All things G1176 - the new "repost" thread.

[Brown Note]

Oops! I had neglected to connect the two primaries (pins 8 and 9) on the Edcor. I'm surprised the thing passed a signal at all the way I had it hooked up. We are now fully operational.

Thanks again. I love this place.

 

[lofi]

How did your build go? any pit falls. just waiting for the postman to come a knocking and im all over this

Iain

 

[MartyMart]

Just finished my mnats 1176 in a "Tat" case and it works, though calibration
has not been done at this point.
I have no issues with noise, just a slight distortion when the input is cranked
passed 1 o'clock - the calibration setup for the fet should solve this.
My question is two fold :
1 - The ratio switch has 6 positions but there's only 4 in the documentation
and on the case "legend" , what are the other two positions ?
The last ( furthest round to the right ) seems like a total clean bypass !!
Between the 20.1 ratio and fifth position, the unit "cuts output" and slowly
raises back to normal operation - sounds like it's still at the 20.1 ratio.

2 - My 24-0-24 toroid produces about 29.5v AC at the board, my board
voltages are almost correct for 30v ( I have 30.9 ) and -10v ( I have -10.3 )
however the regulator, though heat-sinked is running quite hot, as in almost too
hot to touch the heat-sink !!
Any thoughts on this would be great, I'm almost there and VERY pleased
that it seems to work correctly even pre- calibration :grin:

Marty.

 

[lofi]

[quote author="MartyMart"]
1 - The ratio switch has 6 positions but there's only 4 in the documentation
and on the case "legend" , what are the other two positions ?
The last ( furthest round to the right ) seems like a total clean bypass !!
Between the 20.1 ratio and fifth position, the unit "cuts output" and slowly
raises back to normal operation - sounds like it's still at the 20.1 ratio.
Marty.[/quote]

i think the case should have 4, 8, 12, 20 & all on it, so pos 5 would be the Nuke, all buttons in, squash the crap out of it, position 6 i assumed was because 5 positions switches arnt readily available

 

[buschfsu]

ok so ive checked the psu check points on the pcb and get -9.7v and 30.23v but once i power up R36 burns up quickly. ive resoldered Q7 and Q8 and looked for bridges shorts, any idea what would cause it to burn up??


found some direction on page 44

R36 burns if there's shorts, wrong resistors or transistors, or wrongly oriented (or failed) transistors.

 

[gswan]

Check the orientation of Q8 and Q9.

 

[buschfsu]

I will never put another transistor into a pcb without double checking the pinout on the datasheet

I will never put another transistor into a pcb without double checking the pinout on the datasheet

I will never put another transistor into a pcb without double checking the pinout on the datasheet


any way to find out if i damaged upstream transistors without replacing them. when i took out q8 and q9 i checked HFe and it seemed ok so i put them back the correct way.

 

[gswan]

It's unlikely that anything upstream was damaged by incorrect insertion of Q8 and Q9. These provide the drive for the transformer.

 

[sonores]

Hello!

I have search and read this forum for days now, I haven't found anything that could help me with my problem.

The Problem: I have a lot of hum, noise and no compression!!

I'm building a Dual 1176 using Mnats rev J + PSU. When i fired it up for the first time R40 & R41 started to burn, I saw that i had forgot CR1 and CR2 so I put them in and replaced the resistors. I have also replaced Q8 and Q9. Checked the voltages and they look OK according to Gyraf's schematic...btw how much can the voltages varies? some components vary like 0,2-0,5V up in the signal line amp area. I have calibrated the PSU, but after ca 10 min it's down to 29,7V. The negative side doesn't change.

It's working as a signal amp, when the Outpot is OFF it's quite much hum, when I turn it up a lot of noise comes in.....no compression what so ever. I have not calibrated it yet. The meter only moves in GR-mode.

I have checked all wireing, checked soldering....What should I do?

Help please!

 

[gswan]

Solve the hum problem first. Turn off compression and start signal tracing through the unit.

Do both channels have hum? At around the same level? If so then start with your power supply. Check that the noise and ripple on the 30V rail is acceptable. Maybe you have adud cap in there (or reversed).

Then check your grounding configuration, making sure that the PSU ground and signal ground are connected at one point only, usually at the output socket.

You say that there's hum when the output is turned down, so it's appearing somewhere in the output amp circuitry. It could be PSU, it could be grounding. You'll need to check carefully.

Then start looking at the noise problem. It appears to be coming from an earlier stage. Does it happen with the input pot turned down? Is it in both channels? What type of 'noise' is it? Isolate where that's coming from and fix it. Leave compression off when you do this.

Next you can examine the compression problem (is it still exists). You may find that solving the other problems fixes the lack of compression problem.

 

[buschfsu]

back at it with my mnats board. (opamp input) i don't get any audio out so i traced a sign wave with my scope and after the base and emmitter of Q2 the signal goes isn't visible on Q3. I replaced Q2 and 3 and still nothing. any advice on what i should see while tracing? the signal drops orders of magnatude in voltage after R6 but i assume thats normal. DC voltages are all a bit high also.

thanks

 

[gswan]

Perhaps you should show us your DC steady state voltages first.

I'd expect to see the signal on the collector of Q2 and again on the collector of Q3. Remove the FET if the signal 'drops orders of magnitude after R6'. It is likely your FET is conducting and attenuating the signal. Also check the value of R8 and orientation of C2. Remove the FET and check right through your signal path. Then you can start looking at the GR amp.

 

[sonores]

The ground connections are....incoming 220 ground to chassis, ground from XLR 1 (optional in) PIN 1 to chassis. That's all...

On the list of components for the PSU it says that C3, C4 should be monolythic 100n caps...The guy at the store had never heard of it so he got me tantalum instead...is that a problem?

 

[gswan]

Interesting grounding scheme.
Mains ground to chassis is OK. The PSU 0V to gnd I would do at the power supply, not the input connector.

Monolithic ceramic caps are plentiful, you should have no problem finding them. Tantalums are probably OK, but make sure you have the correct voltage rating and do not reverse-polarize them.

 

[sonores]

I have not ground the psu...but if a measure 0V on the psu and the chassis is says 0.1-0.3 Ohm so i figured it gets ground thru the mainboards.
It's the mainboards XLR input that is grounded to chassis as Mnats says on this link....scroll down a little
http://www.geocities.com/m_natsume/1176-wiring.html

But i try an switch those caps and see what happens....thank you!

 

[gswan]

[quote author="sonores"]I have not ground the psu...but if a measure 0V on the psu and the chassis is says 0.1-0.3 Ohm so i figured it gets ground thru the mainboards. [/quote]

That's how you get hum, ground currents causing potential differences where you don't want them!

 

[sonores]

But when I wire from PSU 0 output to incoming 220 gnd or chassis it's start humming like crazy....When I place the shielded input cable over the trafo the humming increase, when i place it on the side it decrease. could the trafo wireing couse trouble. it's wired like this.

I ----------red *start of secondary windings
I (24V)
I ----------yellow

I ----------blue *start of secondary windings
I (24V)
I ----------grey

PSU:
AC-grey
CT-yellow/blue
AC-red

 

[gswan]

Then you've probably got loops from other inadvertant connections to the chassis.
The transformer wiring is OK, you are creating a 'centre tap' connecting the yellow/blue wires together.

If you can change the amplitude of the hum by moving the wires around then you've got a lot of induced noise as well. Modify your internal layout to move the input wiring well away from the transformer, and move the transformer well away from any audio signal cabling.

 

[buschfsu]

ok i removed fets and get these
DC votages C B E
Q1 out out out
Q2 1.78 1.21 0.52
Q3 23v 1.54 0.92
Q4 30.25 12.1 11.67
Q5 -28.5 -4.97 3.07
Q6 -13.61 -28.53 29.11
Q7 9.5 20.88 29.74
Q8 30.23 13.61 13
Q9 1mv 12.3 12.92
Q10 out out out

should i measure again with fets in or is this a good place to start?

 

[gswan]

[quote author="buschfsu"]ok i removed fets and get these
DC votages C B E
Q1 out out out
Q2 1.78 1.21 0.52
Q3 23v 1.54 0.92
Q4 30.25 12.1 11.67
Q5 -28.5 -4.97 3.07
Q6 -13.61 -28.53 29.11
Q7 9.5 20.88 29.74
Q8 30.23 13.61 13
Q9 1mv 12.3 12.92
Q10 out out out

should i measure again with fets in or is this a good place to start?[/quote]

It's a good starting place, since a few things look wrong here.
Q2: Vbe seems a little high.
Q3: Vc should be about 12V. R18 is probably wrong.
Q5: Your measurements are wrong here. You should not have a -30V rail anywhere. Vbe is completely wrong. Check your resistor values.
Q6: Measurements are wrong.
Q7: Vbe way out. Vc should be around 14V. The B of Q8 is connected to the C of Q7 and Q6, so they should all read the same. Yours don't.
Q9: Vb and Ve about 0.4V low. Check again after fixing the other problems.