[BUILD] 1176LN Rev D DIY

bxershrts said:

My apologies for adding the separating dash in my response. These are all positive voltages.  The voltages on each side of R79 are 3.66 and 28.85 vdc. There is no negative voltage as per Base and emitter on Q12 or Source on Q11

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Right - that is a totally different scenario. Is your negative 10 volt supply (-10V) working? If so, what is the voltage at the junction of R66, R76 and R72?

bxershrts said:

The voltage differences at the base of Q12 and the source of Q11 are what led me to think a bad transistor.

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A difference between connected points in a circuit would usually indicate a poor connection between the two.

bxershrts said:

The one unit works brilliantly. I did sub a 5k pot to have more swing on the Qbias.

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You have the perfect situation to make direct comparisons between a working unit and a non-working one.

bxershrts said:

I first checked all voltages as per your schematic. I have stopped at the GR Meter Driver. This morning I moved on  As I then fed a 1k signal to the input , I checked the output to look through the rest of the circuit and I only see ( .5 volts) at the output xlr - even with the output pot all the way up. SO looks like I will have to see whats going on there too. Perhaps my first issue affects my low voltage at the output?

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Read Hairball Audio's layman's description of how the circuit works to see why your voltages in the meter section might cause low audio output.

I have measure the pcb : here are my finidings.

28.65 R87
-0.973 CR6

GR CONTROL AMP

Q7 C 14.48
        B 4.37
        E 3.81

Q8 C 28.65
        B 14.44
        E 13.85

Q9  C 16.61
        B 3.34
        E 2.76

Q10 C 28.64
          B 16.61
          E 16.04

GR METER DRIVER

Q11 D 0.600
            S 0.248
            G 0.870

Q12 C -0.435
            B 0.248
            E -0.441

Q13  C 0.576
            B -0.678
            E -0.821

SIGNAL PRE AMP

Q2 C 1.743
        B  1.002
        E 0.512

Q3  C 10.93
        B 1.742
        E 1.150

Q14  C 28.64
            B 10.94
            E 1034

SIGNAL LINE AMP

Q4  C 4.43
        B 0.951
        E 0.396

Q5  C 23.48
          B 3.135
          E 2.596

Q6 C 25.97
        B 2.597
        E 2.205


Q11,Q12 AND Q13 are obviously askew. I have reflowed all connections and replaced  transistors. this appears to me my problem spot.

the next issue is : with the input @ 0dbfs / 0 .775 volts the output only shows 0.050 volts Ac on pin 2 and 3. this is with I/o knobs at 12 o clock, attack off and release cw, 20:1 and Gr mode.  with out fully clockwise I only see 0.396 vac.

I can try replacing the output tranny? Or ideas where else I can check?

Thanks for all your thoughts ideas and wisdom.

Steve

Hello  Mnats and Mike,

I have been a measuring mad man and replacing stuff here and there.  I cannot seem to get bigger volts at the output.  I read the circuit function and it makes sense.  I also see it is moot for me to compare voltages in my unit compared to mnats calibrated one and everything changes with changing the trim pots.  As I compare the 2 builds of mine - one working and non working they both react the same way.  Except one has low  AC output voltage.  The power supply is working and 29.8 and - 9.98.  Do you have any suggestions to test flow toward the output?

Stumped.....

bxershrts said:

Hello  Mnats and Mike,

I have been a measuring mad man and replacing stuff here and there.  I cannot seem to get bigger volts at the output.  I read the circuit function and it makes sense.  I also see it is moot for me to compare voltages in my unit compared to mnats calibrated one and everything changes with changing the trim pots.  As I compare the 2 builds of mine - one working and non working they both react the same way.  Except one has low  AC output voltage.  The power supply is working and 29.8 and - 9.98.  Do you have any suggestions to test flow toward the output?

Stumped.....

Click to expand...

You need to sort out where the gain is getting messed up.

Set input and output mid-way.  Attack "off" (aka bypass), release CW. Feed a 1KHz tone into the input.  Confirm you see 0.775V AC between pins 2 and 3 of the input.

Ok.  Measuring AC (ground as reference).

What is you AC at:

1. + at the input (this will be low..little under 0.1 V AC.
2. + pad of C7
3. C8 (either pad)
4. Brown wire, output tranny.
5. Pin 2 output XLR

Mike

You need to sort out where the gain is getting messed up.

Set input and output mid-way.  Attack "off" (aka bypass), release CW. Feed a 1KHz tone into the input.  Confirm you see 0.775V AC between pins 2 and 3 of the input.

Ok.  Measuring AC (ground as reference).

confirmed***

What is you AC at:

1. + at the input (this will be low..little under 0.1 V AC. ========0.881vac
2. + pad of C7 =============0.018vac
3. C8 (either pad)  ==========0.001vac
4. Brown wire, output tranny =========== 0.147vac
5. Pin 2 output XLR =========0.044vac

Stephen

bxershrts said:

You need to sort out where the gain is getting messed up.

Set input and output mid-way.  Attack "off" (aka bypass), release CW. Feed a 1KHz tone into the input.  Confirm you see 0.775V AC between pins 2 and 3 of the input.

Ok.  Measuring AC (ground as reference).

confirmed***

What is you AC at:

1. + at the input (this will be low..little under 0.1 V AC. ========0.881vac
2. + pad of C7 =============0.018vac
3. C8 (either pad)  ==========0.001vac
4. Brown wire, output tranny =========== 0.147vac
5. Pin 2 output XLR =========0.044vac

Stephen

Click to expand...

You have a problem in that first stage.  Somewhere in the box called "Signal Preamp".  If you don't see any errors, remove the FET (Q1) and measure that stuff again.  See if that fixes your gain.

Mike

Hello Mike,

I removed Q1 and the needle pinned to the right. I checked pins 2 and 3 at the output and i have lots of gain finally! so now what?

bxershrts said:

Hello Mike,

I removed Q1 and the needle pinned to the right. I checked pins 2 and 3 at the output and i have lots of gain finally! so now what?

Click to expand...

Something is wrong with or FET or more likely your bias circuit.  I'm away for a bit. I'll post soon.

mnats]Is your negative 10 volt supply (-10V) working? [color=blue]If so said:

I have measure the pcb : here are my finidings.

28.65 R87
-0.973 CR6

Click to expand...

bxershrts said:

The power supply is working and 29.8 and - 9.98. 

Click to expand...

There is a big difference between -0.973 and -9.98. If it is in fact -9.98 what is the answer to the second question I asked?

Other measurements appear to vary from post to post. Example:

bxershrts said:

I have just checked the voltages at Q11S and Q12B and they are both identical at 3.843 volts dc.

Click to expand...

bxershrts said:

Q12   
B 0.248

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Be sure you apply enough pressure to the test probe to get a stable reading. It's not possible to help you in a methodical way unless the data you present is accurate.

Assuming your negative rail is near -10V and not -0.1V (see MNATS post above) you need to examine your QBias voltage.

The QBias voltage is a negative DC voltage supplied from the -10V DC rail to the gate of the FET.  If there is near 0 VDC at the gate, your FET will have very low resistance (source-drain) and much of your signal will be dumped to ground.  Further explanation can be found on the "Introduction" page of the build guide on my site (trap door analogy).  Seems like that is your issue.  By removing the FET you've removed that low resistance to ground and you've got your gain back.

So why is that?

First issue could be that you're neg rail is too low.  If it's really -0.973 that's you're problem. If you have the right rail, then something is wrong between the rail and the gate bias.  Typically a gate voltage would be -0.70 to -1.50 after setting the QBias.  The range varies because the transfer curve of the FETs vary.

Open the D schematic. In the lower right you'll see two resistors. R35 and R60.  These form a simple voltage divider and their purpose is just to knock the -10V DC rail to a lower voltage for the trimmer R59 which sets that Bias voltage (-0.7 0 to -1.50). One end of R35 is connected to the neg rail and one end of R60 is connected to ground. Where they meet is the divided voltage.  That voltage is roughly -2.75 volts.  R59 sits between that voltage and ground (0V).  The wiper of R59 trims that range down to what ever you need for QBias. Before setting the QBias you need to start with that trimmer at max resistance to make sure you bias is as close to that full negative voltage.  If you're still losing signal test that circuit. 

What is your DC at either side of those two resistors. R35 should be your neg rail voltage and roughly -2.75.  R60 should be roughly -2.75 and 0V.

What is your DC V at pad 18 (wiper of R59). It should roughly -2.75 with trimmer all the way in one direction (also where you should start QBias calibration) and closer to 0V in the other direction.  All that checking out?

From there that neg voltage travels from pad 18 through the attack/release side chain (check all of that wiring as well as R and C on the attack and release and is wired over tho pad 7 which connects to the gate of Q1 and the meter FET.  Pad 7 has a pretty high impedance so it's hard to measure it with a common DMM but you can try and see what you have there.  0V could indicate and issue with wiring from pad 18 to pad 7.

Finally if all of that checks out, you may have a bad FET.

Go through all of this carefully and report back.

Mike

hi all i am very very new to group dyi and have no clue how this works. mike i spoke to you today that i cut my power transformer cable today too short and i am using some of the green 16 gwd cable to make it longer. so all is hoked up from thepower supply page and i am testing it with my fluke mm and i have it set on V DC and it reads -.036 i think it is supose to be + 30 ,,,, so no clue wha is going on.... i might just die now lol ..

also how do i know if i get notified by my post? like i said i am so new at this page... feel free to email me [email protected] i am doing the rev D ... thanks!!!!

offthewallstudio said:

hi all i am very very new to group dyi and have no clue how this works. mike i spoke to you today that i cut my power transformer cable today too short and i am using some of the green 16 gwd cable to make it longer. so all is hoked up from thepower supply page and i am testing it with my fluke mm and i have it set on V DC and it reads -.036 i think it is supose to be + 30 ,,,, so no clue wha is going on.... i might just die now lol ..

also how do i know if i get notified by my post? like i said i am so new at this page... feel free to email me [email protected] i am doing the rev D ... thanks!!!!

Click to expand...

You need to slow down and consider having a professional wire your power supply (please).  Also jokes about injury are not funny at all.

We'd be happy to refund your kit as is now if it's above what you feel comfortable doing. This is not a good first build for people who don't understand electronics.

If you continue to move forward, you need to follow the guide carefully and stuff the power supply section and check the test points as described in great detail. If you've done all that, is the unit plugged in? Do you have the fuse in place?

Email me if you want to return your kit.

Mike

Hairball Audio said:

offthewallstudio said:

hi all i am very very new to group dyi and have no clue how this works. mike i spoke to you today that i cut my power transformer cable today too short and i am using some of the green 16 gwd cable to make it longer. so all is hoked up from thepower supply page and i am testing it with my fluke mm and i have it set on V DC and it reads -.036 i think it is supose to be + 30 ,,,, so no clue wha is going on.... i might just die now lol ..

also how do i know if i get notified by my post? like i said i am so new at this page... feel free to email me [email protected] i am doing the rev D ... thanks!!!!

Click to expand...

You need to slow down and consider having a professional wire your power supply (please).  Also jokes about injury are not funny at all.

We'd be happy to refund your kit as is now if it's above what you feel comfortable doing. This is not a good first build for people who don't understand electronics.

If you continue to move forward, you need to follow the guide carefully and stuff the power supply section and check the test points as described in great detail. If you've done all that, is the unit plugged in? Do you have the fuse in place?

Email me if you want to return your kit.

Mike

Click to expand...

Thanks Mike
I didn't mean die as in from this unit i mean by how tough it is lol
.. so i did everything on this unit for the power supply.  Yes fuse is in. I do not have it plugged to the wall. Am suppose to?? Lol newbie here lol. I thought the meter could test it with out it being plugged in. Whooooopssss lol... plz let me know.. how do i get notified of a response here cuz i just stopped by and notice ur comments. I want to keep it an finish it..
.

Lastly for the white and black wire that go to the off switch. Does the black go on top or the white?

For best practices (120V USA/Canada), you want to have the two wires with the dots on them (look at your transformer) that are tied together ultimately go to the L terminal on your IEC inlet. The other two to the N terminal.

So if your doted wires are on the top of your switch you want the black wire to be on the top as well (next terminal in) then to the L on the IEC.  Then the other wires and the white on the bottom and then to N terminal.

Which is top and which is bottom doesn't matter.  Just make sure the dotted end up at the L and the non-dotted on the N (again look at the transformer label).

Yes you need to turn the unit on once wired to measure voltages.

The guide lays it all out pretty clearly.

Mike

Hairball Audio said:

For best practices (120V USA/Canada), you want to have the two wires with the dots on them (look at your transformer) that are tied together ultimately go to the L terminal on your IEC inlet. The other two to the N terminal.

So if your doted wires are on the top of your switch you want the black wire to be on the top as well (next terminal in) then to the L on the IEC.  Then the other wires and the white on the bottom and then to N terminal.

Which is top and which is bottom doesn't matter.  Just make sure the dotted end up at the L and the non-dotted on the N (again look at the transformer label).

Yes you need to turn the unit on once wired to measure voltages.

The guide lays it all out pretty clearly.

Mike

Click to expand...

yes mike it was clear sorry.

i do not see anything with a dot on it from the black and white wires. on the plug input part (IEC) i beleieve i have the black wire on the bottom and white on top

Quick question -

When you solder the wires to the meter switch and the iec inlet, do you tin the wire and then put it in the hole and then solder?  I'm having trouble getting the tinned wire to fit in.  Do you ever fill the hole with solder and then solder the tinned wire to it without putting it in the hole, just resting along side?  It seems a lot easier this way but maybe the connection is not as good?  What is the common practice for this?

Thanks

Hairball Audio said:

offthewallstudio said:

hi all i am very very new to group dyi and have no clue how this works. mike i spoke to you today that i cut my power transformer cable today too short and i am using some of the green 16 gwd cable to make it longer. so all is hoked up from thepower supply page and i am testing it with my fluke mm and i have it set on V DC and it reads -.036 i think it is supose to be + 30 ,,,, so no clue wha is going on.... i might just die now lol ..

also how do i know if i get notified by my post? like i said i am so new at this page... feel free to email me [email protected] i am doing the rev D ... thanks!!!!

Click to expand...

You need to slow down and consider having a professional wire your power supply (please).  Also jokes about injury are not funny at all.

We'd be happy to refund your kit as is now if it's above what you feel comfortable doing. This is not a good first build for people who don't understand electronics.

If you continue to move forward, you need to follow the guide carefully and stuff the power supply section and check the test points as described in great detail. If you've done all that, is the unit plugged in? Do you have the fuse in place?

Email me if you want to return your kit.

Mike

Click to expand...

hi mike so i successfully build the power supply i think. Your first test calls for 30 volts that test mine read 40 volts on my fluke mm. The second test was spot on and read minus 9 volts just like yours. Is this bad??? If so what should i do?

40V is much too high for you positive rail. 

Something is wrong with your build.  You'll have to go through and and figure out what's wrong.  You may have your voltage regulator in backwards.

thp said:

Quick question -

When you solder the wires to the meter switch and the iec inlet, do you tin the wire and then put it in the hole and then solder?  I'm having trouble getting the tinned wire to fit in.  Do you ever fill the hole with solder and then solder the tinned wire to it without putting it in the hole, just resting along side?  It seems a lot easier this way but maybe the connection is not as good?  What is the common practice for this?

Thanks

Click to expand...

I always put it through the hole.  Even if it means not tinning.

One of the basic principles of soldering is that there should be a good solid mechanical connection between the two conductors before the solder is applied.    "Solder isn't glue".  Especially on the 120v connections - this is a safety issue.