in the schematic (+4,+8,GR) using a 2-pole Lorlin switch (soldered the two resistors to the switch.

I compared the ratio boards, they look the same to me, maybe someone has some insights at where I should look next for issues??

thanks 2 all!

 

[Rob Flinn]

Bit of an issue here with a rev D,  that is causing me much hair loss.

The unit is working but I'm experiencing some distortion as compression starts happening.  Basically if you look at the attached scope trace of a square wave I'm feeding the unit, all is ok until compression starts happening when the waveform developes the spike on the bottom leading edge, which increases the more compression is happening.    I'm tearing my hair out on this one.

Any ideas ?

 

[Echo North]

Bit of an issue here with a rev D,  that is causing me much hair loss.

The unit is working but I'm experiencing some distortion as compression starts happening.  Basically if you look at the attached scope trace of a square wave I'm feeding the unit, all is ok until compression starts happening when the waveform developes the spike on the bottom leading edge, which increases the more compression is happening.    I'm tearing my hair out on this one.

Any ideas ?

First thought would be a bad GR FET or qbias issue.  What is your DC at the GR FET gate?

The unit is fine in GR off mode?

 

[Echo North]

Also maybe check your AC at pad 22 in each ratio position and your DC at pad 21 in each ratio position.  See if those are are odd.

 

[Rob Flinn]

fet gate is at -1.27v & yes fine in bypass & before compression.

 

[Echo North]

Check those pads.  I don't have the exact values on hand but they are controlled by two different voltage dividers on ratio switch.  Pad 22 should be a fraction of whatever is on the - side of C7.  So if the signal is 1VAC there you'll see that get smaller as you move from 20-4 on the switch.  Same with 21 except you start with -10VDC and decrease.

If these are out of whack it could cause saturation at your FET.

 

[Rob Flinn]

I do seem to be getting the signal getting smaller on both pad 21 & 22.  Pad 21 starts at about -7.5 with full on compression.  Pad 22 starts about 1v pk2pk.  These values change until there is nothing when there is no compression.

 

[Echo North]

I do seem to be getting the signal getting smaller on both pad 21 & 22.  Pad 21 starts at about -7.5 with full on compression.  Pad 22 starts about 1v pk2pk.  These values change until there is nothing when there is no compression.

More concerned with the DC at pad 21.  This sets the threshold.  What are you DC readings at pad 21 in each position?  Shouldn't matter if GR is on or not.  No signal.